Method for preparing high-quality fresh waxy corn flour by coupling drying pretreatment with enzymolysis

Abstract

According to the preparation method of the fresh waxy corn source high-quality whole grain type corn flour and the obtained product, drying pretreatment is performed in a proper temperature range of 70-80 DEG C, so that the net structure of protein and tight combination with starch are preliminarily destroyed, the concentration of an initial substrate is increased, and quick start of an enzymolysis reaction is triggered; the whole grain product is endowed with brand-new brewing performance and excellent quality by coupling drying pretreatment and enzymolysis, accurately regulating and controlling the whole process and adopting an enzymatic reaction with specific combination, sequence, dosage and reaction conditions, and compared with a control group, the WSI is increased by 16.63%-60.63%, the soluble protein is increased by 5.66%-24.18%, and the soluble sugar is increased by 9.92%-34.64%; the loose stacking density is reduced by 21.42% to 54.35%, and the tap stacking density is reduced by 13.85% to 39.19%; the hydroxyl free radical scavenging capacity is 90.33%-96.99%, and the hydroxyl free radical reducing power is 0.891%-0.893%; the repose angle and the dispersion index are obviously reduced. The novel whole-grain corn flour product prepared by the invention has high brewing performance, excellent rheological property, good flavor and taste, and antioxidant health-care efficacy at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and in particular to a method for preparing high-quality fresh glutinous corn flour by coupling drying pretreatment with enzymatic hydrolysis and the obtained product. Background Art

[0002] Fresh glutinous corn is fresh ears picked at the milky stage. Currently, its processing methods are mainly direct fresh ear consumption, quick-frozen storage, and steaming and vacuum packaging. In production, some glutinous corns are not up to standard size and are directly used as feed, resulting in low utilization rate. To address this problem, it is of great significance to use appropriate processing methods to make it into powder to increase the application range of glutinous corn in food.

[0003] Black Pearl Waxy Corn belongs to the black corn series. The average composition of fresh black glutinous corn is about: 69%~75% moisture, 8%~11% crude protein, 4.6%~5.7% crude fat, 69%~75% carbohydrates, 0.7%~1.3% crude fiber, 1.0%~1.9% ash, 0.5% other substances (on a dry basis). The waxy keratin of black glutinous corn is thick and tough, the cell structure is tight, the starch granules are surrounded by a continuous protein matrix, the cells and contents are surrounded by cellulose cell walls in various ways, making the cell structure more compact and the content of amylopectin is high. Black pearl glutinous corn also contains rich anthocyanins and phenolic components. Anthocyanin pigments are flavonoid compounds with strong free radical scavenging and antioxidant capabilities, and are known for their high efficiency, low toxicity, and high bioavailability. Anthocyanin pigments can effectively scavenge free radicals in the human body, reduce the production of peroxides, and prevent visible light and ultraviolet radiation. They have anti-tumor, anti-aging, and skin care effects. Black pearl glutinous corn has a fragrant and glutinous taste and is rich in nutrients. It is an excellent whole grain health ingredient. Because the protein and starch particles in black glutinous corn often exist in the form of macromolecules, compared with other varieties of corn, the starch inside the corn particles is too tightly wrapped by protein, and the epidermis contains a large amount of insoluble cellulose, and the starch particles are difficult to release. It is manifested as solid particles that are not easy to disperse in the medium water as fine particles suspended in the dispersion medium and easily precipitate, resulting in poor dissolution of whole grain corn flour.

[0004] Protease, cellulase and amylase are often used in corn to improve nutrition and quality. Neutral protease is an endoprotease that can decompose macromolecular proteins into products such as polypeptides and amino acids under certain temperature and pH conditions, thereby reducing the molecular weight of proteins. The enzymatic reaction of neutral protease improves the solubility of proteins and improves the dispersibility of proteins, which is conducive to the effective absorption and utilization of proteins. While improving the decomposition of cellulose and hemicellulose, cellulase can promote the dissolution of plant cell walls and dissolve more soluble substances in plant cells, because human digestive enzymes cannot hydrolyze plant cell wall polysaccharides. The existence of intact plant cell walls that encapsulate macromolecules (starch, lipids and proteins) can serve as a structural barrier to prevent digestive enzymes from diffusing during digestion. Amylase can hydrolyze starch and glycogen. α-amylase is the most important type of enzyme and the largest enzyme preparation variety, and is widely used in industrial production.

