In order to improve the quality of surimi products, the effects of safflower seed oil emulsion (10 mL/100 g) loaded with resveratrol on the gel properties, microstructure and oxidative stability of Nemipterus virgatus surimi gel were investigated, and the effects of resveratrol addition at different levels (0.1%–0.3%) on the quality of surimi gels were compared. The results showed that the whiteness, water-holding capacity and bound water content of N. virgatus surimi gel were increased by adding safflower seed oil emulsion, together with an improvement in the texture characteristics and a decrease in the cooking loss percentage (P < 0.05). In addition, the pore size of the three-dimensional network structure of the gel was reduced. The distribution of oil droplets in the gel matrix with safflower seed oil emulsion was not uniform, the average diameter of oil droplets was great than 2.0 μm, and the oxidation of oil increased with storage time (P < 0.05). Furthermore, after adding safflower seed oil emulsion loaded with resveratrol, the whiteness and water-holding capacity were significantly increased together with a decrease in the cooking loss percentage (P < 0.05) and a significant enhancement in the texture and oil oxidation stability of the gel (P < 0.05). Resveratrol still had strong antioxidant activity in the surimi gel matrix. Resveratrol could contribute to the emulsification of safflower seed oil, making fine oil droplets be evenly distributed in the gel matrix, and the interaction between resveratrol and proteins in surimi promoted the formation of gel networks. The average diameter of oil droplets in the emulsion with 0.3% resveratrol was less than 1.5 μm, and the three-dimensional network structure of the gel with 0.3% resveratrol exhibited the smallest pore size and a uniform and dense spatial hierarchy. Therefore, safflower seed oil emulsion loaded with resveratrol could improve the gel characteristics of N. virgatus surimi and enhance the oxidative stability of the gel, which will be useful for the development of new surimi products.

In this study, the effect of addition of gallic acid (GA) (0%–0.25%) on the gel properties, microstructure and intermolecular forces of surimi from Nemipterus virgatus, prepared by a two-step heating method, was investigated. The surimi was digested under in vitro gastrointestinal conditions and evaluated for antioxidant activity and cholesterol-lowering activity in order to determine the improving effect of GA addition on the functional properties of surimi gels. The results showed that addition of GA could improve the gel strength and texture properties, but worsen the whiteness of surimi gels. Surimi gels with 0.15% of GA had the best texture properties and highest whiteness and water-holding capacity as well as a dense microstructure, and the major chemical force maintaining the gels was disulfide bonds. The results of digestion in vitro showed that addition of GA increased the protein digestibility of surimi gels (P < 0.05), and enhanced the biological activity of the digested products (P < 0.05). The scavenging percentages of the digested surimi gel with 0.15% of GA toward 1,1-diphenyl-2-picrylhydrazine (DPPH) radical, 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical and hydroxyl radical were increased all 80% (P < 0.05), and the inhibition percentages toward cholesterol esteraseand cholesterol micellization were increased to 50.82% and 41.88%, respectively (P < 0.05). These results indicated that surimi with added GA still retained its biological activity after heat treatment and in vitro digestion. Therefore, addition of an appropriate amount of GA can effectively improve the heat-induced gel properties of N. virgatus surimi while retaining its functional properties, which provides a basis for the development of new functional surimi products.

In order to improve the quality of freshwater fish surimi products, the effect of adding 4% of native cassava starch or modified cassava starch (starch phosphate, hydroxypropyl starch, acetylated distarch phosphate, or a 3:2 (m/m) mixture of acetylated distarch phosphate and hydroxypropyl starch) on improving the quality of surimi gels prepared from frozen tilapia surimi was investigated by measuring texture, rheological properties, water-holding capacity, moisture distribution and microstructure. The results showed that compared with the control group, the whiteness of tilapia surimi gels with native and modified cassava starch significantly decreased (P < 0.05), the gel strength, hardness, chewiness and water-holding capacity significantly increased (P < 0.05), the percentage of cooking loss decreased (P < 0.05), the bound water content increased (P < 0.05), and the microstructure was more uniform and compact. The best gel texture and highest water-holding capacity were achieved with the addition of the modified starch mixture. Low-field magnetic resonance imaging and optical microscopy results showed that both native and modified cassava starch could effectively keep the water in the surimi gel. The native and modified starch could absorb water and expand during the heating process, concentrating and filling the surimi gel network structure, and the surimi gel structure with the modified starch mixture was most compact and uniform. Therefore, addition of acetylated distarch phosphate-hydroxypropyl starch mixture can effectively improve the quality of tilapia surimi products, which will provide theoretical support for the development of freshwater fish surimi products.