Method for preparing nutritionally fortified vegetable restructured rice

Abstract

The application discloses a preparation method of nutritionally fortified vegetable reprocessed rice, and belongs to the technical field of food processing. The method is used for solving the problems of difficulty in extrusion molding of reprocessed rice with high proportion of vegetable powder and easy degradation of chlorophyll. The method comprises the following steps: mixing rice powder, broccoli powder and yam powder with monoglyceride fatty acid ester and water; adopting sectional temperature control extrusion; sequentially dividing six independent sections along the material flow direction; setting a constant temperature delay section between the second section and the third section; the temperature of the constant temperature delay section is 100-110 DEG C; the length of the constant temperature delay section is 60-100 mm; a reverse thread element is arranged on the screw; the pitch and thread depth of the reverse thread element are respectively 50-80% and 70-90% of those of the adjacent advancing thread section; a spiral groove is processed on the inner wall of the cylinder of the constant temperature delay section; the pitch of the spiral groove is the same as that of the reverse thread element, and the direction is opposite; the material stays for 10-20 s; the material is rotary cut into particles; and the particles are dried. The application is used for preparing nutritionally fortified vegetable reprocessed rice.

Description

Technical Field

[0001] This invention relates to the field of food processing technology. More specifically, this invention relates to a method for preparing fortified vegetable processed rice. Background Technology

[0002] Rice is my country's primary staple food, but natural japonica and indica rice are relatively low in dietary fiber and micronutrients. With rising consumer demand and increased health awareness, market demand for staple foods has shifted from simply providing sustenance to prioritizing nutrition. However, modern rice processing techniques are becoming increasingly refined, resulting in significant losses of the bran and germ during polishing and hulling, further reducing the nutritional density of the finished rice, particularly in dietary fiber, vitamins, and some antioxidants. Extrusion reconstituted rice technology can re-granulate rice flour and nutritional ingredients to create products with the appearance and cooking characteristics of natural rice, providing a feasible way to improve the nutritional structure of staple foods.

[0003] In the production of extruded reconstituted rice, process parameters such as temperature and screw configuration affect the product's molding quality and nutrient retention. In particular, when a high proportion of vegetable powder is added, the vegetable raw materials, rich in dietary fiber and heat-sensitive natural pigments, present the extrusion process with two mutually constraining technical challenges.

[0004] Firstly, the molding stability is poor. The dietary fiber in the vegetable powder interferes with the gelatinization of starch granules and the formation of a gel network, making it difficult for the material to form a continuous, dense melt in the extruder. After demolding, cracks and pores appear on the surface of the rice grains, making them prone to loosening and cracking during drying and cooking, resulting in incomplete particle shape. When the amount of vegetable powder added exceeds a certain proportion, the binding properties of rice flour alone are insufficient to meet the molding requirements. Especially in leafy vegetable systems, without appropriate structural auxiliary components and temperature control, problems such as extrusion puffing, brittleness after drying, and incomplete particle shape after cooking are more likely to occur.

[0005] Secondly, natural pigments are easily degraded during high-temperature extrusion. Taking green vegetables as an example, their vibrant green color comes from chlorophyll. Under normal extrusion temperatures, chlorophyll readily undergoes a demagnesiation reaction to produce pheophytin, causing the product to turn from green to yellowish-brown, severely affecting its appearance and consumer acceptance. If the extrusion temperature is lowered to protect the chlorophyll, starch gelatinization will be insufficient, further deteriorating the formability and making it difficult to simultaneously achieve the goals of formability and color protection. In addition, the competition for water absorption by dietary fiber in vegetable powder exacerbates the instability of the extrusion process, while the sensitivity of natural pigments to heat and oxygen further increases the difficulty of process control.

[0006] Although vegetable powder is widely used in flour products, puffed foods, and compound powder products, it still faces challenges in rice-based staple food systems, including difficulties in formula matching, poor formability, and insufficient sensory qualities. The resulting products are prone to defects such as dull color, excessive hardness, or excessive softness. Therefore, developing a preparation method that can simultaneously achieve good extrusion formability and chlorophyll retention when adding a high proportion of vegetable powder has become a pressing technical problem in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing fortified vegetable-based processed rice, addressing the problems that arise during extrusion molding when a high proportion of vegetable powder is added. These problems include loose grains, cracking, incomplete grain shape, extrusion puffing, and brittleness after drying, as well as the fading of chlorophyll at high temperatures leading to dull color, excessively hard or soft texture. This invention, through the synergistic effect of specific raw material ratios, segmented temperature-controlled extrusion processes, and modifications to the internal structure of the extruder, enables the processed rice to achieve good extrusion molding properties and intact grain shape after cooking, while significantly inhibiting the thermal degradation of chlorophyll during the extrusion process, thereby improving the product's color quality and texture uniformity.

[0008] To address the aforementioned problems and achieve the objectives and other advantages of this invention, a method for preparing fortified vegetable processed rice is provided, comprising the following steps:

[0009] S1: Weigh the raw materials according to the following formula, with the proportions of raw materials as mass fractions: rice flour 70%~90%, broccoli flour 5%~15%, yam flour 5%~15%; and add monoglyceride fatty acid esters accounting for 0.3%~1.5% of the total mass of raw materials and water 15%~25%, and mix well;

[0010] S2: The mixed material is fed into a single-screw extruder, employing a segmented temperature-controlled extrusion method. The extrusion process is divided into six independent segments along the material flow direction: segment 1 (80-100℃), segment 2 (100-120℃), segment 3 (120-140℃), segment 4 (120-140℃), segment 5 (100-120℃), and segment 6 (90-100℃). A constant-temperature delay segment with a length of 60-100mm is set between segment 2 and segment 3, maintaining the temperature of the constant-temperature delay segment at 100-110℃. A set of reverse threaded elements is installed on the extruder screw within the constant-temperature delay segment, covering the constant-temperature delay section. The pitch of the reverse thread element in the entire working length of the constant temperature delay section screw is 50%~80% of the pitch of the extrusion screw drive thread section located upstream of the constant temperature delay section and adjacent to the reverse thread element, and the thread depth of the reverse thread element is 70%~90% of the thread depth of the extrusion screw drive thread section located upstream of the constant temperature delay section and adjacent to the reverse thread element; a helical groove is machined on the inner wall of the cylinder in the constant temperature delay section, the pitch of the helical groove is the same as the pitch of the reverse thread element, and the helical direction of the helical groove is opposite to the thread direction of the reverse thread element; the residence time of the material in the constant temperature delay section is 10~20s by controlling the screw speed;

[0011] S3: The extruded material is immediately rotary cut into granules, which are then dried to obtain processed rice.

[0012] Preferably, in the method for preparing the nutritionally fortified vegetable rice, the raw materials in S1 are passed through a 60-120 mesh sieve before mixing, and are poured into a mixing bucket and stirred at a speed of 20-40 r / min for 1-5 min during mixing;

[0013] In S2, the mixed material is fed into a single screw extruder at a feed temperature of 40~50℃.

[0014] The blade speed during rotary cutting in S3 is 2500~3000 r / min.

[0015] Preferably, in the method for preparing the fortified vegetable processed rice, after drying in step S3, the method further includes a step of spraying a pregelatinized starch layer onto the surface of the processed rice, specifically:

[0016] Heat water to 40-50℃, slowly add pregelatinized rice starch or pregelatinized cassava starch while stirring, so that the final concentration of pregelatinized rice starch or pregelatinized cassava starch is 5%-10% of the total mass of the solution, and continue stirring until completely dissolved; then add 0.5%-1.0% of glycerol by mass of pregelatinized rice starch or pregelatinized cassava starch, and continue stirring for 8-10 minutes to obtain a pregelatinized starch solution;

[0017] The prepared pregelatinized starch solution is sprayed onto the surface of processed rice by atomization. The amount of spraying is 1% to 2% of the mass of processed rice, and the spraying temperature is 40 to 50℃.

[0018] The coated reconstituted rice is dried again at 50-60℃ for 30-60 minutes to reduce the moisture content of the reconstituted rice to 6%-10%.

[0019] Preferably, in the method for preparing the fortified vegetable processed rice, the monoglyceride in S1 is glyceryl monostearate, and the amount of glyceryl monostearate added is 1.2% to 1.5% of the total mass of the raw materials; the amount of water added is 18% to 20% of the total mass of the raw materials.

[0020] In S2, the temperature of the third section is 135~140℃, the temperature of the fourth section is 130~135℃, the temperature of the fifth section is 110~115℃, and the temperature of the sixth section is 90~92℃.

[0021] Preferably, in the preparation method of the fortified vegetable processed rice, after drying in step S3, the processed rice is placed in a sealed container and warmed at 40-50°C for 2-4 hours to allow the internal moisture of the processed rice to migrate to the surface; then, atomized water is sprayed into the sealed container to uniformly wet the surface of the processed rice and raise the moisture content to 12%-14%, and then it is left to stand for 30-60 minutes; finally, the processed rice is placed in hot air at 50-60°C with a wind speed of 0.5-1.0 m / s and dried for 10-20 minutes to reduce the surface moisture content of the processed rice to 6%-10%, and then packaged.

