Storage Temperatures and Conditioning Effect On Bioactive Compounds During Prolonged Grapefruit Storage

Chilling injury is physiological disorder occurring in citrus fruits when fruits are stored at low temperatures for prolonged period. Various treatments are used to reduce incidence of chilling injury in citrus such as pre-storage temperature conditioning, intermittent warming, use of different waxes and vegetable oils and modified atmosphere packaging. Pre-storage conditioning of citrus fruits prior to cold storage is commercially practiced by storing the fruits at 16°C for 7 days and later transferring them to cold temperature below 5°C.  Physiological and metabolic studies determining the effects of conditioning on chilling injury in citrus are reported. However, studies on the influence of conditioning treatment on bioactive compounds in grapefruits are limited.  In the current study, three storage treatments in Star ruby grapefruit were compared. Fruits were stored for 16 weeks at 11°C, 2°C and conditioned at 16°C for 7 days and later stored at 2°C. Samples were collected at an interval of 4 weeks and were analyzed for vitamins and bioactive compounds such as limonoids, flavonoids, furocoumarins and total phenolics. Concentration of β-carotene was significantly higher in fruits stored at 11°C and conditioned fruits as compared to fruits stored at 2°C. No significant difference was observed in vitamin C content, TSS, acidity and ripening ratio between treatments. Flavonoids content was significantly higher in fruits stored at 11°C, with no difference between conditioned and fruits stored at 2°C. Conditioned fruits showed higher furocoumarins content, taste scores and less decay development as compared to fruits stored at 11°C and 2°C.  Fruit quality degraded in fruits stored at 11°C with eight fold higher decay incidence as compared to other two treatments after 16 weeks of storage. While conditioning helped to reduce chilling injury, fruits stored at 11°C showed no chilling injury. It can be concluded that for prolonged storage, low temperature conditioning treatment is preferable to reduce chilling injury and to maintain taste and quality of fruits. However for short storage period, 11°C temperature is more effective to maintain quality. It is possible that growers can implement these treatments depending upon the period of time the fruits will be stored to increase shelf life and to maintain fruit quality and nutrition.