Processing method for improving properties of glutinous rice protein by wet heat combined with microwave treatment

Abstract

The invention belongs to the technical field of food processing, and relates to a processing method for improving the properties of glutinous rice protein by wet heat combined with microwave treatment, comprising: taking an appropriate amount of water and spraying it evenly on the surface of glutinous rice to adjust the moisture content of glutinous rice to 14-16%, sealing for 11-13 hours, drying at 45-55°C for 1-3 hours, cooling to 35-45°C and continuing to dry for 2-4 hours, crushing and sieving; then adding distilled water to glutinous rice flour according to the material-liquid ratio of 1g:4-6ml to prepare a powder emulsion, stirring until there is no obvious precipitation, and performing short-term microwave treatment for multiple times; adjusting the pH to 8-9 with alkali solution, alkali extraction at 50°C for 1.5-2h, taking the supernatant after centrifugation to adjust the acid to near the isoelectric point, standing acid precipitation, centrifuging again, and vacuum freeze drying the precipitate. The process of the invention is simple, and microwave alone can improve the properties of glutinous rice protein, but the combined effect of wet heat and microwave is greater than the single effect, and the modification effect on glutinous rice protein is much greater than the single effect, and the combined effect improves the comprehensive properties of glutinous rice protein and reduces the waste of high-value resources.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, relates to the deep processing of glutinous rice protein, and in particular to a processing method for improving the properties of glutinous rice protein by combining wet heat with microwave treatment. Background Art

[0002] Glutinous rice protein is a high-quality protein, which is composed of four proteins: albumin, globulin, alcohol-soluble protein and gluten. In the process of glutinous rice flour processing, glutinous rice protein is a by-product, either treated with wastewater or simply recycled as feed. The amino acid composition of glutinous rice protein is relatively complete, and the biological value of glutinous rice protein is high. It is an antigenic protein that does not cause allergic reactions. Its nutritional value ranks first among various grains. In addition, glutinous rice protein also has health care effects. When the protein is decomposed into small molecular polypeptides or amino acids, it can be made into a functional nutrient solution with a certain amino acid content. It can also be used as a food additive or a raw material for health food after extraction and concentration. It has the function of reducing the cholesterol content in serum. In summary, glutinous rice protein has a high research value. Improving the characteristics of glutinous rice protein can expand its application rate in the fields of health food, food additives, etc., which is of practical significance for reducing the waste of high-protein resources.

[0003] The structure and functional properties of proteins may change due to the intervention of physical, chemical and biological methods, thereby changing its application scope in the food field. Glutinous rice protein has poor solubility and emulsification, which directly affects its application in the field of food processing, so protein modification is one of the problems that need to be solved urgently. The modification methods of proteins mainly include physical modification, chemical modification and enzymatic modification. Physical modification is to change the molecular structure and aggregation mode of proteins by means of heat treatment, ultrasound, microwave treatment, high pressure treatment or mechanical energy, so as to modify protein molecules. This method is simple, green and safe. With the continuous development of microwave technology, it is not only used in the food ripening process in the food industry, but also a new technology for protein modification. Related studies have shown that wet heat treatment can enhance the interaction between polymer chains, modify glutinous rice protein and optimize its functional properties.

[0004] Currently, there is no method for modifying protein by combining wet heat treatment with microwaves. The present invention adopts a mild wet heat treatment temperature and combines wet heat and microwaves for treatment. Experiments have shown that the combined effect is significantly greater than that of the single effect. Summary of the invention

[0005] In view of the shortcomings of the prior art in which the in-depth utilization of glutinous rice protein is restricted by its functional properties, the purpose of the present invention is to provide a processing method for improving the properties of glutinous rice protein by combining wet heat with microwave treatment.

