Epsilon Open Archive

Abstract

Preserving cucumber (Cucumis sativus L.) quality by film wrapping is common practice in Sweden. Nevertheless, no theoretical background is available to explain the choice of the films currently used. A better understanding of the phenomena involved in preserving quality by film wrapping of greenhouse cucumbers can be achieved by means of mathematical modelling of the gas exchanges. An apparatus controlled by a computer was developed to measure gas exchanges in fresh produce. The transpiration and respiration rates evolution of film-wrapped cucumbers was investigated by emulation of the different gas levels present in the packages. A modification of this set-up was used to study the effect of various films on preserving the quality of cucumbers. In further experiments, the influence of surrounding conditions on the respective role of cuticular and stomatal permeability in the gas exchanges was investigated. It appeared that a reduction of moisture loss was of highest importance in the preservation of cucumber mass. Both respiration and transpiration rates were strongly influenced by the surrounding temperature and relative humidity. The transpiration rate under constant conditions decreased rapidly resulting in severe loss of quality directly after harvest. Film wrapping reduced significantly the effect of surrounding temperature and relative humidity. Moreover the introduction of a modified atmosphere inside the packages reduced both respiration and transpiration rates. However, the appearance of water vapour condensation inside the film favours microbial hazard. Based on data from the experiments and known physiological and physical phenomena, a mathematical model of the gas exchanges was designed. Two versions were derived to study the gas concentration in a jar corresponding to the experiments, as well as giving a closer insight into what happens between the epidermis and a film. These models take into account many parameters relative to the cucumber such as permeability, degree of opening or distribution of stomata. Furthermore, film properties such as thickness, size of perforation or permeability could also be investigated. Simulations from the implementation of the mathematical model enable theoretical studies of the importance of those parameters when direct measurements are not possibl