Freezing of meat and aquatic food: Underlying mechanisms and implications on protein oxidation

Precooked state based on protein denaturation kinetics impacts moisture status, protein oxidation and texture of prepared chicken breast

The quality of meat in prepared dishes deteriorates due to excessive protein denaturation resulting from precooking, freezing, and recooking. This study aimed to link the precooked state with chicken breast's recooked quality. Cooked Value (CV), based on protein denaturation kinetics, was established to indicate the doneness of meat during pre-heating. The effects of CVs after pre-heating on recooked qualities were investigated compared to fully pre-heated samples (control). Mild pre-heating reduced water migration and loss. While full pre-heating inhibited protein oxidation during freezing, intense oxidation during pre-heating led to higher oxidation levels. Surface hydrophobicity analysis revealed that mild pre-heating suppressed aggregation during recooking. These factors contributed to a better texture and microstructure of prepared meat with mild pre-heating. Finally, a potential mechanism of how pre-heating affects final qualities was depicted. This study underlines the need for finely controlling the industrial precooking process to regulate the quality of prepared meat.

In Vivo Surface-Enhanced Transmission Raman Spectroscopy and Impact of Frozen Biological Tissues on Lesion Depth Prediction

Plasmonic surface-enhanced transmission Raman spectroscopy (SETRS) has emerged as a promising optical technique for detecting and predicting the depths of deep-seated lesions in biological tissues. However, in vivo studies using SETRS are scarce and typically show shallow penetration depths. Moreover, the optical parameters used in the prediction process are often derived from frozen samples and there is limited understanding of how freezing affects the optical properties of biological tissues and the accuracy of depth prediction in living models. In this work, we conduct in vivo SETRS measurements on thick abdominal tissue region of the live rats to investigate the impact of freezing on the measured optical properties for the purpose of depth prediction. First, we fabricated ultrahigh bright surface-enhanced Raman spectroscopy (SERS) nanotags and utilized a custom transmission Raman system. We then measured the change of optical attenuation at two different wavelengths (Δμ) for four types of rat tissues (including skin, fat, muscle, and liver) following freezing. The freezing process dramatically affects Δμ values, even after only 1 day of freezing. In contrast, Δμ values obtained from fresh samples enable precise localization of SERS lesion phantoms in the live rat with only 5% deviation. The total thickness of the live rat is 2.6 cm, which, to the best of our knowledge, is the highest value of in vivo SETRS studies so far. This work helps to fill the gap in the SERS field of tissue localization and optical coefficient studies in highly heterogeneous tissues, and demonstrates the potential of the SETRS technique to achieve precise clinical localization of deep lesions.

Effect and mechanisms of mechanical pre-dehydration treatment on gelling and physicochemical properties of unwashed silver carp (Hypophthalmichthys molitrix) surimi

Washing improves the overall quality of surimi production. However, the washing process significantly increases wastewater discharge from factories, thus raising environmental concerns and highlighting the need for more sustainable methods of surimi production. This study aimed to investigate the possibility of improving the quality of unwashed freshwater surimi by mechanical pre-dehydration and to explore the changes in gelling properties and physicochemical characteristics during frozen storage. The results indicate that the gel strength and water-holding capacity (WHC) of mechanically pre-dehydrated unwashed surimi can reach 522.50 g·cm and 68.12 %, which were equivalent to surimi subjected to two washes. During frozen storage, the pre-dehydration exhibited beneficial effects on the gel properties and water retention of surimi. Furthermore, SDS-PAGE analysis indicated that pre-dehydration retarded protein degradation during frozen storage. Indicators such as sulfhydryl groups, carbonyl content, protein solubility, and TBARS indicated that pre-dehydration could reduce the rate of protein and lipid oxidation. Focusing on the changes in endogenous components during the pre-dehydration, we showed that the dehydration could reduce the fat content (from 83.8 g/kg to 68.03 g/kg) and activities of cathepsin B (from 13.1 U/g to 7.3 U/g), lipoxygenase (from 621.3 U/g to 416 U/g), and gelatin-degrading enzymes in unwashed surimi, thereby enhancing the gel properties and frozen stability. Therefore, mechanical pre-dehydration can enhance the quality of unwashed surimi, thus providing a more environmentally friendly surimi production method.

Oxidative regulation and cytoprotective effects of γ-polyglutamic acid on surimi sol subjected to freeze-thaw process

Frozen surimi sol incline to protein oxidation, but the quality control strategies based on oxidation remain limited. Hence, the antioxidant and cryoprotective effects of γ-polyglutamic acid (γ-PGA) on freeze-thawed salt-dissolved myofibrillar protein (MP) sol were investigated. Results showed that γ-PGA could effectively regulate protein oxidation of MP sol during freeze-thawing with lower carbonyl contents and less oxidative cross-linking. Meanwhile, γ-PGA primely maintained sol protein structures, showing reduction of 15.28% of salt soluble protein contents at γ-PGA addition of 0.04% under unoxidized condition. Additionally, compared to the control group without oxidation treatment, cooking loss of heat-induced gel with 0.04% γ-PGA decreased by 47.19%, while gel strength obviously increased by 57.22% respectively. Overall, moderate γ-PGA addition (0.04%) could inhibit protein oxidation of sol, further improving frozen stability of sol through hydrogen bonds and hydrophobic interaction, but excessive γ-PGA was adverse to sol quality due to severe cross-linking between γ-PGA and MP.

Effect of liquid nitrogen freezing pretreatment on the meat quality of gazami crab (Portunus trituberculatus) during frozen storage

Liquid nitrogen freezing (LNF) pretreatment is an effective means of maintaining seafood quality during frozen storage. To improve the meat quality of gazami crab (Portunus trituberculatus) during frozen storage, this study investigated the effects of LNF temperatures on the meat quality of gazami crab. Fresh crab was pre-treated with different LNF temperatures (-60 °C, -80 °C, -100 °C, -120 °C), and then freeze in refrigerator at -18 °C. The changes in protein structure and meat quality of gazami crab during long-term frozen storage were measured. The results showed that -100 °C LNF more effectively inhibited the oxidative deterioration of crab meat during storage, which is lower than the optimal LNF temperature for shell free aquatic products such as fish, extending the shelf life of frozen gazami crab to 4 months. This study enriches the application parameters of LNF in freezing industry of crustacean aquatic products, providing guidance for exploring the optimal LNF temperature of aquatic products.

