Preparation of enzymatic hydrolysate of blue round scad (Decapterus maruadsi) protein isolate and its anti-retrogradation effect on rice starch

The protein from marine fish is regarded as an ideal resource of high-quality protein thanks to their high nutritional value and good digestibility. The application of fish protein in infant rice flour products can not only give the product a richer flavor, but also improve the nutritional value of the product and meet the nutritional requirements of infants. To further expand the application of marine fish protein in food products, the enzymatic modification of blue round scad (Decapterus maruadsi) protein isolate was carried out to obtain blue round scad protein isolate hydrolysate (BPIH) with good solubility. The inhibitory effects of BPIH on short-term retrogradation of rice starch (RS) was investigated. The enzymatic modification process was optimized by response surface methodology, and was added to RS at concentrations of 3%, 6% and 9% (W/W). The measurements of coagulability, dynamic viscoelasticity, and thermal properties and microstructure of RS were carried out to evaluate the anti-retrogradation activities of BPIH. The results showed that the optimal conditions determined by response surface methodology were: enzyme bottom ratio of 5 000∶1 (U/g), enzymatic digestion time of 3 h, feed-to-liquid ratio of 1.00∶3.81, enzymatic digestion temperature of 46.36 ℃, and enzymatic pH of 6.30. The actual value of nitrogen solubility index (NSI) was 85.41%±0.82%, which was close to the predicted value of 86.37%. The degree of BPIH hydrolysis reached 21.62% under these enzymatic conditions. The peptides less than 1,000 u in BPIH accounted for 79.94%, which were mainly small oligopeptides. The addition of BPIH attenuated the coagulation phenomenon of RS, reduced the energy storage modulus (G') of RS during storage at 4 ℃, and significantly reduced the peak temperature (T_p) and enthalpy (ΔHr) of RS after aging (P<0.05); the rice starch added with BPIH had larger pores in the microstructure after aging, which enhanced the ability of starch to retain internal water after pasting. These results indicate that BPIH can inhibit the formation of gel network and microcrystalline structure of RS during storage at 4 ℃, and may also limit the aggregation between starch molecules and inhibit or delay the short-term aging of RS. The present study provides a theoretical reference for the application of the enzymatic hydrolysate of blue round scad protein isolate in food protein ingredients.