Whey protein coating treated brown rice and preparation process thereof

Abstract

The invention discloses whey protein coating treated brown rice and a preparation process thereof, the whey protein coating treated brown rice comprises a wall material and a core material, the wall material is maltodextrin and whey protein, the mass ratio of the maltodextrin to the whey protein is (15-60): 7, the thickness of the wall material is 0.2-0.3 mm, and the core material is brown rice. The whey protein and the maltodextrin are compounded according to a certain proportion, the emulsion is prepared and sprayed on the outer surface of the brown rice, a protective film is formed on the outer surface of the brown rice after drying, the quality guarantee period of the brown rice can be effectively prolonged, the quality guarantee period of the coated brown rice self-sealing bag package under the storage condition of 20 DEG C is 187 days, and the coated brown rice self-sealing bag package has a good market prospect. And the shelf life under the storage condition of 37 DEG C is 120 days. The whey protein is high in nutritional value and easy to digest and absorb, contains various active ingredients, and improves the high-quality protein content of the brown rice, so that the nutritional value of the brown rice is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of brown rice processing, and in particular to a whey protein-coated brown rice with a long shelf life and its preparation process. Background Art

[0002] Brown rice is the caryopsis after removing the outer protective cortex (husk) of paddy rice, and the rice grain with the inner protective cortex (pericarp, seed coat, nucellus) intact. Due to the relatively high content of crude fiber, bran wax, etc. in the inner protective cortex, the taste is relatively rough, the texture is tight, and it takes more time to cook, but its slimming effect is remarkable. Compared with ordinary refined white rice, brown rice is richer in vitamins, minerals and dietary fiber, and is regarded as a green and healthy food.

[0003] The shelf life of raw brown rice packed in a self-sealing bag under the storage condition of 20°C is 113 days. During the storage period, the change of the fatty acid value of brown rice is not significant, and there are no obvious changes in color, smell and eating quality. However, after the storage period, the color of brown rice gradually darkens, turns yellow, and gradually shows sour and rancid smells, and the eating quality will seriously decline and it will not be suitable for consumption. Moreover, as the weather temperature rises, the shelf life of brown rice will be shortened. Some studies have shown that at 37°C in summer, the shelf life of brown rice packed and stored in a self-sealing bag is less than 60 days. Summary of the Invention

[0004] To solve the problem that the existing brown rice has a short shelf life, especially less than 60 days at high temperatures in summer, the present invention provides a whey protein-coated brown rice and its production method. By compounding whey protein and maltodextrin in a certain proportion, an emulsion is prepared and sprayed on the outer surface of brown rice. After drying, a protective film is formed on the outer surface of brown rice, which can effectively extend the shelf life of brown rice.

[0005] To achieve the above object, the present invention provides a whey protein-coated brown rice, including a wall material and a core material. The wall material is maltodextrin and whey protein, and the mass ratio of maltodextrin to whey protein = (15 - 60):7. The thickness of the wall material is set to 0.2 - 0.3 mm, and the core material is brown rice.

[0006] Preferably, the mass ratio of maltodextrin to whey protein = 30:7.

[0007] The present invention also provides the preparation process of the above-mentioned whey protein-coated brown rice, including the following steps: S1. Preparation of the spraying emulsion: Dissolve whey protein in deionized water and stir at room temperature for 0.5 - 1 h to obtain a whey protein emulsion with a concentration of 14%. Dissolve maltodextrin in deionized water and stir at room temperature for 0.5 - 1 h to obtain a maltodextrin solution with a concentration of 60%. Add the 14% whey protein emulsion in step 1 to the 60% maltodextrin solution, continue to stir for 0.5 - 1 h to obtain a mixture, and perform high-temperature denaturation treatment on the mixture to obtain the spraying emulsion; S2. Coating of brown rice: Lay the brown rice evenly on the surface of the tin foil. Spray the spraying emulsion prepared in step S1 evenly on the surface of the brown rice with a spray gun. Place the sprayed brown rice in an oven at 40 - 45 °C and dry for 5 - 6 min; After taking it out, turn the whole brown rice over, spray the brown rice with the spray gun for the second time, and then place it in an oven at 40 - 45 °C and dry for 5 - 6 min; After taking it out, stir and mix the brown rice evenly, then lay it flat on the surface of the tin foil again, and place it in an oven at 40 - 45 °C and dry for 5 - 6 min; After taking it out, cool it at room temperature and then bag it for storage.

