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Ice Recrystallization Inhibition Effect of Cellulose Nanocrystals: Influence of Sucrose Concentration
Abstract
Stabilizers are commonly used to inhibit the ice recrystallization process that leads to the formation of large ice crystals, decreasing consumer acceptance of ice cream. However, the ice recrystallization inhibition (IRI) effect of stabilizers is very dependent on measurement conditions. The cause of this dependence is not clear, which imposes problems in comparing the IRI activity and understanding the IRI mechanism of stabilizers. This study investigated the influence of sucrose concentration on the IRI effect of cellulose nanocrystals (CNCs), which are newly identified IRI active materials. A splat assay and a sandwich assay were used to determine IRI activities of CNCs at sucrose concentrations from 2.0% to 49.0% w/w and incubation temperature of -8°C for 30 min. The IRI activities of CNCs were higher at low sucrose concentrations, almost disappeared at medium sucrose concentrations, and restored slightly at high sucrose concentrations. The IRI effect of CNCs is correlated with the ratio between CNCs concentration in the unfrozen phase and total surface area of ice crystals. This surface area-related IRI effect was also observed with guar gum, locust bean gum, and poly(vinyl alcohol). It is a strong evidence of an ice-binding mechanism for the IRI effect of stabilizers. These research findings offer a new perspective in comparing and understanding the measurement condition-dependent IRI effect of stabilizers, which could potentially benefit the ice cream industry in developing new materials and recipes to control ice recrystallization.
... Although their cryoprotective benefits in frozen food have been proved (Kaleda et al., 2018;Kashyap et al., 2020), the practical applications of AF(G)Ps are facing technical challenges in mass production as well as potential health risks. In addition, studies have continuously found that polysaccharides extracted from nature have antifreeze activity, such as carrageenans (Gaukel et al., 2014;Kiran-Yildirim et al., 2021;Kiran-Yildirim & Gaukel, 2020;Leiter et al., 2017;Leiter et al., 2018), nanocellulose (Li et al., 2019;Li, Dia, & Wu, 2021;Li, Li, Dia, et al., 2020;Li, Luckett, & Wu, 2021;Li, Zhong, Zhao, et al., 2020), wheat bran polysaccharide , and polysaccharides from cold-adapted organisms (Carillo et al., 2015;Casillo et al., 2017Casillo et al., , 2021Guerreiro et al., 2020). Some have begun to be applied in frozen food, such as ice cream and sorbet, to inhibit ice recrystallization (BahramParvar et al., 2013;Kamińska-Dwórznicka et al., 2015). ...
... Enhance IRI activity by decreasing molecular weight to a certain range (viscosity also decreased, data not shown), such as 224.04 kDa and 90.41 kDa, also lends support to this. It is also consistent with the recent findings of IRI-active polysaccharides, such as carrageenan (Kiran-Yildirim et al., 2021;Kiran-Yildirim & Gaukel, 2020), guar gum, locust bean gum, and nanocellulose (Li, Dia, & Wu, 2021;. Compared to TSP-0, increased activity of intermediate-Mw (224.04 kDa and 90.41 kDa) TSP fractions may be due to their reduced tendency to form self-and intermolecular aggregation. ...
... It has been reported that the IRI effect of polysaccharide stabilizers (including nanocellulose, guar gum, and locust bean gum) is correlated with the ratio between the stabilizer concentration in the unfrozen phase and the total surface area of ice crystals, suggesting strong evidence of an ice-binding mechanism of polysaccharide stabilizers (Li, Dia, & Wu, 2021). Li, Luckett, and Wu (2021) also found that cellulose nanocrystals showed a time-dependent surface coverage on ice crystals. ...
This study aimed to investigate the inhibition effects of tamarind seed polysaccharide (TSP) on ice recrystallization and to figure out its possible molecular weight-dependent effects. TSP fractions (2412.38–20.75 kDa) were prepared while preserving the natural structure. Ice recrystallization was effectively inhibited by TSP. Decreasing the molecular weight to a certain range, such as 224.04 kDa and 90.41 kDa, could enhance the activity of TSP due to the reduction of self- and intermolecular aggregation. Adding TSP into water decreased the melting temperature of bulk ice. Raman spectra showed that partial group vibrations or deformations of TSP molecules were restricted upon solution freezing and also revealed a destructuring effect of TSP on the H-bond network of water. These findings suggested the potential of TSP as a novel food cryoprotectant and help produce TSP fractions with enhanced activity, and shed new light on understanding the antifreeze mechanism of natural polysaccharides.
... In some food systems, cellulose nanomaterials have shown significant beneficial effects on the growth and recrystallization of ice crystals, thus preserving their quality (Li et al., , 2021Nahr et al., 2015;Tan et al., 2022). Cellulose is a renewable, biodegradable, and nontoxic carbohydrate, and when isolated in the form of nanofibers, this material has the shape of fibrils with a diameter of 10 to 100 nm; in addition, cellulose can be obtained via mechanical homogenization of lignocellulosic biomass (Nechyporchuk et al., 2016). ...
... Investigations by Welti et al. (2009) indicated that particles with a size of 1 to 100 nm can induce ice nucleation; thus, in food applications, this nanometric material may function by inducing the formation of ice crystals uniformly distributed throughout the food matrix. In addition, studies have shown that nanocellulose has an amphipathic structure that exhibits high performance in inhibiting ice recrystallization (Li et al., 2021Tan et al., 2022). Figure 3 shows the DSC curves obtained for the freezing and melting processes of aqueous solutions containing GH and CNF at different concentrations. ...
In this study, the combined effect of gelatin hydrolysate (GH) and cellulose nanofibers (CNF) on the quality parameters of frozen potatoes with and without temperature fluctuation was evaluated. Potatoes were cut, blanched, impregnated with different concentrations of GH (0.08 to 4.32% w/w) and CNF (0.08 to 4.32% w/w) combined in a central composite rotational design and frozen with and without temperature fluctuation. Bleached samples without impregnation were used as controls. Electrophoresis and FTIR analyses indicated the presence of polypeptides in the gelatin hydrolysate, and electron microscopy indicated that cellulose nanofibers have nanometric diameters (20 to 90 nm); these characteristics influence the freezing of water. The solution containing 2.20% w/w GH and 2.20% w/w CNF showed a lower freezable water content by DSC analysis (92.49 ± 0.42%), indicating greater interaction of the compounds with water in this condition. When impregnated in potato cuts, this solution promoted lower losses of fluid (19.06 ± 0.51% and 28.71 ± 0.21%, respectively) and texture (23.30 ± 0.54% and 41.95 ± 0.55%, respectively) when subjected to storage without and with temperature fluctuations, thus delaying the recrystallization of the ice. Furthermore, smaller losses in the microstructure and color of the plant tissue were observed when using this treatment. A reduction in the freezing temperature of the impregnated samples was also observed (temperatures lower than the control − 0.615 °C). The results indicated that GH and CNF have effective cryopreservation potential.
... Among them, κ-carrageenan has been proven to possess IRR activity and display good outcomes in ice cream and sorbet mixes (Gaukel, Leiter, & Spieβ, 2014;Kamińska-Dwórznicka et al., 2015;Leiter, Emmer, & Gaukel, 2018;Leiter, Ludwig, Gaukel, & Volker, 2017;Regand & Goff, 2003). Nanocellulose and its derivatives have been proven to possess IRR activity in phosphate buffer saline (PBS) and sucrose systems (Li, Dia, & Wu, 2021;Li, Luckett, & Wu, 2022;Li, Zhao, Zhong, & Wu, 2019;, but the application effect in frozen desserts remains to be investigated. Recently, Reeder, Li, Li, and Wu (2023) also reported corn cob hemicelluloses showing promising potential as an ice cream stabilizer to retard ice recrystallization. ...
... On the basis of this, molecular aggregation and gelation of κ-carrageenan causing the IRR effect to decrease could be explained by fewer molecules freely available in interacting with the ice crystal surface (Leiter et al., 2017(Leiter et al., , 2018. Li et al. (2021; have also shown that sufficient surface coverage of cellulose nanocrystals and other stabilizers on ice crystals may contribute to their IRR activities. These experimental observations supported the speculation of ice-binding/adsorption of polysaccharide stabilizers to retard ice recrystallization, but further evidence is still needed to show the action details. ...