[0005] At present, there are few studies on preparing whole grain enzymatic hydrolyzed corn products by finely controlling the enzymatic hydrolysis process and improving the nutritional quality and mixing performance of the products. Many scholars at home and abroad have conducted research on the preparation of corn protein hydrolyzates, and the core of their research is only to maximize the hydrolysis degree of corn protein, or focus on the extraction of soluble / insoluble dietary fiber. Pi Shiyu et al. (Optimization of corn yellow powder pretreatment process and analysis of its protein hydrolysis components, Food Industry Science and Technology, Issue 13, 2020) used corn yellow powder (also known as corn protein powder, which is a by-product of corn wet production of starch or ethanol extraction) as raw material, first treated it with cellulase, then with α-amylase, and then with alkaline protease, and examined the performance in terms of hydrolysis degree, solubility, and foaming. However, this study did not use whole grain corn as raw material, and did not involve research on rheology, antioxidant properties, etc. Lin Xuhui et al. (Study on Extraction of Soluble Dietary Fiber from Corn Bran Residue by Composite Enzyme Method, Food Science and Technology, Issue 11, 2006) used α-amylase, papain, and cellulose mixed enzyme = 1:0.8:2 to enzymatically hydrolyze corn bran residue treated with anhydrous ethanol to produce water-soluble dietary fiber. Ren Jian et al. (Chinese Patent: 202210013195.8) disclosed a method for the synergistic production of whole corn flour by bacterial enzymes, using whole corn kernels as raw materials, extrusion puffing pretreatment, and synergistic production of whole corn flour by cellulase and / or hemicellulase and lactic acid bacteria. Although the patent produces whole grain corn flour, it is not specifically targeted at glutinous corn, especially black glutinous corn, and uses a relatively complex extrusion puffing pretreatment, which has requirements for process equipment, and has not studied the performance in terms of solubility, rheology, and antioxidant properties.

[0006] Whole grain fresh black glutinous corn has its special composition, structure and physical and chemical properties. The reaction process is complicated during compound enzyme treatment, and its microstructure changes significantly, which has a significant impact on the product's rehydration performance, rheological properties and nutritional quality. How to use whole grain fresh black glutinous corn as raw material and obtain products with excellent rehydration properties, rheological properties, antioxidant properties and nutritional quality through effective enzymatic hydrolysis is a frontier hot issue in the field of corn processing, and it is also an issue that needs to be urgently solved in the field of fresh corn processing. Summary of the invention

[0007] Purpose of the invention: The purpose of the present invention is to provide a method for preparing high-quality whole-grain corn flour from fresh glutinous corn, and the whole-grain corn flour prepared by the method, especially corn flour obtained by processing black pearl glutinous corn as raw material and its preparation method.

[0008] Technical problem: To solve the technical problems existing in the existing technology, such as low utilization rate of fresh glutinous corn, poor solubility, rheological properties, antioxidant properties of glutinous corn whole grain flour, etc.

[0009] Technical solution: The inventive concept of the present invention is based on the composition and structural characteristics of fresh glutinous corn kernels (especially black pearl glutinous corn), and utilizes moderate drying pretreatment coupled with a specific enzymatic hydrolysis process to process the fresh black glutinous corn, thereby significantly improving the quality of fresh glutinous corn flour.

[0010] The technical solution of the present application relates to a method for preparing high-quality whole-grain corn flour from fresh glutinous corn, which is carried out according to the following steps: (1) Drying pretreatment: corn kernels are taken from fresh ears of glutinous corn, mixed and homogenized at high speed, corn slurry is spread on a stainless steel plate, and the corn slurry is naturally dried at room temperature until constant weight is reached. After drying, the corn slurry is crushed with a pulverizer, sieved to obtain fresh slurry corn flour, and sealed in a desiccator for storage; (2) Preparation of fresh corn syrup: fresh corn flour and deionized water are mixed and dispersed in a mass ratio of 2:1 (w / w) to obtain fresh corn syrup; (3) Enzymatic reaction: Add neutral protease and cellulase to fresh corn slurry at a rate of 15-30 U / g corn slurry and a ratio of 2:1. Perform enzymolysis at a pH of 5.5-6.0 and a temperature of 50-60°C for 1.0-2.0 h. Then continue to add α-amylase and cellulase at a rate of 20-30 U / g corn slurry and a ratio of 2:1. Perform enzymolysis at a pH of 5.0-6.0 and a temperature of 55-60°C for 1-2.0 h. (4) Inactivation of enzyme: After the enzymatic reaction is completed, inactivate the enzyme in a 95°C water bath for 5 minutes and cool to room temperature; (5) The enzyme-inactivated corn slurry is freeze-dried to obtain whole-grain corn flour.

[0011] Furthermore, the pretreatment in step (1) is replaced by the following pretreatment: corn kernels are taken from fresh ears of glutinous corn, mixed and homogenized at high speed, corn slurry is spread on a stainless steel plate, and the corn slurry is subjected to continuous hot air drying at 70-80° C. until constant weight is obtained, during which a mild Maillard reaction occurs. After drying, the corn slurry is crushed with a pulverizer, sieved to obtain fresh slurry corn flour, and sealed in a desiccator for storage.

