Abstract
Agricultural control systems are characterized by complexity and uncertainly. A skilled grower can deal well with crops based on his own intuition and experience. In this study, an intelligent optimization technique mimicking the simple thinking process of a skilled grower is proposed and then applied to dynamic optimization of temperature that minimizes the water loss in fruit during storage. It is supposed that the simple thinking process of a skilled grower consists of two steps: 1) “learning and modeling” through experience and 2) “selection and decision of an optimal value” through simulation of a mental model built in his brain by the learning. An intelligent control technique proposed here consists of a decision system and a feedback control system. In the decision system, the dynamic change in the rate of water loss as affected by temperature was first identified and modeled using neural networks (“learning and modeling”), and then the optimal value (l-step set points) of temperature that minimized the rate of water loss was searched for through simulation of the identified neural-network model using genetic algorithms (“selection and decision”). The control process for 8 days was divided into 8steps. Two types of optimal values, a single heat stress application, such as 40℃, 15℃, 15℃, 15℃, 15℃, 15℃, 15℃and 15℃, and a double heat stress application, such as 40℃, 15℃, 40℃, 15℃, 15℃, 15℃, 15℃and 15℃, were obtained under the range of 15℃￡T￡40℃. These results suggest that application of heat stress to fruit is effective in maintaining freshness of fruit during storage.
Highlights
Storage temperature for fruits is usually maintained constant at low level
Comparing to the two values of the rate of water loss at the same temperature, before increasing and after dropping the temperature, it is found that the values after dropping the temperature are lower than those before increasing the temperature at both the 25 ̊C and 35 ̊C conditions. These results suggest that a temperature operation that first rises to the high level (35 ̊C to 40 ̊C) and drops to the prior level has a tendency to reduce the rate of water loss, as compared to when the temperature was maintained constant throughout the control process
The reduction of the water stress caused by the heat stress suggests that the heat-stress fruits acquired a transient thermo tolerance
Summary
Storage temperature for fruits is usually maintained constant at low level. This is because the low temperature effectively reduces microbial spoilage and water loss of the fruit. A dynamic optimization technique will give us the solution It is, very difficult to treat and realize optimization control of water loss of fruits during storage when we take the response of thermo tolerance caused by heat stress into consideration. Very difficult to treat and realize optimization control of water loss of fruits during storage when we take the response of thermo tolerance caused by heat stress into consideration This is because the physiological behaviors between the temperature and the water loss of the fruit, including the effect of thermo tolerance, are quite complex and uncertain. In this study, the dynamic optimization control is carried out based on the fruit responses, aiming at the qualitative improvement of the fruit during storage
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