Food hydrocolloids, such as naturally sourced polysaccharide stabilizers, are becoming potential candidates for retarding ice recrystallization in frozen desserts. Tamarind seed polysaccharide (TSP) and its depolymerized fraction (DTSP) possessed ice recrystallization retardation (IRR) activity by a splat cooling assay. This study is a follow-up work aiming to investigate their application effects to retard ice recrystallization in ice cream mixes (ICMs) and delve into the ice-binding behavior at the ice/water interface. Native TSP worked for or against IRR in the ICMs depending on the concentration, while DTSP possessed an increased IRR effect under the addition of higher concentration (3.0%). Compared to TSP, adding DTSP caused less of an increase in the viscosity of the ICMs. Molecular dynamics was used to simulate ice growth in the presence of TSP (oligomer) and showed that the TSP possessed activity for retarding ice growth along the prismatic planes. During the propagation of ice crystals, the TSP was bound onto the ice and caused evident structural defects of ice layers. The findings of this study proved that TSP and DTSP have a promising application to retard ice recrystallization in ice cream and shed new light on understanding the mechanism of natural polysaccharides to retard ice growth.
... Further work has suggested that the IRI activity of nanocelluloses was associated with amphiphilicity, and higher hydrophobicity led to an increase in IRI activity until aggregation occurs [18]. Thus, an ice-binding/or adsorption mechanism for polysaccharide stabilizers has also been proposed [12,19]. However, except for the weak ice-shaping effect [12], strong and direct proof is still lacking to show that these polysaccharides bind/ or adsorb to ice. ...
... Previous studies proposed that polysaccharide chain hydration (effect on water mobility) and the interaction with ice surface contribute to their IRI activities [12,16,17,19]. However, our results of the ice shaping assay and MD simulation of the oligomers evidenced that DDTSP-H did not show changes in specific ice-binding attributes and local hydration properties of molecular chains. ...
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.
... In addition to inhibiting the formation of large ice crystals, CNF can also achieve direct cryopreservation of seafood components through its high permeability and rich reactivity, thus slowing lipid oxidation and related damage. 27 CB and SS also have better performance in antifreezing protection, and the inhibition effect on ice crystal formation is higher than CK. This is because the addition of sugar reduces the freezing point and phase change enthalpy of the sample, reduces the latent heat required for freezing, and enables the fish to pass through the maximum ice crystal formation zone faster, forming small and uniform crystals, and reducing the damage to the structure of the fish by the growth of ice crystals. ...
BACKGROUND
The formation of ice crystals will have adverse effects on aquatic products, and the key to ensure the long‐term preservation and better quality preservations of the product is to evaluate the intercellular ice crystal formation to find suitable refrigeration conditions and cryoprotectants.
RESULTS
The ice crystal formation was successfully captured by using an inverted microscope cryomicroscopic system equipped with a low‐temperature stage, the ice crystals formed under different freezing methods between tuna muscle cells were observed directly, the deformation degree of muscle tissue pores during crystallization was evaluated, and the effect of freeze–thaw times on tuna samples was analyzed. The effects of the use of cryoprotectant such as cellobiose and carboxylated cellulose nanofibers on ice‐growth inhibition were investigated, and the reliability of the ice crystal observation results was further verified by the determination of physical properties. The results showed that carboxylated cellulose nanofibers had the best ice‐growth inhibition effect, they prevented about 50% cell deformation compared with the control group, and also reduced the minimum size of ice crystal formation. In addition, the addition of cellobiose and sodium tripolyphosphate gave the ice crystals a more uniform size and roundness.
CONCLUSION
The experiment proposed a stable and clear observation method for the process of intercellular ice crystal formation, and the accuracy of the observation method was further verified by some physical indicators. This may help in the selection of suitable measurement methods to directly observe ice crystal formation behavior and screen cryoprotectants. © 2024 Society of Chemical Industry.
... However, some studies suggested polysaccharides might attach itself to the ice's surface and prevent the ice from recrystallizing. 18 Hence, this research showed that SIC2, in particular, has a better microstructure due to the prevention of ice recrystallization, which results in smaller ice crystals. ...
Ice cream, which includes dairy product, is a good carrier of addition probiotics and prebiotics. This study was designed to assess the microbiological, physicochemical, and sensory properties of the ice cream. The characteristics of ice cream made from fermented milk using L. plantarum Dad-13 combined with inulin (0%, 1%, and 2%) were evaluated such as cell viability, pH, titratable acidity, overrun, melting rate, sensory evaluation with hedonic test, microstructure using scanning electron microscopy, and volatile organic compounds using HS-GC-MS. The results showed that cell viability in synbiotic ice cream with 2% inulin decreased by 1 log cycle, which showed the most stable value during storage until the 12th week was still 1.03 x 107 CFU/g. Synbiotic ice cream with 2% inulin showed the highest overrun value of 35.72% and the slowest melting rate of 40.71% of ice cream melted in 20 minutes. Overall attributes in the hedonic test of synbiotic ice cream with 2% inulin showed a value of 4, which means the most preferred by panelists. Hence, this research showed that ice cream containing 2% inulin, in particular, has a better microstructure due to the prevention of ice recrystallization, which results in smaller ice crystals. The ketone volatile organic compound only found in ice cream with 1% inulin was cyclopentadecanone, 2-hydroxy- with percentage of area 10.25% while for ice cream that contains 2% inulin, it was oxacyclotetradecan-2-one with percentage of area 9.31%. Furthermore, several volatile organic compounds, such as 2-trifluoroacetoxydodecane, 4-propionyloxytridecane, and anthracene, 9-butyltetradecahydro, were only found in the synbiotic ice cream. This study has the potential to be a novel functional food containing probiotic indigenous L. plantarum Dad-13 and prebiotic inulin.
... 79 The LS-S samples had the retention of all bands even after subjecting to oven-drying, suggesting that inulin and phenolic compounds from liquid smoke prevented the proteolysis of MHC, actin, and troponin. Li et al. 80 reported that inulin can form complexation with polyphenol (e.g., epicatechin and its oligomers) which enhances the antioxidant activity. In the present study, the combination of inulin with liquid smoke was found to be efficient for maintaining the stability of the Pangasius mince sausage. ...
The objective of this study was to investigate the effects of the kiln (SK-S) and liquid smoking (LS-S) processes on the quality of inulin-fortified emulsion-type Pangasius mince sausages. The moisture content during the storage significantly (p < 0.05) decreased in C-S (control) sausages and increased (p < 0.05) in SK-S and LS-S sausages. The protein content decreased (p < 0.05) in C-S, SK-S, and LS-S throughout the storage period. Initially, among the three processed sausages, LS-S showed a lower pH value, and as the days of storage progressed, all the treatments exhibited a declining trend (p < 0.05). A significant (p < 0.05) increase in the PV was observed in all the sausages during the storage days at 5 ± 1 °C, but the intensity of the increase was lower in SK-S and LS-S. The total viable count of C-S and SK-S sausages reached the limit of acceptability (6 log10cfu g–1) on the 20th day and on the 24th day of storage. The electrophoretic protein pattern of LS-S samples exhibited retention of all bands, indicating the lower proteolysis of MHC, actin, and troponin T in comparison with other treatments. The hardness (p < 0.05) and cohesiveness (p > 0.05) values of both SK-S and LS-S reduced as the storage days progressed. The present study indicates that the emulsion-type Pangasius sausages incorporated with inulin powder (2%) exposed to kiln smoking and commercial liquid smoking retained good-to-better sensory attributes up to day 16 (C-S) and day 20 (SK-S and LS-S) under refrigerated storage at 5 ± 1 °C in low-density vacuum polyethylene (LDPE) pouches.
