Ultrasound-assisted Modification Of Cowpea Protein Glycosylation And Its Application In Sausages

Kidney bean protein contains eight essential amino acids, which belongs to the full-price protein, but it is susceptible to the changes of pH and temperatures et al resulting in the protein denaturation and impede its application in the food industry. In order to improve the functional properties of kidney bean protein and make it be better utilized, the glycosylation of kidney bean protein is modified assisted with ultrasound and the optimum process conditions are determine in this study according to the theory and methods of biochemistry, protein chemistry and spectroscopy. Moreover, the changes in the solubility, emulsibility, whipability and hydrophobicity, thermal denaturation temperature and other properties of the modified protein are in-depth discussed in this study. Numerical analysis methods like Fourier transform infrared spectroscopy(FTIR)and Raman spectroscopy are used to analyze its structure, and to investigate its application and additive in the sausage production process. The main conclusions are as follows:Firstly, the process to modify the kidney bean protein glycosylation by ultrasound-assisted method is optimized. The effects of temperature, time, ultrasonic power, pH, kidney bean protein-to-glucosamine ratio and kidney bean protein concentration on the degree of grafting(DG)were also explored. And with the significant factors as single factors, the DG of kidney bean protein and glucosamine as response value, the software of Design Expert 8.0.6.1 is use to analysis the response surface. And the kidney bean protein that is not modified assisted with ultrasound is used for comparison. The optimal conditions were as follow: reaction temperature 70℃, ultrasonic power 270 W, ultrasonic time 40 min, pH 9.75, kidney bean protein-to-glucose ratio 1:2 and the kidney bean protein concentration 9mg/mL, DG 39.07%. The difference with theoretical prediction(39.63%) is 0.55%, which indicates that the actual verification is consistent with the model. And this value is greater than the DG of not assisted with ultrasound(26.32%), which indicating ultrasound can improve the DG of kidney bean protein and glucosamine and the test is feasible.Secondly, the functional propertie of kidney bean protein, glycosylated kidney bean protein with ultrasound(GU) and glycosylated kidney bean protein not with ultrasound(GNU) were researched. The results showed that: compared with the kidney bean protein, the optimum solubility of GU and GNU increased by 17.3% and 10.10%, respectively; the emulsibility increased by 20.89% and12.59%, respectively; the emulsion stability increased by 16.52% and 10.02%, respectively; the whipability increased by 2.5% and 1.25%, respectively. But the foam stability decreased 14.23% and 9.73%, hydrophobicity decreased 280 Ho 、 110 Ho, and denaturation temperature decreased 3.1℃ and 1.95℃, respectively. From polyacrylamide gel electrophoresis(SDS-PAGE) can be seen, proteins react with glucose resulting in the color of subunit bands lighter and forming protein-sugar copolymers. And from infrared spectroscopy can be seen, they were all β- sheet structure-based, and compared with the kidney bean protein, the helix structure of α-, β- sheet structure of modified protein were increased, the β- corner structure and random coil were decreased, which indicating kidney bean protein and amino sugars occurred graft reaction and changed its structure. From raman spectrum can be seen, compared with the kidney bean protein, the α-helix structure, β-sheet structure were increased, β-corner structure, random coil structure of modified kidney bean protein were all declined, which indicating glycosylation modification had effect on secondary structure of kidney beans.Thirdly, this thesis respectively applied kidney bean protein and ultrasound-assisted glycosylated modified kidney bean protein into the sausage system and discussed the influence of kidney bean protein and ultrasound-assisted glycosylated modified kidney bean protein addition on the sausage yield rate, overall texture, luster, pH value and sensory evaluation. In addition, the thesis also compared their influence on the sausage quality. The comparison outcome indicated the two sausage yield rates grew with increase of protein addition. In case of 5% of protein addition, the sausage registered its highest yield rate. In case of 2%-3% of protein addition, texture characteristics of two sausages achieved their best performance. Through colorimeter analysis, with the increase of protein, it was found luster(L) increased in the first and then decreased, redness(a) of two sausages weakened, yellowness(b) increased. In case of 3%-5% of addition amount, the yellowness(b) witnessed obvious increase. Through measures of pH value of the two sausages, it was found their pH values grew with increase od protein addition, but the pH values were still not obvious by comparison with pure meat system.Through sensory evaluation and analysis, the sausage was scored 89.03 when the addition amount of ultrasound-assisted glycosylated modified kidney bean protein achieved 2%. In case of 2% addition of kidney bean protein, the sausage was scored 75.86 at maximum. On basis of measured indicators and practical economic factors, the thesis concluded comprehensive quality of pure meat sausages can be greatly improved by adding in 2% of kidney bean protein and ultrasound-assisted glycosylated modified kidney bean protein. In addition, sausages with ultrasound-assisted glycosylated modified kidney bean protein were better than those with just kidney bean protein. This further proved addition of ultrasound-assisted glycosylated modified kidney bean protein could improve yield rate, overall texture characteristics, sensory evaluation and other quality characteristics of sausages.