Preserving frozen stallion sperm on dry ice using polymers that modulate ice crystalization kinetics

Cryopreserved semen is routinely shipped in liquid nitrogen. Dry ice could serve as an alternative coolant, however, frozen storage above liquid nitrogen temperatures (LN2, -196 °C) may negatively affect shelf-life and cryosurvival. In this study, we determined critical temperatures for storage of cryopreserved stallion sperm. We evaluated: (i) effects of cooling samples to different subzero temperatures (-10 °C to -80 °C) prior to storing in LN2, (ii) stability at different storage temperatures (i.e., in LN2, dry ice, -80 °C and -20 °C freezers, 5 °C refrigerator), and (iii) sperm cryosurvival during storage on dry ice (i.e., when kept below -70 °C and during warming). Furthermore, (iv) we analyzed if addition of synthetic polymers (PVP-40, Ficoll-70) modulates ice crystallization kinetics and improves stability of cryopreserved specimens. Sperm motility and membrane intactness were taken as measures of cryosurvival, and an artificial insemination trial was performed to confirm fertilizing capacity. We found that adding PVP-40 or Ficoll-70 to formulations containing glycerol reduced ice crystal sizes and growth during annealing. Post-thaw sperm viability data indicated that samples need to be cooled below -40 °C before they can be safely plunged and stored in LN2. No negative effects of relocating specimens from dry ice to LN2 and vice versa became apparent. However, sample warming above -50 °C during transport in dry ice should be avoided to ensure preservation of viability and fertility. Moreover, addition of PVP-40 or Ficoll-70 was found to increase sperm cryosurvival, especially under non-ideal storage conditions where ice recrystallization may occur.

Self-assembly of tamarind seed polysaccharide via enzymatic depolymerization and degalactosylation enhanced ice recrystallization inhibition activity

Polysaccharides are becoming potential candidates for developing food-grade cryoprotectants due to their extensive accessibility and health-promoting effects. However, unremarkable ice recrystallization inhibition (IRI) activity and high viscosity limit their practical applications in some systems. Our previous study found a galactoxyloglucan polysaccharide from tamarind seed (TSP) showing moderate IRI activity. Herein, the enhancement of the IRI performance of TSP via enzymatic depolymerization and degalactosylation-induced self-assembly was reported. TSP was depolymerized and subsequently removed ∼40 % Gal, which induced the formation of supramolecular rod-like fiber self-assembles and exhibited a severalfold enhancement of IRI. Ice shaping assay did not show obvious faceting of ice crystals, indicating that both depolymerized and self-assembled TSP showed very weak binding to ice. Molecular dynamics simulation confirmed the absence of molecular complementarity with ice. Further, it highlighted that degalactosylation did not cause significant changes in local hydration properties of TSP from the view of a single oligomer. The inconsistency between molecular simulation and macroscopic IRI effect proposed that the formation of unique supramolecular self-assemblies may be a key requirement for enhancing IRI activity. The findings of this study provided a new opportunity to enhance the applied potential of natural polysaccharides in food cryoprotection.

Octenyl succinic anhydride-modified amyloid protein fibrils demonstrate enhanced ice recrystallization inhibition activity and dispersibility

Octenyl succinic anhydride (OSA) modification of amyloid proteins fibrils (APFs) was employed to improve dispersibility and ice recrystallization inhibition activity. OSA mainly reacted with the amino groups of APFs without significantly changing morphology. OSA-modified APFs (OAPFs) had lower pI, carried more negative charges, and were more hydrophobic. OSA-modification showed a pH-dependent effect on the dispersibility of fibrils. At pH 7.0, OSA-modification improved dispersibility and inhibited heat-induced gelation of fibrils at weakened electrostatic repulsion. OAPFs were more prone to aggregation with lower dispersity at acidic pH values and demonstrated stronger IRI activity than unmodified fibrils at pH 7.0. Our findings indicate OSA-modification favors the industrial application of APFs as an ice recrystallization inhibitor with enhanced dispersibility.