To manufacture ice cream and frozen dairy dessert of the highest quality, it is essential to have ingredients of excellent quality, a mix that is formulated and balanced to provide proper function of each component, and excellent processing, freezing, and hardening processes. However, the selection of high-quality ingredients is, without doubt, the most important factor in successful manufacture of frozen desserts. The clean, fresh, creamy flavor desired in ice cream can be achieved only by the use of ingredients that have been carefully produced and handled and are themselves of excellent flavor quality. Frozen desserts can be made with a wide variety of ingredients, which can be grouped by category (fat sources, milk solids-not-fat sources, water sources, sweeteners, stabilizers, and emulsifiers). The functions and limitations of the components of mixes were described in Chap. 2. This chapter will focus on the sources and selection of the mix ingredients to supply the major components.
Once ice cream and frozen dessert products leave the storage freezer in the manufacturing plant, they typically go through a shipping and handling system (“cold-chain”) designed to deliver the products to the consumer with the highest possible quality. The shelf life that assures this quality is almost totally dependent on temperature and temperature fluctuations that the product has been exposed to in distribution. Limitations of shelf life are mostly related to ice recrystallization or other structural rearrangements that lead to structural or textural defects. Microorganisms do not grow at freezer temperatures, enzymatic reactions occur only very slowly, and flavor changes are rare; therefore, the “end” of shelf life is usually a textural consideration and it can vary from many months at −30 °C to a few days at −14 °C before changes would begin to become noticeable. It is critically important that manufacturers build into their products some resilience to the rigors of heat shock and temperature abuse, so that shelf life remains sufficiently long to get product through the distribution network and when product is warmed to eating temperatures, as in scooping cabinets. Besides ice recrystallization, air coarsening and shrinkage, lactose crystallization and sandiness, gumminess and flavor changes are also discussed.
Essential oils (EOs), such as thyme essential oil (TEO), are widely known for their antimicrobial properties; however, their direct application in food systems is limited due to their poor stability, which affects their efficacy. This study aims to improve the stability and antimicrobial efficacy of TEO by encapsulating it in Pickering emulsions stabilized with cellulose nanocrystals (CNC). Two formulations of Pickering emulsions with 5% and 10% TEO were prepared and compared to traditional surfactant-based emulsions. The stability of the emulsions was assessed over 21 days, and particle size, zeta potential, Raman spectroscopy, and FTIR were used for characterization. The antimicrobial activity was tested against several foodborne pathogens, with minimum inhibitory concentration (MIC) values determined. The 10% TEO Pickering emulsion showed antimicrobial activity, with MIC50 values of 4096 µg/mL against Staphylococcus aureus and Escherichia coli, while the 5% TEO formulation had no effect at MIC50 > 8192 µg/mL. The CNC-stabilized Pickering emulsions exhibited superior stability, showing no phase separation over 21 days. The findings suggest that CNC-stabilized Pickering emulsions are effective at improving the stability and antimicrobial performance of TEO, making them a promising natural preservative for food packaging and safety. Further research is recommended to optimize the formulation and broaden TEO’s application in food preservation.
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.
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.
Ice recrystallization adversely affects the quality of frozen foods. Therefore, food-grade materials with ice recrystallization inhibition (IRI) activity are attracting growing attention. Our previous study has found IRI activity of amyloid protein fibrils (APFs); however, as with most other food-grade IRI active materials, the IRI activity of APFs is moderate and needed to be enhanced. Here, we report that IRI activity is greatly enhanced when APFs serve as Pickering emulsion stabilizer. Adsorption of APFs to the oil-water interface resulted in the formation of microsized Pickering emulsion droplets. The IRI activity resulted from the adsorbed APFs rather than steric hindrance of emulsion droplets because self-induced emulsion droplets without APFs on the surface had no IRI activity. The oil core chemistry does not affect the IRI activity of adsorbed APFs. A structure−activity relationship analysis revealed that IRI activity of adsorbed APFs increases with larger particle size and emulsion droplet number (total number of droplets per unit volume). The enhancement of IRI activity caused by oil-water interface adsorption is reasonably ascribed to enlarged size, crowding of APFs on the surface of emulsion droplets, and enhanced ice adsorption of APFs. Compared with free APFs, adsorbed APFs were more IRI active at higher annealing temperatures and higher unfrozen water contents. Given the amphiphilic nature of most IRIactive materials, the findings of this study shed light on the application of IRI-active materials as emulsifiers to improve the quality of frozen food containing emulsions, such as ice cream and frozen meat paste.
Balancing physicochemical properties and sensory properties is one of the key points in expanding edible packaging applications. The work consisted of two parts, one was to investigate the effects of cellulose nanocrystals (CNC) on the packaging-related properties of whey protein isolate films with natural colorants (curcumin, phycocyanin, and lycopene) under freeze-thaw (FT) conditions; the other was to test oral tactility and visual sensory properties of the edible films and their overall acceptability in packed ice cream. FT treatment reduced the mechanical strength and moisture content and increased the water vapor permeability of the films, as water-phase transformation not only disrupted hydrogen bonds but also the film network structure through physical stress. The oral tactility produced by CNC and the visual effect produced by colorants could affect participants’ preference for edible films. This study provides a good reference for the consumer-driven product development of packaged low-temperature products.
Au cours de la congélation des produits alimentaires, une structure cristalline de glace se développe et continue d'évoluer tout au long de la chaine du froid notamment durant les étapes de stockage où les produits sont susceptibles de subir des variations de températures. Les phénomènes de cristallisation et de recristallisation vont contribuer à modifier la microstructure des produits et ainsi altérer leur qualité. Dans ce contexte, le principal objectif de ce travail de thèse est d'étudier l'impact couplé de la congélation et des conditions de stockage sur l’évolution de la microstructure d'une génoise surgelée, afin de mieux comprendre les mécanismes de cristallisation et de recristallisation ainsi que la formation et la localisation de glace dans une matrice poreuse.Deux types de génoises ont été étudiés : une génoise modèle non réactive et une génoise de référence réactive. Leur protocole de fabrication a été validé par une série de mesures des propriétés thermo-physiques (densités, teneur en eau, porosité). Des mesures par DSC ont été réalisées afin de déterminer la température de congélation commençante et la fraction d’eau congelable dans la génoise cuite. Différentes techniques ont ensuite été mises en œuvre afin de caractériser l’évolution de la microstructure des génoises congelées au cours de la chaîne du froid : la cryo-MEB et la micro-tomographie RX. Concernant la microtomographie, deux types d’essais ont été réalisés : (i) des échantillons de génoise modèle ont été congelés à deux vitesses différentes (congélation lente et rapide) puis stockés pendant deux semaines dans des conditions stables ou avec fluctuations de températures. Ces échantillons ont été ensuite visualisés à l’état congelé à très haute résolution en utilisant une cellule thermostatée CellStat installée sur la ligne ANATOMIX du synchrotron Soleil ; (ii) dans le cas de la génoise de référence, l’évolution de la microstructure d’un même échantillon de génoise pendant sa congélation et son stockage (avec fluctuations de température) a pu être suivie en continu pendant 6 jours à l'aide de la cellule thermostatée CellDyM installée sur un microtomographe de laboratoire. Dans ce cas, une méthode de traitement d’image spécifique basée sur la corrélation digitale volumique (DVC) a été mise en œuvre pour segmenter les images et suivre l’évolution de la microstructure.L’ensemble des résultats obtenus a ainsi permis de montrer que la congélation rapide et lente de la génoise modèle donne lieu respectivement (i) à des cristaux de glace petits et grossiers à l'intérieur de la matrice d'amidon et (ii) à des couches de glace plus ou moins épaisse à l’interface des pores. Dans le cas d'une congélation lente, la majorité de la glace se forme à ces interfaces reflétant une plus grande migration d'eau de la matrice vers les pores. Au cours du stockage, la microstructure cristalline évolue quelle que soit la vitesse de congélation initiale et les conditions de conservation. Cependant, les changements de microstructure sont plus importants lorsque les produits sont congelés lentement quelles que soient les conditions de stockage. Par ailleurs, nos résultats montrent que même si les avantages de la congélation rapide sont réduits à la fin de la période de stockage de deux semaines, les produits ont toujours une meilleure qualité que les échantillons congelés lentement. Enfin, les résultats obtenus avec la cellule CellDyM ont permis de mettre en évidence différents phénomènes, comme la rétraction de la matrice poreuse lors de la congélation et du cyclage thermique ainsi que la formation et la croissance des cristaux à l’interface des pores qui sont des sites préférentiels pour la nucléation de la glace. L’ensemble de ces résultats originaux ouvrent de nombreuses perspectives en termes de modélisation et d’optimisation des paramètres de la chaîne du froid pour préserver la qualité des produits.
