The Effect of Multiple Freeze-Thaw Cycles on the Microstructure and Quality of Trachurus murphyi

Experimental evidence demonstrating how freeze-thaw patterns affect spoilage of perishable cached food

For the small number of temperate and boreal species that cache perishable food, previous research suggests that increasing freeze-thaw events can have a negative impact on fitness by degrading the quality of cached food. However, there is no experimental evidence that directly links freeze-thaw events to cache quality. To examine how the timing, frequency, duration, and intensity of freeze-thaw events influenced cached food mass loss, a proxy for caloric content, we conducted a series of month-long laboratory experiments by placing simulated caches (raw chicken placed between two pieces of black spruce Picea mariana bark) in programmable freezers. Freeze-thaw treatments were modelled after weather data from Algonquin Provincial Park, Ontario, where a population of Canada jays (Perisoreus canadensis), a species that caches perishable food for overwinter survival and to support late-winter breeding, has declined by >  70% since the 1980s. First, we found no evidence that an increased frequency of freeze-thaw events influenced mass loss, suggesting that microstructural damage caused by crystal reformation does not significantly influence cache quality. Instead, our experimental results demonstrated that mass loss was positively influenced by longer individual thaws, which likely reflects increased microbial growth, oxidation, and progressive drip loss. We also found that caches lost more weight when subjected to early freeze-thaw events compared to late freeze-thaw events. Finally, we show that milder freezes led to less mass loss and, unexpectedly, warmer than average thaws post-freeze also led to less mass loss. Our results suggest that longer thaw periods post-freezing and milder freezes cause or lead to significantly increased spoilage of perishable cached food. All of these temperature-related conditions are closely associated with long-term changes in climate and, thus, the effects on cache degradation reported in these experiments should be applicable to species caching perishable food in the wild.

The Effect of Ice-Binding Protein from Leucosporidium sp. AY30 (LeIBP) on the Physicochemical Quality and Microstructure of Largemouth Bass During Freeze-Thaw Cycles

This study investigated the effect of various concentrations (0.01%, 0.05%, 0.1%, 0.2%, 0.5%) of ice-binding protein from Leucosporidium sp. AY30 (LeIBP) on the freezing efficiency, microstructure, and physicochemical quality of largemouth bass during freeze-thaw cycles and demonstrated the optimal addition conditions of LeIBP. This study found that LeIBP could effectively lower the freezing point of fish without altering the phase transition time significantly. LeIBP can significantly reduce the cross-sectional area and diameter of ice crystals and inhibit recrystallization. LeIBP was found to maintain the stability of protein secondary structure and prevented protein denaturation by increasing the proportion of α-helix. The inclusion of LeIBP retained the water-holding capacity of fish effectively. Furthermore, LeIBP treatment could partially prevent the degradation of fish meat texture. The lightness and whiteness values of fish treated with LeIBP were increased, while the redness and yellowness values were decreased. At the end of freeze-thaw cycle, the LeIBP-treated group presented pH values similar to fresh fish. Overall, 0.05% LeIBP was observed to be the most effective concentration to inhibit ice crystal growth, thereby maintaining the quality of the fish.

Exploring the anatomy of Linguatula serrata using micro-computed tomography

Micro-computed tomography (micro-CT) is an emerging tool in parasitology that can assist in analysing morphology and host-parasitic interactions. It is a non-destructive, cross-sectional imaging technique that offers good resolution and the ability to create three-dimensional (3D) reconstructions. Here, we used micro-CT to study Linguatula serrata, which is a zoonotic pentastome parasite that infects dogs and ruminants throughout the world. The aims of this study were to describe the internal and external anatomy of adult L. serrata specimens using micro-CT, and to describe and compare specimens stained with 0.3% phosphotungstic acid (PTA) and 1% iodine (I2). Ten adult L. serrata specimens were subjected to micro-CT examination. The specimens were fixed in 70% ethanol and stained with 0.3% PTA or 1% I2. Both stains offered good tissue contrast. The main identifying external features of L. serrata (hooks, mouth, buccal cadre) were clearly visible. Virtual sections and 3D reconstructions provided a good overview of the coelomic cavity, with visualisation of the digestive tract, nervous system, and male and female reproductive organs. These micro-CT images and morphological descriptions may serve as an anatomical reference for L. serrata, in particular, the internal anatomy which has not been described in recent years.