[0012] Preferably, in the pretreatment, corn kernels are taken from fresh ears of glutinous corn, mixed and homogenized at 2500-3000 r / min for 90-120 s; spread to a thickness of 1 cm; crushed and sieved through a 100-150 mesh sieve to obtain fresh corn slurry; in the step (2), fresh corn slurry is prepared by mixing fresh corn slurry with deionized water in a mass ratio of 2:1 (w / w), and dispersing at 50-100 r / min for 90-120 s.

[0013] Preferably, the enzymatic reaction in step (3) is as follows: adding neutral protease and cellulase to fresh corn slurry, wherein the amount of neutral protease and cellulase added is 30 U / g corn slurry, and the amount ratio of neutral protease and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 1.5 h; then continuing to add α-amylase and cellulase, wherein the amount of α-amylase and cellulase added is 30 U / g corn slurry, and the amount ratio of α-amylase and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 1.5 h.

[0014] Preferably, the (3) enzymatic reaction: adding neutral protease and cellulase to fresh corn slurry, the addition amount of neutral protease and cellulase is 15U / g corn slurry, the dosage ratio of neutral protease and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 2.0h; then continuing to add α-amylase and cellulase, the addition amount of α-amylase and cellulase is 15U / g corn slurry, the dosage ratio of α-amylase and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 60°C for 2.0h.

[0015] Preferably, the fresh glutinous corn ears in step (1) are fresh black pearl glutinous corn ears, and the room temperature is preferably 20-25°C; in step (4), the enzyme is inactivated: after the enzymatic reaction is completed, the enzyme is inactivated in a water bath at 95°C for 5 minutes, and then cooled to room temperature; in step (5), the freeze drying is vacuum freeze drying. Conventional processes, i.e., parameters, can be selected for freeze drying.

[0016] The present application also obtains whole grain corn flour prepared by any of the above preparation methods.

[0017] The present application also relates to the application of the above method in significantly improving the solubility, rheological properties, antioxidant properties of digestion products, and flavor and taste of whole-grain corn flour.

[0018] The present invention has achieved the following beneficial effects: 1. The present invention performs a moderate drying pretreatment at a temperature range of 70-80°C on the raw material of fresh black glutinous corn, which leads to a mild Maillard reaction and effectively retains amylopectin. While improving the flavor and taste, it preliminarily destroys the protein network structure, and the close binding of protein and starch is also preliminarily destroyed. A part of the protein and starch granules are exposed, which changes the existence state of the substrate to a certain extent, increases the concentration of the initial substrate, and triggers the rapid start of the subsequent enzymatic hydrolysis reaction. Based on previous research on the subject, under normal circumstances, as the drying temperature increases, the dispersion time of corn flour will be prolonged and the dispersibility will decrease. However, the researchers unexpectedly found that drying treatment at a moderate temperature before enzymatic hydrolysis can actually promote the improvement of the final product's dispersibility, rheology and nutritional value, and achieve an unexpected synergistic effect; 2. By coupling drying pretreatment with enzymatic treatment and precisely controlling the entire process, the enzymatic reaction with specific combination, sequence, dosage and reaction conditions is adopted to significantly improve the preparation performance and nutritional quality of fresh black glutinous corn flour. That is, after appropriate drying pretreatment, neutral protease and cellulase are added to the fresh corn slurry, the added amount of neutral protease and cellulase is 15~30U / g corn slurry, the dosage ratio of neutral protease and cellulase is 2:1, and enzymolysis is carried out at pH 5.5~6.0 and temperature 50~60℃ for 1.0~2.0h; then α-amylase and cellulase are continued to be added, the added amount of α-amylase and cellulase is 20~30U / g corn slurry, the dosage ratio of α-amylase and cellulase is 2:1, and enzymolysis is carried out at pH 5.0~6.0 and temperature 55~60℃ for 1~2.0h; the dissolving performance of fresh glutinous corn flour is significantly improved, the rheology is good, and the nutritional flavor and antioxidant effect are improved. After moderate drying pretreatment to change the internal structure of the raw materials and increase the substrate concentration to a certain extent, the enzymatic hydrolysis process is immediately triggered with the addition of enzymes. First, neutral protease and cellulase are used simultaneously to act on the fresh glutinous corn slurry to preliminarily decompose cellulose to reduce the shielding effect of a large amount of cellulose in the epidermis and reduce the volume of cellulose molecules; at the same time, protein enzymes are used to destroy the protein layer that wraps the starch, completely destroy the complete network structure of the protein, and completely change the binding mode of protein and starch, exposing more starch tightly wrapped by protein. The amount of protease added at this stage is adapted to the concentration of the protein substrate, which can break the covalent bonds between the polypeptide chains inside the protein or between proteins as quickly and as greatly as possible, thereby reducing the relative molecular mass of the protein and also causing more starch to be released; in the second enzymatic hydrolysis stage, starch becomes the first macro-component of the corn slurry, α- The opportunistic use of amylase can fully hydrolyze most of the exposed starch internal α -1,4 glycosidic bonds, thereby changing the structure, chain length and molecular weight of starch, and hydrolyzing it into dextrin, oligosaccharides and monosaccharides, etc. The viscosity of starch can be changed after the action of amylase, and the ratio of amylopectin to straight-chain starch can be changed to improve the dispersibility of the product. At the same time, the appropriate amount of cellulase can accelerate the complete degradation of cellulose, destroy the cell wall to form a looser and more porous structure, change the spatial structure and ratio between the crystalline region and the amorphous region, expose more polar and non-polar groups, and make the corn flour particles easier to spread and disperse; the protease in the first stage, under the synergistic effect of the cellulase and amylase in the second stage, the protease continues to deeply enzymolyze proteins and peptides. The concentration and dosage of the enzyme in the entire enzymatic hydrolysis process are optimally adapted to the corresponding substrate concentration, and the ideal effect of the product is the result of the combined action of various factors; 3. The technical means of this application endows whole grain products with new rehydration performance and excellent quality. The rehydration performance of the obtained black glutinous corn flour is significantly improved. Compared with the control group, the WSI of the glutinous corn modified product prepared in this application is significantly increased ( P< 0.05 ), increased by 16.63%-60.63%, soluble protein increased by 5.66%-24.18% ( P<0.05 ), soluble sugar increased by 9.92%-34.64% ( P<0.05 ), the dispersion index decreased. The rheological properties of black glutinous corn flour were also significantly improved. Compared with the control group, the loose bulk density and tapped bulk density of the powder decreased by 21.42%-54.35% and 13.85%-39.19%, respectively, and the angle of repose was also significantly reduced. In addition, the hydroxyl radical scavenging ability and reducing power of the in vitro digestion product of black pearl glutinous corn enzymatic modification were higher than those of the control group, which were 90.33%-96.99% ( P<0.05 )、0.891-0.893( P<0.05 ); 4. The process of the present application is simple and easy to operate. Compared with the control example 4, the raw material and time costs can be greatly saved. In addition, the present application prepares a new whole-grain corn flour product with high dissolving performance, excellent rheological properties, good flavor and taste, and antioxidant health care effects, which fills the market gap and is conducive to expanding the application scope of fresh glutinous corn in the food industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : The finished product of the black pearl glutinous corn enzymatic modification obtained by each treatment in this application In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work. DETAILED DESCRIPTION

