COMPARATIVE PERFORMANCE OF PRECOOLING METHODS FOR THE STORAGE OF MANGOES (MANGIFERA INDICA L. CV. AMRAPALI)

Abstract

ABSTRACT Precooling is an important postharvest unit operation for tropical fruits like mangoes because of its short postharvest life. Even though it is desirable that the precooling process be as fast as possible, the cooling should not result in any chilling injury to the fruits. Liquid nitrogen (LN2) is a cooling medium with ample potential for use in precooling operations because of its high cooling capacity and inertness of the vaporized nitrogen gas; however, its severe cold temperatures raise concerns on the possibility of chilling injury to the fruits. Hence, the present study was undertaken to compare a system where LN2 was employed in combination with mechanical refrigeration system as the cooling medium, in comparison to common precooling techniques for mangoes (cv. Amrapali) like hydrocooling and air cooling. The precooling performances were compared for the cooling rate, and cooling coefficient and fruit quality were assessed in terms of fruit firmness, color and chilling injury indices. The pH, total soluble solids and titratable acidity of the ripened fruits subjected to the different precooling techniques were also compared. The results of the study indicated that the LN2 system (LN2 flow rate: 20.5 kg/h; average gas temperature: –85C) had no adverse effect on the quality of the fruits, and improved the cooling coefficient of the air cooling process by 40%. Hence, judicious design of the system and control of exposure time would help in realizing the potential of LN2 in precooling operations for fruits, which would be practically useful in technologies like control atmosphere storage system in particular. PRACTICAL APPLICATIONSLiquid nitrogen (LN2) has ample potential as a refrigerant because of its excellent refrigeration capacity. The use of LN2 in cooling of horticultural produce is especially beneficial in techniques like controlled atmosphere storage, where it is desirable to have a lower oxygen concentration in the storage space. Because LN2 cooling has a high expansion ratio, during its vaporization, it also displaces the oxygen gas from the storage space. However, the use of LN2 as a refrigerant in precooling operations for fruits and vegetables is limited because of concerns of the very cold temperature of the cryogenic liquid resulting in chilling injury to the produce. The present study helps to address the same concerns and proves that if the system is so designed to avoid direct contact between LN2 and the fruits, its refrigerant potential can be successfully tapped.