Advances in Precooling techniques and their implications in horticulture sector: A Review
Abstract
Maintenance of market quality from quality loss is vital importance for the success of horticultural industry. After harvest, many horticultural products are susceptible to deterioration and it is necessary to cool them as quick as possible. The process of precooling is the removal of field heat which arrest the deteriorative and senescence processes so as to maintain a high level of quality that ensures customer satisfaction. Different precooling methods employed to cool down the produce includes room cooling, forced-air cooling, hydro-cooling, package icing, vacuum cooling and cryogenic cooling. These methods use different modes and media for their function. Room cooling and forced-air cooling use cold air, hydrocooling makes use of cold water, package iced products have direct contact with ice, vacuum cooling employs the evaporation of water and cryogenic cooling involves liquid nitrogen. Fruits are normally cooled with cold air, although stone fruits benefit from hydrocooling, while vegetables and flowers may be cooled by employing any of the above-mentioned cooling methods, depending on the physiology and market requirements. So, it has been pointed out that precooling is the most important of all the operations used in the maintenance of any desirable, fresh and saleable produce.
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Introduction
After harvest, many horticultural products are susceptible to deterioration and it is necessary to cool them as quick as possible. One important factor which is often under emphasized when considering the cooling of horticultural products is the lag time between harvesting and the commencement of precooling. Delayed pre-cooling increased the loss of water, lowers tissue firmness, and increased metabolic activities in fruits. Precooling was first introduced by Powell and his coworkers in the US Department of Agriculture in 1904. Since then precooling has been given various definitions: the removal of field heat from freshly harvested produce in order to slow down metabolism and reduce deterioration prior to transport or storage; immediate lowering of commodity field heat following harvest; and the quick reduction in temperature of the product. With a reference [1] precooling is likely the most important of all the operations used in the maintenance of desirable, fresh and salable produce. Precooling grapes to a temperature of 0 to 2°C for four hours ensures storage life to 60 days [2].
Conclusion
The importance of precooling can be clearly recognized as it is portrayed as an intricate and essential part of the proper temperature management of all horticultural crops. Precooling is in essence the removal of heat or the reduction in temperature of the perishable produce as soon as possible after harvest. This process slows the respiration rate and minimizes other deteriorative processes and thus helps to maintain quality at a high level. Precooling in conjunction with the proper storage or transportation allows for the extension of shelf or vase life of the horticultural produce which results in more satisfied customers at all levels of purchase. Within precooling a variety of different techniques exist for use in the horticultural industry. Hydrocooling, vacuum cooling, room cooling, icing, forced air cooling, and cryogenic cooling are the principal methods in commercial use at present. Each of these individual techniques also has many variations, leading to a great diversity of perishable produce which may be precooled. As consumer awareness and sophistication are ever increasing due to the growing fear of chemical residues and the uncertainty surrounding genetically modified foods presently, and with the change to organic products continuing, alternative techniques of extending shelf life and maintaining high level of quality are being investigated. Precooling is one of the techniques which adheres to this ethos and should be applied widely throughout the entire horticultural industry to attain its true potential.