Role of Cryoprotectants in Surimi and Factors Affecting Surimi Gel Properties: A Review

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.

Assessment of the impact of whey protein hydrolysate on myofibrillar proteins in surimi during repeated freeze-thaw cycles: Quality enhancement and antifreeze potential

The quality of surimi, widely used in processed seafood, is compromised by freeze-thaw cycles, leading to protein denaturation and oxidative degradation. The objective of this study is to explore the effects of adding natural whey peptide hydrolysate (WPH) on the myofibrillar proteins of repeatedly freeze-thawed surimi. Results indicated surimi treated with 15% WPH exhibited only a 128% increase in surface hydrophobicity and a maximum peroxide value of 7.84 μg/kg, significantly lower than the control group. Additionally, salt-soluble protein content, emulsification activity, and stability decreased with the increase in freeze-thaw cycles. With a 15% WPH offering the most significant protective effect, evidenced by reductions of only 25.02%, 42.52% and 37.02% in salt-soluble protein content, emulsification activity, and stability, respectively. These outcomes demonstrate that WPH effectively reduces protein denaturation during repeated freeze-thaw processes. Future research should explore the molecular mechanisms underlying WPH's protective effects and evaluate their applicability in other food systems.

A review of inhibition mechanisms of surimi protein hydrolysis by different exogenous additives and their application in improving surimi gel quality

It is well known that aquatic products such as fish and shellfish, when stored for a long period of time under inappropriate conditions, can suffer from muscle softening. This phenomenon is mainly caused by endogenous proteases, which are activated during heating and accelerates the degradation of myofibrillar proteins, directly leading to weaker gels and poorer water retention capacity. This paper reviews the changes in fish proteins during storage after death and the factors affecting protein hydrolysis. A brief overview of the extraction of protease inhibitors, polysaccharides and proteins is given, as well as their mechanism of inhibition of protein hydrolysis in surimi and the current status of their application to improve the properties of surimi.

Screening and characterization of an antifreeze peptide from sea cucumber intestinal protein hydrolysates

Protein deterioration caused by ice crystals is an important factors affecting the frozen storage of fish. In this study, antifreeze peptides extracted from hydrolysates of sea cucumber intestinal protein with inhibition of protein denaturation were screened and characterized. The peptide Leu-Pro-Glu-Phe-Thr-Glu-Glu-Glu-Lys (LPEFTEEEK), derived from neutral protease hydrolysates of sea cucumber intestinal protein, was investigated for its potential to enhance the quality of salmon fillets during three freeze-thaw cycles. The results showed that the application of LPEFTEEEK effectively maintained the texture of fish fillets, as well as the oxidative and conformation stability of myofibrillar protein during the freezing process. Additionally, molecular dynamics simulations verified that LPEFTEEEK could bind to ice crystals and inhibit their recrystallization, thus preventing organisms from being damaged by freezing. This suggests that LPEFTEEEK holds significant promise as a novel cryoprotective agent for marine-derived antifreeze peptides.

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.

Cryoprotective effect of epigallocatechin gallate replacing sucrose on Hypophythalmichthys molitrix surimi during frozen storage

BACKGROUND

The present study aimed to investigate the cryoprotective effect of epigallocatechin gallate (EGCG) replacing sucrose on surimi during frozen storage. Substitution or partial substitution of 0.1% EGCG for sucrose (1.5%) was added to surimi, and the surimi samples without and with commercial cryoprotectants (4% sucrose and 4% sorbitol) were used as the control group.

RESULTS

The results obtained suggest that, with the increase in frozen storage time, the structural performance of surimi protein gradually weakened (e.g. the decrease in the surface hydrophobicity, the increase in the total sulfhydryl and solubility, and the protein myosin heavy chain bands became shallow) and surimi gel quality gradually deteriorated (e.g. the decrease in water-holding capacity, gel strength and all texture profile attributes). However, compared with the other three group surimi samples during the frozen period, the surimi proteins with partial replacement of sucrose by EGCG had a higher total sulfhydryl group content and solubility of proteins, as well as lower surface hydrophobicity of protein, suggesting that the addition of EGCG as a partial substitute for sucrose can enhance the antifreeze ability of surimi. Meanwhile, the surimi gel with the partial replacement of sucrose by EGCG had a higher water retention capacity, gel strength and texture attributes (e.g. hardness, springiness, cohesiveness, chewiness, and resilience), indicating that the addition of EGCG as a partial substitute for sucrose can inhibit the deterioration of surimi gel quality.

CONCLUSION

Overall, EGCG partially replacing sucrose can play an alternative cryoprotectant with a lower sweetness to prevent the quality of surimi from deteriorating. © 2024 Society of Chemical Industry.

Cryoprotective effects and mechanisms of soybean oligosaccharides on the grass carp (Ctenopharyngodon idellus) surimi during frozen storage

BACKGROUND

Conventional cryoprotectant mixtures (sucrose and sorbitol) impart excessive sweetness and calories to surimi. Therefore, there is a need to explore alternative cryoprotectants with low sweetness and low-calorie content. The cryoprotective effects and possible mechanisms of soybean oligosaccharides (SBOS) on the frozen stability of grass carp (Ctenopharyngodon idellus) surimi were investigated during 120 days of frozen storage in a comparison with commercial cryoprotectants (4% sucrose and 4% sorbitol, w/w).

RESULTS

SBOS at 6-8% (w/w) and commercial cryoprotectants could restrain water mobility and reduce thawing loss of frozen surimi by increasing non-freezable water content. SBOS could maintain the structural stability of proteins by preventing sulfhydryl groups from being rapidly oxidized to disulfide bonds, retarding the reduction of the solubility, Ca2+-ATPase activity and α-helix content of myofibrillar proteins (MP), as well as hindering the increasing surface hydrophobicity of MP of surimi during 120 days of frozen storage. The introduction of SBOS increased the gel strength and water-holding capacity of frozen-stored surimi. Compared with commercial cryoprotectants, 8% SBOS was more effective in stabilizing protein structure, whereas it was slightly less effective with respect to ice-forming inhibition.

CONCLUSION

The results obtained in the present study suggest that 8% SBOS could be potentially developed as a new cryoprotectant for surimi as a result of its ice-forming inhibition abilities and protein structure stability. © 2024 Society of Chemical Industry.