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention. Example 1

[0021] A method for preparing high-quality whole-grain corn flour from fresh glutinous corn: (1) Pretreatment: corn kernels were taken from fresh ears of black pearl glutinous corn, mixed and homogenized at 3000 r / min for 90 s, 2000 g of corn slurry was taken and spread on a stainless steel plate with a thickness of about 1 cm, the corn slurry was dried with continuous hot air at 70°C until constant weight was reached, and after drying, it was crushed with a pulverizer, sieved through a 100-mesh sieve to obtain fresh slurry corn flour, and sealed in a desiccator for storage; (2) Preparation of fresh corn slurry: 1000 g of the fresh corn slurry prepared in step (1) was mixed with deionized water at a mass ratio of 2:1 (w / w), and dispersed at 60 r / min for 90 s to obtain fresh corn slurry; (3) Enzymatic reaction: Add neutral protease and cellulase to fresh corn slurry, the addition amount of neutral protease and cellulase is 30U / g corn slurry, the dosage ratio of neutral protease and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 1.5h; then continue to add α-amylase and cellulase, the addition amount of α-amylase and cellulase is 30U / g corn slurry, the dosage ratio of α-amylase and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 1.5h; (4) Inactivation of enzyme: After the enzymatic reaction is completed, inactivate the enzyme in a 95°C water bath for 5 minutes and cool to room temperature; (5) The corn slurry is subjected to conventional vacuum freeze-drying to obtain whole grain black pearl glutinous corn flour. Example 2

[0022] A method for preparing high-quality whole-grain corn flour from fresh glutinous corn: (1) Pretreatment: corn kernels were taken from fresh ears of black pearl glutinous corn, mixed and homogenized at 3000 r / min for 90 s, 2000 g of corn slurry was taken and spread on a stainless steel plate with a thickness of about 1 cm, the corn slurry was naturally dried at room temperature of 25°C until constant weight was reached, and after drying, it was crushed with a pulverizer, sieved through a 100-mesh sieve to obtain fresh slurry corn flour, and sealed in a desiccator for storage; (2) Preparation of fresh corn slurry: 1000 g of the fresh corn slurry prepared in step (1) was mixed with deionized water at a mass ratio of 2:1 (w / w), and dispersed at 60 r / min for 90 s to obtain fresh corn slurry; (3) Enzymatic reaction: Add neutral protease and cellulase to fresh corn slurry, the addition amount of neutral protease and cellulase is 30U / g corn slurry, the dosage ratio of neutral protease and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 1.5h; then continue to add α-amylase and cellulase, the addition amount of α-amylase and cellulase is 30U / g corn slurry, the dosage ratio of α-amylase and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 1.5h; (4) Inactivation of enzyme: After the enzymatic reaction is completed, inactivate the enzyme in a 95°C water bath for 5 minutes and cool to room temperature; (5) The corn slurry is subjected to conventional vacuum freeze-drying (also the same as in Example 1) to obtain whole grain black pearl glutinous corn flour. Example 3

