การประยุกต์แก๊สโอโซนความเข้มข้นสูงเพื่อยืดอายุลำไยสด

Abstract

Longan is a tropical fruit with highly rotten decay and postharvest disease which greatly shortens its shelf-life at room temperature. The objective of this work was to apply the high concentration ozone (HCO) gas to extend shelf-life of longan fruit during cold storage. The first part was conducted on the longan cv. “Daw” by fumigating it at a concentration of 4,000 ppm for 5 min. Longan were packed using 3 different types of packaging materials, namely, polyethylene bag (PE), polypropylene bag (PP) and foam tray wrapped with polyvinyl chloride (PVC) film (WF). Results show that as storage time progressed, all longans became more susceptible to disease incidences, pericarp browning, and weight loss in all treatments. Among the three different types of packaging, the HCO longan stored in PE yielded the longest storage time with a shelf-life of up to 36 days, accounting for 140% longer shelf-life than that of the control. In the second part, the effects of ozone concentration on fresh quality of longan fruit were studied. Longan was exposed to ozone gas at varied concentrations of 4,000 8,500 and 13,000 ppm with holding time of 5 10 and 15 min and packed with PE bag. Results show that the HCO longan exposed to ozone gas at 8,500 ppm for 5 min was considered an optimal treatment to extend shelf-life up to 35 days, account for 57% longer shelf-life than that of the non-ozonated longan with shelf-life of 10 days. The shorter shelf-life of HCO longan in the second part than that of the first part is possibly due to differences in quality longan between in-season (1st part) and off-season (2nd part). For third part, the kinetics of deterioration on the HCO longan was studied. At 8,500 ppm for 5 min, the HCO longan exhibited the deterioration rate constants (k) of 0.74x10-2 day-1, which were approximately 3 folds lower than that of the non-ozonated longan. The SEM images reveal that the non-ozonated longan was covered with surface epidermal hairs more than the ozonated longan. The existence of epidermal hairs may inhabitant the microorganisms and cause the shelf-life decay. From shelf-life prediction using polynomial equation, the HCO longan had a shelf-life of 36 days, which was 2 folds longer shelf-life than that of the control. The HCO treatment on the quality of fresh longan during cold storage can be further developed as an environmental friendly alternative to sulfur dioxide fumigation to extend the shelf-life of longan