A method for simultaneously improving starch hydrolysis rate and protein quality in hot-pressed peanut meal

Abstract

The present invention belongs to the technical field of deep processing of peanuts, and specifically relates to a method and application thereof for simultaneously improving the starch hydrolysis rate and protein quality in hot-pressed peanut meal. The specific method is that the peanut meal is pretreated first: water is added after ultrafine grinding, the pH is adjusted to 2, and constant temperature extraction is performed; after extraction, the pH is adjusted to 6, high temperature α-amylase is added, constant temperature oscillation is performed for enzymolysis, the pH is adjusted to 4.2-4.7, the enzyme is inactivated, and centrifugation is performed; protein extraction: water is added to the precipitate after centrifugation, the pH is adjusted to 8-10, and the precipitate is obtained by centrifugation; the precipitate is repeatedly extracted once, the supernatant is combined and the pH value is adjusted, and the precipitate is collected by centrifugation again; it is washed with deionized water, the pH is adjusted to 7.0-7.2, and the peanut meal protein is dried to obtain. The method of the present invention combines pretreatment with enzyme treatment technology; on the one hand, it can improve the degree of starch hydrolysis and increase the content of reducing sugars; on the other hand, the protein purity, emulsification, emulsification stability and the content of amino acids of peanut meal protein are improved; and the added value of the product is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of peanut deep processing, and particularly relates to a method for simultaneously improving the starch hydrolysis rate and protein quality in hot-pressed peanut meal, and also relates to application of the method. Background Art

[0002] Peanut is one of the most important oil-bearing economic crops in the world. Peanut meal is a byproduct of shelled peanuts after oil extraction. It is usually used as feed or fertilizer, with low added value and waste of resources. Peanut meal contains a large amount of nutrients, such as flavonoids, phenols, amino acids, proteins, oils, sugars, triterpenes or steroid compounds; it is rich in carbohydrates and protein, and the starch content is between 15% and 30%. According to different pressing processes, peanut meal can be divided into hot-pressed peanut meal, solvent-extracted peanut meal and cold-pressed peanut meal; China's peanut meal is mainly hot-pressed peanuts.

[0003] At present, the utilization of peanut meal is only to effectively extract the protein therein; after hot pressing, the viscosity of peanut meal increases and the solubility is very low. The starch contained therein has low hydrolysis efficiency and insufficient development and utilization, and has not been effectively utilized; secondly, the methods for extracting peanut meal protein in the prior art include alcohol washing method, water enzyme method, alkali extraction and acid precipitation method, reverse micelle extraction method, physical assisted extraction method, etc.; but the protein nitrogen solubility index obtained by the single alcohol washing method is low, and the reverse micelle extraction method is mostly small molecular proteins due to the limitation of the internal water content of the polar core formed by the contact between the hydrophilic head and water, and the surfactant is easy to remain. In addition, the emulsification performance of the peanut protein obtained by directly hydrolyzing the hot-pressed peanut meal with amylase is not ideal.

[0004] In order to practice the big food concept and develop food resources in an all-round and multi-channel manner, a peanut meal processing method is needed that can not only fully utilize the starch content in the peanut meal, but also improve the emulsification performance of peanut protein; provide a more effective way to deeply develop and utilize peanut meal resources, and realize the effective added value of peanut processing industry by-products. Summary of the invention

[0005] The present invention uses peanut meal as raw material, enzymolyzes starch in the peanut meal through pretreatment and enzymolysis processes, and then extracts peanut meal protein through alkali extraction and acid precipitation to achieve the purpose of synchronously utilizing starch and protein; the method can not only improve the degree of starch hydrolysis, but also improve the content of essential amino acid components in peanut meal, the emulsification performance of protein and its stability, and further improve the nutritional value of peanut meal protein.

[0006] The method for simultaneously improving the starch hydrolysis rate and protein quality in hot-pressed peanut meal mainly comprises pre-treating the hot-pressed peanut meal before enzymolysis with amylase; the pre-treatment step comprises placing the hot-pressed peanut meal in an acid solution and soaking it at 50-70°C for 5-10 hours.

[0007] The acid solution is one of a hydrochloric acid solution or a citric acid solution.

[0008] Preferably, the acid solution is a hydrochloric acid solution.

