Cryoprotective Activity and Action Mechanism of Antifreeze Peptides Obtained from Tilapia Scales on Streptococcus thermophilus during Cold Stress

Frozen dough steamed products: Deterioration mechanism, processing technology, and improvement strategies

Fresh dough products lead to instability in product quality, high production costs, and more production time, which seriously affects the industrial production of the food industry. The frozen dough technology mitigates the problems of short shelf-life and easy deterioration of quality during storage and transportation. It has shown a series of advantages in large-scale industrialization, high-quality standardization, and chain operation. However, the further development of frozen dough is restricted by the deterioration of the main components (gluten, starch, and yeast) caused by freezing. This review summarizes the main production process of frozen steamed bread and buns, and the deterioration reasons for the main component of frozen dough. The improvement mechanisms of raw ingredients, processing technology, processing equipment, and additives on frozen dough quality were analyzed from the perspective of improving gluten network integrity and yeast freeze tolerance. From prefermented frozen raw to steamed products without thawing has become the preferred production process to improve production efficiency. Wheat flour mixed with other flour can maintain the gluten network continuity of frozen dough. The freeze tolerance of yeast was improved by treatment with yeast suspension, yeast cell encapsulation, screening hybridization, and genetic engineering. Process optimization and new technology-assisted fermentation and freezing effectively reduce freezing damage. Various additives improve the freeze resistance of the gluten-starch matrix by promoting protein cross-linking and inhibiting water migration. In addition, ice structural proteins and ice nucleating agents have been proven to change the growth morphology and formation temperature of ice crystals. More new technologies and additive synergies need to be further explored.

Insight into the structure-activity relationship of thermal hysteresis activity of cod collagen peptides through peptidomics and bioinformatics approaches

To elucidate the correlation between variations in thermal hysteresis activity (THA) and the physicochemical properties and structure, antifreeze peptides (AFPs) of isolated fractions (CCP-1 and CCP-2) were characterized on based peptidomics and bioinformatics. The results revealed a positive correlation between the THA of cod collagen antifreeze peptide (CCAFP) and peptide chain length, isoelectric point, and hydrophobic amino acid content. Notably, the THA of CCP-1, which has higher alkaline amino acid content, was 2.60 °C at a concentration of 10 mg/mL, significantly higher than CCP (1.90 °C) and CCP-2 (2.27 °C). Glycine, proline, and valine were the vital amino acids to the formation of hydrogen bonds. Conversely, aspartic and glutamic acids at terminal regions of AFPs tended to introduce kinks in their structures. This distortion reduced binding sites for ice crystals, thereby decreasing their THA, providing a theory for understanding the physicochemical properties and structure of AFPs that influence their THA.

Performance and protein conformation of thermally treated silver carp (Hypophthalmichthys molitrix) and scallop (Argopecten irradians) blended gels

BACKGROUND

The quality of surimi-based products can be improved by combining the flesh of different aquatic organisms. The present study investigated the effects of incorporating diverse ratios of unwashed silver carp (H) and scallop (A) and using various thermal treatments on the moisture, texture, microstructure, and conformation of the blended gels and myofibrillar protein of surimi.

RESULTS

A mixture ratio of A:H = 1:3 yielded the highest gel strength, which was 60.4% higher than that of scallop gel. The cooking losses of high-pressure heating and water-bath microwaving were significantly higher than those of other methods (P < 0.05). Moreover, the two-step water bath and water-bath microwaving samples exhibited a more regular spatial network structure compared to other samples. The mixed samples exhibited a microstructure with a uniform and ordered spatial network, allowing more free water to be trapped by the internal structure, resulting in more favorable gel properties. The thermal treatments comprehensively modified the tertiary and quaternary structures of proteins in unwashed mixed gel promoted protein unfurling, provided more hydrophobic interactions, enhanced protein aggregation and improved the gel performance.

CONCLUSION

The findings of the present study improve our understanding of the interactions between proteins from different sources. We propose a new method for modifying surimi's gel properties, facilitating the development of mixed surimi products, as well as enhancing the efficient utilization of aquatic resources. © 2024 Society of Chemical Industry.