[0008] The specific reaction of whey protein and maltodextrin at high temperature can significantly improve the film-forming performance (mechanical strength, flexibility, barrier property) of the spraying emulsion: 1) Maillard reaction (covalent cross-linking) - can enhance the mechanical strength and water resistance of the film; 2) Protein-polysaccharide physical cross-linking - can improve the flexibility and uniformity of the film; 3) Polysaccharide glass transition - can improve the continuity of the film and reduce its brittleness; 4) Hydrophobic interaction - can enhance the barrier property of the film (barrier to water vapor and oxygen).

[0009] Preferably, in step S1, the mixing ratio of the 60% maltodextrin solution to the 14% whey protein emulsion is 1:1 - 2:3; In step S1, the high-temperature denaturation process is to heat the mixture while stirring, the heating temperature is 70 - 90 °C, and the heating time is 15 - 55 min.

[0010] Preferably, in step S1, the mixing ratio of the 60% maltodextrin solution to the 14% whey protein emulsion is 2:1 or 1:1; In step S1, the high-temperature denaturation process is to heat the mixture while stirring, the heating temperature is 75 - 80 °C, and the heating time is 25 - 35 min.

[0011] Preferably, in step S1, the mixing ratio of the 60% maltodextrin solution to the 14% whey protein emulsion is 1:1, and in step S1, the high-temperature denaturation process is to heat the mixture while stirring, the heating temperature is 80 °C, and the heating time is 35 min.

[0012] Preferably, in step S1, the high-temperature denaturation process is to heat the mixture while stirring, and the stirring speed is set at 600 - 800 rpm.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: By compounding whey protein and maltodextrin in a certain proportion, an emulsion is prepared and sprayed on the outer surface of brown rice. After drying, a protective film is formed on the outer surface of brown rice, which can effectively extend the shelf life of brown rice. The shelf life of the coated brown rice packaged in a self-sealing bag is 187 days under the storage condition of 20°C and 120 days under the storage condition of 37°C. Whey protein has high nutritional value, is easily digested and absorbed, contains a variety of active ingredients, improves the high-quality protein content of brown rice, and thus improves the nutritional value of brown rice. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a water contact angle detection diagram of the composite film sample prepared from the spraying emulsion of Examples 1-13 of the present invention; Figure 2 It is a breaking elongation rate detection diagram of the composite film sample prepared from the spraying emulsion of Examples 1-13 of the present invention; Figure 3 It is a tensile strength detection diagram of the composite film sample prepared from the spraying emulsion of Examples 1-13 of the present invention; Figure 4 It is a moisture content measurement result diagram of Example 3 of the present invention and the raw brown rice in self-sealing packaging and vacuum packaging under the storage conditions of 15°C, 37°C and 47°C; Figure 5 It is a color measurement result diagram of Example 3 of the present invention and the raw brown rice in self-sealing packaging and vacuum packaging under the storage conditions of 15°C, 37°C and 47°C; Figure 6 It is a free fatty acid value measurement result diagram of Example 3 of the present invention and the raw brown rice in self-sealing packaging and vacuum packaging under the storage conditions of 15°C, 37°C and 47°C; Figure 7 It is a peroxide value measurement result diagram of Example 3 of the present invention and the raw brown rice in self-sealing packaging and vacuum packaging under the storage conditions of 15°C, 37°C and 47°C; Figure 8 It is an odor measurement result diagram of Example 3 of the present invention and the raw brown rice in self-sealing packaging and vacuum packaging under the storage conditions of 15°C, 37°C and 47°C; Figure 9 It is a taste score measurement result diagram of Example 3 of the present invention and the raw brown rice in self-sealing packaging and vacuum packaging under the storage conditions of 15°C, 37°C and 47°C. DETAILED DESCRIPTION OF THE INVENTION

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Example

[0016] Example 1 provides a whey protein-coated brown rice, including a wall material and a core material. The wall material is maltodextrin and whey protein, and the mass ratio of maltodextrin to whey protein is 60:7. The thickness of the wall material is 0.241 mm, and the core material is brown rice.