Corn cob hemicelluloses as stabilizer for ice recrystallization inhibition in ice cream

Food stabilizers, such as guar gum and locust bean gum (LBG), are often added to ice cream to improve its texture and to combat its main shelf-life concern - ice recrystallization. Recently these gums have become increasingly expensive due to the limited supplies. In this study, holocellulose nanocrystals (holoCNCs) and hemicelluloses (hemiCs) were prepared from readily available corn cobs and tested for ice recrystallization inhibition (IRI) activities in the 25.0 % sucrose solution and ice cream mixes (ICMs). In the sucrose solution, holoCNCs were not IRI active at a concentration of 0.5 %, but hemiCs demonstrated a good IRI activity, even at 0.1 %. In the ICMs, the IRI activity of hemiCs was better than those of guar gum and LBG at a concentration of 0.2 %. Adding 0.2-0.5 % hemiCs had no negative influences on the physicochemical properties of ICMs and ice cream, including viscosity profile, particle size distribution, overrun, hardness, and meltdown rate. These research findings demonstrated corn cob hemiCs' potential as a more sustainable ice cream stabilizer.

Ice recrystallization inhibition effect of cellulose nanocrystals at constant and cycling temperatures

Understanding the effects of ice recrystallization inhibitors at varying temperatures is critical for evaluating their applications. We studied the ice recrystallization inhibition (IRI) effects of cellulose nanocrystals (CNCs) at constant and cycling temperatures. A splat assay using a 3.0 % sucrose solution showed that the IRI effect of 0.2 % CNCs decreased with increasing temperatures from -10 °C to -2 °C; the IRI effects of 0.5 % and 1.0 % CNCs remained unchanged for an increase in temperature from -10 °C to -4 °C but decreased at the temperature of -2 °C. A sandwich assay using a 25.0 % sucrose solution revealed that IRI effects increased with increasing temperatures, except in the presence of 0.2 % and 0.5 % CNCs at -5 °C and - 4 °C. A sandwich assay using a 35.0 % sucrose solution revealed that better IRI effects were observed at higher temperatures at all CNCs concentrations. At cycling temperatures, CNCs were inactive for storage times for ≤2 h, regardless of the rate, holding time, and amplitude of temperature fluctuation, but were active for storage times of 2 and 10 days. The IRI effects of CNCs at different temperatures may be related to the coverage of CNCs on ice surface, diffusion rate of CNCs to ice surface, and types of ice recrystallization.

Succinylation of zein and gelatin hydrolysates improved their ice recrystallization inhibition activity

The goal of this research was to enhance the ice recrystallization inhibition (IRI) activity of zein and gelatin hydrolysates (ZH and GH, respectively) by succinylation modification. ZH was prepared by Alcalase treatment for 3 h and then modified by succinic anhydride (SA); whereas GH was made by Alcalase hydrolysis for 0.25 h and succinylated by n-octylsuccinic anhydride (OSA). After 0.5 h of annealing at -8 °C at 40 mg/mL, modified hydrolysates decreased the average Feret's diameter of ice crystal from 50.2 μm (polyethylene glycol, negative control) to 28.8 μm (SA modified ZH) and 29.5 μm (OSA modified GH) in comparison to the unmodified hydrolysates, which had the crystal size of 47.2 μm (ZH) and 45.4 μm (GH). Also, the two succinylated samples had altered surface hydrophobicity, which potentially contributed to their enhanced IRI activity. Our results indicate that succinylation of food-derived protein hydrolysates can improve their IRI activity.