The improvement of gel properties and volatiles for frozen egg white melted assisted with ultrasound

The variation in thawing time, deterioration behavior, secondary structure, surface hydrophobicity, and average particle size of frozen egg whites (EW) thawed with or without ultrasound were characterized to evaluate the effect of ultrasound on the gel properties and volatiles of egg white thermogel (EWG). The texture, water holding capacity, etc., gel properties and microstructure were well maintained in frozen EW thawed by ultrasound (UEW) resulted from the mitigation of deterioration behavior due to shorter melting time (reduced 91.3 %). Moreover, the deterioration of VOCs in fresh EWG due to freeze-thawing could be mitigated when thawed using ultrasound. Meanwhile, the formation of pleasant VOCs and reduction in unpleasant VOCs in EWG were also promoted by ultrasound-assisted thawing. The improvement mechanism of gel properties and volatiles for (frozen) egg white melted assisted with ultrasound were systematically elucidated and this study provided a new insight into improvement of VOCs in frozen food.

Classification of frozen-thawed pork loins based on the freezing conditions and thawing losses using the hyperspectral imaging system

This study investigated the suitability of a hyperspectral imaging (HSI) system for the classification of frozen-thawed pork loins according to their quality properties. The pork loin slices were frozen at -20, -50, and -70 °C for 1, 2, and 3 months (the 9 freezing conditions). After thawing pork loins at 2 °C, the hyperspectral image was obtained. The photomicrographs of the loins showed that the extracellular spaces were the biggest in the loins frozen at -20 °C for 3 months. The denaturation of myofibrillar proteins measured by the intrinsic tryptophan intensity and surface hydrophobicity was higher in the loins frozen at -20 °C than that of loins frozen at -50 and -70 °C for 2 and 3 months (P < 0.05). The highest and lowest thawing loss was observed in loins frozen at -20 °C for 3 months (9.1 %) and at -70 °C for 1 month (3.6 %), respectively. The classification by the HSI system for 10-class (the 9 freezing conditions and the 1 fresh loin) showed that the highest correct classification (CC%) rates were 83.20 % and 81.82 % in the calibration and prediction sets, respectively, when partial least squares discriminant analysis (PLS-DA) with pre-processing by baseline offset and second derivative was used. In addition, 93.36 % and 91.92 % of CC in the calibration and prediction sets, respectively, were found in the classification of 4-class (the 3 thawing losses and the 1 fresh loin) with the PLS-DA and read-once-write-many-columnar. This study demonstrates that the HSI system can be used to present information on the quality of frozen-thawed pork loin.

Mitigation of mechanical damage and protein deterioration in giant river prawn (Macrobrachium rosenbergii) by multi-frequency ultrasound-assisted immersion freezing

In order to investigate the effects of multi-frequency ultrasound-assisted immersion freezing (MUIF) on the meat quality of Macrobrachium rosenbergii, tail meat was subjected to different MUIF treatments respectively, namely 20 + 40 kHz (MUIF-20 + 40), 20 + 60 kHz (MUIF-20 + 60), 40 + 60 kHz (MUIF-40 + 60) and 20 + 40 + 60 kHz (MUIF-20 + 40 + 60), and the immersion freezing (IF) as control. Results showed that average diameter of ice crystals was 28 μm in IF, and that was only 8 μm in MUIF-20 + 40 + 60. When compared to IF, MUIF alleviated oxidative deterioration of lipids and proteins, but only at higher ultrasound frequency (MUIF-40 + 60; MUIF-20 + 40 + 60). Carbonyl content of MUIF-20 + 40 + 60 was only 40% of that in IF. Similarly, protein denaturation was inhibited in MUIF (except for MUIF-20 + 40). Transmission electron microscopy showed greater distortion of the ultrastructural components in IF, MUIF-40 + 60, and MUIF-20 + 40 + 60, suggested by bended Z-line. In conclusion, MUIF can be an effective strategy to mitigate mechanical damage and protein deterioration in the meat of Macrobrachium rosenbergii.

Effect of protein oxidation on the structure and emulsifying properties of fish gelatin

This study aimed to investigate the effect of oxidation on fish gelatin and its emulsifying properties. Fish gelatin was oxidized with varying concentrations of H2O2 (0-30 mM). Increased concentrations of the oxidant led to a decrease in amino acids in the gelatin, including glycine, lysine, and arginine. Additionally, the relative content of ordered secondary structure and triple helix fractions decreased. Zeta potential decreased, while particle size, surface hydrophobicity, and water contact angle increased. Regarding emulsifying behavior, oxidation promoted the adsorption of gelatin to the oil-water interface and reduced interfacial tension. With increased degrees of oxidation, the zeta potential and size of the emulsion droplets decreased. The oxidized gelatin exhibited better emulsifying activity but worse emulsifying stability. Based on these results, a mechanism for how oxidation affects the emulsifying properties of gelatin was proposed: the increase in gelatin's hydrophobicity and the decrease in triple helix structure induced by oxidation reduced the interfacial tension at the oil-water interface. This promoted protein adsorption at the oil-water interface, allowing the formation of smaller oil droplets and enhancing gelatin's emulsifying activity. However, the decrease in electrostatic repulsion between emulsion droplets and the decrease in solution viscosity increased the flocculation and aggregation of oil droplets, ultimately weakening the emulsifying stability of gelatin.

Metabolomic profile of muscles from tilapia cultured in recirculating aquaculture systems and traditional aquaculture in ponds and protein stability during freeze-thaw cycles

Muscle protein stability during freeze-thaw (F-T) cycles was investigated with tilapia cultured in recirculating aquaculture systems (RAS) and traditional aquaculture in ponds (TAP). This study found that fatty acids (eg., palmitic acid) were enriched in TAP, while antioxidants (eg., glutathione) were enriched in RAS. Generally, proteins in the RAS group exhibited greater stability against denaturation during the F-T cycle, suggested by a less decrease in haem protein content (77% in RAS and 86% in TAP) and a less increase in surface hydrophobicity of sarcoplasmic protein (63% in RAS and 101% in TAP). There was no significant difference in oxidative stability of myofibrillar protein between the two groups. This study provides a theoretical guide for the quality control of tilapia cultured in RAS during frozen storage.