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.

Characterization of the extracellular proteases from Bacillus inaquosorum strain E1-8 and its application in the preparation of hydrolysates from plant and animal proteins with antioxidant, antifreeze and anti-browning properties

BACKGROUND

Bacillus inaquosorum strains is widely recognized for their plant-growth-promoting and biocontrol capabilities, yet their roles in protease production remain unclear. The present study aimed to comprehensively assess the protease-producing performance of B. inaquosorum strain E1-8, at the same time as exploring the novel application of agricultural Bacillus proteases in the preparation of protein hydrolysates for fresh-cut fruits preservation.

RESULTS

First, genomic sequencing revealed the diversity of E1-8 proteases, indicating 15 putative extracellular proteases. Subsequently, the fermentation conditions for E1-8 protease production were optimized, with sweet potato powder and soybean meal identified as the most suitable carbon and nitrogen sources, respectively, resulting in a maximum protease activity of 321.48 U mL-1. Upon culturing the strain under these optimized conditions, only an S8 family serine protease and an M48 family metalloprotease were revealed by secretomic analysis and protease inhibitor assays. Additionally, the optimal protease conditions for generating protein hydrolysates from soy, pea, fish and porcine proteins were determined. The molecular weight of the hydrolysates primarily ranged from 2000 to 180 Da, with a total of 17 amino acids identified. The application of these hydrolysates demonstrated a 2,2-diphenyl-1-picrylhydrazyl (i.e. DPPH) scavenging activity ranging from 58.64% to 84.12%, significantly reducing of the melting peaks and the freezing points. Furthermore, the browning index of apple slices stored at 4 °C decreased by 14.81% to 22.15% on the second day, and similar effects were observed in fresh-cut banana stored at 4 °C for 7 days.

CONCLUSION

The protein hydrolysates obtained exhibit remarkable antioxidant, antifreeze and anti-browning properties for fresh-cut fruits. © 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.

Composition-antifreeze property relationships of gelatin and the corresponding mechanisms

The inherent functional fractions (gelation and ice-affinitive fractions) of gelatin enable it as a promising cryoprotectant alternative. However, the composition-antifreeze property relationships of gelatin remain to be investigated. In this study, the HW-PSG and LW-PSG fractions of gelatin from fish scales were obtained, according to the critical gelation conditions and ice-binding measurements, respectively. Thermal hysteresis (THA) value, associated with ice nucleation, of LW-PSG was higher than that of HW-PSG. Besides, the relatively low-sized ice crystals (210-550 μm2) indicated that HW-PSG showed strong ice recrystallization inhibition (IRI) ability, compared to other groups. These results suggested that LW-PSG inhibited ice nucleation, while HW-PSG displayed the strong IRI ability. Furthermore, the antifreeze mechanisms were clarified through IRI measurements and molecular dynamics simulation. The minimum size of ice crystals was found for HW-PSG gels with dense microstructure, suggesting the HW-PSG retarded the growth of ice crystals by restricting the migration and phase transformation of water molecules. The hydrogen bond interactions between the ice crystal surface and ASN1294 and PRO1433 residues of LW-PSG, and hydrophobic interactions contributed to inhibiting the nucleation of ice crystals. This study provided some references to further enhance antifreeze performance of gelatin by modulating fragment composition.

Integrated extraction, structural characterization, and activity assessment of squid pen protein hydrolysates and β-chitin with different protease hydrolysis

