the handbook of food engineering practice crc press chapter 10 ...

10.1 INTRODUCTION
Quality is an attribute of food, on which understandably a lot of consideration
is focused. Food quality
can be defined as the assemblage of properties which
differentiate individual units and influence the degree of acceptability of the food by the
consumer or user (Kramer and Twigg, 1968). Due to the nature of foods as a
physicochemically and biologically active systems, food quality is a dynamic state
continuously moving to reduced levels (with the notable exception of the cases of
maturation and aging). Therefore, for each particular food, there is a finite length of time
after production it will retain a required level of quality organoleptically and safetywise,
under stated conditions of storage. This period of time can be generally defined as the
shelf life of the food product. There is no established, uniformly applicable definition of
shelf life. The definition of shelf life and the criteria for the determination of the end of
shelf life are dependent on specific commodities and on the definition's intended use (i.e.,
for regulatory vs. marketing purposes). Food related authorities have proposed various
definitions that can serve as guidelines. The International Institute of Refrigeration (IIR)
recommendations for frozen food (IIR, 1972) introduce two different definitions. 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 definition 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 organoleptic 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, and defined as the time during which the foodstuff retains its
specific 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.
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