Method for delaying aging and retrogradation of refrigerated rice through combination of cooking-first and steaming-second technology and magnetic field

Abstract

The invention discloses a method for delaying aging and retrogradation of refrigerated rice by combining a cooking-prior-to-steaming process with a magnetic field, and belongs to the technical field of food processing. The method comprises the following steps; treating the raw materials, boiling, steaming, and refrigerating with assistance of a magnetic field. According to the method, a certain amount of starch is washed away through a cooking process, water is promoted to permeate into rice grains to participate in starch gelatinization, finished rice with fluffy rice grains and tender taste is obtained through a steaming process, and the retrogradation and rearrangement process of rice starch molecules in the refrigeration process is delayed through magnetic field assisted refrigeration. The cooking and steaming process is combined with the magnetic field to assist refrigeration for cooperative treatment, and aging and retrogradation of the rice in the refrigeration process can be effectively delayed. The method disclosed by the invention is simple in process, and the prepared rice has lower retrogradation degree under the same storage condition, and has the advantages of low hardness, good viscosity, better taste quality and longer shelf life.

Description

Technical Field

[0001] The invention relates to a method for delaying aging and regeneration of refrigerated rice by a cooking-before-steaming process combined with a magnetic field, and belongs to the technical field of food processing. Background Art

[0002] Rice is one of the most important food crops and staple foods. Eating steamed rice directly is the main way to eat rice, which can obtain the best taste quality of rice. However, in recent years, with the accelerated pace of life, traditional family-style steaming and cooking rice is time-consuming and labor-intensive, and it is difficult to adapt to the modern fast-paced life. Instant rice and cold chain rice are developing rapidly due to their convenience, speed and high nutritional value, and have a very broad market prospect.

[0003] Cold chain rice refers to rice products that have been cooked and properly packaged and have a certain storage time. It is a convenient staple food that quickly reduces the core temperature of steamed rice to below 10°C and maintains it in subsequent circulation links. In the fast-paced lifestyle, cold chain rice is widely used in convenience stores, fast food restaurants, airports, high-speed trains and other fields because of its convenience, economy and speed. The demand for cold chain rice is increasing. Cold chain rice requires that the cooked rice grains are complete, distinct, soft inside and tough outside, elastic, and maintain the aroma of the rice. After the cold chain rice is made, it can be put on the market after proper packaging and sterilization. Consumers can eat it after purchase with or without reheating.

[0004] Cold chain rice usually goes through several consecutive processes before being eaten, including raw material cleaning, rice cooking, rice cooling and cold chain refrigeration. During the cold chain storage process, rice often becomes hard, has poor viscoelasticity, and becomes hardened into lumps. The main reason is the starch regeneration problem caused by water migration and aggregation of starch molecules to form crystals, which seriously affects the quality and taste of rice, shortens the shelf life of cold chain rice, and greatly restricts the development of the cold chain rice industry. Therefore, it is urgent to find a method to delay the aging and regeneration of rice during the refrigeration process.