[0017] The preparation process of this Example 1 includes the following steps: S1. Prepare the spraying emulsion: Dissolve whey protein in deionized water and stir at room temperature for 0.5 - 1 h to obtain a whey protein emulsion with a concentration of 14%. Dissolve maltodextrin in deionized water and stir at room temperature for 0.5 - 1 h to obtain a maltodextrin solution with a concentration of 60%. Add the 14% whey protein emulsion in step 1 to the 60% maltodextrin solution, and the mixing ratio of the 60% maltodextrin solution to the 14% whey protein emulsion is 2:1. Continue to stir for 0.5 - 1 h to obtain a mixed solution, and perform high-temperature denaturation treatment on the mixed solution; The high-temperature denaturation process is to heat the mixed solution while stirring, set the stirring speed at 600 - 800 rpm, the heating temperature at 80 °C, and the heating time at 35 min. Obtain the spraying emulsion; S2. Spray the brown rice: Spread the brown rice evenly on the surface of the tin foil, spray the spraying emulsion prepared in step S1 evenly on the surface of the brown rice with a spray gun, and put the sprayed brown rice into an oven at 40 °C and dry for 5 min; After taking it out, turn the whole brown rice over, spray the brown rice with a spray gun for the second time, and then put it into an oven at 40 °C and dry for 5 min; Take it out, stir and mix the brown rice evenly, then spread it on the surface of the tin foil again, and put it into an oven at 40 °C and dry for 5 min; Take it out, cool it at room temperature, and then bag it for storage.

[0018] The component ratios and preparation methods of Example 2 and Example 1 are basically the same, the difference being that the mixing ratio of the 60% maltodextrin solution to the 14% whey protein emulsion in Example 2 is 3:2 respectively.

[0019] The component ratios and preparation methods of Example 3 and Example 1 are basically the same, the difference being that the mixing ratio of the 60% maltodextrin solution to the 14% whey protein emulsion in Example 2 is 1:1 respectively.

[0020] Example 4 is basically the same as Example 1 in terms of component ratio and preparation method, except that the mixing ratios of 60% maltodextrin solution and 14% whey protein emulsion in Example 2 are 2:3 respectively.

[0021] Example 5 is basically the same as Example 1 in terms of component ratio and preparation method, except that the mixing ratios of 60% maltodextrin solution and 14% whey protein emulsion in Example 2 are 1:2 respectively.

[0022] Example 6 is basically the same as Example 3 in terms of component ratio and preparation method, except that the heating temperature for high-temperature denaturation is 70 °C.

[0023] Example 7 is basically the same as Example 3 in terms of component ratio and preparation method, except that the heating temperature for high-temperature denaturation is 75 °C.

[0024] Example 8 is basically the same as Example 3 in terms of component ratio and preparation method, except that the heating temperature for high-temperature denaturation is 85 °C.

[0025] Example 9 is basically the same as Example 3 in terms of component ratio and preparation method, except that the heating temperature for high-temperature denaturation is 90 °C.

[0026] Example 10 is basically the same as Example 3 in terms of component ratio and preparation method, except that the heating time for high-temperature denaturation is 15 min.

[0027] Example 11 is basically the same as Example 3 in terms of component ratio and preparation method, except that the heating time for high-temperature denaturation is 25 min.

[0028] Example 12 is basically the same as Example 3 in terms of component ratio and preparation method, except that the heating time for high-temperature denaturation is 45 min.

[0029] Example 13 is basically the same as Example 3 in terms of component ratio and preparation method, except that the heating time for high-temperature denaturation is 55 min.

[0030] Performance test: 1. Take 8 ml of each of the spraying emulsions prepared in Examples 1 - 13, pour them into a flat plate, and dry them at 28 °C and 70% RH for 12 h to form composite films. Test the water contact angle, tensile strength, and elongation at break of each composite film. The test results are shown in Figure 1 、 Figure 2 、 Figure 3 。

[0031] The contact angle is the angle (θ) at the junction of the solid-liquid interface and the gas-liquid interface. When θ < 90°, the solid surface is hydrophilic, which means that the liquid can wet the solid more easily. Therefore, the larger the contact angle value, the higher the hydrophobicity of the sample.

