Our group prefer frozen food. In Malaysia, frozen food help people that working and has hectic life to minimum the preparation time to prepare for meal during breakfast, lunch and dinner. Nowadays, there are many food industry that produce frozen food and there are lot of brands, varieties in size, color and packaging of frozen food that can be able to reach in supermarket and event at the small retailer shop. The brands of frozen foods that usually can be seen in supermarket are Ayamas, Marina, Ramly and Nikudo Seafood. Frozen food does not involved processing food only, but it also can involve raw material of food such as chicken, fishery product, fruit and vegetable, bakery product and sugary product. Rather that bought frozen food at the supermarket, the easier ways to obtain frozen foods is by prepare it by yourself using home refrigerator. This process involved the low temperature part of refrigerator.
To maintain food in frozen condition, frozen storage is the most prefer. Generally, frozen storage requires temperature of -18oC or below. This frozen storage able to preserve foods for months or even years (Potter, 2013). Such food that suitable to be frozen are beef, lamb, most fruits and vegetable, fried foods, packaged chicken and bakery products. This type of food able to be store in long time under temperature of -18oC. The storage periods obtain according to this temperature for the food given are in range 10-12 months.
The rearrangement and the random motion of molecules in matrix is reduce by the freezing process. As the low temperature involve in the freezing, thus the reactions in the matrix take place in slow rates. The reactions and states in the matrix also can be effected by the presence of ice and the increase of the solute due to the change due to freezing process. The present of ice during the freezing process occur as during the freezing, water is converted into ice. Thus, this formation of ice removes water from food system that cause the water activity reduced. Reduce in water activity inhibit others reaction in food (Rahman, 2007).
The production of ice crystal is due the water turn into ice when cooling. Firstly, during the freezing process, the sensible is removed then followed by the latent heat of the freezing. At temperature 0oC, pure water freeze into ice crystal and for the entire freezing process, the temperature will remains constant. Generally, about 80% of water that associated in the food materials will freeze at the temperature range -1oC to -5oC. This is range is known as zone of maximum ice crystal formation. This zone involve the release of latent heat of freezing that resulting in the formation of ice. The size of ice crystal dictate by the rate of food material when passes through the temperature zone. The formation of larger ice crystals is due to the slow freezing process while the formation ice crystals is due to the rapid freezing (Neoh et al., 2016).
The highest temperature at which ice crystal have a stable existence in a food material is called freezing point. Freezing point is varies and different among food as water contents and other amount of solid dissolved that dissolve in water are different. Thus, the requirement time to food reach their freezing point to reach solidity frozen state also different event come from same cultivar grown (Potter, 2013).
In commercial used, there are three basic freezing method that are freezing in air, freezing by direct immersion in refrigerating medium and freezing by indirect contact with refrigerant. Still-air ‘sharp’ freezer, blast freezer and fluidized freezer are example of air freezing that used various velocity of cold air to move the particles of material to be frozen. For freezing by direct immersion in refrigerating medium, this method involve the direct contact of food with refrigerant by spraying the cold liquid to the food or to the package of the food and by submerging the food to the cold liquid. The commercial immersion method are heat exchanger fluid, compressed gas and refrigerant spray. Commercial indirect contact freezing involve the slush freezer, single plate, double plate and pressure plate. The food or the food package will contact with surface that being cooled by refrigerant and does not contact with the refrigerant directly (Potter, 2013).