[0022] Preferably, in the preparation method of the fortified vegetable processed rice, after hot air drying and before packaging, the processed rice is placed in an environment with a temperature of 25~30℃ and a relative humidity of 40%~50% and left to stand for 1~2 hours.

[0023] Preferably, in the method for preparing fortified vegetable rice, the total residence time of the material in the three-segment and four-segment sections in S2 is 45-60 seconds.

[0024] Preferably, in the preparation method of the nutritionally fortified vegetable processed rice, in step S3, after secondary drying, the processed rice is cooled to 0~5℃, stirred at a speed of 10~20r / min for 1~2min, then passed through a 20~40 mesh sieve, and then placed in a sealed container to warm up to 20~25℃ before packaging.

[0025] The present invention has at least the following beneficial effects:

[0026] This invention provides a suitable temperature window for the dissolution of yam polysaccharides by setting a constant-temperature delay zone between the second and third temperature zones, maintaining the temperature of the delay zone at 100-110℃, and controlling the residence time of the material in the delay zone to 10-20 seconds. This also prevents premature degradation of chlorophyll at higher temperatures. The reverse-threaded element installed in the constant-temperature delay zone and the spiral grooves on the inner wall of the cylinder generate a strong shearing and mixing effect, promoting full contact and uniform mixing of yam polysaccharides and broccoli chlorophyll. In the subsequent high-temperature zones, namely the third and fourth temperature zones, yam polysaccharides and rice starch form a highly dense, low-water-activity glassy matrix. Through high-viscosity steric hindrance and low free water content, this effectively inhibits the thermal motion and demagnesiation reaction of chlorophyll molecules, forming a stable protective barrier. Thus, without adding any exogenous color-protecting agents, a good chlorophyll retention effect is achieved, resulting in a bright green and natural product color.

[0027] This invention employs a segmented temperature-controlled extrusion method, allowing the material to pass through six segments sequentially, gradually increasing the temperature to the highest level to achieve full starch gelatinization and fiber softening. Then, it is gradually cooled to increase melt viscosity. Combined with the low-temperature die head control where the temperature of the six segments does not exceed 100°C, it effectively prevents excessive expansion of the material when it exits the die, ensuring that the surface of the rice grains is smooth and dense. This significantly reduces the risk of cracking during drying and cooking, resulting in a product with intact and non-loose grains after cooking.

[0028] This invention, through the coordination of screw configuration and rotation speed, ensures that the residence time of the material in the isothermal delay zone is 10-20 seconds, while the total residence time in the three- and four-segment zones is 45-60 seconds. This ensures that the starch is fully gelatinized, the fiber is fully softened, and the blended matrix undergoes a rapid glass transition, fixing chlorophyll in a dense structure and forming an effective thermal degradation barrier. As a result, a product with moderate hardness and good elasticity is obtained, avoiding textural defects such as excessive hardness or softness.

[0029] This invention adds a reheating-rehydration-re-drying process after drying. The reheating causes the internal moisture of the processed rice to migrate to the surface, the spraying of atomized water softens the hard shell on the surface of the processed rice, and the short-term hot air drying forms a three-phase structure of dry outside, porous inside, and moist inside. This effectively inhibits starch retrogradation and significantly improves the taste of the processed rice after re-steaming after storage. This allows the product to maintain its soft and elastic texture even after long-term storage, and is close to the freshly steamed state.

[0030] This invention involves spraying a pregelatinized starch layer onto the surface of dried processed rice to form a water-absorbing buffer layer. This slows down the rate at which water penetrates into the rice grains during the initial stage of cooking, preventing excessive gelatinization of the surface and adhesion between rice grains. This results in a smooth surface and good dispersibility of the cooked rice grains. At the same time, the pregelatinized starch layer provides auxiliary protection for the stability of chlorophyll on the surface.

[0031] This invention combines rice flour, broccoli flour, and yam flour in a specific ratio, utilizing the physical bridging effect of viscous polysaccharides in yam flour to significantly improve the cohesiveness of the materials during extrusion. This effectively solves the molding difficulties caused by dietary fiber interfering with the starch network after adding a high proportion of vegetable flour, such as loose rice grains, cracking, extrusion puffing, and incomplete grain shape after cooking.

[0032] This invention, through the synergistic effect of the above-mentioned process steps, achieves its core color-protecting and molding mechanism without relying on traditional chemical color-protecting agents (such as copper sulfate, sodium copper chlorophyllin, etc.) and exogenous binders (such as xanthan gum, carrageenan, etc.). Instead, it utilizes the inherent viscous polysaccharides of yam powder and innovative processing techniques. In a further surface coating scheme, a trace amount of glycerol is used as a plasticizer for the pregelatinized starch film. This glycerol is not a color-protecting or binding component but is only used to improve the physical properties of the coating and meets food safety requirements. This invention achieves excellent extrusion molding of high-proportion vegetable powder-based rice, retention of natural pigments, dense structure, and improved taste after re-steaming, resulting in a product with superior overall quality.

[0033] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0034] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0035] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0036] This invention provides a method for preparing fortified vegetable processed rice, comprising the following steps:

[0037] S1: Weigh the raw materials according to the following formula, with the following mass fractions: rice flour 70%~90%, broccoli flour 5%~15%, yam flour 5%~15%; add 0.3%~1.5% monoglyceride fatty acid ester and 15%~25% water (by mass of the total raw materials) to the raw materials and mix thoroughly. It should be noted that although the addition of yam flour objectively increases the total dietary fiber content of the system, its functional role is completely different from that of leafy vegetable fibers such as broccoli flour. Leafy vegetable fibers are mostly rigid, insoluble fibers, mainly acting as steric hindrance and network interruption; while yam flour is rich in viscous soluble polysaccharides such as mannan. Under the temperature and shear fields of extrusion, its exudates can function as a binder and bridger similar to hydrocolloids. This effect is not a simple superposition of fiber properties, but rather stems from the positive reshaping of the rheological properties of the system by the polysaccharide components. At this point, the negative physical barrier caused by a small amount (5-15%) of yam fiber is far less than the huge binding gain brought about by its dissolved polysaccharides, thus achieving a net improvement in the extrudability of the mixed system overall.

[0038] S2: The mixed material is fed into a single-screw extruder, employing a segmented temperature-controlled extrusion method. The extrusion process is divided into six independent segments along the material flow direction: segment 1 (80-100℃), segment 2 (100-120℃), segment 3 (120-140℃), segment 4 (120-140℃), segment 5 (100-120℃), and segment 6 (90-100℃). A constant-temperature delay segment with a length of 60-100mm is set between segment 2 and segment 3, maintaining the temperature of the constant-temperature delay segment at 100-110℃. A set of reverse threaded elements is installed on the extruder screw within the constant-temperature delay segment. The reverse threaded elements cover the entire working length of the screw in the constant-temperature delay segment, and the pitch of the reverse threaded elements is located upstream of the constant-temperature delay segment and parallel to the reverse thread. The screw of the extruder adjacent to the threaded element advances 50% to 80% of the thread pitch of the threaded section, and the thread depth of the reverse threaded element is 70% to 90% of the thread depth of the extruder screw advancing the threaded section upstream of the isothermal delay section and adjacent to the reverse threaded element. Helical grooves are machined on the inner wall of the cylinder of the isothermal delay section. The pitch of the helical grooves is the same as the pitch of the reverse threaded element, and the helical direction of the helical grooves is opposite to the thread direction of the reverse threaded element. The residence time of the material in the isothermal delay section is controlled to be 10 to 20 seconds by controlling the screw speed. Segmented temperature control means that the set temperatures of each adjacent segment are different, thus forming a temperature gradient along the material flow direction, while each independent segment maintains that set temperature, including the isothermal delay section specifically designed in this scheme. The isothermal delay section is an independent short cylinder section, 60 to 100 mm in length, with connecting flanges at both ends, and is installed between the end of the second-section cylinder and the beginning of the third-section cylinder. It is equipped with an independent electric heating jacket and cooling circulation path, and is equipped with thermocouples to achieve independent and precise temperature control of 100~110℃. The spiral groove covers the entire working length of the inner wall of the constant temperature delay section cylinder. The cross-sectional shape of the spiral groove is preferably rectangular or trapezoidal, which is easy to process and conducive to generating shearing action. The width of the spiral groove is 30%~40% of the pitch, and the depth is equal to 10%~15% of its pitch. It is formed on the inner wall of the cylinder by means of electrical discharge machining or broaching. After installation, the radial clearance between the outer edge of the thread of the reverse thread element and the bottom of the spiral groove on the inner wall of the cylinder is 0.3~1.0mm, and the radial clearance between the root of the thread of the reverse thread element and the top of the spiral groove on the inner wall of the cylinder is 0.5~1.2mm. This clearance ensures that the material can form a continuous lubricating film under high shear action, avoiding dry friction and collision between metals, and ensuring long-term stable operation of the equipment.

[0039] S3: The extruded material is immediately rotary cut into granules, and after drying, it becomes processed rice.