Squid pen (SP) is a valuable source of protein and β-chitin. However, current research has primarily focused on extracting β-chitin from SP. This study innovatively extracted both SP protein hydrolysates (SPPHs) and SP β-chitin (SPC) simultaneously using protease hydrolysis. The effects of different proteases on their structural characteristics and bioactivity were evaluated. The results showed that SP alcalase β-chitin (SPAC) had the highest degree of deproteinization (DP, 98.19 %) and SP alcalase hydrolysates (SPAH) had a degree of hydrolysis (DH) of 24.47 %. The analysis of amino acid composition suggested that aromatic amino acids accounted for 17.44 % in SPAH. Structural characterization revealed that SP flavourzyme hydrolysates (SPFH) had the sparsest structure. SPC exhibited an excellent crystallinity index (CI, over 60 %) and degree of acetylation (DA, over 70 %). During simulated gastrointestinal digestion (SGD), the hydroxyl radical scavenging activity, ABTS radical scavenging activity, Fe2+ chelating activity, and reducing power of the SPPHs remained stable or increased significantly. Additionally, SPFC exhibited substantial inhibitory effects on Staphylococcus aureus and Escherichia coli (S. aureus and E. coli), with inhibition circle diameters measuring 2.4 cm and 2.1 cm. These findings supported the potential use of SPPHs as natural antioxidant alternatives and suggested that SPC could serve as a potential antibacterial supplement.

Effect of cryoprotectant-induced intracellular ice formation and crystallinity on bactria during cryopreservation

Cryopreservation is widely used for the long-term storage of bacteria. Glycerol is one of the traditional cryoprotectants used widely to prevent cryoinjury during the cryopreservation of bacteria,although it may be toxic to the cells. To overcome these issues, synthetic antifreeze polymers are also used as cryoprotectants to inhibit ice formation. In the study, we compared the performance of various antifreeze synthetic polymers including poly(vinyl alcohol) (PVA), poly(vinylpyrrolidone), poly(ethylene glycol), and dextran with glycerol, among which PVA performed best on decreasing the ice growth rate.The impacts of glycerol, trehalose, combined with PVA on the survival of S. thermophilus were also explored. Notably,. S. thermophilus stored in 100 mg/mL trehalose and 1 mg/mL PVA +50 mg/mL trehalose combo showed significantly enhanced survival when compared with those in traditional cryoprotectant (20% [v/v] glycerol), which achieved the survival percentage of only 41.03 ± 0.09%. The effects of the freezing temperature and crystallinity on the survival of S. thermophilus were elucidated.

Optimization of a Novel Tyrosinase Inhibitory Peptide from Atrina pectinata Mantle and Its Molecular Inhibitory Mechanism

In order to realize the multi-level utilization of marine shellfish resources and to develop the potential biological activity of processing by-products of Atrina pectinata, gelatin was extracted from the mantle and the potential whitening effect of its enzymatic peptides was explored. Taking tyrosinase inhibitory activity as the evaluation index, the enzyme hydrolysate process was optimized by response-surface methodology, and the optimal enzyme hydrolysate conditions were as follows: pH 5.82, 238 min enzyme hydrolysate time, and temperature of 54.5 °C. Under these conditions, the tyrosinase inhibition activity of Atrina pectinata mantle gelatin peptide (APGP) was 88.6% (IC50 of 3.268 ± 0.048 mg/mL). The peptides obtained from the identification were separated by ultrafiltration and LC-MS/MS, and then four new peptides were screened by molecular docking, among which the peptide Tyr-Tyr-Pro (YYP) had the strongest inhibitory effect on tyrosinase with an IC50 value of 1.764 ± 0.025 mM. The molecular-docking results indicated that hydrogen bonding is the main driving force for the interaction of the peptide YYP with tyrosinase. From the Lineweaver-Burk analysis, it could be concluded that YYP is inhibitory to tyrosinase and exhibits a mixed mechanism of inhibition. These results suggest that YYP could be widely used as a tyrosinase inhibitor in whitening foods and pharmaceuticals.