DNA metabarcoding unveils the hidden species composition in fish surimi: Implications for the management of unlabeled and mixed seafood products

Fish surimi products are traditional foods primarily made from fish meat and may contain a complex species composition. In Taiwan, the abundant fishery resources and diverse fish species lead to local catches being widely used as ingredients in fish surimi products. However, due to growing market demand and increasingly scarce resources, some surimi products contain sensitive species, such as sharks, posing potential threats to the ecological environment and biodiversity. In this study, by applying metabarcoding techniques, we analyzed 120 fish surimi product samples from different brands and types throughout the four seasons in Taiwan's market. The main fish species identified included milkfish (Chanos chanos), dolphinfish (Coryphaena hippurus), Pomfret (Taractes rubescens), swordfish (Istiophorus spp.) and cartilaginous. Moreover, at least 37 species of cartilaginous fish, including 26 endangered species, were found. Through comprehensive and accurate species identification of surimi product ingredients, we unveiled the usage of sensitive species in products on the market. This finding is important for the surimi industry's quality control and market supervision. Furthermore, it can promote the sustainable use of Taiwan's fishery resources and protect biodiversity.

Effect of Soy Protein Isolate on the Quality Characteristics of Silver Carp Surimi Gel during Cold Storage

This study mainly investigated the effect of soy protein isolate (SPI) on the gel quality of silver carp surimi under different storage conditions (storage temperatures of 4 °C, -20 °C, and -40 °C, and storage times of 0, 15, and 30 d). The results found that 10% SPI could inhibit the growth of ice crystals, improve the water distribution, enhance the water holding capacity of the gels, and strengthen the interaction between surimi and proteins. Compared to the control group, the composite silver carp surimi gel exhibited superior quality in texture, chemical interactions, and rheological properties during cold storage. Fourier transform infrared spectroscopy revealed an increasing trend in α-helix and β-turn content and a decreasing trend of β-sheet and random coil content. As storage time increased, the gel deterioration during cold storage inhibitory effect of the treatment group was superior to the control group, with the best results observed at -40 °C storage conditions. Overall, SPI was a good choice for maintaining the quality of silver carp surimi gel during cold storage, which could significantly reduce the changes in the textural properties during cold storage with improved water holding capacity.

Cryoprotective effect of soluble soybean polysaccharides and enzymatic hydrolysates on the myofibrillar protein of Nemipterus virgatus surimi

Cryoprotective effect and potential mechanism of soluble soybean polysaccharides (SSPS) and enzymatic hydrolysates on surimi was investigated. After hydrolysis, the molecular weight of SSPS significantly decreased, and the hydrolysates prepared by endo-polygalacturonase (EPG-SSPS) was the lowest (154 kDa). Infrared spectrum analysis revealed that enzymatic hydrolysis didn't alter the functional groups of SSPS, but it did augment the exposure to hydroxyl groups. Surimi containing 5 % EPG-SSPS had the lowest freezable water after 20 days of frozen storage. Furthermore, the 5 % EPG-SSPS group manifested the highest metrics in total sulfhydryl (8.0 × 10-5 mol/g), active sulfhydryl content (6.7 × 10-5 mol/g), Ca2+-ATPase activity, and exhibited the lowest level in carbonyl content, surface hydrophobicity (153 μg). Notably, the 5 % EPG-SSPS maintained the stability of protein structure. Conclusively, SSPS enzymatic hydrolysate using endo-polygalacturonase imparted superior cryoprotective effect on the myofibrillar protein of surimi, and the mechanism might be a decrease in molecular weight and exposure of hydroxyl groups.

Effect of different freezing conditions on ice crystal formation behavior and ice-growth inhibition by cryoprotectants

BACKGROUND

The formation of ice crystals will have adverse effects on aquatic products, and the key to ensure the long-term preservation and better quality preservations of the product is to evaluate the intercellular ice crystal formation to find suitable refrigeration conditions and cryoprotectants.

RESULTS

The ice crystal formation was successfully captured by using an inverted microscope cryomicroscopic system equipped with a low-temperature stage, the ice crystals formed under different freezing methods between tuna muscle cells were observed directly, the deformation degree of muscle tissue pores during crystallization was evaluated, and the effect of freeze-thaw times on tuna samples was analyzed. The effects of the use of cryoprotectant such as cellobiose and carboxylated cellulose nanofibers on ice-growth inhibition were investigated, and the reliability of the ice crystal observation results was further verified by the determination of physical properties. The results showed that carboxylated cellulose nanofibers had the best ice-growth inhibition effect, they prevented about 50% cell deformation compared with the control group, and also reduced the minimum size of ice crystal formation. In addition, the addition of cellobiose and sodium tripolyphosphate gave the ice crystals a more uniform size and roundness.

CONCLUSION

The experiment proposed a stable and clear observation method for the process of intercellular ice crystal formation, and the accuracy of the observation method was further verified by some physical indicators. This may help in the selection of suitable measurement methods to directly observe ice crystal formation behavior and screen cryoprotectants. © 2024 Society of Chemical Industry.

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.

Kappa-carrageenan and xylooligosaccharide effect on water mobility and structural changes in silver carp proteins during frozen storage

BACKGROUND

The cryoprotective effect of xylooligosaccharide (XO) and kappa-carrageenan (KC) mixture on silver carp proteins in fluctuated frozen storage from 4 to -18 °C was analyzed. Positive control as a conventional cryoprotectant mixture of sucrose (4%) and sorbitol (4%), KC (3%) and XO/KC (3%) treatments were incorporated in silver carp surimi and myofibrillar proteins to analyze the water mobility and its influence on structural attributes.

RESULTS

The temperature fluctuation significantly increased the structural alteration in samples with no treatments due to oxidative changes, protein denaturation and recrystallization. Meanwhile, the mixture of XO and KC (XO/KC 3%) significantly reduced the tertiary and secondary structural alterations by preventing the oxidative changes in α-helix and tryptophan (Trp) residues. Moreover, XO/KC (3%) inhibited water mobility, hindering the T22 relaxation time, as compared to the samples added with KC (3%) and the positive control. Interestingly, the XO/KC (3%) mixture significantly reduced the formation of extracellular spaces and recrystallization by restricting the partial dehydration of muscles and extracellular solution concentration.

CONCLUSION

From the current results, it can be concluded that the XO/KC mixture could be efficient in protecting aquatic food proteins during fluctuating frozen storage by preventing the exposure of Trp residues and α-helix contents. Moreover, XO/KC restricted the water mobility by establishing a bond and making water unavailable for crystallization and recrystallization. Therefore, XO/KC could be used as an effective mixture to prevent fluctuated and frozen storage changes in aquatic foods. © 2024 Society of Chemical Industry.

