Identification and Evaluation of Cryoprotective Peptides from Chicken Collagen: Ice-Growth Inhibition Activity Compared to That of Type I Antifreeze Proteins in Sucrose Model Systems

Research progress on quality deterioration mechanism and control technology of frozen muscle foods

Freezing can prolong the shelf life of muscle foods and is widely used in their preservation. However, inevitable quality deterioration can occur during freezing, frozen storage, and thawing. This review explores the eating quality deterioration characteristics (color, water holding capacity, tenderness, and flavor) and mechanisms (irregular ice crystals, oxidation, and hydrolysis of lipids and proteins) of frozen muscle foods. It also summarizes and classifies the novel physical-field-assisted-freezing technologies (high-pressure, ultrasound, and electromagnetic) and bioactive antifreeze (ice nucleation proteins, antifreeze proteins, natural deep eutectic solvents, carbohydrate, polyphenol, phosphate, and protein hydrolysates), regulating the dynamic process from water to ice. Moreover, some novel thermal and nonthermal thawing technologies to resolve the loss of water and nutrients caused by traditional thawing methods were also reviewed. We concluded that the physical damage caused by ice crystals was the primary reason for the deterioration in eating quality, and these novel techniques promoted the eating quality of frozen muscle foods under proper conditions, including appropriate parameters (power, time, and intermittent mode mentioned in ultrasound-assisted techniques; pressure involved in high-pressure-assisted techniques; and field strength involved in electromagnetic-assisted techniques) and the amounts of bioactive antifreeze. To obtain better quality frozen muscle foods, more efficient technologies and substances must be developed. The synergy of novel freezing/thawing technology may be more effective than individual applications. This knowledge may help improve the eating quality of frozen muscle foods.

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.

Tissue extracellular matrix hydrogels as alternatives to Matrigel for culturing gastrointestinal organoids

Matrigel, a mouse tumor extracellular matrix protein mixture, is an indispensable component of most organoid tissue culture. However, it has limited the utility of organoids for drug development and regenerative medicine due to its tumor-derived origin, batch-to-batch variation, high cost, and safety issues. Here, we demonstrate that gastrointestinal tissue-derived extracellular matrix hydrogels are suitable substitutes for Matrigel in gastrointestinal organoid culture. We found that the development and function of gastric or intestinal organoids grown in tissue extracellular matrix hydrogels are comparable or often superior to those in Matrigel. In addition, gastrointestinal extracellular matrix hydrogels enabled long-term subculture and transplantation of organoids by providing gastrointestinal tissue-mimetic microenvironments. Tissue-specific and age-related extracellular matrix profiles that affect organoid development were also elucidated through proteomic analysis. Together, our results suggest that extracellular matrix hydrogels derived from decellularized gastrointestinal tissues are effective alternatives to the current gold standard, Matrigel, and produce organoids suitable for gastrointestinal disease modeling, drug development, and tissue regeneration.

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.

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.

Comparative Study on the Cryoprotective Effects of Three Recombinant Antifreeze Proteins from Pichia pastoris GS115 on Hydrated Gluten Proteins during Freezing

During the freezing process, ice crystal formation leads to the deterioration in physicochemical properties and networks of gluten proteins. The cryoprotective effects of recombinant carrot ( Daucus carota) antifreeze protein (rCaAFP), type II antifreeze protein from Epinephelus coioides (rFiAFP), and Tenebrio molitor antifreeze protein (rTmAFP) produced from Pichia pastoris GS115 on hydrated gluten, glutenin, and gliadin during freezing were investigated. The thermal hysteresis (TH) activity and ice crystals' morphology modification ability of recombinant antifreeze proteins (rAFPs) were analyzed by differential scanning calorimetry (DSC) and cryomicroscope, respectively. The freezing and melting properties, water state, rheological properties, and microstructure of hydrated gluten proteins were studied by DSC, low field nuclear magnetic resonance, rheometer, and scanning electron microscopy, respectively. The rTmAFP exhibited strongest TH activity and ice crystals' morphology modification ability, followed by rFiAFP and rCaAFP. The addition of the three rAFPs caused freezing hysteresis and weakened the damage of freezing to the networks of hydrated gluten, glutenin, and gliadin. During freezing, the cryoprotective effects of the three rAFPs on the freezable water content, water mobility and distribution, and rheological properties of hydrated gluten were achieved by protecting these corresponding properties of hydrated glutenin. Among the three rAFPs, rTmAFP was most effective in the cryoprotective activities on hydrated gluten proteins during freezing. The results demonstrate the potential of these rAFPs, especially rTmAFP, to preserve the above properties of hydrated gluten proteins during the freezing process.

