Fresh-keeping brown rice treated by superheated steam and preparation method of fresh-keeping brown rice

Abstract

The invention provides fresh-keeping brown rice treated by superheated steam and a preparation method of the fresh-keeping brown rice, and belongs to the technical field of food processing. The invention provides a preparation method of fresh-keeping brown rice subjected to superheated steam treatment, which comprises the following steps: grinding brown rice, and then carrying out superheated steam treatment; the grinding degree of the ground brown rice is 0-2%. The temperature of the superheated steam treatment is 110-150 DEG C, and the treatment time is 5 seconds to 2 minutes. By exploring the interaction relationship between the superheated steam treatment condition and the brown rice grinding degree, the accurate superheated steam treatment temperature, time and pressure and the influence of each parameter on the brown rice quality under the condition of different brown rice grinding degrees are obtained. The technical method for processing brown rice through superheated steam can be directly applied to the field of processing of brown rice food and processing of agricultural products such as brown rice, so that the processing efficiency and the product quality of brown rice food are improved.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, in particular to fresh-keeping brown rice treated with superheated steam and a preparation method thereof. Background Art

[0002] Whole grains have received more and more attention due to their nutritional and healthy properties. Brown rice is a kind of whole grain. my country is a country where rice is the staple food, but the proportion of whole grain brown rice is extremely low. Brown rice contains more vitamins, dietary fiber, polyphenols, protein and other nutrients than white rice, but brown rice has certain shortcomings in eating quality and storage quality, mainly manifested in the rough taste of brown rice, long cooking time, high hardness, difficult to chew, poor taste and flavor acceptance, short storage shelf life, easy to be oxidized and rancid to produce bad flavor. These problems seriously affect their potential consumer market as staple food. Traditional thermal processing technology, such as high-temperature fluidized bed drying technology, may induce oxidation reaction during food material processing, thereby affecting the quality of food. In addition, due to high-temperature treatment, food materials may lose water seriously or even burn. In extrusion puffing technology, starch gelatinization and protein denaturation will occur under the action of high temperature and high pressure, which may lead to the loss of nutrients and affect the digestion and absorption rate of food. Although microwave heating can achieve uniform heating and short processing time, it may make it difficult to destroy the protective layer of the outer layer of brown rice composed of cellulose, hemicellulose and pectin, thus affecting the taste of the brown rice and the ease of cooking.

[0003] Due to its high heat penetration capacity, superheated steam technology can provide better product quality (color, taste and sensory quality), reduce oxidation losses and improve energy efficiency in the field of food processing, especially in food drying and grain processing. In addition, superheated steam technology is also used to passivate the activity of enzymes such as lipase, lipoxygenase, peroxidase, polyphenol oxidase in food materials, reduce oxidative rancidity of food materials during storage, and maintain the stability of food quality.

[0004] Given that traditional heat treatment technology has problems such as long processing time, high cost, poor environmental protection, and the possibility of causing rice to be too soft and sticky, there is an urgent need to develop new green processing technologies to meet the needs of greening the process, making the product healthier, saving grain and reducing losses. Compared with traditional heat treatment technology, superheated steam technology has the advantages of higher heat and mass transfer efficiency, higher energy efficiency, energy saving and time saving, as well as the ability to reduce food oxidation in an anaerobic environment. It is expected to become an effective means to improve the edible quality of brown rice. Summary of the invention

[0005] The invention aims to prolong the shelf life of brown rice, improve the physical and chemical properties of brown rice and enhance the edible sensory quality.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing fresh-keeping brown rice treated with superheated steam, wherein the brown rice is ground and then treated with superheated steam;

[0008] The grinding degree after the grinding is 0-2%.

[0009] The temperature of the superheated steam treatment is 110-150° C., and the treatment time is 5 s-2 min.

[0010] Preferably, the pressure range of the superheated steam treatment is 0.15-0.40 MPa.

[0011] Preferably, the brown rice has a grinding degree of 1-2% after grinding.

[0012] Preferably, the temperature of the superheated steam treatment is 110-130° C., and the treatment time is 1 min-2 min.

[0013] Preferably, the temperature of the superheated steam treatment is 130°C.