[0009] Preferably, hydrochloric acid solution is added to make the pH of the mixture of hot-pressed peanut meal and acid solution reach between 1.9 and 2.1.

[0010] Preferably, the hot-pressed peanut meal is placed in a hydrochloric acid solution so that the pH of the mixture formed by the two is 2, and is soaked at 60° C. for 8 hours.

[0011] The hot-pressed peanut meal is mixed with the hydrochloric acid solution in a weight-to-volume ratio of 1 g:(5-15) mL.

[0012] The method for simultaneously improving the starch hydrolysis rate and protein quality in hot-pressed peanut meal comprises the following steps:

[0013] (1) dry-grinding the hot-pressed peanut meal with an ultrafine pulverizer for 1-3 minutes, and passing through a 60-100 mesh sieve to obtain hot-pressed peanut meal powder;

[0014] (2) Pretreatment: Mix the hot-pressed peanut meal powder in (1) with a hydrochloric acid solution at a weight-to-volume ratio of 1 g:(5-15) mL, soak at 50-70° C. for 5-10 h, and adjust the hydrochloric acid solution so that the pH of the mixture formed by the hot-pressed peanut meal powder and the hydrochloric acid solution is 1.9-2.1;

[0015] (3) After soaking, the pH of the mixture is adjusted to 6, 120-180 u / g of high temperature α-amylase is added, and constant temperature oscillation enzymolysis is performed at 90-98° C. and 100-160 r / min for 120-160 minutes, the pH is adjusted to 4.2-4.7, the enzyme is inactivated at 130-145° C. for 5-10 minutes, and centrifuged at 8000-12000 r / min and 0-6° C. for 8-10 minutes to obtain an enzymatic solution and a precipitate, respectively;

[0016] (4) adding water to the precipitate obtained in (3) at a g / mL solid-liquid ratio of 1:8-15, adding 0.1-0.3 mol / L NaOH solution to adjust the pH to 8-10, reacting at 55-65°C for 2h, and centrifuging to obtain a precipitate;

[0017] (5) Extract the precipitate in (4) again under the same conditions, combine the supernatants, and discard precipitate I; adjust the pH of the supernatant to the protein isoelectric point of 4.2-4.5, and centrifuge to collect precipitate II;

[0018] (6) repeatedly washing the precipitate II 3-5 times with deionized water at a pH of 40-4.7, dispersing the precipitate II with deionized water, adjusting the pH to 7.0-7.2, and drying to obtain peanut meal protein.

[0019] Preferably, in (3), the amount of high temperature α-amylase added is 150-180 u / g, and the enzymolysis time is 120-150 minutes.

[0020] Preferably, in (3), the temperature of the constant temperature oscillator is 90-95°C and the rotation speed is 120-150 r / min; the enzyme inactivation temperature is 135-140°C and the enzyme inactivation time is 5-8 minutes.

[0021] Preferably, in (3), the centrifugation time is 9-10 minutes, the centrifugation speed is 10000-12000 r / min, and the centrifugation temperature is 2-6°C.

[0022] The method of the invention can be used to prepare a protein product with high emulsification performance.

[0023] The peanut protein prepared by the method of the present invention can be used in the preparation of low-cholesterol meat products.

[0024] Currently, the most widely used protein in meat products is soy protein, but the price of soy protein continues to rise and the supply is in short supply. Peanut protein has a high nutritional value. With its good water and oil holding properties, it can effectively ensure that the moisture of meat is not lost, and it has broadened the protein source for meat product companies. Adding peanut protein to meat products can not only increase the protein content, but also reduce cholesterol and fat, improve product quality, and reduce production costs. However, in hot-pressed peanut meal, starch is difficult to hydrolyze. If amylase is used directly to hydrolyze starch, the hydrolysis rate is low and the protein quality is not high.

