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.

Ice morphology: fundamentals and technological applications in foods.

Tubular ice system for scale-up of progressive freeze-concentration

Crystallization techniques in wastewater treatment: An overview of applications.

In conventional processes, such as evaporation, higher levels of concentration can be reached compared with freeze concentration or membrane techniques. However, the advantage of the freeze concentration technique is based on the quality of the product obtained due to the low temperatures used in the process, which makes it a very suitable technology for the processing of fruit juices. There are two basic methods for concentrating solutions by freezing: suspension and film freeze concentration. Suspension freeze concentration systems (FCS) already have operating equipment in the food industry, while film FCSs, also called layer crystallization, is still at an experimental stage. This review summarizes the most important studies relating to the suspension and film freeze concentration in fruit juices and sugar solutions, illustrating the different possibilities that freeze concentration has in the fruit juices industry; it also presents trends and suggests improvements for the future development of this technology. It is noted that most recent publications refer to the film FCS. The technology used to design, build and maintain layer crystallization equipment is simple and it can be available to any operator in the food industry, layer systems will be used in the future if their results can be improved in terms of ice purity and degree of fluid concentration.

Review. Freeze Concentration in the Fruit Juices Industry

A thorough literature survey was conducted on the freezing‐melting (FM) process for desalination. Collected literatures were studied and analyzed to identify the current state‐of‐the‐art of the FM process, and its practical limitations. The main advantages of the FM process are the requirement of low energy and low temperature operation compared to thermal desalination. Other advantages are less scaling or fouling and fewer corrosion problems, ability to use inexpensive plastics or low‐cost material, and absence of pretreatment. The three broad classes of FM process are: direct contact freezing, indirect contact freezing, and vacuum freezing. Different types of processing options in each class are discussed with their operating principles and merits and downsides of each process.

Freezing‐Melting Process and Desalination: I. Review of the State‐of‐the‐Art

Progressive freeze-concentration was effectively applied to concentrate glucose in a model solution. Effective partition constants of the solute between the liquid and solid phases were determined experimentally. The constant was strongly dependent on the stirring rate at the ice front and the advance rate of the ice front. Increasing stirring rate and reduced rate of advance lowered the effective partition constant: an improvement in freeze concentration performance. A concentration polarization model was useful to describe the effects of the operating conditions on the effective partition constant.

Effective Partition Constant of Solute between Ice and Liquid Phases in Progressive Freeze-Concentration

Progressive freeze-concentration utilizes the concentration phenomena of a solute at the ice-solution interface moving from one end of a vessel to the other end. It is characterized by having only a single ice crystal in the system so that the separation of the ice crystal from the concentrated solution is very easy compared with the conventional method of freeze-concentration. Progressive freeze-concentration was applied to a solution containing glucose and/or blue dextran as a model liquid food. The freeze-concentration ratio and apparent partition coefficient of a solute between the ice and the solution phases were strongly dependent on the moving speed of the freezing front and the stirring speed at the ice-solution interface. A lower moving speed and a higher stirring speed produced a better freeze-concentration ratio.

Progressive Freeze-Concentration of Model Liquid Food

Progressive freeze-concentration was applied to concentrate tomato juice. Effective partition constants of the solute between the solid and liquid phases were experimentally determined for total solid and potassium chloride (KCl)-equivalent salts. The partition constants were strongly dependent on the stirring rate at the ice front and the advance rate of that front. Increasing stirring rate and reducing advance rate of the ice front lowered the effective partition constant and improved freeze concentration performance. The partition constant was different between total solid and salts suggesting a different mechanism in the partition phenomena between the two components. Tomato juice of 4.3 wt% in solid content was concentrated up to 18.8 wt%. After the reconstitution of freeze concentrated tomato juice based on Brix, no substantial differences, except for salt content, were observed in acidity, vitamin C content, or color quality compared with before the concentration.

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Progressive Freeze-Concentration of Tomato Juice

A physical method is proposed that uses a cooling plate with many small holes to prevent initial supercooling in progressive freeze-concentration, and thus avoid serious contamination of the ice produced. The higher chance for ice nucleation of the water molecules in the holes due to the temperature gradient in the cooling plate resulted in the initial supercooling being completely prevented. Accordingly, the purity of the ice initially formed was substantially improved when compared with that by the standard vessel without holes in the cooling plate.

https://www.tandfonline.com/doi/pdf/10.1271/bbb.62.2467

Ling Liu

Papers

Tubular ice system for scale-up of progressive freeze-concentration

Effective Partition Constant of Solute between Ice and Liquid Phases in Progressive Freeze-Concentration

Progressive Freeze-Concentration of Model Liquid Food

Progressive Freeze-Concentration of Tomato Juice

Prevention of Initial Supercooling in Progressive Freeze-concentration.