[0014] The invention also provides fresh-keeping brown rice obtained by the preparation method.

[0015] The present invention obtains the precise temperature, time and pressure of superheated steam treatment and the influence of each parameter on the quality of brown rice under different grinding conditions by exploring the interaction between superheated steam treatment conditions and brown rice grinding degree. The exploration process found that superheated steam treatment has a significant effect on the quality of brown rice. The key lies in the precise control of the temperature and time of the treatment, especially after increasing the grinding degree. The control of superheated steam treatment parameters is more important. Specifically, under the influence of the grinding degree, the extension of superheated steam treatment time and the increase of temperature will significantly affect the appearance, taste value and flavor of brown rice. Therefore, the precise control of these two parameters is crucial to ensure the quality of brown rice. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The effect of superheated steam treatment on lipase activity of brown rice with 0% (A), 1% (B) and 2% (C) milling degree in Example 1;

[0017] Figure 2 The effect of superheated steam treatment on the peroxidase activity of 0% (A), 1% (B), and 2% (C) milling degree brown rice in Example 1;

[0018] Figure 3 The effect of superheated steam treatment on the appearance and color of 0%, 1% and 2% milling degree brown rice in Example 1;

[0019] Figure 4 The sensory evaluation analysis of the brown rice with a grinding degree of 0% (A), 1% (B), and 2% (C) treated with superheated steam in Example 1;

[0020] Figure 5 The effect of superheated steam treatment on the moisture absorption ratio and volume expansion rate of brown rice with 0% (A), 1% (B) and 2% (C) milling degree in Example 1;

[0021] Figure 6 The figure shows the effect of superheated steam treatment on the cooking time of brown rice with 0%, 1% and 2% grinding degrees in Example 1. DETAILED DESCRIPTION

[0022] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0023] Example 1

[0024] First, weigh 25g of brown rice, and use a rice yield detector (220V / 50Hz) to perform single rice milling. Mill the rice for 4s and 8s at a power of 0.5KW to obtain three types of brown rice with grinding degrees of 0%, 1% (4s), and 2% (8s). Spread the three types of brown rice evenly on a flat plate, and ensure that the brown rice is evenly distributed by gently shaking. Then, quickly put the brown rice into the steam heater and start accurate timing. The temperature setting range is between 110 and 150°C, the time is controlled between 1min and 6min, and the pressure is controlled at 0.3Mpa. See the specific test parameters below for details. 0%, 1%, and 2% brown rice that has not been treated with hot steam are used as the control group.

[0025] 1. Lipase activity

[0026] Since lipase converts triglycerides into free fatty acids, the shelf life of brown rice will be shortened. Therefore, the inactivation of lipase plays an important role in the storage stability of brown rice. Therefore, the lipase activity of brown rice with different milling degrees was measured at 110℃, 130℃ and 150℃ for 1, 2, 3, 4, 5 and 6 minutes respectively. The method for determining the lipase activity refers to the national standard GB / T5523-2008 "Determination of lipase activity of grains and oils in grain and oil inspection". The results are as follows Figure 1 And as shown in Table 1.

[0027] Depend on Figure 1It can be seen that at 110℃, 2min, 130℃, 1min, 150℃, 1min, the lipase activity of 0% milling brown rice decreased by 20.65%, 43.80%, 50.14%, respectively, the lipase activity of 1% milling brown rice decreased by 20.99%, 43.90%, 50.94%, respectively, and the lipase activity of 2% milling brown rice decreased by 18.19%, 41.72%, 56.83%, respectively. On the other hand, in short-term treatment, the temperature increased and the rate of decrease of lipase activity was faster. When the treatment time was extended to 6min, the lipase activity decreased by 43.04%, 58.63%, 61.30%, 44.82%, 57.20%, 65.59% and 43.94%, 56.99%, 67.29%, respectively. According to the results, increasing the temperature and extending the treatment time have a significant effect on the inactivation of lipase, but if the treatment time is too long, it will have a greater impact on the appearance damage of brown rice with different milling degrees (confirmed by subsequent experiments).

[0028] Table 1 Effects of milling degree and superheated steam treatment on brown rice lipase activity.