[0023] A method for preparing high-quality whole-grain corn flour from fresh glutinous corn: (1) Pretreatment: corn kernels were taken from fresh ears of black pearl glutinous corn, mixed and homogenized at 3000 r / min for 100 s, 2000 g of corn slurry was taken and spread on a stainless steel plate with a thickness of about 1 cm, the corn slurry was dried at 75°C with continuous hot air until constant weight was obtained, and a mild Maillard reaction was performed. After drying, the corn slurry was crushed with a pulverizer, sieved through a 120-mesh sieve to obtain fresh slurry corn flour, and sealed in a desiccator for storage; (2) Preparation of fresh corn syrup: 1000 g of the fresh corn syrup prepared in step (1) was mixed with deionized water at a mass ratio of 2:1 (w / w), and dispersed at 60 r / min for 110 seconds to obtain fresh corn syrup; (3) Enzymatic reaction: Add neutral protease and cellulase to fresh corn slurry. The amount of neutral protease and cellulase added is 20U / g corn slurry, and the ratio of neutral protease and cellulase is 2:1. Enzyme hydrolysis is carried out at pH 5.5 and temperature 50°C for 1.5h. Then continue to add α-amylase and cellulase. The amount of α-amylase and cellulase added is 25U / g corn slurry. The ratio of α-amylase and cellulase is 2:1. Enzyme hydrolysis is carried out at pH 6 and temperature 60°C for 1h. (4) Inactivation of enzyme: After the enzymatic reaction is completed, inactivate the enzyme in a 95°C water bath for 5 minutes and cool to room temperature; (5) The corn slurry is subjected to conventional vacuum freeze drying (Example 1) to obtain whole grain black pearl glutinous corn flour. Example 4

[0024] A method for preparing high-quality whole-grain corn flour from fresh glutinous corn: (1) Pretreatment: corn kernels were taken from fresh ears of black pearl glutinous corn, mixed and homogenized at 3000 r / min for 120 s, 2000 g of corn slurry was taken and spread on a stainless steel plate with a thickness of about 1 cm, the corn slurry was dried at 80°C with continuous hot air until constant weight was obtained, and a mild Maillard reaction was performed. After drying, the corn slurry was crushed with a pulverizer, sieved through a 150-mesh sieve to obtain fresh slurry corn flour, and sealed in a desiccator for storage; (2) Preparation of fresh corn syrup: 1000 g of the fresh corn syrup prepared in step (1) was mixed with deionized water at a mass ratio of 2:1 (w / w), and dispersed at 60 rpm for 120 seconds to obtain fresh corn syrup; (3) Enzymatic reaction: Add neutral protease and cellulase to fresh corn slurry. The amount of neutral protease and cellulase added is 15U / g corn slurry, and the ratio of neutral protease to cellulase is 2:1. Enzyme hydrolysis is carried out at pH 5.5 and temperature 55°C for 2.0 h. Then continue to add α-amylase and cellulase. The amount of α-amylase and cellulase added is 15U / g corn slurry. The ratio of α-amylase to cellulase is 2:1. Enzyme hydrolysis is carried out at pH 5.5 and temperature 60°C for 2.0 h. (4) Inactivation of enzyme: After the enzymatic reaction is completed, inactivate the enzyme in a 95°C water bath for 5 minutes and cool to room temperature; (5) The corn slurry is subjected to vacuum freeze drying (same as in Example 1) to obtain whole grain black pearl glutinous corn flour.

[0025] Comparative test: The previous research results of the research team have shown that the combined use of three enzymes is better than single enzymes or double enzymes. Therefore, a comparative test was carried out on the use of three enzymes. Comparative Example 1

[0026] Based on Example 1, step (3) was adjusted to add three enzymes in a mixed manner. The details are as follows: (3) Enzymatic reaction: A mixture of neutral protease, cellulase, and α-amylase was added to the fresh corn slurry of black glutinous corn. The total amount of enzyme added was 60 U / g corn slurry, including 20 U / g corn slurry of neutral protease, 20 U / g corn slurry of cellulase, and 20 U / g corn slurry of α-amylase. The enzymatic reaction was carried out at pH 5.5 and temperature 55°C for 3.0 h. Comparative Example 2

[0027] Step (3) was adjusted based on Example 1, and the order of adding the two-stage enzymes was adjusted.