Inhibiting ice recrystallization by amyloid protein fibrils

Ice recrystallization is harmful to the quality of frozen foods and the cryopreservation of cells and biological tissues, requiring biocompatible materials with ice recrystallization inhibition (IRI) activity. Emerging studies have associated IRI activity with amphiphilic structures. We propose amphiphilic amyloid protein fibrils (APFs) may be IRI-active. APFs were prepared from whey protein isolate (WPI) in water (W-APFs) and in trifluoroethanol (TFE-APFs). W-APFs and TFE-APFs were more IRI-active than WPI over a concentration range of 2.5-10.0 mg/mL. Both APFs showed stronger IRI activity at pH 3.0 than at pH 5.0, 7.0, and 10.0, which was ascribed to the effect of water dispersibility and fibril length. The reduced IRI activity of the two APFs with increasing NaCl content was caused by fibril aggregation. Ice binding by APFs was absent or very weak. Ordered water was observed for the two APFs, which might be essential for IRI activity. Our findings may lead to the use of APFs as novel ice recrystallization inhibitors.

Antifreezing Hydroxyl Monolayer of Small Molecules on a Nanogold Surface

The rational design of ice recrystallization inhibition (IRI) materials is challenging due to the poor understanding of the IRI mechanism at the molecular level. Here we report several new findings about IRI. (1) A dense hydroxyl monolayer of small molecules, e.g. 6-aza-2-thiothymine (ATT), adsorbed on a nanogold surface was demonstrated, for the first time, to have IRI activity. Five structural analogues adsorbed on groups nanogold with outward hydroxyl or methyl were created to evidence the origin of IRI activity. (2) Their IRI mechanism is closely related to the density of hydroxyls on a nanogold surface. However, the hydrophobic interaction in our model is not essential for macroscopic IRI activity. (3) A molecular dynamics simulation elucidates the hydroxyl density dependent IRI trajectories underlying the experimental observations, and the radial distribution function reveals that the methyl even slightly hinders the formation of hydrogen bonding due to a hydrophobic interaction. This work sheds more light on the IRI mechanism that should help in the customization of novel IRI materials.

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.

Antifreeze proteins and their biomimetics for cell cryopreservation: Mechanism, function and application-A review

Cell-based therapy is a promising technology for intractable diseases and health care applications, in which cryopreservation has become an essential procedure to realize the production of therapeutic cells. Ice recrystallization is the major factor that affects the post-thaw viability of cells. As a typical series of biomacromolecules with ice recrystallization inhibition (IRI) activity, antifreeze proteins (AFPs) have been employed in cell cryopreservation. Meanwhile, synthesized materials with IRI activity have emerged in the name of biomimetics of AFPs to expand their availability and practicality. However, fabrication of AFPs mimetics is in a chaotic period. There remains little commonality among different AFPs mimetics, then it is difficult to set guidelines on their design. With no doubt, a comprehensive understanding on the antifreezing mechanism of AFPs in molecular level will enable us to rebuild the function of AFPs, and provide convenience to clarify the relationship between structure and function of these early stage biomimetics. In this review, we would discuss those previously reported biomimetics to summarize their structure characteristics concerning the IRI activity and attempt to develop a roadmap for guiding the design of novel AFPs mimetics.

Anti freeze proteins (Afp): Properties, sources and applications - A review

Extreme cold marine and freshwater temperatures (below 4 °C) induce massive deterioration to the cell membranes of organisms resulting in the formation of ice crystals, consequently causing organelle damage or cell death. One of the adaptive mechanisms organisms have evolved to thrive in cold environments is the production of antifreeze proteins with the functional capabilities to withstand frigid temperatures. Antifreeze proteins are extensively identified in different cold-tolerant species and they facilitate the persistence of cold-adapted organisms by decreasing the freezing point of their body fluids. Various structurally diverse types of antifreeze proteins detected possess the ability to modify ice crystal growth by thermal hysteresis and ice recrystallization inhibition. The unique properties of antifreeze proteins have made them a promising resource in industry, biomedicine, food storage and cryobiology. This review collates the findings of the various studies carried out in the past and the recent developments observed in the properties, functional mechanisms, classification, distinct sources and the ever-increasing applications of antifreeze proteins. This review also summarizes the possibilities of the way forward to identify new avenues of research on anti-freeze proteins.