Intracellular Expression of Antifreeze Peptides in Food Grade Lactococcus lactis and Evaluation of Their Cryoprotective Activity

Antifreeze peptides can protect living organisms from low temperatures by preventing damage or killing due to ice crystal formation between cells. Therefore, antifreeze peptides can be used as a low temperature protectant for cryopreservation of cells and tissues, and also in food production. In this study, a recombinant SF-P gene was constructed and inserted into pNZ8149 to construct a food grade expression vector, which was then electroporated into Lactococcus lactis NZ3900. The expression of the target protein was induced using Nisin, and the optimal expression condition was determined to be a pH of 6.0, Nisin concentration of 25 ng/mL, temperature of 37 °C, and incubation time of 6 hr. Compared to the strain NZ3900 and the recombinant strain SF-P₁ without addition of Nisin, the recombinant strain SF-P₂ showed the highest cell survival and thermal hysteresis activity, and had a reduction in the changes of activities of extracellular and intracellular lactate dehydrogenase and β-galactosidase after freezing. Moreover, analysis by SEM showed that SF-P₂ cells were more completely and regularly shaped than other strains, displayed no obvious leakage of cell contents, and had an intact boundary between cells after freezing. These results indicate that the recombinant strain SF-P₂ has a protective effect against freezing. This paper presents a food grade expression system for an antifreeze peptide SF-P using L. lactis as a host, and shows that the intracellular expression of antifreeze peptide could protect the cellular integrity and physiological functions of L. lactis.

PRACTICAL APPLICATION

The recombinant Lactococcus lactis with intracellular expression of antifreeze peptides SF-P could reduce the damage of bacteria cells induced by freezing or freeze drying, so, it could be applied in the process of freezing food without separation, such as the manufacture of yoghurt ice cream, frozen dough, and so on.

Why do antifreeze proteins require a solenoid?

Proteins whose presence prevents water from freezing in living organisms at temperatures below 0 °C are referred to as antifreeze proteins. This group includes molecules of varying size (from 30 to over 300 aa) and variable secondary/supersecondary conformation. Some of these proteins also contain peculiar structural motifs called solenoids. We have applied the fuzzy oil drop model in the analysis of four categories of antifreeze proteins: 1 - very small proteins, i.e. helical peptides (below 40 aa); 2 - small globular proteins (40-100 aa); 3 - large globular proteins (>100 aa) and 4 - proteins containing solenoids. The FOD model suggests a mechanism by which antifreeze proteins prevent freezing. In accordance with this theory, the presence of the protein itself produces an ordering of water molecules which counteracts the formation of ice crystals. This conclusion is supported by analysis of the ordering of hydrophobic and hydrophilic residues in antifreeze proteins, revealing significant variability - from perfect adherence to the fuzzy oil drop model through structures which lack a clearly defined hydrophobic core, all the way to linear arrangement of alternating local minima and maxima propagating along the principal axis of the solenoid (much like in amyloids). The presented model - alternative with respect to the ice docking model - explains the antifreeze properties of compounds such as saccharides and fatty acids. The fuzzy oil drop model also enables differentiation between amyloids and antifreeze proteins.