Red swamp crawfish were blanched, vacuum packaged, frozen at three different temperatures (−20, −40 and −55 ℃) until the internal temperature reached −15 ℃, and stored at two different temperatures (−20 and −40 ℃) for up to 24 weeks. The fat and free fatty acids (FFAs) contents, fatty acid composition, peroxide value (POV), and thiobarbituric acid reactive substance (TBARS) value of crawfish meat were measured to investigate the effect of freezing temperature and frozen storage temperature on lipid oxidation. The results showed that as storage time prolonged, the contents of fat, unsaturated fatty acids (UFAs), and polyunsaturated fatty acids (PUFAs) decreased significantly (P < 0.05), while the contents of FFAs and saturated fatty acids (SFAs) as well as POV and TBARS values increased significantly (P < 0.05). At the same frozen storage temperature, the POV and TBARS values of crayfish meat frozen at –20 ℃ were significantly higher than those of crayfish meat –40 and –55 ℃, while there was not a significant difference in FFAs contents or fatty acid composition; at the same frozen temperature, the fat and FFAs contents, POV, and TBARS values of crayfish meat stored at–20 ℃ were significantly higher than those of crayfish meat stored at –40 ℃, but the contents of UFAs and PUFAs during storage at –20 ℃ were slightly lower than at –40 ℃. In addition, SFAs contents during storage at –20 ℃ was higher than, but not significantly different from, those during storage at –40 ℃. These results indicated that freezing at –40 or –55 ℃ and frozen storage at –40 ℃ alleviated the degree of hydrolysis and oxidation of lipids from crayfish meat.

To investigate the effects of roasting temperature and time on the quality attributes of roasted grass carp fillets, fresh grass carp fillets were deodorized, salted and roasted in an electric oven at different temperature (180, 200, or 220 ℃) for 15 min or 200 ℃ for different periods of time (10, 15, or 20 min). The shear force, color, moisture, ash and fat contents, thiobarbituric acid reactive substances (TBARS) value, acid value, and volatile composition of roasted fish were evaluated, the physicochemical properties (secondary structure, surface hydrophobicity, and total sulfhydryl group and disulfide bond contents) of myofibrillar protein extracted from roasted fish, and sensory evaluation was also conducted. The results showed that as the roasting temperature increased or the roasting time prolonged, the shear force increased; the color parameter L^* value decreased, while the a^* and b^* values showed an upward trend; the color became deeper; the tenderness and chroma first improved and then deteriorated; the sensory score increased first and then decreased; the moisture content had a significant declining trend (P < 0.05); the fat and ash contents decreased first and then increased; the degree of lipid oxidation increased gradually; the relative contents of aldehydes and alcohols displayed a decreasing trend; the secondary structure of myofibrillar protein changed from a stable state to an unstable state; the surface hydrophobicity index (H₀) and the content of disulfide bonds increased gradually, while the content of total sulfhydryl groups decreased gradually. Compared to other roasting conditions, the roasted grass carp fillets at 200 ℃ for 15 min, having a bright golden color, tasted better and had higher moisture content and lower fat content, and the structure of myofibrillar protein from it was more complete. These results suggested that the roasting temperature and time significantly affected the physicochemical properties of protein and lipid oxidation in grass carp fillets, thereby resulting in changes in the quality attributes of roasted grass carp fillets.