Ice recrystallization inhibition activity varies with ice-binding protein type and does not correlate with thermal hysteresis

Ice-binding proteins (IBPs) inhibit the growth of ice through surface adsorption. In some freeze-resistant fishes and insects, circulating IBPs serve as antifreeze proteins to stop ice growth by lowering the freezing point. Plants are less able to avoid freezing and some use IBPs to minimize the damage caused in the frozen state by ice recrystallization, which is the growth of large ice grains at the expense of small ones. Here we have accurately and reproducibly measured the ice recrystallization inhibition (IRI) activity of over a dozen naturally occurring IBPs from fishes, insects, plants, and microorganisms using a modified 'splat' method on serial dilutions of IBPs whose concentrations were determined by amino acid analysis. The endpoint of IRI, which was scored as the lowest protein concentration at which no recrystallization was observed, varied for the different IBPs over two orders of magnitude from 1000 nM to 5 nM. Moreover, there was no apparent correlation between their IRI levels and reported antifreeze activities. IBPs from insects and fishes had similar IRI activity, even though the insect IBPs are typically 10x more active in freezing point depression. Plant IBPs had weak antifreeze activity but were more effective at IRI. Bacterial IBPs involved in ice adhesion showed both strong freezing point depression and IRI. Two trends did emerge, including that basal plane binding IBPs correlated with stronger IRI activity and larger IBPs had higher IRI activity.

Expression of ice recrystallization inhibition protein in transgenic potato lines associated with reduced electrolyte leakage and efficient recovery post freezing injury

Potato (Solanum tuberosum L.) is considered to be frost-susceptible as short spells of frost can reduce the tuber yield and quality. Ice recrystallization inhibition (IRI) protein helps prevent growth of ice crystals in the cell apoplast during frost and help prevent damage associated with freezing stress. In this study, we investigated the in planta potential of Lolium perenne derived IRI3 transgene in improving the tolerance of transgenic potato lines for freezing stress. The codon optimized IRI3 transgene was introduced into potato cultivar Diamant through Agrobacterium mediated transformation. Three transgenic potato lines were successfully generated which were confirmed for transgene insertion and genomic integration by polymerase chain reaction and Southern blot. It was evident that the IRI3 transcript decreased in initial 24 h of cold stress treatment while the IRI3 mRNA expression up regulated in subsequent hours of cold treatment with maximum increase to 20 folds at 96 h post stress. A similar trend was also revealed in ion-leakage assay which showed that during cold stress, the transgenic potato lines depicted reduced ion leakage of 14-22% as compared to non-transgenic control plants. Further, the generated transgenic potato lines were tolerant to the frost spell in quarantine field conditions as compared to the non-transgenic potato lines. Additionally, the transgenic lines exhibited efficient recovery post frost injury in field conditions. The biochemical profiles of chlorophyll, proline and higher levels of antioxidant enzyme (superoxide dismutase, Catalase) activity and malondialdehyde levels showed that despite the phenotypic impact of low temperature, the transgenic potato lines quickly adjusted to maintain their cellular homeostasis post freezing stress by increasing the antioxidant defenses. This study suggests that up regulation of IRI3 transcript and regulatory network of cold stress response in transgenic potato lines improve frost tolerance and help stabilize yield in cultivated potato.

