Preparation method, application and product of a high RS-resistant rice flour

Abstract

This application relates to a method for preparing high-RS resistant rice flour using rice broken rice or rice, and the application of high-RS resistant rice flour in the preparation of low-GI yogurt. This application improves the prior art. By controlling the feeding speed and screw speed, and increasing the temperature in the cooking zone (melting zone), and cooperating with a specific length-diameter ratio, the pressure formed at the die is regulated to reduce the mechanical damage caused by high shear force during the extrusion puffing process, so that the content of resistant starch (RS) in rice is significantly increased, from 7.40% in the raw material zone to 33.79% in the extrusion zone. Further, in combination with a specific retrogradation method, the content of RS-type resistant starch is increased from 7.40% in the raw material zone to 39.98% after the retrogradation treatment, that is, an increase of 5-6 percentage points on the basis of the extrusion zone. The present invention adds high-RS resistant rice or rice broken rice flour to skim milk, and the prepared set yogurt has a low GI value, strong water holding capacity, a good protein cross-linking structure, a delicate and smooth taste with Q elasticity, and a rich and mellow flavor.

Description

Technical Field

[0001] This application relates to the technical field of functional foods, in particular to a preparation method for preparing high-RS resistant rice flour using broken rice or rice, and the application of the high-RS resistant rice flour in the preparation of low-GI yogurt. Background Art

[0002] Rice, also known as paddy rice, is known as the "king of the five grains" and is one of the main food crops for the people in our country. The starch content in rice accounts for about 75-78%. According to the digestibility, starch can be divided into rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS). Compared with other types of resistant starch, rice RS resistant starch has unique properties, with fine and white particles and good anti-digestive properties. It can be used as a stable functional ingredient in low-glycemic index foods, which has positive practical significance for reducing the risk of type II diabetes.

[0003] With the improvement of the national living standard, the sugar intake in people's daily diet has increased and the diet structure is unreasonable, resulting in one of the fastest-growing diabetes prevalence rates in the world in our country. According to the data of the International Diabetes Federation, about 425 million adults in the world have diabetes, and 114 million people in China, and it is predicted to reach 629 million people by 2045, which will seriously affect people's physical health. In response to the above situation, our country has always listed the prevention and treatment of diabetes as a key task, and with the gradual improvement of people's awareness of blood sugar control, there are higher requirements for food ingredients and health functions.

[0004] The glycemic index (GI) is one of the detection indexes reflecting the increase of human blood sugar caused by food. At present, adding dietary fiber, resistant starch, etc. to food is a common method to reduce the blood sugar value of food. These additives slow down the increase of postprandial blood sugar by inhibiting the digestion and absorption rate of carbohydrates in the intestine, thereby inhibiting the increase of the GI value of food and further reducing the prevalence of complications such as diabetes. Yogurt is a dairy product fermented by lactic acid bacteria, which helps with food digestion, and can also play a role in moistening the intestines and relieving and treating constipation, and is deeply loved by consumers.

[0005] In the prior art, there are various methods for preparing RS resistant starch, including hydrothermal treatment methods such as heat-moisture treatment and autoclaving; debranching treatment methods, that is, preparing by enzymatic hydrolysis and acid hydrolysis; ultrasonic method, microwave method, etc., and also including the combined use of the above methods with each other. Extrusion puffing to prepare RS mainly relies on a screw extruder. Through the rapid rotation of the screw, the starch milk is gelatinized under the action of high temperature, high pressure and high shear during the extrusion puffing process. During the gelatinization process, the helical structure of the starch unfolds and amylose is released to increase the opportunity for the formation of RS. During the cooling process, amylose molecules recrystallize to form RS resistant starch. The extrusion puffing method will cause mechanical damage to the starch due to the high shear force during the extrusion puffing process, which will have a certain impact on the yield of RS resistant starch. And it is affected by various factors such as raw materials, barrel temperature, moisture content, feeding rate, screw speed, etc. The interaction relationship between various factors is not clear and there is uncertainty. It is difficult to obtain a process and parameters with a high yield of RS resistant starch. Even when using the extrusion puffing technology alone, the effect is not satisfactory. Therefore, the extrusion puffing technology is limited in the preparation of RS resistant starch alone and is currently usually used as a mechanical auxiliary method in combination with other methods. However, the twin-screw extrusion puffing technology has attracted the attention of researchers because of its characteristics of saving time, pollution-free, high efficiency, and being able to achieve high temperature and high pressure processing simultaneously in a short time, which can effectively improve the starch structure. Nowadays, high-RS resistant starch can be obtained through various physical modification methods, but currently the content of RS resistant starch prepared from rice in industry is not high. In particular, there is no method for preparing rice RS resistant starch solely by using the extrusion puffing technology. How to make good use of the extrusion puffing technology to prepare rice RS resistant starch is an urgent problem to be solved in the food field.