[0025] The beneficial effects of the present invention are:

[0026] (1) The pretreatment and enzyme treatment processes are combined; on the one hand, the starch in the peanut meal can be enzymatically hydrolyzed, the degree of starch hydrolysis can be improved, and the reducing sugar content can be increased; on the other hand, the protein can be effectively extracted by the alkali extraction and acid precipitation method, thus achieving the simultaneous utilization of starch and protein;

[0027] (2) At the same time, pre-treatment of hot-pressed peanut meal can also help improve the protein purity, emulsification, emulsification stability and optimize the amino acid composition of peanut meal protein, greatly improving the added value and nutritional value of the product;

[0028] Among them, protein purity increased by 1.3%; emulsification increased by 26.41%; emulsification stability increased by 32.71%; foaming increased by 5%; foaming stability increased by 2%; surface hydrophobicity increased by 80.2; water holding capacity increased by 214%; oil holding capacity increased by 172%; essential amino acid content increased by 2.14%; a large amount of nutrients and functional activities in peanut meal were fully utilized;

[0029] (3) The starch content in peanut meal can be fully utilized, and after being hydrolyzed into maltodextrin, it can be subsequently converted into maltooligosaccharide, thereby improving its commodity value and resource utilization rate; providing a more effective way to deeply develop and utilize peanut meal resources, and realizing the effective value-added of peanut processing industry by-products;

[0030] (4) The present invention not only solves the problem of handling peanut processing by-products, but also effectively and comprehensively utilizes carbohydrates and proteins in peanut meal, thereby improving the economic value and nutritional utilization rate of peanut meal, which is of great significance for achieving sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the glucose standard curve;

[0032] Figure 2 The effect of different pH soaking pretreatment on the content of reducing sugar in liquefaction;

[0033] Figure 3 The effect of different pretreatment liquid-to-solid ratios on the liquefied reducing sugar content;

[0034] Figure 4 is the effect of different pretreatment temperatures on the content of reducing sugars in liquefaction;

[0035] Figure 5 is the effect of different pretreatment time on the reducing sugar content of liquefaction;

[0036] Figure 6 The effect of different enzyme pretreatments on the reducing sugar content of liquefaction in bio-enzyme treatment;

[0037] Among them, (a) the effect of different protease pretreatments on the reducing sugar content of liquefaction; (b) the effect of cellulase pretreatment on the reducing sugar content of liquefaction; (c) the effect of lipase pretreatment on the reducing sugar content of liquefaction;

[0038] Figure 7 Effect of steam explosion pretreatment on reducing sugar content in liquefaction. DETAILED DESCRIPTION

[0039] 1. Experimental Materials

[0040] Hot-pressed peanut meal, provided by Shandong Luhua Group Co., Ltd.;

[0041] Water bath constant temperature oscillator, Tianjin Sateris Experimental Analysis Instrument Manufacturing Factory;

[0042] Freeze dryer, Beijing Boyikang Laboratory Instrument Co., Ltd.;

[0043] Thermoamylase, standard product, Beijing Solaibao Technology Co., Ltd.;

[0044] Sodium hydroxide, analytical grade, Shandong Lierkang Medical Technology Co., Ltd.

[0045] 2. Embodiment

[0046] Example 1

[0047] 1.1 A method for simultaneously improving the starch hydrolysis rate and protein quality in hot-pressed peanut meal, comprising the following steps:

[0048] (1) dry-grinding the hot-pressed peanut meal with an ultrafine grinder for 2 minutes, passing through an 80-mesh sieve, and obtaining hot-pressed peanut meal powder;

[0049] (2) Pretreatment

[0050] Take multiple portions of raw materials with the same ratio and perform the following operations:

[0051] Take 5 g of the hot-pressed peanut meal powder in (1), place it in a 100 mL centrifuge tube, add water according to the following solid-liquid ratio and mix thoroughly, adjust the pH with HCl solution, put it in a constant temperature water bath, and extract at a constant temperature of 30-70°C for 2-10 hours;

[0052] Here, the material-liquid ratio is set to 1g:5mL, 1g:10mL, 1g:15mL, 1g:20mL, 1g:25mL; pH 2; temperature is set to 50℃; pretreatment time is set to 10h;

[0053] Here, the pH was adjusted to 2, 3, 4, 6, 8, 10, and 12 respectively; the material-liquid ratio was: 1 g: 10 mL; the temperature was set to 50 °C; and the pretreatment time was set to 8 h;

[0054] Here, the temperature of the constant temperature water bath is set to 30℃, 40℃, 50℃, 60℃, and 70℃ respectively; the material-liquid ratio is: 1g:10mL; pH 2; the pretreatment time is set to 8h;

[0055] Here, the pretreatment time is set to soak for 2h, 4h, 6h, 8h, 10h, and 12h respectively; the material-liquid ratio is: 1g:10mL; the temperature is set to 50℃; pH2;