[0028] Enzymatic reaction: add α-amylase and cellulase to the fresh corn slurry of black glutinous corn, the addition amount of α-amylase and cellulase is 30U / g corn slurry, the dosage ratio of α-amylase and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 1.5h; then continue to add neutral protease and cellulase, the addition amount of neutral protease and cellulase is 30U / g corn slurry, the dosage ratio of neutral protease and cellulase is 2:1, and enzymolysis is carried out at pH 5.5 and temperature 55°C for 1.5h. Comparative Example 3

[0029] Step (3) was adjusted based on Example 1. The dosage ratio of the enzyme was adjusted.

[0030] (3) Enzymatic reaction: Add neutral protease and cellulase to fresh corn slurry at a rate of 30 U / g corn slurry and a ratio of 3:1. Perform enzymatic hydrolysis at pH 5.5 and 55°C for 1.5 h. Then continue to add α-amylase and cellulase at a rate of 30 U / g corn slurry and a ratio of 3:1. Perform enzymatic hydrolysis at pH 5.5 and 55°C for 1.5 h. Comparative Example 4

[0031] Based on Example 1, step (3) was adjusted, and the three enzymes were added in order (preferably cellulase was used to break the cell wall first), and the most suitable pH, temperature, addition amount, and enzymolysis time in the single factor test of the three were used. The details are as follows: (3) Enzymatic reaction: First, add cellulase at a rate of 30 U / g corn slurry to the fresh corn slurry of black pearl glutinous corn, and perform enzymatic hydrolysis at pH 5.0 and temperature 60°C for 1.0 h. Then, add neutral protease at a rate of 15 U / g corn slurry, and perform enzymatic hydrolysis at pH 6.5 and temperature 50°C for 1.5 h. Finally, add α-amylase at a rate of 20 U / g corn slurry, and perform enzymatic hydrolysis at pH 6.0 and temperature 60°C for 1.0 h. Determination method and results:

[0032] The performance indicators of Examples 1-4 and Control Examples 1-4 were measured: It should be noted that in addition to the method used in this application, other conventional methods in the art may also be used, and adjustments may also be made to the method of this application to present differences between groups.

[0033] Dispersion performance measurement: including but not limited to soluble protein content, soluble sugar content, water solubility index, and dispersion index.

[0034] Determination of soluble protein content: The soluble protein content in the product was determined by the Folin phenol method.

[0035] Determination of soluble sugar content: The soluble sugar content was determined by the anthrone-ethyl acetate method.

[0036] Determination of water solubility index (WSI): This index reflects the penetration rate of water into solid particles in the product and the diffusion of soluble components out of the particles.

[0037] The specific steps are as follows: accurately weigh 2.50 g of glutinous corn flour sample into a 50 mL centrifuge tube, add 30 mL (90°C) deionized water, stir at 90°C for 5 min, centrifuge at 600 r / min for 35 min, pour the supernatant into a dried constant weight weighing bottle, and dry in a 105°C oven to constant weight. The calculation formula is as follows: Water solubility index (%) = supernatant dry weight / sample dry weight × 100%.

[0038] Determination of dispersion index: Accurately weigh 1g of sample, pass it through a glass funnel with an inner diameter of 1cm, slowly add it into a beaker filled with 20mL of 40℃ deionized water, stir it at 40r / min under a magnetic stirrer, and record the time (seconds) for the powder to be completely dispersed in the water, which is the dispersion index. The results of the preparation performance test are shown in Table 1: Rheological properties measurement: including but not limited to the measurement of loose bulk density, tapped bulk density and angle of repose.

[0039] The specific steps are as follows: accurately weigh 10 g (m 1 ) sample, transfer it to a 25 mL measuring cylinder through a funnel, hold the top of the measuring cylinder with your hand, place the bottom of the measuring cylinder on a vortex shaker and oscillate until the scale of the measuring cylinder stops decreasing. Note the scale V at this time. l Continue to tap the bottom of the measuring cylinder gently on the table until the scale of the measuring cylinder stops decreasing. Note the scale V at this time. 2 The calculation method is as follows: Loose bulk density (BD, g / mL) = 10 / V 1 Tapped bulk density (TD, g / mL) = 10 / V 2 V l : Place the bottom of the measuring cylinder on a vortex shaker and oscillate until the scale shows that the cylinder scale no longer decreases; V 2 : Gently tap the bottom of the measuring cylinder on the table until the measuring cylinder scale shows that it will not go down any further.

[0040] Determination of the angle of repose: The specific steps are as follows: fix a glass funnel on an iron frame, with the lower end of the funnel 5 cm above the operating platform. The sample powder slowly forms a powder cone on the platform through the funnel. When the top of the cone contacts the bottom of the funnel, stop adding powder and use a vernier caliper to measure the diameter D of the cone. The calculation method is as follows: Angle of repose (°) = tan -1 (10 / D) D: Vernier caliper measures the diameter of the cone.