[0040] To address the two mutually reinforcing technical challenges of poor forming quality and degradation of natural pigments when extruding reconstituted rice after adding a high proportion of vegetable powder to rice flour, existing common methods for vegetable-based reconstituted rice extrusion typically involve mixing rice flour with a certain amount of vegetable powder, adding monoglyceride fatty acid esters and water, and then feeding the mixture into a single-screw extruder. The extruder barrel is usually divided into two temperature zones, such as one at 80-100℃ and the other at 120-140℃, or three temperature zones with a transition zone of 100-120℃ between the two zones. After passing through the melting zone, the material is directly extruded through a die, granulated, and dried to obtain the final product.

[0041] This technology has the following drawbacks: when the amount of vegetable powder added is high, cracks and pores easily appear on the surface of the rice grains after demolding, resulting in significant brittleness after drying. After steaming and cooking, the rice grains become loose, cracked, and incomplete in shape. Simultaneously, the product color changes from bright green to yellowish-brown, appearing dull. Furthermore, the texture of the rice grains is uneven, exhibiting phenomena such as being too hard or too soft. The reason for these defects is that the dietary fiber in the vegetable powder severely interferes with starch gelatinization and gel network formation, while the high temperature during extrusion causes rapid magnesium degradation of chlorophyll. Simply lowering the temperature will worsen the molding process, and adding color-protecting agents or thickeners will increase the complexity of the ingredient formulation. Therefore, existing technologies cannot simultaneously solve the molding and color-protecting problems without introducing exogenous additives.

[0042] The preparation method of the present invention systematically solves the above problems through the following steps.

[0043] Step S1

[0044] The specified ingredient ratio by mass fraction is: 70%~90% rice flour, 5%~15% broccoli flour, 5%~15% yam flour, and 0.3%~1.5% monoglyceride fatty acid ester and 15%~25% water by mass of the total ingredients, and then mix evenly.

[0045] This specific ingredient ratio is fundamental to solving molding difficulties. Broccoli powder at 5%–15% provides sufficient dietary fiber and chlorophyll, but exceeding 15% will excessively interfere with the starch network. Yam powder, at a ratio similar to broccoli powder at 5%–15%, is rich in viscous polysaccharides that dissolve during subsequent heating. These polysaccharides act as a physical bridge between rice starch granules and broccoli dietary fiber, significantly improving the viscosity and cohesiveness of the melt. This inhibits the loosening, cracking, and uneven grain shape after cooking caused by fiber interfering with the starch network.

[0046] Meanwhile, yam polysaccharides can synergistically combine with rice gelatinized starch at appropriate temperatures to form a highly dense, low-water-activity glassy matrix, which effectively delays the thermal degradation of chlorophyll by restricting molecular diffusion and reducing water activity.

[0047] Monoglyceride fatty acid esters act as emulsifiers and puffing inhibitors, controlling excessive puffing during extrusion, preventing air bubbles and pores on the rice grain surface, and reducing the risk of brittleness after drying. The preferred monoglyceride fatty acid ester is glyceryl monostearate, which has a high melting point and good thermal stability. It can more effectively maintain the emulsified state of the material and exert a puffing-inhibiting effect in the high-temperature extrusion stage. Its long carbon chain structure also helps to form a complex with rice starch, further improving the surface density and cooking resistance of the rice grains. The addition of 15%–25% water ensures good flowability of the material and promotes starch gelatinization.

[0048] Step S2

[0049] The mixture is fed into a single-screw extruder and extruded using a segmented temperature-controlled method. The extruder barrel is divided into six independent temperature-controlled zones along the material flow direction: Zone 1 (80-100℃) preheats the material and initiates water absorption and swelling; Zone 2 (100-120℃) further heats the material into a plasticized state, and starch begins to gelatinize; Zone 3 (120-140℃) reaches the highest temperature, fully gelatinizes the starch, softens the vegetable fiber, and simultaneously dissolves yam polysaccharides and mixes thoroughly with chlorophyll; Zone 4 (120-140℃) maintains the high temperature to further integrate and homogenize the components in the material, stabilizing the blend matrix of polysaccharides, starch, and chlorophyll, and fixing chlorophyll in situ; Zone 5 (100-120℃) cools the material, increasing melt viscosity in preparation for molding; Zone 6 (90-100℃) further cools and solidifies the material at the die head, rapidly forming a dense skin on the surface, inhibiting over-expansion, and ensuring a smooth surface and dense structure for the rice grains. This temperature gradient allows the material to gradually heat up to the highest temperature and then gradually cool down, which is beneficial for starch gelatinization and fiber softening. At the same time, it controls the degree of expansion when demolding and reduces the risk of cracking during drying and cooking.

[0050] Chlorophyll protection mechanism

[0051] To address the issue of chlorophyll thermal degradation, a constant-temperature delay zone with a length of 60-100 mm was specially set up between the second and third sections. The temperature of the constant-temperature delay zone was stably maintained at 100-110℃, and the residence time of the material in the constant-temperature delay zone was controlled to 10-20 seconds by adjusting the screw speed.

[0052] 100-110℃ is a critical temperature window: at this temperature, yam polysaccharides dissolve rapidly, while the rate of chlorophyll demagnesiation remains low, and no significant discoloration occurs; a residence time of 10-20 seconds is sufficient for the polysaccharides to fully dissolve and come into full contact with the chlorophyll in the broccoli powder, without causing chlorophyll degradation due to excessive residence time. The isothermal delay zone, combined with the rapid curing in the subsequent high-temperature zone, solves the problem of dark color.

[0053] Within the isothermal delay zone, the present invention also incorporates two mechanical structures to enhance the effects of polysaccharide dissolution, mixing, and matrix protection.

[0054] The first structure involves installing a set of reverse thread elements on the extruder screw. The reverse thread elements cover the entire working length of the screw in the constant temperature delay section. The pitch of the reverse thread elements is 50% to 80% of the pitch of the extruder screw advance thread section located upstream of the constant temperature delay section and adjacent to the reverse thread elements, and its thread depth is 70% to 90% of the depth of the adjacent advance thread section.

[0055] The second structure involves machining helical grooves on the inner wall of the cylinder in the constant temperature delay zone. The pitch of the helical grooves is the same as the pitch of the reverse thread element, and the helical direction of the helical grooves is opposite to the thread direction of the reverse thread element.

[0056] The two structures work synergistically as follows: the reverse threaded element applies reverse resistance to the forward movement of the material, prolonging its residence time in the isothermal delay zone and increasing the filling degree of the region; simultaneously, the reverse threaded element and the oppositely oriented spiral grooves on the inner wall of the cylinder work together to generate strong interlayer slippage, folding, and high-frequency material interface renewal in the material. The reverse threaded element establishes local high pressure and forces material recirculation; while the spiral grooves on the inner wall of the cylinder provide directional flow channels for the recirculated material, and the two work together to form a constrained three-dimensional circulating flow. This flow mode aims to break laminar flow and promote microscopic mixing and effective component contact between different material micro-elements, rather than simple macroscopic stirring. This design aims to maximize the dissolution of polysaccharides from yam powder and distribute them evenly in the system, laying the foundation for the efficient construction of the subsequent blend matrix. This non-ideal mixing flow mode allows the material to achieve repeated shearing and redistribution at the microscopic level within a macroscopic timescale (average residence time 10-20 s).

[0057] Its core functions are twofold: first, it breaks down yam powder particles, promoting the rapid release of polysaccharides from the cell wall; second, it greatly increases the contact interface between polysaccharides, starch, and chlorophyll, thereby enabling the in-situ synergistic construction of both bridging and protective carrier functions in a short period of time.

[0058] The released yam polysaccharides exhibit kinetic competition in their function: some polysaccharide molecular chains preferentially adsorb and bridge between rice starch granules and broccoli dietary fiber, forming a physical cross-linking network that immediately enhances melt adhesion; while other polysaccharide molecules rapidly migrate to the lipid-soluble chlorophyll surface, utilizing their amphiphilicity to achieve physical adsorption, allowing the polysaccharide molecules to adhere tightly to the chlorophyll surface, laying the foundation for the subsequent in-situ protective carrier construction of the glassy matrix.

[0059] The strong shear environment of this invention, by generating a huge contact area and interface renewal in an extremely short time, enables the two processes, which depend on molecular diffusion and adsorption, to occur efficiently and synergistically. This achieves both bridging and protective carrier construction functions at the millisecond-level micro-mixing scale. This enhanced mixing also solves the problem of localized clumping of yam powder, ensuring that yam polysaccharides are uniformly dispersed throughout the material, better exerting their binding effect, thereby further improving formability and reducing brittleness and incomplete particle shape during drying and cooking.

[0060] After being processed in the isothermal delay zone, the material enters the third-stage zone at 120-140℃. The continuous phase, rich in yam polysaccharides and starch, rapidly undergoes a glass transition, forming a highly dense, low-water-activity continuous matrix. This matrix formation, on the one hand, greatly restricts the thermal motion of chlorophyll molecules and their contact with demagnesiation factors through high viscosity and steric hindrance; on the other hand, its extremely low free water content inhibits the rate of hydration-dependent chlorophyll demagnesiation. This reduces direct contact between chlorophyll and air in the subsequent high-temperature zone, ultimately yielding a product with a natural green color and uniform texture.

