Application of chitosan in grain preservation

Abstract

The invention discloses an application of chitosan in preservation of grains. The chitosan is one of silkworm chrysalis chitosan or tenebrio molitor chitosan, and the grain is milled rice with embryo; chitosan is an alkaline polysaccharide naturally existing on crustacean and insect epidermis, and has excellent characteristics of good biocompatibility, degradability, film-forming property, hygroscopicity, antioxidant activity, antibacterial activity and the like; besides, chitosan is a natural material with relatively high safety, the reduction of hydrolase activity and lipoxygenase activity during the storage period of the milled rice with embryo can be remarkably inhibited by treating the milled rice with embryo with a chitosan solution, the increase of fatty acid value, amylose and malondialdehyde content is delayed, and the cooking quality is also improved; therefore, the application range of the chitosan is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of grain preservation, and relates to the application of chitosan in grain preservation, in particular to the preservation of germ rice. Background Art

[0002] Germ-retained rice, a processed active rice product, refers to brown rice that has been milled to retain the germ at least 80%. This is also known as germ-retained rice. It is not only rich in various nutrients, including carbohydrates, protein, fat, vitamins, and minerals, but also contains significant amounts of beneficial unsaturated fatty acids and essential amino acids. Because the husk and bran layers protecting the germ are removed after milling, the germ is directly exposed to the external environment. As a hydrophilic colloid, germ-retained rice is highly susceptible to the effects of oxygen, insects, mold, temperature, and humidity. Rice grains absorb moisture and breed mold, further deteriorating their quality. Furthermore, as an active product, germ-retained rice has a strong respiration rate. During storage, this accelerates the hydrolysis and oxidation of fats, starches, and proteins, accelerating spoilage and causing the metabolism of nutrients, leading to a decrease in quality. Under room temperature storage conditions, germ-retained rice can only be stored for approximately 30 days, failing to meet the production, processing, transportation, and sales requirements of conventional markets. It is one of the most difficult grains to preserve. Summary of the Invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a chitosan that can maintain good texture properties during storage, delay quality deterioration during storage, and improve the antioxidant and antibacterial capabilities of germ rice for use in grain preservation, especially germ rice preservation.

[0004] Technical solution: Application of the chitosan of the present invention in food preservation.

[0005] Furthermore, the chitosan is one of silkworm pupa chitosan and mealworm chitosan.

[0006] Furthermore, the grain is germ rice.

[0007] Furthermore, the germ rice is preserved as follows: the prepared chitosan solution is sprayed on the germ rice, which is then placed in a ziplock bag and stored in a constant temperature and humidity incubator.

[0008] Furthermore, the concentration of the chitosan solution is 2.0-8.0 mg·mL -1 .

[0009] Furthermore, the temperature of the constant temperature and humidity incubator is: 25°C.

[0010] Furthermore, the relative humidity of the constant temperature and humidity incubator is 65%.

[0011] Furthermore, during the storage process, samples were taken every 5 days for index determination, that is, samples were taken on the 0th, 5th, 10th, 15th, 20th, 25th, and 3rd days respectively.

[0012] Furthermore, the chitosan can achieve food preservation through at least one of the following ways:

[0013] (1) Inhibit the decrease of amylase activity during storage of grain;

[0014] (2) It delays the increase of lipolysis enzyme activity, lipoxygenase activity, fatty acid value, amylose and malondialdehyde content during storage;

[0015] (3) Maintaining good texture characteristics of germ rice during storage.

[0016] Chitosan is a natural alkaline polysaccharide found in the skin of crustaceans and insects. It has excellent properties such as good biocompatibility, degradability, film-forming ability, hygroscopicity, antioxidant activity and antibacterial activity. Therefore, chitosan is a natural material with high safety. Toxicity studies have shown that chitosan exhibits extremely low toxicity in acute toxicity tests in mice, with an LD of 50 (Median lethal dose) greater than 5000 mg·kg -1 , much higher than salt (LD 50 =3000mg·kg -1 ); Chitosan is widely used in the food industry, such as food additives, food preservatives, food packaging, and health foods. Among them, research on food preservation technology is mostly focused on the preservation of fruits and vegetables, and few studies focus on the preservation of grains.