[0029]

[0030] Analysis of Table 1 shows that not only the temperature and time of superheated steam treatment have a significant effect on the lipase activity of brown rice, but also different milling degrees affect the treatment effect of superheated steam. For example, there is no significant difference in the lipase activity of 2% milling brown rice treated at 150℃ for 1min and 6min, but there is a significant difference between the two conditions of 1% milling brown rice, and finally the degree of reduction of lipase activity of 1% milling brown rice treated at 150℃ for 6min is higher than that of 1% milling brown rice treated at 150℃ for 1min. This shows that the milling degree and superheated steam treatment have an interactive effect and jointly affect the activity of lipase.

[0031] 2. Peroxidase activity

[0032] Peroxidase plays a key role in promoting oxidative rancidity and accelerates unnecessary chemical changes in grains. Its activity is closely related to changes in grain quality during storage. Therefore, the peroxidase activity of brown rice with different milling degrees was measured at 110℃, 130℃ and 150℃ for 1, 2, 3, 4, 5 and 6 minutes respectively. The peroxidase activity was measured according to the steps specified in the Boxbio peroxidase kit. The results are shown in Figure 2 shown.

[0033] Depend on Figure 2It can be seen that when the 0% milling degree brown rice was treated at 110°C for 2, 4, and 6 minutes, the peroxidase activity gradually decreased, decreasing by 22.24%, 37.14%, and 57.81% respectively. When the temperature was raised to 130°C, the inactivation efficiency of the enzyme was significantly improved. When the brown rice of different milling degrees was treated at 130°C for 1 minute and 2 minutes, the peroxidase activity of the brown rice of different milling degrees decreased by 68.04%, 69.14%, 69.19%, 69.40% and 68.34%, 68.76% respectively. When the temperature was raised to 150°C and treated for 6 minutes, the peroxidase activity of the brown rice of different milling degrees decreased by 85.90%, 88.83%, and 90.06%. However, the increase in temperature and the extension of the heating time have a greater impact on the appearance of the brown rice of different milling degrees (confirmed by subsequent experiments).

[0034] 3. Appearance and color

[0035] Color is an important factor in consumer acceptance of brown rice and related products. Color changes caused by thermal processing can affect taste, flavor, shelf life and application. Figure 3 As shown. Higher superheated steam treatment temperatures resulted in increased lightness (L* value), redness (a* value), and yellowness (b* value). As the temperature increased and the heating time prolonged, the color of the brown rice gradually darkened and shifted toward red and yellow, probably due to the Maillard reaction and caramelization reaction at higher temperatures. In contrast, SS (superheated steam) treated brown rice of different milling degrees showed a significant increase in L* value, indicating a brighter color. The enhancement in lightness can be attributed to the drying effect caused by SS, which resulted in a decrease in moisture content and a change in light refraction.

[0036] 4. Sensory evaluation

[0037] The sensory evaluation of brown rice treated with different superheated steam conditions was carried out. Figure 4As shown. Superheated steam treatment has different effects on the smell, appearance, cold rice texture, taste and palatability of brown rice with different milling degrees. The sensory evaluation data of short-time superheated steam treatment and untreated brown rice are close. Too high temperature or too long treatment time will make the score lower than the untreated group. Specifically, short-time superheated steam treatment can make the beneficial aroma of brown rice escape, and excessive superheated steam treatment will produce rice bran smell. Superheated steam treatment will increase the brightness and whiteness of brown rice, and Maillard reaction will occur, increasing its chroma, and moderate processing can maintain the integrity of rice grains. When the temperature is raised to 130℃ and the treatment time is greater than 2min, the "burst rate" of rice grains is significantly increased compared with the untreated group. Compared with untreated brown rice, rice treated with short-time superheated steam shows improved brown rice cold rice texture. Superheated steam increases the gaps in brown rice, making it easier for water to enter. In addition, it may be the result of short-term starch aging. Long-term superheated steam treatment will cause starch dissolution and reduce the score of cold rice texture. The palatability and taste are similar to the evaluation results of cold rice texture. Superheated steam treatment will increase the hardness of brown rice. The rice bran smell produced by excessive treatment is difficult for consumers to accept, and the taste is seriously reduced compared with untreated rice.