[0005] At present, the methods commonly used to inhibit the retrogradation of rice starch include raw material regulation, enzymatic modification, addition of quality improvers, and physical treatment. Raw material regulation is to inhibit the retrogradation of rice by selecting rice with lower amylose content or using rice blending technology. For example, patent CN109673952B discloses a method for improving the anti-retrogradation of instant rice starch. The starch retrogradation of instant rice is reduced by combining rice of different varieties and regions, so that the degree of retrogradation and hardness of instant rice after storage are reduced. However, this has high requirements on raw materials and is not universal; enzymatic modification is to add enzymes to change the molecular chain length. The enzymes generally used are α-amylase, β-amylase, maltogenic amylase, etc. For example, patent CN102669538A discloses a method for delaying the regeneration of rice, by adding an extremely heat-stable maltogenic amylase to a mixture of raw rice grains and water in advance, and then directly steaming the mixture. However, enzymatic modification is prone to generate various hydrolysis products, and the dissolution of short-chain starch generated by enzymatic hydrolysis increases the viscosity of the rice, affects the taste, and produces unpleasant flavors; adding quality improvers includes sugars (such as polysaccharides such as sorbitol and trehalose, small molecule sugars such as monosaccharides, disaccharides, and oligosaccharides), hydrophilic colloids (guar gum, xanthan gum, carrageenan, etc.), and hydrophilic colloids (such as guar gum, xanthan gum, and carrageenan). etc.), emulsifiers (monoglycerides, lecithin, gluconolactone, etc.), plant extracts (tea polyphenols, bilberry extract, grape seed extract), etc. For example, patent CN110786462B discloses a production process of a prepared food based on compound soybean polysaccharides - anti-aging instant rice, which is compounded with water-soluble soybean polysaccharides, guar gum, oligofructose and carrageenan to prepare an anti-aging agent, which is then used with sorbitol as water for cooking rice, and is packaged together with the raw rice in a packaging box and sealed, and the rice is cooked with high-temperature steam to obtain instant rice. Although the method It has a certain anti-rejuvenation effect, but the taste quality is poor, and there are potential food safety issues, which are not easily accepted by consumers; physical means of treatment include ultrasonic treatment, wet heat treatment, ultra-high pressure treatment, etc. For example, patent CN103416677B discloses a method for delaying the rejuvenation of rice by ultrasonic assisted cooking. Ultrasonic treatment is applied to the steaming stage of rice, so that the rice can obtain lower rejuvenability after refrigeration. Physical treatment means do not have food safety issues and are highly accepted by consumers, but the processing technology is complicated and the anti-aging performance is poor.

[0006] Therefore, it is necessary to develop a simple, safe, additive-free processing method from the perspective of the entire rice cooking process, which can significantly delay the aging and recovery of rice during the refrigeration process, so that the rice can have better taste quality and a longer shelf life. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a method for delaying the aging and recovery of rice during the refrigeration process by combining a cooking-before-steaming process with a magnetic field-assisted refrigeration process. The method of the present invention is simple, safe and additive-free, and can effectively delay the recovery of rice during the refrigeration process. The prepared rice has a lower degree of recovery under the same storage conditions, and at the same time has lower hardness and better stickiness, and can better maintain the original taste quality of the rice, so that the rice has a longer shelf life.

[0008] The present invention provides a method for delaying the aging and regeneration of rice during the refrigeration process by combining a cooking-before-steaming process with a magnetic field-assisted refrigeration process, which specifically comprises the following steps:

[0009] (1) Raw material processing: washing and soaking the rice, and draining the water after soaking;

[0010] (2) Cooking: Cooking the drained rice, and draining the water after cooking;

[0011] (3) Steaming: Steaming the rice drained from step (2) to obtain uniform and fluffy rice;

[0012] (4) Magnetic field-assisted refrigeration: The uniformly fluffy rice is cooled and placed in a refrigerated environment with a magnetic field applied.

[0013] In one embodiment of the present invention, in step (1), the rice is washed 2 to 4 times with clean water and gently stirred clockwise for 10 to 20 circles to avoid breaking the outer surface of the rice grains.

[0014] In one embodiment of the present invention, in step (1), the rice includes but is not limited to one of Wuchang Daohuaxiang rice, Nanjing 9108 rice, and Yunnan soft rice.

[0015] In one embodiment of the present invention, in step (1), the temperature of the rice soaked in water is 20-25° C., and the soaking time is 20-30 minutes, until the water is fully absorbed.

[0016] In one embodiment of the present invention, in step (1), the mass ratio of rice to water during soaking of rice is 1:1-2.

[0017] In one embodiment of the present invention, in step (2), the rice is cooked in boiling water for 5 to 10 minutes at a power of 800 to 1000 W, with a rice to water mass ratio of 1:5 to 8, so as to avoid the rice grains sticking to the pot and overcooking.

[0018] In one embodiment of the present invention, in step (2), when the rice grains are detected by a texture analyzer or an optical microscope to have translucent gelatinization characteristics on the surface of the rice grains but the rice core is not completely gelatinized (i.e., has a hard core), they are immediately fished out and quickly drained to prevent excessive water absorption from causing the rice to become sticky.

[0019] In one embodiment of the present invention, in step (3), the drained rice is spread out in a steamer and placed above the steam for steaming. The steaming time is 10 to 20 minutes and the steaming power is 800 to 1000W.

