Post harvest Management of Horticultural Crops (2+1)

Factors for effective cold storage

Factors involved for effective cold storage of the produce

• Product quality: Fresh horticultural produce intended for storage should be free from physical damage, of optimum maturity and free from infections.
• Temperature: Low temperature storage is recommended for perishables as it retards respiration and metabolic activity, aging due to ripening, softening and textural and colour changes, moisture loss, spoilage due to diseases and undesirable growth (sprouting/ cooling). Maintenance of uniform temperature constantly, continuously and also adoption of optimum low temperature for each specific produce are very essential.
• Relative Humidity: The relative humidity of the air in storage rooms directly affects the keeping quality of the produce held in them. If it is too low, wilting or shrivelling is likely to occur, if it is too high, it may favour the development of decay. An RH of 85-90% is recommended for most perishables.
• Air circulation and package spacing: Air must be circulated to keep a cold storage room at an even temperature throughout the storage. This is required to remove respiratory heat. Entry of outside air and proper spacing of containers on pellets are also important.
• Respiration rates, heat evolution and refrigeration: When the storage of fresh produce is considered, it should be remembered that these commodities are alive and carry on all activities of living tissues, the most important being respiration. During this process, energy is released in the form of heat which varies with the commodity and the temperature. This `vital heat' expressed in BTU (British thermal units) is of paramount importance in calculating the refrigeration load of the commodity.
• Weight loss in storage: Loss of water from harvested horticultural crops is a major cause of deterioration in storage. Some loss can be tolerated but losses great enough to cause wilting or shrivelling must be avoided. Under good handling conditions with recommended humidity and temperature, moisture loss can be held under control.
• Sanitation and Air purification: Good air circulation alone is of considerable value in minimizing surface moulds. Accumulation of odours and volatiles may contribute to off flavours and hasten deterioration.
• Temperature management: Refrigeration (Low temperature and humidity) requirements vary with different kinds of fresh produce and the maturity stages. For most of the fresh fruits and vegetables (except onion, garlic) the relative humidity in cold storage should be kept in the range of 85 to 95%. Temperature Management involving storage at optimum temperature requirement of each produce (as shown in the tables) is very essential to maintain quality and extend storage life. Chilling injury, to which the tropical fruits and vegetables are susceptible/sensitive, is a major problem, if they are stored at lower than optimum temperature.

Key words

• Refrigeration – is the process of removing heat from an enclosed space or commodity. Main function is to lowering the temperature and maintaining the lower temperature.
• Cooling - it refers to any natural or artificial process by which heat is dissipated.
• Cryogenics – process of artificially producing extremely cold temperature by using cryogenic refrigerants such as liquid nitrogen.
• Cold – it is absence of heat. To decrease the temperature, heat must be removed rather than adding cold.
• Refrigeration ton/tonne – is the unit used to quantify the refrigeration load.
• One tonne of refrigeration - is defined as the energy removed from the one metric tonne (1000kg) of water to freeze within 24hr at 00C.
• One tonne of refrigeration =13898kj/hr = 3.861kw
• One tonne of refrigeration is about 10% larger than 1 ton of refrigeration (3.517 kW).
• Capacity requirement - 1 Ton(3.5 kw) of refrigeration required to cool 18 T produce.
• Variation in whole cold storage should not exceed ± 10C, whereas it should not exceed ± 0.50C in one position
• 1kg of melting ice absorbs 325kj of heat