Freezing food

In the past, most of frozen food be cooked before consumption, providing an important contribution to the development of the microbiological safety. More recently, the focus has shifted to facilities and much wider range of products available, many of which have been specifically designed to be preserved and disseminated in a frozen state. These more " modern " frozen products can be pre-cooked food components and entire dishes that just need to be warmed before use. In addition, many frozen cakes and desserts (including ice-cream) are intended to be eaten on the defrosting or directly from the freezer without any consumer preparation step. Remove any consumer cooking step so microbiological safety is an essential prerequisite before freezing and defines processes before and during freezing. However, the quality of supply is a growing concern for consumers and a challenge for the frozen foods industry is to preserve the nutrients without prejudice to the microbiological safety.

An important step in the freezing to reduce the temperature of the foods to avoid or at least minimize, microbiological and chemical changes. However, as noted in other chapters of this book, the freezing of natural and fabricated products results in complex physical and chemical changes. In General, as the temperature falls below 0C water in food, is increasingly turning to ice. As a result, dissolved solutes are becoming increasingly concentrated in the remaining water in the liquid state, thus further reducing its freezing. Depending on their physical structure and chemical composition of natural products in the frozen state can contain up to 8% of the water in the liquid phase. This liquid phase contains a complex mixture of cellular metabolites at non-physiologically high concentration. In addition, as the ice crystals grow in the natural structure of the power they can break the intercellular and intracellu-lar walls and membranes, resulting in release and mixing the pre-shared substrates, enzymes.

Therefore, although the contents of the products at temperatures below zero, potentially reducing the rate of reactions with potentially disastrous consequences for safety, quality and supply, changes in substrate concentration and access to enzymes can act to increase the speed of such reactions. Due to physical and chemical changes that may still occur frozen, heat treatment before freezing is required for many products, especially vegetables (see below)to ensure that within a reasonable shelf life. Heat treatment prior to freezing, commonly known as 'white', is primarily designed for inactivation of enzymes that are responsible for harmful changes in the sensory quality. However, blanching reaches the objective of preserving the nutritional value, particularly for nutrients such as ascorbic acid (vitamin C), which are susceptible to enzymatic oxidation and decomposition.

In blanching step in itself can have significant effects on nutrients and, therefore, the effect of these and other steps in the process, which arise before freezing should be considered in understanding the nutritional value of the frozen products. At the beginning of the literature describing the factors that affect the nutrients in the frozen foods was considered Bender (1978, 1993). This overview summarizes the principles and draws attention to the more recent research and new products entering the frozen food supply.

Micro-organisms of importance in food products are usually divided into organisms. and those with potential to cause human disease pathogens. Saving systems in food products tend to target prevent the growth of organisms. and ensuring that no harmful levels of pathogens or their toxins). Since freezing essentially stops the activity of microorganisms for the control of microbial spoilage for an indefinite period of time, provided that, if the temperature is low enough, e.g. below 10C). However, many micro-organisms, like many other biological systems, can survive in freezing conditions and preserve their ability to multiply when the conditions become relatively more favourable. Although there are no hard and fast rules " in respect of the survival of pathogens during freezing some groups of organisms differ greatly in their susceptibility or resistance to freezing.

Higher organisms such as protozoa and parasites, are very sensitive to freezing and storage of frozen and will be destroyed. Gram-negative bacteria are more stable than the simplest, but, as a rule, are more sensitive than Gram-positive bacteria. Viruses retain their ability to infect a host cell after freezing and bacterial spores absolutely resistant to freezing. Mold and yeast vary in their sensitivity to freezing and frozen storage. For public health, survival of pathogens is an important factor. Generally speaking, if frozen foods have the potential to Harbor pathogens in dangerous concentrations, they require further treatment (e.g. cooking), to reduce these pathogens to levels that are not of concern for public health. Where low infectious dose organisms are concerned, the body must be excluded from the frozen products is fully...