Effect of three unsaturated fatty acids on the protein oxidation and structure of myofibrillar proteins from rainbow trout (Oncorhynchus mykiss)

In this study, the impact of three unsaturated fatty acids (Oleic acid: OA, Eicosapentaenoic acid: EPA, Docosahexaenoic acid: DHA) on the oxidation and structure of rainbow trout myofibrillar protein (MP) was explored. The findings revealed a notable increase in carbonyl content (P < 0.05) and a significant decrease in total sulfhydryl content (P < 0.05) of MP with the concentration increase of the three unsaturated fatty acids. Endogenous fluorescence spectroscopy and surface hydrophobicity analyses showed that unsaturated fatty acids can cause unfolding and exposure of hydrophobic groups in MP. In addition, SDS-PAGE showed that disulfide bonds were associated with MP cross-linking and aggregate size induced by unsaturated fatty acids. Overall, three unsaturated fatty acid treatments facilitated the oxidation of myofibrillar proteins, and the extent of protein oxidation was closely associated with the concentration of unsaturated fatty acids.

Uncovering quality changes of surimi-sol based products subjected to freeze-thaw process: The potential role of oxidative modification on salt-dissolved myofibrillar protein aggregation and gelling properties

Frozen surimi quality generally correlates with oxidation, but impacts of protein oxidation on salt-dissolved myofibrillar protein (MP) sol in surimi remain unclear. Hence, physicochemical and gelling properties of MP sol with different oxidation degrees were investigated subjected to freeze-thaw cycles. Results showed that mild oxidation (≤1 mmol/L) improved unfrozen MP gel quality with lowest cooking loss (3.29 %) and highest hardness (829.76 N). Whereas, oxidized sol suffering freeze-thawing degenerated severely, showing reduction of 23.85 % of salt soluble protein contents with H2O2 concentrations of 10 mmol/L. Shearing before heating influenced gelling properties of freeze-thawed sol, depending on oxidation levels. Oxidized gel with shearing displayed disorganized network structures, whereas gel without shearing displayed relatively complete appearances without holes under high oxidation condition (10 mmol/L). Overall, freeze-thaw process aggravated denaturation extents of MP sol subjected to oxidation, further causing high water loss and yellow color of heat-induced gel, especially to gel with shearing.

Soy Protein Isolate Gel Subjected to Freezing Treatment: Influence of Methylcellulose and Sodium Hexametaphosphate on Gel Stability, Texture and Structure

Freezing affects texture and induces the loss of gel quality. This study investigated the effects of methylcellulose (MC) (0.2%, 0.4%, 0.6%) and sodium hexametaphosphate (SHMP) (0.15%, 0.3%) on the gel textural and structural properties of SPI gels before and after freezing, and explores the synergistic enhancement of gel texture and the underlying mechanisms resulting from the simultaneous addition of SHMP and MC to SPI gels. It was revealed that MC improved the strength of SPI gels through its thickening properties, but it could not inhibit the reduction of SPI gels after freezing. The 0.4% MC-SPI gel exhibited the best gel strength (193.2 ± 2.4 g). SHMP inhibited gel reduction during freezing through hydrogen bonding and ionic interactions; it enhanced the freezing stability of SPI gels. The addition of 0.15% SHMP made the water-holding capacity in SPI gels reach the highest score after freezing (58.2 ± 0.32%). The synergistic effect of MC and SHMP could improve the strength and the freezing stability of SPI gels. MC facilitated the release of ionizable groups within SPI, causing negatively charged SHMP groups to aggregate on the SPI and inhibit the freezing aggregation of proteins. These results provide a strong basis for the improvement of cryogenic soy protein gel performance by SHMP and MC.

Thawed drip and its membrane-separated components: Role in retarding myofibrillar protein gel deterioration during freezing-thawing cycles

Myofibrillar proteins are crucial for gel formation in processed meat products such as sausages and meat patties. Freeze-thaw cycles can alter protein properties, impacting gel stability and product quality. This study aims to investigate the potential of thawed drip and its membrane-separated components as potential antifreeze agents to retard denaturation, oxidation and gel deterioration of myofibrillar proteins during freezing-thawing cycles of pork patties. The thawed drip and its membrane-separated components of > 10 kDa and < 10 kDa, along with deionized water, were added to minced pork at 10 % mass fraction and subjected to increasing freeze-thaw cycles. Results showed that the addition of thawed drip and its membrane separation components inhibited denaturation and structural changes of myofibrillar proteins, evidenced by reduced surface hydrophobicity and carbonyl content, increased free sulfhydryl groups, protein solubility and α-helix, as compared to the deionized water group. Correspondingly, improved gel properties including water-holding capacity, textural parameters and denser network structure were observed with the addition of thawed drip and its membrane separation components. Denaturation and oxidation of myofibrillar proteins were positively correlated with gel deterioration during freezing-thawing cycles. We here propose a role of thawed drip and its membrane separation components as cryoprotectants against myofibrillar protein gel deterioration during freeze-thawing cycles.

Myofibrillar protein lipoxidation in fish induced by linoleic acid and 4-hydroxy-2-nonenal: Insights from LC-MS/MS analysis

The oxidation of fish lipids and proteins is interconnected. The LOX (lipoxygenase)-catalyzed LA (linoleic acid) oxidation system on MPs (myofibrillar proteins) was established in vitro, to investigate the impact of lipoxidation on the physicochemical properties of fish MPs. By detecting HNE (4-hydroxy-2-nonenal) concentration during LA oxidation, the HNE treatment system was established to investigate the role of HNE in this process. In addition, the site specificity of modification on MPs was detected utilizing LC-MS/MS. Both treatments could induce sidechain modification, increase particle size, and cause loss of nutritional value through the reduction in amino acid content of MPs. The HNE group is more likely to alter the MPs' surface hydrophobicity compared to the LA group. By increasing the exposure of modification sites in MPs, the HNE group has more types and number of modifications compared to the LA group. LA group mainly induced the modification of single oxygen addition on MPs instead, which accounted for over 50 % of all modifications. The LA group induced a more pronounced reduction in the solubility of MPs as compared to the HNE group. In conclusion, HNE binding had a high susceptibility to Lys on MPs. Protein aggregation, peptide chain fragmentation, and decreased solubility occurred in the LA group mainly induced by peroxide generated during lipid oxidation or the unreacted LA instead of HNE. This study fills in the mechanism of lipoxidation on protein oxidation in fish and sheds light on the HNE modification sites of MPs, paving the way for the development of oxidation control technology.

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.