In this research, a total of 20 plain ice-cream samples, including 10 local and 10 industrial plain ice-cream samples presented for consumption in Erzurum province, were collected from the market and microbiological, physical and chemical analyzes were carried out on these samples. As a result of the microbiological analyzes, the average total aerobic mesophilic bacteria count (TAMB), yeast and mould count, number and group of coliform bacteria count in local ice cream samples have been calculated as 5.89 log cfu/g, 4.22 log cfu/g and 2.26 log cfu/g, respectively. Identical analyzes have also been performed for industrial ice-cream samples, and all data mentioned for local samples have been calculated. These values are determined as 4.72 log cfu/g
Frozen aquatic products undergo unavoidable quality changes owing to temperature fluctuations during frozen storage and distribution. This study investigated the effects of 1% cellobiose (CB), and 0.5 and 1% carboxylated cellulose nanofibers (CNF) on ice crystal growth and recrystallization of frozen large yellow croaker fillets exposed to temperature fluctuations. Denser and more uniformly distributed ice crystals were observed in the CB- and CNF-treated samples than in the water-treated samples. Furthermore, the addition of CB and CNF suppressed the conversion of bound water to frozen water in the samples during temperature fluctuation cycles, played a positive role in fixing the ionic and hydrogen bonds that stabilize the protein structure, limited the conformational transition from α-helix to β-sheet, and improved protein thermal stability. Based on turbidity, zeta potential, and confocal laser scanning microscopy (CLSM) analyses, the presence of CB and CNF restricted the protein aggregation. Compared with CB, CNF molecules with abundant carboxyl functional groups and longer morphology exhibited better cryoprotective effects. Moreover, the fillets were more improved protected from mechanical damage induced by large ice crystals at a higher CNF concentration. This study reveals the potential of CB and CNF as novel cryoprotectants.
Although freezing is by far the most common method of food preservation, deteriorative changes in food quality are inevitable because of the formation of ice crystals and other physicochemical reactions. In recent years, cryoprotective agents from natural sources have attracted great interest and been applied to the frozen food industry to overcome freezing damage. Natural polysaccharides have been proved to inhibit ice crystals formation. They possess cryo-stabilized effects due to their rheological properties and antioxidant activity, thus showing great potential in food to achieve the desired cryoprotection levels. In this review, we first summarized the quality damage of food during freezing and frozen storage. Next, the effects of natural polysaccharides on the formation of ice crystals were discussed from the three aspects of ice nucleation, growth, and ice recrystallization. The review focused on the action mechanism of polysaccharides on ice recrystallization inhibition (IRI), in which the polysaccharide-ice interaction and the water perturbation by hydration of polysaccharides might play critical roles in the IRI. Moreover, the cryo-stabilized effects of polysaccharides on food systems were discussed. This review is expected to shed new light on the antifreeze mechanism of natural polysaccharides, inspiring further research into exploring and applying new polysaccharide resources for food cryoprotection.
Ice binding proteins modulate ice nucleation/growth and have huge (bio)technological potential. There are few synthetic materials that reproduce their function, and rational design is challenging due to the outstanding questions about the mechanisms of ice binding, including whether ice binding is essential to reproduce all their macroscopic properties. Here we report that nanoparticles obtained by polymerization-induced self-assembly (PISA) inhibit ice recrystallization (IRI) despite their constituent polymers having no apparent activity. Poly(ethylene glycol), poly(dimethylacrylamide), and poly(vinylpyrrolidone) coronas were all IRI-active when assembled into nanoparticles. Different core-forming blocks were also screened, revealing the core chemistry had no effect. These observations show ice binding domains are not essential for macroscopic IRI activity and suggest that the size, and crowding, of polymers may increase the IRI activity of “non-active” polymers. It was also discovered that poly(vinylpyrrolidone) particles had ice crystal shaping activity, indicating this polymer can engage ice crystal surfaces, even though on its own it does not show any appreciable ice recrystallization inhibition. Larger (vesicle) nanoparticles are shown to have higher ice recrystallization inhibition activity compared to smaller (sphere) particles, whereas ice nucleation activity was not found for any material. This shows that assembly into larger structures can increase IRI activity and that increasing the “size” of an IRI does not always lead to ice nucleation. This nanoparticle approach offers a platform toward ice-controlling soft materials and insight into how IRI activity scales with molecular size of additives.
Understanding the ice recrystallisation inhibition (IRI) activity of antifreeze biomimetics is crucial to the development of the next generation of cryoprotectants. In this work, we bring together molecular dynamics simulations and quantitative experimental measurements to unravel the microscopic origins of the IRI activity of poly(vinyl)alcohol (PVA)—the most potent of biomimetic IRI agents. Contrary to the emerging consensus, we find that PVA does not require a “lattice matching” to ice in order to display IRI activity: instead, it is the effective volume of PVA and its contact area with the ice surface which dictates its IRI strength. We also find that entropic contributions may play a role in the ice-PVA interaction and we demonstrate that small block co-polymers (up to now thought to be IRI-inactive) might display significant IRI potential. This work clarifies the atomistic details of the IRI activity of PVA and provides novel guidelines for the rational design of cryoprotectants.
Water freezing is ubiquitous and affects areas as diverse as climate, the chemical industry, cryobiology and materials science. Ice nucleation is the controlling step in water freezing1–5 and has, for nearly a century, been assumed to require the formation of a critical ice nucleus6–10. But there has been no direct experimental evidence for the existence of such a nucleus, owing to its transient and nanoscale nature6,7. Here we report ice nucleation in water droplets containing graphene oxide nanosheets of controlled sizes and show that they have a notable impact on ice nucleation only above a certain size that varies with the degree of supercooling of the droplets. We infer from our experimental data and theoretical calculations that the critical size of the graphene oxide reflects the size of the critical ice nucleus, which in the case of sufficiently large graphene oxides sits on their surface and gives rise to ice formation behaviour consistent with classical nucleation theory. By contrast, when the graphene oxide size is smaller than that of the critical ice nucleus, pinning at the periphery of the graphene oxide deforms the ice nucleus as it grows. This gives rise to a much higher free-energy barrier for nucleation and suppresses the promoting effect of the graphene oxide11. The results provide experimental information on the existence and temperature-dependent size of the critical ice nucleus, which has previously only been explored theoretically and through simulations12–16. As pinning of a pre-critical nucleus at a nanoparticle edge is not specific to the ice nucleus on graphene oxides, we expect that our approach could be extended to probe the critical nuclei in other nucleation processes. Nucleation experiments with water droplets containing differently sized graphene oxide nanosheets provide an experimental indication of the temperature-dependent size of the critical ice nucleus.
Antifreeze glycoproteins from polar fish are the most potent ice recrystallization (growth) inhibitors known, and synthetic mimics are required for low tem- perature applications such as cell cryopreservation. Here we introduce facially amphipathic glycopolymers which mimic the 3-dimensional structure of AFGPs. Glycopol- ymers featuring segregated hydrophilic and hydrophobic faces were prepared by ring-opening metathesis polymer- ization and their rigid conformation was confirmed by small-angle neutron scattering. Ice recrystallization inhi- bition (IRI) activity was reduced when a hydrophilic oxo- ether was installed on the glycan-opposing face, but sig nificant activity was restored by incorporating a hydro- phobic dimethylfulvene residue. This biomimetic strategy demonstrates that segregated domains of distinct hydrophilicity/hydrophobicity are a crucial motif to introduce IRI activity, and increases our under- standing of the complex ice crystal inhibition processes.
