This study addressed the effect of polysaccharide hydrocolloids on the crust characteristics and oil penetration of fried battered and breaded fish nuggets (BBFNs). Fish pieces were battered with a mixture of wheat starch (WS) and wheat gluten (WG) at a ratio of 11:1 (m/m) added with 0.3% sodium carboxymethyl cellulose (CMC-Na), 0.2% guar gum (GG), or 0.2% xanthan gum (XG), breaded, and fried at 170 ℃ for 40 s followed by 190 ℃ for 30 s. The fluorescence intensity, surface hydrophobicity (H₀), sulfydryl and disulfide bond contents, and secondary structure of WG and the crystal structure of WS in the crust were determined, and the oil penetration in the crust was evaluated. Results showed that the H₀, fluorescence intensity, disulfide bond content, relative contents of β-sheet and β-turn in the crusts with the three polysaccharide hydrocolloids were greater than those in the control (without the addition of any polysaccharide hydrocolloids), while the free sulfydryl content and the relative contents of α-helix and random coil of WG, and the relative crystallinity of WS were lower than those in the control. The H₀, fluorescence intensity, sulfydryl content and relative α-helix content of WG and the relative crystallinity of WS were lowest for the crust with XG, followed by CMC-Na and GG, while an opposite trend was observed for the disulfide bond content and relative β-sheet content. Furthermore, Sudan red staining area was largest for the control, and smallest for fried BBFNs with XG (present only in the crust), followed by CMC-Na and GG. These results indicated that due to their high hydrophilicity and unique structures, the three polysaccharide hydrocolloids can interact with WG to improve the stability of the crust, thereby inhibiting the oil penetration of fried BBFNs.

To establish a model based on near-infrared (NIR) spectra for quickly detecting the freshness of frozen crayfish, NIR spectra of thawed crayfish (tail, meat, and mince) were collected, and data were pretreated by first derivative, multiple scattering correction, wavelet transform (WT), or standard normal transform. The original and pretreated spectral data were correlated to total volatile basic nitrogen (TVB-N) contents using partial least squares (PLS) or convolutional neural network (CNN), and different quantitative prediction models were established and compared. The best model was selected to investigate its accuracy and applicability. The results showed that pretreatment methods had a significant influence on the accuracy of the model, and the CNN model established after spectral preprocessing had a better ability to predict the TVB-N content of crayfish compared with the PLS model. The CNN model based on the WT pretreated spectra of crayfish meat had the highest prediction accuracy for the validation set with correlation coefficients of 0.97 and 0.96, and root mean square errors of 1.26 and 0.93 mg/100 g for the calibration set and validation set, respectively. Moreover, the accuracy, precision, and sensitivity of the NIR method were within reasonable limits, and it had good figures of merit. According to the requirements of fast operation, accurate results, and low damage in practice, the WT-CNN-crayfish meat model was determined as the optimal model for predicting the TVB-N content in frozen crayfish. These results suggested that the WT-CNN-crayfish meat model have a great potential for predicting the TVB-N content and rapidly evaluating the freshness of frozen crayfish.

To enhance the liquid nitrogen freezing efficiency and improve the quality of frozen prepared Monopterus albus, the effect of variable temperature liquid nitrogen quick-freezing combined with composite cryoprotectant treatment on the quality of prepared M. albus was investigated. Deep-fried cured M. albus was treated with a novel composite cryoprotectant consisting of 4% xylooligosaccharides, 4% sorbitol and 0.3% sodium bicarbonate before precooling followed by liquid nitrogen freezing at variable temperatures (from -80 to -50 ℃). Internal temperature, moisture content, thawing loss, centrifugal loss, moisture state, thiobarbituric reactive substances (TBARS) value, acid value (AV), fluorescent compound content, and total volatile basic nitrogen (TVB-N) content were measured, and ice crystal morphology and microstructure were observed. The results indicated significantly lower thawing loss (3.80%), centrifugal loss (11.6%) and free water percentage (24.4%) under variable temperature liquid nitrogen quick-freezing compared with freezer freezing (P < 0.05), and significantly lower thawing loss under variable temperature liquid nitrogen quick-freezing compared with constant temperature liquid nitrogen quick-freezing (P < 0.05). After freezing for 24 weeks, prepared M. albus treated with the cryoprotectant exhibited significantly lower ice crystal size, thawing loss, centrifugal loss, TBARS value, AV, fluorescent compound content, and TVB-N content as well as more complete microstructure of muscle fibers, and its quality did not significantly differ from that of M. albus treated with a commercial cryoprotectant (P > 0.05). These findings suggested that pre-cooling followed by variable temperature liquid nitrogen quick-freezing combined with the novel composite cryoprotectant could enhance the quality of prepared M. albus during frozen storage, which will offer theoretical support for the development of highly efficient freezing and preservation technology for prepared M. albus products.

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.