[0017] The present invention uses uniformly spread germ rice to investigate its effects on the textural properties, physiological indicators such as fatty acids, lipase and fat oxidation synthase, amylose, and crude protein of germ rice. The germ rice treated with chitosan solution can maintain good textural properties during storage and significantly delay quality deterioration during storage.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following features: the present invention expands the application scope of chitosan, which is an alkaline polysaccharide naturally present in the epidermis of crustaceans and insects, and has excellent properties such as good biocompatibility, degradability, film-forming property, hygroscopicity, antioxidant activity and antibacterial activity; therefore, treating germ rice with chitosan solution can significantly inhibit the decrease in hydrolase activity and lipoxygenase activity of germ rice during storage, delay the increase in its fatty acid value, amylose and malondialdehyde content, and its cooking quality is also improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is a comparative diagram of the effects of silkworm pupa and mealworm chitosan on the lipolysis enzyme content in embryo-retained rice according to an embodiment of the present invention;

[0020] Figure 2 This is a comparative diagram of the effects of silkworm pupa and mealworm chitosan on the lipoxygenase content of embryo-retained rice in an embodiment of the present invention;

[0021] Figure 3 This is a comparison chart of the effects of silkworm pupa and mealworm chitosan on the fatty acid value of embryonic rice in the embodiments of the present invention;

[0022] Figure 4 This is a comparison chart of the effects of silkworm pupa and mealworm chitosan on α-amylase activity in the examples of the present invention;

[0023] Figure 5 This is a comparison chart of the effects of silkworm pupa and mealworm chitosan on β-amylase activity in the examples of the present invention;

[0024] Figure 6 This is a comparison chart of the effects of silkworm pupa and mealworm chitosan on amylose content in the examples of the present invention;

[0025] Figure 7 This is a comparison chart of the effects of silkworm pupa and mealworm chitosan on the malondialdehyde content of embryo-retained rice in the examples of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0027] Example 1: A method for preserving grain

[0028] The chitosan solution is evenly sprayed on the surface of the germ rice, and the rice is put into a food ziplock bag and stored in a constant temperature and humidity incubator at 25° C. and a relative humidity of 65%.

[0029] Test example:

[0030] (1.1) Test method:

[0031] (1.1.1) Experimental Group:

[0032] 300g of germinated rice from the same batch, with the same specifications and no difference in freshness and other indicators were randomly divided into three groups, with 100g in each group;

[0033] The experimental groups were treated with germinated rice in the same manner as in Example 1: the first group was sprayed with a silkworm pupa chitosan solution, the second group was sprayed with a mealworm chitosan solution, and the third group served as a control group;

[0034] The control group was not treated in any way and was packed in food ziplock bags and stored in a constant temperature and humidity incubator at 25°C and 65% relative humidity.

[0035] Samples were taken every 5 days for index determination, i.e. samples were taken on days 0, 5, 10, 15, 20, 25 and 3 respectively, and the lipase activity, lipoxygenase activity, fatty acid value, amylose and malondialdehyde content, and texture characteristics of the germ rice were determined;

[0036] (1.2) Determination method:

[0037] (1.2.1) Method for determining texture characteristics:

[0038] 1. Sample preparation

[0039] The preparation of rice with germ-retained rice strictly follows the "Sensory Evaluation Method for the Quality of Rice and Rice Cooked in Cereals and Oils Inspection"; the rice with germ-retained rice is placed in an automatic rice cooker and cooked in a conventional manner until the rice is fully cooked; after cooking, the rice is quickly transferred to a suitable container and allowed to cool naturally to room temperature to ensure that the sample remains stable before measurement;

[0040] 2. Measuring instruments and parameter settings

[0041] The texture of cooked rice cooled to room temperature was measured using a texture analyzer. The parameters of the texture analyzer were set as follows:

[0042] (1) Compression probe: Use TA / 36R cylindrical probe;

[0043] (2) Pre-measurement speed: set to 2.00 mm / s. This speed allows the probe to approach the sample surface smoothly, avoiding disturbance of the sample's initial state due to excessive speed;

[0044] (3) Test speed: set to 1.00 mm / s. During the compression process, this speed allows the probe to apply pressure evenly, ensuring accurate assessment of the rice texture;

[0045] (4) Post-test speed: also set to 1.00 mm / s to ensure that the probe can exit smoothly after compression is completed without affecting the final state of the sample and the integrity of data collection;

[0046] (5) Deformation ratio: set to 50%, that is, the compression degree of the probe on the rice sample is half of its original height. This deformation ratio can fully reflect the texture characteristics of rice such as elasticity and viscosity;

[0047] 3. Measurement process

[0048] Place the cooled, germ-retained rice sample evenly on the test platform of the texture analyzer to ensure a smooth surface. Start the texture analyzer and perform the measurement according to the above-mentioned parameter settings. During the measurement, the instrument automatically records the pressure changes applied by the probe to the sample, generating a texture curve for analyzing the rice's texture indicators, such as hardness, elasticity, and stickiness. To ensure the reliability of the measurement results, perform five parallel measurements on each sample, using a fresh sample for each measurement, and ensuring that the sample preparation and testing conditions are consistent.