Ice Recrystallization Inhibition Activity of Soy Protein Hydrolysates

Identifying and developing ice recrystallization inhibitors from sustainable food proteins such as soy protein isolate (SPI) can lead to practical applications in both pharmaceutical and food industries. The objective of this study was to investigate the ice recrystallization inhibition (IRI) activity of SPI hydrolysates, and this was achieved by using an IRI activity-guided fractionation approach and relating IRI activity to interfacial molecular activity measured by vibrational sum frequency generation (VSFG). In addition, the impact of molecular weight (MW) and enzyme specificity was analyzed using three different proteases (Alcalase, trypsin, and pancreatin) and varying hydrolysis times. Using preparative chromatography, hydrolysates from each enzyme treatment were fractionated into five different MW fractions (F1-F5), which were then characterized by high-performance liquid chromatography (HPLC). All SPI hydrolysates had IRI activity, resulting in a 57-29% ice crystal diameter reduction when compared to native SPI. The F1 fraction (of 4-14 kDa) was most effective among all tested hydrolysates, while the lower MW peptide fractions lacked activity. One sample (SPI-ALC 20-F1) had a 52% reduction of ice crystal size at a lower concentration of 2% compared to the typical 4% used. SFG showed a difference in H-bonding and hydrophobic interactions of the molecules on the water/air interface, which may be linked to IRI activity. This study demonstrates for the first time the ability of SPI hydrolysates to inhibit ice crystal growth and the potential application of SFG to study molecular interaction at the interface that may help illustrate the mechanism of action.

New insight into the mechanism by which antifreeze peptides regulate the physiological function of Streptococcus thermophilus subjected to freezing stress

INTRODUCTION

Antifreeze peptides regulate the physiological functions of frozen cells and even their apoptosis; however, the mechanisms by which antifreeze peptides regulate these processes remain unclear, although the interactions between cell membranes and ice are well known to be important in this process.

OBJECTIVES

Our study aims to investigate how antifreeze peptides regulate cell physiological functions during the freezing process.

METHODS

We investigated the cryoprotective effect of rsfAFP on the physiological functions of S. thermophilus under freezing stress by measuring cellular metabolism activity, intracellular enzyme activity, cell membrane characterization, and cell apoptosis. The mechanism by which rsfAFP impacts S. thermophilus physiological functions under freezing stress was investigated using multispectral techniques and cryo-TEM.

RESULTS

We show that a recombinant antifreeze peptide (rsfAFP) interacts with the extracellular capsular polysaccharides and peptidoglycan of Streptococcus thermophilus and ice to cover the outer layer of the membrane, forming a dense protective layer that regulates the molecular structure of extracellular ice crystals, which results in reduced extracellular membrane damage, depressed apoptosis and increased intracellular metabolic activity. This interaction mechanism was indicated by the fact that S. thermophilus better maintained its permeability barrier, membrane fluidity, membrane structural integrity, and cytoplasmic membrane potential during freezing stress with rsfAFP treatment.

CONCLUSION

These results provide new insights into the mechanism by which rsfAFP regulates frozen cellphysiological functionsand apoptosis under freezing stress.

Identification of Novel Antifreeze Peptides from Takifugu obscurus Skin and Molecular Mechanism in Inhibiting Ice Crystal Growth

Foodborne hydrolyzed antifreeze peptides have been widely used in the food industry and the biomedical field. However, the components of hydrolyzed peptides are complex and the molecular mechanism remains unclear. This study focused on identification and mechanism analysis of novel antifreeze peptides from Takifugu obscurus skin by traditional methods and computer-assisted techniques. Results showed that three peptides (EGPRAGGAPG, GDAGPSGPAGPTG, and GEAGPAGPAG) possessed cryoprotection via reducing the freezing point and inhibiting ice crystal growth. Molecular docking confirmed that the cryoprotective property was related to peptide structure, especially α-helix, and hydrogen bond sites. Moreover, the antifreeze peptides were double-faces, which controlled ice crystals while affecting the arrangement of surrounding water molecules, thus exhibiting a strong antifreeze activity. This investigation deepens the comprehension of the mechanism of antifreeze peptides at molecular scale, and the novel efficient antifreeze peptides can be developed in antifreeze materials design and applied in food industry.

