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Frozen aquatic products undergo unavoidable quality changes owing to temperature fluctuations during frozen storage and distribution. This study investigated the effects of 1% cellobiose (CB), and 0.5 and 1% carboxylated cellulose nanofibers (CNF) on ice crystal growth and recrystallization of frozen large yellow croaker fillets exposed to temperature fluctuations. Denser and more uniformly distributed ice crystals were observed in the CB- and CNF-treated samples than in the water-treated samples. Furthermore, the addition of CB and CNF suppressed the conversion of bound water to frozen water in the samples during temperature fluctuation cycles, played a positive role in fixing the ionic and hydrogen bonds that stabilize the protein structure, limited the conformational transition from α-helix to β-sheet, and improved protein thermal stability. Based on turbidity, zeta potential, and confocal laser scanning microscopy (CLSM) analyses, the presence of CB and CNF restricted the protein aggregation. Compared with CB, CNF molecules with abundant carboxyl functional groups and longer morphology exhibited better cryoprotective effects. Moreover, the fillets were more improved protected from mechanical damage induced by large ice crystals at a higher CNF concentration. This study reveals the potential of CB and CNF as novel cryoprotectants. • Temperature fluctuation significantly affected the quality change of frozen sample. • CB and CNF suppressed the growth and recrystallization of ice crystals. • CNF could maintain the quality of frozen croaker fillets better than CB. • The CNF concentration were associated with size and distribution of ice crystals [ABSTRACT FROM AUTHOR]

Ultrasonic treatment (UT) was used to thaw large yellow croaker in this study, and the effect of various ultrasonic power levels on the quality of large yellow croaker was evaluated after thawing. The effects of ultrasonic on water holding capacity (WHC), moisture distribution, thiobarbituric acid‐reactive substance (TBARs), total volatile base nitrogen (TVB‐N), ATP degradation (related to K value), surface color change, free amino acid (FAA) content, total sulfhydryl group (SH) content, Fourier transform infrared absorption spectra (FT‐IR), fluorescence emission spectra, and microscopic observations of large yellow croaker myofibrillar proteins were investigated. The thawing times of the control sample, 200UT, 240UT, 280UT, and 320UT samples were 1750, 1190, 810, 580, and 570 s, respectively, which indicated that ultrasonic radiation could improve thawing efficiency. Additionally, ultrasonic thawing maintained better freshness and color and inhibited lipid oxidation. Compared with fresh samples, the TVB‐N of large yellow croaker thawed by ultrasonication increased by 12.68%, and the K value increased by 0.9%. The 240UT sample had tightly arranged myofibrils and fewer changes in the structures of myogenic fibrillar proteins than the fresh samples, and the SH content of 240UT was decreased by 8.17%. Use of excessive ultrasonic power (320 W) damaged the protein microstructure and the microstructure of large yellow croaker. In conclusion, sample 240UT maintained the quality of large yellow croaker better with minimal damage, which is recommended for rapid thawing. Practical Application: Ultrasonic waves improve the thawing efficiency of large yellow croaker and maintain the freshness and color of the fish. According to results, sample 240UT exhibited slight changes in the structure of the myofibril protein, but excessive ultrasonic power destroyed the microstructure and protein structure. Appropriate ultrasonic treatment to the thawing of fish has good prospects. [ABSTRACT FROM AUTHOR]

• The water properties and protein stability of croaker during freezing were studied. • Ice crystal size had an effect on protein secondary and tertiary structure. • Protein stability significantly correlation with water properties. • The greatest contribution to water loss is the degeneration of myosin. This study aimed to investigate the changes in water properties and protein stability of large yellow croaker during freezing. The changes of ice crystals and muscle tissue were assessed using X-ray computed tomography (CT) and light microscopy, respectively. The results of water-holding capacity (WHC), low-field nuclear magnetic resonance, Fourier transform infrared, intrinsic fluorescence, differential scanning calorimetry (DSC), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that compared to the control, freezing treatment resulted in the reduction of WHC and protein stability of the samples. Large ice crystals had a greater effect on muscle water loss, protein secondary and tertiary structure, and protein thermal stability than small ice crystals. The results of Pearson analysis confirmed significant correlation between water properties and protein stability at different ice crystal size. Therefore, these results suggested the beneficial effects of small ice crystals on the water properties and protein stability of croaker, but the effect of low-temperature fracture on the product need to be concerned. [ABSTRACT FROM AUTHOR]

