ABSTRACT
Advances in new, cost-efcient, environmental friendly and versatile methods of food processing and preservation have been presented and implemented over the past years to meet the continually increasing consumer demands for quality foods with particular focus on their nutritional and functional aspects. The quality of processed foods is not a simple property; it depends not only on the initial integrity of the raw materials but also on the changes occurring during processing and subsequent storage that may result in potential losses and decreased bioavailability. Therefore, quality is an attribute of food, on which understandably a lot of consideration is focused. Food quality can be dened as the assemblage of properties that differentiate individual units and inuence the degree of acceptability of the food by the consumer or user (Kramer and Twigg 1968). Owing to the nature of foods as physicochemically and biologically active systems, food quality is a dynamic state continuously moving to reduced levels (with the
15.1 Introduction .................................................................................................. 529 15.2 Kinetics of Food Reactions ........................................................................... 531
15.2.1 Basic Principles ................................................................................ 531 15.2.2 Determining the Order of Reaction .................................................. 533
15.2.2.1 Differential Methods .......................................................... 533 15.2.2.2 Integral Methods ................................................................ 534 15.2.2.3 Method of Half Lives ......................................................... 534
15.2.3 Effect of Environmental Factors ....................................................... 535 15.2.3.1 Temperature ....................................................................... 535 15.2.3.2 Effect of Other Environmental Factors.............................. 541
15.3 Reaction Kinetics in Shelf-Life Prediction ................................................... 545 15.3.1 Accelerated Shelf-Life Testing ......................................................... 545 15.3.2 Temperature Dependence of Main Shelf-Life Indices .....................548 15.3.3 Shelf-Life Prediction and Management of the Food Chain ..............548
15.4 Application of Food Kinetics in Shelf-Life Prediction: Examples of Shelf-Life Modeling of Food Products ......................................................... 550
15.5 Application of TTI as Shelf-Life Predictors during Distribution ................. 559 References .............................................................................................................. 561
notable exception of the cases of maturation and aging). Therefore, for each particular food, there is a nite length of time after production within which it will retain a required level of quality organoleptically and safetywise, under stated conditions of storage. This period of time can be generally dened as the shelf life of the food product. There is no established, uniformly applicable denition of shelf life. The denition of shelf life and the criteria for the determination of the end of shelf life are dependent on specic commodities and on the de- nition’s intended use (i.e., for regulatory vs. marketing purposes). Food-related authorities have proposed various denitions that can serve as guidelines. The International Institute of Refrigeration (IIR) recommendations for frozen food (IIR 1972) introduce two different denitions. High quality life (HQL) is the time from freezing of the product for a just noticeable sensory difference to develop (70-80% correct answers in a triangular sensory test). Another type of shelf-life denition that can be extended to other types of food products is the practical storage life (PSL). PSL is the period of proper (frozen) storage after processing (freezing) of an initially high-quality product during which the sensory quality remains suitable for consumption or for the process intended. PSL is usually in the order of two to three times longer than HQL. Time of minimum durability, introduced by the EEC directive on food labeling, is dened as the time during which the foodstuff retains its specic properties when properly stored is different in principle from the aforementioned ones, in that it relates to properties of the product itself and not to considerations of its use. It is a working denition for the food scientist satisfying the often made fundamental assumption that the highest quality product is the freshly processed (or harvested) one. However, since characteristic properties are overlaid, a decision has to be made at what level the change in a certain characteristic or the development of an undesirable one can be detected by the consumer. For example, if having a specic avor means the absence of off-avors, it has to be decided at what intensity levels these avors are detectable by the consumer. Thus, this denition is closely related to the HQL denition. Chemical, microbiological, and physical tests are being used widely in the study of food quality. Characteristics used by the consumer for evaluation of a product, such as avor, color, and textural properties can be measured instrumentally or chemically. The study of the chemical and biological reactions and physical changes that occur in the food during and after processing allow the recognition of the ones that are most important to its safety, integrity, and overall quality. Physicochemical or microbiological parameters can be used to quantitatively assess quality. The values of these parameters can be correlated to sensory results for the same food and a limit that corresponds to the lowest acceptable sensory quality can be set. However, caution should be drawn to the fact that correlation of values of individual chemical parameters to sensory data is often not straightforward because overall organoleptic quality is a composite of a number of changing factors (Trant et al., 1981). The relative contribution of each factor to the overall quality may vary at different levels of quality or at different storage conditions. Food kinetics is based on the thorough study of the rates at which physicochemical reactions proceed. The area of kinetics in food systems has received a great deal of attention in past years, primarily due to efforts to
