Extraction of antifreeze proteins from cold acclimated leaves of Drimys angustifolia and their application to star fruit (Averrhoa carambola) freezing

Brassica juncea leaf cuticle contains xylose and mannose (xylomannan) which inhibit ice recrystallization on the leaf surface

MAIN CONCLUSION

Conjugated sugars showed antifreeze activity in the cuticle by ice recrystallization inhibition rather than thermal hysteresis, enhancing freezing capacity at the surface of B. juncea leaves. Antifreeze biomolecules play a crucial role in mitigating the physical damage from frost by controlling extracellular ice crystal growth in plants. Antifreeze proteins (AFPs) are reported from the apoplast of different plants. Interestingly, there is no report about antifreeze properties of the cuticle. Here, we report the potential antifreeze activity in the Brassica juncea (BJ) leaf cuticle. Nano LC-MS/MS analysis of a cuticle protein enriched fraction (CPE) predicted over 30 putative AFPs using CryoProtect server and literature survey. Ice crystal morphology (ICM) and ice recrystallization inhibition (IRI) analysis of ABC supernatant showed heat and pronase-resistant, non-protein antifreeze activities as well as hexagonal ice crystals with TH of 0.17 °C and IRI 46%. The ZipTip processed ABC supernatant (without peptides) had no effect on TH activity, confirming a non-protein antifreeze molecule contributing to activity. To understand the origin and to confirm the source of antifreeze activity, cuticular membranes were isolated by pectinase and cellulase hydrolysis. FTIR analysis of the intact cuticle showed xylose, mannose, cellulose, and glucose. Xylanase and cellulase treatments of the ZipTip processed ABC supernatant led to an increase in sugar content and 50% loss in antifreeze activity. UV spectroscopy and NMR analysis supported the finding of FTIR and enzyme hydrolysis suggesting the contribution of xylose and mannose to antifreeze activity. By TLC analysis, conjugated sugars were found in the cuticle. This work has opened up a new research area where the antifreeze capacity needs to be established with regard to complete characterization and mechanism of action of the antifreeze carbohydrates (conjugated sugars) on the leaf surface.

Effect of antifreeze proteins on the freeze-thaw cycle of foods: fundamentals, mechanisms of action, current challenges and recommendations for future work

Freezing is widely used in food preservation, but if not carried out properly, ice crystals can multiply (nucleation) or grow (recrystallization) rapidly. This also affects thawing, causing structural damage and affecting overall quality. The objective of this review is to comprehensively study the cryoprotective effect of antifreeze proteins (AFPs), highlighting their role in the freeze-thaw process of food. The properties of AFPs are based on their thermal hysteresis capacity (THC), on the modification of crystal morphology and on the inhibition of ice recrystallization. The mechanism of action of AFPs is based on the adsorption-inhibition theory, but the specific role of hydrogen and hydrophobic bonds/residues and structural characteristics is also detailed. Because of the properties of AFPs, they have been successfully used to preserve the quality of a wide variety of refrigerated and frozen foods. Among the limitations of the use of AFPs, the high cost of production stands out, but currently there are solutions such as the use the production of recombinant proteins, cloning and chemical synthesis. Although in vitro, in vivo and human studies have shown that AFPs are non-toxic, their safety remains a matter of debate. Further studies are recommended to expand knowledge about AFPs, to reduce costs in their large-scale production, to understand their interaction with other food compounds and their possible effects on the consumer.

Cold adaptation strategies in plants—An emerging role of epigenetics and antifreeze proteins to engineer cold resilient plants

Cold stress adversely affects plant growth, development, and yield. Also, the spatial and geographical distribution of plant species is influenced by low temperatures. Cold stress includes chilling and/or freezing temperatures, which trigger entirely different plant responses. Freezing tolerance is acquired via the cold acclimation process, which involves prior exposure to non-lethal low temperatures followed by profound alterations in cell membrane rigidity, transcriptome, compatible solutes, pigments and cold-responsive proteins such as antifreeze proteins. Moreover, epigenetic mechanisms such as DNA methylation, histone modifications, chromatin dynamics and small non-coding RNAs play a crucial role in cold stress adaptation. Here, we provide a recent update on cold-induced signaling and regulatory mechanisms. Emphasis is given to the role of epigenetic mechanisms and antifreeze proteins in imparting cold stress tolerance in plants. Lastly, we discuss genetic manipulation strategies to improve cold tolerance and develop cold-resistant plants.