In the present study, the effect of the interaction between wheat starch and gluten on oil distribution in deep-fried battered and breaded fish nuggets (BBFNs) from silver carp surimi was investigated. Deep-fried BBFNs were prepared using batters consisting of wheat starch (WS) and gluten (WG) blends (at mass ratios of 15:1, 13:1, 11:1, 9:1 and 7:1), and then the surface hydrophobicity (H₀), free sulfydryl content, disulfide bond content, secondary structure of WG and the crystalline structure of WS in the crust, as well as the surface oil and penetrated surface oil contents of deep-fried BBFNs were evaluated. The microstructure and oil distribution in the crust were also observed. The results showed that as the WS/WG ratio decreased, the H₀ value increased firstly then decreased, and the free sulfydryl and disulfide bond contents gradually decreased and increased, respectively. Meanwhile, the β-turn structure of WG was gradually converted into β-sheet, and the surface oil and penetrated surface oil contents of deep-fried BBFNs as well as the relative crystallinity of WS decreased firstly then increased. The size of pores in the crust and oil distribution decreased at first and then increased. Among the tested WS/WG ratios, deep-fried BBFNs with a WS/WG ratio of 11:1 had the highest H₀ (8990), and the lowest surface oil (2.1%) and penetrated surface oil contents (5.8%), and the lowest relative crystallinity of WS (17.8%), and the crust exhibited the most compact microstructure and the least oil distribution. Therefore, the interaction between WS and WG is affected by changes in WS/WG ratio, which can in turn affect oil distribution in deep-fried BBFNs.

This study was executed in order to investigate quality deterioration caused by lipid oxidation during the frozen storage of Acipenser sinensis. Fish pieces were stored at -18 ℃ for 24 weeks after being frozen using a freezer (-20 or -50 ℃) or liquid nitrogen (-80 or -110 ℃). The central temperature, fat and free fatty acid (FFA) contents, fatty acid composition, peroxide value (POV), thiobarbituric reactive substance (TBARS) value, and fluorescent compound content were measured and the microstructure of muscle fibers was also observed during the storage period for the purpose of evaluating the influence of freezing methods on lipid oxidation and muscle microstructure in Acipenser sinensis during frozen storage. The results showed that with increasing storage time, the fat and polyunsaturated fatty acid (PUFA) contents of the four fish samples decreased, while POV, TBARS value, and the contents of FFAs, saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and fluorescent compounds increased. The gap between muscle fibers increased, which was accompanied by breaking of myofibrils. In addition, the contents of fat and PUFAs in liquid nitrogen frozen samples were significantly higher than those in freezer frozen ones (at the end of storage, the freezer frozen sample frozen at -20 ℃ contained 7.89% of fat compared to 9.13% for the liquid nitrogen frozen one at -80 ℃), while POV, TBARS value, and the contents of FFAs, SFAs, MUFAs and fluorescent compounds were significantly lower than those in freezer frozen samples (P < 0.05), and the muscle fiber structure was more complete. The above results indicated that liquid nitrogen frozen alleviated the degree of myofibrillar damage and lipid hydrolysis in Acipenser sinensis during frozen storage, thereby reducing the speed of lipid oxidation.

To investigate the effect of dietary fiber on batter characteristics and oil penetration in deep-fried battered and breaded fish nuggets (BBFNs) from silver carp surimi, deep-fried BBFNs were prepared with model batters (composed of wheat starch and gluten) added with 8% apple fiber, 6% soybean fiber or 12% wheat bran fiber. The moisture adsorption isotherms of dietary fiber, wheat starch and gluten, and the pick-up of BBFNs were evaluated, the viscosity, rheological behavior and calorimetric properties of batters were measured, and the thermogravimetric properties of the crust, the water state and oil penetration of deep-fried BBFNs were also evaluated. The results showed that the moisture absorption capacity of wheat starch was the largest, followed by soybean fiber, apple fiber, wheat bran fiber, and gluten. Compared to that the control group (without dietary fiber), the addition of 8% apple fiber, 6% soybean fiber or 12% wheat bran fiber significantly increased the viscosity of batters and the pick-up of BBFNs (P < 0.05). The loss modulus (G’) and storage modulus (G”) of batters were decreased firstly, then increased rapidly and ultimately remained stable with an increase in oil temperature, and soybean fiber resulted in the highest G’ and G”, which contributed to the fastest formation of gels and the highest thermal stability of the crust after frying. The addition of each of the dietary fibers resulted in transformation of free water into bound water and increased the total moisture content of the crust. Soybean fiber resulted in the lowest oil penetration in deep-fried BBFNs, followed by apple fiber, wheat bran fiber and the control group. This study indicated that the addition of the three dietary fibers in model batter systems can accelerate the formation of gels, significantly improve the strength of the gels formed, and ultimately inhibit oil penetration in deep-fried BBFNs.