144 Produce Degradation: Reaction Pathways and their Prevention
temperature abuse, the effect of temperature on respiration rate and on the O 2 and
CO 2 transmission rates of films must be introduced in Equation 5.1 with Equation
5.4. It should be noted that when distribution occurs at ambient temperature, the
optimal permeability of the film must be calculated for the highest temperature likely
to be encountered. The modified atmosphere reached at lower temperatures, however,
will not be optimal for preserving the sensory qualities of the commodity. Software
developed in the Netherlands predicts changes in modified atmospheres for the case
of variable temperature (linear interpolation) [28]. After this last step, the packaging
parameters should be tested, since numerous variables are not taken into account in
the theoretical calculations, which are based on an extreme simplification of fruit
and vegetable physiology. For example, models do not take into account microbial
growth which may be responsible for a fourfold increase in the apparent respiration
rate of soybean sprouts within 14 h at 20°C [38]. Some models [29] can also simulate
catabolic deviation (commonly called anaerobic or fermentative catabolism), but
many of the parameters required in the model are difficult to determine experimen-
tally. Numerous other parameters can also interfere; for example, some plant tissues
are sensitive to carbon dioxide, maturation (stage of maturity and ripeness), chilling
injury, etc.
5.4 CONCLUSION
The effects of gases on the quality attributes of fruits and vegetables have been
investigated and commercially used for more than 70 years. Yet the question posed
recently by Salveit [150] about the possibility of finding an optimal controlled
atmosphere is still controversial. Salveit [150] defined this optimal CA as “the
storage conditions that produce the best quality product,” but as stated by Harker et
al. [151], the quality of fruits and vegetables is a relative concept depending on
consumer beliefs, attitudes, perceptions, and preferences. Therefore, the quality
keeping targets of CA will have to be adapted to the consumer’s expectations.
Moreover, as discussed in this chapter, modifying gas composition may have oppo-
site effects on quality attributes. The natural variability in the physiological responses
of plant tissues to gases and their changes during storage make the choice of a stable
optimal atmosphere empirical in real conditions. Nevertheless, new developments
are designed to overcome this problem. Veltman et al. [152] proposed a dynamic
control system that monitors ethanol concentration in the headspace of the CA room
and regulates the O 2 concentration during apple storage. This system takes into
account batch variability and physiological changes during storage but ignores most
other causes of spoilage.
In any case, CA storage of fruit is continuously improving and, when conducted
reasonably in terms of duration and temperature, this technique gives satisfactory
results [153]. Modified atmosphere packaging is still a more difficult issue. Because
the atmosphere is regulated passively, the variability of respiratory parameters is of
major importance. Optimization of the MAP system would require the determination
of the respiration rate of each batch to be packed. It should also be recalled that