Applications of heat stress and low temperature for qualitative improvement of fruit during storage.

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In this study, combinatorial uses of a heat stress (40℃) and a low temperature (-2℃) was investigated for maintaining the freshness of fruit during storage using intelligent control techniques and then its capability for practical use was examined.Dynamic changes in the rate of the water loss and the respiration rate of fruit during storage, as affected by temperature in the range of -2 to 40℃, were investigated. Although the rate of the water loss (or respiration rate) decreased with decreasing the temperature, they had constant values under the same low temperature. However, increasing the temperature to 40℃ from -2℃ for 12 hours and then dropping it to -2℃ provided the significant reduction of the rate of water loss.The dynamic change in the rate of water loss as affected by temperature was first identified using neural networks, and then the optimal heat stress application was investigated using genetic algorithms. Under the 6-step control process and the range of 15【less than or equal】T【less than or equal】40℃, the optimal temperature operation was the time series of {40, 15, 15, 15, 15 and 15℃}. In particular, the sudden drop in temperature from the highest level to the lowest level provided lower values of the rate of water loss than maintaining the temperature constantly at the lowest level throughout the control process.Optimal heat stressed fruits (e.g., tomato) not only have tolerance against high temperature (40-50℃), but they also had tolerance to low temperature (-2℃). Optimal heat stressed fruits significantly reduced the chilling injury of the fruit during storage. This means that a heat stress application technique is effective for lower temperature storages.Finally, a simple and low cost heat stress application technique was investigated and then applied to the storage process for Iyokan fruit which is the special product of Ehime prefecture.