[0006] A large amount of broken rice is generated during the rice processing. Preparing rice flour with a high content of RS resistant starch from broken rice will greatly improve the effective utilization rate and added value of broken rice, broaden the application range of broken rice, and has practical application significance and value.

[0007] In addition, although there is currently the application of RS-type resistant starch in fermented milk, which is used to regulate the intestinal flora, improve intestinal function, control blood lipids and blood sugar index, and can also be used as a thickener. But how to obtain specific yogurt products with good efficacy, high nutrition and good quality and taste is also an urgent problem to be solved in the food processing field. Summary of the Invention

[0008] Object of the Invention: To provide a method for preparing high-RS resistant rice flour by twin-screw extrusion puffing and obtain a rice flour product. At the same time, to provide a set-type low-GI yogurt product with good efficacy and excellent sensory quality.

[0009] Technical Solution: To provide a method for preparing high-RS resistant rice flour by twin-screw extrusion puffing, which is prepared according to the following steps:

[0010] (1) Grind rice or broken rice into rice flour. The rice flour passes through a 30 - 50 mesh sieve, and the initial moisture content is 11 - 12%.

[0011] (2) Feed the material into a twin - screw extruder.

[0012] (3) Extrusion and puffing treatment: Adjust the moisture content to 23 - 26%; under certain feeding speed, screw rotation speed, and extrusion and puffing conditions: the feeding speed is 15 - 40 kg / h; the screw rotation speed is 90 - 100 r / min; the feeding zone temperature of the twin - screw extruder is 30 - 60 °C, the mixing zone temperature is 70 - 90 °C, the cooking zone temperature is 160 - 180 °C, the die - head zone temperature is 40 - 60 °C, control the die - head forming pressure to be 4 - 6 MPa; the screw diameter is 11 - 24 mm, and the L / D ratio is 39 - 41:1.

[0013] (4) Wet - grind and pulverize the extrudate.

[0014] (5) Freeze - dry and screen to obtain high - RS resistant rice powder.

[0015] Further, after step (3), add a retrogradation treatment step: Cool the die - head extrudate to 25 °C at a cooling rate of 2 - 2.5 °C / min, and apply a wind with a speed of 5 - 7 m / s, at 25 °C, and a humidity of 75 - 80% during this cooling process; then continue to cool to 4 °C at a cooling rate of 1 - 1.5 °C / min, and let it stand for 12 h for retrogradation treatment at 4 °C.

[0016] Further, adjust the moisture content, preferably in the form of constant - flow water addition at a certain water - feeding speed during the extrusion process, and calculate according to the following formula (1):

[0017] Water - feeding speed × 1.12 = designed moisture content (1)

[0018] Further, the amylose content of the rice starch is 20 - 30%; preferably, the amylose - to - amylopectin ratio is 1 / 3.5 - 1 / 4 or 1 / 2.3 - 1 / 2.7.

[0019] Further, the feeding speed is 15 kg / h; the screw rotation speed is 90 r / min; the feeding zone temperature is 40 °C, the mixing zone temperature is 80 °C, the cooking zone temperature is 170 °C, the die - head zone temperature is 50 °C; the screw diameter is 20 mm, and the L / D ratio is 40:1; the material adjusts the feeding speed through a feeder.

[0020] Further, in the wet - grinding and pulverizing, the mass ratio of rice flour to deionized water is 1:5 - 8, preferably 1:7; for the freeze - drying and screening, the rice flour passes through a 200 - 300 mesh sieve, preferably through a 200 - mesh sieve.

[0021] This application also provides high - RS resistant rice flour prepared by the above - mentioned methods.

[0022] The present application also provides a coagulated low GI yogurt, which is prepared according to the following method:

[0023] (1) Mixing ingredients

[0024] The skim milk and the high RS resistance rice flour are mixed evenly, preheated to 55-65°C, and Aloet (sweetener), high methoxy pectin and xanthan gum are added, and stirring is continued. The mixture is kept warm for 30 minutes, and the mixture is mixed evenly to obtain a liquid. The mass ratio of the high RS resistance rice flour to the skim milk is 1:250-1:100. The mass ratio of the skim milk to Aloet is 1:0.03-0.08, the mass ratio of the skim milk to high methoxy pectin is 1:0.02-0.03, and the mass ratio of the skim milk to xanthan gum is 1:0.01-0.02.

[0025] (2) Homogenization sterilization

[0026] The liquid obtained in step (1) is homogenized twice at a pressure of 30-40 MPa, sterilized at 90-92°C, and kept warm for 10-20 min;

[0027] (3) Fermentation and ripening

[0028] Cool to 42-45℃ in an ice water bath, add direct-injection starter, stir evenly and ferment at 42-45℃ to pH 4.5, and post-ripen at 2-6℃ for 12h to obtain the solidified low-GI yogurt product.

