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A hot-water dip for 2 min at 52-53 degrees C prevented decay for at least one week in lemon fruit inoculated with Penicillium digitatum. The mode of action of hot water in reducing decay was investigated by studying the effects of this treatment on the pathogen and on the resistance mechanisms of the fruit. The hot-water dip had a transient inhibitory effect on the pathogen, arresting its growth for 24-48 h. During this lag period, the combined effects of the pathogen and the hot-water dip induced the build up of resistance in the peel. Lignin production in the inoculated sites began within 24 h after inoculation or wounding. When inoculation was followed by the hot-water dip, lignin accumulation continued for a week. Inoculated lemons that were not dipped in hot water rotted completely within 3 days after inoculation and their lignin content did not rise or even decreased. The scoparone concentration in the inoculated sites of hot dipped fruit started to rise 24 h after treatment and reached a level sufficient to inhibit the pathogen within 2 days after treatment. Parallel to scoparone accumulation, scopoletin was detected in inoculated and heat-treated lemons. Without the pathogen challenge or wounding, heat treatment by itself was not able to induce any of the above-mentioned defensive effects. Our data do not support the involvement of ethanol-extractable aldehydes, associated in the literature with wound gum, or of citral in decay inhibition in hot-water dipped lemons.

A model for atmosphere in a package containing fresh fruits was analyzed theoretically and validated by experiments with red bell pepper fruit. The model was based on two processes: fruit respiration and film permeability. Mathematical analysis showed that when rates of 0, consumption and CO, evolution due to respiration are equal, and film permeability to CO, is greater than that to O,, the time course curve of CO, concentration has a maximum. In a closed system, the time course of the sum of the gases could indicate a change of respiratory quotient. These results are independent of model for respiration. To predict extent of overshoot and for a computerized simulation, the equation of Michaelis-Menten type with noncompetitive inhibition was adopted to describe respiration. Utilizing computer simulations enabled evaluation of film specifications and package dimensions best for a given commodity.

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