Identification of antifreeze peptides in shrimp byproducts autolysate using peptidomics and bioinformatics

In the present study, a novel method based on peptidomics and bioinformatic was applied to identification and characterization of antifreeze peptides (AFPs) from shrimp byproducts autolysate (SBPA). According to the results of in silico prediction and high peptide structural inflexibility, DEYEESGPGIVH and EQICINFCNEK were picked as potential AFP-1 and AFP-2, respectively. The outcomes of DSC determination indicated that TH of synthesized AFP-1 and AFP-2 (10 mg/mL) were 1.37 °C and 1.57 °C, respectively. Besides, 0.1 %-3 % AFPs showed significant cryoprotection in shrimp muscle after 3 and 6 freeze-thaw cycles, evidenced by higher SSP content, Ca²⁺-ATPase activity, sulfhydryl content and lower surface hydrophobicity than control; while the higher concentration resulted in better protection against freeze induced denaturation. Both AFP-1&2 showed favorable hydrogen bonding affinity which facilitated ice binding and ice crystal growth inhibition. This work could provide new ideals for identification and characterization of AFPs.

The Antifreeze and Cryoprotective Activities of a Novel Antifreeze Peptide from Ctenopharyngodon idella Scales

The purpose of this study is to obtain new antifreeze peptides (AFPs) that are natural, safe, and high activity from Ctenopharyngodon idella scales. The optimal hydrolysis conditions were investigated, and chromatography-based isolation was conducted using thermal hysteresis activity (THA) as an index. Molecular dynamic simulation (MDs) was explored to reveal the antifreeze mechanism of the AFPs. The results showed that the optimal hydrolysis conditions were 4000 U/g papain enzyme for 60 °C at pH 5.0 and substrate concentration (1:10) for 3 h, as unveiled by single-factor experiment results. The AFPs documented a THA of 2.7 °C when the T_h was 1.3 °C. Hydrophilic peptide, named GCFSC-AFPs, with a THA of 5.09 °C when the T_h was 1.1 °C was obtained after a series isolation of gel filtration, ion exchange, and reversed-phase HPLC chromatography. The AFPs had a molecular weight of 1107.54~1554.72 Da with three main peptides in the amino acid sequence of VGPAGPSGPSGPQ, RGSPGERGESGPAGPSG, and VGPAGPSGPSGPQG, respectively. The survival rate of yeast with GCFSC-AFPs reached 84.4% following one week of exposure at −20 °C. MDs indicated that GCFSC-AFPs interfered with the ice-water interaction and thus inhibited the ice crystallization process. Our data suggested that the GCFSC-AFPs were a novel and potential antifreeze agent in the food industry.

Preparation, Characterization, and Mechanism of Antifreeze Peptides from Defatted Antarctic Krill (Euphausia superba) on Lactobacillus rhamnosus

Defatted Antarctic krill powder is the main by-product in the manufacturing of krill oil. Exploring a high value-added approach for utilizing this protein-rich material has received much attention in research and industry. Given this, the preparation and primary characterization of antifreeze peptides from defatted Antarctic krill (AKAPs) were carried out in this study. The cryoprotective effect of AKAPs on Lactobacillus rhamnosus ATCC7469 was also investigated. The results showed that Protamex was the optimum protease for AKAP preparation from defatted Antarctic krill. AKAPs were found to be rich in short peptides, with the MW ranging from 600 to 2000 Da (69.2%). An amino acid composition analysis showed that AKAPs were rich in glutamic acid (18.71%), aspartic acid (12.19%), leucine (7.87%), and lysine (7.61%). After freezing, the relative survival rate of Lactobacillus rhamnosus in the 1.0 mg/mL AKAP-treated group (96.83%) was significantly higher than in the saline group (24.12%) (p < 0.05). AKAPs also retarded the loss of acidifying activity of L. rhamnosus after freezing. AKAPs showed even better cryoprotective activity than three commercial cryoprotectants (sucrose, skim milk, and glycerol). In addition, AKAPs significantly alleviated the decrease in β-galactosidase and lactic dehydrogenase activities of L. rhamnosus (p < 0.05). Furthermore, AKAPs effectively protected the integrity of L. rhamnosus cell membranes from freezing damage and alleviated the leakage of intracellular substances. These findings demonstrate that AKAPs can be a potential cryoprotectant for preserving L. rhamnosus, providing a new way to use defatted Antarctic krill.

