A. Nathan Reed
Once fruit are harvested, the main goal is to maintain freshness and quality. Cooling is the primary mechanism used to minimize reduction in quality. A fruit is a living entity and continues to metabolize following harvest. Respiration is a major part of metabolism and is the process of breaking down stored carbohydrates to produce energy. A warm fruit has a higher rate of respiration, which leads to accelerated ripening, depleted energy reserves, and decreased potential storage life. The faster a fruit respires, the quicker it will ripen and eventually deteriorate. For example, lowering the temperature of 'Granny Smith' apples from 20 to 0°C decreases the rate of deterioration by a factor of five. Exposing fruit to direct sunlight can lead to elevated respiration rates and internal fruit temperatures that greatly exceed the surrounding ambient temperature. Removing fruit from direct sunlight is the first step in the cooling process. Placing fruit in the shade or using mechanical covers and reflective materials can significantly decrease surface and internal fruit temperatures. Lowering fruit temperature by 10°C reduces respiration rate by a factor of two and also reduces reactivity to ethylene, a gaseous ripening hormone.
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