[0056] (3) After extraction, the pH was adjusted to 6, 150 u / g of high temperature α-amylase was added, and enzymolysis was performed at 95° C. and 120 r / min for 150 min under constant temperature oscillation, the pH was adjusted to 4.5, the enzyme was inactivated at 140° C. for 5 min, and the solution was centrifuged at 10,000 r / min and 2° C. for 10 min to obtain an enzymatic hydrolyzate and a precipitate, respectively;

[0057] (4) adding water to the precipitate obtained in (3) at a solid-liquid ratio of 1:8-15 (g / mL), adding 0.1 mol / L NaOH solution to adjust the pH to 9, reacting at 60°C for 2 h, and centrifuging to obtain a precipitate;

[0058] (5) Extract the precipitate in (4) again (without changing the conditions and methods), combine the supernatants, and discard precipitate I; adjust the pH of the supernatant, let it stand for 20 minutes, and then centrifuge it at room temperature at 2500 r / min for 30 minutes to collect precipitate II;

[0059] (6) The precipitate II is repeatedly washed 3-5 times with deionized water at a pH of 4.5, and the precipitate II is dispersed with a small amount of deionized water, the pH is adjusted to about 7.0, and the peanut meal protein is obtained by freeze-drying.

[0060] 1.2 Index determination

[0061] 1.2.1 Detection of starch hydrolysis degree: The degree of starch hydrolysis can be characterized by the soluble sugar content in the starch solution. The DNS method is used to determine the glucose content produced by enzymatic hydrolysis.

[0062] Drawing of glucose standard curve: Take 6 15mL test tubes, add samples according to the table below, adjust to zero with 0, use an ELISA reader to detect absorbance at 540nm, and use the absorbance value as the ordinate and the standard concentration (mg / mL) as the abscissa to obtain the standard curve. Figure 1 As shown, the glucose content and the absorbance value have a good linear relationship, the linear equation is y = 0.0846x + 0.0296, and the correlation coefficient R 2 =0.9913.

[0063] Table 1 Glucose standard curve

[0064]

[0065]

[0066] After the sample is centrifuged, 1 mL of the sample supernatant is added with 2 mL of DNS reagent. The rest of the operation is the same as that of the standard curve. After shaking, 200 μL of the sample is added to a 96-well ELISA plate and the absorbance is measured at 540 nm. The absorbance value is substituted into the glucose standard curve to obtain the reducing sugar content.

[0067] DNS method was used to determine the reducing sugar content of pretreatments with different solid-liquid ratios (immersion at 50℃ for 10h, pH=2), different temperatures (solid-liquid ratio 1:10, immersion for 10h, pH=2), different immersion times (solid-liquid ratio 1:10, temperature 50℃, pH=2) and different pH conditions (solid-liquid ratio 1:10, temperature 50℃, immersion for 10h). The results are shown in the figure. Figure 2-5 .

[0068] The hydrolysis rate in the following table refers to the hydrolysis rate of starch. The hydrolysis rate is an integer. The conversion formula between reducing sugar and starch hydrolysis rate (or hydrolysis degree) is as follows: Hydrolysis rate = [reducing sugar content / (17.8×0.9)]×100%, wherein 17.8 is the starch content in the hot-pressed peanut meal used in this application, and 0.9 is the conversion coefficient between glucose and starch, and the same applies below.

[0069] Table 2 Reducing sugar content measured by pretreatment under different material-liquid ratios

[0070] Material-liquid ratio Reducing sugar content (g / 100g) Hydrolysis rate (%) 1g: 5mL 6.53 41 1g: 10mL 11.63 73 1g: 15mL 12.48 78 1g: 20mL 12.6 79 1g: 25mL 12.99 81

[0071] Table 3 Reducing sugar content measured by pretreatment at different pH

[0072] pH Reducing sugar content (g / 100g) Hydrolysis rate (%) 2 12.42 78 3 9.83 61 4 6.97 44 6 6.13 38 8 5.18 32 10 7.07 44 12 6.33 40

[0073] Table 4 Reducing sugar content measured by pretreatment at different temperatures

[0074] Temperature(℃) Reducing sugar content (g / 100g) Hydrolysis rate (%) 30 7 44 40 8.35 52 50 10.59 66 60 11.36 71 70 11.26 70

