| Goose is a kind of nutrition and health food, which is low-fat, low cholesterol and high protein. The salt-soluble meat proteins (SSMP) are the most important parts of muscle. Therefore, it is necessary to study the goose salt soluble protein gels and its hydrolysis product features, which has important theoretical significance for the processing of goose and the development of goose high-end products.The effect of sodium chloride, pH, temperature, calcium chloride and phosphates on gel hardness and water-holding capacity (WHC) of goose salt soluble protein were studied in this paper. The regression models of gel hardness and retention were established by the response surface experiment to analyze the impact of various factors on them and the relationship between the two. Furthermore, the effect of substrate concentration, pH and temperature on DPPH radical scavenging rate and degree of hydrolysis were studied according to the regression model. Finally, the hydrolysis products of salt soluble protein were separated roughly into several molecular components by ultrafiltration membranes. The molecular weight range of components of better functional properties was determined by comparing the features of all components. The main results were as follows:1. The optimization of the prepared process of goose salt soluble protein gel. The single factor test showed that NaCl concentration, pH and temperature were the main factors on hardness and water holding capacity of gel. Based on the result of response surface, the optimum preparation conditions of the gel are NaCl (0.65mol/L), pH (7.20 ) and temperature (78℃). In the optimum conditions, the gel hardness and water-holding capacity were 88.05g and 91.48%, respectively.2. Additives on the goose salt soluble protein gel. Tetrasodium pyrophosphate (TSPP), sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP) and calcium chloride were selected to add into the preparation of goose salt soluble protein gel. Using the gel hardness and water retention as indicators, the addition of the four additives was optimized and the optimum ratio of compound phosphate was obtained, the results are CaCl2 (0.02mol/L), TSPP (0.21%), SHMP (0.16%), STPP (0.11%) and the ratio of compound phosphate was 4:3:2. At the same time, the scanning electron microscopy (SEM) results showed that the four additives have different degrees of impact on the ultrastructure of gels. The ultrastructure of gels at optimum conditions is more dense, uniform and smooth. The optimal addition of compound phosphate was identified as 0.3% according to the Hygiene Standards of Food Additives. 3. The optimization of hydrolysis of goose salt soluble protein. The effect of several process parameters: substrate concentration, pH and temperature on the DPPH radical scavenging rate and degree of hydrolysis were examined. Results showed that the optimum extraction conditions are 240mg/5mL substrate concentration, 7.80 of pH value and 48.5℃of temperature. In the optimum conditions, the DPPH radical scavenging rate and degree of hydrolysis were 74.01% and 20.35% respectively, that are basically correspond to model prediction value.4. The functional properties of hydrolysis products for goose salt soluble protein. The hydrolysis products were divided into four components (>5kDa, 3~5kDa, 2~3kDa and <2kDa) with ultrafiltration membranes and they were measured in iron reduction capacity, the ability to inhibit the ACE activity and free radical scavenging. Results showed that the component at the molecular weight range of 2~3kDa has strong antioxidant capacity and the component of <2kDa has strong ability to inhibit the ACE activity. Thus, it is easy to see that the compositions of goose salt soluble protein hydrolysates are multiple, and its functional properties are different. According to the different needs for consumers, the deep processing products of goose can be produced with different functions.
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