[0032] It can be seen from Figure 1 that the contact angle values of the treated samples are all less than 90°. As the addition amount of maltodextrin, the action temperature and time increase, the water contact angle shows a trend of increasing first and then decreasing. After the ratio of maltodextrin to whey protein is greater than 1:1, the water contact angle of the composite film gradually decreases, indicating a decrease in hydrophobicity; the increase in temperature causes a change in the conformation of whey protein, exposing hydrophobic groups, resulting in an enhanced hydrophobic interaction. The increase in the contact angle is also because during the heating process, protein gelation is enhanced, and the gelled protein forms a dense network structure. The polysaccharide fills this dense structure and forms strong intermolecular forces. The film formed by this dense structure has the ability to block the wetting of other liquid phases (water or oil). The conjugation of whey protein and polysaccharide will also increase the contact angle. Some researchers have pointed out that the glycosylation reaction of sugar and protein will induce a change in the protein conformation (exposure of hydrophilic and hydrophobic groups). The unfolding of the globular structure makes the peptide chain more flexible and flexible, and the increase in surface hydrophobic groups enhances hydrophobicity. However, as the temperature gets higher and higher, the protein coagulates, destroying the original formed structure, resulting in a decrease in the water contact angle. As the heating time increases, water loss occurs, the solution becomes viscous, and the surface of the composite film becomes rougher, resulting in a decrease in the water contact angle value.

[0033] It can be seen from Figure 2 and Figure 3 that the elongation at break and tensile strength change significantly under different treatment conditions.

[0034] It can be seen from Figure 2 that as the concentration of maltodextrin decreases, the elongation at break of the composite film continuously decreases, indicating that glycosylation modification makes the protein film more flexible. This may be related to the combination of the amino group of the protein and the carbonyl group of glucose during the Maillard reaction. The combination of the two forms a more stable and tough network structure inside the film. As the modification temperature and modification time increase, the elongation at break of the modified protein film first increases and then decreases. When the heating temperature is less than 80 °C, the gelation degree of the film-forming solution is not high, and the intermolecular force is not strong, resulting in a low elongation at break. The increase in heating temperature can promote the process of the Maillard reaction. At the same time, the polypeptide chain of the protein is fully unfolded and reacts fully with maltodextrin, thus strengthening the interaction between sugar and protein, also strengthening the binding between proteins. The intermolecular force is stronger, and the intermolecular cohesion is greater, resulting in an increase in the elongation at break. However, too high a temperature or too long a heating time will cause the opposite effect.

[0035] It can be seen from Figure 3It can be seen that the tensile strength shows an increasing trend after the ratio of maltodextrin to whey protein is lower than 1:1. With the increase of the action temperature and time, the tensile strength of the composite film shows a trend of first decreasing and then increasing. Within an appropriate range, the interaction between maltodextrin and whey protein will be enhanced with the extension of time, thereby improving the mechanical properties of the film. The composite film has a high tensile strength. This is because the hydrophobic groups embedded in the protein core are exposed. Under the influence of hydrophobic forces, intermolecular disulfide bonds are re-formed. Under the combined action of disulfide bonds, hydrogen bonds and other secondary bonds, polypeptide chains form denser aggregates. This aggregate with a dense network structure enhances the mechanical properties of the film. However, if the time is too long, the protein will aggregate and denature excessively, which will have a negative impact on the extensibility of the film.

[0036] The comprehensive effects of different ratios of maltodextrin to whey protein, different heating temperatures and different heating times on the water contact angle and mechanical strength of the composite film are scored: the tensile strength and elongation at break are each assigned 30 points, and the water contact angle is assigned 40 points, with a full score of 100 points. The maximum value obtained from the test is used as the full score, and the remaining scores are converted according to the percentage. The scoring results are shown in Table 1.

[0037] Table 1

[0038] From the comprehensive scoring results in Table 1, it can be seen that when the ratio of maltodextrin to whey protein in the composite film is 1:1, the highest score is 86.3 points. Similarly, the highest scores are obtained at 80 °C and 35 minutes under the temperature and time treatment conditions respectively. Therefore, the optimal process for the composite film is that the ratio of maltodextrin to whey protein is 1:1, the temperature is 80 °C, and the time is 35 min, which is the process parameters of Example 3 of the present invention.