[Display omitted] • Due to freeze-concentration, the pH change of solution at difference location varies. • Acidification induces the aggregates to become tightly packed during freezing. • Good's buffer show alkalinization during freezing. • Good's buffers inhibit the selective crystallization of Na 2 HPO 4 ·12H 2 O. • Good's buffers (MES, MOPS and HEPES) inhibit denaturation of MFP. The current systematic study sought to examine the potential use of three Good's buffers (MES, MOPS and HEPES) in inhibiting myofibrillar protein (MFP) denaturation induced by acidity changes. The highest degree of acidity variation was found in the center and bottom of large bottles due to the freeze-concentration effect. Good's buffer tended to basify during freezing, and it could prevent the crystallization of sodium phosphate (Na-P) buffer. Acidification upon freezing Na-P disrupted the natural conformation of MFP and induced the formation of large proteins aggregates with tight packing. The 15 mM MES, 20 mM MOPS, and 30 mM HEPES were respectively added to neutralize the strong acidity drop induced by freezing 20 mM Na-P, and all of them significantly improved the stability of the MFP conformation (P < 0.05). This work is not only critical to meet the growing demand for protein, but also groundbreaking for broadening the applicability of Good's buffers in the food industry. [ABSTRACT FROM AUTHOR]

Herein, we investigated the potential relationship between freeze-concentration and myofibrillar protein (MFP) denaturation during freezing, and explored the inhibitory effect of cellobiose (CB) on the freeze-concentration. To observe the freeze-concentration of solutes in 2 L solutions, homogeneous sections of three frozen solutions (NaCl, NaCl + MFP and NaCl + MFP + CB) were performed sequentially and the solute concentrations of 45 representative samples for each frozen solution were analyzed. The results indicated that all solutes during freezing were concentrated toward the center and bottom of the solution. Nevertheless, the addition of cellobiose resulted in a more uniform solute distribution, which could be attributed to the lower specific heat of solution induced by cellobiose, accelerating the freezing rate. Additionally, the formation of protein aggregation caused by freeze-concentration was effectively inhibited by the addition of cellobiose. The cellobiose may be a beneficial additive to improve the quality of frozen aquatic products. [Display omitted] • Freeze-concentration formation upon freezing of protein solution was studied. • Myofibrillar protein or cellobiose reduced the specific heat of NaCl solution. • The solutes concentrated in the center and bottom of the solution after freezing. • Cellobiose narrowed the degree of heterogeneity in frozen protein system. • Cellobiose inhibited protein aggregation formation caused by freeze-concentration. [ABSTRACT FROM AUTHOR]

• Selective crystallization of Na 2 HPO 4 ·12H 2 O caused the pH changes. • The increasing freeze-thaw cycles enhanced myofibrillar protein instability. • Cellobiose prevented buffer crystallization and attenuated the pH shift. • Cellobiose minimized freeze-thaw damage to myofibrillar protein. The aim of this study was to investigate myofibrillar protein (MFP) denaturation induced by pH changes during freeze–thaw (FT) cycles, and to propose an effective mitigation strategy. Owing to the selective crystallization of Na 2 HPO 4 ·12H 2 O and the consequent pH change, a pH change of 3.32 units was observed when the MFP solution were frozen. The surface hydrophobicity, particle size and confocal laser scanning microscopy showed that the protein molecules gradually unfolded and formed larger protein aggregation as the number of FT cycles increases. Additionally, protein degradation, secondary and tertiary structure alterations suggested that the FT cycle could disrupt structural integrity. The addition of cellobiose could maximize the inhibition of pH changes (decrease of ∼0.62 unit), no Na 2 HPO 4 ·12H 2 O crystallization was observed by X-ray diffraction. Cellobiose could minimize FT damage to myofibrillar protein, which was closest to the control. Thus, cellobiose can be used as a new and effective cryoprotectant. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the role of pH change and freezing rate on myofibrillar protein (MFP) denaturation during freezing. To demonstrate that the pH change was a cause of freezing-induced MFP denaturation, the sodium phosphate buffer was added to the MFP solution utilizing selective crystallization of Na 2 HPO 4 •12H 2 O that resulted in a pH decrease. Freezing MFP solution from 4 to −20 °C caused pH decreases of ~2.80 and ~3.91 units when the buffer concentration was 20 mM and 200 mM, respectively. The pH change disrupted the secondary and tertiary structures of MFP. As the pH decreased, the unfolding of protein molecules progressively increased. The exposure of internal hydrophobic groups resulted in aggregation and larger size formation of MFP. Compared to slow freezing, part of the protons was trapped in the small ice crystals formed by fast freezing, which attenuated the pH shift (decrease of ~3.26 unit) and reduced protein denaturation. These results suggested that pH change was an important factor for freezing-induced MFP denaturation, and the increase of freezing rate could diminish the pH decrease, which was conducive to maintain the stability of MFP. • Freezing of MFP solution caused pH change by selective crystallization of Na 2 HPO 4. • The magnitude of pH decrease was proportional to the buffer concentration. • The increase of freezing rate could attenuate the magnitude of pH shift. • PH change had a significant effect on the secondary and tertiary structure of MFP. • As the pH decreased, the MFP molecule gradually unfold and significantly aggregated. [ABSTRACT FROM AUTHOR]

