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Ice Morphology: Fundamentals and Technological Applications in Foods
Abstract and Figures
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
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... In particular, the freezing process, a traditional food technology, has habitually been associated with the storage and preservation of foods, since water's activity can be reduced by maintaining a low-temperature environment; thus, chemical and enzymatic reaction rates are decreased, preventing the growth of unwanted microorganisms and, in turn, allowing the extension of the shelf life of foods and an increase in the conservation of valuable nutritional and organoleptic attributes [2][3][4][5]. In practical terms, ice morphology (circularity, size distribution, clast roundness, fractal dimension, among others) is a relevant parameter during the freezing process of solutions and/or liquid foods [8], since it is closely related to the growth and formation of ice crystals (cooling temperature and heat transfer area), the crystal growth rate that affects ice nucleation and, later, ice crystals' generation and the temperature and presence of solutes [11]. ...
... Thereby, some microscopy technologies have been successfully used for the observation of ice crystals in foods, such as optical microscopy (LM) [16], transmission electron microscopy (TEM) [17], scanning electron microscopy (SEM) [18], and confocal laser scanning microscopy (CLSM) [19]. Moreover, indirect or nondestruc- In practical terms, ice morphology (circularity, size distribution, clast roundness, fractal dimension, among others) is a relevant parameter during the freezing process of solutions and/or liquid foods [8], since it is closely related to the growth and formation of ice crystals (cooling temperature and heat transfer area), the crystal growth rate that affects ice nucleation and, later, ice crystals' generation and the temperature and presence of solutes [11]. ...
... In contrast, a quick freezing rate produces an ice morphology with small crystals at locations inside and outside of the cells, and, as a consequence, high-quality frozen foods. (2) The freezing temperature should be kept constant, because any fluctuations in the storage freezing temperature tend to reduce the quality of frozen foods; for example, drip losses after thawing, which are mainly due to ice morphology changes as a result of recrystallization [8]. ...
Freezing is an effective technology with which to maintain food quality. However, the formation of ice crystals during this process can cause damage to the cellular structure, leading to food deterioration. A good understanding of the relationship between food microstructure and ice morphology, as well as the ability to effectively measure and control ice crystals, is very useful to achieve high-quality frozen foods. Hence, a brief discussion is presented on the fundamentals/principles of optical microscopic techniques (light microscopy), electronic microscopic techniques (transmission electron microscopy (TEM) and scanning electron microscopy (SEM)), as well as other non-invasive techniques (X-rays, spectroscopy, and magnetic resonance) and their application to measuring ice formation rates and characterizing ice crystals, providing insight into the freezing mechanisms as well as direct monitoring of the entire process. And, in addition, this review compares (the negative and positive aspects of) the use of simple and cheap but destructive technologies (optical microscopy) with detailed microscopic technologies at the micro/nanometer scale but with pretreatments that alter the original sample (SEM and TEM), and non-destructive technologies that do not require sample preparation but which have high acquisition and operational costs. Also included are images and examples which demonstrate how useful an analysis using these techniques can be.
... Thus, microscopic displacement and alteration in casein micelles and concomitant textural-functional changes can be anticipated. Also, Petzold and Aguilera (2009) and Pham (2008) reported that, at early stages of freezing, dendrite or hexagonal ice crystals are the most common ice forms in foods, hence, the same can be safely assumed for cheeses as well. However, detailed studies on ice crystals in cheeses are scarce, and this presents an important knowledge gap. ...
... During freezing, the product is subjected to a temperature of −18 • C or below resulting in a decreased rate of deterioration of fruits and vegetables (Jha et al., 2017). The physical, textural, and nutritional qualities of frozen commodities are dependent on the size and distribution of ice crystals (Petzold & Aguilera, 2009). Rapid or quick-freezing results in a multitude of fine sized ice crystals, distributed evenly on the outside and inside of cells, thereby ensuring minimum damage to the texture, which preserves the quality parameters of the food products . ...