Cryoprotective Activity of Different Characterized Fractions Isolated from Enzymatic Hydrolysates of Croceine Croaker (Pseudosciaena crocea)

In this study, ultrafiltration fractions (<3 k Da, LMH; >3 k Da, HMH) and solid-phase extraction fractions (hydrophilic hydrolysate, HIH; hydrophobic hydrolysate, HOH) from trypsin hydrolysate purified from croceine croaker (Pseudosciaena crocea) isolate were obtained to investigate the cryoprotective effects of the different fractions, achieved by means of maceration of turbot fish meat after three freeze-thaw cycles. Alterations in the texture, color, moisture loss, myofibrillar protein oxidation stability and conformation, and microstructure of the fish were analyzed after freezing and thawing. The results demonstrate that HIH maximized the retention of fish texture, reduced moisture loss, minimized the oxidation and aggregation of myofibrillar proteins, and stabilized the secondary and tertiary structures of myofibrillar proteins compared to the control group. In conclusion, the HIH component in the trypsin hydrolysates of croceine croaker significantly contributes to minimizing freeze damage in fish meat and acts as an anti-freezing agent with high industrial application potential.

Exploring the versatility of carbohydrates in surimi and surimi products: novel applications and future perspectives

Carbohydrate is one kind of the most important additives in the production of surimi and surimi products, mainly due to its wide range of sources and superior functionality. In recent years, new carbohydrates (oligosaccharides and polysaccharides) have been gradually applied in the production of surimi and surimi products which is mainly driven by consumer requirement on nutritional and the flavors or taste quality and producer requirement on extending the shelf life, like low calorie intake, dietary fiber enrichment, rich taste and improvement of antioxidant properties. Besides anti-freezing and improvement in gelling ability, novel functionalities have been explored such as fat substitution, improving flavor, antibacterial effect, antioxidant effect and improving three-dimensional printability. With an in-depth study of the mechanism of carbohydrate improving the qualities of surimi and surimi products, the application of carbohydrates in surimi would be more effective. Therefore, this review summarizes the new carbohydrates applied in the processing of surimi and surimi products, and their novel functionalities. Additionally, progress of the research on the mechanism of carbohydrate improving the qualities of surimi is also reviewed. © 2023 Society of Chemical Industry.

The Protection of Quinoa Protein on the Quality of Pork Patties during Freeze-Thaw Cycles: Physicochemical Properties, Sensory Quality and Protein Oxidative

The present study investigated the impact of quinoa protein (QP) on the physicochemical properties, sensory quality, and oxidative stability of myofibrillar protein (MP) in pork patties during five freeze-thaw (F-T) cycles. It was observed that repeated F-T cycles resulted in a deterioration of pork patty quality; however, the incorporation of QP effectively mitigated these changes. Throughout the F-T cycles, the sensory quality of the QP-treated group consistently surpassed that of the control group. After five F-T cycles, the thiobarbituric acid reactive substance (TBARS) content in the control group was measured at 0.423 mg/kg, whereas it significantly decreased to 0.347 mg/kg in the QP-treated group (p < 0.05). Furthermore, QP inclusion led to a decrease in pH and an increase in water-holding capacity (WHC) within pork patties. Following five F-T cycles, Ca2+-ATPase activity exhibited a significant increase of 11.10% in the QP-treated group compared to controls (p < 0.05). Additionally, supplementation with QP resulted in elevated total sulfhydryl content and reduced carbonyl content, Schiff base content, and dityrosine content within myofibrillar proteins (MPs), indicating its inhibitory effect on MP oxidation. In particular, after five F-T cycles, total sulfhydryl content reached 58.66 nmol/mL for the QP-treated group significantly higher than that observed for controls at 43.65 nmol/mL (p < 0.05). While carbonyl content increased from 2.37 nmol/mL to 4.63 nmol/mL between the first and fifth F-T cycle for controls; it only rose from 2.15 nmol/mL to 3.47 nmol/mL in the QP-treated group. The endogenous fluorescence levels were significantly higher (p < 0.05) in the QP-treated group compared to controls. In conclusion, the addition of QP enhanced the quality of pork patties and effectively inhibited the oxidative denaturation of MP during F-T cycles.

A mini review on manipulation of carbohydrate for better use in surimi and surimi products: modification and compounding

Carbohydrate is widely used in the production of surimi and surimi products to improve their qualities, such as anti-freezing capability, gelling ability, nutrition, flavor and 3D printability. More and more native carbohydrates have been modified through physical methods (e.g., ball milling, irradiation and differential sedimentation), chemical method (e.g., deacetylation, hydroxypropylation and acetic acid esterification) or enzymatic method (e.g., chitosanase) before being used in the processing of surimi and surimi products in recent years. At the same time, different carbohydrates are compounded and applied to surimi and surimi products. The modified and compounded carbohydrates in surimi have been proved to improve quality of surimi and surimi products more pronouncedly than native carbohydrates. Therefore, this review summarizes the manipulation of carbohydrate by modification and compounding to improve the qualities of surimi and surimi products. Moreover, the prospects for carbohydrate modification and compounding for use in surimi and surimi products are discussed. © 2023 Society of Chemical Industry.

Promising effects of β-glucans on gelation in protein-based products: A review

Gel property is one of the most important abilities to endow protein-based food products with a unique texture and higher overall acceptability. Cereal β-glucan (BG) is widely applied in protein-based products to improve the stability of the protein gel by increasing water holding capacity, storage modulus (G'), loss modulus (G") and linking with protein through more exposed sites, making it easier to form a stronger three-dimensional gel network. In addition, BG may be cross-linked with proteins, or physically embedded and covered in protein network structures, interacting with proteins mainly through non-covalent bonds including hydrogen bonding and electrostatic interaction. Furthermore, the transition of the α-helix to the β-form in the protein secondary structure also contributes to the stability of the protein gel. The practical applications of BG from different cereals in protein-based products are summarized, and the rheological properties, microstructure of protein as well as the underlying interaction mechanisms between BG and protein are discussed. In conclusion, cereal BG is a promising polysaccharide in developing nutritional protein-based products with better sensory properties.