[0041] The results of rheological properties are shown in Table 2: Determination of antioxidant activity of in vitro digestion products: including but not limited to hydroxyl radical scavenging rate and reducing power.

[0042] The obtained black glutinous corn flour product was subjected to simulated in vitro protein digestion according to conventional methods, the enzyme was inactivated and then cooled to room temperature, freeze-dried and then dried to constant weight, the protein content was determined, a sample solution with the required protein concentration was prepared, and the hydroxyl radical scavenging rate and reducing power were determined.

[0043] Determination of hydroxyl radical scavenging rate: The specific steps are as follows: take 2 mL of sample solution with a protein concentration of 2 mg / mL, add 2 mL of 6 mmol / L ferrous sulfate and 2 mL of 6 mmol / L hydrogen peroxide, mix well and let stand for 10 min, then add 2 mL of 6 mmol / L salicylic acid, shake and mix well, let stand for 30 min, and then measure the absorbance at 510 nm and record it as A. i ; The absorbance value measured by replacing salicylic acid with deionized water is recorded as A j The blank control group used deionized water instead of the sample, and the absorbance value was recorded as A 0 ; The calculation formula is: K(%) = [1-(A i -A j ) / A 0 ]×100% Determination of reducing power: The specific steps are as follows: Take 2 mL of sample solution with a protein concentration of 2 mg / mL, add 2 mL of 0.2 mol / L phosphate buffer with a pH of 6.6, then add 2 mL of 1% potassium ferricyanide solution and shake well, place in a 50°C water bath for 20 min, then add 2 mL of 10% trichloroacetic acid solution, shake quickly, and centrifuge at 4000 rpm for 10 min. Take 2 mL of supernatant, add 2 mL of deionized water and 0.4 mL of 0.1% ferric chloride solution, shake well, bathe at 50°C for 10 min, and measure its absorbance at 700 nm. The results of the determination of hydroxyl radical scavenging rate and reducing power of the in vitro digestion products of black pearl glutinous corn enzymatic modification are shown in Table 3: Table 1 Test results of corn flour preparation performance

[0044] Note: Different lowercase letters in the same column indicate significant differences ( P< 0.05).

[0045] As shown in Table 1, compared with the control group, the WSI of the modified waxy corn product of the present application was significantly increased ( P<0.05 ), increased by 16.63%-60.63%. Compared with the control group, the soluble protein and soluble sugar content of the modified glutinous black corn product prepared in the present application were significantly increased, with soluble protein increased by 5.66%-24.18% and soluble sugar increased by 9.92%-34.64%. Compared with the control group, the dispersion index decreased.

[0046] Table 2 Effects of various treatments on the flow properties of black pearl glutinous corn flour

[0047] Note: Different lowercase letters in the same column indicate significant differences ( P< 0.05).

[0048] As shown in Table 2, compared with the control group, the loose bulk density and tapped bulk density of the powder prepared in this application are significantly reduced. P<0.05 ), decreased by 21.42%-54.35% and 13.85%-39.19% respectively, which indicates that the structure between particles has become looser. The angle of repose is one of the main characteristics of the friction between powder particles. Compared with the control group, the angle of repose is also significantly reduced, indicating that the fluidity is significantly improved.

[0049] Table 3 Determination of hydroxyl radical scavenging rate and reducing power of corn flour in vitro digestion products

[0050] Note: Different lowercase letters in the same column indicate significant differences ( P<0.05).

[0051] As shown in Table 3, the hydroxyl radical scavenging ability and reducing power of the in vitro digestion products of black pearl glutinous corn enzymatic modification are higher than those of the control group. The hydroxyl radical scavenging rate of the in vitro digestion products of the glutinous corn modified in this application is as high as 90.33%-96.99%. This is because the active sites of corn protein after enzymatic hydrolysis are exposed, which makes it easier to combine with hydroxyl radicals and remove them, thereby increasing the hydroxyl radical scavenging rate. Enzymatic treatment gives the in vitro digestion products of glutinous corn modification a strong reducing ability of 0.891-0.893. The results show that the addition of α-starch agent is beneficial to improving the reducing power of the in vitro digestion products of glutinous corn modification. This is because a large number of reducing groups can be exposed after effective enzymatic hydrolysis, and the antioxidant capacity is improved.

