Explore chapters and articles related to this topic
Refrigeration and Freezing of Foods
Published in C. Anandharamakrishnan, S. Padma Ishwarya, Essentials and Applications of Food Engineering, 2019
C. Anandharamakrishnan, S. Padma Ishwarya
Ice formation ceases once the temperature of food product reaches the glass transition temperature (temperature below which the product exists in the glassy solid or rigid state). Nevertheless, the freezing rate influences the ice crystal formation and eventually the product quality. While rapid freezing leads to the formation of smaller ice crystals, slow freezing forms larger ice crystals. While small ice crystals do not affect the product structure and texture, larger ice crystals have a deteriorative effect on the product. During slow freezing, the large ice crystals grow between the cells of the food structure and hence rupture the cell wall. The detrimental effect of ice crystals is attributed to their lower water vapor pressure when compared to that within the cells. Due to this gradient, water moves from the cells to ice crystals. With the progress in the freezing process, the solute concentration increases and the cells become dehydrated and ultimately lead to structural collapse. On the other hand, during rapid freezing, fine ice crystals form in both the intracellular and intercellular spaces. With fast freezing, due to the absence of a gradient in water vapor pressure, the dehydration effect is reduced and the structural and textural damages are prevented (Fellows, 2000).
Food Freezing and Frozen Food Storage
Published in Dennis R. Heldman, Daryl B. Lund, Cristina M. Sabliov, Handbook of Food Engineering, 2018
A third type of direct-contact freezing system is the immersion freezer. In such systems the product is exposed to a liquid refrigerant that is undergoing phase change as the freezing process occurs. A schematic of the process is shown in Figure 7.16, where the movement of product through the refrigerant is illustrated. The common refrigerants used for immersion freezers—nitrogen, carbon dioxide, and Freon—must be approved for food product contact. A commercial immersion freezing system is shown in Figure 7.17. The product particles or pieces pass through a compartment filled with cold refrigerant vapor where the produce is exposed to a spray of liquid refrigerant. In general, very rapid freezing of product is achieved, resulting in superior product quality when rate of ice crystal formation influences quality. Overall process efficiency is influenced by the ability to recover expansive refrigerant as the freezing process is completed.
Computerized Food Freezing/Chilling Operations
Published in Gauri S. Mittal, Computerized Control Systems in the Food Industry, 2018
Hosahalli S. Ramaswamy, Shyam S. Sablani
While it has been recognized that the quality of frozen food is affected by the size and number of ice crystals, quantitative understanding of ice crystallization processes is necessary to achieve high-quality frozen foods. Accurate data on frozen food properties and understanding of mathematical models describing heat transfer during freezing are needed for the optimized design of freezing equipment and for achieving optimum freezing processes. Freezing equipment manufacturers are continually improving and refining the many types of food freezers and updating them to meet changing market needs. In the last decade, process development has focused on improving the heat transfer between refrigerant and food product, thereby improving overall cooling capabilities, making efficient use of refrigerant to reduce freezing times, and increasing throughput for a given size of freezer. Equipment development has mainly concentrated on (1) accessibility, ease of cleaning, and maintenance, and (2) electronic control for efficient operations. In future, computers are expected to play a major role at every stage in the freezing operations, e.g., more complex models for the determination of frozen food properties, freezing times/rates, and process control.
Modulation of ice crystal formation behavior in pectin-sucrose hydrogel by freezing temperature: Effect on ice crystal morphology and drying properties
Published in Drying Technology, 2023
Youchuan Ma, Jinfeng Bi, Jianyong Yi, Shuhan Feng, Jian Peng, Shaoqiang Zou, Shusong Guo, Zhonghua Wu
The drying process is found to be significantly affected by the freezing process.[9] The ice crystals formed during freezing may significantly affect the food structure, resulting in drying properties of food quality. Numerous studies have shown that drying time is negatively correlated with the ice crystal diameter.[10,11] For example, Jin et al.[10] demonstrated that nucleation proteins could transform ice crystals into lamellar structures and larger crystals, resulting in 28.5% energy savings during freeze-drying. The sublimation of ice crystals during primary drying produces identical-sized pores. Larger pores would reduce the water vapor sublimation resistance to mass transfer.[10] Therefore, freezing optimization is an important step in FD for reducing drying time.[12] The freezing process can be divided into four stages: supercooling, heterogeneous nucleation, growth, and recrystallization.[13]
Ultrasonic freezing of polymers of various compositions before freeze drying: Effect of ultrasound on freezing kinetics and ice crystal size
Published in Drying Technology, 2023
Elizaveta Mokhova, Mariia Gordienko, Natalia Menshutina, Igor Gurskiy, Antonina Tvorogova
The morphology of ice crystals and size distribution, which affect the structure and quality of the material after freeze drying, are laid down at the nucleation stage.[2,27] It should be noted that nucleation is a stochastic phenomenon occurring over a wide range of temperatures.[28] For samples of the same composition, the nucleation temperature may differ, which can lead to a different average diameter of the formed ice crystals. Thus, in the subsequent freeze-drying step, samples in the same batch will take different times to reach the target moisture content. Which subsequently leads to the heterogeneity of the resulting batch of samples, not only in terms of the target moisture content, but also in terms of the specific surface area of the materials, mechanical strength, and consumer properties. In the article,[2] it is noted that the nucleation temperature is the main factor determining the rate of freeze drying in the first period. A strong correlation was found between the total freeze-drying rate in the first period and the nucleation temperature, i.e., the drying rate increased with increasing nucleation temperature. Therefore, another important task is to achieve controlled nucleation, as well as the correct organization of the method for measuring temperature during the freezing process.
Effect of high-voltage electrostatic field-assisted freeze-thaw pretreatment on the microwave freeze drying process of hawthorn
Published in Drying Technology, 2023
Yuchuan Wang, Zhengming Guo, Bo Wang, Jiguang Liu, Min Zhang
Different pretreatments had certain effects on the ARD of the samples compared with the untreated group (Figure 6(a)). The porosity of the samples in the H-FT group had different degrees of reduction, and the ARD gradually decreased with increasing freeze-thaw times. The differences in the ARD of HVEF-treated hawthorn were not significant, which indicated that the effect of HVEF on the structure of hawthorn was small. Although the difference in ARD showed a decreasing trend, the group difference was not significant, and there was no significant difference compared with untreated samples. However, compared with CFT2, the ARD of dried hawthorn was markedly reduced after H-FT treatment. This might be because the presence of HVEF induced a decrease in the volume of ice crystals formed in hawthorn, thus reducing the damage to the hawthorn structure by repeated formation of ice crystals during freeze-thawing. Thus, the original structure of the hawthorn was maintained. A previous study showed that excessive ice crystal formation resulted in the degradation of food quality, and smaller ice crystals caused less water loss during the thawing process, which could improve food quality.[33]