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The effects of salting and subsequent freezing on the physicochemical and histological properties of frozen-thawed tuna meat were investigated. Salting facilitated the microstructural recovery as indicated by the decrease or disappearance of intracellular holes. The yield of the 0.5 M and 1 M salted samples increased by 20% which was evaluated by the mass ratio of products to raw material. Morphological transformation from ice columns to spherical or ellipsoidal ice crystals was tentatively attributed to the extraction/solubilization of myofibrillar proteins, contributing to increased water-holding capacity. However, increased thawing loss and centrifuging loss after thawing were observed in the 2 M and 3 M salted samples with large ice crystals and enlarged extracellular spaces. These modifications were closely associated with the changes in protein properties. In conclusion, enhanced water-holding capacity, high yield, and good freezing stability can be achieved by optimal salting., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Hairtail fish samples were stored at different freezing temperatures of -5 °C, -20 °C, -40 °C and -80 °C. To establish an effective quality evaluation approach for hairtail samples during frozen storage, fractal dimension was used to observe the porous microstructure that resulted from the ice crystal formation in frozen hairtail meat. The results showed that the initial value of fractal dimension of all the samples was 1.968. After frozen storage, the fractal dimension of samples at -5 °C, -20 °C, -40 °C and -80 °C decreased to 1.539, 1.682, 1.856 and 1.896, respectively. Traditional quality indicators such as water activity, color and textural properties (i.e., hardness, springiness and chewiness) also exhibited a similar decreasing trend, and the rate of change decreased with a decrease in storage temperature. The relationships were analyzed, and these traditional quality indicators were correlated with the fractal dimension with determined correlation coefficients within ±0.900. Moreover, based on the fractal dimension model, the first-order kinetic equation of fractal dimension variation during storage was [Formula: see text], which can be used to predict the shelf life of preserved hairtails at different storage temperatures. The results demonstrated fractal dimension was a novel and feasible method to evaluate the quality of hairtails in frozen storage.

The objective of this study was to investigate the advantages of liquid nitrogen freezing (LNF) over normal contact freezing (NCF) and individual quickly freezing (IQF). The quality attributes of LNF on crayfish (Procambarus clarkia) were characterized by biochemical and structural properties. Compared with NCF and IQF, LNF presented lower total viable counts (TVC) value of 5.83 log(CFU/g), thiobarbituric acid (TBA) value of 0.74 mg/kg, total volatile basic nitrogen (TVB‐N) content of 23.43 mg/100 g and α‐glucosidase and β‐acetyl glucosaminidase enzyme activities. SDS‐PAGE patterns confirmed less protein denaturation in LNF. Meanwhile, texture parameters analysis indicated LNF held texture quality better, while scanning electron microscope patterns revealed that muscle fibers in LNF were more uniform. The mathematical models exhibited the significant correlation among biochemical and structural properties. Therefore, LNF was a promising freezing process for crayfish preservation, due to the formation of small intracellular ice crystals and maintenance of cell integrity. Novelty impact statement: The LNF which was considered as a promising freezing method was applied in crayfish preservation.The preservation behavior of LNF was characterized and the related protective mechanism was illustrated.The mathematical models were established to clarify the inner relationship between freezing conditions and quality attributes. [ABSTRACT FROM AUTHOR]

The fresh keeping ability of ultrasound‐assisted immersion freezing (UIF), immersion freezing (IF), and refrigerator freezing (RF) was compared in Fenneropenaeus chinensis (F. chinensis). Observation of muscle microstructure indicated that UIF treatment had the smallest ice crystals formation with uniform distribution, resulting in minimal damage to muscle tissues. Meanwhile, UIF‐treated F. chinensis showed slower pH change, lower values of total volatile basic nitrogen (TVB‐N), and thiobarbituric acid reactive substances (TBARS). The higher values of salt soluble protein content，Ca2+‐ATPase activity, and water‐holding capacity revealed that UIF could inhibit protein degeneration and moisture loss. In addition, an excellent sensory evaluation score also verified the efficient fresh keeping capacity of UIF. Our results indicate the potential of UIF in maintaining the freshness and quality of F. chinensis during frozen storage. Novelty impact statement: Preservation effects of different freezing methods to Fenneropenaeus chinensis were compared.Ultrasound‐assisted immersion freezing caused less tissue damage to shrimp and could inhibit the spoilage during frozen storage.Ultrasound assistance is efficient for the fresh keeping of aquatic products. [ABSTRACT FROM AUTHOR]