From Fish Scale Gelatin to Tyrosinase Inhibitor: A Novel Peptides Screening Approach Application

Bioaffinity ultrafiltration combined with LC-Orbitrap-MS/MS was applied for the first time to achieve rapid screening and identification of tyrosinase inhibitory peptides (TYIPs) from grass carp scale gelatin hydrolysates. The binding mode of TYIPs with tyrosinase was investigated by molecular docking technology. The whitening effect of TYIPs was further studied by evaluating the tyrosinase activity and melanin content in mouse B16F10 cells. Four new TYIPs were screened from hydrolysates, among which DLGFLARGF showed the strongest tyrosinase inhibition with an IC50 value of 3.09 mM. Molecular docking showed that hydrogen bonds were the main driving force in the interaction between the peptide DLGFLARGF and tyrosinase. The addition of DLGFLARGF significantly inhibited the tyrosinase activity and melanin production of B16F10 melanoma cells. These results suggest that DLGFLARGF is a promising skin whitening agent for the treatment of potential pigment-related diseases.

Antifreeze Peptides Preparation from Tilapia Skin and Evaluation of Its Cryoprotective Effect on Lacticaseibacillus rhamnosus

Antifreeze peptides can protect cell membranes and maintain the cell viability of probiotics under cold stress. Given this, antifreeze peptides were prepared from tilapia processing byproducts of tilapia skin by enzymolysis using the response surface methodology (RSM) method. The cryoprotective effects on Lacticaseibacillus rhamnosus ATCC7469 were investigated. Trypsin was selected as the protease for tilapia skin hydrolysis. The optimal hydrolysis conditions consisted of the amount of enzyme (2200 U/g), solid–liquid ratio (1:10, w/v), reaction temperature (49 °C), and reaction time (6.8 h), and the relative survival rate of L. rhamnosus reached 98.32%. Molecular weight (M_w) distribution and peptide sequences of the antifreeze peptides prepared from tilapia skin (APT) under the optimal conditions were analyzed. APT significantly reduced the leakage of extracellular proteins and protected β-galactosidase and lactate dehydrogenase activities of L. rhamnosus. Compared with the saline group, scanning electron microscopy (SEM) observation showed that cells had a more normal, smooth, and entire surface under the protection of APT. These findings indicate that APT can be a new cryoprotectant in preserving probiotics.

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.

Snow flea antifreeze peptide for cryopreservation of lactic acid bacteria

Cryogenic machining is one of the most commonly used techniques for processing and preserving in food industry, and traditional antifreeze agents cannot regulate the mechanical stress damage caused by ice crystals formed during recrystallization or thawing. In this study, we successfully developed an express system of a novel recombinant snow flea antifreeze peptide (rsfAFP), which has significant ice recrystallization inhibition ability, thermal hysteresis activity and alters ice nucleation, thus regulating extracellular ice crystal morphology and recrystallization. We showed that rsfAFP improved the survival rate, acid-producing ability, freezing stability, and cellular metabolism activity of Streptococcus thermophilus. We further showed that rsfAFP interacts with the membrane and ice crystals to cover the outer layer of cells, forming a dense protective layer that maintains the physiological functions of S. thermophilus under freezing stress. These findings provide the scientific basis for using rsfAFP as an effective antifreeze agent for lactic acid bacteria cryopreservation or other frozen food.

