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.

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.