[0029] It is further preferred that the high RS resistant rice flour is mixed with deionized water in a mass ratio of 1:25-1:12.5, heated to 85°C, kept warm for 15-20 minutes, and then the RS resistant rice flour water mixture: skim milk is 1:25-1:12 by mass.

[0030] The extrusion and expansion machine preferably adopts a detachable parallel co-rotating twin-screw extruder, and an independent temperature control zone is installed in the barrel. Preferably, the material is used to adjust the feeding speed through the feeder. Any other conventional extrusion and expansion machine that can realize the present application can also be used.

[0031] Preferably, the freeze-dried rice is sieved and the rice flour is sieved through a 200-mesh sieve.

[0032] Preferably, the skimmed milk has a fat content of ≤0.5g / 100g, a protein content of ≥3.2g / 100g, and a carbohydrate content of ≥5.0g / 100g.

[0033] Preferably, the auxiliary materials include Alete (sweetener) (purchased from Nanjing Jinhe Yikan Biotechnology Co., Ltd.), high methoxyl pectin (purchased from CPKELCO, USA), and xanthan gum (purchased from Henan Wanbang Industrial Co., Ltd.).

[0034] Aloesweet can also be replaced by commonly used sweeteners such as white sugar or sucrose, and the dosage is 1 / 3 of Aloesweet. High methoxyl pectin and xanthan gum can be replaced by commonly used thickeners and stabilizers in this field, and the dosage can be added appropriately according to the sensory quality requirements.

[0035] Technical effect:

[0036] 1. The present application is improved on the basis of conventional technology according to the composition and processing characteristics of rice raw materials. By reducing the feeding speed and the screw speed, increasing the temperature of the cooking zone (melting zone), and combining a specific aspect ratio, the die opening is regulated to form a pressure of 4-6 MPa to reduce the mechanical damage caused by the high shear force during the puffing process, thereby significantly increasing the RS resistant starch content of rice from 7.40% in the raw material zone to 33.79% in the extrusion zone.

[0037] Analyzing the possibility from the perspective of starch crystal structure, the amylose molecules in starch are easier and more dissolved from the original starch under high temperature conditions. At the same time, the lower feeding speed and screw speed as well as the appropriate pressure formed in the cavity significantly reduce the extrusion shear force. The amylose molecules are not excessively broken and maintain a certain polymerization force, forming a gel (i.e. gelatinization) with water in the form of irregular curls. As the temperature decreases, more short amylose molecules with similar structures or lengths and not excessively broken approach the amylose molecules in the original starch, and re-form regular bundles of double helical structures with hydrogen bonds, and further form a crystalline network. Relatively long chains form longer and more stable helical structures, which are further stabilized by hydrogen bonds and distributed throughout the crystalline area, resulting in a decrease in digestibility. In addition, the specific extrusion treatment causes the amylose molecular chains to be locally tightly stacked in the amorphous area, which inhibits the hydrolysis of digestive enzymes to a certain extent, resulting in an increase in the content of resistant starch after extrusion treatment. From the analysis of starch granule morphology, during the extrusion process, the starch double helix structure is destroyed, the starch granules begin to swell, the birefringence disappears, and the starch granules completely change from swelling and rupture to being fully gelatinized, which completely changes the size and morphological structure of the starch granules. After the starch is gelatinized, during the cooling and regeneration process, the water evaporates, causing the gelatinized starch to recrystallize, the granule size to increase, and the starch aggregates to form.

[0038] The type of raw materials, amylose content, moisture content of the material, extrusion temperature, feeding rate, screw speed, pressure, etc. are all factors that affect the RS resistant starch content of rice. Moreover, the interactions between these factors during the extrusion process are extremely complex, and the factors do not show a simple positive or negative correlation with the RS resistant starch content.

[0039] During the high-temperature extrusion process, when the moisture content is low, it is not conducive to the dissolution of amylose molecules. However, when the moisture content is too high, it is not conducive to the entanglement and polymerization of starch molecules, which affects the yield of resistant starch. Therefore, the adjustment of moisture needs to be considered as a whole.

[0040] 2. In the extrudate with the content of RS-type resistant starch already increased, appropriate low-shear extrusion and puffing conditions enable the presence of a certain amount of short amylose molecules in the extrudate. Continuing to cooperate with a specific retrogradation method further significantly increases the content of RS-type resistant starch, from 7.40% in the raw material area to 39.98% after the retrogradation treatment, which is about 5 - 6 percentage points higher than that in the extrusion area.

