Cooling of agricultural produce.

LiveJournal Tags: Cooling of agricultural produce,Effect of storage temperature on agricultural produce,Post harvest technology

During harvest time, the temperature of harvested produce is almost the same as ambient temperature.
Sometimes it can be high as 40⁰ degrees depending on the surrounding environment.
If temperatures are high, the respiration rate of the produce increases consequently increasing the evolution of ethylene, a gas responsible for ripening and senescence.
The objective cooling of produce is to slow down the rate of respiration thus prolong its shelf life.
PRE-COOLING
Pre-cooling is the rapid lowering of the field heat from freshly harvested produce before a comprehensive cooling regime is undertaken so as to maintain its quality.
Methods of pre-cooling vary from plant produce to produce. For example when cut flowers like roses are harvested, they are dipped in a bucket containing water mixed with a fungicide before being taken to a cold room.
Conversely tea is kept under a shed or in a cool place after harvest as the application of water to it, will reduce its storage life and encourage rotting.
Other produce like grapes should not be immersed in water as this will remove the natural wax layer on the fruit.
The natural wax is important in enhancing long storage life; furthermore it is a quality requirement of the market.
For most crops, storing them where cool air is circulating, under a shed, is sufficient to remove field heat.
Precautions to consider during cooling agricultural produce
Inappropriate cooling temperatures or methods may subject produce to abnormal ripening or chilling injury.
Abnormal ripening is mostly observed in fruits. They either ripen very fast or fail to do so when exposed to room temperature.
During cooling, a high relative humidity is maintained to prevent an excessive loss of water.
Such loss may result to wilting, shriveling, flaccidness or loss of nutritional value of produce.
Ethylene is an important gas produced naturally in fruits and vegetables as it promotes ripening.
However, during storage it should be absent or present in minute amounts; ripening is desired after the produce has reached the customer.
To prevent its production during storage, cooling must be done rapidly.
High ethylene producing commodities like fruits should not be stored together with low ethylene producing commodities like vegetables.
The produce must also be cooled at temperature which is above freezing point for temperate commodities or chilling point for tropical and subtropical commodities.
Chilling or freezing of produce affects the flavor of fruits its quality in terms of or will result to chilling injuries.
Unfortunately, these methods are not used by small scale farmers because they are at times at far flung areas away from power lines and the cost involved.
The quicker the temperature of the produce is lowered after harvest, the longer the storage life.