Assessing the Gel Quality and Storage Properties of Hypophythalmalmichthys molitrix Surimi Gel Prepared with Epigallocatechin Gallate Subject to Multiple Freeze-Thaw Cycles

Epigallocatechin gallate (EGCG) with concentrations of 0-0.03% was added to manufacture surimi gels, respectively, while effects on gel quality and storage properties indicators during freeze-thaw (F-T) cycles were investigated. The results implied that the gel quality and storage properties of surimi gels added without EGCG were seriously destroyed during F-T cycles. The addition of EGCG could inhibit the decline of texture and gel strength. Moreover, EGCG has effect on inhibiting the microbial growth and the formation of off-odor compounds such as total volatile basic nitrogen (TVB-N) and malondialdehyde (MDA). Low-field nuclear magnetic resonance (LF-NMR) and water-holding capacity (WHC) results showed that immobilized water migrated to free water with the extension of F-T cycles. The scanning electron microscope (SEM) observed denser protein networks and smaller holes from the surimi gels added with EGCG. However, excessive (0.03%) EGCG showed the loose network structure and moisture loss. Overall, EGCG in 0.01-0.02% addition was good for resisting damage of surimi gels during F-T cycles.

Ice structuring protein extract of Hordeum vulgare var. dolma grain reduces drip loss and loss of soluble vitamin content in peas during frozen storage

The Himalayan plants face low temperature during their life cycle and are expected to possess antifreeze proteins. The present work describes screening of six plant species that grow in Himalayas, for their ice structuring properties with an aim to provide a vegetarian source of ice structuring proteins. The ice-structuring protein extract of barley [Hordeum vulgare; variety Dolma (HvISE)] and wheat [Triticum aestivum; variety Him Pratham DH 114 (TaISE) ]showed inhibition of growth of ice crystals during the process of recrystallization. This property was analyzed for its application in frozen peas by pretreatment with HvISE before freezing. The drip loss was measured in frozen peas after thawing. Further, the water-soluble vitamins; thiamine, pyridoxine, riboflavin, and ascorbic acid were quantified before and after freezing of green peas by UHPLC-PDA. The pretreatment with HvISE reduced the loss of ascorbic acid, riboflavin, and pyridoxine during their frozen storage. The present study identified barley as a remarkable source of ice structuring proteins and validated its potential for frozen peas. The work has enormous implications in frozen food industry, in general.

Traditional Uses, Phytochemical Constituents and Pharmacological Properties of Averrhoa carambola L.: A Review

Averrhoa carambola L. (star fruit) is an edible fruit that is extensively cultivated in southern China, Southeast Asia, India, and northern South America. It has a sweet and juicy taste and is frequently used in fruit salads and fruit platters, as a garnish in cocktail drinks and beverages, or squeezed into juice and served as a beverage. Traditionally, it has been used for treating diabetes and diabetic nephropathy, arthralgia, vomiting, lithangiuria, coughing, hangovers, and chronic paroxysmal headache for thousands of years. Currently, approximately 132 compounds have been isolated from A. carambola. Among them, flavonoids, benzoquinone, and their glycosides have been considered as biologically active substances, which are responsible for various biological activities. Pharmacological studies have revealed that crude extracts or monomeric compounds from A. carambola exhibit multiple bioactivities, such as anti-oxidant, anti-hyperglycemic, anti-obesity, anti-hyperlipidemic, anti-tumor, anti-inflammatory, hepatoprotective, cardioprotective, anti-hypertensive, neuroprotective, and others. Thus, A. carambola is a valuable treatment in Chinese medicine with therapeutic potential for multiple diseases, especially diabetes and diabetes-related diseases. Even though it is a very promising candidate in the development of functional food and the pharmaceutical industry, reports on its bioactivities have only been conducted in vivo and in vitro and there is a gap in research regarding clinical settings and safety. This review therefore provides a comprehensive and systematic overview of current progress on botany, ethnopharmacology, phytochemistry, pharmacology, and toxicity of A. carambola, providing a valuable reference for further developments and applications of A. carambola in the pharmaceutical industry and functional food.

Changes of aggregation and structural properties of heat-denatured gluten proteins in fast-frozen steamed bread during frozen storage

The aim of this research was to clearly clarify the deterioration mechanism of heat-denatured gluten proteins by exploring the change of aggregation and structural characteristics of heat-denatured gluten proteins in the steamed bread system and the steamed gluten system during frozen storage. An increase in the total SDS-soluble protein content was determined, which mainly attributed to the soluble monomer protein content increased. Combined with the significant increase of free sulfhydryl, from 3.12 μmol/g to 5.06 μmol/g and 2.64 μmol/g to 3.29 μmol/g, respectively, it can be inferred that the proteins depolymerization induced by frozen storage was mainly involved in the breakdown of heat-induced glutenin-gliadin disulfide cross-linking. Frozen storage induced the conversion of random coil structure to β-sheet structure and a ruptured microstructure with small fragment was observed. Moreover, the protein of steamed bread system was easier to depolymerize than that of the steamed gluten system.