[0020] In one embodiment of the present invention, in step (4), the rice is spread out and placed in a magnetic field assisted refrigeration device for assisted refrigeration treatment. The magnetic field assisted refrigeration device can be a magneto-electric coupled freezer refrigerator with a magnetic field strength of 3 to 9 mT, preferably 6 mT; the magnetic field assisted refrigeration time is 2 to 6 hours, preferably 4 hours; and the refrigeration temperature is 3 to 5°C.

[0021] In one embodiment of the present invention, in step (4), the rice is cooled to 30-40°C, and after being subjected to magnetic field-assisted refrigeration treatment, it is taken out and immediately placed in a 4°C refrigerator for refrigeration.

[0022] [Beneficial Effects]

[0023] (1) The present invention achieves the purpose of delaying the aging and regeneration of rice during the refrigeration process by combining the process of boiling first and then steaming with the assisted refrigeration treatment of magnetic field. Compared with the rice directly refrigerated at 4°C without the process, the hardness of the rice after 7 days of refrigeration can be reduced by 16.36% to 27.70%, the viscosity can be increased by 29.84% to 64.34%, and the relative crystallinity can be reduced by 27.87% to 29.50%;

[0024] (2) The present invention cooks the soaked rice, and the rice starch particles gradually dissolve into the rice soup during cooking, thereby reducing the starch content in the rice particles. At the same time, the cooking time is controlled to ensure the integrity of the rice particles. The rice starch is fully gelatinized by steaming, and the hard core and mushy bottom of the rice caused by lack of water or uneven heating in the traditional cooking method are not likely to occur. The cooking also washes away the starch on the surface of the rice particles, thereby reducing the content of the adhesion layer on the surface of the finished rice obtained by the cooking-before-steaming process, which is manifested as distinct rice grains with less adhesion to each other. At the same time, the quality deterioration caused by aging can be delayed after storage, thereby improving the taste quality of the rice after storage.

[0025] (3) The rice produced by the process of boiling before steaming reduces the starch content of rice from the source of cooking, which is directly reflected in reducing the degree of aging and regeneration of rice during cold storage; at the same time, due to boiling, the cracks in the rice grains increase, which promotes more water to enter the rice grains and gelatinize with the rice starch; the magnetic field will affect the distribution of the electron cloud in the water molecules and the interaction of the hydrogen bond network between molecules. Through the treatment of magnetic field-assisted cold storage, the hydrogen bond between the water in the rice and the starch granules is enhanced, slowing down the rearrangement of the combination between the starch molecules to form a neat crystal structure, thereby achieving the purpose of delaying the aging and regeneration of rice during cold storage; in addition, magnetic field-assisted cold storage also has a certain effect of inhibiting the growth of microorganisms; the process of boiling before steaming combined with magnetic field-assisted cold storage synergistic treatment, the two work synergistically, further delaying the aging and regeneration of rice during cold storage, while obtaining better taste quality and longer shelf life;

[0026] (4) The process used in the present invention is simple, and no additives are used. Only physical means are used for synergistic treatment, which is more in line with the current consumer demand for green food and has high consumer acceptance. The rice can still maintain low retrogradation characteristics and good taste quality after refrigeration, extending the shelf life of the rice during the refrigeration process, and has good social value and economic benefits. In addition, the method of the present invention has low requirements for rice raw materials and is generally applicable to various types of rice on the market. DETAILED DESCRIPTION

[0027] The magnetoelectric coupling freezer-refrigerator of the embodiment of the present invention and the comparative example was purchased from Indust (Wuxi) Induction Technology Co., Ltd.

[0028] The present invention utilizes the TPA full texture mode in the texture analyzer to simulate two chewings to analyze the texture characteristics of rice, obtains data such as hardness and viscosity, and characterizes the quality of the rice after refrigeration.

[0029] The present invention utilizes an X-ray diffractometer (XRD) to measure the relative crystallinity of rice stored at 4° C. for different storage times.

[0030] The measuring method of the present invention

[0031] (1) Texture determination method

[0032] The texture characteristics of rice were analyzed by simulating two chewings using the TPA full texture mode in a physical property analyzer equipped with a P / 36R cylindrical probe. The specific test conditions were: pre-test speed of 2 mm / s, test speed of 1 mm / s, post-test speed of 2 mm / s, strain of 50%, and trigger force of 5.0 g.