[0061] Step S3

[0062] The extruded material is immediately rotary-cut into granules, which are then dried to obtain processed rice. Rapid rotary cutting prevents granules from sticking together, and drying reduces the product moisture content to a safe storage level of 6%–10% while maintaining granule shape. The granule shape of the processed rice can be controlled by selecting dies with different apertures and shapes, and adjusting the rotary cutting head speed. For example, it can be made into short cylindrical shapes or granules that approximate the shape of natural rice grains to meet different consumer needs.

[0063] Example 1

[0064] S1: Take 80kg of rice flour, 10kg of broccoli flour, and 10kg of yam flour, add 1.2kg of glyceryl monostearate (1.2% of the total raw material mass) and 18kg of water (18% of the total raw material mass), and mix well. First, pass the rice flour, broccoli flour, and yam flour through an 80-mesh sieve, then pour them into a mixing bucket and stir at 30r / min for 3min.

[0065] S2: The mixed material is fed into a single-screw extruder at a feed temperature of 45℃. A segmented temperature-controlled extrusion method is employed, with six independent segments sequentially set along the material flow direction: segment 1 (90℃), segment 2 (110℃), segment 3 (138℃), segment 4 (132℃), segment 5 (112℃), and segment 6 (91℃). An 80mm long constant-temperature delay section cylinder is installed between segments 2 and 3, maintaining the temperature at 105℃. This cylinder has connecting flanges at both ends, installed between the end of segment 2 and the beginning of segment 3, respectively. It is equipped with an independent electric heating jacket and cooling circulation path, and thermocouples to achieve independent and precise temperature control at 105℃. A set of reverse threaded elements is installed on the extruder screw within the isothermal delay section. These reverse threaded elements cover the entire working length of the screw in the isothermal delay section. The upstream feed thread of the reverse threaded element has a pitch of 20 mm and a depth of 5 mm. The reverse threaded element itself has a pitch of 13 mm (65% of the upstream feed thread pitch) and a depth of 4 mm (80% of the upstream feed thread depth). Helical grooves are machined on the inner wall of the isothermal delay section cylinder. These grooves cover the entire working length of the inner wall of the cylinder and have a rectangular cross-section. The pitch of the helical grooves is the same as that of the reverse threaded elements, 13 mm. The width is 35% of the pitch (approximately 4.6 mm), and the depth is 12% of the pitch (approximately 1.6 mm). The helical direction of the helical grooves is opposite to the thread direction of the reverse threaded elements. After installation, the radial clearance between the outer edge of the reverse thread element and the bottom of the spiral groove on the inner wall of the cylinder is 0.3~1.0mm, and the radial clearance between the root of the reverse thread element and the top of the spiral groove on the inner wall of the cylinder is 0.5~1.2mm. By controlling the screw speed, the residence time of the material in the constant temperature delay zone is made 15s, and the screw speed is adjusted to make the total residence time of the material in the three-section and four-section zones 52s. The two residence times are achieved by coordinating the adjustment of the same screw speed.

[0066] S3: The extruded material is immediately rotary-cut into granules at a speed of 2800 r / min. Then, it is dried in a cool and ventilated place until the moisture content drops to 9%, resulting in nutrient-fortified vegetable processed rice with regular grain shape and uniform size.

[0067] Example 2

[0068] The difference from Example 1 is that in S1, 80 kg of rice flour, 8 kg of broccoli flour, 12 kg of yam flour, 1.2 kg of glyceryl monostearate, and 18 kg of water are mixed evenly. The rest is exactly the same as in Example 1.

[0069] Example 3

[0070] The difference from Example 1 is that S2 has three temperature zones at 135°C, four temperature zones at 130°C, five temperature zones at 110°C, and six temperature zones at 90°C; the constant temperature delay zone is 100mm long and has a residence time of 20s; the total residence time of the material in the three and four temperature zones is 60s. Everything else is exactly the same as in Example 1.

[0071] Comparative Example 1 (Conventional two-stage extrusion method with transition section)

[0072] The difference from Example 1 is that S2 does not have a constant temperature delay section, and the cylinder is divided into three independent sections along the material flow direction: a first section at 90°C, an intermediate transition section at 110°C, and a second section at 130°C; there are no reverse threaded elements and no spiral grooves on the inner wall of the cylinder. Everything else is exactly the same as in Example 1.

[0073] Comparative Example 2 (without yam powder)

[0074] The difference from Example 1 is that no yam powder is added in S1, the broccoli powder is changed to 20 kg, the rice powder remains unchanged at 80 kg, and the rest is exactly the same as in Example 1.

[0075] Comparative Example 3 (without isothermal delay section)

[0076] The difference from Example 1 is that the constant temperature delay section is not set in S2, that is, the second section is directly connected to the third section, and the rest is exactly the same as Example 1.

[0077] Comparative Example 4 (without reverse threads and helical grooves)

[0078] The difference from Example 1 is that the reverse thread element in the constant temperature delay section is replaced with the same forward push thread as the upstream section, and the inner wall of the cylinder is not machined with a helical groove. Otherwise, it is exactly the same as Example 1.

[0079] Comparative Example 5 (Six-stage temperature too high)

[0080] The difference from Example 1 is that the temperature of the six sections in S2 is set to 105°C, while the rest is exactly the same as in Example 1.

[0081] Comparative Example 6 (Water Quantity Too Low)

[0082] The difference from Example 1 is that the amount of water added in S1 is changed to 12% of the total mass of the raw materials, while the rest is exactly the same as in Example 1.

[0083] Comparative Example 7 (Excessive Water Quantity)

[0084] The difference from Example 1 is that the amount of water added in S1 is changed to 28% of the total mass of the raw materials, while the rest is exactly the same as in Example 1.

[0085] Performance evaluation methods:

[0086] Surface cracks: Randomly select 50 grains of processed rice and count the number of cracks with a surface length greater than 0.2 mm on each grain under a stereomicroscope, and take the average value.

[0087] Color: Use a colorimeter to measure the a* value (positive value leans towards red, negative value leans towards green) and the b* value (positive value leans towards yellow), and evaluate visually.

[0088] Integrity of cooked rice: Take 50g of processed rice, add 75mL of water, place it in a 500mL beaker, and steam in a boiling water bath for 15 minutes, then let it sit for 5 minutes. Gently pour the cooked rice grains into a sieve and rinse once slowly with room temperature water (just enough to avoid breaking the rice grains). Count the percentage of intact rice grains (without obvious cracks or breakage) out of the total number of grains.

[0089] Chlorophyll retention rate: This reflects the proportion of chlorophyll retained throughout the entire extrusion process. The calculation method is as follows:

[0090] Take the mixture to be extruded and determine its total chlorophyll content as the initial baseline value.

[0091] Take the finished product and process it into rice, then determine its total chlorophyll content.

[0092] Chlorophyll retention rate (%) = (Total chlorophyll content of finished reconstituted rice ÷ Total chlorophyll content of mixture before extrusion) × 100%.

[0093] It should be noted that the chlorophyll in the pre-extrusion mixture almost entirely comes from broccoli powder (rice powder and yam powder contain virtually no chlorophyll). Therefore, this indicator truly reflects the degree to which broccoli chlorophyll is retained after the entire process (mixing, shearing, high-temperature extrusion, drying, etc.). This retention rate is an instantaneous value measured immediately after extrusion, followed by rapid cooling and freeze-drying in the dark. It aims to measure the maximum chlorophyll protection potential of the extrusion process.

[0094] Hardness: Take 10 whole rice grains after steaming and cook, and use a texture analyzer (P / 36R probe, compression rate 70%, test speed 1mm / s) to measure the hardness and take the average value.

[0095] The performance test results are shown in Table 1.

[0096] It should be noted that all data in Table 1 are results obtained from performance evaluations conducted directly after the samples were freshly prepared.

[0097] Table 1 Performance test results of each embodiment and comparative example

[0098]

[0099] Results analysis:

[0100] Examples 1, 2, and 3 all achieved a crack-free surface, a vibrant green color (a* value between -8.0 and -7.2, b* value between +9.8 and +10.8), a cooking integrity rate of 95% to 96%, a chlorophyll retention rate of 82% to 84%, and a moderate hardness of 278 to 292g. These results comprehensively solved problems such as demolding cracks, demolding puffing, drying brittleness, loosening and cracking during cooking, incomplete particle shape, dull color, and excessive hardness or softness. In particular, the chlorophyll retention rate of the finished products from Examples 1 to 3 all reached over 82%. This indicates that although broccoli chlorophyll underwent rigorous processing such as high-temperature extrusion, the core color-protecting mechanism of this invention ensured that the vast majority was successfully retained, and degradation loss was controlled to a very low level.

[0101] The differences between the three embodiments stem from variations in formulation and process parameters.

[0102] Example 1 (10 kg of broccoli powder and 10 kg of yam powder) showed excellent performance in all indicators, with a cooking integrity rate of 95%, a chlorophyll retention rate of 83%, and a hardness of 285 g. It achieved a good balance between formability, color protection effect, and texture, and had excellent overall performance.

[0103] Example 2 (8 kg of broccoli powder and 12 kg of yam powder) had the lowest proportion of broccoli powder and the highest proportion of yam powder. Because the yam powder had a higher content of viscous polysaccharides, it had a stronger protective effect on chlorophyll and improved melt adhesion, resulting in the highest chlorophyll retention rate (84%), the highest cooking integrity rate (96%), and the lowest hardness (278 g). It had advantages in color protection and the soft, glutinous texture after re-steaming.