Protection of Whey Polypeptide on the Lipid Oxidation, Color, and Textural Stability of Frozen-Thawed Spanish Mackerel Surimi

Repeated freeze-thaw (FT) cycles can have an impact on surimi quality. In this study, we used 0.02% BHA as a positive control group. We examined the effects of different concentrations (0%, 5%, 10%, and 15%) of whey protein hydrolysate (WPH) on surimi, focusing on alterations in color metrics (L* for brightness, a* for red-green, b* for yellow-blue, and overall whiteness), textural characteristics, and antioxidant capacity during various freeze-thaw (FT) cycles. The results showed that the lipid oxidant values of surimi, as well as its a* and b* values, rose as the number of FT cycles increased; whereas the adhesiveness, resilience, gumminess, and shear force dropped, as did L* and the whiteness values, leading to an overall darkening of color and gloss. By contrast, the study found that the addition of WPH could effectively slow down the decrease of surimi textural stability after repeated freeze-thawing, with the textural stability of the group with 15% WPH being significantly superior to those of the other groups (p < 0.05). Under the same number of cycles, adding 15% WPH to the experimental group could successfully lower total volatile basic nitrogen (TVB-N) and effectively increase the antioxidant activity of surimi. This finding suggested that 15% WPH had the greatest effect on increasing surimi FT stability. To conclude, it was proved that WPH can be added to frozen surimi and improve its quality.

Observation on the ice crystal formation process of large yellow croaker (Pseudosciaena crocea) and the effect of multiple cryoprotectants pre-soaking treatments on frozen quality

By observing the formation behavior of ice crystals, the quality of food products under different freezing conditions can be intuitively judged. In this paper, large yellow croaker was taken as the research object, and a novel cryomicroscopic system was developed to directly observe the structure of ice crystals during the freezing process. The cryoprotective effects of 4% sucrose +4% sorbitol (SU + SO), 4% xylo-oligosaccharide (XO), 4% xylo-oligosaccharide + 0.3% tetrasodium pyrophosphate (XO + TSPP) and 0.2% antifreeze protein (AFP) at different freezing temperatures were investigated. And the evaluation indicators, such as cell deformation degree, equivalent diameters, roundness, elongation and fractal dimension were introduced to quantify the damage of ice crystals to muscle tissues and fibers. The results indicate that reducing the freezing temperature and adding cryoprotectants can improve the quality of large yellow croaker. AFP has the best cryoprotective effect, with a reduction in cell deformation degree of 54.78% and 67.83% compared to the Control group at -5 °C and -20 °C, respectively. SU + SO and XO have the equivalent antifreeze effect, which is slightly inferior to XO + TSPP. In addition, physical parameters of large yellow croaker samples were measured to verify the influence of ice crystal structure on product quality. Therefore, direct observation of the ice crystal formation process and evaluation of ice crystal structure can accurately reflect the quality of frozen products, which is of great significance for the development of refrigeration and preservation technology.

Dual cryoprotective and antioxidant effects of young apple polyphenols on myofibrillar protein degradation and gelation properties of bighead carp mince during frozen storage

Commercial cryoprotectants can delay quality loss in frozen fish mince, but they are associated with a sweet taste and high calorie content. Young apple polyphenols (YAP), extracted from unripe apples, show potential as an alternative cryoprotectant. This study evaluated the cryoprotective effect of YAP at varying levels (0.3%, 0.7%, and 1%) in unwashed bighead carp mince. The changes in sulfhydryl content, carbonyl content, thiobarbituric acid reactive substances, intrinsic fluorescence intensity, and Fourier transform infrared spectrum indicated that YAP retarded oxidation and structural changes in myofibrillar proteins during the first 8 weeks of frozen storage, as well as lipid oxidation, which protected the structure of myofibrillar protein. At higher concentrations (0.7% and 1%), YAP maintained gel properties, gel springiness, and water-holding capacity of the gel prepared from frozen fish mince, potentially through the promotion of cross-linking of myofibrillar proteins. Overall, YAP can be used as a cryoprotectant and antioxidant in fish mince. PRACTICAL APPLICATION: Our research found that young apple polyphenols have the potential to be an alternative to commercial cryoprotectants. Young apple polyphenols may be used as a sugar-free and healthy cryoprotectant for frozen fish mince production in the future.

Effect of cellulose on gel properties of heat-induced low-salt surimi gels: Physicochemical characteristics, water distribution and microstructure

The processing of surimi products requires the addition of high levels of salt, which makes it a high-salt food that poses a risk to human health. The search for exogenous additives to reduce the salt content of surimi products while ensuring their quality characteristics is crucial. Therefore, the effect of different species of cellulose on enhancing the quality characteristics of low-salt surimi gels was investigated and the best-modified cellulose was identified. Carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose (HPMC), and microcrystalline cellulose (MCC) were selected for this study to compare with high-salt control and low-salt control. The results showed that cellulose could induce conformational transitions of proteins and promote the formation of an ordered and dense surimi gel network and the minimum porosity of 15.935% was obtained in the MCC-treated group. The cellulose-treated group conferred good textural properties to the surimi gels, significantly improved gel strength and water retention capacity (p < 0.05), and reduced the amount of water lost after cooking treatment (p < 0.05). Low-field NMR results showed that cellulose reduced the release of water, converting more free water to immobile water, thus increasing the water proton density. The higher energy storage modulus G' in the presence of cellulose indicated a more stable surimi gel system dominated by springiness. In summary, cellulose could confer better quality characteristics to low-salt surimi gels and MCC performance was superior to other cellulose species. This study helps the understanding of the mechanism of cellulose-surimi action on the development of high-quality low-salt surimi gels.

Integrated volatile compounds and non-targeted metabolomics analysis reveal the characteristic flavor formation of proteins in grouper (Epinephelus coioides) during cold storage

Microorganisms, lipids, and proteins always interact in a complex way in the fish matrix, which becomes a hindrance to evaluate the quality of the individual factors affecting them. In order to investigate the relationship between protein deterioration and volatile compounds (VOCs) in grouper during cold storage, the myofibril protein (MP) was used as a single-factor study to exclude microorganisms and lipids effects. The oxidation and degradation of MP during storage at 4 ℃ were evaluated, including MP content, total sulfhydryl content, carbonyl content, spatial structure and microstructure. Headspace-solid phase microextraction- gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to analyze the VOCs of grouper MP, and a total of 7 key VOCs were selected, including three ketones (2-nonanone, 2-undecanone and 2-tridecanone), three esters (methyl butyrate, methyl palmitate and methyl ester 9-octadecenoic acid) and one alcohol (3-methyl-1-butanol). At the same time, a non-targeted metabolomics method based on UPLC-Q-Extractive Orbitrap was used to investigate the changes in metabolites during MP storage. A total of 107 up-regulated differential metabolites and 7 down-regulated metabolites were annotated, and 6 metabolic pathways highly related to proteins were screened. Spearman correlation analysis showed that 7 key VOCs are associated with the biosynthesis and metabolism of ornithine and lysine. And a possible solution to protein deterioration in grouper was proposed, which provided a reference for improving protein quality and regulating flavor formation during cold storage of grouper at source.

