Internal modified atmospheres of coated fresh fruits and vegetables: Understanding relative humidity effects*
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The objective of this chapter is to use steady-state mathematical models to understand the influence of relative humidity (RH) on the performance of hydrophilic films formed as coatings on fruits, and to explain in part the conflictive results found in the literature. The fruit system model is analyzed as a Modified Atmosphere (MA) model system. The MA model is described as a function of the internal atmospheres. The chapter uses the lac model and the tac model for the specific case of complete surface coverage and gas exchange mainly through pores. Gas exchange depends on coating permeability and thickness for achieving internal MA. The assumptions considered for the model are steady-state condition, constant temperature, no effect of CO2 on respiration rate, and no internal atmosphere composition gradients within the fruit. The model consists of equations that describe hit respiration rate, diffusion through skin and coating, and the coating permeability dependence on the RH. It is possible, when using the approach described, to observe and understand the interaction of storage conditions (e.g. RH) and composition of film coatings applied to a fruit surface. This analysis can explain, in part, the variability of results observed when coatings are applied on a commercial scale and in research. The approach supports the idea that film coating thickness and permeability play an important role in internal gas modification of coated fruits. 2005 Elsevier Ltd All rights reserved.