[0049] (1.2.2) Determination of fatty acids

[0050] The fatty acid content was determined according to the GB / T 20569-2006 standard method. The specific steps are as follows:

[0051] Sample processing (rice flour with germ retained):

[0052] (1) Weigh 10.00 g (accurate to 0.01 g) of the prepared rice flour with embryo left in it and place it in a conical flask;

[0053] (2) Add 50 mL of anhydrous ethanol, seal the container, and place on a reciprocating shaker for 10 minutes for extraction.

[0054] (3) Centrifuge the contents of the conical flask at 4000 r / min for 10 min to separate the supernatant;

[0055] Titration operation:

[0056] (1) Use a pipette to accurately transfer 25 mL of supernatant into a beaker and add 50 mL of distilled water;

[0057] (2) Add 3 to 4 drops of phenolphthalein indicator and titrate with 0.01 mol / L potassium hydroxide standard titration solution until the solution turns slightly red and does not fade within 30 seconds;

[0058] (3) Repeat the titration three times and record the volume of potassium hydroxide solution consumed.

[0059] Sample processing (GBR flour):

[0060] (1) Weigh 10.00 g of GBR flour (accurate to 0.01 g) and place it in a 250 mL plastic centrifuge tube;

[0061] (2) Add 100 mL of anhydrous ethanol, seal the container, and invert it three times to mix thoroughly.

[0062] (3) Place the centrifuge tube on a tabletop shaker and shake for 30 minutes to extract;

[0063] Centrifugation and titration:

[0064] (1) After standing for 1 minute, centrifuge the tube at 3000 r / min for 10 minutes to separate the supernatant;

[0065] (2) Take 25 mL of the supernatant, add 3 to 4 drops of phenolphthalein indicator, and titrate with 10 mmol / L potassium hydroxide ethanol solution until the solution turns slightly red and does not fade within 30 seconds;

[0066] (1.2.3) Determination of lipase

[0067] According to the standard "Determination of lipase activity in grains and oilseeds", the specific steps are as follows:

[0068] Sample processing:

[0069] (1) Weigh an appropriate amount of embryonic rice sample to an accuracy of 0.01 g and place it in a conical flask;

[0070] Extraction and centrifugation:

[0071] (1) Add an appropriate amount of extraction solvent according to the standard requirements and perform extraction under the specified temperature and time conditions;

[0072] (2) After the extraction is completed, centrifuge at the speed specified by the standard to separate the supernatant;

[0073] Measurement operation:

[0074] (1) Determine according to the titration or colorimetric method described in detail in GB / T 5523-2008;

[0075] (2) Record key data during the measurement process, such as the volume of solution consumed in the titration or the absorbance value;

[0076] Result calculation:

[0077] (1) Calculate the lipase activity value based on the measured data according to the formula provided in GB / T 5523-2008;

[0078] (2) Repeat the measurement three times and take the average value as the final result;

[0079] (1.2.4) Determination of lipoxygenase

[0080] The specific steps are as follows:

[0081] (1) Sample processing:

[0082] After defatting the embryo-retained rice sample, 50 mL of sodium phosphate buffer (0.2 mol / L, pH 6.8) was added;

[0083] (2) Extraction and centrifugation:

[0084] 1. Stir and extract at room temperature of 25℃ for 2h;

[0085] 2. Centrifuge at 15000r / min for 10min to separate the supernatant;

[0086] (3) Preparation of linoleic acid solution:

[0087] 1. Prepare a linoleic acid solution using 140 mg of linoleic acid, 140 mg of Tween, 20 mL of Tween, and 8 mL of distilled water.

[0088] (4) Solution dilution and determination:

[0089] 1. Dilute the linoleic acid solution with sodium phosphate buffer;

[0090] 2. Measure the absorbance at 280 nm. One unit of enzyme activity is the absorbance increase per minute.

