The traditional pulverizing technologies face limitations such as nutrient loss, risk of dust explosions and poor properties of powder. Liquid nitrogen freezing and pulverizing (LNFP) is an innovative technology combining low-temperature freezing and pulverizing, which can maintain high nutritional value and performance of food powders. This paper primarily reviews the basic principles of LNFP, the advantages compared to traditional pulverizing technologies (e.g., high-speed airflow pulverizing and ball pulverizing), relevant equipment, applications in animal-derived products, the improvement and innovation direction, and the combination with other food processing techniques. Although LNFP has potential in food processing, it still faces challenges such as food form, thawing loss and enzyme changes. In addition, the cost is also an issue. In the future, combining auxiliary methods with LNFP technology may improve product quality and processing outcomes of animal-derived products.

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.

Phyllostachys praecox shoots were frozen using liquid nitrogen at –60, –90 or –120 ℃ to an internal temperature of –18 ℃, or frozen at –90 ℃ to an internal temperature of –6, –12 or –18 ℃, vacuum-packed and stored in a freezer at –18 ℃ for 24 weeks. In order to analyze the effect of liquid nitrogen freezing on physiological and biochemical characteristics of P. praecox shoots during frozen storage, L-phenylalanine ammonialyase (PAL) and peroxidase (POD) activities, total phenolic content, relative electrical conductivity, and water state were measured and ice crystal structure and cell morphology were observed. The results showed that with increasing freezing time, the PAL and POD activities, total phenolic content, and peak area of free water in all six groups decreased significantly (P < 0.05), while the relative electrical conductivity increased significantly (P < 0.05), with the ice crystals and cells being deformed and damaged to varying degrees. Lower freezing temperature led to smaller ice crystals, lower PAL and POD activities and relative electrical conductivity, higher total phenolic content, and better maintenance of cell morphology, but there was no significant difference in physiological and biochemical properties between P. praecox shoots frozen at –90 and –120 ℃ (P > 0.05). The PAL and POD activities and relative conductivity of P. praecox shoots frozen at –6 ℃ were higher than those frozen at –12 and –18 ℃, and the size of ice crystals was smaller and the degree of cell damage was greater in P. praecox shoots frozen at –6 ℃ than at –12 and –18 ℃. The difference between P. praecox shoots frozen at –12 and –18 ℃ was not significant (P > 0.05). Collectively, these findings indicated that the most suitable liquid nitrogen freezing conditions of P. praecox shoots are –90 and –12 ℃ for freezing and internal temperature, respectively.

Aquatic animal products are rich in protein, lipids, and moisture and are often stored at frozen temperature. However, aquatic animal products are prone to deterioration caused by ice crystal formation, lipid oxidation and protein denaturation. Quick freezing is crucial for preserving the quality of aquatic animal products by preventing the formation of large ice crystals. Liquid nitrogen quick-freezing (LNF) provides a fast-freezing rate, minimal ice crystal formation, preservation of product texture and nutritional properties, shelf-life extension, energy efficiency, and quality and safety improving. This review comprehensively illustrates the mechanism of LNF, the impact of LNF on qualities of aquatic animal products including flavor, texture, color, and nutrition. Additionally, LNF devices applied on aquatic animal products are also discussed. Furthermore, future prospects and research directions are suggested, including optimizing freezing processes, understanding the impact on nutritional value and considering sustainability and energy consumption. However, challenges such as freezing damage, cost considerations, and quality control issues for LNF application need to be addressed.