Studies On Soybean Protein Modified By Enzyme And Application In Pork Sausage

As one of the crops of the longest history, soybean is an important grain resource. The protein in soybean is a kind of plant protein, which, in comparison with animal protein, has some advantages in both nutrition and price. In order to make up the insufficient provision of plant protein, many countries have taken active measures to make the soy protein a new resource of protein and use it in all kinds of foods. Soybean proteins consist of two major components, 7S and 11S globulins, which play an important role in all phisico-chemical properties of the soybean proteins. In recent years, the molecule structure and thermal stability of 7S and 11S globulins have been studied in other countries, but less researches are performed in our country. At the present, there are not many researches on the technology of respectively modifying 7S and 11S globulins at the molecule structure. In this paper, the most appropriate was screened out from the six types of proteins by comparing the influence on pork sausage of SPI of the six types of soybean. Then the structure and functional properties of 7S, 11S globulins and SPI of this type of protein were compared. After being modified by alcalase, 7S and 11S globulins were subject to investigation and analysis on the change of structural and functional properties and the effect on gel properties of pork sausage. The results are as the following:(1) Selection of Soybean ProteinsThe contents of subunits in six varieties soybean was analyzed by BandScan electrophoresis software. The ratio of 7S and 11S globulins was between 0.25-0.27, and bean 36's was much higher, as 0.268.Through analyzing the effects on gel properties of pork sausage of the six variety of soybean in texture, yield and color, it has been found that the addition of SPI from bean 36 can achieve more remarkable flexibility, chewiness, cohesion, resilience and gel strength than SPI from other variety of soybean. It can also significantly improve the yield and color of pork sausage.(2) The investigation on structural and functional properties of 7S, 11S globulins and SPIPilot studies on the structure of 7S, 11S globulins and SPI were carried out by FT-IR, SEM and ANS. It can be concluded by the results of FT-IR spectrum that the secondary structure of 7S, 11S globulins and SPI are mainlyα-helix, and with equal amplification of SEM, differences in appearance can be observed: SPI monomer has smooth surface, the surface of 7S globulins had hole, and 11S globulins had scalelike surface. In the present study, the sulfhydryl content of SPI was higher than others, but 11S globulins had higher hydrophobic.By comparing the functional properties of SPI, 7S and 11S globulins, the result shows that SPI has more water-soluble protein than the other two, 11S globulins has better gel property and oil-absorbing capacity, 7S globulins has better capabilities in water-holding and emulsification.(3) The application of 7S, 11S globulins and SPI in pork sausageFrom the result of analysis on TPA property, yield and color shown, dupont protein significantly enhanced hardness, springiness, chewiness, resilience, yield and color of pork sausage. In the contrast, the texture of pork sausage by solely adding SPI, 7S and 11S globulins shows worse.(4) The change of structure of 7S and 11S globulins modified by enzyme, and the application in pork sausageThe results indicate the structural and functional properties of 7S and 11S globulins alter after the modification of enzyme. Texture, yield and color of pork sausage by added 7S, or 11S globulins vary with different hydrolysis degree. The results were showed as follow:As the hydrolysis degree increases, Amide II in 7S globulin disappears in infrared spectrum; the surface structure of 7S globulin became loosened, the tightness weakens, oil-absorbing capacity and emulsification ability improve, and the emulsification stability first improves then declines. 7S globulin could enhance property of pork sausage, when the hydrolysis degree is 12%. The results of orthogonal experiments shows that the best condition of technics can be achieved when hydrolysis degree is 11% and the addition1.5g.After the 11S globulin being hydrolyzed, Amide II in 11S globulin disappears in infrared spectrum; the surface structure of 11S globulin becomes loosened, then breaks up. 11S globulin could enhance property of pork sausage, when the hydrolysis degree is 9%. The results of orthogonal experiments showes that the best condition of technics can be achieved when hydrolysis degree is 10% and the addition 1.5g.