[0091] (5) Parallel determination:

[0092] 1. Parallel measurement was performed 3 times and the average value was taken as the final result;

[0093] (1.2.5) Determination of amylose content

[0094] The specific steps are as follows:

[0095] Sample processing:

[0096] (1) Grind the embryo rice sample into powder using a cyclone mill and immediately defat it with n-hexane by Soxhlet extraction to remove the oil component;

[0097] (2) Weigh 0.1 g of defatted rice flour with germ remaining to the nearest 0.0001 g and place it in a 100 mL conical flask;

[0098] Solution preparation and reaction:

[0099] (1) Add 1 mL of anhydrous ethanol and 9 mL of 1 mol / L sodium hydroxide solution to a conical flask and mix well;

[0100] (2) Place the conical flask in a boiling water bath and heat for 10 minutes to ensure that the solution is fully reacted;

[0101] (3) After taking out, cool to room temperature, and then dilute to 100 mL with distilled water;

[0102] Dilution and pH adjustment:

[0103] (1) Use a pipette to take 5 mL of the above solution and transfer it to a 100 mL volumetric flask;

[0104] (2) Add 1 mL of 0.1 mol / L acetic acid solution and adjust the pH to 6.5;

[0105] (3) Add 1 mL of 0.2 g / L iodine solution and dilute to 100 mL with distilled water;

[0106] Absorbance determination:

[0107] (1) Measure absorbance at 720 nm using a Synergy HT microplate reader;

[0108] (2) Perform the measurement three times in parallel and record the absorbance value of each measurement;

[0109] Result calculation:

[0110] (1) Calculate based on the measured absorbance value;

[0111] (2) The average value of three parallel measurements was taken as the final result;

[0112] The α-amylase activity and β-amylase activity were determined using a kit produced by a bioengineering institute;

[0113] (1.2.6) Method for determining the content of phthalaldehyde

[0114] The specific steps are as follows:

[0115] Sample processing:

[0116] (1) Weigh 2.00 g of rice flour with embryo retained, accurate to 0.01 g, and place it in a 100 mL round-bottom centrifuge tube;

[0117] Extraction and centrifugation:

[0118] (1) Add 10 mL of 10% trichloroacetic acid (TCA) solution, shake well, and centrifuge at 4000 rpm for 15 min.

[0119] (2) The supernatant obtained by separation is the sample extract;

[0120] Volume determination and reaction:

[0121] (1) After the supernatant is drawn out, the volume is made up to 10 mL with TCA solution;

[0122] (2) Take 4 mL of supernatant, add 4 mL of 0.6% thiobarbituric acid (TBA) solution, and mix well;

[0123] Boiling water bath reaction and cooling:

[0124] (1) The mixture was placed in a boiling water bath and reacted for 15 min. 4 mL of distilled water was added to the blank group.

[0125] (2) After the reaction is completed, take out the sample and cool it to room temperature;

[0126] Centrifuge and measure again:

[0127] (1) Centrifuge again at 4000 r / min for 15 min and collect the supernatant;

[0128] (2) Measure the absorbance of the supernatant at wavelengths of 600 nm, 532 nm, and 450 nm respectively;

[0129] Parallel determination:

[0130] (1) Parallel measurement was performed 3 times and the average value was taken;

[0131] Result calculation:

[0132] (1) Calculate the content of malondialdehyde according to the following formula:

[0133] c (μmol / L) = 6.45 × (OD 532 -OD 600 )-0.56×OD 450

[0134]

[0135] Where: c represents the concentration of malondialdehyde in the sample (μmol / L); V represents the volume of the extract (mL); m represents the mass of the rice flour with germ (g); OD 532 Indicates the absorbance value at 532nm wavelength, OD 600 Indicates the absorbance value at 600nm wavelength, OD 450 Indicates the absorbance value at a wavelength of 450nm;

[0136] Preparation of 0.6% TBA (thiobarbituric acid solution) solution:

[0137] (1) Weigh 0.6 g of thiobarbituric acid (TBA);

[0138] (2) Dissolve it with a small amount of 1 mol / L sodium hydroxide (NaOH) solution;

[0139] (3) Add 10% TCA solution to make up to 100 mL;

[0140] (4) Place the prepared solution in a dark place for later use;

[0141] (1.3) Test results:

[0142] Table 1

[0143]

[0144] Note: Different letters in the same column indicate significant differences between the data (p<0.05)

[0145] Table 2

[0146]

[0147] Note: Different letters in the same column indicate significant differences between the data (p<0.05)

[0148] Table 3

[0149]