[0039] 2. The brown rice treated with the whey protein coating prepared in Example 3 of the present invention and the raw brown rice are respectively packaged in self-sealing bags and vacuum bags, 100 g per bag. The samples are respectively named raw brown rice self-sealing, raw brown rice vacuum, coated brown rice self-sealing, and coated brown rice vacuum for storage performance testing: 1) Moisture content detection, the detection standard is GB 5009.3—2016 "National Food Safety Standard Determination of Moisture in Foods", and the determination results are shown in Figure 4 , and Figures (A), (B), and (C) in the figure are the determinations at storage temperatures of 15 °C, 37 °C, and 47 °C respectively.

[0040] From Figure 4It can be seen that the moisture contents of the two brown rice samples always meet the requirements of the national standard (moisture content ≤ 14%). The initial moisture contents are relatively high. During the initial period of storage, the moisture content decreases significantly. As the storage time extends, the moisture content basically remains unchanged. The sharp decrease in moisture content is due to the exchange of moisture between the samples with relatively high moisture at the beginning of the storage experiment and the moisture in the environment, resulting in an obvious decrease in the moisture content of brown rice. During the subsequent storage experiment, a dynamic balance is maintained and the change range is not obvious. Compared with self-sealing packaging, the moisture fluctuation of vacuum packaging is smaller. The increase in free fatty acids during grain storage is more affected by humidity than by temperature. At the same storage temperature, the higher the moisture content of brown rice, the faster the change in fatty acid value and the easier it is to mildew. The higher the moisture content of brown rice, the faster the respiration rate, which is not conducive to long-term storage. After coating treatment, the moisture content of brown rice is less than that of the raw brown rice at any temperature. Therefore, in terms of the moisture content index, the brown rice after coating treatment in the embodiments of this patent is easier to store for a long time.

[0041] 2) The color of brown rice was measured using a color difference meter. The measurement results are shown in Figure 5 .

[0042] The change in the color of brown rice during storage is easily noticeable. The reasons for the change in color are diverse, including fatty acid oxidation, the action of polyphenol oxidase, etc. As the storage time extends, the color of brown rice will change to dull, grayish, and in severe cases, yellow or dark yellow. The change in the chromaticity of brown rice is measured using a portable color difference meter. Among them, the L* value represents lightness and darkness, the a* value represents red and green, and the b* value represents yellow and blue. The changes in the L* value and b* value are more obvious during the storage of brown rice. The L* value and b* value of the coated brown rice are lower than those of the raw brown rice because the brown rice is wrapped by a coating formed by whey protein and maltodextrin, and the color will be slightly darker.

[0043] When brown rice is stored at 15 °C, the changes in the L*, a*, and b* values are not obvious, indicating that low-temperature storage is beneficial to maintaining the color of brown rice. The smaller the L* value, the darker the color. When stored at 37 °C and 47 °C, the L* value of brown rice shows a downward trend, indicating that the color of brown rice gradually darkens during storage. For the coated brown rice at 37 °C and 47 °C, the change range of the L* value is smaller than that of the raw brown rice. When the raw brown rice is stored in a self-sealing package at 37 °C for 84 days and at 47 °C for 35 days, the increase in the L* value is because during storage, due to the loss of the protection of the rice husk, the epidermis is damaged and the phenomenon of "chaffing" occurs, and many white spots will appear on the surface of the brown rice.

[0044] Under storage conditions at different temperatures, the a* values of the samples used were all negative, indicating that the color of brown rice was more inclined to green. After storing at 37 °C for 120 days and at 47 °C for 49 days, the a* values of the raw brown rice in self-sealing packages decreased sharply, and the change in a* value was greater at 47 °C, indicating that the higher the storage temperature, the easier the color of brown rice turned green. When the b* value was positive, the larger the value, the more yellow the color. As the storage time increased, the b* values of the samples showed an upward trend. The b* value of the raw brown rice in self-sealing packages increased significantly after storing at 47 °C for 70 days, probably because the lipid substances on the surface of brown rice oxidized and deteriorated, resulting in a darker yellow color. From the b* value graphs at 37 °C and 47 °C, it was found by comparison that the higher the temperature, the more obvious the upward trend of the b* value. Comparing vacuum packaging with self-sealing packaging, it was found that the chromaticity change in the self-sealing packaging group was larger, indicating that vacuum packaging could delay the color change of brown rice.