Electrosterically stabilized cellulose nanocrystals demonstrate ice recrystallization inhibition and cryoprotection activities

Ice recrystallization inhibitors have emerged as novel cryoprotectants to improve cell viability for cryopreservation. Nanocelluloses were identified as new materials for ice recrystallization inhibition (IRI); however, conventional nanocelluloses aggregate and lose IRI activity at high ionic strengths, which limit their application as cryoprotectants. In this study, we synthesized a novel group of nanocelluloses - electrosterically stabilized cellulose nanocrystals (ECNCs), which remained dispersed and IRI-active at high ionic strengths. ECNCs improved the post-thaw viability of HCT-116 colorectal cancer cells in slow/fast freezing-slow thawing protocols in the presence of 1-20% v/v dimethyl sulfoxide (DMSO), as well as in slow/fast freezing-fast thawing protocols at reduced DMSO concentrations. The effectiveness in cryoprotection did not match the IRI activity in ECNCs, polyethylene glycol (PEG), and polyvinyl alcohol (PVA); and in ECNCs with different surface charge densities. Overall, ECNCs demonstrated IRI and cryoprotection activities, but the mechanism of cryoprotection remains unknown.

Effect of pH on the activity of ice-binding protein from Marinomonas primoryensis

The ability of an ice-binding protein (IBP) from Marinomonas primoryensis (MpIBP) to influence ice crystal growth and structure in nonphysiological pH environments was investigated in this work. The ability for MpIBP to retain ice interactivity under stressed environmental conditions was determined via (1) a modified splat assay to determine ice recrystallization inhibition (IRI) of polycrystalline ice and (2) nanoliter osmometry to evaluate the ability of MpIBP to dynamically shape the morphology of a single ice crystal. Circular dichroism (CD) was used to relate the IRI and DIS activity of MpIBP to secondary structure. The results illustrate that MpIBP secondary structure was stable between pH 6 and pH 10. It was found that MpIBP did not interact with ice at pH ≤ 4 or pH ≥ 13. At 6 ≤ pH ≥ 12 MpIBP exhibited a reduction in grain size of ice crystals as compared to control solutions and demonstrated dynamic ice shaping at 6 ≤ pH ≥ 10. The results substantiate that MpIBP retains some secondary structure and function in non-neutral pH environments; thereby, enabling its potential utility in nonphysiological materials science and engineering applications.

Effect of surface charge density on the ice recrystallization inhibition activity of nanocelluloses

Recently nanocelluloses have been found to possess ice recrystallization inhibition (IRI) activity, which have several potential applications. The present study focuses on the relationship between the surface charge density (SCD) of nanocelluloses and IRI activity. Cellulose nanocrystals (CNCs) and 2, 2, 6, 6-tetramethylpiperidine-1-oxyl oxidized cellulose nanofibrils (TEMPO-CNFs) with similar degrees of polymerization (DP) or fibril lengths but with different SCDs were prepared and characterized for IRI activity. When the SCD of CNCs was progressively reduced, an initial increase of IRI activity was observed, followed by a decrease due to fibril aggregation. CNCs with a low SCD became IRI active at increased unfrozen water fractions and higher annealing temperatures. TEMPO-CNFs with a low SCD also had higher IRI activity. Additionally, lowering pH to protonate the carboxylate groups of TEMPO-CNFs enhanced the IRI activity. These research findings are important in producing nanocelluloses with enhanced IRI activity and understanding their structure-activity relationship.

Type II Ice-Binding Proteins Isolated from an Arctic Microalga Are Similar to Adhesin-Like Proteins and Increase Freezing Tolerance in Transgenic Plants

Microalgal ice-binding proteins (IBPs) in the polar region are poorly understood at the genome-wide level, although they are important for cold adaptation. Through the transcriptome study with the Arctic green alga Chloromonas sp. KNF0032, we identified six Chloromonas IBP genes (CmIBPs), homologous with the previously reported IBPs from Antarctic snow alga CCMP681 and Antarctic Chloromonas sp. They were organized with multiple exon/intron structures and low-temperature-responsive cis-elements in their promoters and abundantly expressed at low temperature. The biological functions of three representative CmIBPs (CmIBP1, CmIBP2 and CmIBP3) were tested using in vitro analysis and transgenic plant system. CmIBP1 had the most effective ice recrystallization inhibition (IRI) activities in both in vitro and transgenic plants, and CmIBP2 and CmIBP3 had followed. All transgenic plants grown under nonacclimated condition were freezing tolerant, and especially 35S::CmIBP1 plants were most effective. After cold acclimation, only 35S::CmIBP2 plants showed slightly increased freezing tolerance. Structurally, the CmIBPs were predicted to have β-solenoid forms with parallel β-sheets and repeated TXT motifs. The repeated TXT structure of CmIBPs appears similar to the AidA domain-containing adhesin-like proteins from methanogens. We have shown that the AidA domain has IRI activity as CmIBPs and phylogenetic analysis also supported that the AidA domains are monophyletic with ice-binding domain of CmIBPs, and these results suggest that CmIBPs are a type of modified adhesins.