[0075] Table 5 Reducing sugar content measured at different pretreatment times

[0076] Pretreatment time (h) Reducing sugar content (g / 100g) Hydrolysis rate (%) 2 8.33 52 4 9.12 57 6 10.45 65 8 11.35 71 10 11.41 71

[0077] Combined with the above table and attached Figure 2-5 It can be seen that:

[0078] (1) The best reaction effect was achieved after pretreatment at pH 2, where the reducing sugar content was 12.42 g / 100 g and the starch hydrolysis rate reached 78%. However, the degradation degree was not high in neutral and alkaline environments, and the reducing sugar content was low, only 1 / 2 or 2 / 3 of that in acidic conditions.

[0079] (2) When the material-liquid ratio is 1g:10mL and the reducing sugar content is 11.63g / 100g, the reducing sugar content increases slowly even if the amount of deionized water is increased. Therefore, the material-liquid ratio of 1g:10mL is selected as the pretreatment process condition for peanut meal.

[0080] (3) With the increase of pretreatment temperature, the reducing sugar content in the enzymatic hydrolyzate increased sharply. When the temperature was 60°C, the reducing sugar content reached 11.36 g / 100 g. When the temperature was further increased, the increasing amount of reducing sugar was slow. Therefore, 60°C was selected as the pretreatment process condition for peanut meal.

[0081] (4) Before the pretreatment time of 8 h, the reducing sugar content of liquefaction showed an upward trend and reached 11.35 g / 100 g. As time went on, the reducing sugar content did not increase significantly, so 8 h was selected as the pretreatment time.

[0082] After comprehensive consideration, the present invention conducted a pretreatment orthogonal experiment, and the experimental conditions are shown in Table 6 below:

[0083] Table 6 Orthogonal test factor levels and level coding table

[0084]

[0085] Table 7 Orthogonal experiment results

[0086]

[0087]

[0088] From the analysis of Table 6 and Table 7, it can be seen that the material-liquid ratio and soaking time have a significant effect on the reducing sugar content in the peanut meal starch liquefaction, while the soaking temperature has no significant effect on the reducing sugar content. And the order of influencing factors is: material-liquid ratio> soaking time> soaking temperature. The optimal process combination is A2B3C3, that is, material-liquid ratio 1:10, soaking time 10h, soaking temperature 60℃.

[0089] After investigation, the best solution is as follows:

[0090] (1) dry-grinding the hot-pressed peanut meal with an ultrafine grinder for 2 minutes, passing through an 80-mesh sieve, and obtaining hot-pressed peanut meal powder;

[0091] (2) Pretreatment: The hot-pressed peanut meal in (1) was mixed with a hydrochloric acid solution at a weight-to-volume ratio of 1 g:10 mL, and the mixture was soaked at 60° C. for 10 h. The hydrochloric acid solution was adjusted so that the pH of the mixture formed by the hot-pressed peanut meal and the hydrochloric acid solution was 2;

[0092] The other steps are the same as those in Example 1, and the sample obtained under this condition is recorded as a preferred example.

[0093] Table 8 Comparison of hydrolysis effects before and after pretreatment

[0094] Reducing sugar content (g / 100g) Hydrolysis rate (%) Comparison example 6.12 38 Preferred Example 13.24 83

[0095] The control example is (if not otherwise specified in the following examples, this case is used as the control example): Compared with the method in Example 1, the pretreatment method in step (2) is not used, that is, the acid soaking treatment is not performed; the details are as follows:

[0096] (1) dry-grinding the hot-pressed peanut meal with an ultrafine grinder for 2 minutes, passing through an 80-mesh sieve, and obtaining hot-pressed peanut meal powder;

[0097] (2) adjusting the pH of the material in (1) to 6, adding 150 u / g high temperature α-amylase, performing constant temperature oscillation enzymolysis at 95° C. and 120 r / min for 150 min, adjusting the pH to 4.5, inactivating the enzyme at 140° C. for 5 min, and centrifuging at 10000 r / min and 2° C. for 10 min to obtain an enzymatic hydrolyzate and a precipitate, respectively;

[0098] (3) adding water to the precipitate obtained in (2) at a solid-liquid ratio of 1:8-15 (g / mL), adding 0.1 mol / L NaOH solution to adjust the pH to 9, reacting at 60°C for 2 h, and centrifuging to obtain a precipitate;

[0099] (4) Extract the precipitate in step (3) again (without changing the conditions or methods), combine the supernatants, and discard precipitate I; adjust the pH of the supernatant, let it stand for 20 minutes, and then centrifuge it at room temperature at 2500 r / min for 30 minutes to collect precipitate II;

[0100] (5) The precipitate II is repeatedly washed 3-5 times with deionized water at a pH of 4.5, and the precipitate is dispersed with a small amount of deionized water, the pH is adjusted to about 7.0, and the peanut meal protein is obtained by freeze-drying.