Structural and functional changes on polyhydroxy alcohol-mediated curing pork myofibrillar protein: Experimental and molecular simulation investigations

This study aimed to investigate the structural and functional changes in polyhydroxy alcohol-mediated curing on pork myofibrillar proteins (MP). The results obtained from total sulfhydryl groups, surface hydrophobicity, fluorescence and Raman spectroscopies, and solubility demonstrated that the polyhydroxy alcohols (especially xylitol) significantly modified the MP tertiary structure, making this structure more hydrophobic and tighter. However, no significant differences were detected in the secondary structure. Furthermore, the thermodynamic analysis revealed that polyhydroxy alcohols could develop an amphiphilic interfacial layer on the MP surface, significantly increasing the denaturation temperature and enthalpy of denaturation (P < 0.05). On the other hand, the molecular docking and dynamics simulations showed that polyhydroxy alcohols interact with actin mainly through hydrogen bonds and van der Waals forces. Therefore, this could help reduce the effect of high-content salt ions on MP denaturation and improve the cured meat quality.

Progress in the application of novel cryoprotectants for the stabilization of myofibrillar proteins

In this review, the physicochemical and conformational changes of myofibrillar proteins (MPs) of freeze-induced mince-based aquatic foods were comprehensively summarized in depth. Studies have demonstrated that temperature fluctuation and long-time freezing negatively affect food quality, resulting in texture alteration, drip fluid, flavor degradation, and nutrition loss due to MPs denaturation, aggregation, and oxidation. Attempts have been made in ice-recrystallization inhibition, freezing point depression, and ice shape and growth control for better cryopreservation. Moreover, to further minimize the quality deterioration, cryoprotectants were acknowledged to reduce the denaturation and aggregation of the MPs effectively. Recently, interest in novel functional ingredients, including oligosaccharides, protein hydrolysates, and natural polyphenols demonstrated excellent cryoprotective effects while avoiding health concerns and undesirable flavor caused by traditional sugar-based or phosphates-based cryoprotectants. Therefore, the present review provides a systematic overview of these low molecular weight multifunctional substances with a particular sequence and highlights their underlying mechanism in the inhibition of ice recrystallization the stabilization of MPs.

The mechanisms and applications of cryoprotectants in aquatic products: An overview

Frozen storage technology has been widely used for the preservation of Aquatic products. However, ice crystals formation, lipid oxidation and protein denaturation still easily causes aquatic products deterioration. Cryoprotectants are a series of food additives that could efficiently prolong the shelf life and guarantee the acceptability of frozen aquatic products. This review comprehensively illustrated the mechanism of protein denaturation caused by the ice crystal formation and lipid oxidation. The cryoprotective mechanism of various kinds of antifreeze agents (saccharides, phosphates, antifreeze proteins and peptides) and these cryoprotective structure-activity relationship, application efficiency on the quality of aquatic products were also discussed. Moreover, the advantages and disadvantages of each cryoprotectant are also prospected. Compared with others, antifreeze peptides show higher commercial and application values. While, lots of scientific research works are still required to develop novel antifreeze agent as a versatile ingredient with commercial value, applicable in the aquatic products preservation industry.

Inulin for surimi gel fortification: Performance and molecular weight-dependent effects

Inulin is a prebiotic carbohydrate widely used in food industry due to its health benefits and unique rheological properties. For the first time, this study explores the potential of natural inulin as a sustainable food additive to enhance surimi gel characteristics, specifically focusing on understanding its molecular weight effects. The good solubility of inulin facilitates the conversion of α-helix to other secondary conformations which are favorable for protein denaturation and aggregation during gelation. Moreover, the abundant -OH groups at the surface of inulin can boost the chemical forces within surimi proteins to reinforce the gel network. Compared to short-chain inulin, long-chain inulin can alleviate proteolysis, enhance hydrophobic interactions and intertwine with myosin molecules, thereby reinforcing the gel network. A more viscous long-chain inulin solution formed within surimi gels fills the space between aggregated proteins and facilitates the lock of water molecules, improving the water-holding capacity (WHC). Thus, an addition of 12 % long-chain inulin leads to an enhanced hardness of surimi gel from 943 to 1593 and improved WHC from 72 % to 85 %. A new inulin-myosin interaction mechanism model is also proposed to provide useful guidelines for surimi processing and expanding the application of inulin within the food industries.

Lyoprotectant Formulation and Optimization of the J-Aggregates Astaxanthin/BSA/Chitosan Nanosuspension

Astaxanthin is a carotenoid with excellent antioxidant activity. However, this small lipid-soluble molecule is insoluble in water and has low stability. Although this situation can be improved when astaxanthin is prepared as a nanosuspension, the aqueous form is still not as convenient and safe as the dry powder form for storage, transport, and use. The lyophilization process provides better protection for thermosensitive materials, but this leads to collapse and agglomeration between nanoparticles. To improve this situation, appropriate lyophilization protectants are needed to offer support between the nanoparticles, such as sugars, amino acids, and hydroxy alcohols. The purpose of this work is to screen lyophilization protectants by single-factor experiments and response surface optimization experiments and then explore the optimal ratio of compound lyophilization protectants, and finally, make excellent astaxanthin/BSA/chitosan nanosuspension (ABC-NPs) lyophilized powder. The work shows that the optimal ratio of the compounding lyophilization protectant is 0.46% oligomeric mannose, 0.44% maltose, and 0.05% sorbitol (w/v). The ABC-NPs lyophilized powder prepared under the above conditions had a re-soluble particle size of 472 nm, with a ratio of 1.32 to the particle size of the sample before lyophilization. The lyophilized powder was all in the form of a pink layer. The sample was fluffy and dissolved entirely within 10 s by shaking with water. Consequently, it is expected to solve the problem of inconvenient storage and transportation of aqueous drugs and to expand the application of nanomedicine powders and tablets.