Near-Infrared Spectroscopy for Rapid Differentiation of Fresh and Frozen-Thawed Common Carp (Cyprinus carpio)

This study aimed to investigate near-infrared spectroscopy (NIRS) in combination with classification methods for the discrimination of fresh and once- or twice-freeze-thawed fish. An experiment was carried out with common carp (Cyprinus carpio). From each fish, test pieces were cut from the dorsal and ventral regions and measured from the skin side as fresh, after single freezing at minus 18 °C for 15 ÷ 28 days and 15 ÷ 21 days for the second freezing after the freeze-thawing cycle. NIRS measurements were performed via a NIRQuest 512 spectrometer at the region of 900-1700 nm in Reflection mode. The Pirouette 4.5 software was used for data processing. SIMCA and PLS-DA models were developed for classification, and their performance was estimated using the F1 score and total accuracy. The predictive power of each model was evaluated for fish samples in the fresh, single-freezing, and second-freezing classes. Additionally, aquagrams were calculated. Differences in the spectra between fresh and frozen samples were observed. They might be assigned mainly to the O-H and N-H bands. The aquagrams confirmed changes in water organization in the fish samples due to freezing-thawing. The total accuracy of the SIMCA models for the dorsal samples was 98.23% for the calibration set and 90.55% for the validation set. For the ventral samples, respective values were 99.28 and 79.70%. Similar accuracy was found for the PLS-PA models. The NIR spectroscopy and tested classification methods have a potential for nondestructively discriminating fresh from frozen-thawed fish in as methods to protect against fish meat food fraud.

Comparison of freezing and heating treatment sequence on biochemical properties and flavor of swimming crabs (Portunus Trituberculatus) meat during freeze-thaw cycles

The objective of this study was to compare the effect of freezing and heating treatment sequences on the biochemical properties and flavor of crab (Portunus trituberculatus) meat during freeze-thaw cycles. The results showed that pH, color, K and microstructure changes in the H-F group were not significant with increasing number of freeze-thaw cycles, but TVB-N values increased and WHC values decreased. However, with the increase in the number of freeze-thaw cycles, pH and WHC significantly decreased and TVB-N, L* and K values significantly increased in the C and F-H groups. Proteins were degraded in all groups, but the lower degree of degradation occurred in the H-F group. Although the total free amino acid content decreased with increasing number of freeze-thaw cycles in each group, the high content of AMP and IMP in the H-F group suggested that it still had a better flavor.

Effect of multiple freeze-thaw cycles on water migration, protein conformation and quality attributes of beef longissimus dorsi muscle by real-time low field nuclear magnetic resonance and Raman spectroscopy

Repeated freezing and thawing (F-T) happens during long-term storage and transportation due to the temperature variation, causing quality deterioration of beef products and influencing consumer acceptance. This study was aimed to investigate the relationship between quality attributes, protein structural changes and water real-time migration of beef with different F-T cycles. The results showed that multiply F-T cycles damaged the muscle microstructure and protein structure tended to denature and unfold, led lower population of water reabsorbed, thus triggering the decrease of water capacity, especially a decrease of T₂₁ and A₂₁ of completely thawed beef samples, finally affected the quality, such as tenderness, color and lipid oxidation of beef muscle. Beef should not be abused by F-T cycles >3 times, the quality extremely degraded when subjected to 5 or more F-T cycles, and real-time LF-NMR provided a new aspect to help us control the thawing process of beef.

Analysis of the water state and microfractal dimension of tilapia fillets during freezing and thawing

To study the effects of freezing and thawing times and freezing temperatures on the water state and microstructure of tilapia fillets, experiments on tilapia fillets were carried out at -4 and -18°C with one to four freezing and thawing cycles (FTCs). Low-field nuclear magnetic resonance (LF-NMR) and nuclear magnetic resonance imaging were used to observe the water state after different treatments, and scanning electron microscopy (SEM) and frozen sections were used to observe the microstructure changes. Fractal dimension (FD) was used to quantitatively characterize the microstructure of the fish tissue, and the correlation between FD and fish fillet quality parameters was studied by principal component analysis (PCA). The findings showed that with the increase of FTCs, the thawing loss increased, and the water holding capacity (WHC) fell. FTCs cause a decrease in immobilized water and an increase in free water in the fillet. This indicates the migration of immobilized water to free water. SEM and frozen slice images showed that the growth of ice crystals led to the destruction of myogenic fibers. A decrease in freezing temperature inhibited ice crystal growth. The FD value dropped in accordance with an increase in FTCs. PCA demonstrated that the WHC, NMR data, and FD value had a strong correlation with the quality changes in the tilapia fillets. Therefore, FD and water state can reflect the quality characteristics of tilapia fillets. PRACTICAL APPLICATION: The water migration in tilapia fillets is detected with LF-NMR, and the microscopic image may be quantified using the FD value. Both approaches can offer fresh perspectives on how to assess the quality of tilapia fillets and reflect changes in their quality.