Effects of nano freezing-thawing on myofibrillar protein of Atlantic salmon fillets: Protein structure and label-free proteomics

This study investigated the impact of magnetic nanoparticles (MNPs) -assisted cryogenic freezing integrated with MNPs combined microwave thawing (NNMT) on the structural integrity of myofibrillar proteins and alterations in protein profiles in salmon fillets. The NNMT showed the lowest myofibrillar fragmentation index (MFI) value (2.73 ± 0.31) among the four freezing-thawing groups. The myofibrillar structure exhibited the highest level of integrity, while the myofibrillar proteins demonstrated minimal aggregation and displayed the most stable secondary and tertiary structures in response to NNMT treatment. Compared with the other three treatments, NNMT exhibited a high abundance of ionic and hydrogen bonds, resulting in stronger interactions between the proteins and water molecules. The label-free proteomics analysis revealed that different freezing-thawing methods primarily affected the cytoskeletal proteins, with collagen and myosin being down-regulated due to degradation caused by cold stress and recrystallization. Additionally, NNMT demonstrated a superior capability in stabilizing salmon cytoskeletal proteins.

Low-voltage electrostatic field enhances the frozen force of -12 ℃ to suppress oxidative denaturation of the lamb protein during the subsequent frozen storage process after finishing initial freezing

The effect of low-voltage electrostatic field (LVEF) assisted -9 °C (LVEF-9) and -12 °C (LVEF-12) frozen, non-LVEF-assisted -9 °C (NLVEF-9) and -12 °C (NLVEF-12) frozen, and conventional frozen (CF-18, -18 °C) storage on the muscle microstructure and the oxidative denaturation of the lamb protein during the subsequent frozen storage process after finishing initial freezing was investigated. Compared with NLVEF-9, LVEF-9, and NLVEF-12, LVEF-12 maintained the better integrity of muscle microstructure, demonstrated by smaller holes, more complete Z-line and M-line, and no significant difference with CF-18 (P > 0.05). Furthermore, LVEF-12 effectively inhibited protein oxidative denaturation as shown by the lower carbonyl content, surface hydrophobicity, and higher total/active sulfhydryl groups and Ca2+-ATPase activity. Moreover, LVEF-12 effectively maintained the integrity of the secondary and tertiary structure of proteins, reduced cross-linking aggregation of proteins, and sustained better functional properties, as shown by higher α-helix content, fluorescence intensity, protein solubility, and lower R-value, disulfide bonds.

Effects of freeze-thaw cycles on in-vitro digestive properties of myofibrillar protein in mirror carp (Cyprinus carpio L.), based on protein degradation, oxidation, and structural properties

The in-vitro digestive properties of myofibrillar protein (MP) in mirror carp (Cyprinus carpio L.) after freeze-thaw (F-T) cycles were analyzed in terms of the relationship between protein degradation, oxidation, and structural properties. The F-T samples exhibited a significant increase in glucosidase activity, N-acetyl-β-d-glucosidase activity, total protease activity, and non-protein nitrogen content. α-aminoadipate semialdehyde and γ-glutamate semialdehyde contents increased by 23.17% and 123.12%, respectively. Furthermore, 53.97% decrease in the total nitrogen content and changes in the content of different soluble proteins were observed. X-ray diffraction intensity, thermal stability, free amine content, hydrolysis degree, and digestibility of the MP samples decreased, and the 2θ angle and zeta potential were reversed. Besides, changes in the amide band wavenumbers were also detected. Therefore, the protein structure was unfolded and aggregates were formed through degradation and oxidation induced by the F-T cycles, ultimately making the in-vitro digestion of MP difficult.

Oxidation affects pH buffering capacity of myofibrillar proteins via modification of histidine residue and structure of myofibrillar proteins

The pH buffering capacity is an important functionality of muscle proteins, and muscle foods are susceptible to being oxidized during storage and processing. In order to study the effect of oxidation on the pH buffering capacity of myofibrillar proteins, myofibrils extracted from snakehead fish (Channa argus) were oxidized with H2O2. Results showed that increased oxidation led to loss of free sulfhydryl groups, formation of carbonyl groups, increased surface hydrophobicity, and aggregation of myofibrillar proteins. In addition, there was a significant reduction in the content of histidine in oxidized myofibrillar proteins. The pH buffering capacity of myofibrillar proteins significantly decreased from 3.14 ± 0.03 mM H+/(mL × ΔpH) down to 2.55 ± 0.03 mM H+/(mL × ΔpH) after oxidation with 50 mM H2O2. Both oxidized myofibrillar proteins and histidine showed a high pH buffering capacity at pH near 5.8, which is the histidine pKa value. Here, we hypothesize that oxidation-induced changes in the pH buffering capacity of myofibrillar proteins were driven by oxidative modification of histidine and structural changes of myofibrillar proteins. The significance of this study to food industry may be the awareness that protein oxidation may affect pH through changes in buffering capacity. And the use of antioxidants, especially those targeting at histidine will be promising in addressing this issue.

Novel protective aspects of dietary polyphenols against pesticidal toxicity and its prospective application in rice-fish mode: A Review

The rice fish system represents an innovative and sustainable approach to integrated farming, combining rice cultivation with fish rearing in the same ecosystem. However, one of the major challenges in this system is the pesticidal pollution resulting from various sources, which poses risks to fish health and overall ecosystem balance. In recent years, dietary polyphenols have emerged as promising bioactive compounds with potential chemo-preventive and therapeutic properties. These polyphenols, derived from various plant sources, have shown great potential in reducing the toxicity of pesticides and improving the health of fish within the rice fish system. This review aims to explore the novel aspects of using dietary polyphenols to mitigate pesticidal toxicity and enhance fish health in the rice fish system. It provides comprehensive insights into the mechanisms of action of dietary polyphenols and their beneficial effects on fish health, including antioxidant, anti-inflammatory, and detoxification properties. Furthermore, the review discusses the potential application methods of dietary polyphenols, such as direct supplementation in fish diets or through incorporation into the rice fields. By understanding the interplay between dietary polyphenols and pesticides in the rice fish system, researchers can develop innovative and sustainable strategies to promote fish health, minimize pesticide impacts, and ensure the long-term viability of this integrated farming approach. The information presented in this review will be valuable for scientists, aqua-culturists, and policymakers aiming to implement eco-friendly and health-enhancing practices in the rice fish system.