[0033] (2) Relative crystallinity determination method

[0034] The crystallinity was determined by X-ray diffractometer (XRD). The refrigerated rice was soaked in anhydrous ethanol (1:3, g / g) for 12 hours, and then dried in a constant temperature blast drying oven at 37°C for 12 hours. After drying, the sample was crushed and passed through a 100-mesh sieve, and balanced in a dryer overnight before measurement. The voltage during the test was 40 kV, the radiation wavelength was 0.154 nm, the scanning range was 5 to 40° (2θ), and the scanning rate was about 3° / min.

[0035] The calculation formula of relative crystallinity is: relative crystallinity=crystalline peak area / total area of ​​diffraction region×100%.

[0036] (3) The detection method for determining the semi-transparent gelatinization characteristics of the rice grains and the incomplete gelatinization state of the rice core can be any one of the following two:

[0037] (a) Physical detection method: The rice grains are compressed using a texture analyzer and the compression curve is recorded. Rice grains with different gelatinization degrees will show different compression characteristics. When the compression curve shows a fast-growing hardness mutation peak, the rice grains have reached a semi-transparent gelatinization characteristic and the rice core is in an incompletely gelatinized state.

[0038] (b) Optical detection method: Use the method reported in the article "Structural changes of starch under different milling degrees affect the cooking and textural properties of rice" to place the rice grains between two glass slides, squeeze the glass slides to disperse the rice grains, and observe their texture profiles, or slice the rice grains and observe them under an optical microscope. When the outer layer of the rice grains is observed to be uniformly translucent under a microscope, while the rice core remains white and opaque, the rice grains have reached the translucent gelatinization characteristics and the rice core is in an incompletely gelatinized state.

[0039] Example 1

[0040] A method for delaying the aging and regeneration of rice during refrigeration by combining a cooking-before-steaming process with a magnetic field-assisted refrigeration process, the specific steps are as follows:

[0041] (1) Washing: Weigh 200 g of Wuchang Daohuaxiang rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0042] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0043] (3) Cooking: The rice drained from step (2) is placed in boiling water with a rice-water mass ratio of 1:6 and cooked for 5 min at a cooking power of 900 W. The rice grains are gently stirred during the cooking process to prevent the rice from sticking to the pot. During the cooking process, when the surface of the rice grains shows translucent gelatinization characteristics but the rice core is not completely gelatinized, the rice grains are removed and the water is drained;

[0044] (4) Steaming: Spread the drained rice flat in a steamer and steam it over steam for 15 min at a steaming power of 900 W until the rice is fully cooked to obtain finished rice;

[0045] (5) Refrigeration: The finished rice was quickly cooled to 35°C and spread out in a magneto-electric coupled freezer refrigerator. The rice was refrigerated for 4 h at a magnetic field strength of 6 mT and a refrigeration temperature of 4°C. The rice was immediately taken out and placed in a refrigerator at 4°C for refrigeration.

[0046] Example 2

[0047] The preparation method is consistent with that in Example 1, except that the magnetic field intensity and refrigeration time in step (5) are adjusted to 3 mT and 4 h, respectively. See Table 1 for details.

[0048] Example 3

[0049] The preparation method is consistent with that in Example 1, except that the magnetic field intensity and refrigeration time in step (5) are adjusted to 9 mT and 4 h, respectively. See Table 1 for details.

[0050] Example 4

[0051] The preparation method is consistent with that in Example 1, except that the magnetic field intensity and refrigeration time in step (5) are adjusted to 6 mT and 2 h, respectively. See Table 1 for details.

[0052] Example 5

[0053] The preparation method is consistent with that in Example 1, except that the magnetic field intensity and refrigeration time in step (5) are adjusted to 6 mT and 6 h, respectively. See Table 1 for details.

