| The pork back-fat is usually used in the processing of traditional emulsion-type sausage. After mixed, a part of back-fat melts into oil droplets. The myofibrillar proteins play an important role as emulsifying agent by absorbing on them. However, today the customers care about the nutrition and health, so the high content of saturated fatty acid in pork back-fat does not conform to this new tendency. In order to reduce the content of saturated fatty acid in the meat products, pre-emulsified vegetable oil is used to replace animal fat. But studies show that sodium caseinate and myofibrillar proteins may have an interaction of competitive emulsification on the surface of oil droplet or animal fat, and may result in the modification of constructure and stability of the composite emulsion.In this study, vegetable oil was firstly emulsified with different content of sodium caseinate, and then with the myofibrillar proteins, formed a SC-MP-vegetable oil composites emulsion system. The interaction between sodium caseinate and myofibrillar proteins was investigated by SDS-PAGE electrophoresis and its effects on the emulsion were studied through measuring particle size and distribution of the oil droplets, viscosity, emulsifying activity index (EAI) and emulsifying stability index (ESI) of the emulsion. Also the texture characteristics and water holding capacity (WHC) of the heat-induced gel based on this emulsion system were investigated. They provide a theoretical basis for the development of the low-saturated fatty acid emulsion-type meat products.The specific content and results are as follows:(1) Effects of five different emulsion methods on amount of protein adsorbed per unit surface of protein-emulsified vegetable oil composites emulsion was ingestigated. SDS-PAGE electrophoresis was used to detect the adsorbed proteins on the interface of the emulsion. The results showed that sodium caseinate had a better capacity of emulsion than myofibrillar proteins, and that it was able to emulisify oil before myofibrillar proteins. The effects of vegetable oil pre-emulsified with different content of sodium caseinate (O、0.5%、1.0%、1.5%、2.0%、2.5%、3.0%) on the emulsion system were then investigated. The results showed that with the increase of sodium caseinate content, the particle size of the oil droplets significantly decreased, the viscosity increased from9.55Pa·s to13.40Pa·s, which suggest that the sedimentation rate reduced and the system was more stabilized. Besides, sodium caseinate can significantly improve EAI and ESI of the composite emulsion.(2) Effects of vegetable oil pre-emulsified with different content of sodium caseinate on texture characteristics and WHC of the heat-induced gel of myofibrillar proteins were studied. The water mobility of the gel was characterized through using low-field nuclear magnetic resonance (NMR) T2relaxometry. The results showed that sodium caseinate can significantly improve firmnes, springiness and WHC of the gel. The NMR data showed three states of water:bound, mobile and free water, and their energy exchange. With the increase of sodium caseinate content, T22relaxation time decreased from292.13ms to192.20ms and its peak area fraction increased from73.52%to90.37%, so water mobility capacity decreased and the system stability improved. Correlation among emulsifying and gelling properties showed that ESI had a significant positive correlation with viscosity of the emulsion (correlation coefficient is0.88) and WHC(correlation coefficient is0.88); T22relaxation time had a significant negative correlation with WHC(correlation coefficient is-0.90); T21relaxation time and firmness had a significant negative correlation (correlation coefficient is-0.90). |
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