[0150] Note: Different letters in the same column indicate significant differences between the data (p<0.05)

[0151] Table 4

[0152]

[0153]

[0154] Note: Different letters in the same column indicate significant differences between the data (p<0.05)

[0155] Table 5

[0156]

[0157] Note: Different letters in the same column indicate significant differences between the data (p<0.05)

[0158] It can be seen from Tables 1 to 5 that, compared with conventional storage conditions, the rice treated with silkworm pupae and mealworm chitosan had lower hardness, higher elasticity, stickiness, resilience, and chewiness, and all texture indicators were better than those of the rice stored under conventional conditions at 35 days. Therefore, silkworm pupae and mealworm chitosan have a significant preservation effect, which can effectively control the quality deterioration of the rice and maintain the flavor and edible quality of the rice.

[0159] The results of the effects of chitosan solution on lipolysis enzyme activity, lipoxygenase activity, fatty acid value, amylose, and malondialdehyde content of embryo-retained rice are shown in Figure 1-Figure 7 .

[0160] according to Figure 1It can be seen that the growth trend of lipolysis enzyme in germ-retained rice treated with chitosan solution is much lower than that in the control group, indicating that compared with germ-retained rice stored under conventional conditions, the treated germ-retained rice can effectively delay the increase of lipolysis enzyme activity during storage.

[0161] according to Figure 2 It can be seen that the growth trend of lipoxygenase in germ-retained rice treated with chitosan solution is much lower than that in the control group, indicating that compared with germ-retained rice stored under conventional conditions, the treated germ-retained rice can effectively delay the increase of lipoxygenase activity during storage.

[0162] according to Figure 3 It can be seen that the growth trend of the fatty acid value of the germ-retained rice treated with chitosan solution is much lower than that of the control group, indicating that compared with the germ-retained rice stored under conventional conditions, the treated germ-retained rice can effectively delay the increase of fatty acid value during storage.

[0163] according to Figure 4 It can be seen that the growth trend of α-amylase activity of germ-retained rice treated with chitosan solution is much higher than that of the control group, indicating that compared with germ-retained rice stored under conventional conditions, the treated germ-retained rice can effectively delay the decrease of α-amylase activity of germ-retained rice during storage.

[0164] according to Figure 5 It can be seen that the growth trend of β-amylase activity in germ-retained rice treated with chitosan solution is much higher than that in the control group, indicating that compared with germ-retained rice stored under conventional conditions, the treated germ-retained rice can effectively delay the decrease of β-amylase activity in germ-retained rice during storage.

[0165] according to Figure 6 It can be seen that the growth trend of the amylose content in the germ-retained rice treated with chitosan solution is much lower than that in the control group, indicating that compared with the germ-retained rice stored under conventional conditions, the treated germ-retained rice can effectively delay the increase of the amylose content in the grain during storage.

[0166] according to Figure 7 It can be seen that the growth trend of the malondialdehyde content in the germ-retained rice treated with chitosan solution is much lower than that in the control group, indicating that compared with the germ-retained rice stored under conventional conditions, the treated germ-retained rice can effectively delay the increase of the malondialdehyde content in grain during storage.

[0167] As shown above, compared with the germ-retained rice stored under conventional conditions, the treated germ-retained rice can effectively delay the deterioration of grain quality during storage.

Claims

1. Application of chitosan in grain preservation.

2. The use according to claim 1, characterized in that The chitosan is one of silkworm pupa chitosan and mealworm chitosan.

3. The use according to claim 2, characterized in that The chitosan is silkworm pupa chitosan.

4. The use according to claim 2, characterized in that The chitosan is Tenebrio molitor chitosan.

5. The use according to claim 1, characterized in that The food is germ rice.

6. The use according to claim 5, characterized in that: The steps of preserving the germ rice are as follows: spraying the prepared chitosan solution on the germ rice, putting the germ rice into a ziplock bag and storing the bag in a constant temperature and humidity incubator.

7. The use according to claim 6, characterized in that: The concentration of the chitosan solution is 2.0-8.0 mg·mL -1 .

8. The use according to claim 6, characterized in that: The temperature of the constant temperature and humidity incubator is 25°C.

9. The use according to claim 6, characterized in that: The relative humidity of the constant temperature and humidity incubator is 65%.

10. The use according to claim 4, characterized in that: During the storage process, samples were taken every 5 days for index determination, that is, samples were taken on the 0th, 5th, 10th, 15th, 20th, 25th and 3rd days respectively.

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