The Effects Of Different Solid Concentrations On Wheat Enzymatic Hydrolysis

At present, wheat is one of the most important food crops in the world. Wheat gluten is the by-product in wheat starch production. Because of its unique composition, wheat gluten is very difficult to dissolve in the water. For its low solubility, it limited the application of wheat gluten in food and non-food area. It can improve the functional properties of protein and the production of polypeptides with different physiological activities significantly by enzymatic modification. For its low investment, low energy consumption, low cost, high utilization rate of equipment, simplified process and increased efficiency of the plant, high solid concentration hydrolysis has become a hot spot in research.It is studied in this thesis that the effects of different solid concentrations on wheat gluten enzymatic hydrolysis with the employment of Alcalase and PR23 enzyme. The physical and chemical characteristics of two enzymatic hydrolysis systems with different solid concentrations were monitored during the whole process. The enzymatic hydrolysis sensitivity and features of hydrolysates of two enzymatic hydrolysis systems were studied. The kinetic equation of the enzymatic hydrolysis under different solid concentrations was established. The potential inhibiting factors in high solid concentration were analyzed. All of these researches were aimed to providing a theoretical basis and guidance for the application of high solid concentration in wheat gluten enzymatic hydrolysis.The physical and chemical characteristics of two enzymatic hydrolysis systems with different solid concentrations were monitored during the whole hydrolysis process. It is found that the higher solid concentration was, the less pH decreased in Alcalase system, and the more pH increased in PR23 system. The pH changed the most in the first 6 h of the hydrolysis in both systems. The water activity of both systems showed similar characteristics. It is found that the higher solid concentration was, the more and the faster water activity decreased. The water activity of PR23 hydrolysates was lower than that of Alcalase system. The dark matter in two systems increased with the solid concentration rising and the content of dark matter in Alcalase system was higher than that in PR23 system. The higher solid concentration was, the greater red and yellow index changed. Greater changes were observed in PR23 system. The viscosity and shear stress increased when solid concentration increased. During the whole process, the viscosity and shear stress dropped all the time in Alcalase system, but the viscosity and shear stress would grow at the beginning of the process.The enzymatic hydrolysis sensitivity of wheat gluten with different solid concentration in the whole process was studied. The hydrolysates with higher solid concentrations had a higher content of amino nitrogen and a greater increase. The content of amino nitrogen was larger in PR23 hydrolysis system. Lower degree of hydrolysis was in the sample with higher solid concentration, which indicated that increasing solid concentration led to inhibitory in hydrolysis. The content of total nitrogen, quantity of centrifugal suspensions and protein recovery were higher in the hydrolysates with lower solid concentration. The total nitrogen content in suspensions of Alcalase system was less than that in PR23 system, but it had more centrifugal suspensions and greater protein recovery. The hydrolysates with larger solid concentration had greater content of total acid and increased more. PR23 system had larger quantity of total acid. The molecular weight of majority of peptides in hydrolysates was less than 1kDa. With enzymatic hydrolysis going on, the ratio of this fraction declined, but the content increased at the same time. There were more peptides whose molecular weight is more than 10 kDa contained in the hydrolysates with higher solid concentration. The change of molecular weight distribution differed with the solid concentration. It was conducive to preserve glutamine in PR23 hydrolysates, whose ration of amino acid is more reasonable and more nutritional. The hydrolysates with higher solid concentration had lower peptide yields, however, the change of the yield was more obvious. Hydrolysates obtained by PR23 had a higher peptide yield. Increasing solid concentration led to a reduction of average length of peptide. In the whole process, the average length of peptide was smaller and changed less in the hydrolysates obtained by PR23.According to the changes of the degree of hydrolysis in wheat gluten hydrolysates with different solid concentrations, a kinetic model was built and the relationship between kinetic parameters and solid concentration was found. There were three characteristics in the hydrolysis system with high solid concentration, high viscosity, low water content and the existence of solid effect, which might be the reasons for poor efficiency of enzymatic hydrolysis.