Summary: Enzymatic supramolecular assembly was applied to increase the thermal hysteresis activity (THA) of tilapia skin collagen peptides and their applicability as cryoprotectants. The THA value of the glutamine‐assembled product increased by 61.5% and its ice crystal content dropped by 33.93% compared to the collagen peptides. Following initial separation and purification, the THA of Gln‐AFPs was further elevated by 28.6%. After five freeze–thaw cycles, tilapia surimi treated with 8% Gln‐AFPs had high levels of salt‐soluble protein, total sulfhydryl content, Ca2+‐ATPase activity, and water‐holding capacity. Additionally, the cryoprotective effect of Gln‐AFPs on the surimi was found to be superior to that of commercial antifreeze. The majority of the Gln‐AFPs turns folded, according to FTIR analysis, and ‐helices were produced. After supramolecular assembly, the Gln‐AFPs structure also smoothed out. As a result, the enzymatic supramolecular assembly drastically increased the antifreeze activity of the tilapia skin‐collagen peptides, which could eventually be developed into a novel antifreeze additive in the food industry. [ABSTRACT FROM AUTHOR]

The combined effect of weakly acidic electrolyzed water (WAEW) and modified atmosphere packaging (MAP) treatments on the quality of puffer fish (Takifugu obscurus) during cold storage was studied on aspects of microbiological activity, texture, total volatile basic nitrogen (TVB‐N), trimethylamine (TMA), free amino acids (FAAs), thiobarbituric acid reactive substance (TBARS), ATP‐related compounds and K value, volatile organic compounds (VOCs), and organoleptic properties. As a result, significantly (p <.05) higher inhibitory effects on total viable counts (TVC), H2S‐producing bacteria (including Shewanella putrefaciens), Pseudomonas spp., and lactic acid bacteria (LAB) were observed in WAEW‐treated puffer fish packaged in 60%CO2/5%O2/35%N2 atmosphere than that in air package and vacuum package with/without WAEW‐treated samples. In addition, chemical results showed that WAEW together with MAP treatments were highly efficient in maintaining lower TVB‐N, TMA, and TBARS values in refrigerated puffer fish. Moreover, the presence of WAEW combined with MAP treatments showed positive effects on retarding the relative content of fishy flavor compounds, such as 1‐octen‐3‐ol, 1‐penten‐3‐ol, hexanal, heptanal, nonanal, decanal, (E)‐2‐octenal, and 2,3‐butanedione. As a whole, the combined effect of WAEW and MAP on refrigerated puffer fish is advisable to maintain better quality and extend the shelf life. [ABSTRACT FROM AUTHOR]

Summary: Litopenaeus vannamei heads were autolysed at a constant temperature of 50 °C, pH 7.0 for a maximum duration of 5 h, and the antifreeze activity and physicochemical properties of the head autolysates were determined. Thermal hysteresis (TH) was used as an index for determining the antifreeze activity of the shrimp head autolysates. The highest thermal hysteresis activity was 1.82 °C which was measured in the 5 h‐shrimp head autolysate. The highest negative zeta potential value (−41.06 ± 2.08 mV) and surface hydrophobicity (295.575 ± 9.7819) were in the 5 and 1.5 h autolysate groups, respectively. Generally, <2000 Da components accounted for over 85% of the total molecular weight in all shrimp head autolysate groups. Pearson correlation analysis was used to investigate how physicochemical properties influenced the thermal hysteresis index. Although at varying degrees, the analysis confirmed that a positive correlation existed between TH activity and molecular weight, hydrophobic amino acid content, and surface hydrophobicity. A negative correlation existed between TH activity and zeta potential, and hydrophilic amino acids. The findings of our study suggest that Litopenaeus vannamei head autolysate has a potential antifreeze effect and that the physicochemical properties influence its thermal hysteresis. [ABSTRACT FROM AUTHOR]