Animal by-products collagen and derived peptide, as important components of innovative sustainable food systems-a comprehensive review

In 2020, the world's food crisis and health industry ushered into a real outbreak. On one side, there were natural disasters such as the novel coronavirus (2019-nCoV), desert locusts, floods, and droughts exacerbating the world food crisis, while on the other side, the social development and changes in lifestyles prompted the health industry to gradually shift from a traditional medical model to a new pattern of prevention, treatment, and nourishment. Therefore, this article reviews animal by-products collagen and derived peptide, as important components of innovative sustainable food systems. The review also considered the preparation, identification, and characterization of animal by-product collagen and collagen peptides as well as their impacts on the food system (including food processing, packaging, preservation, and functional foods). Finally, the application and research progress of animal by-product collagen and peptide in the food system along with the future development trend were discussed. This knowledge would be of great significance for a comprehensive understanding of animal by-product collagen and collagen peptides and would encourage the use of collagen in food processing, preservation, and functional foods.

Inhibiting effect of ice structuring protein on the decreased gelling properties of protein from quick-frozen pork patty subjected to frozen storage

The effect of ice structuring protein (ISP) on the gelling properties of myofibrillar protein from quick-frozen pork patty during frozen storage was investigated by determining and comparing protein solubility, turbidity and gel properties. Protein solubility was increased by 10.23% and turbidity was decreased after ISP treated. The gel whiteness and strength of myofibrillar protein from patty with ISP were 8.38% and 13.70% higher than that of the control after frozen for 180 days. And the addition of ISP could weaken the influence of frozen storage on water mobility and reduce the water loss. Furthermore, ISP retrained the decrease in the maximum elastic (G') value and loss factor (tan δ) value of samples. Through observing by scanning electron microscope (SEM), ISP retarded the destruction of gel microstructure and maintained the relatively complete tissue of gel. These findings confirmed the importance of ISP in myofibrillar protein gel quality assurance of pork patty during frozen storage.

Effect of ice structuring protein on the quality of quick-frozen patties subjected to multiple freeze-thaw cycles

The inhibitory effect of ice structuring protein (ISP) on the quality deterioration of quick-frozen pork patties subjected to multiple freeze-thaw (F-T) cycles was investigated. The inhibitory effect of ISP on patty quality deterioration was obvious after five F-T cycles (P < 0.05). The hardness and springiness of patties with 0.20% ISP were 3.84% and 10.61% higher than those of patties without ISP, and the thawing loss of patties with 0.20% ISP was 43.64% lower than that of patties without ISP (P < 0.05). In addition, ISP effectively restrained moisture migration and destruction of pork patty microstructure during F-T cycles. More importantly, thiobarbituric acid reactive substance levels and carbonyl contents in the patties with 0.20% ISP were 25% and 32% lower than those in the control group (no significant difference with patties with 0.30% ISP) after five F-T cycles. Therefore, these results illustrated the potential benefits of ISP in meat products.

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.

Identifying Antifreeze Proteins Based on Key Evolutionary Information

Antifreeze proteins are important antifreeze materials that have been widely used in industry, including in cryopreservation, de-icing, and food storage applications. However, the quantity of some commercially produced antifreeze proteins is insufficient for large-scale industrial applications. Further, many antifreeze proteins have properties such as cytotoxicity, severely hindering their applications. Understanding the mechanisms underlying the protein-ice interactions and identifying novel antifreeze proteins are, therefore, urgently needed. In this study, to uncover the mechanisms underlying protein-ice interactions and provide an efficient and accurate tool for identifying antifreeze proteins, we assessed various evolutionary features based on position-specific scoring matrices (PSSMs) and evaluated their importance for discriminating of antifreeze and non-antifreeze proteins. We then parsimoniously selected seven key features with the highest importance. We found that the selected features showed opposite tendencies (regarding the conservation of certain amino acids) between antifreeze and non-antifreeze proteins. Five out of the seven features had relatively high contributions to the discrimination of antifreeze and non-antifreeze proteins, as revealed by a principal component analysis, i.e., the conservation of the replacement of Cys, Trp, and Gly in antifreeze proteins by Ala, Met, and Ala, respectively, in the related proteins, and the conservation of the replacement of Arg in non-antifreeze proteins by Ser and Arg in the related proteins. Based on the seven parsimoniously selected key features, we established a classifier using support vector machine, which outperformed the state-of-the-art tools. These results suggest that understanding evolutionary information is crucial to designing accurate automated methods for discriminating antifreeze and non-antifreeze proteins. Our classifier, therefore, is an efficient tool for annotating new proteins with antifreeze functions based on sequence information and can facilitate their application in industry.