[0054] Table 1 Hardness, viscosity and relative crystallinity of rice with different magnetic field intensities and refrigeration time after 7 days of storage

[0055] Magnetic field strength and refrigeration time Hardness(g) Viscosity (g.sec) Relative crystallinity (%) 6mT, 4h (Example 1) <![CDATA[12536.71±834.99 d ]]> <![CDATA[23.83±1.40 a ]]> <![CDATA[13.50±0.27 c ]]> 3mT, 4h (Example 2) <![CDATA[15154.74±376.35 a ]]> <![CDATA[21.79±1.71 c ]]> <![CDATA[15.35±0.53 b ]]> 9mT, 4h (Example 3) <![CDATA[14234.94±552.83 c ]]> <![CDATA[19.74±2.07 d ]]> <![CDATA[14.72±0.89 b ]]> 6mT, 2h (Example 4) <![CDATA[15898.51±478.39 b ]]> <![CDATA[17.98±1.49 e ]]> <![CDATA[16.29±1.37 a ]]> 6mT, 6h (Example 5) <![CDATA[12145.23±145.28 e ]]> <![CDATA[22.65±0.91 b ]]> <![CDATA[13.81±0.64 c ]]>

[0056] Comparative Example 1

[0057] (1) Washing: Weigh 200 g of Wuchang Daohuaxiang rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0058] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0059] (3) Steaming: After washing and soaking, the rice is steamed in an ordinary rice cooker at a rice-to-water ratio of 1:1.2. After steaming, the rice is simmered for 10 minutes to balance the moisture;

[0060] (4) Refrigeration: After finishing, take out the product and quickly cool it to 35°C, then immediately place it in a 4°C refrigerator for refrigeration.

[0061] Comparative Example 2

[0062] (1) Washing: Weigh 200 g of Wuchang Daohuaxiang rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0063] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0064] (3) Steaming: After washing and soaking, the rice is steamed in an ordinary rice cooker at a rice-to-water ratio of 1:1.2. After steaming, the rice is simmered for 10 minutes to balance the moisture;

[0065] (4) Refrigeration: After the rice is finished, take it out and quickly cool it to 35°C. Spread it flat in a magneto-electric coupled freezer and refrigerator. Use a magnetic field strength of 6 mT and a refrigeration temperature of 4°C to assist in refrigeration for 4 h. Immediately take out the rice and place it in a 4°C refrigerator for refrigeration.

[0066] Comparative Example 3

[0067] (1) Washing: Weigh 200 g of Wuchang Daohuaxiang rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0068] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0069] (3) Cooking: placing the rice drained from step (2) in boiling water with a rice-to-water ratio of 1:6 and cooking for 5 min, gently stirring the rice grains during the cooking process to prevent the rice from sticking to the pot. During the cooking process, when the surface of the rice grains shows translucent gelatinization characteristics but the rice core is not completely gelatinized, remove the rice grains and drain the water;

[0070] (4) Steaming: Spread the drained rice flat in a steamer and steam it over steam for 15 minutes until the rice is fully cooked to obtain finished rice;

[0071] (5) Refrigeration: The finished rice is quickly cooled to 35°C and immediately placed in a 4°C refrigerator.

[0072] The finished rice of Example 1 is distinct in grains and fluffy and soft, while the rice of Comparative Examples 1 to 3 is sticky and elastic and sticks to each other.

[0073] The texture and relative crystallinity of the Wuchang rice of Example 1 and Comparative Examples 1 to 3 after refrigeration for 0d, 1d, 3d and 7d were measured to compare and illustrate the beneficial effects and effects of the present invention on delaying the aging and regeneration of rice during refrigeration. The experimental results are shown in Table 2. The hardness and relative crystallinity of the rice treated by the present invention during storage are significantly lower than those of the comparative sample (P<0.05), and the viscosity is significantly higher than that of the comparative sample (P<0.05). In the hardness, viscosity and crystallinity test after refrigeration for 7 days, the hardness of the rice treated by the present invention is reduced by 27.70%, the viscosity is increased by 64.34%, and the crystallinity is reduced by 29.50% compared with the comparative example 1; the hardness is reduced by 21.26%, the viscosity is increased by 26.82%, and the crystallinity is reduced by 15.68% compared with the comparative example 2. It can be seen that the cooking-before-steaming process of the present invention can delay the quality deterioration of the rice caused by aging after storage, and improve the taste quality of the rice after storage; the hardness is reduced by 25.94%, the viscosity is increased by 35.09%, and the crystallinity is reduced by 22.59% compared with the comparative example 3. In addition, there is a significant correlation between hardness and viscosity and taste quality, and these texture indicators can also indirectly reflect the taste quality of rice. The synergistic effect of the cooking-then-steaming process and magnetic field-assisted refrigeration can effectively delay the aging process of rice during refrigeration and achieve better taste quality.