[0104] Example 3 (10 kg broccoli powder, 10 kg yam powder, but the temperature of the three-section section was reduced to 135°C, the four-section section to 130°C, the five-section section to 110°C, and the six-section section to 90°C; the length of the constant-temperature delay section was increased to 100 mm, and the dwell time was 20 s; the total dwell time of the three-section and four-section sections was increased to 60 s). Due to the extended heating time of the constant-temperature delay section and the three-section and four-section sections, the chlorophyll retention rate slightly decreased to 82%, the firmness slightly increased to 292 g, and the cooking integrity rate remained at 95%. Its texture was firmer than that of Examples 1 and 2, suitable for consumers who prefer a slightly firmer texture, and the parameter combination was still far superior to all comparative examples, falling within an acceptable preferred range.

[0105] In summary, all three embodiments can achieve the objectives of this invention, and producers can flexibly choose according to the color, taste positioning, and processing conditions of the target product. If maximizing chlorophyll retention and a soft, chewy texture is the primary goal, the parameter combination of Embodiment 2 is more advantageous; if a balance between shaping, color protection, and texture is desired, Embodiment 1 is preferred; if a more robust product texture is required, the parameter combination of Embodiment 3 is more suitable.

[0106] Comparative Example 1, employing conventional three-stage extrusion (without a constant-temperature delay section, without reverse threads, and without helical grooves), lacks the core structure of this invention, resulting in as many as 2.5 cracks per grain, a deterioration in color to yellowish-brown (a* value +4.5, b* value +22.0), almost complete loss of green color, a cooking integrity rate of only 52%, a chlorophyll retention rate of only 40%, and a hardness as high as 410g (excessively hard). All indicators are significantly inferior to Examples 1, 2, and 3. The data from Comparative Example 1 demonstrate that conventional three-stage extrusion cannot simultaneously solve the problems of molding and color protection.

[0107] Comparative Example 2, without the addition of yam powder (broccoli powder was replaced with 20 kg, and rice powder remained unchanged at 80 kg), completely lacked the binding and protective effects of yam polysaccharides. This led to two consequences: first, the materials could not form effective bonds, resulting in a loose product structure, a significant increase in cracks (3.1 cracks / particle), and a sharp drop in the cooking integrity rate to 42%; second, the loss of chlorophyll protection caused chlorophyll to rapidly degrade at high temperatures, with a retention rate of only 31%, and severe product discoloration (a* value +6.0, b* value +24.0). The formability, color protection effect, and cooking quality of Comparative Example 2 were significantly inferior to Examples 1, 2, and 3. This demonstrates that without yam polysaccharides, even with a constant-temperature delay section and a synergistic shearing structure between the cylinder and screw, it is impossible to effectively protect chlorophyll and ensure formability; therefore, yam powder is indispensable in the formulation of this invention.

[0108] Comparative Example 3, lacking the isothermal delay section (with the rest of the structure identical to Example 1), resulted in a chlorophyll retention rate of only 42%, a dark brown color (a* value +2.3, b* value +23.0), and a cooking integrity rate of 77%. Both the color-protecting effect and cooking quality were inferior to Examples 1, 2, and 3. This demonstrates that the isothermal delay section is crucial for color protection.

[0109] Comparative Example 4, lacking both reverse threads and helical grooves (only ordinary feed threads) in the isothermal delay zone, exhibited insufficient mixing, resulting in fine surface lines (0.8 lines / particle), a yellowish-green color (a* value -6.5, b* value +13.5), an 82% cooking integrity rate, a 67% chlorophyll retention rate, and a relatively hard 330g. Its formability and color protection effects were inferior to Examples 1, 2, and 3. This indicates that the synergistic structure of reverse threads and helical grooves significantly contributes to the uniform dispersion of polysaccharides and the protection of chlorophyll.

[0110] Comparative Example 5, with the sixth-stage temperature set at 105℃, resulted in excessive puffing upon demolding, with only 50% of the material remaining intact after cooking. The material was unevenly softened at 220g and had a yellowish color (a* value of -4.8, b* value of +17.0). Its formability, texture, and color retention were significantly inferior to Examples 1, 2, and 3. When the sixth-stage temperature exceeded 100℃, moisture in the material flashed at the die head, indicating that the sixth-stage temperature must be controlled below 100℃ to prevent puffing.

[0111] Comparative Example 6 had only 12% water added, resulting in insufficient starch gelatinization, 2.7 cracks per grain, a cooking integrity rate of only 46%, excessive hardness (490g), and severe yellowing (a* value -3.9, b* value +18.5). All indicators were inferior to Examples 1, 2, and 3. This proves that the water addition should be between 15% and 25%.

[0112] Comparative Example 7 had a water content as high as 28%, resulting in an excessively soft melt, flattened particle shape, and a hardness of 135g, which was also too soft. Although the cooking integrity rate was 80%, the color remained bright green (a* value -7.5, b* value +9.5), but the texture was severely deteriorated, and the overall quality was inferior to Examples 1, 2, and 3. This proves that the water content should not exceed 25%.

[0113] In summary, all indicators of Examples 1-3 are significantly superior to those of all comparative examples, fully verifying the systematic advantages and synergistic effects of the technical solution of the present invention (including specific raw material ratios, zoned temperature control, constant temperature delay zones, reverse threaded elements, spiral grooves on the inner wall of the cylinder, water addition of 15%-25%, and six-stage temperature ≤100℃, etc.). This successfully solves the dual technical challenges of shaping and color protection in the preparation of high-proportion vegetable powder reconstituted rice. The parameter combinations of Examples 1-3 are all within the protection range and all achieve excellent results. Producers can select specific parameters within the protection range according to their specific needs.

[0114] In another embodiment, in the method for preparing the nutritionally fortified vegetable processed rice, the raw materials in S1 are passed through a 60-120 mesh sieve before mixing, and are poured into a mixing bucket and stirred at a speed of 20-40 r / min for 1-5 min during mixing.

[0115] In S2, the mixed material is fed into a single screw extruder at a feed temperature of 40~50℃.

[0116] The blade speed during rotary cutting in S3 is 2500~3000 r / min.

[0117] In S1, the raw materials are sieved through a 60-120 mesh screen before mixing to remove larger particles and agglomerates, resulting in a more uniform particle size distribution. This is beneficial for the consistent dispersion of components during subsequent mixing and extrusion. During mixing, the mixture is stirred at a speed of 20-40 r / min for 1-5 minutes, which ensures thorough mixing without generating excessive heat or mechanical damage due to excessively high speed.

[0118] In S2, controlling the feed temperature at 40~50℃ can maintain the material's appropriate fluidity and temperature before it enters the extruder, avoiding the problem of excessively low temperature causing excessively high material viscosity and making conveying difficult, and also avoiding the problem of excessively high temperature causing premature gelatinization of the material.

[0119] In S3, the rotary cutter head speed is set to 2500~3000 r / min, which enables the extruded material to be quickly cut into uniform short particles with a smooth cut, reducing burrs and irregular edges on the particle surface. This results in rice-like particles with regular shape and uniform size, while avoiding particle sticking or stringing caused by excessively low speed. The synergistic effect of these parameters further improves the molding uniformity and appearance quality of the product, and helps maintain the stability of the extrusion process.

[0120] In another embodiment, the method for preparing fortified vegetable processed rice includes, after drying in step S3, a step of spraying a pregelatinized starch layer onto the surface of the processed rice, specifically:

[0121] Heat water to 40-50℃, slowly add pregelatinized rice starch or pregelatinized cassava starch while stirring, so that the final concentration of pregelatinized rice starch or pregelatinized cassava starch is 5%-10% of the total mass of the solution, and continue stirring until completely dissolved; then add 0.5%-1.0% of glycerol by mass of pregelatinized rice starch or pregelatinized cassava starch, and continue stirring for 8-10 minutes to obtain a pregelatinized starch solution;

[0122] The prepared pregelatinized starch solution is sprayed onto the surface of processed rice by atomization. The amount of spraying is 1% to 2% of the mass of processed rice, and the spraying temperature is 40 to 50℃.

[0123] The coated reconstituted rice is dried again at 50-60℃ for 30-60 minutes to reduce the moisture content of the reconstituted rice to 6%-10%.

[0124] In the basic scheme, Example 2 has achieved excellent results such as no surface cracks, 96% cooking integrity, and 84% chlorophyll retention, indicating that the two core problems of difficult molding and chlorophyll degradation have been fundamentally solved. However, further analysis revealed that the surface gloss after cooking was not ideal, and there was slight adhesion between rice grains, indicating slightly poor dispersibility. In addition, the surface chlorophyll still slowly oxidizes and degrades during long-term storage. To address these refined issues related to surface characteristics, an additional step of spraying a pregelatinized starch layer onto the surface was added after the basic scheme.