[0101] 1.3 Protein-related assays

[0102] (1) Determination and comparison of protein functional properties:

[0103] Table 9 Functional properties of peanut meal protein before and after pretreatment

[0104] nature Comparison example Preferred Example NSI% 85.30 69.70 Emulsification % 63.87 90.28 Emulsion stability % 114.29 147.00 Foaming % 50 45 Foaming stability % 25 27 Surface hydrophobicity 1791.20 1871.40 Water holding capacity% 76 290 Oil retention % 295 467

[0105] Note: The nitrogen solubility index (NSI) is usually used to express the solubility of protein.

[0106] It can be seen from the above table that after acid soaking pretreatment, the starch can not only be fully hydrolyzed and utilized, but also the NSI of peanut meal protein decreases from 85.3% to 69.7% when peanut protein is subsequently extracted. This is mainly because during the pretreatment process of peanut meal, in an acidic environment, protein denaturation and aggregation are prone to occur, resulting in further reduction in solubility.

[0107] Moreover, the emulsification performance increased from 63.87% to 90.28%; the emulsification stability also increased from 114.29% to 147%, the foaming performance decreased from 50% to 45%, the foaming stability increased from 25% to 27%, the surface hydrophobicity increased from 1791.2 to 1871.4, the water holding performance increased from 76% to 290%, an increase of about 4 times; the oil holding capacity increased from 295% to 467%, an increase of nearly one-fold. From the above data, it can be seen that the quality of protein is significantly improved through acid pretreatment, achieving unexpected technical effects. The reason for this may be that the original ordered structure of the protein is broken during the acid pretreatment of the peanut meal, and the conformation and interfacial behavior of the protein are changed, so that the side chains hidden inside are further dissociated and unfolded, the nitrogen solubility is reduced, the lipophilic hydrophobic groups inside the molecule are exposed, and the surface tension is reduced, which is conducive to the combination with the oil phase, thereby improving the emulsification, emulsification stability, water holding capacity, and oil holding capacity of the protein.

[0108] (2) Amino acid composition analysis

[0109] Table 10 Amino acid composition and content of peanut meal protein

[0110] Amino Acids Control example (g / 100g) Preferred example (g / 100g) Serine 4.06 4.46 Glycine 3.94 4.17 Histidine 2.11 2.39 Arginine 11.58 11.62 Threonine* 1.95 2.36 Alanine 3.13 3.5 Tyrosine 3.75 4.04 Valine* 3.19 3.58 Isoleucine* 2.71 2.93 Leucine* 5.82 6.43 Phenylalanine* 4.71 5.29 Lysine* 2.21 2.25 Essential amino acid content 20.59 22.84

[0111] Note: The amino acids marked with * are essential amino acids.

[0112] It can be seen from the above table that after the hot-pressed peanut meal is pretreated, the starch is hydrolyzed more fully, and the quality of the protein is also significantly improved, which is specifically manifested in that the content of essential amino acids such as leucine and alanine in the obtained peanut meal protein increases to varying degrees, for example, leucine increases from 5.82g / 100g to 6.43g / 100g, an increase of about 10%; serine increases from 4.06g / 100g to 4.46g / 100g, an increase of about 10%; phenylalanine increases from 4.71g / 100g to 5.29g / 100g, an increase of about 12.3%; the amino acid content changes significantly, which shows that the pretreatment of the present invention can further improve the nutritional value of peanut meal protein and achieve unexpected technical effects.