[0074] Table 2 Hardness, viscosity and relative crystallinity of Example 1 and Comparative Examples 1-3 stored at 4°C for 0-7 days

[0075]

[0076] Example 6

[0077] A method for delaying the aging and regeneration of rice during refrigeration by combining a cooking-before-steaming process with a magnetic field-assisted refrigeration process, wherein the specific steps are as follows:

[0078] (1) Washing: Weigh 200 g of Nanjing 9108 rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0079] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0080] (3) Cooking: The rice drained from step (2) is placed in boiling water with a rice-water mass ratio of 1:6 and cooked for 5 min at a cooking power of 900 W. The rice grains are gently stirred during the cooking process to prevent the rice from sticking to the pot. During the cooking process, when the surface of the rice grains shows translucent gelatinization characteristics but the rice core is not completely gelatinized, the rice grains are removed and the water is drained;

[0081] (4) Steaming: Spread the drained rice flat in a steamer and steam it over steam for 15 min at a steaming power of 900 W until the rice is fully cooked to obtain finished rice;

[0082] (5) Refrigeration: The finished rice was quickly cooled to 35°C and spread out in a magneto-electric coupled freezer refrigerator. The rice was refrigerated for 4 h at a magnetic field strength of 6 mT and a refrigeration temperature of 4°C. The rice was immediately taken out and placed in a refrigerator at 4°C for refrigeration.

[0083] Comparative Example 4

[0084] (1) Washing: Weigh 200 g of Nanjing 9108 rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0085] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0086] (3) Steaming: After washing and soaking, the rice is steamed in an ordinary rice cooker at a rice-to-water ratio of 1:1.2. After steaming, the rice is simmered for 10 minutes to balance the moisture;

[0087] (4) Refrigeration: After finishing, take out the product and quickly cool it to 35°C, then immediately place it in a 4°C refrigerator for refrigeration.

[0088] Comparative Example 5

[0089] (1) Washing: Weigh 200 g of Nanjing 9108 rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0090] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0091] (3) Steaming: After washing and soaking, the rice is steamed in an ordinary rice cooker at a rice-to-water ratio of 1:1.2. After steaming, the rice is simmered for 10 minutes to balance the moisture;

[0092] (4) Refrigeration: The rice was rapidly cooled to 35°C and spread flat in a magneto-electric coupled freezer refrigerator. A magnetic field strength of 6 mT and a refrigeration temperature of 4°C were used to assist in refrigeration for 4 h. The rice was immediately taken out and placed in a 4°C refrigerator for refrigeration.

[0093] Comparative Example 6

[0094] (1) Washing: Weigh 200 g of Nanjing 9108 rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0095] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0096] (3) Cooking: placing the rice drained from step (2) in boiling water with a rice-to-water ratio of 1:6 and cooking for 5 min, gently stirring the rice grains during the cooking process to prevent the rice from sticking to the pot. During the cooking process, when the surface of the rice grains shows translucent gelatinization characteristics but the rice core is not completely gelatinized, remove the rice grains and drain the water;

[0097] (4) Steaming: Spread the drained rice flat in a steamer and steam it over steam for 15 minutes until the rice is fully cooked to obtain finished rice;

[0098] (5) Refrigeration: The finished rice is quickly cooled to 35°C and immediately placed in a 4°C refrigerator.