Evidence of myofibrillar protein oxidation and degradation induced by exudates during the thawing process of bighead carp fillets

Oxidation of myofibrillar proteins (MPs) is considered as an important reason for the quality deterioration of frozen stored fish fillets, but the impact of the thawing process on the oxidation and thereby property changes of MPs has been largely neglected. In this study, we incubated MPs for 24 h at 4 °C with thawing exudates collected from fish fillets stored at -20 °C for 0-5 months to mimic the thawing process. Exudates treatment induced the increased content of carbonyls, Schiff bases, and dityrosine, structural changes, and the decreased water-holding capacity of MPs. SDS-PAGE and LC-MS/MS results indicated that exudates caused the degradation of MPs with the potential involvement of lipid oxidation products, hemoglobin, and proteases. Prolonged frozen storage decreased antioxidant enzyme activity and increased lipid oxidation products in exudates, which might be the reason for exudates from fillets frozen for longer periods can cause more severe oxidation and degradation of MPs.

Proteomic evidence of protein degradation and oxidation in brined bighead carp fillets during long-term frozen storage

Protein degradation and oxidation are two major alterations during the storage of processed bighead carp fillets. This study conducted a comparative analysis of degraded and oxidized products as well as oxidation sites in fresh, frozen and brined frozen bighead carp fillets. Frozen storage played a dominant role in protein degradation and oxidation, and brining promoted these changes. In brined frozen samples, the decreased SDS-PAGE band intensities for tropomyosin, troponin, and myosin light chain were mainly due to their degradation. Myosin heavy chain fast skeletal muscle was the most oxidized and degraded protein during storage, with modifications such as monooxidation, protein-lipid peroxidation adducts, and α-aminoadipic semialdehydes formation. Amino acids in the tail portion of myosin were prone to oxidation than the head portions. Our results provided comprehensive insights into protein degradation and oxidation in bighead carp during storage, helping to assess the specific fate of oxidative products in future dietary investigations.

Effect of sodium alginate ice glazing on the quality of the freeze-thawed fish balls

The effect of 1.0 % (w/v) sodium alginate (SA) glazing on surface frost formation and the quality of frozen fish balls in repeated freeze-thaw (F-T) cycles was studied. The optimal glazing property of 1.0 % SA solution was manifested by high transmittance, excellent water resistance, and high ice glazing rate. After seven F-T cycles, compared with the control, the ice production, thawing loss, and total volatile base nitrogen (TVB-N) value of samples with 1.0 % ice glazing decreased by 28.30 %, 21.02 %, and 27.35 %, while the chewiness and whiteness were increased by 15.02 % and 10.40 %, respectively. Moreover, compared to the control, the microstructure of fish balls glazed with 1.0 % SA was smoother and more uniform, and the ice crystal diameter was smaller. Therefore, 1.0 % SA glazing effectively inhibits the formation of ice crystals, reducing water migration and loss while minimizing damage to the meat structure, thus enhancing the quality of meat products.

The Research Field of Meat Preservation: A Scientometric and Visualization Analysis Based on the Web of Science

Meat plays a significant role in human diets, providing a rich source of high-quality protein. With advancements in technology, research in the field of meat preservation has been undergoing dynamic evolution. To gain insights into the development of this discipline, the study conducted an analysis and knowledge structure mapping of 1672 papers related to meat preservation research within the Web of Science Core Collection (WOSCC) spanning from 2001 to 2023. And using software tools such as VOSviewer 1.6.18 and CiteSpace 5.8.R3c allowed for the convenient analysis of the literature by strictly following the software operation manuals. Moreover, the knowledge structure of research in the field of meat preservation was synthesized within the framework of "basic research-technological application-integration of technology with fundamental research," aligning with the research content. Co-cited literature analysis indicated that meat preservation research could be further categorized into seven collections, as well as highlighting the prominent role of the antibacterial and antioxidant properties of plant essential oils in ongoing research. Subsequently, the future research direction and focus of the meat preservation field were predicted and prospected. The findings of this study could offer valuable assistance to researchers in swiftly comprehending the discipline's development and identifying prominent research areas, thus providing valuable guidance for shaping research topics.

The impact of freezing methods on the quality, moisture distribution, microstructure, and flavor profile of hand-grabbed mutton during long-term frozen storage

The aim of present study was to investigate the influence of conventional freezing (CF, -18 °C), low-temperaturefreezing (LF, -40 °C), and ultra-low-temperature freezing (ULF, -80 °C) on the quality, moisture distribution, microstructure, and flavor profile of hand-grabbed mutton (HGM) during frozen storage (0, 30, 60, 90, 120, 150 and 180 days). The TPC, TVB-N, and TBARS values increased significantly with prolonged storage, while the moisture content decreased (P < 0.05). Additionally, the concentrations of aldehydes, alcohols, ketones, acids, and alkenes decreased significantly as the storage duration increased. However, the concentrations of esters and heterocyclics increased (P < 0.05). Notably, at 30-180 days of storage, the TBARS and TVB-N values in ULF samples were significantly lower than those in CF and LF samples, while the moisture content was significantly higher (P < 0.05). Low field-nuclear magnetic resonance (LF-NMR) analysis showed that ULF decreased water migration and maintained the original texture characteristics of HGM during frozen storage. The ULF and LF groups had significantly higher levels of volatiles than the CF group (P < 0.05). The findings show that ULF, with its relatively rapid freezing rates, can still maintain the high quality of HGM after 180 days of frozen storage, contributing to quality control.

Challenges and processing strategies to produce high quality frozen meat

Freezing is an effective means to extend the shelf-life of meat products. However, freezing and thawing processes lead to physical (e.g., ice crystals formation and freezer burn) and biochemical changes (e.g., protein denaturation and lipid oxidation) in meat resulting in loss of quality. Over the last two decades, several attempts have been made to produce thawed meat with qualities similar to that of fresh meat to no avail. This is due to the fact that no single technique exists to date that can mitigate all the quality challenges caused by freezing and thawing. This is further confounded by the consumer perception of frozen meat as lower quality compared to equivalent fresh-never-frozen meat cuts. Therefore, it remains challenging for the meat industry to produce high quality frozen meat and increase consumer acceptability of frozen products. This review aimed to provide an overview of the applications of novel freezing and thawing technologies that could improve the quality of thawed meat including deep freezing, high pressure, radiofrequency, electro-magnetic resonance, electrostatic field, immersion solution, microwave, ohmic heating, and ultrasound. This review will also discuss the development in processing strategies such as optimising the ageing of meat pre- or post-freezing, and the integration of freezing and thawing in one process/regime to collapse the difference in quality between thawed meat and fresh-never-frozen equivalents.