Investigation on the quality regulating mechanism of antifreeze peptides on frozen surimi: From macro to micro

Freeze denaturation of protein caused by ice crystals is the main motivation for the quality deterioration of surimi during circulation and storage. This investigation aimed to cryoprotect surimi by adding antifreeze peptides from Takifugu obscurus skin (TsAFP) which can inhibit ice recrystallization, and to elucidate regulating mechanism. The comprehensive results showed that 4% TsAFP, half dosage of commercial cryoprotectant, had good cryoprotection on surimi by reducing the moisture variation and maintaining protein solubility of surimi at macro level, as well as inhibiting the degeneration and structure changes of myofibrillar proteins at micro level. Meanwhile, TsAFP could directly bind to the structural cavity of myosin, inhibit protein freezing-induced oxidation, maintain the spatial structure of myosin and water retention ability to preserve the surimi quality. This study helped better comprehend the protective mechanisms of antifreeze peptides in frozen surimi and was expected to provide a promising cryoprotectant for low-sweetness and low-calorie surimi.

Processing Technology and Quality Change during Storage of Fish Sausages with Textured Soy Protein

The addition of textured soy protein (TSP) to surimi products extends the supply of fish protein and improves nutritional and sensory properties, which has attracted considerable research interest. In this study, a single-factor experiment and orthogonal experiment were used to determine the optimal process conditions and to assess the quality indicators of fish sausages during frozen storage. The results indicated that the optimal process conditions were as follows: the addition of 15% TSP, 8% potato starch, and 5% lard oil, resulting in a gel strength of 1894.32 g·cm. During storage of the formulation-optimized fish sausages for 180 days, the water-holding capacity, whiteness, texture properties, and gel strength of the fish sausages all decreased, whereas cooking loss, thawing loss, thiobarbituric acid reactive substances value, and total volatile base nitrogen value all increased. Consequently, TSP is beneficial to improve the gel strength and sensory score of fish sausages. The quality of fish sausages with added TSP was acceptable after storage at -18 °C, for 120 days.

Improving the Gel Quality of Threadfin Bream (Nemipterus spp.) Surimi Using Salted Duck Egg White Powder

The effect of salted duck egg white powder (SDEWP) as a source of salt at different salt equivalent (SE) levels (0−2.5% SE) on gel qualities and texture properties of threadfin bream surimi was investigated. SDEWP possessed a high protein (64.59%) and salt (34.86%) concentration. The breaking force of surimi gel increased by the amount of SDEWP (p < 0.05). The addition of SDEWP up to 1.5% SE into the surimi gel has significantly increased the deformation (13.8%) and decreased the expressible moisture content (38.5%). Hardness, gumminess, and chewiness were augmented as higher levels of SDEWP were added, whereas cohesiveness decreased when the SDEWP above 1.5% SE was used. The incorporation of SDEWP had no significant effect on the springiness (p < 0.05). Less proteolytic degradation was observed in the surimi gel fortified with SDEWP. A higher amount of added SDEWP enhanced the whiteness of the surimi gel (p < 0.05). A denser and more ordered gel network was attained when SDEWP with 1.5% SE was added. SDEWP could be exploited as a source for salt and non-fish proteins in threadfin bream surimi, in which SDEWP containing 1.5% SE could significantly improve the quality of surimi gel.

Role of low molecular additives in the myofibrillar protein gelation: underlying mechanisms and recent applications

Understanding mechanisms of myofibrillar protein gelation is important for development of gel-type muscle foods. The protein-protein interactions are largely responsible for the heat-induced gelation. Exogenous additives have been extensively applied to improve gelling properties of myofibrillar proteins. Research has been carried out to investigate effects of different additives on protein gelation, among which low molecular substances as one of the most abundant additives have been recently implicated in the modifications of intermolecular interactions. In this review, the processes of myosin dissociation under salt and the subsequent interaction via intermolecular forces are elaborated. The underlying mechanisms focusing on the role of low molecular additives in myofibrillar protein interactions during gelation particularly in relation to modifications of the intermolecular forces are comprehensively discussed, and six different additives i.e. metal ions, phosphates, amino acids, hydrolysates, phenols and edible oils are involved. The promoting effect of low molecular additives on protein interactions is highly attributed to the strengthened hydrophobic interactions providing explanations for improved gelation. Other intermolecular forces i.e. covalent bonds, ionic and hydrogen bonds could also be influenced depending on varieties of additives. This review can hopefully be used as a reference for the development of gel-type muscle foods in the future.

Mechanism of polyhydroxy alcohol-mediated curing on moisture migration of minced pork tenderloin: On the basis of molecular docking

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Polyhydroxy alcohols affect salt diffusion and moisture migration.

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Polyhydroxy alcohols cause the water to migrate out to reduce aw in meat.

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Polyhydroxy alcohols retard salt diffusion into the meat by forming a viscose barrier.

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Polyhydroxy alcohols can prevent meat structural damage by binding to myosin.

This study investigated the mechanism of glycerol, xylitol, and sorbitol-mediated curing of cured minced pork tenderloin. The use of polyhydroxy alcohol during mediated curing significantly reduced the salt content (p < 0.01) and water activity (aw) of the cured pork tenderloin. Low-field nuclear magnetic resonance (LFNMR) revealed that 1 % glycerol, 1 % xylitol, 1 % sorbitol, and 10 % glycerol-mediated curing decreased water mobility, and improved water holding capacity (WHC), and produced uniform dense microstructures. Raman spectroscopy and molecular docking indicated that polyhydroxy alcohols formed hydrogen bonds with myosin, as well as hydrogen bonds with free water molecules to convert free water into bound water to reduce aw, and altered the hydrophobic environment of myosin surface to reduce structural damage caused by high salt content. In conclusion, using polyhydroxy alcohol to mediate curing can effectively reduce the salt content of cured meat and provide a theoretical basis for its application in the cured meat industry.