In this research, the effect of CO 2 (0%, 20%, 60%, and 100%) on the spoilage potential of Shewanella putrefaciens (S. putrefaciens) during 4 °C cold storage was evaluated. Results revealed that the growth curves of S. putrefaciens were effectively affected by CO 2 with prolonged lag phases and delayed logarithmic phases. Protein oxidation of inoculated large yellow croakers was noticeably delayed with the treatment of CO 2 by keeping higher myofibrillar protein, total sulfhydryl groups and Ca2+-ATPase activity, and lower carbonyl groups. Spatial structures of samples treated with 20%–100% CO 2 were better in organized secondary structure and better-stabilized tertiary structure. Meanwhile, the myofibrillar microstructure detected by scanning electron microscope (SEM) and transmission electron microscopy (TEM) was also much well-organized than the control, with relative tightly attached myofibrils and intact sarcomere structure (clear A-band, I-band and M-lines). Furthermore, CO 2 treated samples have better texture and stronger moisture holding capacity. These results synergistically demonstrated that the spoilage ability of S. putrefaciens target at proteins was effectively suppressed by CO 2. [Display omitted] • The spoilage potential of S. putrefaciens target at proteins was inhibited by CO 2. • CO 2 prolonged lag phases and delayed logarithmic phase of S. putrefaciens. • Protein oxidation and degradation of inoculated samples were inhibited by CO 2. • A more effective inhibition by 100% CO 2 was observed. [ABSTRACT FROM AUTHOR]

• CO 2 efficiently inhibited the metabolism and spoilage potential of S. putrefaciens. • The production of unpleasant flavour compounds was inhibited by CO 2. • A more effective inhibition by 100% CO 2 was observed. To investigate the regulation mechanism of CO 2 (0% CO 2 , 20% CO 2 , 60% CO 2 , and 100% CO 2) on the spoilage potential of S. putrefaciens target to flavour compounds, the metabolic activity of S. putrefaciens and the changes in flavour compounds extracted from inoculated large yellow croakers were evaluated. Results showed that CO 2 significantly reduced biofilm formation capacity and suppressed synthesis of intracellular adenosine triphosphate (ATP). The production of unpleasant flavour compounds, such as total volatile basic nitrogen (TVB-N), trimethylamine (TMA), inosine (HxR), hypoxanthine (Hx), histidine, lysine, histamine, putrescine, 1-octen-3-ol, hexanal and benzaldehyde, was inhibited by CO 2. The hydrolysis and oxidation of lipid in CO 2 -treated samples were alleviated and unsaturated fatty acids (UFAs) were in a higher percentage. In summary, CO 2 efficiently reduced the spoilage potential of S. putrefaciens and contributed to better flavour quality of samples during 4 °C storage. A more effective inhibition by 100% CO 2 was observed. [ABSTRACT FROM AUTHOR]

To compare the bioavailability of protein-binding zinc, we investigated the impact of baking on the structure of zinc-binding proteins. The results showed that zinc-binding proteins enriched in zinc with relative molecular weights distributed at 6 kDa and 3 kDa. Protein-binding zinc is predisposed to separate from proteins' interiors and converge on proteins' surface after being baked, and its structure tends to be crystalline. Especially -COO, -C-O, and -C-N played vital roles in the sites of zinc-binding proteins. However, baking did not affect protein-binding zinc's bioavailability which was superior to that of ZnSO 4 and C 12 H 22 O 14 Zn. They were digested in the intestine, zinc-binding complexes that were easily transported and uptaken by Caco-2 cells, with transport and uptake rates as high as 62.15% and 15.85%. Consequently, baking can alter the conformation of zinc-binding proteins without any impact on protein-binding zinc's bioavailability which is superior to that of ZnSO 4 and C 12 H 22 O 14 Zn. [Display omitted] • Baking can alter the binding sites between proteins and zinc ions. • The binding sites of proteins to zinc ions are mainly R 1 -COO-Zn, R 2 -C-O-Zn, and R 3 -C-N-Zn. • Zinc of zinc-binding proteins is absorbed in the form of zinc-binding complexes rather than zinc ions. The bioavailability of protein-binding zinc is superior to that of ZnSO 4 and C 12 H 22 O 14 Zn. [ABSTRACT FROM AUTHOR]