Use of hydrocolloids as cryoprotectant for frozen foods

Dual cryoprotection of gelatin-tea polyphenol microgels on surimi by targeting for ice inhibition and component stabilization

In this study, the gelatine-polyphenol microgels with dual cryoprotective roles were constructed by regulating the ratio of gelatin to tea polyphenols (1:50-1:250). The physicochemical attributes, ice recrystallization inhibition ability of microgels, and their dosage effects (1 %, 2.5 % and 4 %, w/w) on surimi were investigated. The results indicated that increased gelatin caused the reduced size and enhanced viscosity of microgels. Except for high viscosity and antioxidant activity, the GP-5 group also showed great IRI ability with minimum size distribution (125-214 μm2) of ice crystals. Furthermore, 2.5 G group and S group had a comparable TVB-N (3.81, 4.34 mg/100 g), TBARS (1.18, 1.32 mg/kg), sulfhydryl contents (29.52, 25.48 μmol/g) and Ca2+-ATPase activity (0.44, 0.36 μmolPi/gprot/h). Compared to uneven free water distribution of control group, S and 2.5 G group show more even immobilized-water distribution. Thereafter, the dual cryoprotective functions of microgels in surimi offer valuable insights for the development of effective antifreeze agents.

Mitigating the Effects of Starch Derivatives on Cold Denaturation of Gluten Protein: Insights from Hydration Capacity and Conformation Behavior

Mitigating the cold denaturation of gluten protein during frozen storage is crucial for the quality improvement of frozen cereal products. Our previous study observed that starch derivatives, especially short-clustered maltodextrin (SCMD), could significantly improve frozen dough quality, alleviating the deterioration of gluten-network structure. To further reveal the cryoprotection mechanism of SCMD on gluten protein during frozen storage, the modulatory roles of SCMD in the hydration capacity and conformation behavior of gluten protein were explored, in comparison with DE2 maltodextrin (MD) and pregelatinized starch (PGS). Results demonstrated that SCMD significantly facilitated the reservation of bound water and decreased the surface hydrophobicity of gluten protein after 8 weeks of frozen storage. Remarkable effects of SCMD on stabilizing the secondary structure and microenvironment of aromatic amino acids of gluten protein were observed. Further mechanistic investigation showed that when the temperature dropped from 300 to 250 K, the short-clustered structure could stabilize the α-helixes more evidently than linear structures through hydrogen bonds with water and steric hindrance effect, rather than directly with protein. Our findings will provide novel insights into the cold denaturation of gluten protein and useful guidance in selecting the optimum structure to suppress this denaturation, improving the quality of frozen cereal products.

Effects of sanxan on water and ice crystal status of salt free frozen cooked noodles during freeze-thaw cycles

This study compared four biocolloids (sanxan, xanthan gum, curdlan, and guar gum) in different concentrations to replace NaCl in improving the recooking quality of salt free frozen cooked noodles (SF-FCNs). Sanxan outperformed NaCl and other biocolloids significantly improving the firmness (21.0%), chewiness (63.5%), and toughness (15.4%) of SF-FCNs after 10 freeze-thaw (FT) cycles. The results of the freezing-thawing curves showed SF-FCNs had prior FT stability when sanxan was added at 1.2%. Subsequently, the result of differential scanning calorimetry and nuclear magnetic resonance revealed sanxan reduced the content and mobility of freezable water while increasing the content of bound water. The scanning electron microscope, mercury intrusion, and optical microscopy analyses indicated that sanxan reduced the size and volume of ice crystals and the structural damage of SF-FCNs by controlling the water. The work contributes to a theoretical framework for enhancing SF-FCNs quality through precise water and ice crystal control.

Effects of cell morphology on the textural attributes of fruit cubes in freeze-drying: Apples, strawberries, and mangoes as examples

The influence of cell morphology on the textural characteristic of freeze-dried apple, strawberry, and mango cubes was evaluated. Corresponding restructured cube samples without intact cell morphology were prepared as controls. Results indicated that the presence of cell morphology strengthened the shrinkage and collapse of samples during freeze-drying, especially in mangoes due to the high content of sugar. Intact cell morphology was found in natural fruit cubes after freeze-drying by scanning electron microscopy (SEM) observation, making them exhibit a more regular microporous structure, further resulting in higher hardness than the restructured cubes. However, the intact cell morphology negatively affected the crispness of freeze-dried cubes since it enhanced structural collapse. The freeze-dried samples without cell morphology would destroy the cellulose structure and form a continuous open-pore structure under the concentration effect of ice crystals during freezing, which accelerates the escape of water molecules, increases the drying rate, and avoid collapse. Sensory experiments found that restructured cubes without intact cell morphology exhibited greater comprehensive acceptance, suggesting the potential application of cell morphology disruption in the future freeze-drying industry.