Draft genome sequences of bacteria isolated from the Deschampsia antarctica phyllosphere

Genome analyses are being used to characterize plant growth-promoting (PGP) bacteria living in different plant compartiments. In this context, we have recently isolated bacteria from the phyllosphere of an Antarctic plant (Deschampsia antarctica) showing ice recrystallization inhibition (IRI), an activity related to the presence of antifreeze proteins (AFPs). In this study, the draft genomes of six phyllospheric bacteria showing IRI activity were sequenced and annotated according to their functional gene categories. Genome sizes ranged from 5.6 to 6.3 Mbp, and based on sequence analysis of the 16S rRNA genes, five strains were identified as Pseudomonas and one as Janthinobacterium. Interestingly, most strains showed genes associated with PGP traits, such as nutrient uptake (ammonia assimilation, nitrogen fixing, phosphatases, and organic acid production), bioactive metabolites (indole acetic acid and 1-aminocyclopropane-1-carboxylate deaminase), and antimicrobial compounds (hydrogen cyanide and pyoverdine). In relation with IRI activity, a search of putative AFPs using current bioinformatic tools was also carried out. Despite that genes associated with reported AFPs were not found in these genomes, genes connected to ice-nucleation proteins (InaA) were found in all Pseudomonas strains, but not in the Janthinobacterium strain.

Applications of Antifreeze Proteins: Practical Use of the Quality Products from Japanese Fishes

Numerous embryonic ice crystals are generated in water at the moment of freezing. These crystals grow and merge together to form an ice block that can be generally observed. Antifreeze protein (AFP) is capable of binding to the embryonic ice crystals, inhibiting such an ice block formation. Fish-derived AFP additionally binds to membrane lipid bilayers to prolong the lifetime of cells. These unique abilities of AFP have been studied extensively for the development of advanced techniques, such as ice recrystallization inhibitors, freeze-tolerant gels, cell preservation fluids, and high-porosity ceramics, for which mass-preparation method of the quality product of AFP utilizing fish muscle homogenates made a significant contribution. In this chapter, we present both fundamental and advanced information of fish AFPs that have been especially discovered from mid-latitude sea area, which will provide a hint to develop more advanced techniques applicable in both medical and industrial fields.

Modulation of antifreeze activity and the effect upon post-thaw HepG2 cell viability after cryopreservation

Most antifreeze proteins (AFPs) exhibit two types of "antifreeze activity" - thermal hysteresis (TH) and ice recrystallization inhibition (IRI) activity. The mechanism of TH activity has been studied in depth and is the result of an adsorption of AFPs to the surface of ice with an ice-binding face (IBF). In contrast, the mechanism of ice recrystallization and its inhibition is considerably less understood. In this paper, we examine several different antifreeze proteins, glycoproteins and mutants of the Lolium perenne AFP (LpAFP) to understand how IRI activity is modulated independently of TH activity. This study also examines the ability of the various AF(G)Ps to protect HepG2 cells from cryoinjury. Post-thaw cell viabilities are correlated to TH, IRI activity as well as dynamic ice shaping ability and single ice crystal growth progressions. While these results demonstrate that AF(G)Ps are ineffective as cryoprotectants, they emphasize how ice crystal habit and most importantly, ice growth progression affect HepG2 cell survival during cryopreservation.