[0041] In the actual production of the existing technology, generally, the lower the cooling rate of cooling and retrogradation is, the better. This is because when the speed is too fast, the short amylose in the starch gel does not have time to re-polymerize to form crystals, which hinders the formation of RS-type resistant starch. Therefore, in actual production, subsequent aging and retrogradation are carried out at a slow cooling rate and for a long time, which also indicates that the cooling rate is the key factor affecting the effect of treating aging and retrogradation. However, during the experiment, the research group found that on the basis of the obtained extrudate, by first rapidly cooling (2 - 2.5 °C / min) and simultaneously applying a wind speed of 5 - 7 m / s, at 25 °C, and with a humidity of 75 - 80%, and then slowly cooling to 4 °C and standing for 12 h at 4 °C for retrogradation, the content of rice RS resistant starch is significantly increased again, and its content exceeds 38%. This may be because the wind treatment not only regulates the moisture content but also changes the migration speed and molecular potential energy of amylose in the starch, increasing the opportunities for starch molecule entanglement, polymerization, and tendency to order, and promoting the short-term retrogradation of amylose. In addition, rice flour is different from rice starch and contains a certain proportion of protein and fat. The structures of protein and fat also change during the extrusion and puffing process, which will also have an inhibitory effect on the formation of RS resistant starch.

[0042] 3. The present invention also greatly improves the effective utilization rate of rice broken rice, increases the added value of rice broken rice, broadens the application scope of broken rice, and has practical application significance and value. This method is not only applicable to rice or broken rice with a relatively high amylose / amylopectin ratio but also applicable to medium and low-grade ones.

[0043] 4. The present invention adds high-RS resistant rice or broken rice flour to skim milk. The prepared set yogurt has a low GI value, strong water-holding capacity, no whey separation during storage, has a good protein cross-linking structure, a smoother and more delicate taste with Q elasticity, a rich and mellow flavor, and all physical and chemical and microbiological indicators meet the national yogurt product standards.

[0044] Index determination method:

[0045] RS determination method:

[0046] Disperse 200 mg of the sample in 10 mL of sodium acetate buffer. After boiling in a water bath at 100 °C for 30 min, equilibrate at 37 °C for 30 min to obtain the digestion solution. Dissolve α-amylase (290 U / mL) and amyloglucosidase (50 U / mL) in the digestion solution and start digestion at 37 °C. Take 0.5 mL of the hydrolysis solution at 0, 20, and 120 min respectively, mix with 4.5 mL of absolute ethanol, and centrifuge at 4000×g for 15 min. Measure the glucose concentration of the sample using a D-glucose assay kit (K-GLUK, GOPOD, Megazyme). Calculate the contents of RDS, SDS, and RS using the following formulas (2), (3), and (4):

[0047]

[0048] where FG is the amount of free glucose in the sample; TS is the mass of total starch in the sample; G 20 and G 120 represent the amounts of glucose in the enzymatically hydrolyzed sample at 20 min and 120 min respectively. RDS - rapidly digestible starch; SDS - slowly digestible starch; RS - resistant starch.

[0049] The determination of RS is not limited to the method of the present invention, and other conventional determination methods can also be used, aiming to characterize the results and trends

[0050] Physicochemical analysis: Analyze the ash, fat, protein, total solids content, and carbohydrates according to the national standard GB19302—2010 of the People's Republic of China.

[0051] Texture analysis: Analyze the hardness, elasticity, viscosity, cohesiveness, and chewiness of this product using a Brookfield texture analyzer. Select the AB-E / 40 probe, set the measurement mode to the TPA mode, the trigger point load to 4.5 g, the target distance to 30 mm, and the speed to 1 mm / s. Take out the yogurt refrigerated at 4 °C and immediately measure it at an ambient temperature of 25 °C.

[0052] GI determination: 10 g of the sample and 10 mL of 0.9% NaCl solution (pH = 6). Add 0.3 mL of simulated saliva (α-amylase, enzyme activity 100 U / mL) to the mixture, and incubate with shaking in a water bath at 37 °C for 2 min. Then add 1 mL of simulated gastric juice to each sample, with the pepsin addition ratio being 0.05 mL / g of the digested sample (pH = 3), and stir at 37 °C (100 rpm). From 0 to 120 min, take out the digested sample (1 mL) from each test tube every 30 min. Immediately boil the sample in a boiling water bath at 100 °C for 5 min. Then, add 2.5 mL of simulated intestinal fluid (40 mg of trypsin and 250 mg of bovine bile salts dissolved in 10 mL of 0.1 mol / L NaHCO3), with the addition ratio being 0.125 mL / g of the digested sample. Take out the enzyme hydrolysate (1 mL) at 0, 30, 60, 90, and 120 min respectively. Measure the free glucose using the GOPOD kit. Take 0.1 mL of glucose (1 mg / mL) as the standard sample control. Calculate the GI using the following formula (5):

[0053]

[0054] where IAUC (样品) is the incremental area under the blood glucose curve of the test substance within 2 h after a meal; IAUC (标准品) is the incremental area under the blood glucose curve within 2 h after a meal.