[0006] Technical Solution

[0007] A processing method for improving the properties of glutinous rice protein by combining wet heat with microwave treatment comprises the following steps:

[0008] (1) Selecting glutinous rice for wet heat treatment: taking an appropriate amount of water and spraying it evenly on the surface of the glutinous rice to adjust the moisture content of the glutinous rice to 14-16%, preferably 15%, sealing for 11-13 hours, drying at 45-55° C. for 1-3 hours, cooling to 35-45° C. and continuing to dry for 2-4 hours, and crushing and sieving;

[0009] (2) adding glutinous rice flour to distilled water at a material-liquid ratio of 1 g:4-6 ml, preferably 1 g:5 ml, to prepare a powder emulsion, stirring until no obvious precipitation occurs, and subjecting to multiple short-term microwave treatments;

[0010] (3) The treated glutinous rice flour emulsion is adjusted to a pH of 8 to 9 with an alkali solution, and alkali extraction is performed at a constant temperature of 50° C. for 1.5 to 2 h. After centrifugation, the supernatant is taken and the acid is adjusted to near the isoelectric point, and the acid is allowed to settle. The precipitate is centrifuged again, and the precipitate is vacuum freeze-dried to obtain glutinous rice protein.

[0011] In the preferred disclosed examples of the present invention, the multiple short-term microwave treatments in step (2) have a total microwave treatment time of 40 to 60 seconds, a microwave frequency of 2 to 6 times, and a microwave power of 200 to 600 W. Preferably, the total microwave treatment time is 50 seconds, the frequency is 4 times, and the power is 400 W.

[0012] In a preferred disclosed example of the present invention, the alkali solution in step (3) is a NaOH solution with a mass percent concentration of 2%.

[0013] In a preferred embodiment of the present invention, the isoelectric point in step (3) is a pH value of 5 to 6.

[0014] The present invention firstly performs a wet heat treatment on the glutinous rice raw material, and the wet heat treatment strengthens the interaction between polymer chains, forms resistant starch and enhances the digestibility of glutinous rice starch, and then dries, crushes and screens, adds water to modulate into an emulsion, and then performs microwave treatment for a short time for many times, and microwaves act on hydrogen bonds and hydrophobic bonds that maintain the secondary structure, thereby changing the configuration of the protein, and then affecting the structure and functional characteristics of glutinous rice protein. The present invention uses microwave non-thermal effect and thermal effect as well as wet heat treatment to affect the protein structure, including: the increase or decrease of α-helix, β-fold, β-turn and irregular curling structure in the secondary structure of the protein to varying degrees, the exposure of protein hydrophobic groups, the enhancement of the interaction between water molecules and protein molecules, and the improvement of the adsorption of protein on the interface. Protein structure is closely related to protein properties, and changes in structure directly lead to changes in protein properties. Changes in the properties of glutinous rice protein directly affect the application of glutinous rice products in the field of food processing.

[0015] The invention changes the secondary structure of glutinous rice protein and expands its spatial structure. Under the action of microwaves, hydrogen and peptide bonds in the protein are destroyed to form aggregates. In addition, the reduction of α-helices in the secondary structure leads to the reduction of surface hydrophobic groups, which increases the hydrophilicity of protein molecules, thereby increasing the solubility and swelling power of glutinous rice protein and affecting other functional properties. At the same time, wet heat treatment can also improve the functional properties of glutinous rice protein by changing the structure of glutinous rice protein.

[0016] Beneficial Effects

[0017] The method of wet heat combined with microwave treatment used in the present invention is simple, green and environmentally friendly, has a simple processing technology, saves implementation costs, and microwave alone can improve the properties of glutinous rice protein, but the combined effect of wet heat and microwave is greater than the single effect, and the modification effect on glutinous rice protein is much greater than the single effect, and the combined effect improves the comprehensive properties of glutinous rice protein. Compared with protein chemistry and enzyme modification, it is more green, safe, and economical, and the combined treatment effect is stronger than a single physical modification method. The improvement of the comprehensive properties of glutinous rice protein promotes the development and utilization of glutinous rice protein resources and reduces the waste of high-value resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 .The effect of different microwave powers on the solubility of glutinous rice protein treated with wet heat;

[0019] Figure 2 .The effect of different microwave powers on the swelling capacity of glutinous rice protein treated with heat and humidity;

[0020] Figure 3 .The effect of different microwave powers on the emulsification of glutinous rice protein treated with heat and humidity;

[0021] Figure 4 .The effect of different microwave powers on the emulsification stability of glutinous rice protein treated with heat and humidity;