[0045] In summary, the deterioration of brown rice can be reflected by the color of brown rice. Low-temperature storage and vacuum packaging are more beneficial to the storage of brown rice. The chromaticity change of the coated brown rice is smaller than that of the raw brown rice, and the color change has less impact during storage.

[0046] 3) Determination of the free fatty acid value. The determination standard is GBT15684-2015 "Determination of Fatty Acid Value of Milled Cereal Products". The determination results are shown in Figure 6 During the storage of brown rice, the change of lipids can best reflect the deterioration of brown rice quality. The changes in lipids include oxidation and hydrolysis. Under the action of oxygen, microorganisms, light, enzymes, etc., primary metabolites and secondary metabolites are generated. The primary metabolites are mainly lipid hydroperoxides, and the decomposition of lipid hydroperoxides will generate a variety of secondary metabolites, including aldehydes, ketones, alcohols, acids, and hydrocarbons, etc. These products not only affect the quality and flavor of food, but also cause important harm to human health. The degree of fat oxidation can be expressed by the fatty acid value. The higher the degree of fat oxidation, the larger the fatty acid value.

[0047] From Figure 6As can be seen from the figures at 15°C, within the 6-month storage period, the fatty acid values of all brown rice samples were 25 mg / 100 g, meeting the national standard requirements. From the figures at 37°C and 47°C, it can be seen that the fatty acid value showed an upward trend with the increase in the storage period. The raw brown rice showed a downward trend when stored at 37°C for 132 days and at 47°C for 63 days because unsaturated fatty acids reacted with oxygen molecules to form aldehydes and other stimulating metabolites. The fatty acid value of the raw brown rice in self-sealing packaging exceeded 25 mg / 100 g earliest at 37°C for 60 days and at 47°C for 21 days, while the fatty acid value of the coated brown rice in self-sealing packaging exceeded 25 mg / 100 g at 37°C for 120 days and at 47°C for 63 days, indicating that the brown rice was no longer suitable for storage at this time. The fatty acid values of the raw brown rice in vacuum packaging exceeded 25 mg / 100 g after being stored at 37°C for 84 days and at 47°C for 42 days respectively, while the fatty acid values of the coated brown rice in vacuum packaging exceeded 25 mg / 100 g after being stored at 37°C for 132 days and at 47°C for 70 days respectively, indicating that the coating treatment was beneficial to the storage of brown rice, and vacuum packaging could delay lipid oxidation.

[0048] 4) Determination of peroxide value. The determination standard is GB5009.227-2023 "National Food Safety Standard - Determination of Peroxide Value in Foods". The determination results are shown in Figure 7 .

[0049] During the storage of brown rice, the peroxide value is one of the important indicators to measure the degree of lipid oxidation. From Figure 7 it can be seen that the peroxide value showed an upward trend during storage, increasing slowly in the early stage and increasing rapidly in the later stage of storage because the activity of peroxidase gradually decreased, and the generation rate of hydrogen peroxide could not be balanced with the degradation rate of peroxidase on it, resulting in a large accumulation of peroxide value in the later stage. When stored at 15°C for 6 months, the peroxide value of the raw brown rice in self-sealing packaging was 0.231 g / 100 g. After being stored at 37°C for 156 days and at 47°C for 91 days, the peroxide value was much higher than 0.6 g / 100 g. Under the storage conditions of 37°C and 47°C, the peroxide value of the coated brown rice in the examples of the present invention was significantly lower than that of the raw brown rice, indicating that the coating treatment could effectively inhibit lipid oxidation.

[0050] 5) Determination of malondialdehyde. The determination results are shown in Figure 8 .