[0038] 5. Taste value

[0039] The taste value is related to the edible quality. The comprehensive score after superheated steam treatment, including the appearance and taste score, was found to be consistent with the untreated brown rice after 130℃ and 1min treatment. The taste can be maintained, but the increase in temperature or the extension of heating time will cause the comprehensive score to be significantly lower than that of the untreated brown rice. Therefore, the selection of appropriate milling degree and superheated steam treatment conditions can improve the taste of brown rice.

[0040] Table 2 Viscosity characteristics and taste values ​​of 20% milled round brown rice after superheated steam treatment

[0041]

[0042] As shown in Tables 2 to 4, the overall appearance score of brown rice treated with superheated steam (130°C, 1 min) at 0% and 2% milling degree was lower than that of the control group, while the overall appearance score of brown rice treated with superheated steam (130°C, 1 min) at 1% milling degree was higher than that of the control group. The taste value of rice is affected by multiple factors, among which the effects of amylose and protein content are the most significant. The interaction between milling degree and superheated steam improves the taste value of brown rice.

[0043] Table 3 Viscosity characteristics and taste value of 1% milled round brown rice after superheated steam treatment

[0044]

[0045]

[0046] Table 4 Viscosity characteristics and taste value of 2% milled round brown rice after superheated steam treatment

[0047]

[0048] 6. Cooking quality and cooking time

[0049] Cooking quality and cooking time results are as follows Figure 5 , Figure 6 As shown. Superheated steam treatment significantly changes the cooking quality of brown rice. Compared with untreated brown rice, the cooking time, water absorption rate and volume expansion rate of brown rice treated with superheated steam change. The cooking time of brown rice with 1% and 2% grinding degree is significantly shortened after superheated steam treatment, and the change is more obvious than that of brown rice with 0% grinding degree. It is found that the brown rice with different grinding degrees is treated with superheated steam at 110℃, 2min, 130℃, 1min, which increases the water absorption rate and volume expansion rate of brown rice. The pores formed on the surface of brown rice treated with superheated steam are conducive to the penetration of water into the core of rice grains, which can increase the water absorption rate of brown rice and shorten the cooking time. The increase in water absorption causes the expansion and stretching of brown rice grains, thereby causing a significant increase in the volume expansion rate of brown rice.

[0050] 7. Gelatinization characteristics

[0051] The gelatinization property of brown rice changes mainly due to the properties of its protein and the molecular structure of starch granules. The gelatinization property measurement results of each group of brown rice in this embodiment are shown in Tables 5 to 7. Peak viscosity reflects the swelling capacity of starch granules before rupture during gelatinization. Brown rice flour is subjected to superheated steam treatment at 110°C and 130°C, and the peak viscosity of brown rice flour presents an upward trend. The rise of peak viscosity may be due to the swelling increase and looseness of the crystal structure of starch granules caused by superheated steam treatment. On the other hand, the protein-starch complex formed during the SS treatment process can provide mechanical support for starch granules, resulting in greater shear force, thereby resulting in higher peak viscosity. Under 150°C and 130°C temperature conditions, the peak viscosity of brown rice flour decreases after treatment for 6min, which may be caused by high temperature treatment causing serious damage to starch granules. Under the same treatment conditions, between different milling degrees, the peak viscosity of brown rice flour presents an increasing trend, which is mainly due to the decrease in the content of macromolecular substances such as cellulose, protein, lipid and non-starch polysaccharides in brown rice bran layer with the increase of milling degree, which reduces its obstruction to starch gelatinization, and increases the percentage of starch, which eventually leads to the increase of gelatinization viscosity. The final viscosity of brown rice flour treated with superheated steam at 110℃, 6min, 130℃, 4min and 130℃, 6min increased compared with the untreated group, while the final viscosity of brown rice flour treated with 1% and 2% milling degree at 130℃, 4min increased compared with the untreated group. The amylose and amylopectin leached from starch granules played an important role in the final viscosity of starch, which can be attributed to the reorganization and interaction between starch and non-starch components induced by superheated steam. The attenuation value reflects the stability of swollen starch granules under continuous heating and shearing force. The lower the attenuation value, the stronger the shear resistance and the better the thermal stability. Compared with the control group, the attenuation value first increased and then decreased, which may be because when the temperature is below 130℃ and the treatment time is less than 6min, the fat and protein on the surface of starch granules have an inhibitory effect on water. With the increase of treatment temperature and the increase of treatment time at 130℃, the thermal stability increases.