The effects of κ-carrageenan and its hydrolysates on modification of the freezing process and also on inhibition of excessive recrystallisation of ice in sucrose solutions during storage were compared. Acid hydrolysis of κ-carrageenan was carried out using sulphuric (H2SO4) and hydrochloric acid (HCl). Most effective in the hydrolysis process turned out to be H2SO4, which degraded κ-carrageenan to a molecular mass of around 3 × 106 Da, after 1.5 h of hydrolysis. Addition of 0.005% of the new poligeenan (degraded carrageenan), to a sucrose solution (30%), frozen at −20 °C, caused a nearly 50% reduction in the phase-change stages, and consequently, the total time of freezing was shorter. Significant retardation of recrystallisation was observed for both types of poligeenan, but a stronger effect was observed for the oligosaccharides obtained after HCl hydrolysis, and after 96 h of storage at −8 °C, the equivalent diameter of ice crystals was not greater than 11 μm.
ABSTRACT Over the past decade, ice cream manufacturers have developed a strong understanding of the functionality of key ingredients and processing, developing effective explanations for the link between structure forming agents, stability mechanisms and perceived quality. Increasing demand for products perceived as healthier / more natural with minimal processing has identified a number of new tools to improve quality and storage stability of frozen dairy desserts. Ingredients such as dietary fibre, polysaccharides, prebiotics, alternate sweeteners, fat sources rich in unsaturated fatty acids and ice structuring proteins have been successfully applied as cryoprotective, texturizing and structuring agents. Emerging minimal processing technologies including hydrostatic pressure processing, ultrasonic or high pressure assisted freezing, low temperature extrusion and enzymatically induced biopolymers crosslinking have been evaluated for their ability to improve colloidal stability, texture and sensory quality. It is therefore timely for a comprehensive review.
Ice cream as a complex food consists of small air cells dispersed in a partially frozen, continuous aqueous phase. Its desired quality is achieved by both proper processing and formulation. Stabilizers are substances that, despite their low usage level in ice cream mix, have very important functions, such as increase in viscosity of ice cream mix, aeration improvement, cryoprotection, and control of meltdown. Various materials, including both commercial and local gums, have been used as stabilizers. In this review, types of stabilizers, their functions, and limitations on excessive use of stabilizers in ice cream are discussed.
This review article focuses on the mechanisms of ice crystallization and recrystallization and factors that influence them in ice creams. Ice crystallization is an important factor that determines ice cream's final quality. The smaller the ice crystal size is in the final product, the better the quality is. Large ice crystals cause a coarse, grainy, and icy texture in ice cream. The initial ice crystals are formed in the freezer barrel and then grow in size during hardening and storage. Recrystallization during storage is influenced by various factors, including total solids, initial freezing temperature, unfrozen water, stabilizer type, sweetener type, and storage temperature. The roles of these factors, especially stabilizers, are discussed.
Antifreeze proteins (AFPs) are a subset of ice-binding proteins that control ice crystal growth. They have potential for the cryopreservation of cells, tissues, and organs, as well as for production and storage of food and protection of crops from frost. However, the detailed mechanism of action of AFPs is still unclear. Specifically, there is controversy regarding reversibility of binding of AFPs to crystal surfaces. The experimentally observed dependence of activity of AFPs on their concentration in solution appears to indicate that the binding is reversible. Here, by a series of experiments in temperature-controlled microfluidic devices, where the medium surrounding ice crystals can be exchanged, we show that the binding of hyperactive Tenebrio molitor AFP to ice crystals is practically irreversible and that surface-bound AFPs are sufficient to inhibit ice crystal growth even in solutions depleted of AFPs. These findings rule out theories of AFP activity relying on the presence of unbound protein molecules.
Freezing is the process of ice crystallization from supercooled water. Ice crystal morphology plays an important role in the
textural and physical properties of frozen and frozen-thawed foods and in processes such as freeze drying, freeze concentration,
and freeze texturization. Size and location of ice crystals are key in the quality of thawed tissue products. In ice cream,
smaller ice crystals are preferred because large crystals results in an icy texture. In freeze drying, ice morphology influences
the rate of sublimation and several morphological characteristics of the freeze-dried matrix as well as the biological activity
of components (e.g., in pharmaceuticals). In freeze concentration, ice morphology influences the efficiency of separation
of ice crystals from the concentrated solution. The cooling rate has been the most common variable controlling ice morphology
in frozen and partly frozen systems. However, several new approaches show promise in controlling nucleation (consequently,
ice morphology), among them are the use of ice nucleation agents, antifreeze proteins, ultrasound, and high pressure. This
paper summarizes the fundamentals of freezing, methods of observation and measurement of ice morphology, and the role of ice
morphology in technological applications.
KeywordsIce-Crystal morphology-Freezing-Freeze drying-Freeze concentration-Microstructure
Neutral cellulose nanocrystals dispersed in water were shown in a previous work to stabilize oil/water interfaces and produce Pickering emulsions with outstanding stability, whereas sulfated nanocrystals obtained from cotton did not show interfacial properties. To develop a better understanding of the stabilization mechanism, amphiphilic properties of the nanocrystals were modulated by tuning the surface charge density to investigate emulsifying capability on two sources of cellulose: cotton linters (CCN) and bacterial cellulose (BCN). This charge adjustment made it possible to determine the conditions where a low surface charge density, below 0.03 e/nm(2), remains compatible with emulsification, as well as when assisted by charge screening regardless of the source. This study discusses this ability to stabilize oil-in-water emulsions for cellulose nanocrystals varying in crystalline allomorph, morphology, and hydrolysis processes related to the amphiphilic character of nonhydrophobized cellulose nanocrystal.
Antarctic fishes synthesise antifreeze proteins which can effectively inhibit the growth of ice crystals. The mechanism relies on adsorption of these proteins to the ice surface. Ellipsometry has been used to quantify glycopeptide antifreeze adsorption to the basal and prism faces of single ice crystals. The rate of accumulation was determined as a function of time and at concentrations between 0.0005 and 1.2 mg/ml. Estimates of packing density at saturation coverage have been made for the basal and prism faces.
Background
Interest in high internal-phase emulsions, a type of highly concentrated emulsion system, has rapidly increased in the food industry. However, traditional stabilizers made from inorganic particles and synthetic surfactants have led to adverse health effects (e.g., interference with the normal gastrointestinal tract, gut microbiota, and cell toxicity), which has triggered researchers to isolate and characterize new Pickering particles from natural sources.
Scope and approach
Biopolymer-based particles have been suggested as efficient stabilizers of high internal-phase Pickering emulsions to satisfy consumer demand for “all natural” products and the industrial drive to provide “clean-label” food products. In this review, the particle properties including wettability, particle size, and surface charge, which govern the formation, microstructure characterization, and rheology of highly concentrated emulsions, are highlighted. Recent progress with emphasis on different types of Pickering particles assembled from biopolymers and their use in emulsions for emerging food applications are discussed.
Key findings and conclusions
High internal-phase Pickering emulsions stabilized by biopolymer-based particles have promising food applications due to their advantages of well-controlled droplet size distribution, tailored morphology and rheology, surfactant-free character, low toxicity, and superior stability against physical and chemical changes as well as environmental stresses. Pickering particles are classified into three categories: polysaccharide, protein, and complex (e.g., protein-protein, protein-polysaccharide, protein-polysaccharide-lipid, and protein-protein-polysaccharide) particles. Recent food applications include encapsulation and controlled release, texture design and modification, lipid oxidation reduction, and trans-fat replacement. A future perspective concerning the fabrication of biopolymer-derived particles to promote their use in highly concentrated emulsions for large-scale production is proposed.
Ice recrystallization inhibition assays are used to screen for compounds that possess the ability to inhibit ice recrystallization. The most common of these assays are the splat cooling assay (SCA) and sucrose sandwich assay (SSA). These two assays possess similarities; however, they vary in their sample size, cooling rate, and the solution used to dissolve the analyte. In this chapter, both assay methods are described in detail, and we perform a direct comparison of the assays by evaluating the IRI activity of an antifreeze protein (AFP I). IRI activity is quantified by using ImageJ software to analyze ice crystals, and a quantitative value describing the efficiency of the inhibitor is generated. This analysis emphasizes the importance of choosing the right assay to measure IRI activity.