Recent Trends in Active Packaging Using Nanotechnology to Inhibit Oxidation and Microbiological Growth in Muscle Foods

Muscle foods are highly perishable products that require the use of additives to inhibit lipid and protein oxidation and/or the growth of spoilage and pathogenic microorganisms. The reduction or replacement of additives used in the food industry is a current trend that requires the support of active-packaging technology to overcome novel challenges in muscle-food preservation. Several nano-sized active substances incorporated in the polymeric matrix of muscle-food packaging were discussed (nanocarriers and nanoparticles of essential oils, metal oxide, extracts, enzymes, bioactive peptides, surfactants, and bacteriophages). In addition, the extension of the shelf life and the inhibitory effects of oxidation and microbial growth obtained during storage were also extensively revised. The use of active packaging in muscle foods to inhibit oxidation and microbial growth is an alternative in the development of clean-label meat and meat products. Although the studies presented serve as a basis for future research, it is important to emphasize the importance of carrying out detailed studies of the possible migration of potentially toxic additives, incorporated in active packaging developed for muscle foods under different storage conditions.

Effect of Capsaicin and Dihydrocapsaicin in Capsicum on Myofibrillar Protein in Duck Meat

Spice and its extracts have gained widespread utilization as natural and eco-friendly additives, imparting enhancements in flavor, color, and antioxidative attributes to meat-based products. This work aims to study the effect mechanism of capsaicin (CA) and dihydrocapsaicin (DI) in capsicum (chili pepper) on the structure and function of myofibrillar proteins (MPs) in duck meat during thermal treatment. The results showed that at a CA-DI to MP ratio of 1:500 (g/g) following a 12 min heat treatment, the carbonyl content of MPs in duck meat decreased by 48.30%, and the sulfhydryl content increased by 53.42%. When the concentration was 1:500 (CA-DI, g/g) after 24 min of heat treatment, the •OH and DPPH radical scavenging rates were highest at 59.5% and 94.0%, respectively. And the initial denaturation temperature of MPs was the highest at 96.62 °C, and the thermal absorption was lowest at 200.24 J g-1. At the parameter, the smallest particle size and size distribution range of MP were 190 nm (9.51%). Furthermore, the interplay between CA-DI and MPs contributed to a reduction in the protein particle size and intrinsic fluorescence. In summary, the combination of CA-DI and MPs played a crucial role in inducing protein unfolding and disintegration.

Cryoprotective Effect of NADES on Frozen-Thawed Mirror Carp Surimi in Terms of Oxidative Denaturation, Structural Properties, and Thermal Stability of Myofibrillar Proteins

Quality degradation due to the formation and growth of ice crystals caused by temperature fluctuations during storage, transportation, or retailing is a common problem in frozen surimi. While commercial antifreeze is used as an ingredient in frozen surimi, its high sweetness does not meet the contemporary consumer demand for low sugar and low calories. Therefore, the development of new green antifreeze agents to achieve an enhanced frozen-thawed stability of surimi has received more attention. The aim of this study was to develop a cryoprotectant (a mixture of citric acid and trehalose) to enhance the frozen-thawed stability of surimi by inhibiting the oxidative denaturation and structural changes of frozen-thawed mirror carp (Cyprinus carpio L.) surimi myofibrillar protein (MP). The results showed that the amounts of free amine, sulfhydryl, α-helix, intrinsic fluorescence intensity, and thermal stability in the control significantly decreased after five F-T cycles, while the Schiff base fluorescence intensity, amounts of disulfide bonds and surface hydrophobicity significantly increased (p < 0.05). Compared to sucrose + sorbitol (SS), the natural deep eutectic solvents (NADES) effectively inhibited protein oxidation. After five F-T cycles, the α-helix content and Ca2+-ATPase activity of the NADES samples were 4.32% and 80.0%, respectively, higher, and the carbonyl content was 17.4% lower than those of the control. These observations indicate that NADES could inhibit oxidative denaturation and enhance the structural stability of MP.

Effects of 2,2'-Azobis(2-methylpropionamidine) Dihydrochloride Stress on the Gel Properties of Duck Myofibrillar Protein Isolate

The aim of this study was to investigate the biochemical properties and gel-forming capacity of duck myofibrillar proteins under the effects of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH)-mediated oxidation. Duck myofibrillar proteins were extracted and treated with different concentrations of AAPH solutions (0, 1, 3, 5, 10 mmol/L) and then analysed for carbonyl content, dynamic rheology, protein profiles and gel-forming properties (colour, water holding capacity, gel strength and microstructure). The results showed that with increasing AAPH concentration, the carbonyl content of the proteins exhibited an increasing trend (p < 0.05); SDS-PAGE pattern changes indicated that moderate oxidation (3 mmol/L AAPH) induced myosin aggregation via covalent bonds including disulfide, enhanced protein-protein interactions, and thus affected the gel strength of the DMPs' heat-induced gels. However, high oxidation (5 and 10 mmol/L AAPH) led to the partial degradation of the myosin heavy chain (MHC) isoforms, as evidenced by lower storage modulus and irregular microstructures, which significantly reduced gelation ability. These results suggest that the internal relationship between alkylperoxyl radical-induced oxidation should be taken into account in the processing of duck meat, as mild protein oxidation is conducive to improving gel quality.

Effects of Different Freezing Rate and Frozen Storage Temperature on the Quality of Large-Mouth Bass (Micropterus salmoides)

In order to clarify the individual role of freezing and frozen storage on the quality of fish, fillets of large-mouth bass (Micropterus salmoides) were subjected to different freezing rates (freezing with -18 °C (A), -60 °C (B), and -60 °C with forced air circulation at 2 m/s (C), respectively) followed by frozen storage at -18 °C for 30 and 90 days. Another two groups were frozen at -60 °C, followed by storage at -40 °C (D) and -60 °C (E), respectively. Results showed that water-holding and TVBN were mainly affected by storage time. No significant changes were found in free thiol content among treatments. A greater freezing rate and lower storage temperature generally led to lower TBARS. GC × GC-TOFMS revealed a total of 66 volatile compounds, which were related to lipid oxidation. PLS-DA showed that fresh samples were separated from the frozen-thawed ones, and fillets in groups D and E were relatively close to fresh fillets in the composition of oxidation-related volatiles. In conclusion, freezing rate and storage temperature had a significant impact on lipid oxidation and protein denaturation in the fillets of large-mouth bass, while protein oxidation was more affected by freezing rate.