[0052] Table 50% milling degree brown rice gelatinization characteristics after superheated steam treatment

[0053]

[0054] Table 6 Gelatinization characteristics of 1% milling degree brown rice after superheated steam treatment

[0055]

[0056] Table 72% milling degree brown rice gelatinization characteristics after superheated steam treatment

[0057]

[0058] It can be seen from the above embodiments that the present invention has the following beneficial effects:

[0059] (1) The interaction between superheated steam treatment conditions and brown rice milling degree has an inactivation effect on lipase, and the milling degree and superheated steam treatment have a synergistic interaction effect on lipase activity. For example, there is no significant difference in lipase activity between 2% milling degree treated at 150℃ for 1 min and 6 min, but there is a significant difference between the two conditions of 1% milling degree. Finally, the lipase activity of 1% milling degree brown rice treated at 150℃ for 6 min is the lowest. The activity of peroxidase decreases significantly with the increase of superheated steam treatment temperature, time and milling degree. Although the higher the temperature, the better the enzyme inactivation effect, the brown rice variety and milling degree still need to be considered comprehensively.

[0060] (2) Regarding appearance, the color of brown rice gradually darkened and turned to red and yellow with increasing temperature and prolonged heating time, probably due to the Maillard reaction and caramelization reaction at higher temperature. In contrast, brown rice of different milling degrees treated with SS (superheated steam) showed a significant increase in L* value, indicating a brighter color. The enhancement of brightness can be attributed to the drying effect caused by SS, which leads to a decrease in moisture content and subsequent changes in light refraction. Figure 3 It can be seen that the appearance is best under the conditions of 130℃ and 1min.

[0061] (3) For sensory evaluation, the sensory evaluation data of short-time superheated steam treatment and untreated brown rice are close. Too high temperature or too long treatment time will make the score lower than the untreated group. The best superheated steam treatment condition is 130℃, 1min, and the best grinding degree under this condition is 2%.

[0062] (4) For the taste value, the overall appearance score of brown rice treated with superheated steam (130℃, 1min) at 0% and 2% grinding degree was lower than that of the control group, while the overall appearance score of brown rice treated with superheated steam (130℃, 1min) at 1% grinding degree was higher than that of the control group, which reflects the interaction effect between superheated steam treatment and grinding degree on the taste value of brown rice. The optimal superheated steam treatment condition is 130℃, 1min.

[0063] (5) In general, superheated steam treatment improved the cooking quality of brown rice. Regarding the gelatinization characteristics, the final viscosity of brown rice treated with superheated steam at 0% grinding degree, 110℃, 6 min, 130℃, 4 min and 130℃, 6 min increased compared with that of the untreated group, while the final viscosity of brown rice with 1% and 2% grinding degree at 130℃, 4 min increased compared with that of the untreated group. This was mainly attributed to the reorganization and interaction between starch and non-starch components induced by superheated steam treatment.

[0064] On the whole, under the premise of pursuing the preservation and quality of brown rice, it is most appropriate to set the grinding degree of brown rice to 2% and the superheated steam treatment conditions to 130℃ and 1min.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing fresh-keeping brown rice treated with superheated steam, characterized in that: After the brown rice is milled, it is treated with superheated steam; The grinding degree after the grinding is 0 to 2%; The temperature of the superheated steam treatment is 110-150° C., and the treatment time is 5 s-2 min.

2. The preparation method according to claim 1, characterized in that The pressure range of the superheated steam treatment is 0.15-0.40 MPa.

3. The preparation method according to claim 2, characterized in that: The degree of grinding of the brown rice after grinding is 1-2%.

4. The preparation method according to claim 3, characterized in that: The temperature of the superheated steam treatment is 110-130° C., and the treatment time is 1 min-2 min.

5. The preparation method according to claim 4, characterized in that: The temperature of the superheated steam treatment is 130°C.

6. Fresh-keeping brown rice obtained by the preparation method according to any one of claims 1 to 5.

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