Fruits and vegetables are rich in essential nutrients such as minerals, vitamins, and antioxidants; however, they have short shelf life. Freezing is a superior method of preservation compared to other techniques with respect to nutrient retention and maintenance of sensory attributes. However, several physical and textural quality changes associated with freezing and thawing pose a serious problem to the quality of frozen products. Some of the disadvantages associated with the currently employed methods for freezing fruits and vegetables include low rates of heat exchange in blast freezers, shape limitation in plate freezers, high cost of operation in cryogenic freezing, and freezing solution dilution in immersion freezing. Therefore, novel freezing technologies have been developed to achieve controlled ice nucleation and crystallization, enhanced freezing rate, decreased phase transition time, and maintained temperature stability. This review discusses some of the most recent approaches employed in freezing and points to their adoption for maintaining the quality of fruits and vegetables with extended storage.
... The fried and frozen okra after one month of storage (FF1) is shown to have the highest total flavonoid contents (64.08 mg QE/100g) among other treatments, but significantly lower than the total flavonoid contents of the fresh sample (105.1 mg QE/100g). These results confirmed that the frozen product still has changes during freeze storage and can induce different changes affecting the bio-accessibility of phytochemical compounds as compared to fresh vegetables [26]. No significant differences were observed in the flavonoid contents of fried and frozen okra during storage. ...
Very few studies have thus far evaluated the impact of various processing and preservation techniques (blanching, frying, freezing, dehydration, and sun drying) on the levels of total phenolics, flavonoids, and antioxidant activities of okra. The primary objective of this study was to evaluate the effects of different processing and preservation methods on the levels of phenolics, flavonoids, and antioxidant activities of okra. The ethanolic extracts of each sample were analyzed before and after preservation and storage for a period of three months. The results showed a significant improvement (p < 0.05) in total phenolic content (134.1 mg GAE/100g) and DPPH (1-1-diphenyl1-2-pricrylhydrazyl) scavenging activity (IC50 value of 3.0 mg/mL) in blanched okra when compared to fresh okra (86.35 mg GAE/100g and IC50 value of 3.8 mg/mL, respectively). Fresh okra exhibited the highest flavonoid content (105.75 mg QE/100g), while sun-dried okra samples stored for three months exhibited a decrease in total phenolic content (14.45 mg GAE/100g), total flavonoid contents (13.25 mg QE/100g), reducing power activity (23.30%), and DPPH scavenging activity (IC50 value of 134.8 mg/mL). The DPPH inhibition activities of all okra treatments showed a significant and positive correlation with the okra phenolic and flavonoid content (r = 0.702 and 0.67, respectively). The reducing power activity (%) of okra treatments exhibited a strong correlation (r) with phenolic contents (r = 0.966), and the correlation with flavonoid contents was 0.459. Generally, different processing and preservation methods of okra revealed that the impact on total phenolic and flavonoid contents, as well as antioxidant activities, was slightly significant among samples preserved using the same method during storage. In addition, blanched and frozen okra resulted in the highest retention of phenolic contents and antioxidant activities.
... Ice formation on various surfaces of material and particle plays a fundamental role in many ways [1][2][3][4][5], including the atmospheric science, cloud seeding, and food preservation. In most * Author to whom any correspondence should be addressed. ...
Using molecular dynamics simulations, we investigated the effect of external electric field on ice formation with the present of a substrate surface. It turns out that the electric field can affect the ice formation on substrate surface by altering the dipole orientation of interfacial water molecules: a crossover from inhibiting to promoting ice formation with the increase of electric field strength. According to the influence of the electric field on ice formation, the electric field strength range of 0.0 V/nm – 7.0 V/nm can be divided into three regions. In the region I and region III, there are both ice formation on the substrate surface. While, the behavior of interfacial water molecules in the region I and region III are distinguished, including the arrangements of oxygen atoms and the dipole orientation distribution. In region II, ice formation does not occur in the system within 5 × 200 ns simulations. The interfacial water molecules show a disorder structure, preventing the ice formation process on substrate. The interfacial water molecular orientation distribution and 2-dimentional free energy landscape reveals that the electric field can alter the dipole orientation of the interfacial water and lead a free energy barrier, making the ice formation process harder. Our result demonstrates the external electric field can regulate the behavior of interfacial water molecules, and further affect the ice formation process. The external electric field act as a crystallization switch of ice formation on substrate, shedding light into the studies on the control of ice crystallization.