[0113] Comparative Example 1

[0114] The hot-pressed peanut meal was not acid-soaked before the enzymatic hydrolysis with amylase. Instead, different bio-enzyme methods were used to pre-treat the hot-pressed peanut meal. The effects of alkaline protease (Dalian Meilun Biotechnology Co., Ltd.), neutral protease (Dalian Meilun Biotechnology Co., Ltd.), composite protease (Beijing Solebaugh Technology Co., Ltd.), cellulase (Shanghai MacLean Biochemical Technology Co., Ltd.), and lipase (Shanghai MacLean Biochemical Technology Co., Ltd.) on the starch hydrolysis rate were investigated.

[0115] The specific steps are as follows:

[0116] (1) dry-grinding the hot-pressed peanut meal with an ultrafine grinder for 2 minutes, passing through an 80-mesh sieve, and obtaining hot-pressed peanut meal powder;

[0117] (2) Take 5 g of the hot-pressed peanut meal powder in step (1), place it in a 100 mL centrifuge tube, add water at a solid-liquid ratio of 1:10 (g / mL) and mix thoroughly, adjust the pH according to the table below, add different types of biological enzymes and adjust them to the optimal temperature of the enzyme, place it in a constant temperature oscillator, and perform enzymolysis at a speed of 140 r / min for 6 hours. After the enzymolysis is completed, heat the enzymolysis mixture in a boiling water bath for 10 minutes to inactivate the enzyme;

[0118] (3) Take out the mixture after enzyme inactivation and adjust the pH to 6.3, add 150u / g high temperature α-amylase, put it into a constant temperature oscillator, adjust the temperature to 90℃, the speed to 140r / min, and enzymolysis for 150min. After the enzymolysis is completed, adjust the pH to 4.5 to inactivate the enzyme activity. Then centrifuge at a speed of 10000r / min and a temperature of 4℃ for 10min, and measure the reducing sugar content by DNS method. At the same time, set up a blank control experiment for enzymatic pretreatment. The reducing sugar content was measured by DNS method. The results are as follows Figure 6 shown.

[0119] Table 11 Setting of different biological enzyme action conditions

[0120]

[0121]

[0122] Table 12 Comparison of starch hydrolysis under different enzyme pretreatments

[0123] Biological enzyme Reducing sugar content g / 100g Hydrolysis rate (%) Comparison example 6.12 38 Preferred Example (Acid Treatment) 13.24 83 Alkaline protease 8.28 52 Neutral protease 7.17 45 Compound protease 9.15 57 Cellulase 6.68 42 Lipase 6.44 40

[0124] From the data in Table 12, it can be seen that the reducing sugar content of the preferred example obtained by acid treatment after starch hydrolysis is 13.24, while the content of reducing sugar changes slightly when the hot-pressed peanut meal is pretreated by enzyme method, which shows that the effect of using enzyme method to pretreat the hot-pressed peanut meal is not ideal for improving the starch hydrolysis rate. At the same time, the acid soaking pretreatment also changes the performance of the protein to a certain extent, and optimizes the quality of the protein, such as improving the emulsification, water holding capacity, oil holding capacity, purity, emulsification stability, foaming, surface hydrophobicity and other properties of the protein product.

[0125] Since the bio-enzymatic pretreatment method cannot effectively improve the starch hydrolysis rate, the impact of these methods on protein quality will no longer be investigated.

[0126] Comparative Example 2

[0127] Pretreatment by physical method

[0128] (1) dry-grinding the hot-pressed peanut meal with an ultrafine grinder for 2 minutes, passing through an 80-mesh sieve, and obtaining hot-pressed peanut meal powder;

[0129] (2) The crushed hot-pressed peanut meal powder was mixed with 35% water in a volume-mass ratio, soaked for 12 hours, and steam-exploded at a pressure of 1 MPa and a pressure maintenance time of 180 seconds; 5 g of the hot-pressed peanut meal powder after steam explosion was taken, the material-liquid ratio was adjusted to 1:10 (g / mL) with distilled water, the pH was adjusted to 6, 150 u / g of high-temperature α-amylase was added, and the mixture was placed in a constant temperature oscillator at 90°C and a speed of 140 r / min for enzymolysis for 150 minutes. After the enzymolysis was completed, the pH was adjusted to 4.5 to inactivate the enzyme;

[0130] (3) Centrifuge for 10 min at a speed of 10,000 r / min and a temperature of 4°C. Determine the reducing sugar content using the DNS method. At the same time, set up a blank control experiment for steam explosion pretreatment. Figure 7 .