A review on recent advances in the applications of composite Fe3O4 magnetic nanoparticles in the food industry

Fe3O4 magnetic nanoparticles (MNPs) have attracted tremendous attention due to their superparamagnetic properties, large specific surface area, high biocompatibility, non-toxicity, large-scale production, and recyclability. More importantly, numerous hydroxyl groups (-OH) on the surface of Fe3O4 MNPs can provide coupling sites for various modifiers, forming versatile nanocomposites for applications in the energy, biomedicine, and environmental fields. With the development of science and technology, the potential of nanotechnology in the food industry has also gradually become prominent. However, the application of composite Fe3O4 MNPs in the food industry has not been systematically summarized. Herein, this article reviews composite Fe3O4 MNPs, including their properties, modifications, and physical functions, as well as their applications in the entire food industry from production to processing, storage, and detection. This review lays a solid foundation for promoting food innovation and improving food quality and safety.

Effects and mechanism of antifreeze peptides from silver carp scales on the freeze-thaw stability of frozen surimi

The objective of this work was to investigate the cryoprotective effects of antifreeze peptides obtained from silver carp scales (ScAFPs) on the freeze-thaw stability of surimi, and to explore the action mechanisms of ScAFPs on frozen surimi. The comprehensive analysis of ice crystal size, myofibril protein oxidation, water retention, surimi gel properties, and rheological properties of surimi after different freeze-thaw cycles were investigated. Results showed that frozen surimi treated with ScAFPs exhibited a higher Ca²⁺-ATPase activity, salt-soluble protein concentration and sulfhydryl group content, while lower surface hydrophobicity, carbonyl content and disulfide bond content. Moreover, the gel properties and water holding capacity of surimi and surimi gel were improved significantly by regulating the size of ice crystals during freeze-thaw process. These findings indicate that ScAFPs could serviced as a new food ingredient with anti-freezing function for frozen products.

Asian Carp, an Alternative Material for Surimi Production: Progress and Future

Asian carp is a general designation for grass carp, silver carp, bighead carp, and black carp. These fish species belong to the family Cyprinidae. In 2018, more than 18.5 million tons of Asian carp were produced globally. Asian carp can be used for producing surimi, a stabilized myofibrillar protein concentrate that can be made into a wide variety of products such as imitation crab sticks, fish balls, fish cakes, fish tofu, and fish sausage. Surimi is usually made from marine fish, but Asian carp have been widely used for surimi production in China. The quality of surimi is affected by various factors, including the processing methods and food additives, such as polysaccharides, protein, salt, and cryoprotectant. With an impending shortage of marine fish due to overfishing and depletion of fish stocks, Asian carp have a potential to serve as an alternative raw material for surimi products thanks to their high abundancy, less emissions of greenhouse gases from farming, desirable flesh color, and sufficient gel forming ability. The utilization of Asian carp in surimi production could also contribute to relieving the overflow of Asian carp in the United States.

Investigation of the cryoprotective mechanism and effect on quality characteristics of surimi during freezing storage by antifreeze peptides

Freezing technology is important for storage of animal products such as surimi. However, mechanical damage caused by ice crystals would lead to quality deterioration. This study aims to investigate the protective effect of antifreeze peptides (AFPs) on the quality of surimi during freezing storage and its possible mechanism. We found that AFPs exhibited a strong inhibition of ice crystal recrystallization, and the molecular weight ranged from 180 to 3000 Da. AFPs can prevent the degeneration of myofibrillar protein by reducing the loss of Ca²⁺-ATPase activity, slowing oxidation of sulfhydryl groups to disulfide bonds, and maintaining surface hydrophobicity and solubility of myofibrillar protein. Moreover, AFPs can reduce the influence of freezing stress on water mobility, thereby protecting the surimi from losing immobilized water and bound water during frozen storage. These findings indicate that AFPs could potentially serve as a food ingredient with antifreeze functional for the storage of surimi products.

Role of Food Hydrocolloids as Antioxidants along with Modern Processing Techniques on the Surimi Protein Gel Textural Properties, Developments, Limitation and Future Perspectives

Texture is an important parameter in determining the quality characteristics and consumer acceptability of seafood and fish protein-based products. The addition of food-based additives as antioxidants (monosaccharides, oilgosaccharides, polysaccharides and protein hydrolysates) in surimi and other seafood products has become a promising trend at an industrial scale. Improvement in gelling, textural and structural attributes of surimi gel could be attained by inhibiting the oxidative changes, protein denaturation and aggregation with these additives along with new emerging processing techniques. Moreover, the intermolecular crosslinking of surimi gel can be improved with the addition of different food hydrocolloid-based antioxidants in combination with modern processing techniques. The high-pressure processing (HPP) technique with polysaccharides can develop surimi gel with better physicochemical, antioxidative, textural attributes and increase the gel matrix than conventional processing methods. The increase in protein oxidation, denaturation, decline in water holding capacity, gel strength and viscoelastic properties of surimi gel can be substantially improved by microwave (MW) processing. The MW, ultrasonication and ultraviolet (UV) treatments can significantly increase the textural properties (hardness, gumminess and cohesiveness) and improve the antioxidative properties of surimi gel produced by different additives. This study will review potential opportunities and primary areas of future exploration for high-quality surimi gel products. Moreover, it also focuses on the influence of different antioxidants as additives and some new production strategies, such as HPP, ultrasonication, UV and MW and ohmic processing. The effects of additives in combination with different modern processing technologies on surimi gel texture are also compared.

Effect of Trehalose on the Physicochemical Properties of Freeze-Dried Powder of Royal Jelly of Northeastern Black Bee

Trehalose is known for its effect of improving the stability of freeze-dried foods. In this work, vacuum freeze-drying (VFD) technology was employed to prepare northeast black bee royal jelly into lyophilized powder and a novel method mixing trehalose into royal jelly is successfully developed to enhance the free radical scavenging ability and the nutrition stability of royal jelly lyophilized powder. The effects of different trehalose content (0, 0.1, 0.3, 0.5, 0.7 and 0.9 wt.%) on the physicochemical properties of lyophilized royal jelly powder were studied. With systematic analysis, it was found that the incorporation of suitable trehalose content in lyophilized royal jelly powder can reduce the loss of the protein, total sugar, total flavone content during the VFD process and enhance the total phenolic antioxidant capacity, solubility, angle of repose, and bulk density of the royal jelly powder. Finally, lyophilized royal jelly with 0.5 wt.% trehalose is selected as the suitable addition content which exhibits the best radical scavenging ability as well as the lowest hygroscopicity. From the perspective of sensory evaluation, all royal jelly lyophilized powders with trehalose are acceptable.