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.
Ice cream of high quality has smooth consistency due to ice crystal sizes between 20 and 50 μm, which depends on ice cream formulation and thermal stress during storage. Ice crystals of 3 “traditional” (milk proteins and stabilisers) and 2 vegan (inulin and potato proteins) ice cream formulations were studied using a cold stage microscope under frozen conditions. Samples were observed before and after a temperature fluctuation (cycles of −18 °C and −6 °C for 14 days), and the data obtained compared with the results of a melting test. Results showed that milk proteins and stabilisers conferred structural stability to ice cream, both in terms of small crystal size (20–50 μm) and behaviour during melting, suitable for storage. Ice creams without one of the two constituents or in presence of potato proteins or inulin, showed a crystal size increase; in this case ice creams were for immediate consumption.
Biocompatible materials with ice recrystallization inhibition (IRI) activity have potential applications in several fields. Emerging studies have associated the IRI activity of antifreeze proteins/glycoproteins and several mimics of synthetic materials with a facially amphipathic structure. Nanocelluloses are a new family of renewable materials that demonstrate amphiphilicity. Herein the IRI activity of cellulose nanocrystals (CNCs) and 2, 2, 6, 6-tetramethylpiperidine-1-oxyl oxidized cellulose nanofibrils (TEMPO-CNFs) is reported. In 0.01 M NaCl, ice recrystallization was effectively inhibited by 5.0 mg/mL CNCs or 2.0 mg/mL TEMPO-CNFs. In phosphate-buffered saline, appreciable IRI activity was still observed with 30.0 mg/mL CNCs. IRI assays in sucrose solutions showed that the decreased IRI activity of nanocelluloses in saline was caused by the aggregation of nanocelluloses due to charge screening. Neither thermal hysteresis nor dynamic ice shaping activity was observed in nanocelluloses. These findings may lead to the use of nanocelluloses as novel ice recrystallization inhibitors.
Cellulose nanocrystals (CNCs), usually considered as isotropically polar nanoparticles, are sheet-like crystalline assemblies of cellulose chains. Here, we link the anisotropy of the CNC structure to an amphiphilic behavior in suspension. The Hansen solubility parameters (HSP: δD;δP;δH) of wood-based H2SO4-hydrolyzed CNCs were measured from sedimentation tests in a wide set of 59 solvents and binary mixtures. Two sets of cohesion parameters corresponding to a polar surface (18.1; 20.4; 15.3) ± (0.5; 0.5; 0.4) MPa1/2 and to a mildly non-polar one (17.4; 4.8; 6.5) ± (0.3; 0.5; 0.6) MPa1/2 were determined, with respective solubility radii of 7.8 and 2.1 MPa1/2. The polar sphere is thought to correspond to the (110) & (11¯0) surfaces of cellulose Iβ nanocrystals, while the smaller non-polar sphere is coherent with the exposure of (200) surfaces. The HSP graph provides new insights on the amphiphilic nature of CNCs and a mapping of their chemical affinity for solvents and polymer matrices.
Antifreeze proteins are produced by extremophile species to control ice formation and growth, and have potential applications in many fields. There are few examples of synthetic materials which can reproduce their potent ice recrystallization inhibition property. We report that self-assembled enantiomerically-pure, amphipathic metallohelicies inhibited ice growth at just 20 μM. Structure-property relationships and calculations support the hypothesis that amphipathicity is the key motif for activity. This opens up a new field of metallo-organic antifreeze protein mimetics and provides insight into the origins of ice-growth inhibition.
Safranine O, a synthetic dye, was found to inhibit growth of ice at millimolar concentrations with an activity comparable to highly evolved antifreeze glycoproteins. Safranine inhibits growth of ice crystals along the crystallographic a axis, resulting in bipyramidal needles extended along the <0001> directions and plane-specific thermal hysteresis (TH) activity. The interaction of safranine with ice is reversible, distinct from previously reported behavior of antifreeze proteins. Spectroscopy and molecular dynamics indicate that safranine forms aggregates in aqueous solution at micromolar concentrations. Metadynamics simulations and aggregation theory suggested that as many as 30 safranine molecules were preorganized in stacks at the concentrations where ice growth inhibition was observed. The simulations and the single-crystal X-ray structure of safranine revealed regularly spaced amino and methyl substituents in the aggregates, reminiscent of the ice-binding interface of antifreeze proteins. Collectively, these observations suggest an unusual link between supramolecular assemblies of small molecules and functional proteins.
Ice recrystallization occurs during cryopreservation and is correlated with reduced cell viability after thawing. Therefore, ice recrystallization inhibition (IRI) activity is a very desirable property for an effective cryoprotectant. Antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs) were the first compounds discovered with this property, however they are poor cryoprotectants due to their unique ability to bind to ice and alter habits of ice crystals. Consequently, AFGP analogues with “custom-tailored” antifreeze activity have been developed which exhibit potent IRI activity but do not bind to ice. Subsequent to this, it was reported that simple mono- and disaccharides exhibit moderate IRI activity and this has ultimately facilitated the discovery of several small carbohydrate-based ice recrystallization inhibitors with IRI activity similar to that of native AFGP-8. This represents a major advancement in the field of ice recrystallization inhibitors (IRIs). The recent developments of IRIs will be reviewed, focusing on novel small molecules that have great potential for use as cryoprotectants.
The inhibition of ice recrystallization (RI) processes in frozen sucrose solutions containing antifreeze proteins (AFP I, AFP III and AFGP), hydrocolloids (sodium alginate, κ-carrageenan) or mixtures of those was analyzed in detail. Noticeable RI effects were observed in all samples. The impact of the individual antifreeze proteins on the recrystallization process increased in the order AFP III, AFP I and AFGP which follows a different trend than thermal hysteresis activity already reported by other authors. AFP mixtures increased the RI effect compared with the pure AFP. The hydrocolloid κ-carrageenan caused a similar effect like AFPs but at higher concentrations. Sodium alginate in contrast showed only a small influence on RI. The shape of ice crystals in the κ-carrageenan solution were similar to the shapes found in AFP solutions which suggests that κ-carrageenan may act in a way comparable to AFPs. A synergistic effect between hydrocolloids and antifreeze proteins was also observed.
The hypothesis advanced in this issue of CELLULOSE [Springer] by Bjorn Lindman, which asserts that the solubility or insolubility characteristics of cellulose are significantly based upon amphiphilic and hydrophobic molecular interactions, is debated by cellulose scientists with a wide range of experiences representing a variety of scientific disciplines. The hypothesis is based on the consideration of some fundamental polymer physicochemical principles and some widely recognized inconsistencies in behavior. The assertion that little-recognized (or under-estimated) hydrophobic interactions have been the reason for a tardy development of cellulose solvents provides the platform for a debate in the hope that new scientific endeavors are stimulated on this important topic.
ABSTRACT In ice cream manufacturing, control of ice crystal growth,through,proper formulation,and storage tem- perature is important,for stability during storage. The objective of this study was,to investigate the influence of sweetener (sucrose, 20 dextrose equivalent corn syrup, 42 dextrose equivalent corn syrup, and 42 high fructose corn syrup), with and without stabilizer, on ice recrystallization in ice cream,at three storage temperatures. The relationship between,thermal,and physical properties and ice recrystallization rate was also studied. Mean size of ice crystals increased to the one-third power,as storage,time,increased. Recrystallization rate increased,as temperature,increased,, amount,of frozen water. Recrystalli- zation rate did not depend,uniformly,on the difference between,storage,temperature,and,apparent,glass transition temperature,for all ice creams; specific ef- fects of sweetener,and,stabilizer were,observed. Stabilizer generally inhibited recrystallization, but some,samples,showed,greater effects than,others. ( Key words: recrystallization, formulation, storage temperature, ice cream) Abbreviation key: CS = corn syrup, DE = dextrose
Storage under low constant temperature (–30°C) had no effect on the overall ice crystal size of stabilized or unstabilized ice cream samples; storage at a higher temperature (–16°C) showed clear evidence, based on sample microstructure, of recrystallization, probably through Ostwald ripening and accretion. Temperature cycles (–15 ± 5°C) of samples after hardening (–30°C) had an even greater effect than did storage at a high constant temperature (–16°C). Also, increase of the number or time length of cycles had greater impact than did an increase in amplitude. After extended thermal fluctuation, smaller crystals disappeared. The predominant recrystallization mechanism at this stage would have most likely involved partial melting and refreezing of ice crystals. With this mechanism, stabilizers exerted a measurable effect of retarding or preventing crystal growth.