[0099] The texture and relative crystallinity of Nanjing 9108 rice were measured after 0d, 1d, 3d and 7d of refrigeration in Example 6 and Comparative Examples 4-6, to compare and illustrate the beneficial effects and effects of the present invention on delaying the aging and regeneration of rice during refrigeration. The experimental results are shown in Table 3. The hardness and relative crystallinity of the rice treated by the present invention during storage are significantly lower than those of the comparative sample (P<0.05), and the viscosity is significantly higher than that of the comparative sample (P<0.05). In the hardness, viscosity and crystallinity test after refrigeration for 7 days, the hardness of the rice treated by the present invention is reduced by 16.36%, the viscosity is increased by 59.75%, and the crystallinity is reduced by 29.32% compared with the untreated rice (Comparative Example 4); the hardness is reduced by 9.80%, the viscosity is increased by 20.39%, and the crystallinity is reduced by 20.99% compared with the comparative example 5. It can be seen that the cooking-before-steaming process of the present invention can delay the quality deterioration caused by aging of the rice after storage and improve the taste quality of the rice after storage; the hardness is reduced by 11.80%, the viscosity is increased by 31.31%, and the crystallinity is reduced by 22.39% compared with the comparative example 6. The synergistic effect of the cooking-before-steaming process and magnetic field-assisted refrigeration can effectively delay the aging process of the rice during refrigeration.

[0100] Table 3 Hardness, viscosity and relative crystallinity of Example 6 and Comparative Examples 4-6 stored at 4°C for 0-7 days

[0101]

[0102] Example 7

[0103] A method for delaying the aging and regeneration of rice during refrigeration by combining a cooking-before-steaming process with a magnetic field-assisted refrigeration process, wherein the specific steps are as follows:

[0104] (1) Washing: Weigh 200 g Yunnan soft rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0105] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0106] (3) Cooking: The rice drained from step (2) is placed in boiling water with a rice-water mass ratio of 1:6 and cooked for 5 min at a cooking power of 900 W. The rice grains are gently stirred during the cooking process to prevent the rice from sticking to the pot. During the cooking process, when the surface of the rice grains shows translucent gelatinization characteristics but the rice core is not completely gelatinized, the rice grains are removed and the water is drained;

[0107] (4) Steaming: Spread the drained rice flat in a steamer and steam it over steam for 15 min at a steaming power of 900 W until the rice is fully cooked to obtain finished rice;

[0108] (5) Refrigeration: The finished rice was quickly cooled to 35°C and spread out in a magneto-electric coupled freezer refrigerator. The rice was refrigerated for 4 h at a magnetic field strength of 6 mT and a refrigeration temperature of 4°C. The rice was immediately taken out and placed in a refrigerator at 4°C for refrigeration.

[0109] Comparative Example 7

[0110] (1) Washing: Weigh 200 g Yunnan soft rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0111] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0112] (3) Steaming: After washing and soaking, the rice is steamed in an ordinary rice cooker at a rice-to-water ratio of 1:1.2. After steaming, the rice is simmered for 10 minutes to balance the moisture;

[0113] (4) Refrigeration: After finishing, take out and quickly cool to 35°C, and immediately place in a 4°C refrigerator;

[0114] Comparative Example 8

[0115] (1) Washing: Weigh 200 g Yunnan soft rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0116] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0117] (3) Steaming: After washing and soaking, the rice is steamed in an ordinary rice cooker at a rice-to-water ratio of 1:1.2. After steaming, the rice is simmered for 10 minutes to balance the moisture;

[0118] (4) Refrigeration: Spread the rice flat in a magneto-electric coupled freezer and refrigerator, use a magnetic field strength of 6 mT and a refrigeration temperature of 4 °C to assist refrigeration for 4 h. Immediately take out the rice and place it in a 4 °C refrigerator for refrigeration.

[0119] Comparative Example 9

[0120] (1) Washing: Weigh 200 g Yunnan soft rice, wash the raw rice with clean water for 3 times, gently stir clockwise for 15 circles, pour out the rice washing water immediately after washing and drain the excess water;

[0121] (2) soaking: adding deionized water with a rice-water mass ratio of 1:2 to the rice drained in step (1), and soaking at a constant temperature of 20° C. for 30 min until the rice fully absorbs water. After soaking, remove the rice and drain the water;

[0122] (3) Cooking: placing the rice drained from step (2) in boiling water with a rice-to-water ratio of 1:6 and cooking for 5 min, gently stirring the rice grains during the cooking process to prevent the rice from sticking to the pot. During the cooking process, when the surface of the rice grains shows translucent gelatinization characteristics but the rice core is not completely gelatinized, remove the rice grains and drain the water;

[0123] (4) Steaming: Spread the drained rice flat in a steamer and steam it over steam for 15 minutes until the rice is fully cooked to obtain finished rice;

[0124] (5) Refrigeration: Quickly cool the finished rice to 35°C and immediately place it in a 4°C refrigerator.

