Ripening process need to be controlled during handling and storage of fruits and vegetables. Ripening process need to be hastened when there is high demand in the market and ripening process need to be controlled or delayed when there is no demand in the market. Precooling, Changes in atmospheric composition, temperature manipulation, hypobaric storage and irradiation are common practices in controlling the ripening process.
Precooling: precooling refers to rapid removal of field heat from freshly harvested commodities before shipment, storage or processing. Precooling reduces spoilage and helps to retard the loss of pre-harvest freshness and quality. Precooling to required temperature inhibits the growth of decay causing microorganism, restricts enzymatic and respiratory activity and reduces ethylene production. Precooling can be carried out by following methods.
- Hydro-cooling: cooling fruits and vegetables by spraying or immersing in water.
- Vacuum cooling: low pressure cooling. Causes increased evaporation rate
- Air cooling: evaporation causes cooling but relative humidity must be maintained
- Content icing: fruits and vegetables are cooled by direct contact with ice
- Package icing: packaging of precooled fruits and vegetables is brought in contact with ice
Changes in atmospheric composition: by changing atmospheric composition, we can alter metabolic rate of fruits and vegetables. It is generally combined with low temperature to reduce metabolic activity. Atmospheric composition is altered as O2 (<8%) and CO2 (3 -5%) but depends on the sensitivity of produce. Sensitivity of produce to ethylene may be reduced by low temperature, low O2 level, low N2 level and increased CO2 level. If outside temperature is higher, air should be cooled before entering into the store.
Temperature manipulation: refrigerated storage is recommended for many perishable commodities because it retards
- Ageing due to ripening, softening, textural and color changes
- metabolic changes and respiratory heat production
- Moisture loss and wilting
- Spoilage due to yeast, mold and bacteria
- Undesirable sprouting
Hypobaric storage: storage of fruits under less than atmospheric pressure is termed as hypobaric storage. When the atmospheric pressure is reduced to 0.1 atm., the oxygen concentration is lowered from 21 to 2.1 % which is desirable for most apples. At 0.1 atm. pressure, level of ethylene is reduced to 0.1 ppm which doesn’t stimulate ripening. The ethylene concentration of mature but unripe apple is about 0.1 ppm.
Irradiation: irradiation is generally used for the prevention of sprouting of potatoes, onion etc. 103 – 104 rads is effective for controlling sprouting of potatoes and onions.