Locust bean gum (LBG) and guar gum (GG) are two galactomannan stabilizers that help maintain smooth textures in ice cream by slowing down ice crystal growth during constant and fluctuating temperatures. LBG and GG were dissolved in sucrose solutions without or with milk solids-not-fat (MSNF), fat, and/or emulsifier. Solutions were temperature cycled at subzero temperatures and measured after each cycle with a controlled stress rheometer to obtain yield stress and frequency sweep data. LBG solutions developed weak gel structures with temperature cycling, especially in the presence of MSNF, but GG solutions did not. Fat droplets interfered with the formation of LBG weak gel networks while emulsifiers did not change the rheological properties of emulsions. The ability of a polysaccharide to cryo-gel with temperature cycling and protein/stabilizer incompatibility leading to phase separation both helped create elastic structures. More realistic ice cream model emulsions containing fat showed different rheological responses, emphasizing caution in comparing model systems to real systems.
Hydrocolloids are added in ice-creams and frozen desserts to produce smooth texture and protect the product during its storage. The high-pressure freezing techniques also aimed to enhance product qualities. In this work, both the hydrocolloid and the high-pressure processing actions are combined. A 0.3% (w/w) of guar gum (viscous solution) or of locust bean gum plus xanthan gum (gel) was mixed in sucrose solutions (16% w/w) to analyze whether water mobility affected ice crystal formation. Sucrose solutions with or without hydrocolloids were frozen by high-pressure assisted freezing (HPAF) at 100MPa and by high-pressure shift freezing (HPSF) from 210MPa to 0.1 and 100MPa, to compare their effects on the ice crystal characteristics. Ice crystal sizes were determined from images obtained by low temperature scanning microscopy (LT-SEM). Ice crystals were smaller after HPSF than after HPAF, due to greater supercooling following expansion and to shorter phase transition times. As regards the hydrocolloids, ice crystals were smaller when the mixture of locust bean and xanthan gums were added irrespective of the freezing method. The formation of a gel-like structure at ambient temperature strengthened by a cryo-gelation effect in the frozen state may limit water molecule diffusion and ice crystal growth.
Nonfat (0.5%), low fat (4%), reduced fat (6%), and full fat (9%) chocolate ice creams were made. Whey protein and polydextrose were added as re- quired so that all formulations contained the same amount of total solids. Ice cream was stored at a control temperature of -30°C or was heat-shocked at -12°C. Hardness, viscosity, and melting rate were measured through physical methods. Trained panelists conducted descriptive sensory analyses of the samples at 0 and 4 wk. Attribute ratings were analyzed by analysis of variance and least significant difference mean separation. Milk fat at concentra- tions of 9 and 6% produced more creaminess and smoothness, as well as a less intense cocoa flavor, than it did at concentrations of 4 or 0.5%. Consumer acceptance ( n = 98) did not differ among the fresh ice creams. Data showed that ice creams containing higher milk fat concentrations are better protected against heat shock damage in terms of cocoa flavor and smoothness of texture.
Ice recrystallization rates in simple aqueous solutions comprising fructose and a hydrocolloid stabilizer were measured. The stabilizers were an enzyme-modified guar and a non-gelling high methoxy pectin. The stabilizer concentration dependence of the recrystallization rates for both materials was similar in that increasing the concentration resulted in decreasing rates until a point is reached where further addition had no additional effect. That recrystallization rates were reduced by both gelling and non-gelling stabilizers was strongly suggestive that gelation was not a requirement for recrystallization inhibition and another more specific mechanism applies, for example a weak interfacial effect such as adsorption or blocking. This behavior was also seen with locust bean gum and guar and provided further empirical evidence to support the hypothesis that stabilizers adsorb to ice crystal surfaces.
Recrystallization in ice creams that were made with various combinations of four sweeteners (20 DE (dextrose equivalent) corn syrup solids, 42 DE corn syrup solids, sucrose, and high fructose corn syrup), and four stabilizers (gelatin, locust bean gum, xan- than gum, and carrageenan) was investigated. Ice creams were stored at three different temperatures (-5.2, -9.5, and -15°C). For a given stabilizer, both storage temperature and sweetener type influenced recrystallization rate. For a given temperature, rates were lowest for ice creams made with 20 DE corn syrup solids and the highest for ice creams made with high fructose corn syrup at all storage temperatures. The effects of stabilizers on ice recrystallization rate were more pronounced in combinations of either lower temperature (-15°C) and lower freezing point tem- perature when high fructose corn syrup or sucrose was used or higher temperature (-5.2°C) and higher freezing point temperature when 20 DE corn syrup solids was used. Overall, carrageenan and locust bean gum were most effective in retarding ice crystal growth, but not in all cases. Xanthan gum and gelatin retarded ice recrystallization only at -15°C and when combined with sucrose or high fructose corn syrup.
Ice fraction was measured for solutions containing glucose, sucrose, gelatin, and egg albumin at various concentrations at temperatures from 0 to -20°C. For glucose and sucrose solutions, the ice fraction was accurately measured from phase diagram, which could be interpreted by solution thermodynamics with two parameters. The ice fractions of these sample solutions increased with decreases in both temperature and concentration. Because of the limited applicability of the phase diagram method only to systems with low molecular weight materials, the DSC method was also used for ice fraction measurement. The DSC method, corrected for temperature-dependent latent heat of ice and corrected with Pham’s equation, provided a good approximation for ice fractions with general applicability. The DSC method was used to measure the ice fractions of gelatin and egg albumin gels as a function of solute concentration. The freezing point and bound water of gelatin and egg albumin gels were described as a function of concentration. Effects of the differences in molecular structure on ice fraction were analyzed for various carbohydrate solutions at the same concentration. The ice fraction proved to be strongly dependent on the colligative properties of the solution with nonideal behavior.
Locust bean gum (LBG) and guar were labeled with rhodamine isothiocyanate, and their location within a solution of sucrose or sucrose plus skim milk powder after freezing and during temperature cycling between −18 and −10°C was visualized with fluorescence and brightfield microscopy. LBG was observed to produce a structured gel-like network around the ice crystals, which became more distinct with repeated temperature cycling. Such a network was not evident with guar gum. Image analysis of the ice crystal size distributions showed that LBG had provided much greater resistance to ice recrystallization under these conditions than guar. The same trends were evident in sucrose plus skim milk powder solutions, but the overall increase in ice crystal size was less than it was without skim milk powder. Both the LBG and guar promoted the formation of a phase-separated protein region. Carrageenan successfully reduced the extent of protein/galactomannan phase separation, but solutions containing carrageenan recrystallized to a greater extent than those without carrageenan. It was suggested that a reduction in recrystallization resulted from the formation of a continuous polymer network and structural heterogeneity in the unfrozen phase.
The influence that a range of polysaccharides (galactomannans) had on ice recrystallization was determined. The concentration dependence of the recrystallization inhibition occurring with locust bean and guar gums was determined. The degree of galactose substitution in a range of enzyme modified guars was dominant in the effect of a galactomannan to inhibit recrystallization. The fine structure of the substituents were less important. Where the galactose content of comparable polysaccharides was similar the fine structure became dominant. The influence of sugar size on recrystallization was also investigated. Increasing molecular weight resulted in reduced recrystallization rates. The observed rates appeared to follow Williams -Landell-Ferry kinetics.