[0125] In the solution preparation stage of the additional step, water is heated to 40-50℃, and pregelatinized rice starch or pregelatinized tapioca starch is slowly added while stirring. The final concentration of pregelatinized rice starch or pregelatinized tapioca starch is 5%-10% of the total mass of the solution, and stirring continues until completely dissolved. Pregelatinized starch refers to starch that has already undergone gelatinization and drying, which can disperse in cold water to form a solution with a certain viscosity without the need for heating for gelatinization. The solution mass fraction is controlled at 5%-10% because if the concentration is too low, the film layer formed will be too thin to provide an effective buffering effect; if the concentration is too high, the solution viscosity will be too high, making it difficult to spray evenly, and if the film layer is too thick after drying, it may affect the taste of the rice grains. Heating to 40-50℃ helps the starch granules to fully hydrate, while avoiding starch degradation due to excessive temperature. Then, 0.5%-1.0% of glycerol by mass of pregelatinized rice starch or pregelatinized tapioca starch is added, and stirring continues for 8-10 minutes to obtain the pregelatinized starch solution. Glycerin, as a plasticizer, can increase the flexibility of the film layer and prevent it from becoming brittle after drying. The amount of glycerin added is calculated based on the mass of the pregelatinized starch. For example, adding 0.5~1.0g of glycerin to 100g of pregelatinized rice starch can ensure that the film layer is flexible without making the rice grain surface sticky.

[0126] In the spraying process, the prepared pregelatinized starch solution is atomized and sprayed onto the surface of the processed rice. The spraying amount is 1% to 2% of the mass of the processed rice, and the spraying temperature is 40 to 50°C. Atomized spraying ensures that the solution evenly covers the surface of each grain of rice, forming a thin and continuous film. The spraying amount of 1% to 2% means that 1 to 2g of solution is sprayed per 100g of rice grain. Too little spraying will result in incomplete coverage, while too much will result in an excessively thick film and prolonged drying time. The spraying temperature should be kept consistent with the solution preparation temperature to avoid fluctuations in solution viscosity caused by temperature changes, which would affect the uniformity of the spraying.

[0127] In the secondary drying step, the coated processed rice is dried again at 50-60℃ for 30-60 minutes to reduce the moisture content to 6%-10%. The purpose of the secondary drying is to remove the moisture introduced during the spraying process and to solidify the pregelatinized starch film. The temperature of 50-60℃ is below the gelatinization temperature of starch, which will not damage the film structure; the time of 30-60 minutes ensures that the moisture content is reduced to a safe storage level. The final product's moisture content of 6%-10% ensures both the product's microbial stability and maintains good texture.

[0128] The additional surface coating step serves two purposes: First, the pregelatinized starch film rapidly absorbs water during the initial cooking stage to form a gel layer. This gel layer acts as a buffer, delaying water penetration into the rice grains and preventing excessive gelatinization. This reduces grain adhesion, ensuring the cooked rice grains retain their integrity and have a smooth appearance. Second, the film forms a uniform, dense physical cover on the rice grain surface, reducing the direct contact area between surface chlorophyll and air. Third, the hydrated gel layer formed during the initial cooking stage effectively blocks or delays external factors from damaging the color, thus contributing to the preservation of the finished product's color. Fourth, the added glycerol acts as a plasticizer for the pregelatinized starch film layer. Its addition and residual amounts are extremely low. For example, with 100g of processed rice, if 1.5g of pregelatinized starch solution is sprayed (pregelatinized starch concentration is 8%), and the added glycerol is 0.8% of the pregelatinized starch mass, the final glycerol residue is only about 1mg, which is a trace amount. Glycerin increases the flexibility and extensibility of the film by reducing the hydrogen bonding forces between pregelatinized starch molecular chains, ensuring that the film will not crack during drying and subsequent packaging and transportation, thus maintaining the integrity and functionality of the coating for a long time.

[0129] Example 4

[0130] Based on Example 2, an additional step of spraying a pregelatinized starch layer onto the surface was added. The specific steps were as follows: water was heated to 45°C, and pregelatinized rice starch was slowly added while stirring, until the final concentration of the pregelatinized rice starch was 8% of the total mass of the solution. Stirring continued until completely dissolved. Then, glycerol at 0.8% of the mass of the pregelatinized rice starch was added, and stirring continued for 9 minutes to obtain a pregelatinized starch solution. The pregelatinized starch solution was sprayed onto the surface of the processed rice prepared in Example 2 using an atomizing method, with a spraying amount of 1.5% of the mass of the processed rice and a spraying temperature of 45°C. The sprayed processed rice was then placed in hot air at 55°C for a second drying process of 45 minutes to reduce the moisture content of the processed rice to 9%.

[0131] Example 4 was compared and evaluated with Example 2:

[0132] Cooking test: Take 50g of sample, add 75mL of water, place in a 500mL beaker, cook in a boiling water bath for 15min, and let it sit for 5min. Gently pour the cooked rice grains into a sieve, rinse once slowly with room temperature water, and count the proportion of intact rice grains.

[0133] The results showed that the cooking integrity rate of Example 2 was 96%, with slight adhesion on the surface of the rice grains and average gloss; while the cooking integrity rate of Example 4 was 97%, with smooth rice grains without adhesion and significantly improved gloss.

[0134] Rehydration rate test: Take 20g of sample, add 30mL of water, soak in 80℃ water bath, take out 5 grains every 1min, blot the surface moisture with filter paper, weigh and calculate the water absorption rate.

[0135] The results showed that after soaking for 4 minutes, the water absorption rate of Example 2 was 52%, and that of Example 4 was 31%; the final equilibrium water absorption rate for both was approximately 62%. This indicates that the pregelatinized starch film delayed the initial water penetration, resulting in more uniform rehydration and preventing excessive surface gelatinization.

[0136] After 3 months of storage at room temperature in the dark, the chlorophyll retention rate was measured. In Example 2, it decreased from the initial 84% to 79% (a decrease of 5 percentage points), while in Example 4, it only decreased from the initial 84% to 82% (a decrease of 2 percentage points). This indicates that the surface coating has a positive effect on delaying the oxidation and fading of surface chlorophyll by reducing the direct contact between surface chlorophyll and air. In addition, the hardness of Example 4 was 295g, slightly higher than that of Example 2 (278g), but still within a moderate range, and there was no significant difference in chewing texture.

[0137] In summary, the surface coating with a pregelatinized starch layer further optimizes the appearance, rehydration uniformity, and storage stability of rice grains.

[0138] In another embodiment, in the method for preparing the fortified vegetable processed rice, the monoglyceride in S1 is glyceryl monostearate, and the amount of glyceryl monostearate added is 1.2% to 1.5% of the total mass of the raw materials; the amount of water added is 18% to 20% of the total mass of the raw materials.

[0139] In S2, the temperature of the third section is 135~140℃, the temperature of the fourth section is 130~135℃, the temperature of the fifth section is 110~115℃, and the temperature of the sixth section is 90~92℃.

[0140] Limiting the addition of monoglyceride fatty acid esters to 1.2%~1.5% of the total raw material mass allows for more precise suppression of excessive puffing at the die head, resulting in a denser and smoother rice grain surface, reducing surface defects. It also avoids insufficient puffing suppression due to too low an addition or an oily rice grain surface due to too high an addition. Narrowing the water addition to 18%~20% of the total raw material mass keeps the melt viscosity within the optimal range. This ensures sufficient starch gelatinization to form a continuous network while preventing excessive moisture from causing the melt to be too soft and deformed upon demolding, or insufficient moisture from causing uneven gelatinization and affecting molding. This further improves the cooking integrity rate and grain uniformity.

[0141] The temperatures for the three-stage section were set at 135-140℃, the four-stage section at 130-135℃, the five-stage section at 110-115℃, and the six-stage section at 90-92℃. The three-stage section temperature of 135-140℃ ensured full gelatinization of starch and moderate softening of dietary fiber, while preventing significant magnesium loss in chlorophyll. The four-stage section temperature of 130-135℃ maintained high-temperature homogenization, allowing yam polysaccharides and chlorophyll to fully blend and form an effective thermal degradation barrier. The five-stage section temperature of 110-115℃ rapidly cooled the melt, increasing viscosity and providing sufficient structural strength for subsequent molding. The six-stage section temperature of 90-92℃ ensured rapid surface solidification upon demolding, forming a dense skin and effectively inhibiting over-expansion. By adopting this optimized temperature gradient, the exposure time of the material in the high-temperature zone is effectively controlled within the ideal range. This ensures complete starch gelatinization and integrity of the molding process, resulting in good chlorophyll retention. The product has a smooth, crack-free surface, intact granules after cooking, moderate texture, and excellent overall quality.

[0142] In another embodiment, in the preparation method of the fortified vegetable processed rice, after drying in step S3, the processed rice is placed in a sealed container and warmed at 40-50℃ for 2-4 hours to allow the internal moisture of the processed rice to migrate to the surface; then, atomized water is sprayed into the sealed container to uniformly wet the surface of the processed rice and raise the moisture content to 12%-14%, and then it is left to stand for 30-60 minutes; finally, the processed rice is placed in hot air at 50-60℃ with a wind speed of 0.5-1.0 m / s and dried for 10-20 minutes to reduce the surface moisture content of the processed rice to 6%-10%, and then packaged.

