Effect of Pre-drying on Oil Penetration and Textural Characteristics of Deep-Fried Battered and Breaded Fish Nuggets

This purpose of this study was to evaluate the effect of pre-drying on the oil penetration and texture characteristics of deep-fried battered and breaded fish nuggets. Battered breaded fish nuggets (BBFNs) were dried in a drying oven and dried at 40 ℃ for 3, 4.5, 6, 7.5 and 9 h and deep fried at 180 ℃ for 60 s. Moisture state in dried BBFNs and deep-fried BBFNs was measured, and the oil content and distribution, microstructure and texture characteristics of deep-fried BBFNs were analyzed. The absorption of oil during deep-fat frying was simulated. The results showed that after deep-fat frying, the contents of strongly bound water (T₂₁), weakly bound water (T₂₂) and free water (T₂₃) in the crust, the content of strongly bound water in the fish nuggets, the content of weakly bound water inside muscle fibers, and the content of free content outside muscle fibers were reduced. As the drying time increased, the starting time of peak T₂₂ for the deep-fried crust gradually decreased, indicating declined freedom degree of water, and the signal intensity of peaks T₂₁ and T₂₂ decreased, suggesting that the bound water was converted to free water. In addition, only fish nuggets with 9 h drying showed a left shift in peak T₂₂. The surface oil (SO) and total oil (TO) contents of deep-fried BBFNs decreased while the penetrated surface oil (PSO) content increased. The crust structure was first tight and then became rough, and the surface of the fish was smooth first and then exhibited cracks and holes. The fluorescence intensity of the crust became weaker gradually. The Sudan reddyed region in the crust decreased while that of the junction between the crust and the fish nuggets increased gradually. The hardness and crispiness of the crust first decreased and then increased, while the elasticity and chewiness of the fish nuggets presented the opposite trend. These results indicated that pre-drying alleviated the freedom degree of moisture in BBFNs, and changed the microscopic structure of deep-fried BBFNs, thereby affecting the oil penetration and texture characteristics. The study may provide a theoretical basis and scientific guidance for the large-scale production of low-fat deep-fried BBFNs.