Recrystallization rates of ice in fructose solutions were determined over a range of temperatures and ice phase volumes. Accretive and migratory recrystallization both occur, the dominant mechanism being strongly dependent on the mean size of the crystals. Accretion dominated when crystals were small and close together. Recrystallization rates decreased with decreasing ice phase volume and decreasing temperature. The temperature dependence of the rates was consistent with Williams-Landell-Ferry kinetics. With a mean field correction for ice phase volume the observed data fit the recrystallization theory of Lifshitz, Slyozov and Wagner reasonably well.
ABSTRACTA methodology has been devised to study the effects of sweeteners and a stabilizer on the rate of ice recrystallization. Aqueous solutions of sucrose, corn syrup (62 DE), and high fructose corn syrup with locust bean gum, and solutions of corn syrup with varying levels of locust bean gum were also studied. Microprocessor controlled time-temperature experiments were performed with each sample. Average ice crystal size was measured after each heating/ cooling cycle. Effect of viscosity on ice recrystallization growth rates was also studied. This methodology is an improved technique for providing temperature control during fluctuating temperature studies. Concentration of locust bean gum showed no correlation to ice recrystallization rates. The choice of sweetener used in the aqueous solution was found to affect the rate of ice recrystallization.
The smoothness and perceived quality of an ice cream depends in large part on the small size of ice crystals in the product. Understanding the mechanisms responsible for producing the disc-shaped crystals found in ice cream will greatly aid manufacturers in predicting how processing and formulation changes will affect their product. Because ice cream mix is opaque, it has not yet been possible to observe ice crystallization in ice cream in situ. Studies to date, therefore, have used analogues or have related observed effects to a hypothesized mechanism. Still, some elements of the crystallization mechanism are well accepted. Because of the large supercooling at the freezer wall, ice nucleates there before being swept into the bulk of the freezer. In the bulk, heat and mass transfer cause some crystals to melt and others to grow. By the time the ice cream reaches the freezer exit, the ice crystals have become small, rounded discs.
Rates of ice recrystallization were measured in aqueous fructose solutions containing locust bean gum (LBG). The effects of temperature, ice phase volume and LBG concentration were determined. Decreasing temperature reduced the recrystallization rate: the dependency followed Williams Landell Ferry kinetics. An increase in ice phase volume resulted in an increase in the recrystallization rate. Addition of LBG reduced the recrystallization rate up to a concentration of 0.3% (w/w); further addition resulted in no further decrease. The hypothesized mechanism of action of LBG is via weak adsorption of the polysaccharide to the ice crystal. Freeze concentrated solution viscosity did not correlate with observed recrystallization rates.
Hydrocolloid stabilizers (carrageenan, carboxymethyl cellulose, xanthan gum, sodium alginate, locust bean gum (LBG) and gelatin) were labeled with rhodamine isothiocyanate and incorporated into solutions of sucrose with or without milk solids-not-fat (MSNF). Resultant solutions were quench frozen to −50 °C and cycled between −3.5 and −6 °C, five times. The location of the stabilizer was observed using fluorescence microscopy. Significant retardation of recrystallization was observed in alginate and xanthan sucrose solutions without MSNF. In the presence of proteins, all stabilizers were effective retarding recrystallization except for gelatin. After cycling, a gel-like structure was observed in solutions containing LBG without MSNF, and in LBG, carrageenan and gelatin with MSNF. The fact that some non-gelling stabilizers (i.e. xanthan) were more effective retarding recrystallization than gelling stabilizers (i.e. gelatin) suggests that steric blocking of the interface or inhibition of solute transport to and from the ice interface caused by gelation of the polymer is not the only mechanism of stabilizer action. Molecular interactions between polysaccharides and proteins appear to be key factors in retarding ice recrystallization.
Crystal sizes were measured photographically versus elapsed time for non-uniform ice crystal populations mixed at equilibrium temperatures with sugar solutions. The mass of ice did not change, but crystals smaller than a "neutral diameter," D(n), tended to melt because of their excess surface energy. This subcooled the solution with respect to larger crystals, which consequently grew. This process, "ripening," which slowly increases mean crystal sizes and D(n) is used to produce ice crystals large enough to be cleanly separated from freeze concentrated solutions. "Sequential analysis" was used to determine D(n) and follow changes in the diameters, D(i), of fractions of the ice crystal populations. Rates of change in D(i) for both growth and melting were roughly proportional to (I/D(n) - 1/D(i). Overall mass-transfer coefficients were not markedly different for growth and melting, and decreased from roughly 2 mm/s to roughly 0.5 mm/s as sugar concentration increased 10% to 42%. In 10% sucrose solutions, mass-transfer coefficients decreased from roughly 2 mm/s to roughly 1 mm/s when gelatin was added at levels which increased from 0% to 0.5%. Ripening in freeze concentrated liquid foods apparently can be accelerated by manipulating initial crystal size distributions and temporarily removing high molecular weight components.
The effectiveness of propylene glycol monostearate (PGMS) to inhibit ice recrystallization was evaluated in ice cream and frozen sucrose solutions. PGMS (0.3%) dramatically reduced ice crystal sizes in ice cream and in sucrose solutions frozen in a scraped-surface freezer before and after heat shock, but had no effect in quiescently frozen solutions. PGMS showed limited emulsifier properties by promoting smaller fat globule size distributions and enhanced partial coalescence in the mix and ice cream, respectively, but at a much lower level compared to conventional ice cream emulsifier. Low temperature scanning electron microscopy revealed highly irregular crystal morphology in both ice cream and sucrose solutions frozen in a scraped-surface freezer. There was strong evidence to suggest that PGMS directly interacts with ice crystals and interferes with normal surface propagation. Shear during freezing may be required for its distribution around the ice and sufficient surface coverage.
Lowfat and nonfat chocolate ice creams were made with 2.5% of milk fat, cocoa butter, or one of two whey protein-based fat replacers, Dairy Lo or Simplesse. Polydextrose was added as required so that all formulations contained the same amount of total solids. Ice cream was stored at a control temperature of-30 degrees C. Hardness, viscosity, and melting rate were measured by physical methods. Trained panelists conducted descriptive sensory analyses of the samples at 0, 6, and 12 wk. Attribute ratings were analyzed by analysis o variance with least significant difference mean separation and orthogonal contrasting. Data were also analyzed by multivariate analysis of variance with canonical variate analysis. Consumer acceptance (n = 50) did not differ among the fresh ice creams (wk 0). Ice cream containing milk fat had less intense cocoa flavor and was more resistant to textural changes over time compared with the other ice creams. Simplesse was more similar to milk fat than was Dairy Lo in its effect on brown color, cocoa flavor, cocoa character, and textural stability but was less similar in terms of thickness and mouthcoating.
Ice crystal growth and microstructure of sugarsolutions prepared with stabilizers (carboxymethyl cellulose [CMC], xanthan gum, locust bean gum [LBG], and gelatin) with or without milk solids-nonfat (MSNF) after freezing in a scraped surface heat exchanger and temperature cycling (5 cycles from -6 degrees C to -20 degrees C) were studied. Ice crystal growth was calculated from brightfield microscopic images acquired from samples before and after cycling. Freeze-substitution and low-temperature embedding (LR-Gold resin) were sample preparation techniques utilized for structure analyses by light microscopy and transmission electron microscopy. Differential staining for carbohydrates and proteins allowed the identification of stabilizer gel-like structures in LBG, gelatin, and gelatin/MSNF solutions. In the absence of milk proteins, xanthan and LBG were the most effective at retarding recrystallization, while in their presence, only xanthan had an effect. Cryo-gelation of the LBG was observed but is not the only mechanism of stabilizer action. Thermodynamic incompatibility between biopolymers was observed to promote localized high concentrations of milk proteins located at the ice crystal interface, probably exerting a water-holding action that significantly enhanced the stabilizer effect. Qualitatively, solution heterogeneity (phase separation) was directly proportional to ice crystal growth inhibition. It is suggested that water-holding by stabilizer and proteins, and in some cases steric hindrance induced by a stabilizer gel-like network, caused a reduction in the kinetics of the ice recrystallization phenomena and promoted mechanisms of melt-regrow instead of melt-diffuse-grow recrystallization, thus resulting in the preservation of the ice crystal size and in a small span of the ice crystal size distribution.