VARIATIONS IN CHILLING INJURY AND EPICUTICULAR WAX COMPOSITION OF WHITE GRAPEFRUIT WITH CANOPY POSITION AND FRUIT DEVELOPMENT DURING THE SEASON

摘要

'White grapefruit from interior and exterior tree canopy positions were harvested monthly over an 8-month season, and their epicuticular wax composition and susceptibility to chilling injury during cold storage were determined. Chilling injury was quite pronounced during the entire season in exterior canopy and to a far less degree in interior canopy fruit when stored at 5 degrees C. Fruit from both canopy positions stored at 15 degrees C were free of chilling injury. Levels of wax, as measured by gas chromatography, increased throughout the season but at a more rapid rate and to higher levels in exterior canopy fruit. Levels of total wax increased greatly in fruit from both canopies when the fruit were stored at 15 degrees C, indicating that, in grapefruit, chilling injury is not directly related to the level of total epicuticular wax. The seasonal and 15 degrees C stored fruit increases were most pronounced in the aldehyde, alkane, and linear alcohol wax fractions and less in the triterpene fraction. Chromatograms of the exterior and interior canopy fruit triterpene fractions were quite different, indicating possible relationships of triterpenes, sun exposure, and chilling injury. The sun-exposed and shaded sides of exterior canopy grapefruit were assayed for chilling injury development and relative percentages of components in the triterpene fraction of the wax. Four major triterpenols were greater on sun-exposed surfaces compared with shaded surfaces, while six triterpenones showed the reverse trend. Ratios of the 10 triterpenes in exterior versus interior canopy grapefruit mirrored the respective ratios of 10 triterpenes in sun-exposed and shaded sides of the fruit, indicating that triterpenes may interact with sunlight and possibly alter the susceptibility of grapefruit to chilling injury.