[0143] In the basic scheme, such as the processed rice prepared in Example 2, the internal moisture distribution is not uniform after high-temperature extrusion and subsequent drying. Specifically, the surface of the rice grains, due to direct contact with the heat medium, experiences rapid moisture evaporation, and the starch polymer undergoes a rapid glass transition, forming a continuous, dense hard shell. Meanwhile, the internal moisture content is relatively high due to obstructed migration pathways. This significant internal and external moisture gradient leads to two problems: First, during storage, the uneven moisture content acts as a driving force, accelerating the orderly rearrangement of starch molecular chains, i.e., retrogradation, causing the product to harden after re-steaming. Second, the dense hard shell on the surface becomes a barrier to moisture penetration during re-steaming, resulting in insufficient rehydration in the center of the rice grains, leading to an undercooked or hard core.

[0144] It should be noted that the aforementioned dense, hard shell is not a manufacturing defect, but rather an intentional feature of this invention. It is achieved by controlling the temperature of the six sections at a low temperature of 90-100°C, combined with rapid cooling of the die head. This shell prevents the rice grains from puffing and cracking during demolding, granulation, and initial drying, maintaining their initial shape. It is a key structure for achieving a good product appearance. However, as the product enters the storage and re-steaming stages, the functional requirements of the same structure change: its dense structure becomes a barrier to the bidirectional migration of moisture, hindering internal moisture escape and exacerbating starch retrogradation, while also preventing external moisture penetration during re-steaming, resulting in an undercooked texture.

[0145] To address this issue, a three-step conditioning process—warming, rehydration, and hot air drying—was added after the basic solution. The purpose of this process is not simply to wet the surface of the rice grains, but to precisely control the moisture migration path and modify the dense outer layer formed during the preparation stage in situ. This allows the rice to achieve efficient mass transfer without compromising its overall strength. The two states are switched at different stages, working together to ensure the product's quality throughout its entire lifecycle.

[0146] Warm-up steps:

[0147] The dried rice is placed in a sealed container and reheated at 40-50℃ for 2-4 hours. Within this temperature range, starch does not gelatinize, but the mobility of molecular chains is enhanced. The core purpose of reheating is to promote the directional migration of high-moisture content inside the rice grain to the lower-moisture surface area through diffusion under gentle heat. This process essentially eliminates the stress and moisture gradient inside the rice grain caused by rapid drying, bringing the overall chemical potential of moisture towards equilibrium. Taking a batch of rice grains with an initial moisture content of 9% as an example, after reheating at 45℃ for 3 hours, the internal moisture content can be reduced to about 8%, while the surface moisture content rises to about 10%, creating uniform matrix conditions for the next processing step. Rehydration step:

[0148] Atomized water is sprayed into a sealed container that has undergone rehydration, accompanied by gentle agitation, to evenly moisten the surface of the reprocessed rice, precisely restoring its overall moisture content to 12%–14%, followed by standing for 30–60 minutes. This step is the core of the entire technology. The mechanism here is not simply softening the already formed hard shell, but rather utilizing the plasticizing effect of water on the starch matrix. When the atomized water evenly adheres to the surface of the rice grains, the starch polymer in the dense surface layer swells locally, creating uneven stress within the originally continuous glassy structure. During the subsequent standing process, the water forms interconnected microchannels within the hard shell layer at these local swelling points. Strict control of the moisture content of 12%–14% is crucial: below 12%, swelling is insufficient, and an effective channel network cannot be formed; above 14%, the overall moisture content is too high, causing the rice grains to become sticky, and the channel structure is prone to collapse during subsequent drying. This step successfully transforms the dense hard shell that hinders rehydration into an outer shell with interconnected channels.

[0149] Hot air drying steps:

[0150] The reprocessed rice, after the channel construction is completed, is placed in hot air at 50-60℃ and a wind speed of 0.5-1.0 m / s for short-term directional drying for 10-20 minutes. This allows free moisture on the surface and outside the channels to evaporate rapidly, resulting in a final product moisture content of 6%-10%. This drying process is highly selective: it removes only the free water from the surface layer of the rice grain and the created channels, with minimal impact on the moisture content of the subsurface layer below the hard shell and the center of the rice grain. As a result, the rice grain ultimately forms a novel three-phase structure: the outermost layer is dry and smooth (moisture content 6%-10%), the middle original hard shell layer is modified and filled with interconnected channels, and the central region retains a relatively high moisture content of 10%-12%. The dry and smooth outermost layer facilitates packaging and prevents sticking; the modified middle layer provides an efficient mass transfer path, allowing hot water to quickly penetrate into the center of the rice grain during re-distillation along the channel network; and the higher moisture content in the center maintains the migratory nature of the starch molecular chains, creating an ideal state to inhibit retrogradation.

[0151] Overall effect:

[0152] After the above three-step conditioning process, the reprocessed rice acquires entirely new quality characteristics. First, the high moisture content maintained in the central region gives the starch molecular chains sufficient thermodynamic mobility, effectively preventing recrystallization (retrogradation) during storage and allowing the rice grains to maintain viscoelasticity for a long time. Second, and most importantly, during re-steaming, when hot water comes into contact with the surface of the rice grains, the outermost layer, being extremely thin and having a low moisture content after conditioning, has rapid wetting properties. Moisture penetrates the surface with almost no delay and is immediately absorbed and transported to the center of the rice grain by the intermediate modified layer through capillary effect along the pre-made channel network, completely eliminating the moisture transfer barrier originally caused by the dense hard shell. This instantaneous pathway ensures that the rice grains gelatinize rapidly and synchronously from the outside to the inside, with no hard core in the center. Thus, the soft, resilient, and elastic freshly cooked texture can be completely restored within a very short reheating time, perfectly solving the problem of deterioration in taste after long-term storage and re-steaming.

[0153] Example 5

[0154] Based on Example 2, a reheating-rehydration-re-drying process was added. Specifically, the rice was dried to a moisture content of 9% according to the steps of Example 2. The rice was then placed in a sealed container and reheated at 45°C for 3 hours. Atomized water was sprayed into the container to evenly wet the surface of the rice grains, raising the moisture content back to 13%, and the mixture was left to stand for 45 minutes. Finally, the rice grains were placed in hot air at 55°C with a wind speed of 0.8 m / s for 15 minutes to reduce the surface moisture content to 9%.

[0155] Elastic recovery rate was measured using a texture analyzer in TPA (texture multifaceted analysis) mode, with parameters set in the same manner as for hardness measurement. The results were automatically calculated by the instrument software.

[0156] The re-steaming quality of Example 5 and Example 2 was compared:

[0157] After storing the samples in a sealed container at room temperature for 7 days, they were then boiled according to the boiling conditions in the performance evaluation method, and the re-boiling hardness and elastic recovery rate were measured. The samples were then stored in a sealed container at room temperature for another 30 days, and the re-boiling test was performed again.

[0158] The results showed that, regarding surface cracks, both Example 2 and Example 5 had 0 cracks / particle. Regarding color, Example 2 had an a* value of -8.0 and a b* value of +9.8; Example 5 had an a* value of -7.8 and a b* value of +10.2. There was no significant difference in color between the two, indicating that the conditioning treatment did not adversely affect the product color. Regarding the cooking integrity rate, both Example 2 and Example 5 had a rate of 96%.

[0159] Regarding hardness and elasticity recovery rate, after 7 days of storage and re-steaming, the hardness of Example 2 was 295g and the elasticity recovery rate was 66%; after 7 days of storage and re-steaming, the hardness of Example 5 was 280g and the elasticity recovery rate was 72%. After 30 days of storage, the hardness of Example 2 after re-steaming was 310g and the elasticity recovery rate was 61%; the hardness of Example 5 after re-steaming was 290g and the elasticity recovery rate was 69%. It is particularly noteworthy that the hardness of Example 5 after 7 days of storage (280g) was almost the same as that of Example 2 after fresh preparation and direct steaming (278g), indicating that the warming-rehydration-re-drying treatment enabled the rice grains to maintain a hardness close to that of fresh grains even after one week of storage, effectively inhibiting starch retrogradation. This result further demonstrates the significant effect of the anti-retrogradation technology of the present invention.

[0160] Regarding texture evaluation, after 7 days of storage, Example 5, after re-steaming, exhibited a soft and glutinous texture with good elasticity, while Example 2, after re-steaming, maintained good elasticity, although its hardness was slightly higher than Example 5. After 30 days of storage, Example 5 still maintained good softness and elasticity, while the re-steamed texture of Example 2, although slightly reduced, remained highly acceptable overall, with Example 5 showing a more significant improvement. These results indicate that Example 2 maintained good re-steaming quality after both 7 and 30 days of storage, exhibiting moderate hardness and good elasticity. Example 5, through a reheat-rehydration-re-drying treatment, further delayed the increase in hardness and decrease in elasticity during storage without affecting surface cracks, color, or cooking integrity. Its hardness and elasticity recovery rates were superior to Example 2, improving the re-steamed texture of processed rice after long-term storage. Example 5, while maintaining the excellent shaping and color-preserving effects of Example 2, further enhanced the product's storage stability.

[0161] In another embodiment, in the preparation method of the fortified vegetable processed rice, after hot air drying and before packaging, the processed rice is placed in an environment with a temperature of 25~30℃ and a relative humidity of 40%~50% and left to stand for 1~2 hours.