[0022] Figure 5 Scanning electron microscopy (SEM) images of glutinous rice protein treated with different microwave powers, including (1) 0W, (2) 200W, (3) 400W, (4) 600W, (5) 800W;

[0023] Figure 6 . FTIR spectra of glutinous rice protein treated with different microwave powers;

[0024] Figure 7 .Infrared spectra (FTIR) of glutinous rice protein treated with different microwave powers. DETAILED DESCRIPTION

[0025] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0026] Example 1

[0027] Weigh glutinous rice and place it in a fresh-keeping ziplock bag and let it stand. When the temperature of the glutinous rice reaches room temperature, take an appropriate amount of water and spray it evenly on the surface of the glutinous rice to adjust the moisture content of the glutinous rice to 15%. Then seal it at room temperature for 11 hours, place it in a 45℃ hot air drying device for 1 hour, take it out and spread it out. When the temperature drops to 35℃, continue drying for 2 hours, and let it stand at room temperature for 48 hours. Put the glutinous rice in a grinder for 3 times and grind it for multiple short times.

[0028] Glutinous rice flour was added to distilled water at a material-liquid ratio of 1:4 (g / ml) to prepare a powder emulsion. After stirring with a glass rod until there was no obvious precipitation, it was placed in a variable frequency microwave oven for treatment. In order to prevent the temperature from rising rapidly during microwave treatment and destroying the glutinous rice protein structure, multiple short-term microwave treatments were required. The 200w power group glutinous rice flour emulsion was treated for 30s each time, for a total of 2 times; the 400w power group glutinous rice flour emulsion was treated for 20s each time, for a total of 3 times; the 200w power group glutinous rice flour emulsion was treated for 30s each time, for a total of 2 times; the 600w power group glutinous rice flour emulsion was treated for 15s each time, for a total of 4 times; the 800w power group glutinous rice flour emulsion was treated for 10s each time, for a total of 6 times.

[0029] The prepared glutinous rice flour emulsion is adjusted to pH 8-9 with 2% NaOH solution, placed in a constant temperature material tank at 50°C for alkali extraction for 1.5 hours, and the supernatant is adjusted to near the isoelectric point (pH=5-6) after centrifugation, allowed to stand for acid precipitation, centrifuged again, and the precipitate is vacuum freeze-dried to obtain glutinous rice protein.

[0030] Example 2

[0031] Weigh glutinous rice and place it in a fresh-keeping ziplock bag and let it stand. When the temperature of the glutinous rice reaches room temperature, take an appropriate amount of water and spray it evenly on the surface of the glutinous rice to adjust the moisture content of the glutinous rice to 15%. Then seal it at room temperature for 13 hours, place it in a 55℃ hot air drying device for 3 hours, take it out and spread it out. When the temperature drops to 45℃, continue drying for 3 hours, and let it stand at room temperature for 48 hours. Put the glutinous rice into a grinder three times and grind it for multiple short times.

[0032] Add distilled water to glutinous rice flour at a material-liquid ratio of 1:6 (g / ml) to prepare a powder emulsion. Stir with a glass rod until there is no obvious precipitation and then put it into a variable frequency microwave oven for treatment. In order to prevent the temperature from rising rapidly during microwave treatment and destroying the glutinous rice protein structure, multiple short-term microwave treatments are required. The glutinous rice flour emulsion of the 200w power group is treated for 15s each time, for a total of 3 times; the glutinous rice flour emulsion of the 400w power group is treated for 30s each time, for a total of 2 times; the glutinous rice flour emulsion of the 200w power group is treated for 15s each time, for a total of 4 times; the glutinous rice flour emulsion of the 600w power group is treated for 30s each time, for a total of 2 times; the glutinous rice flour emulsion of the 800w power group is treated for 15s each time, for a total of 4 times.

[0033] The prepared glutinous rice flour emulsion is adjusted to pH 8-9 with 2% NaOH solution, placed in a constant temperature material tank at 50°C for alkali extraction for 2 hours, and the supernatant is adjusted to near the isoelectric point (pH=5-6) after centrifugation, allowed to stand for acid precipitation, centrifuged again, and the precipitate is vacuum freeze-dried to obtain glutinous rice protein.