[0131] From the attached Figure 7 It can be seen that after steam explosion treatment, the reducing sugar content in the starch liquefaction of hot-pressed peanut meal did not increase significantly.

[0132] Table 13 Comparison of the effects of physical treatment methods on the degree of starch hydrolysis

[0133] Reducing sugar content g / 100g Hydrolysis rate (%) Comparison example 6.12 38 Steam Explosion 7.69 48

[0134] It can be seen from Comparative Examples 1 and 2 that although the enzymatic and physical methods can improve the starch hydrolysis rate to some extent, the effects of the two methods are not obvious, and are far less obvious than the effect of acid soaking treatment of hot-pressed peanut meal. Specifically, acid soaking treatment of hot-pressed peanut meal can increase the starch hydrolysis rate to 89%, while the enzymatic method can only increase the starch hydrolysis rate to 57% at most, and the physical pretreatment method can only increase the starch hydrolysis rate to 48% at most.

[0135] From the perspective of protein quality analysis, the starch hydrolysis rate is greatly improved after pretreatment with acid solution (as can be learned from the detection of soluble sugars), thereby further improving the quality of the obtained peanut protein.

[0136] In the present application, acid treatment cannot directly hydrolyze starch, and starch still relies on amylase to hydrolyze it. The effect of pre-treating hot-pressed peanut meal with acid solution is to reduce the difficulty of amylase to directly hydrolyze starch, which may cause changes in starch, protein, cellulose, hemicellulose, etc., so that starch is more exposed and more thoroughly contacted with amylase, and the chain of starch or other components undergoes some changes, so that subsequent hydrolysis under the action of amylase becomes easier, thus significantly improving the hydrolysis rate of starch; at the same time, acid treatment also causes some changes in protein, improving the quality of peanut protein obtained in subsequent steps, which is an unexpected technical effect. As mentioned above, it may be that the ordered structure of the protein of hot-pressed peanut meal is broken during the soaking process of acid solution, and the conformation and interfacial behavior of the protein are changed, so that the side chains hidden inside are further dissociated and unfolded, the lipophilic and hydrophobic groups inside the molecule are exposed, and the surface tension is reduced, which is conducive to the combination with the oil phase, thereby improving the emulsification, emulsification stability, water retention, oil retention and other properties of the protein. However, both enzymatic pretreatment and physical pretreatment cannot significantly increase the starch hydrolysis rate.

Claims

1. A method for simultaneously improving the starch hydrolysis rate and protein quality in hot-pressed peanut meal. It is characterized in that The steps include: (1) Dry-grinding the hot-pressed peanut meal with an ultra-fine grinder for 2 minutes, passing through an 80-mesh sieve, and obtaining hot-pressed peanut meal powder; (2) Pretreatment: The hot-pressed peanut meal powder in (1) was mixed with a hydrochloric acid solution at a weight-to-volume ratio of 1 g:10 mL, and the mixture was soaked at 60°C for 10 h. The hydrochloric acid solution was adjusted so that the pH of the mixture formed by the hot-pressed peanut meal powder and the hydrochloric acid solution was 2; (3) After soaking, the pH of the mixture was adjusted to 6, 150 u / g of high temperature α-amylase was added, and the mixture was subjected to constant temperature oscillation enzymolysis at 95°C and 120 r / min for 150 min. The pH was adjusted to 4.5, the enzyme was inactivated at 140°C for 5 min, and the mixture was centrifuged at 10,000 r / min and 2°C for 10 min to obtain the enzymatic solution and precipitate, respectively. (4) Add water to the precipitate obtained in (3) at a g / mL solid-liquid ratio of 1:8-15, add 0.1 mol / L NaOH solution to adjust the pH to 9, react at 60°C for 2 h, and centrifuge to obtain a precipitate; (5) Extract the precipitate in (4) again under the same conditions, combine the supernatants, and discard precipitate I; adjust the pH of the supernatant to the protein isoelectric point of 4.2-4.5, let it stand for 20 minutes, and then centrifuge it at room temperature at 2500 r / min for 30 minutes to collect precipitate II; (6) Wash the precipitate II repeatedly 3-5 times with deionized water at a pH of 4.5, disperse the precipitate II with deionized water, adjust the pH to 7.0, and dry to obtain peanut meal protein.

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