• •Effect of ice-glazing on frozen swimming crab quality during storage was evaluated. • •Ice-glazed samples display lower TVBN and TBARS from 90 days of storage. • •Ice-glazing sustains microstructure and sensory quality of frozen swimming crab. • •A practical strategy is proposed for quality enhancement of frozen swimming crab. This study investigated the influence of water ice-glazing treatment on the quality attributes of frozen swimming crab by liquid nitrogen spray freezing during storage at -18 °C for 180 days, including water-holding capacity (WHC), thiobarbituric acid-reactive substances (TBARS), total volatile basic nitrogen (TVB-N), sensory score and microstructure. The results showed that water ice-glazing treatment suppressed the variations in overall quality of frozen swimming crab during storage. Ice-glazing treatment can improve maintenance of WHC, microstructure and sensory quality of frozen swimming crab, as well as inhibit the increase of total volatile basic nitrogen (TVB-N). Besides, the degree of primary lipid oxidation in frozen swimming crab was inhibited at a low range by ice-glazing. Water ice-glazing was effective in protecting the quick-freezing swimming crab from undesirable quality changes during frozen storage. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effects of liquid nitrogen freezing (LNF) in long‐term frozen preservation of hairtail. Fresh hairtail was frozen by liquid nitrogen or cold air and stored at −20°C or −80°C for up to 120 days. The contents of carbonyl, TCA‐soluble peptides, AG and NAG enzyme activities increased, whereas Ca2+‐ATPase, Mg2+‐ATPase activity and the contents of sulfhydryl group decreased with the storage time increased. The activities of cathepsin B and B + L could be inhibited by low temperatures in the initial 40 days. However, the inhibition gradually weakened as the storage time increased. Protein surface hydrophobicity increased and reached a peak of 480.23 on day 60 with a subsequent fluctuant decrease. The α‐helix and β‐sheet structures of myofibrillar protein decreased, while the β‐turn and random coil structures increased. And the texture degradation occurred in all the tested four groups. The muscle fibers begun to break in cold air freezing (CAF) group after storage of 60 days. After a storage period of 120 days, large holes appeared in meat sample of CAF group. The muscle fibers of the LNF groups were kept much more complete than that of the CAF groups, indicating the advantages of LNF. Practical Application: In this study, the advantages of liquid nitrogen freezing (LNF) on the quality of hairtail during long‐term frozen preservation were showed by enzyme activity, protein structure and tissue structure. Although LNF causes inevasible damage to the fish meat, the ice crystals during freezing were rather small and distributed homogenously due to fast freezing rate. Thus, the mechanical damage to muscle was much lower than that of the cold air freezing (CAF), showing great advantages of LNF. Liquid nitrogen was recommended for pre‐frozen of hairtail before frozen storage to maintain the quality of hairtail. These results could provide theoretical guidance for the applying of LNF on the hairtail processing for the quality maintenance of hairtail whilst aiming to get maximum nutritional benefits. This knowledge can also be widely applicated in other fishery products preservation. [ABSTRACT FROM AUTHOR]

Effects of air thawing (AT), refrigerator thawing (RT), water immersing thawing (WIT), lotic water thawing (LWT), and microwave thawing (MT) on the quality of swimming crab by liquid nitrogen freezing were investigated. The highest thawing loss was recorded for MT sample (2.70%) followed by AT (2.22%), WIT (1.97%), and LWT (1.52%), while RT had the lowest value (1.06%). RT sample had the lowest TBARS (0.34 mg/kg) and the highest sensory (8.60) score closer to those for fresh meat, but MT sample had the highest TBARS (0.66 mg/kg) with the lowest sensory score (7.83). Besides, microstructural changes indicated that MT induced larger gaps between muscle fibers and broken more muscle fiber bundles than the other methods, while RT had the least negative role on the microstructure of crab meat. Overall, RT could be recommended as a suitable method for preserving the quality of frozen swimming crab. [ABSTRACT FROM AUTHOR]

Hairtail samples were frozen by three different treatments, including conventional air freezing (CAF) at −20  o C, refrigerator cryogenic freezing (RCF) at −80  o C and liquid nitrogen immersion freezing (LIF) at −196  o C. In order to investigate the influence of freezing treatments on the development of ice crystal in hairtail samples, an improved method based on cryosection was applied to observe the formation of ice crystals in frozen hairtail meat, comparing with the traditional method of cryosubstitution. Results showed that cryosectioning was a highly effective tool for intuitionistic view of ice crystals, and greatly shortened the time from 3–5 days to 20–30 min. The equivalent diameter of the ice crystals determined by cryosectioning were 12.6 ± 3.73, 3.62 ± 1.91, and 1.22 ± 0.39 µm for the samples subjected to CAF, RCF and LIF, respectively. Smaller and more regular intracellular ice crystals were observed in hairtail samples frozen by LIF compared with other treatments. The microstructure of three frozen treated samples was profiled by scanning electron microscopy as well. Significant differences were observed in the water holding capacity in frozen samples of CAF (86.8%), RCF (87.4%), and LIF (89.2%). The characteristics of ice crystals, which have a strong influence on the final quality of the food, were considered as an important factor for the quality of hairtail during freezing. [ABSTRACT FROM AUTHOR]