[0034] Select the glutinous rice protein obtained in Example 1 or 2 to measure the solubility and swelling power of glutinous rice protein, weigh the mass of the centrifuge tube as m0, use an analytical balance to weigh 0.1g of glutinous rice protein powder in a centrifuge tube, and record the mass of glutinous rice protein as m. Measure 5ml of distilled water and pour it into a centrifuge tube to prepare a 2% powder emulsion, vortex for 1min, place it in a 50℃ constant temperature water bath and heat it for 30min, cool to room temperature, and centrifuge it at 8000r / min and 4℃ for 10min. Weigh the mass of the evaporating dish as m1, pour the supernatant into the evaporating dish, and dry it to constant weight in a 60℃ forced air drying oven. Weigh the total mass of the evaporating dish and dry matter as m2, and m3 is the total mass of the centrifuge tube and the precipitate. The measurement results are shown in Figure 1 , Figure 2 .

[0035] The calculation formula is as follows:

[0036]

[0037]

[0038] Microwave combined with moist heat treatment can significantly improve the functional properties of glutinous rice protein, and the solubility and swelling power of glutinous rice protein reach the maximum value at a microwave treatment power of about 400w, which are 73.69±5.92% and 26.22±4.38% respectively.

[0039] The glutinous rice protein obtained in Example 1 or Implementation 2 was selected to determine the emulsification and emulsion stability of the glutinous rice protein. The glutinous rice protein solution was prepared at a ratio of 1:100 (g:mL). The pH of the solution was adjusted to 7.0 with a 2% sodium hydroxide solution and a 2% hydrochloric acid solution. 30 mL of the glutinous rice protein solution was taken, 10 mL of soybean oil was added, and 10 mL of 0.1% SDS solution was prepared. The solution with added soybean oil was homogenized with an adjustable high-speed homogenizer (8000 r / min, 1 min). The homogenizer was then turned off and 200 μL of the emulsion was taken from the bottom of the beaker and added to the 10 mL 0.1% SDS solution. The absorbance (A0) was measured at a wavelength of 500 nm, and a 0.1% SDS solution was used as a blank control. After standing at room temperature for 10 min, the absorbance (A1) was measured again. The measurement results are as follows: Figure 3 , Figure 4 .

[0040] Microwave treatment combined with wet heat treatment within a certain power range can enhance the functional properties of glutinous rice protein, and the emulsification and emulsion stability of glutinous rice protein reach their maximum values ​​near the microwave power of 600 W, which are 77.78±1.89 m 2 / g, 359.98±31.06m 2 / g.

[0041] The calculation formula is as follows:

[0042]

[0043] Where: A0 is the absorbance at time 0; N is the dilution factor; φ is the volume fraction of the oil phase; L is the optical path length of the cuvette, 1 cm; c is the mass concentration of glutinous rice protein, g / mL.

[0044]

[0045] Wherein: A0 is the absorbance value at time 0; A1 is the absorbance value at 10 minutes; T0 is the placement time of 0 minutes; T is the placement time of 10 minutes.

[0046] The glutinous rice protein obtained in Example 1 or 2 was selected and observed by electron microscopy for structural changes of the glutinous rice protein. In this experiment, the glutinous rice protein treated with microwave power of 0w, 200w, 400w, 600w, and 800w under the same wet heat treatment conditions was characterized by scanning electron microscopy (SEM). Figure 5Figures (1), (2), (3), (4), and (5) are scanning electron microscopy (SEM) images of glutinous rice protein without microwave treatment (0W), 200W, 400W, 600W, and 800W microwave treatment, respectively. The results show that microwaves have an effect on the folding and unfolding of glutinous rice protein molecules treated with wet heat. As the microwave power increases, the protein clusters become smaller and smaller, and their positions gradually disperse. The protein has a filamentous structure, and the clusters of proteins are connected. There are still protein and starch complexes.