[0055] The detection methods of the above indexes can also use any conventional detection methods in the prior art. Description of the Drawings

[0056] Figure 1 is the scanning electron micrograph (x5000) of the extruded rice RS starch in Example 1;

[0057] Note: A - raw material area; B - feeding area; C - mixing area; D - melting area; E - die area; F - extrudate

[0058] Figure 1 It can be seen that the starch in the raw material area presents a polyhedral structure with relatively small particles. The starch granules in the feeding area and the mixing area gradually lose their edges and corners and polyhedral structure. The starch granules in the melting area present a compact continuous mass, and the surface of the starch in the die area becomes dense. The extrudate adheres into a rougher and more irregular aggregate.

[0059] Figure 2 is the polarized light micrograph (x400) of the extruded rice RS starch in Example 1;

[0060] Note: a, g - raw material area; b, h - feeding area; c, i - mixing area; d, j - melting area; e, k - die area; f, l - extrudate

[0061] Figure 2 It can be seen that the Maltese cross of starch in the feeding area and the mixing area darkens. As the barrel temperature increases, the Maltese cross gradually weakens, indicating the destruction of the starch structure. At the same time, no birefringence phenomenon is found in the melting area (cooking area), die area and extrudate.

[0062] Figure 3 Particle size distribution (A), gelatinization characteristics (B), apparent viscosity (C) and G′ vs. frequency (D) graphs of extruded rice RS starch for Example 1;

[0063] Figure 3 A shows that: the particle size of extruded rice RS starch increases, and compared with the unextruded starch of the control group, the size distribution of the extruded starch particles is relatively wider and shifted to the right. The extrudate particles are distributed around 100 μm, and the generated resistant starch agglomerates become larger.

[0064] Figure 3 B shows that: before 50 °C, there is no significant difference in the initial viscosity of starch (P < 0.05). As the temperature increases, the viscosity of rice starch in the feeding area, mixing area and melting area (cooking area) all increases. The peak viscosity of starch in the melting area is the highest. As the temperature decreases, the retrogradation viscosity of starch in the feeding, mixing and melting areas is higher than that of the control starch (unextruded starch), while the viscosity of starch in the die area and extrudate is lower. The extrusion treatment can extend the aging time of rice starch.

[0065] Figure 3 C shows that: the control starch (unextruded starch) has a higher apparent viscosity, and the apparent viscosity of starch decreases with the increase of shear rate, showing shear thinning behavior. Starch shows weak shear thinning behavior in the feeding area, mixing area and melting area. The apparent viscosity of starch in the die and extrudate decreases significantly. This is mainly due to the breakage of amylopectin and amylose, weakening the internal entanglement of starch.

[0066] Figure 3 D shows that: the recrystallization of leached amylose and the interaction between amylose and swollen starch granules strengthen the cross-linked structure of the starch gel during the cooling and aging process.

[0067] Figure 4 Thermal properties (A), X-ray diffraction pattern (B), FT-IR spectrum (C) and Raman spectrum (D) of extruded rice RS starch for Example 1.

[0068] Figure 4 A shows that: the characteristic endothermic peak of the extrudate starch is at 106.66 °C, and extrusion increases the peak conversion temperature of rice starch and improves the stability of starch.

[0069] Figure 4B shows that significantly different X-ray diffraction patterns were obtained after extrusion treatment. The A-type pattern of the starch in the die area and the extrudate completely disappeared, and the degree of gelatinization of the sample was the highest, with an obvious peak at 20° intensity.

[0070] Figure 4 C shows that an extrusion modification reaction occurred between starch molecules. The intensity ratio of 1047 cm -1 / 1022 cm -1 represents the degree of molecular order in starch. The ratio of 1047 cm -1 / 1022 cm -1 decreased from 1.89 to 1.32 after extrusion, indicating that the ordered structure of starch was destroyed.

[0071] Figure 4 D shows that there was no significant difference between the starch in the feeding area and the mixing area and the raw material starch (P < 0.05). In the melting zone (cooking zone), the peak intensity of the starch molecular chain in the 478 cm -1 band was the highest. However, the peak intensity in the die and the extrudate became weak under the influence of thermal reduction and shear force, indicating that the polymer starch chain was deformed. The peak intensities of starch at 939 cm -1 and 1126 cm -1 weakened in the die and the extrudate, indicating that the crystallization intensity of starch decreased. In the die and the extrudate, the peak intensities near 1339 cm -1 and 1460 cm -1 decreased, indicating that the vibrations of C-O-H and CH2 occurred. The peak observed at 1673 cm -1 in the die and the extrudate was the carbonyl group formed by oxidation. Specific embodiments

[0072] The present invention will be further described below by way of examples. Unless otherwise specified, the materials in the examples were prepared according to existing methods or directly purchased from the market. Example 1:

[0073] A method for preparing high-RS resistant rice flour by twin-screw extrusion expansion is prepared according to the following steps:

[0074] (1) Grind rice broken rice with a amylose content of 20% into rice flour. The rice flour passes through a 30-mesh sieve, and the initial moisture content is 11%.