[0125] The texture and relative crystallinity of the Yunnan soft rice cooked in Example 7 and Comparative Examples 7 to 9 after refrigeration for 0 days, 1 day, 3 days and 7 days were measured to compare and illustrate the beneficial effects and effects of the present invention on delaying the aging and regeneration of rice during refrigeration. The experimental results are shown in Table 4. The hardness and relative crystallinity of the rice treated by the present invention during storage are significantly lower than those of the comparative sample (P<0.05), and the viscosity is significantly higher than that of the comparative sample (P<0.05). In the hardness, viscosity and crystallinity test after 7 days of refrigeration, the hardness of the rice treated by the present invention is reduced by 21.93%, the viscosity is increased by 29.84%, and the crystallinity is reduced by 27.87% compared with the untreated rice (Comparative Example 7); the hardness is reduced by 14.97%, the viscosity is increased by 28.18%, and the crystallinity is reduced by 15.83% compared with the comparative example 8. It can be seen that the cooking-before-steaming process of the present invention can delay the quality deterioration caused by aging of the rice after storage and improve the taste quality of the rice after storage; the hardness is reduced by 20.03%, the viscosity is increased by 24.03%, and the crystallinity is reduced by 22.77% compared with the comparative example 9. The synergistic effect of the cooking-before-steaming process and magnetic field-assisted refrigeration can effectively delay the aging process of the rice during refrigeration.

[0126] Table 4 Hardness, viscosity and relative crystallinity of Example 7 and Comparative Examples 7-9 stored at 4°C for 0-7 days

[0127]

[0128] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for delaying the aging and regeneration of refrigerated rice, characterized in that: The steps include: (1) Raw material processing: washing and soaking the rice, and draining the water after soaking; (2) Cooking: Cooking the drained rice, and draining the water after cooking; (3) Steaming: Steaming the rice drained from step (2) to obtain uniform and fluffy rice; (4) Magnetic field-assisted refrigeration: The uniformly fluffy rice obtained in step (3) is cooled and placed in a refrigerated environment with a magnetic field applied.

2. The method for delaying aging and regeneration of refrigerated rice according to claim 1, characterized in that: In step (1), the temperature of the rice soaked in water is 20-25° C., and the soaking time is 20-30 min.

3. The method for delaying aging and regeneration of refrigerated rice according to claim 1, characterized in that: In step (1), the mass ratio of rice to water during rice soaking is 1:1-2.

4. The method for delaying aging and regeneration of refrigerated rice according to claim 1, characterized in that: In step (2), the cooking power is 800-1000W, the cooking time is 5-10min, and the mass ratio of the cooked rice to water is 1:5-8.

5. The method for delaying aging and regeneration of refrigerated rice according to claim 1, characterized in that: In step (2), during the cooking process, when the surface of the rice grains shows translucent gelatinization characteristics but the rice core is not completely gelatinized, the rice grains are removed and the water is drained.

6. The method for delaying aging and regeneration of refrigerated rice according to claim 5, characterized in that: When the rice grains show translucent gelatinization characteristics on the surface but the rice core is not completely gelatinized as detected by a texture analyzer or an optical microscope, they are immediately taken out and the water is quickly drained.

7. The method for delaying aging and regeneration of refrigerated rice according to claim 1, characterized in that: In step (3), the steaming power is 800-1000W, and the steaming time is 10-20min.

8. The method for delaying aging and regeneration of refrigerated rice according to claim 1, characterized in that: In step (4), the rice is spread out and placed in a magneto-electric coupled freezer refrigerator, the magnetic field strength is 3 to 9 mT, the magnetic field assisted refrigeration time is 2 to 6 hours, and the refrigeration temperature is 3 to 5°C.

9. The method for delaying aging and regeneration of refrigerated rice according to claim 1, characterized in that: In step (4), after the rice is subjected to magnetic field-assisted refrigeration treatment, it is taken out and placed in a refrigerator for refrigeration.

10. Rice prepared by the method according to any one of claims 1 to 9.

Images