[0047] Select the glutinous rice protein obtained in Example 1 or Example 2 and observe the structural changes of the glutinous rice protein using infrared spectroscopy. Figure 6 As shown. Figure 6 It can be seen that the glutinous rice proteins obtained after being treated with different microwave powers all showed basically consistent absorption peaks, including -1 (Amide III band, C-O and C-N stretching, O=C-N and N-H bending), 1480-1580cm -1 (Amide II, C-N stretching, N-H bending), 2850-2980 cm -1 (1C-H telescopic), 1600~1700cm -1 (1 amide I band, C=O stretching), 3000-3500 cm -1 Typical amide band vibrations appeared at both (O-H and N-H stretching), indicating that no new functional groups were generated during the microwave treatment. Figure 7 Medium 1600~1700cm -1 Represents various types of protein secondary structures, 1608-1622 cm -1 Represents β1 (intermolecular antiparallel β-fold), 1622~1637cm -1 Represents intramolecular β-folding, 1637-1645 cm -1 Represents irregular curl, 1646~1662cm -1 Represents α-helix, 1662~1681cm -1 Represents the β-turn, 1682-1700 cm -1 It represents β2 (parallel β-folding between molecules), and the relative content of each secondary structure is compared by comparing the integrated area of ​​each sub-peak.

[0048] The results show that microwave treatment will destroy the secondary structure of glutinous rice protein, and when the microwave is increased to a certain extent, it will also destroy the tertiary structure of glutinous rice protein. When the microwave treatment power is 200W and 400W, only the secondary structure of glutinous rice protein is destroyed; when the microwave treatment power reaches 600W, the tertiary structure of glutinous rice protein is destroyed; when the microwave treatment power is 800W, the tertiary structure of glutinous rice protein is completely destroyed, and the secondary structure is also destroyed to a certain extent, so that the secondary structure content is reduced to a level lower than that of glutinous rice protein that has not been microwaved.

[0049] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for improving the properties of glutinous rice protein by combining moist heat with microwave treatment, characterized in that: The steps include: (1) Take an appropriate amount of water and spray it evenly on the surface of the glutinous rice to adjust the moisture content of the glutinous rice to 14-16%, seal it for 11-13 hours, dry it at 45-55° C. for 1-3 hours, continue drying it for 2-4 hours when the temperature drops to 35-45° C., and crush and sieve it; (2) adding distilled water to glutinous rice flour at a material-liquid ratio of 1 g:4-6 ml to prepare a powder emulsion, stirring until no obvious precipitation occurs, and subjecting the mixture to multiple short-term microwave treatments, wherein the total microwave treatment time is 40-60 s, the number of microwave treatments is 2-6, and the microwave power is 200-600 W; (3) adjusting the pH of the treated glutinous rice flour emulsion to 8-9 with alkali solution, extracting with alkali at a constant temperature of 50°C for 1.5-2h, taking the supernatant after centrifugation and adjusting the acid to near the isoelectric point, allowing the acid to precipitate, centrifuging again, and freeze-drying the precipitate in vacuum to obtain glutinous rice protein; The properties mentioned are solubility, swelling power, emulsification and emulsion stability.

2. The method for improving the properties of glutinous rice protein by combining moist heat with microwave treatment according to claim 1, characterized in that: In step (1), take an appropriate amount of water and spray it evenly on the surface of the glutinous rice to adjust the moisture content of the glutinous rice to 15%.

3. The method for improving the properties of glutinous rice protein by combining moist heat with microwave treatment according to claim 1, characterized in that: In step (2), glutinous rice flour is added to distilled water at a material-liquid ratio of 1g:5ml to prepare a powder emulsion.

4. The method for improving the properties of glutinous rice protein by combining moist heat with microwave treatment according to claim 1, characterized in that: The total microwave treatment time in step (2) is 50 seconds, the number of times is 4 times, and the power is 400W.

5. The method for improving the properties of glutinous rice protein by combining moist heat with microwave treatment according to claim 1, characterized in that: The alkali solution in step (3) is a NaOH solution with a mass percentage concentration of 2%.

6. The method for improving the properties of glutinous rice protein by combining moist heat with microwave treatment according to claim 1, characterized in that: The isoelectric point in step (3) is a pH value of 5 to 6.

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