Prechilling: the second cousin of cold chain in India?
Knowing the fact that the cold chain is one of the ways to decrease post-harvest losses, the Government of India recently gave the green light to establish 27 new cold chain projects. However, it is important to understand that cold storages are only a small portion of the required cold chain infrastructure. There is a whole other world to cold chain than simply keeping perishables ‘cool’. It incorporates reducing the temperature and maintaining the same during transportation while taking care of capacity, warehousing, and at last retail at the rack.
There has been a huge interest in setting up cold storages with limited attention to pre-cooling chambers. This has resulted in a huge gap between the demand and the available infrastructure of pre-cooling chambers (close to 99% deficit), as is evident from a report, published by the National Centre for Cold-chain Development.
Pre-cooling refers to the rapid removal of field heat shortly after the harvest of a crop. Field heat can be defined as the difference in temperature between the temperature of the crop harvested and the optimal storage temperature of that product. In general, the temperature should be cooled down till it reaches 88% of the existing difference in temperature and its optimal storage temperature. Field heat should be removed as fast as possible since, for most produce, an hour delay at field conditions of about 35°C will lead to a loss in shelf-life of about 1 day — even at optimal storage conditions .
So, how does precooling increase the lifetime of perishables?
■ by lowering the required workload of cold storage since optimum storage temperature is reached more quickly
■ by restricting and minimizing respiratory activity, thereby conserving the weight of the produce, and enzymatic degradation of the produce harvested; thus preventing softening, water loss, and wilting
■ by preventing microbial growth, such as bacteria and fungi thereby decreasing the rate of decay
■ by decreasing the rate of ethylene production and the impact on ethylene sensitive produce
■ by delaying chilling injuries for certain fruits
■ by increasing the daily intake into storage facilities which should not exceed 10% of its cooling capacity if the produce is not pre-cooled
Nevertheless, due to biological factors, the importance of rapid pre-cooling varies. According to the Indian Board of Horticulture, grapes, mandarins, berries, cherries, leeches, melons, stone fruits, sapotas, okra, tomatoes, capsicum, chili peppers, eggplant, cucumbers, green beans, peas, and spinach should be rapidly pre-cooled.
However, it is really important to increase the knowledge of our farmers as far as cold chain is concerned. Individual fruits and vegetables require specific storage conditions, starting from pre-chilling to cold transportation. Factors on which parameters of pre-chilling depend, can be listed below
■ Produce characteristics: chilling sensibility of produce takes priority or else cold shock can result in further loss. Airflow capacity should be optimized according to the vegetables stored.
■ Availability of Skilled labor: methods require various levels of skilled and trained personnel. The availability of such trained personnel has to be considered. This is of importance, particularly after the labor migration we observed during the early days of lockdown.
The importance of skilled labor is highlighted because pre-cooling can be achieved in many ways, some of which are highlighted:
● Air cooling: Use of refrigerated air in a conventional cold storage room, or in a special pre-cooling room, powered by a funnel cooler, or a forced-air cooler.
● Water cooling: Uses water to take up the heat from harvested produce. Cold or chilled water is sprayed on produce or the produce is dipped into it. Water should be able to flow through the produce rather than around it.
● Ice cooling: As the name suggests, ice is used to remove heat from fresh produce, but is not preferred given the risk of cold shock.
● Vacuum cooling: Temperature is reduced by placing produce in a metal cylinder in which the atmospheric pressure is reduced which leads to evaporation and a cooling effect.
Given the technological requirements for pre-chilling, Tan90 portable cold storages can be used (and are) as pre-cooling chambers. In addition to taking off the farm heat, Tan90 storage units also limit the respiration rate of fruits and vegetables, thereby extending the shelf life of greens at the far, end for 2.5 to 3 days. Being modular, these units can be stacked in a normal truck and can be moved together to centralized cold storages, thereby filling in the gap at the grassroots.
Technological advancements in thermal energy storage and dissipation can further decrease the operational costs of decentralized pre-cooling chambers and cold storages, and this is something we, at Tan90, have focussed on from our initial days.
The above report has been authored by Dishani Deshamukhya, who is pursuing her MBA from NIT Silchar. She is interning with Tan90, and has been providing the team with critical inputs on agri-practices and agri-finances. Tan90 provides energy-efficient cooling solutions for storage and transportation of perishables to Government organizations and businesses.