Effect of antifreeze proteins on the freeze-thaw cycle of foods: fundamentals, mechanisms of action, current challenges and recommendations for future work

Freezing is widely used in food preservation, but if not carried out properly, ice crystals can multiply (nucleation) or grow (recrystallization) rapidly. This also affects thawing, causing structural damage and affecting overall quality. The objective of this review is to comprehensively study the cryoprotective effect of antifreeze proteins (AFPs), highlighting their role in the freeze-thaw process of food. The properties of AFPs are based on their thermal hysteresis capacity (THC), on the modification of crystal morphology and on the inhibition of ice recrystallization. The mechanism of action of AFPs is based on the adsorption-inhibition theory, but the specific role of hydrogen and hydrophobic bonds/residues and structural characteristics is also detailed. Because of the properties of AFPs, they have been successfully used to preserve the quality of a wide variety of refrigerated and frozen foods. Among the limitations of the use of AFPs, the high cost of production stands out, but currently there are solutions such as the use the production of recombinant proteins, cloning and chemical synthesis. Although in vitro, in vivo and human studies have shown that AFPs are non-toxic, their safety remains a matter of debate. Further studies are recommended to expand knowledge about AFPs, to reduce costs in their large-scale production, to understand their interaction with other food compounds and their possible effects on the consumer.

Freezing-induced denaturation of myofibrillar proteins in frozen meat

Freezing is commonly used to extend the shelf life of meat and meat products but may impact the overall quality of those products by inducing structural changes in myofibrillar proteins (MPs) through denaturation, chemical modification, and encouraging protein aggregation. This review covers the effect of freezing on the denaturation of MPs in terms of the effects of ice crystallization on solute concentrations, cold denaturation, and protein oxidation. Freezing-induced denaturation of MPs begins with ice crystallization in extracellular spaces and changes in solute concentrations in the unfrozen water fraction. At typical temperatures for freezing meat (lower than -18 °C), cold denaturation of proteins occurs, accompanied by an alteration in their secondary and tertiary structure. Moreover, the disruption of muscle cells triggers the release of cellular enzymes, accelerating protein degradation and oxidation. To minimize severe deterioration during the freezing and frozen storage of meat, there is a vital need to use an appropriate freezing temperature below the glass transition temperature and to avoid temperature fluctuations during storage to prevent recrystallization. Such an understanding of MP denaturation can be applied to determine the optimum freezing conditions for meat products with highly retained sensory, nutritional, and functional qualities.

Effects of Dual-Frequency Ultrasound-Assisted Thawing Technology on Thawing Rate, Quality Properties, and Microstructure of Large Yellow Croaker (Pseudosciaena crocea)

This research evaluated the effects of dual-frequency ultrasound-assisted thawing (UAT) on the thawing time, physicochemical quality, water-holding capacity (WHC), microstructure, and moisture migration and distribution of large yellow croaker. Water thawing (WT), refrigerated thawing (RT), and UAT (single-frequency: 28 kHz (SUAT-28), single-frequency: 40 kHz (SUAT-40), dual-frequency: 28 kHz and 40 kHz (DUAT-28/40)) were used in the current research. Among them, the DUAT-28/40 treatment had the shortest thawing time, and ultrasound significantly improved the thawing rate. It also retained a better performance from the samples, such as color, texture, water-holding capacity and water distribution, and inhibited disruption of the microstructure. In addition, a quality property analysis showed that the pH, total volatile basic nitrogen (TVB-N), and K value were the most desirable under the DUAT-28/40 treatment, as well as this being best for the flavor of the samples. Therefore, DUAT-28/40 treatment could be a possible thawing method because it improves the thawing rate and maintains the quality properties of large yellow croaker.

Effects of Freeze-Thaw Cycles on Water Migration, Microstructure and Protein Oxidation in Cuttlefish

This study was conducted to analyze the effects of multiple freeze-thaw (F-T) cycles on microstructural disruption, water migration, protein oxidation and textural properties of cuttlefish. Low-field nuclear magnetic resonance (LF-NMR) showed an increase in the proportion of free water in cuttlefish flesh. It was also observed by scanning electron microscopy (SEM) that multiple F-T cycles increased the gap between muscle fibers and disrupted the original intact and compact structure. The results of Fourier transform infrared spectroscopy, intrinsic fluorescence spectroscopy, Ca2+ATPase content, sulfhydryl content and free amino acid content indirectly prove that multiple F-T cycles can lead to the destruction of the a-helical structure of cuttlefish myofibril protein and the content of irregular curls increased, protein aggregation and degradation, and tryptophan oxidation. In addition, after repeated freezing and thawing, the water holding capacity, whiteness value, elasticity and chewiness of cuttlefish flesh decreased, the total volatile base nitrogen content increased. It can be concluded that the freeze-thaw cycles are very harmful to the quality of the frozen foods, so it is important to keep the temperature stable in the low-temperature food logistics.