Uncovering quality changes of salted bighead carp fillets during frozen storage: The potential role of time-dependent protein denaturation and oxidation

This study aimed to find the specific relationship between quality traits and myofibrillar proteins (MPs) alteration of salted fish during frozen storage. Protein denaturation and oxidation occurred in frozen fillets, with the denaturation occurring before oxidation. In the pre-phase of storage (0-12 weeks), protein structural changes (secondary structure and surface hydrophobicity) were closely related to the water-holding capacity (WHC) and textural properties of fillets. The MPs oxidation (sulfhydryl loss, carbonyl and Schiff base formation) were dominated and associated with changes in pH, color, WHC, and textural properties during the later stage of frozen storage (12-24 weeks). Besides, the brining at 0.5 M improved the WHC of fillets with less undesirable changes in MPs and quality traits compared to other concentrations. The 12 weeks was an advisable storage time for salted frozen fish and our results might provide an available suggestion for fish preservation in aquatic industry.

Chickpea protein hydrolysate as a novel plant-based cryoprotectant in frozen surimi: Insights into protein structure integrity and gelling behaviors

Chickpea protein (CP) and its enzymatic hydrolysates are one of the most widely consumed pulse ingredients manifesting versatile applications in food industry, such as binders, emulsifiers, and meat protein substitutes. Other than those well-known functionalities, however, the use of CP as a cryoprotectant remained unexplored. In this study, we prepared the chickpea protein hydrolysate (CPH) and investigated its cryoprotective effects to frozen surimi in terms of the protein structure integrity and gelling behaviors. Results indicated that CPH could inhibit myofibrillar protein (MP) denaturation and oxidation during the freeze-thaw cycling, as evidenced by their increased solubility, Ca²⁺-ATPase activity, sulfhydryl concentration, and declined content of disulfide bonds, carbonyl concentration and surface hydrophobicity. Freezing-induced changes on MP secondary structures were also retarded. Moreover, gels prepared from CPH-protected frozen surimi demonstrated more stabilized microstructure, uniform water distribution, enhanced elasticity, gel strength and water holding capacity. The CPH alone, at a reducing addition content of 4% (w/w), exhibited comparable cryoprotective performance to that of the commercial formulation (4% sucrose and 4% sorbitol). Therefore, this study provides scientific insights for development of pulse proteins as novel and high-performance food cryoprotectants.

Mechanism of low-voltage electrostatic fields on the water-holding capacity in frozen beef steak: Insights from myofilament lattice arrays

This study investigated the impact of low-voltage electrostatic field-assisted freezing on the water-holding capacity of beef steaks. The enhances mechanism of water-holding capacity by electrostatic field was elucidated through the detection of dynamic changes in the myofilament lattice and the construction of an in vitro myosin filaments model. The findings demonstrated that the disorder of the myofilament array, resulted from the aggregation of myosin filaments during freezing, is a crucial factor responsible for the water loss. The intervention of the electrostatic field can effectively reduce the myofibril density by 18.7%, while maintaining a regular lattice array by modulating electrostatic and hydrophobic interactions between myofibrils. Moreover, the electrostatic field significantly inhibited the migration of immobilized water to free water, thus resulting in an increase in the water-holding capacity of myofibrils by 36%. This work provides insights into the underlying mechanisms of water loss in frozen steaks and its regulation.

Cryoprotective effect of water-tailored trehalose-based natural deep eutectic solvents on frozen-thawed mirror carp (Cyprinus carpio L.) surimi

The inhibitory effect of water-tailored natural deep eutectic solvents (NADES) constructed from citric acid and trehalose with different amounts on the quality deterioration and oxidation of frozen-thawed (F-T) mirror carp (Cyprinus carpio L.) surimi was studied. NADES was obtained by citric acid to trehalose and the effect of moisture addition (v/v) on the structure, physicochemical, and anti-freezing capacity of NADES was assessed. NADES + 10 % H₂O has relatively low viscosity (25 %) and strong freezing resistance. However, a 50 % H₂O addition leads to the disappearance of the hydrogen bond. The addition of NADES effectively inhibits water loss, migration, and mechanical damage on F-T surimi. An inhibitory effect of 4 % (w/w) NADES on oxidation was verified by a decrease in carbonyl contents (17.4 %, 8.63 %) and TBARS (37.9 %, 15.2 %) of surimi compared with control (P < 0.05) and sucrose + sorbitol after 5F-T cycles, suggesting the potential of NADES as a cryoprotectant for the food industry.

Protein oxidation affected the digestibility and modification sites of myofibrillar proteins from bighead carp fillets treated with hydroxyl radicals and endogenous oxidizing system

This study aimed to investigate the effect of hydroxyl radical oxidizing system (HROS) and endogenous oxidizing system (EOS, i.e., frozen storage at -20 °C) on protein oxidation, digestive properties, and peptide modification of myofibrillar proteins (MPs) in bighead carp (Hypophthalmichthys nobilis) fillets. The oxidation degree increased with the frozen time and H₂O₂ concentration as evidenced by carbonyl group generation and sulfhydryl group loss in MPs. The digestibility of protein declined gradually during frozen storage, while it increased after treatment with 5 mM H₂O₂ compared with no H₂O₂ intervention. More modification numbers and types were observed in the EOS group than HROS in digested MPs peptides, which might be due to the complexity of the frozen fillet system such as the presence of lipid. The potential conversion of α-aminoadipic semialdehyde (AAS) to α-aminoadipic acids (AAA) was observed in HROS. Additionally, the myosin heavy chain was more susceptible to oxidation among all MPs by EOS oxidation.

Physicochemical and microstructural mechanisms for quality changes in lightly salted tilapia (Oreochromis niloticus) fillets during frozen storage

BACKGROUND

Frozen tilapia fillet has become a leading aquatic product. High drip loss, dry and fibrous mouthfeel, and an unappealing appearance are its main problems. It was hypothesized that light salting could improve the quality, and that the preparation conditions would affect the storage stability of frozen tilapia fillets.