[0051] Brown rice contains intact embryos and outer cortexes and mainly contains lipid substances. During storage, the lipids in brown rice will be hydrolyzed into free fatty acids, and free fatty acids are easily oxidized to form hydroperoxides, which are then further decomposed into small molecules such as aldehydes and ketones. Aldehyde compounds are the main sources of off-flavor components during the storage of brown rice. Among them, malondialdehyde is one of the important indicators to evaluate the freshness of brown rice, and at the same time, malondialdehyde can also reflect the peroxidation degree of rice membranes.

[0052] From Figure 8 it can be seen that as the storage time increases, the content of malondialdehyde gradually rises. After storage at 15°C, the malondialdehyde content of all samples is lower than that of the samples stored at 37°C and 47°C.

[0053] 6) Determination of odor. The determination standard is the nose-smelling method in GB / T 5492-2008 Grain and Oil Inspection - Identification of Color, Odor and Taste of Grain and Oil Seeds, to evaluate the odor during the storage of brown rice. The odor evaluations at 15°C, 37°C, and 47°C are carried out respectively, and the results are shown in Table 2, Table 3, and Table 4 respectively.

[0054] During the storage of brown rice, the rancid smell of oil will appear, mainly because the oil will be oxidized and decomposed during storage, producing volatile substances such as aldehydes and ketones.

[0055] Table 2 shows the odor evaluation during storage at 15°C

[0056] Table 3 shows the odor evaluation during storage at 37°C

[0057] Table 4 shows the odor evaluation during storage at 47°C

[0058] Note: - indicates having aroma, + indicates no aroma and no peculiar smell, ++ indicates relatively light sour taste or rancid smell, +++ indicates obvious sour taste, rancid smell, ++++ indicates severe sour taste, rancid smell From Table 2 - Table 4, it can be seen that during the storage of brown rice at 15°C for 6 months, the odor change is not obvious. The raw brown rice in self-sealed packaging starts to have odor changes earliest after 72 days of storage at 37°C and 47 days of storage at 47°C, while the coated brown rice in the examples of the present invention in self-sealed packaging starts to have odor changes after 156 days of storage at 37°C and 91 days of storage at 47°C; after the storage at 37°C and 47°C is completed, the raw brown rice already has severe sour taste and rancid smell, while the odor change of the coated brown rice in the examples of the present invention in vacuum packaging is not obvious, indicating that the coated brown rice can delay the oxidation and decomposition of oil, and vacuum packaging can inhibit the generation of bad odors.

[0059] 7) Determination of taste score value. The determination standard is GB / T 20569-2006 Rules for Judging the Storage Quality of Paddy, and the determination results are shown in Figure 9 .

[0060] The taste score value consists of odor, taste, color, and appearance structure. In GB / T 20569 Rules for Judging the Storage Quality of Paddy, it is required that for japonica paddy, the taste score value ≥ 70 under suitable storage conditions.

[0061] It can be seen from Figure 9 that when stored at 15 °C for 6 months, the taste score values of the samples used basically remained unchanged, all greater than 70 points, indicating that low-temperature storage is more conducive to maintaining the edible quality of brown rice. Under the storage condition of 37 °C, the raw brown rice in self-sealing packaging was first unsuitable for consumption at 60 days, and then the taste score value of the raw brown rice in vacuum packaging was lower than 70 points at 84 days of storage. The taste score value of the coated brown rice in self-sealing packaging was lower than 70 points at 120 days of storage, and the taste score value of the coated brown rice in vacuum packaging was lower than 70 points at 132 days of storage. Under the storage condition of 47 °C, the raw brown rice in self-sealing packaging and the raw brown rice in vacuum packaging were respectively unsuitable for consumption at 28 days and 42 days, and the coated brown rice in self-sealing packaging and the coated brown rice in vacuum packaging were respectively unsuitable for consumption at 56 days and 70 days.

[0062] In summary, during storage, the fatty acid value, peroxide value, and malondialdehyde value all showed an upward trend. The raw brown rice was the most prone to deterioration, with the fastest growth rate and large fluctuations in its fatty acid value, peroxide value, and malondialdehyde value. Although the physiological and biochemical indexes of the coated brown rice also showed an upward trend, they were still lower than those of the raw brown rice, indicating that the coating treatment can effectively extend the storage period of brown rice.