Different Thermal Treatment Methods and TGase Addition Affect Gel Quality and Flavour Characteristics of Decapterus maruadsi Surimi Products

Decapterus maruadsi surimi products were prepared using the thermal treatment methods of boiling (BOI), steaming (STE), back-pressure sterilization (BAC), roasting (ROA), microwaving (MIC), and frying (FRI), respectively. The effect of glutamine transaminase (TGase) addition was also investigated. The moisture distribution, water retention, microstructure, color, fracture constant, protein secondary structure, chemical forces, and flavor components of each sample were determined. The differences in gel and favor characteristics between D. maruadsi surimi products caused by thermal treatment methods were analyzed. The results showed that BOI, STE, and FRI had the largest protein secondary structure transitions and formed dense gel structures with high fracture constant. The kinds of flavour components in BOI and STE were completer and more balanced. The high temperature treatment available at BAC and FRI (110 °C and 150 °C) accelerated the chemical reaction involved in flavor formation, which highlighted the flavor profiles dominated by furans or esters. The open thermal treatment environments of ROA, MIC, and FRI gave them a low moisture content and water loss. This allowed the MIC to underheat during the heat treatment, which formed a loose gel structure with a low fracture coefficient. The addition of TGase enhances the gel quality, most noticeably in the ROA. The aldehyde content of the FRI was enhanced in the flavor characteristic. The effect of adding TGase to enhance the quality of the gel is most evident in ROA. It also substantially increased the content of aldehydes in FRI. In conclusion, different heat treatments could change the gel characteristics of surimi products and provide different flavor profiles. The gel quality of BOI and STE was consistently better in all aspects.

Influence of the Mixture of Carrageenan Oligosaccharides and Egg White Protein on the Gelation Properties of Culter alburnus Myofibrillar Protein under Repeated Freezing-Thawing Cycles

This study aims to investigate the influence of the mixture (CGO/EWP) of carrageenan oligosaccharide (CGO) and egg white protein (EWP) (CGO/EWP, CGO: EWP = 1:1, m/m) on the functional, structural, and gelling properties of Culter alburnus myofibrillar protein (MP) during repeated freezing-thawing cycles by treating MP samples separately with EWP, CGO, or CGO/EWP based on the wet weight (1%, m/m), using samples without any cryoprotectant as the blank group. After the second repeated freezing-thawing cycle, the sulfhydryl group content was found to be significantly (p < 0.05) higher in the CGO/EWP (30.57 nmol/mg) and CGO (36.14 nmol/mg) groups than in the EWP group (23.80 nmol/mg), indicating that CGO/EWP and CGO can more effectively delay the oxidative deterioration of functional groups. Additionally, the surface hydrophobicity was shown to be significantly lower in the CGO (25.74) and CGO/EWP (27.46) groups than in the EWP (34.66) and blank (39.32) groups. Moreover, the α-helix content was higher in the CGO (35.2%) and CGO/EWP (32.3%) groups than in the EWP (29.2%) and blank (25.0%) groups. These data indicated that CGO and CGO/EWP could more effectively increase the structural stability, thereby inhibiting the exposure of hydrophobic groups and curbing the decline of α-helix content. During the heat-induced gel-forming process, EWP and CGO/EWP could enhance the gel viscoelasticity and strength. After the second freezing-thawing cycle, when compared with the blank group, the CGO/EWP group showed significantly (p < 0.05) higher water-holding capacity (66.30% versus 53.93%) and shorter T22 relaxation time (413.56 versus 474.99 ms). The integrated results indicated that CGO/EWP could more effectively delay the decrease of protein-water molecular interaction forces in the MP gel. This study shed light on the mechanism of CGO/EWP as a cryoprotective mixture in improving the deterioration of MP gelation properties during repeated freezing-thawing cycles.

Role of Ovalbumin/β-Cyclodextrin in Improving Structural and Gelling Properties of Culter alburnus Myofibrillar Proteins during Frozen Storage

This study aimed to analyze the cryoprotective effect of a ovalbumin (OVA) and β-cyclodextrin (βCD) mixture (3:1, OVA/βCD) on the structure, rheology and gelling properties of myofibrillar proteins (MPs) during 90 days of frozen storage. A mixture of OVA/βCD at different concentrations (0, 2, 4, and 6%) was added to MPs and stored at −18 °C for 90 days. The addition of OVA/βCD significantly decreased the sulfhydryl contents while it increased the surface hydrophobicity, which was closely connected with tertiary structural changes. Circular dichroism analysis showed that the addition of OVA/βCD enhanced the stability of the secondary structure by inhibiting the decline in the α-helix. Rheological properties analysis indicated that 6% OVA/βCD treatment showed better storage modulus (G’) and loss modulus (G”). In addition, treatment of OVA/βCD showed better gel forming properties than the control group (0%), helping to form a homogeneous and denser gel network. The results proved that 6% OVA/βCD could be act as a promising cryoprotectant, which can improve the structure and gel behavior of Culter alburnus MPs during frozen storage. Moreover, OVA/βCD could be a potential alternative to conventional cryoprotectants at the industrial level to increase the economic and commercial values of seafood products.

The role of trifunctional cryoprotectants in the frozen storage of aquatic foods: Recent developments and future recommendations

Freeze-induced changes including protein denaturation, ice crystals formation and lipid oxidation are mainly responsible for the quality deterioration persistent in aquatic foods. Here, for the first time, the cryoprotectants with trifunctional properties have been suggested for aquatic food cryopreservation and have exhibited exceptional cryoprotective abilities. In this study, in-depth discussion of protein denaturation, ice crystal formation and lipid oxidation is added in order to understand their mechanism, emphasizing on the necessity and use of trifunctional cryoprotectants in aquatic foods during frozen storage. Trifunctional cryoprotectants have strong abilities to prevent the formation of malondihaldehyde and aldehydes resulting from lipid oxidation, which further interact with proteins, subsequently lead to protein denaturation. Besides these all cryoprotective properties, ice crystal binding abilities distinguish trifunctional cryoprotectants from conventional cryoprotectants. Moreover, this study added with recent advances in cryoprotectants including antifreeze proteins and protein hydrolysates with their role in retarded freeze-induced changes. This study concluded that trifunctional cryoprotectants are effective owing to their hydrophilic amino acid chains, radical scavenging, water entrapping abilities, as well as the hydroxyl groups, which interact at the functional sites of protein molecules. Furthermore, polysaccharides and protein hydrolysates are the potential ingredients with trifunctional cryoproperties. However, more scientific research is required for material optimization to attain the desired level of cryoprotection.