RESULTS

The quality changes of lightly salted tilapia fillets were evaluated during frozen storage, and the underlying mechanisms were studied from the physicochemicaland microstructural perspectives. Though the salt content was 1.5% in all samples,the amount of ice crystals in frozen tissues decreased with the descending water content and freezing point (P < 0.05). No intracellular voids were observed in the samples prepared under proper salting conditions, and the myofibers were plump and smooth after freezing-thawing, which contributed to the high water-holding capacity of lightly salted fillets. After 28 days,the water-binding capacity of the salted groups was 14.69%-18.62% higher than that of their unsalted counterparts (P < 0.05). The reduced protein solubility in the salted fillets was likely to have occurred because the solubilized and unfolded proteins interacted more easily during frozen storage. The oxidation degree of myofibrillar proteins was also affected by salting condition, and the fillets with less oxidized sulfhydryl groups maintained high springiness after 28 days of frozen storage.

CONCLUSION

The salting condition of 9% NaCl solution for 1 h was recommended for the preparation of lightly salted fillets from freshwater fish, taking into account quality, processing efficiency, and storage stability. The enhanced water-holding capacity and texture of lightly salted tilapia fillets were attributed to modified physicochemical and microstructural properties. These results could provide a scientific basis for the processing and storage of high-quality, frozen, lightly salted fillets from freshwater fish. © 2022 Society of Chemical Industry.

Olfactory visualization sensor system based on colorimetric sensor array and chemometric methods for high precision assessing beef freshness

Beef is easily spoiled, resulting in foodborne illness and high societal costs. This study proposed a novel olfactory visualization system based on colorimetric sensor array and chemometric methods to detect beef freshness. First, twelve color-sensitive materials were immobilized on a hydrophobic platform to acquire scent information of beef samples according to solvatochromic effects. Second, machine vision algorithms were used to extract the scent fingerprints, and principal component analysis (PCA) was employed to compress the feature dimensions of the fingerprints. Finally, four qualitative models, k-nearest neighbor, extreme learning machine, support vector machine (SVM), and random forest, were constructed to evaluate the beef freshness according to the value of total volatile basic nitrogen (TVB-N) and total viable counts (TVC). Results demonstrated that SVM had a preferable prediction ability, with 95.83% and 95.00% precision in the training and prediction sets, respectively. The results revealed that the simple constructed olfactory visualization sensor system could rapidly, robustly, and accurately assess beef freshness.

On the emerging of thawing drip: Role of myofibrillar protein renaturation

This study aimed to facilitate the understanding on the origin of thawing drip under different freezing rate. Eventually we observed significantly greater thaw loss produced by slow freezing (8.58%) as compared to fast freezing (6.41%) after 24 h of thawing. Back to the freezing, ice crystallization induced decline in pH and the cold denaturation of myofibrillar protein. However, independent of freezing rate, we noticed protein renaturation with pH restoring during thawing, evidenced by the decreasing surface hydrophobicity, increasing solubility and thermal stability, and gradually stabilized secondary structure. Meanwhile, the water-holding of myofibrils increased with thawing process along with the rising water mobility. Under fast freezing, the results indicated less extensive protein cold denaturation and lower water mobility during thawing. Besides, we proposed that the microenvironment of lower ionic strength in fast freezing should benefit the protein renaturation and water re-absorption, ultimately contributed to lower thaw loss.

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.

l-Arginine and l-lysine retard aggregation and polar residue modifications of myofibrillar proteins: Their roles in solubility of myofibrillar proteins in frozen porcine Longissimus lumborum

This study investigated the ability of l-arginine and l-lysine to inhibit the adverse effects of freezing on the structure and solubility of myofibrillar proteins extract (MPE) in porcine Longissimus lumborum. The results showed that freezing decreased solubility of MPE, band densities of actin and myosin heavy and light chains, fluorescence intensity, and contents of free amino group and total sulfhydryls, but increased content of carbonyl groups and absolute zeta-potential of MPE. l-Arginine and l-lysine effectively alleviated the adverse effects of freezing. l-Arginine and l-lysine significantly increased β-sheet content, T_max1 and ΔH₁, but decreased α-helix content and disulfide bond content in MPE. Additionally, the SDS-PAGE analysis showed that l-arginine and l-lysine could prevent appearance of bands at about 150 kDa. Overall, this study shows that both l-arginine and l-lysine could not only abate the aggregation and disruption of MPs, but also reduce the oxidation of their polar amino groups, which ultimately contribute to their superior solubility. The results may be interesting in meat industry.

Improvements in chitosan-based slurry ice production and its application in precooling and storage of Pampus argenteus

The effects of microbubbles in chitosan-based slurry ice production were investigated, and the efficiency of chitosan-based slurry ice was evaluated for silver pomfret (Pampus argenteus) precooling and storage at 0 °C. Microbubbles generated though agitation accelerated slurry ice production by promoting ice nucleation and eliminating supercooling. Higher bubble counts improved freezing, but overly large bubbles reduced the performance. The rheological properties of chitosan solutions were also investigaed, and solutions with higher viscosity formed more bubbles. Experiments investigating precooling rates, microbial concentrations, pH, thiobarbituric-acid-reactive substances, and total volatile basic nitrogen all confirmed that chitosan-based slurry ice had higher performance than flake ice or conventional slurry ice. Chitosan-based slurry ice can be used for precooling in the fish industry to reduce energy consumption, accelerate precooling, reduce microbial growth, and improve shelf life.

Freeze-Thawing Treatment as a Simple Way to Tune the Gel Property and Digestibility of Minced Meat from Red Swamp Crayfish (Procambarus clarkiix)

The effects of freezing methods, including rapid freezing (RF) or slow freezing (SF), combined with thawing methods, e.g., water immersing thawing (WT) or cold thawing (CT), on the meat yield, drip loss, gel properties, and digestive properties of meat detached from red swamp crayfish were investigated. RF greatly reduced the freezing time compared to SF, and the thawing time of frozen crayfish was obviously shortened by WT in comparison to CT. RF and CT improved the meat yield but increased the drip loss, probably as a result of the greater protein denaturation or degradation. A soft and flexible gel was obtained by SF-CT, while a hard one was achieved by RF-WT. An SEM analysis showed that SF resulted in rough and irregular microstructures with larger pore sizes. Freeze-thawing led to an increase in the β-sheet content at the expense of α-helix and variations in the microenvironment of tyrosine and tryptophan residues in protein molecules of the gels, which was more pronounced in the SF-CT group. Moreover, freeze-thawing could cause enhanced protein digestibility but reduce the antioxidant activity of gels. These findings underline the promise of the freezing-thawing treatment in tuning the gel-based meat products of crayfish.