Humidity control or Relative humidity plays a key role in maintaining the freshness and nutrition of fruits and vegetables during cold storage, other than the temperature.
Relative Humidity (RH) can be defined as the ratio of the water vapour pressure present in air at an existing temperature to the water vapour pressure that would be present if the vapour were saturated at the same temperature. It directly affects the moisture loss from the produce during the storage period. Moisture loss often leads to defects such as shriveling, wilting and also contributes to weight loss, which is highly undesirable.
Transpiration is the process by which fruits and vegetables lose moisture from the pores present on their surface. Transpiration rates depend upon the relative humidity conditions in the storage. As the relative humidity of the surrounding air rises, the transpiration rate falls. This happens because it is easier for water to evaporate into dryer air than into more saturated air. At high relative humidity, produce maintains salable weight, appearance, nutritional quality and flavor, while wilting, softening and juiciness are reduced. Low relative humidity increases transpiration rates.
A hygrometer can be used to monitor the humidity.
‘Humidifiers’ may be installed to attain the high levels of humidity. These are the devices designed specifically for maintaining the required levels of humidity.
The benefits of humidification in food and produce cold stores are as follows:
• High relative humidity inhibits moisture loss.
• The right humidity level ensures that product quality is maintained.
• Fresh, just picked appearance increases value.
• Improved profitability through maintained product weight.
• Longer storage and greater shelf life.
Direct room humidification ensures the right humidity level evenly around the store, maintaining produce quality throughout. Different levels of humidity are required for different products. 80 to 90% RH is usually required to be maintained during storage. For some fruits, it may be as high as 95%. Careful monitoring ensures right humidity for the right produce and hence keeps the produce fresh for a larger storage period.