Progress in the application of novel cryoprotectants for the stabilization of myofibrillar proteins

In this review, the physicochemical and conformational changes of myofibrillar proteins (MPs) of freeze-induced mince-based aquatic foods were comprehensively summarized in depth. Studies have demonstrated that temperature fluctuation and long-time freezing negatively affect food quality, resulting in texture alteration, drip fluid, flavor degradation, and nutrition loss due to MPs denaturation, aggregation, and oxidation. Attempts have been made in ice-recrystallization inhibition, freezing point depression, and ice shape and growth control for better cryopreservation. Moreover, to further minimize the quality deterioration, cryoprotectants were acknowledged to reduce the denaturation and aggregation of the MPs effectively. Recently, interest in novel functional ingredients, including oligosaccharides, protein hydrolysates, and natural polyphenols demonstrated excellent cryoprotective effects while avoiding health concerns and undesirable flavor caused by traditional sugar-based or phosphates-based cryoprotectants. Therefore, the present review provides a systematic overview of these low molecular weight multifunctional substances with a particular sequence and highlights their underlying mechanism in the inhibition of ice recrystallization the stabilization of MPs.

Freezing-induced denaturation of myofibrillar proteins in frozen meat

Freezing is commonly used to extend the shelf life of meat and meat products but may impact the overall quality of those products by inducing structural changes in myofibrillar proteins (MPs) through denaturation, chemical modification, and encouraging protein aggregation. This review covers the effect of freezing on the denaturation of MPs in terms of the effects of ice crystallization on solute concentrations, cold denaturation, and protein oxidation. Freezing-induced denaturation of MPs begins with ice crystallization in extracellular spaces and changes in solute concentrations in the unfrozen water fraction. At typical temperatures for freezing meat (lower than -18 °C), cold denaturation of proteins occurs, accompanied by an alteration in their secondary and tertiary structure. Moreover, the disruption of muscle cells triggers the release of cellular enzymes, accelerating protein degradation and oxidation. To minimize severe deterioration during the freezing and frozen storage of meat, there is a vital need to use an appropriate freezing temperature below the glass transition temperature and to avoid temperature fluctuations during storage to prevent recrystallization. Such an understanding of MP denaturation can be applied to determine the optimum freezing conditions for meat products with highly retained sensory, nutritional, and functional qualities.

Potent Time-Dependent Ice Recrystallization Inhibition Activity of Cellulose Nanocrystals in Sucrose Solutions

Exploring novel materials with ice recrystallization inhibition (IRI) activity in several fields often starts with a quantitative analysis of ice crystal size change by a splat assay or sandwich assay on a short time scale from 0.5 to 1 h. This study found that this time scale was insufficient to evaluate the IRI activity of cellulose nanocrystals (CNCs) in a model ice cream system-25.0% sucrose solution. No IRI activity was observed in CNCs incubated with ice crystals on a short time scale of 0.5-2.0 h. However, over longer time scales, the growth of ice crystals was entirely inhibited by 1.0% CNCs (between 2 and 24 h) and 0.5% CNCs (between 24 and 72 h) with corresponding final crystal sizes of 25 and 40 μm, respectively. Additionally, ice shaping was observed on a long exposure time, but not on a short exposure time. The findings presented here can be explained by a time-dependent surface coverage of CNCs on ice crystals. The data here indicate the importance of choosing a suitable exposure time for evaluating the IRI activity of new materials and prompt a better understanding of IRI mechanisms involving CNCs.

Preparation and Characterization of κ-Carrageenan Modified with Maleic Anhydride and Its Application in Films

In this work, the physicochemical properties of maleic anhydride (MAH)-modified κ-carrageenan (κCar) (MC) were characterized and compared with those of native κ-carrageenan (NC). The Fourier transform infrared spectrum of MC exhibited that κCar was successfully modified. Thermogravimetric analysis indicated that the thermal stability of MC was decreased. When the degree of substitution was 0.032, MC exhibited a low gel strength (759 g/cm²), gelling temperature (33.3 °C), and dehydration rate (60.3%). Given the excellent film-forming ability of κCar, MC films were then prepared and were found to have better mechanical and barrier properties (UV and water) than NC films. With regard to optical properties, MC films could completely absorb UV light in the range of 200–236 nm. The water contact angle of MC films was higher than that of NC films. Moreover, the elongation at break increased from 26.9% to 163%. These physicochemical property changes imply that MC can be employed in polysaccharide-based films.