Widely used to preserve foods for long-term preservation, freezing is a standard method of preserving food goods. This technique is highly energy-intensive and time-consuming. Utilising shock freezing techniques helps to accelerate the process. The current paper analyses information regarding the technology and application of shock-freezing technologies, including those utilising electromagnetic and electric fields. The results of experiments conducted using a refrigerator equipped with an electromagnetic system are reported. In order to achieve the research objectives, coils were installed in the refrigerator to induce an alternating electromagnetic field with an electromagnetic induction value of up to 0.6 mT. Preliminary experiments were carried out using sodium chloride solutions with various concentrations found in perspective frozen food products.
An installation is described for continuous crystallization of liquids by freezing. The installation performs liquid preliminary cooling under predetermined temperature; adding gas into cooled liquid and their intermixing; delivering mixed liquid and gas through the refrigerated evaporator; winding round mixed liquid and gas into the refrigerated evaporator; a pumpless refrigeration circuit, including compressor, water condenser, cooling tower, indirect refrigerated evaporator, expansion valve, low pressure receiver and required refrigeration accessories, for the realization of cooling volumetric crystallization of liquid flowing through the refrigerated evaporator. These processes cause the formation of a bubble slurry with crystal nuclei, gas bubbles and concentrated, unfrozen liquid; preparation means are described for transportation and further storage or use of bubble slurry...
Freezing is an excellent preservation method for foods [1,2]. The quality of frozen foods is closely related to the size and distribution of ice crystals. Existence of large ice crystals within the frozen food tissue could result in mechanical damage, drip loss, and thus reduction in product quality.
A new technique for characterizing the structure of firn and bubbly ice is presented. This technique, based on observation of etched (sublimation) surfaces in coaxial reflected light, enables une to see simultaneously the pore network of the firn or bubbles in the ice and the crystal boundaries. At the same time, the main stages of image processing used to transform the initial photographs into clean binary images are described.
The article contains Sections titled: 1.Introduction and Classification2.Quality Specifications and Analyses3.Mix Ingredients3.1.Fats3.2.Milk Solids-Not-Fat and other Protein Sources3.3.Sweeteners3.4.Stabilizers and Emulsifiers4.Manufacture of Mix5.Freezing Mix to Produce Ice Cream5.1.Dynamic Freezing5.2.Quiescent Freezing5.3.Flavoring Ingredients5.4.Impulse/Hand-held/“Novelty”/Fancy-molded Products6.Physical Structure and Properties7.Storage and Transportation8.Legal Aspects9.Economic Aspects Frozen desserts in the meaning assumed here are emulsions that are frozen while being whipped to incorporate air and are consumed while still frozen, usually as a scooped product or as a single-serving item. Mix ingredients typically include sources of fat, protein, sweeteners, stabilizers, and emulsifiers. Further classification depends on the presence of nonfat dairy ingredients as the protein source, to make frozen dairy desserts, and the presence and quantity of milk fat, to make ice cream. Frozen desserts are manufactured by the production of a mix, via blending of ingredients, pasteurization and homogenization, freezing that mix dynamically to incorporate air and produce small and discrete ice crystals, incorporation of discrete flavoring particulates (fruits, nuts, etc.) and either packaging and further freezing (hardening) the semifrozen ice cream product or shaping it into novelty or hand-held products (with or without stick insertion) followed by hardening. Quality is often defined by chemical and microbial composition, quantity of air incorporated, and size of the major structural elements (ice crystals and air bubbles). Maintenance of quality post-manufacturing depends heavily on temperatures of storage and distribution.
It is not possible to provide a complete coverage of all aspects of ice cream and frozen desserts in one chapter. However, various aspects are covered in numerous books (1,2), book chapters (3-8), and review papers (9-11).