[0052] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing high-quality whole-grain corn flour from fresh glutinous corn, characterized in that: Follow these steps: (1) Drying pretreatment: corn kernels are taken from fresh ears of glutinous corn, mixed and homogenized at high speed, corn slurry is spread on a stainless steel plate, and the corn slurry is naturally dried at room temperature until constant weight is reached. After drying, the corn slurry is crushed with a pulverizer, sieved to obtain fresh slurry corn flour, and sealed in a desiccator for storage; (2) Preparation of fresh corn syrup: fresh corn flour and deionized water are mixed and dispersed in a mass ratio of 2:1 (w / w) to obtain fresh corn syrup; (3) Enzymatic reaction: Add neutral protease and cellulase to fresh corn slurry at a rate of 15-30 U / g corn slurry and a ratio of 2:

1. Perform enzymatic hydrolysis at pH 5.5-6.0 and 50-60°C for 1.0-2.0 h. Then continue to add α-amylase and cellulase at a rate of 20-30 U / g corn slurry and a ratio of 2:

1. Perform enzymatic hydrolysis at pH 5.0-6.0 and 55-60°C for 1-2.0 h. (4) Inactivation of enzyme: After the enzymatic reaction is completed, inactivate the enzyme in a 95°C water bath for 5 minutes and cool to room temperature; (5) The enzyme-inactivated corn slurry is freeze-dried to obtain whole-grain corn flour.

2. The method for preparing high-quality whole-grain corn flour from fresh glutinous corn according to claim 1, characterized in that: The drying pretreatment in step (1) is replaced by the following pretreatment: corn kernels are taken from fresh ears of glutinous corn, mixed and homogenized at high speed, corn slurry is spread on a stainless steel plate, and the corn slurry is subjected to continuous hot air drying at 70-80° C. until constant weight is obtained. A mild Maillard reaction occurs during the drying process. After drying, the corn slurry is crushed with a crusher, sieved to obtain fresh slurry corn flour, and sealed in a desiccator for storage.

3. The method for preparing high-quality whole-grain corn flour from fresh glutinous corn according to claim 1 or 2, characterized in that: In the pretreatment, corn kernels are taken from fresh ears of glutinous corn, mixed and homogenized at 2500-3000 r / min for 90-120 s; spread to a thickness of 1-2 cm; crushed and sieved through a 100-150 mesh sieve to obtain fresh corn starch; in the step (2), fresh corn starch is prepared by mixing fresh corn starch with deionized water in a mass ratio of 2:1 (w / w), and dispersing at 50-100 r / min for 90-120 s.

4. The method for preparing high-quality whole-grain corn flour from fresh glutinous corn according to any one of claims 1 to 3, characterized in that: The step (3) enzymatic reaction: adding neutral protease and cellulase to fresh corn slurry, the amount of neutral protease and cellulase added is 30U / g corn slurry, the amount ratio of neutral protease and cellulase is 2:1, and enzymolysis is carried out at pH=5.5 and temperature 55°C for 1.5h; then continuing to add α-amylase and cellulase, the amount of α-amylase and cellulase added is 30U / g corn slurry, the amount ratio of α-amylase and cellulase is 2:1, and enzymolysis is carried out at pH=5.5 and temperature 55°C for 1.5h.

5. The method for preparing high-quality whole-grain corn flour from fresh glutinous corn according to any one of claims 1 to 3, characterized in that: (3) Enzymatic reaction: Neutral protease and cellulase were added to fresh corn slurry at a rate of 15 U / g corn slurry and a ratio of 2:

1. Enzymatic hydrolysis was carried out at pH 5.5 and 55°C for 2.0 h. α-amylase and cellulase were then added at a rate of 15 U / g corn slurry and a ratio of 2:

1. Enzymatic hydrolysis was carried out at pH 5.5 and 60°C for 2.0 h.

6. The method for preparing fresh glutinous corn-derived high-concentration corn flour according to any one of claims 1 to 5, characterized in that: In the step (1), the fresh glutinous corn ears are fresh black pearl glutinous corn ears, and the room temperature is 20-25° C.; in the step (4), the enzyme is inactivated: after the enzymatic reaction is completed, the enzyme is inactivated in a water bath at 95° C. for 5 minutes, and then cooled to room temperature; and in the step (5), the freeze-drying is vacuum freeze-drying.

7. Whole-grain corn flour prepared according to the method for preparing high-quality whole-grain corn flour from fresh glutinous corn according to any one of claims 1 to 6.

8. Use of the method according to any one of claims 1 to 7 to significantly improve the solubility, rheological properties, antioxidant properties of digestion products, and flavor and taste of whole-grain corn flour.

9. The use according to any one of claims 1 to 8, characterized in that: WSI increased by 16.63%-60.63%, soluble protein increased by 5.66%-24.18%, and soluble sugar increased by 9.92%-34.64%; the loose bulk density and tapped bulk density decreased by 21.42%-54.35% and 13.85%-39.19%, respectively; the hydroxyl radical scavenging ability and reducing power of the enzymatically modified in vitro digestion products were 90.33%-96.99% and 0.891-0.893, respectively; the angle of repose and dispersion index were significantly reduced.

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