Effect of Postharvest Treatments on Volatiles in 'Rio Red' Grapefruit Juice

The effect of two commercially practiced postharvest treatments, degreening and low-temperature conditioning, on the juice volatiles of 'Rio Red' grapefruit (Citrus paradisi Macf.) were studied. Early season (November) grapefruits were degreened using 3.5 ppm ethylene in a commercial packing-house to accelerate the peel color change. Non-degreened (control) and degreened grapefruits were stored under simulated market conditions for 21 days at 10 ºC, then 14 days at 21 ºC. The volatile constituents were separated on a DB-5MS capillary column by GC and identified by comparing Kovats indices and mass spectral data. Nootkatone gives a characteristic odor to grapefruit, and was higher in non-degreened fruits after 35 days of storage as compared to levels at 0 days. By contrast, nootkatone was not detected in degreened fruits after 21, 28, and 35 days of storage. D-limonene, the major component of volatile oils, decreased in both non-degreened and degreened fruits with longer storage, with highest levels observed at 0 days. After 35 days of storage, no difference was observed in the levels of linalool oxide between both treatments, while β-caryophyllene was higher in non-degreened fruits. Low-temperature conditioning (7 days at 16 ºC) is used prior to cold storage to reduce chilling injury in grapefruits. To examine effect of low-temperature conditioning and storage at 11 ºC and 5 ºC on volatile oils in Rio Red grapefruit, fruits were stored for 12 weeks and juice samples were collected at 3-week intervals. D-limonene levels sharply increased in all three treatments at 3 weeks after storage; however, after 12 weeks, D-limonene levels were similar to levels at 0 days. Nootkatone was higher in the grapefruits stored at 11 ºC than those stored at 5 ºC and CD fruits, but, the grapefruits stored at 5 ºC had higher levels of β-caryophyllene and linalool oxide compared to 11 ºC and CD fruits. This project is based upon work supported by the USDA–NIFA # 2010-34402-20875 “Designing Foods for Health” through the VFIC and Research Grant Award No. TB- 8056 - 08 from the Texas Department of Agriculture, Texas Israel Exchange and the United States–Israel Binational Agricultural Research and Development Fund.