Effect of carboxymethyl chitosan on the storage stability of frozen dough: State of water, protein structures and quality attributes

Carboxymethyl chitosan (CMCh), an ampholetic chitosan derivative, has found broad applications in the food industry. However, its cryo-protective properties remained less explored compared to other viscous polysaccharides, such as carboxymethyl cellulose, carrageenan etc., which have been widely utilized as frozen food additives. In this study, we investigated the effect of CMCh addition to frozen dough in terms of water state, protein structure, and the textural properties of prepared frozen dumpling wrappers. Results indicated that CMCh restricted the water migration in dough and delayed protein deterioration during frozen storage. Specifically, the content of freezable water in dough was reduced and the water distribution became more uniform as reflected by DCS and LF-NMR analysis. CMCh also stabilized disulfide bond and secondary structures of the protein, leading to inhibition of dough rheology changes. Accordingly, the obtained frozen dumplings wrappers demonstrated decreased cracking rate and water loss, and improved textural properties. Moreover, CMCh with higher degree of carboxymethyl substitution (DS: 1.2, CMCh-B) exhibited better cryo-protective effects compared to CMCh of lower DS (DS: 0.8, CMCh-A). Our study provides novel insights and scientific basis for the development of ampholetic polysaccharides as high-performance food additives.

Survivability of Collagen-Peptide Microencapsulated Lactic Acid Bacteria during Storage and Simulated Gastrointestinal Conditions

The intracellular homeostasis of lyophilized lactic acid bacteria (LAB) is destroyed by extreme cold stress, resulting in decreased stability. This study aimed to verify the validity of collagen as a potential protective agent for improving microbial stability deteriorated by freezing. The collagen types used in this study were low molecular weight collagen (LC) of less than 1000 Da and low molecular weight collagen-peptide (LCP) of less than 300 Da. By the accelerated stability test according to the addition of each collagen type, a 3% LCP displaying a protective effect on the viability of various LAB strains (Lactoplantibacillus plantarum MG989, Lactococcus lactis MG5125, Enterococcus faecium MG5232, Bifidobacterium animalis ssp. lactis MG741, and Streptococcus thermophilus MG5140) was finally selected. It was evaluated whether LCP enhances bacterial stability, survivability in the gastrointestinal (GI) tract, and heat resistance. LCP significantly improved the viability of all strains in the GI tract compared to sucrose and skim milk, which are conventional protective agents. Based on morphological observations, LCP was uniformly coated on the cell surface, resulting in protective effects against multiple external stress stimuli. Such findings indicate the applicability of LCP as an unprecedented protective agent, which can improve the stability of various probiotics with antifreeze effects.

Overexpression of BrAFP1 gene from winter rapeseed (Brassica rapa) confers cold tolerance in Arabidopsis

Antifreeze proteins (AFPs) can bind to ice crystals and restrain the formation of larger crystals, a strategy vital to the survival of plants in freezing environments. The BrAFP1 from winter rapeseed cultivars 'Longyou 7' with high cold tolerance was cloned and overexpressed in Arabidopsis. BrAFP1 was localized in the cytoplasm and nucleus. Under cold stress, SOD activity and free proline content were higher, MDA content and relative conductivity were lower in transgenic lines than those in wide-type Arabidopsis. Frostbite of transgenic plants was minimized, whereas frostbite of the Arabidopsis afp1 mutant was severe. Transition of the amino acid at position 17 of BrAFP1 was related to the increased winter survival of the rapeseed cultivar. Cultivars with higher survival rates had a predilection for tyrosine, not tryptophan, at the 17th site in the amino sequence of BrAFP1. Transcription of BrAFP1 was induced more rapidly, and the expression of the gene was also higher, in Longyou 7 than that in Tianyou 4 under cold stress. Overall, the high expression of BrAPF1 confers more cold-tolerance in Longyou 7.

Ice-binding proteins: a remarkable ice crystal regulator for frozen foods

Ice crystal growth during cold storage presents a quality problem in frozen foods. The development of appropriate technical conditions and ingredient formulations is an effective method for frozen food manufacturers to inhibit ice crystals generated during storage and distribution. Ice-binding proteins (IBPs) have great application potential as ice crystal growth inhibitors. The ability of IBPs to retard the growth of ice crystals suggests that IBPs can be used as a natural ice conditioner for a variety of frozen products. In this review, we first discussed the damage caused by ice crystals in frozen foods during freezing and frozen storage. Next, the methods and technologies for production, purification and evaluation of IBPs were summarized. Importantly, the present review focused on the characteristics, structural diversity and mechanisms of IBPs, and the application advances of IBPs in food industry. Finally, the challenges and future perspectives of IBPs are also discussed. This review may provide a better understanding of IBPs and their applications in frozen products, providing some valuable information for further research and application of IBPs.