[0075] (2) Feed it into a twin-screw extruder.

[0076] (3) Extrusion and puffing treatment: Adjust the moisture content to 23%; the feeding speed is 15 kg / h; the screw speed is 90 r / min; the feeding zone of the twin-screw extruder is 50 °C, the mixing zone is 80 °C, the cooking zone is 160 °C, the die zone is 50 °C, and the die forming pressure is 5 MPa; the screw diameter is 16 mm, and the L / D ratio is 39:1;

[0077] (4) Wet grind and pulverize the extrudate; the mass ratio of rice flour to deionized water is 1:6;

[0078] (5) Freeze-dry and screen. The rice flour passes through a 200-mesh sieve to obtain high-RS resistant rice powder. Example 2:

[0079] A method for preparing high-RS resistant rice flour by twin-screw extrusion and puffing is prepared according to the following steps:

[0080] (1) Grind the rice broken grains with a 25% amylose content into rice flour. The whole rice flour passes through a 40-mesh sieve, and the initial moisture content is 12%;

[0081] (2) Feed into the twin-screw extruder;

[0082] (3) Extrusion and puffing treatment: Adjust the moisture content to 25%; the feeding speed is 20 kg / h; the screw speed is 100 r / min; the feeding zone of the twin-screw extruder is 60 °C, the mixing zone is 90 °C, the cooking zone is 170 °C, the die zone is 60 °C, and the die forming pressure is 6 MPa; the screw diameter is 20 mm, and the L / D ratio is 40:1;

[0083] (4) Wet grind and pulverize the extrudate; the mass ratio of rice flour to deionized water is 1:7;

[0084] (5) Freeze-dry and screen. The rice flour passes through a 200-mesh sieve to obtain high-RS resistant rice powder.

[0085] Example 3: (Based on Example 1, add a specific retrogradation treatment method)

[0086] A method for preparing high-RS resistant rice flour by twin-screw extrusion and puffing is prepared according to the following steps:

[0087] (1) Grind the rice broken grains with a 20% amylose content into rice flour. The rice flour passes through a 30-mesh sieve, and the initial moisture content is 11%;

[0088] (2) Feed into the twin-screw extruder;

[0089] (3) Extrusion puffing treatment: Adjust the moisture content to 23%; the feeding speed is 15 kg / h; the screw rotation speed is 90 r / min; the feeding zone of the twin-screw extruder is 50 °C, the mixing zone is 80 °C, the cooking zone is 160 °C, the die zone is 50 °C, and the die forming pressure is 5 MPa; the screw diameter is 16 mm, and the L / D ratio is 39:1;

[0090] (4) Cool the die extrudate to 25 °C at a cooling rate of 2 °C / min, and apply air at 5 m / s, 25 °C, and a humidity of 80% during this cooling process; then continue to cool to 4 °C at a cooling rate of 1 °C / min and carry out a standing retrogradation treatment at 4 °C for 12 h;

[0091] (5) Wet grind and pulverize the extrudate after the retrogradation treatment; the mass ratio of rice flour to deionized water is 1:6;

[0092] (6) Freeze-dry and screen, and the rice flour passes through a 200-mesh sieve to obtain high-RS resistant rice powder.

[0093] Example 4: (Adding a retrogradation treatment on the basis of Example 2)

[0094] A method for preparing high-RS resistant rice flour by twin-screw extrusion puffing is prepared according to the following steps:

[0095] (1) Grind the rice broken grains with a amylose content of 25% into rice flour, and the whole rice flour passes through a 40-mesh sieve, with an initial moisture content of 12%;

[0096] (2) Feed into the twin-screw extruder;

[0097] (3) Extrusion puffing treatment: Adjust the moisture content to 25%; the feeding speed is 20 kg / h; the screw rotation speed is 100 r / min; the feeding zone of the twin-screw extruder is 60 °C, the mixing zone is 90 °C, the cooking zone is 170 °C, the die zone is 60 °C, and the die forming pressure is 6 MPa; the screw diameter is 20 mm, and the L / D ratio is 40:1;

[0098] (4) Cool the die extrudate to 25 °C at a cooling rate of 2.5 °C / min, and apply air at 7 m / s, 25 °C, and a humidity of 75% during this cooling process; then continue to cool to 4 °C at a cooling rate of 1 °C / min and carry out a standing retrogradation treatment at 4 °C for 12 h;

[0099] (5) Wet grind and pulverize the extrudate after the retrogradation treatment; the mass ratio of rice flour to deionized water is 1:7;

[0100] (6) Freeze-dry and screen, and the rice flour passes through a 200-mesh sieve to obtain high-RS resistant rice powder. Example 5:

[0101] This embodiment provides a preparation method for low-GI set yogurt:

[0102] Take the rice flour prepared in Example 1 and mix it evenly with skim milk at a mass ratio of 1:250 (0.4%). Preheat to 60 °C, add Erythritol, pectin and xanthan gum. The mass ratio of skim milk to Erythritol is 1:0.075; the mass ratio of skim milk to high-methoxyl pectin is 1:0.025; the mass ratio of skim milk to xanthan gum is 1:0.015. Keep stirring continuously and keep warm for 30 min. After mixing evenly, obtain the liquid material. Homogenize the prepared liquid material twice at a pressure of 35 MPa, sterilize it at 90 °C, and keep warm for 10 min. Cool it to 42 °C in an ice-water bath, add 0.03% direct vat set, stir evenly and ferment at 43 °C until the pH reaches 4.5. After ripening at 4 °C for 12 h, the finished product of set low-GI yogurt is obtained. Example 6:

[0103] This embodiment provides a preparation method for low-GI set yogurt:

[0104] Take the rice flour prepared in Example 3 and mix it evenly with skim milk at a mass ratio of 1:166.67 (0.6%). Preheat to 60 °C, add Erythritol, pectin and xanthan gum. The mass ratio of skim milk to Erythritol is 1:0.05; the mass ratio of skim milk to high-methoxyl pectin is 1:0.02; the mass ratio of skim milk to xanthan gum is 1:0.01. Keep stirring continuously and keep warm for 30 min. After mixing evenly, obtain the liquid material. Homogenize the prepared liquid material twice at a pressure of 40 MPa, sterilize it at 90 °C, and keep warm for 15 min. Cool it to 43 °C in an ice-water bath, add 0.03% direct vat set, stir evenly and ferment at 43 °C until the pH reaches 4.5. After ripening at 4 °C for 12 h, the finished product of set low-GI yogurt is obtained. Example 7:

[0105] This embodiment provides a preparation method for low-GI set yogurt:

[0106] Take the rice flour prepared in Example 4 and mix it evenly with skim milk at a mass ratio of 1:125 (0.8%). Preheat to 60 °C, add Erythritol, pectin and xanthan gum. The mass ratio of skim milk to Erythritol is 1:0.03; the mass ratio of skim milk to high-methoxyl pectin is 1:0.02; the mass ratio of skim milk to xanthan gum is 1:0.01. Keep stirring continuously and keep warm for 30 min. After mixing evenly, obtain the liquid material. Homogenize the prepared liquid material twice at a pressure of 40 MPa, sterilize it at 90 °C, and keep warm for 20 min. Cool it to 43 °C in an ice-water bath, add 0.03% direct vat set, stir evenly and ferment at 43 °C until the pH reaches 4.5. After ripening at 4 °C for 12 h, the finished product of set low-GI yogurt is obtained.

[0107] Comparative Example 1:

[0108] Based on Example 1, increase the feeding speed and screw rotation speed, lower the cooking zone temperature within the conventional range, and do not control the die pressure.

[0109] A method for preparing high-RS resistant rice flour by twin-screw extrusion and puffing is prepared according to the following steps:

[0110] (1) Grind the broken rice with 20% amylose content into rice flour. The rice flour passes through a 30-mesh sieve, and the initial moisture content is 11%.

[0111] (2) Feed it into the twin-screw extruder.

[0112] (3) Extrusion and puffing treatment: Adjust the moisture content to 23%; the feeding speed is 35 kg / h; the screw rotation speed is 120 r / min; the feeding zone of the twin-screw extruder is 50 °C, the mixing zone is 80 °C, the cooking zone is 150 °C, and the die zone is 50 °C; the screw diameter is 16 mm, and the L / D ratio is 39:1.

[0113] (4) Wet grind and pulverize the extrudate; the mass ratio of rice flour to deionized water is 1:6.

[0114] (5) Freeze-dry and sieve. The rice flour passes through a 200-mesh sieve to obtain high-RS resistant rice powder.

[0115] Comparative Example 2: Mainly based on Comparative Example 1, further increase the retrogradation treatment.

[0116] A method for preparing high-RS resistant rice flour by twin-screw extrusion and puffing is prepared according to the following steps:

[0117] (1) Grind the broken rice with 20% amylose content into rice flour. The rice flour passes through a 30-mesh sieve, and the initial moisture content is 11%.

[0118] (2) Feed it into the twin-screw extruder.

[0119] (3) Extrusion and puffing treatment: Adjust the moisture content to 23%; the feeding speed is 35 kg / h; the screw rotation speed is 120 r / min; the feeding zone of the twin-screw extruder is 50 °C, the mixing zone is 80 °C, the cooking zone is 150 °C, and the die zone is 50 °C; the screw diameter is 16 mm, and the L / D ratio is 39:1.

[0120] (4) Cool the die extrudate to 25 °C at a cooling rate of 2 °C / min. During this cooling process, apply air at 5 m / s, 25 °C, and a humidity of 80%; then continue to cool to 4 °C at a cooling rate of 1 °C / min and carry out retrogradation treatment at 4 °C for 12 h.