[0063] 8) Applying the accelerated storage experiment to predict the storage period of the coated brown rice in the embodiments of the present invention The accelerated food storage test method is an effective and rapid method for predicting the storage period of food. The samples collected according to the experimental requirements were brown rice produced in the same batch, and the samples were in vacuum packaging form, with 100 g of brown rice in each bag. The brown rice in vacuum-sealed packaging and self-sealing bag packaging was placed in an incubator.

[0064] The accelerated storage temperatures selected were 37 °C and 47 °C.

[0065] According to Figure 6 the results in Figures B and C in the figure, under the storage condition of 37 °C, the storage periods of the raw brown rice and the coated brown rice in vacuum packaging were 72 days and 120 days respectively. Under the storage condition of 47 °C, the storage periods of the raw brown rice and the coated brown rice in vacuum packaging were 35 days and 63 days respectively. From the formula Q 10 = it can be calculated that the Q 10 values of the raw brown rice and the coated brown rice were 2 and 1.9 respectively.

[0066] From the formula the formula can be used to calculate that the storage periods of the raw brown rice and the coated brown rice under the storage condition of 20 °C were 113 days and 187 days respectively. After the coating treatment, the storage period of the brown rice was extended.

[0067] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and substitutions can be made, and these improvements and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. A whey protein coated brown rice, characterized in that: It comprises a wall material and a core material, wherein the wall material is maltodextrin and whey protein, the mass ratio of maltodextrin and whey protein is (15-60):7, the thickness of the wall material is set to 0.2-0.3 mm, and the core material is brown rice.

2. The whey protein coated brown rice according to claim 1, characterized in that: The mass ratio of the maltodextrin and whey protein is 30:

7.

3. A process for preparing brown rice treated with a whey protein coating according to claim 1 or 2, characterized in that: The steps include: S1, preparing a spray emulsion: dissolving whey protein in deionized water, stirring at room temperature for 0.5 to 1 h, and obtaining a whey protein emulsion with a concentration of 14%; dissolving maltodextrin in deionized water, stirring at room temperature for 0.5 to 1 h, and obtaining a maltodextrin solution with a concentration of 60%; adding the whey protein emulsion of step 14% to the maltodextrin solution of 60%, and continuing to stir for 0.5 to 1 h to obtain a mixed solution, and subjecting the mixed solution to high temperature denaturation treatment to obtain a spray emulsion; S2, brown rice spraying: brown rice is evenly spread on the surface of tinfoil, the spray emulsion prepared in step S1 is evenly sprayed on the surface of brown rice with a spray gun, and the sprayed brown rice is placed in an oven at 40-45°C for drying for 5-6 min; after taking out, the brown rice is turned over as a whole, the brown rice is sprayed for the second time with a spray gun, and then placed in an oven at 40-45°C for drying for 5-6 min; after taking out, the brown rice is stirred and mixed evenly, then spread on the surface of tinfoil, and again placed in an oven at 40-45°C for drying for 5-6 min; after taking out, it is cooled at room temperature and bagged for storage.

4. The process for preparing brown rice treated with a whey protein coating according to claim 3, wherein: In the step S1, the mixing ratio of 60% maltodextrin liquid and 14% whey protein emulsion is 2:1-1:2; the high temperature denaturation process in the step S1 is to heat the mixed liquid while stirring, the heating temperature is 70-90° C., and the heating time is 15-55 minutes.

5. The process for preparing brown rice treated with a whey protein coating according to claim 3, characterized in that: In the step S1, the mixing ratio of 60% maltodextrin liquid and 14% whey protein emulsion is 2:1 or 1:1; the high temperature denaturation process in the step S1 is to heat the mixed liquid while stirring, the heating temperature is 75-80° C., and the heating time is 25-35 minutes.

6. The process for preparing brown rice treated with a whey protein coating according to claim 3, characterized in that: In the step S1, the mixing ratio of 60% maltodextrin liquid and 14% whey protein emulsion is 1:1, and the high temperature denaturation process in the step S1 is to heat the mixed liquid while stirring, the heating temperature is 80° C., and the heating time is 35 minutes.

7. The process for preparing brown rice treated with whey protein coating according to any one of claims 3 to 6, characterized in that: The high temperature denaturation process in step S1 is to heat the mixed solution while stirring, and the stirring speed is set to 600-800 rpm.

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