Effects of gelatin-based antifreeze peptides on cell viability and oxidant stress of Streptococcus thermophilus during cold stage

Cold stage adversely affects cell proliferation and cell viability of probiotics such as Streptococcus thermophilus in food industry, new type of cryoprotectants continues to be needed. Gelatin-based antifreeze peptide becomes a popular topic because of its cryoprotective effects on cold-stressed probiotics. In this study the effects of tilapia scales antifreeze peptides (TSAPP) on cell viability and oxidant stress of S. thermophilus during cold stage were investigated. The results showed that the percentage of viable cells was increased 10.85 folds compared with control groups. Addition of TSAPP activated the activities of ATPases, relieved the hyperpolarization of cell membrane potential and regulated the intracellular Ca2+ concentration. Furthermore, TSAPP significantly inhibited reactive oxygen species level and malonaldehyde content in cells. Under cryopreservation with TSAPP, cells of S. thermophilus maintained higher activities of antioxidant enzymes including catalase, peroxidase and total antioxidant capacity. These findings indicate that TSAPP likely offered its cellular protection by maintaining membrane integrity and alleviation of oxidative stress.

Physicochemical properties and hepatoprotective effects of glycated Snapper fish scale peptides conjugated with xylose via maillard reaction

The physicochemical properties and hepatoprotective effects of fish scales peptides (FSP) and the glycated peptides conjugated with xylose via Maillard reaction (FSP-MRPs) were investigated. Results showed that the FSP was rich in oligopeptides within 2-10 amino acids, the degree of grafting of FSP-MRPs was 52.97 ± 1.58% and the antioxidant activities in vitro of FSP were improved through Maillard reaction. In order to investigate the antioxidant activities of FSP-MRPs after digestion, the simulated gastrointestinal digestion experiments of FSP and FSP-MRPs in vitro were conducted. Results indicated that the antioxidant activities of FSP and FSP-MRPs remained as stronger as before even under the digestive conditions. Furthermore, FSP-MRPs could significantly reduce the elevated activities of serum aspartate aminotransferase and alanine aminotransferase, decrease the elevated the levels of hepatic malondialdehyde and triglyceride, and inhibit the decrease of hepatic superoxide dismutase, catalase and glutathione peroxidase caused by alcohol-induced liver damage. These findings suggest that the glycated peptides formed by FSP and xylose via Maillard reaction may be potential to be exploited as a potential functional ingredient in food industry.

Bioactive peptides derived from crimson snapper and in vivo anti-aging effects on fat diet-induced high fat Drosophila melanogaster

Crimson snapper scale peptides (CSSPs) prepared from crimson snapper scales exhibited significant antioxidant activity in vitro and anti-aging effects in vivo on fat diet-induced high fat Drosophila melanogaster.

Organic selenium derived from chelation of soybean peptide-selenium and its functional properties in vitro and in vivo

Organic selenium has been widely explored as an important source of selenium (Se) supplement due to its low toxicity and easy absorption. In the present study, a new type of organic selenium was fabricated by chelating Se with soybean protein isolate peptides (SPIPs), and its physio-chemical properties, structural characteristics, and antioxidant activities were investigated. Results indicated that the structure of the SPIP molecule was folded and aggregated during the chelation process. SPIP-Se exhibited stronger hydroxyl radical scavenging activity and reducing power than SPIP in vitro. In addition, SPIP-Se could repair the H2O2-induced oxidative damage of Caco-2 cells by enhancing the activities of antioxidant enzymes. The in vivo assay showed that SPIP-Se showed much less toxicity than inorganic Se supplements, and exhibited a more positive effect on the activities of key enzymes including superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and aspartate aminotransferase (AST). These findings suggest that SPIP-Se could be developed as an effective dietary Se supplement in the food or pharmaceutical field in the future.