[0121] (5) Wet grind and pulverize the extrudate; the mass ratio of rice flour to deionized water is 1:6.

[0122] (6) Freeze-dry and sieving. The rice flour is sieved through a 200-mesh sieve to obtain high-RS resistant rice powder.

[0123] Comparative Example 3: Based on Example 4, the retrogradation method is changed. That is, the die extrusion is cooled to 4°C at a cooling rate of 2°C / min and subjected to a static retrogradation treatment at 4°C for 12 h.

[0124] (5) Wet grind and pulverize the extrudate after the retrogradation treatment. The mass ratio of rice flour to deionized water is 1:6.

[0125] (6) Freeze-dry and sieving. The rice flour is sieved through a 200-mesh sieve to obtain high-RS resistant rice powder.

[0126] Comparative Example 4: Based on Example 4, the retrogradation method is changed. That is: the die extrusion is cooled to 4°C at a cooling rate of 1°C / min and subjected to a static retrogradation treatment at 4°C for 12 h.

[0127] Test results:

[0128] Table 1 In vitro digestion results of rice starch in the extrusion zone of Example 1

[0129]

[0130] As can be seen from Table 1: Under the extrusion treatment under specific conditions, the RS content increases from 7.40 ± 1.25% to 33.79 ± 1.21%. The present invention can significantly increase the RS content. The table also objectively shows that the content of RS in the extruder barrel first increases and then decreases, reflecting an extremely complex internal change process.

[0131] Table 2 RS (%) of extrudate

[0132]

[0133] As can be seen from Table 2, compared with Comparative Examples 1-4, the RS content in the rice flour of the extrudate during the extrusion and puffing stage of the present invention can be increased to 34.83% (P < 0.05), indicating that the extrusion and puffing process and parameters of the present invention play a synergistic role with each other, achieving an unexpected effect. The synergistic short-term retrogradation treatment further reaches 39.22% and 39.98%.

[0134] Table 3 Physical and chemical indexes

[0135]

[0136] Table 3 shows the various physical and chemical indicators of the yogurt of the present invention. Compared with the control non-fat yogurt (without addition), there are no significant differences in the physical and chemical indicators such as ash. However, the glycemic index of the control non-fat yogurt is 89, belonging to high-GI foods (GI > 75), while the glycemic index of the non-fat yogurt added with the extruded rice flour of the present application belongs to low-GI foods (GI ≤ 55).

[0137] Table 4 Product texture analysis

[0138]

[0139] Table 4 shows that the yogurt products obtained by the present invention have good texture characteristics in terms of hardness, elasticity, viscosity, cohesiveness and chewiness. Conventional sensory evaluation also shows that the yogurt of the present invention has good flavor, color and texture state, and the sensory quality is ideal.

Claims

1. A method for preparing high-RS resistant rice flour by twin-screw extrusion puffing, characterized in that, It is prepared according to the following steps: (1) Grind rice into rice flour, and the rice flour passes through a 30-50 mesh sieve with an initial moisture content of 11-12%; (2) Feed it into a twin-screw extruder; (3) Extrusion puffing treatment: Adjust the moisture content to 23-26%; The feeding speed is 15-40 kg / h; The screw speed is 90-100 r / min; The feeding zone of the twin-screw extruder is 30-60 °C, the mixing zone is 70-90 °C, the cooking zone is 160-180 °C, and the die zone is 40-60 °C, and control the die-forming pressure to be 4-6 MPa; The screw diameter is 11-24 mm, and the L / D ratio is 39-41:1; (4) Wet-mill and pulverize the extrudate; (5) Freeze-dry and screen to obtain high-RS resistant rice powder; After step (3), add a retrogradation treatment step: Cool the die extrudate to 25 °C at a cooling rate of 2-2.5 °C / min, and apply a wind of 5-7 m / s, 25 °C, and a humidity of 75-80% during this cooling process; Then continue to cool to 4 °C at a cooling rate of 1-1.5 °C / min and carry out retrogradation treatment at 4 °C for 12 h.

2. The method according to claim 1, wherein The feeding speed is 15 kg / h; The screw speed is 90 r / min; The temperature of the feeding zone is 40 °C, the temperature of the mixing zone is 80 °C, the temperature of the cooking zone is 170 °C, and the temperature of the die zone is 50 °C; The screw diameter is 20 mm, and the L / D ratio is 40:1; The material adjusts the feeding speed through a feeder.

3. The method according to claim 2, wherein In the wet-milling and pulverizing, the mass ratio of rice flour to deionized water is 1:5-8; In the freeze-drying and screening, the rice flour passes through a 200-300 mesh sieve.

4. High-RS resistant rice flour prepared by using the method according to any one of claims 1-3.

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