Brief Overview of Ice Nucleation

The nucleation of ice is vital in cloud physics and impacts on a broad range of matters from the cryopreservation of food, tissues, organs, and stem cells to the prevention of icing on aircraft wings, bridge cables, wind turbines, and other structures. Ice nucleation thus has broad implications in medicine, food engineering, mineralogy, biology, and other fields. Nowadays, the growing threat of global warming has led to intense research activities on the feasibility of artificially modifying clouds to shift the Earth’s radiation balance. For these reasons, nucleation of ice has been extensively studied over many decades and rightfully so. It is thus not quite possible to cover the whole subject of ice nucleation in a single review. Rather, this feature article provides a brief overview of ice nucleation that focuses on several major outstanding fundamental issues. The author’s wish is to aid early researchers in ice nucleation and those who wish to get into the field of ice nucleation from other disciplines by concisely summarizing the outstanding issues in this important field. Two unresolved challenges stood out from the review, namely the lack of a molecular-level picture of ice nucleation at an interface and the limitations of classical nucleation theory.

Antioxidant Activity in Frozen Plant Foods: Effect of Cryoprotectants, Freezing Process and Frozen Storage

The antioxidant activity (AOA) of plant foods is recognized as an index of the potential health benefits resulting from their consumption. Due to their high perishability and seasonality, plant foods are largely consumed or used as processed products and freezing is one of the technologies used for the production of high-quality foods. However, cell breakages occurring during freezing and frozen storage can lead to the release of antioxidant compounds and their degradation due to chemical and enzymatic oxidation reactions, and thus, they could present a lower antioxidant activity compared to the corresponding fresh product. In this context, process conditions, freezing pre-treatments and the use of cryoprotectants can limit the extent of freeze-induced damages and preserve the antioxidant activity of plant foods. This review collects and discusses the state-of-the-art knowledge on the single and combined effect of freezing and frozen storage conditions on the antioxidant activity of fruits and vegetables as well as the role of cryoprotectants. Classes of compounds responsible for the antioxidant activity of plant foods and the most common methods used for the evaluation of the antioxidant activity in vitro are also presented. The freezing principles and the effects of ice nucleation and crystallization on fruits, vegetables and their main derivatives (juices, pulps) have been addressed to highlight their impact on the AOA of plant foods. The effect of freezing and frozen storage on the AOA of plant foods resulted dependant on a series of intrinsic factors (e.g., composition and structure), while the role of extrinsic processing-related factors, such as freezing and storage temperatures, is ambiguous. In particular, many conflicting results are reported in the literature with a high variability depending on the method of analysis used for the AOA evaluation and data expression (fresh or dry weight). Other intrinsic raw material properties (e.g., cultivar, ripening degree), post-harvest conditions, as well as defrosting methods that in the majority of the studies are scarcely reported, contribute to the aforementioned discrepancies. Finally, due to the limited number of studies reported in the literature and the high variability in product processing, the effect of cryoprotectants on the AOA of plant foods remains unclear.

The Influence of Maltodextrin on the Thermal Transitions and State Diagrams of Fruit Juice Model Systems

The state diagram, which is defined as a stability map of different states and phases of a food as a function of the solid content and temperature, is regarded as fundamental approach in the design and optimization of processes or storage procedures of food in the low-, intermediate-, and high-moisture domains. Therefore, in this study, the effects of maltodextrin addition on the freezing points (Tm′, Tm) and glass transition temperatures (Tg′, Tg) required for the construction of state diagrams of fruit juice model systems by using differential scanning calorimetry methods was investigated. A D-optimal experimental design was used to prepare a total of 25 anhydrous model food systems at various dry mass fractions of fructose, glucose, sucrose, pectin, citric acid, and maltodextrin, in which this last component varied between 0 and 0.8. It was found that maltodextrin mass fractions higher than 0.4 are required to induce significant increases of Tg′, Tm′, Tg, and Tm curves. From this perspective, maltodextrin is a good alternative as a cryoprotectant and as a carrier agent in the food industry. Furthermore, solute-composition-based mathematical models were developed to evaluate the influence of the chemical composition on the thermal transitions and to predict the state diagrams of fruit juices at different maltodextrin mass fractions.