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

temperature and is an area of current research (Willocx et al., 1993). Different systems
require different O 2 - CO 2 - N 2 ratios to achieve maximum shelf life extension. Often
excess CO 2 can be detrimental. Alternatively, hypobaric storage, whereby total pressure is
reduced, has been studied. Comprehensive reviews of controlled and modified atmosphere
packaging (CAP/MAP) technology are given by Kader (1986); Labuza and Breene (1988)
and Farber (1991). Bin et al. (1992) review the efforts that have focused on kinetically
modeling the CAP/MAP systems.
Currently experiments with very high pressure technology (1,000 to 10,000 atm)
are being conducted. This hydrostatic pressure, applied via a pressure transfering medium,
acts without time delay and is independent of product size and geometry. It can be
effective at ambient temperatures (Hoover, 1993). Key effects sought from high pressure
technology include (Knorr, 1993): a) Inactivation of microorganisms, b) modification of
biopolymers (protein denaturation, enzyme inactivation or activation, degradation), c)
increased product functionality (e.g. density, freezing temperatures, texture) and d) quality
retention (e.g. color, flavor due to the fact that only nonvalent bonds are affected by
pressure). Kinetic studies of changes occurring during high pressure processing and their
effects on shelf life of the foods are very limited and further research will be needed for
this technology to be fully utilized.
To express the above diccussed effect of different factors in a simple
mathematical form, the concept of the quality function can be used in a more general
approach. Assuming that the quality of the food depends on i different quantifiable
deterioration modes (quality factors), A i , respective quality functions can be defined in
analogy to Eq.14.
Q i (A i ) = k i t (41)
The rate constant k i of each particular deterioration mode is a function of the
aforementioned factors, namely
41