[0162] After hot air drying and before packaging, the processed rice is placed in an environment with a temperature of 25-30℃ and a relative humidity of 40%-50% for 1-2 hours. This allows the residual trace moisture inside the rice grains to diffuse more evenly, eliminating the slight temperature and moisture gradients that may have been caused by hot air drying. Simultaneously, these temperature and humidity conditions, close to room temperature, allow the rice grains to cool slowly to room temperature, preventing condensation inside the packaging due to direct packaging. The relative humidity of 40%-50%, lower than normal ambient humidity, causes slight water loss from the surface of the rice grains, preventing them from becoming damp and sticky after packaging, thus maintaining the looseness and good flowability of the rice grains.

[0163] After a settling process, the product is less prone to sticking or mold growth during subsequent packaging, transportation, and storage, extending its shelf life. Furthermore, the rice grains remain intact and well-dispersed after opening the bag, preventing clumping during cooking. This step does not introduce any external substances; it only further enhances the product's shelf stability and ease of use through environmental temperature and humidity control.

[0164] In another embodiment, in the method for preparing fortified vegetable processed rice, the total residence time of the material in the three-section and four-section zones in step S2 is 45-60 seconds. Through the coordination of screw configuration and rotation speed, the residence time of the material in the isothermal delay zone is 10-20 seconds; simultaneously, the total residence time of the material in the three-section and four-section zones is 45-60 seconds. These two residence times are achieved through coordinated adjustment of the same screw rotation speed.

[0165] The third and fourth temperature zones represent the highest temperature treatment range for the material, where starch gelatinization, fiber softening, and the construction of the protective matrix for chlorophyll by polysaccharides all occur. Controlling the total residence time of the material in these two zones to 45-60 seconds achieves a balance in two aspects: firstly, ensuring complete starch gelatinization and sufficient dissolution of yam polysaccharides, effectively integrating them with chlorophyll to guarantee shape retention and color protection; secondly, avoiding excessive heat degradation of chlorophyll or excessive starch gelatinization leading to a harder rice grain texture due to prolonged high-temperature residence. Below 45 seconds, insufficient starch gelatinization and polysaccharide dissolution result in decreased shape retention and color protection; above 60 seconds, chlorophyll retention decreases, and the product becomes too hard. The optimal range of 45-60 seconds allows the material to achieve the best heat treatment effect in the high-temperature zone, resulting in a smooth product surface, intact grain shape after cooking, moderate hardness, and high chlorophyll retention. This residence time is achieved through the coordinated operation of screw speed and feeding speed, and is one of the key process parameters for ensuring a balance between molding quality and color protection.

[0166] In another embodiment, in the preparation method of the nutritionally fortified vegetable processed rice, after secondary drying in step S3, the processed rice is cooled to 0~5℃, stirred at a speed of 10~20r / min for 1~2min, then passed through a 20~40 mesh sieve, and then placed in a sealed container to warm up to 20~25℃ before packaging.

[0167] After secondary drying, the processed rice is rapidly cooled to 0-5°C. This low temperature inhibits residual stickiness and starch molecule migration on the rice grain surface, causing the surface to harden quickly and reducing adhesion. Then, it is stirred at a low speed of 10-20 rpm for 1-2 minutes. Utilizing the surface rigidity imparted by the low temperature, gentle mechanical force breaks down the slight adhesion between rice grains caused by moisture or residual sugar, separating them without damaging their integrity. Next, the rice is passed through a 20-40 mesh sieve to remove trace amounts of fine powder and irregular fragments, ensuring uniform particle size and a clean appearance. Finally, the sieved rice grains are placed in a sealed container and warmed to 20-25°C to eliminate the risk of condensation that may occur during low-temperature packaging and to restore the rice grain temperature to room temperature, preventing condensation inside the packaging.

[0168] After the above treatment, the product's particle dispersibility is significantly improved, resulting in good flowability, no clumping after packaging, and distinct particles upon opening the bag. It also prevents sticking during cooking, and the removal of fine powder reduces the possibility of mushy soup during cooking. The entire process is achieved solely through physical methods of controlling temperature and mechanical force, without adding any exogenous substances, effectively enhancing the product's appearance and ease of use.

[0169] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A method for preparing fortified vegetable processed rice, characterized in that, Includes the following steps: S1: Weigh the raw materials according to the following formula, with the proportions of raw materials as mass fractions: rice flour 70%~90%, broccoli flour 5%~15%, yam flour 5%~15%; and add monoglyceride fatty acid esters accounting for 0.3%~1.5% of the total mass of raw materials and water 15%~25%, and mix well; S2: The mixed material is fed into a single-screw extruder, employing a segmented temperature-controlled extrusion method. The extrusion process is divided into six independent segments along the material flow direction: segment 1 (80-100℃), segment 2 (100-120℃), segment 3 (120-140℃), segment 4 (120-140℃), segment 5 (100-120℃), and segment 6 (90-100℃). A constant-temperature delay segment with a length of 60-100mm is set between segment 2 and segment 3, maintaining the temperature of the constant-temperature delay segment at 100-110℃. A set of reverse threaded elements is installed on the extruder screw within the constant-temperature delay segment, covering the constant-temperature delay section. The pitch of the reverse thread element in the entire working length of the constant temperature delay section screw is 50%~80% of the pitch of the extrusion screw drive thread section located upstream of the constant temperature delay section and adjacent to the reverse thread element, and the thread depth of the reverse thread element is 70%~90% of the thread depth of the extrusion screw drive thread section located upstream of the constant temperature delay section and adjacent to the reverse thread element; a helical groove is machined on the inner wall of the cylinder in the constant temperature delay section, the pitch of the helical groove is the same as the pitch of the reverse thread element, and the helical direction of the helical groove is opposite to the thread direction of the reverse thread element; the residence time of the material in the constant temperature delay section is 10~20s by controlling the screw speed; S3: The extruded material is immediately rotary cut into granules, which are then dried to obtain processed rice.

2. The method for preparing fortified vegetable processed rice according to claim 1, characterized in that, Before mixing, the raw materials in S1 are passed through a 60-120 mesh sieve. When mixing, they are poured into a mixing bucket and stirred at a speed of 20-40 r / min for 1-5 min. In S2, the mixed material is fed into a single screw extruder at a feed temperature of 40~50℃. The blade speed during rotary cutting in S3 is 2500~3000 r / min.

3. The method for preparing fortified vegetable rice according to claim 1, characterized in that, After drying in S3, the process also includes a step of spraying a pregelatinized starch layer onto the surface of the processed rice, specifically: Heat water to 40-50℃, slowly add pregelatinized rice starch or pregelatinized cassava starch while stirring, so that the final concentration of pregelatinized rice starch or pregelatinized cassava starch is 5%-10% of the total mass of the solution, and continue stirring until completely dissolved; then add 0.5%-1.0% of glycerol by mass of pregelatinized rice starch or pregelatinized cassava starch, and continue stirring for 8-10 minutes to obtain a pregelatinized starch solution; The prepared pregelatinized starch solution is sprayed onto the surface of processed rice by atomization. The amount of spraying is 1% to 2% of the mass of processed rice, and the spraying temperature is 40 to 50℃. The coated reconstituted rice is then dried again at 50-60℃ for 30-60 minutes to bring the moisture content of the reconstituted rice to 6%-10%.

4. The method for preparing fortified vegetable rice according to claim 1, characterized in that, The monoglyceride fatty acid ester mentioned in S1 is glyceryl monostearate, and the amount of glyceryl monostearate added is 1.2% to 1.5% of the total mass of the raw materials; the amount of water added is 18% to 20% of the total mass of the raw materials. In S2, the temperature of the third section is 135~140℃, the temperature of the fourth section is 130~135℃, the temperature of the fifth section is 110~115℃, and the temperature of the sixth section is 90~92℃.

5. The method for preparing fortified vegetable rice according to claim 1, characterized in that, After drying in S3, the processed rice is placed in a sealed container and warmed at 40-50℃ for 2-4 hours to allow the internal moisture of the processed rice to migrate to the surface. Then, atomized water is sprayed into the sealed container to evenly wet the surface of the processed rice and raise the moisture content to 12%-14%. After that, it is left to stand for 30-60 minutes. Finally, the processed rice is placed in hot air at 50-60℃ with a wind speed of 0.5-1.0 m / s and dried for 10-20 minutes to reduce the surface moisture content of the processed rice to 6%-10% before packaging.

6. The method for preparing fortified vegetable processed rice according to claim 5, characterized in that, After hot air drying and before packaging, the processed rice is placed in an environment with a temperature of 25~30℃ and a relative humidity of 40%~50% and left to stand for 1~2 hours.

7. The method for preparing fortified vegetable rice according to claim 1, characterized in that, The total residence time of the material in S2 in the three-section and four-section sections is 45~60s.

8. The method for preparing fortified vegetable processed rice according to claim 3, characterized in that, In S3, after secondary drying, the processed rice is cooled to 0~5℃, stirred at 10~20r / min for 1~2min, then passed through a 20~40 mesh sieve, and then placed in a sealed container to warm up to 20~25℃ before packaging.

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