Cuticular wax composition of ʻCelesteʼ and ʻSomersetʼ cherry fruit
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The cuticular layer plays an important role in protecting fruits against water loss and invasive microorganisms and insects, both during on-tree development and postharvest storage. There is also experimental evidence that cuticle composition and structure may be a relevant factor accounting for firmness
and other textural attributes. Waxes are important cuticle components, together with the polymer matrices cutin and cutan. In this work, the chemical composition of waxes in the skin of 'Celeste' and 'Somerset' cherry (Prunus avium L.) fruit, which display quite different firmness levels, was investigated by means of gas chromatography-mass spectrometry (GC-MS). Fruit were picked at commercial maturity, and cuticles isolated enzimatically at harvest and after 3 days at 20°C. Total waxes were identified and quantified by means of GC-MS and GC-FID, respectively. In all cases, the most abundant constituent of cuticular waxes was the triterpene ursolic acid, which accounted for 49-56% ('Celeste') and 47% ('Somerset') of total wax composition. Important amounts of the alkanes nonacosane (6-10%, depending on cultivar and days at 20°C) and heptacosane (1-2%), as well as of the fatty acid linoleic acid (5-10%), were also found. Total alkane content was higher in 'Somerset' than in 'Celeste', but in contrast 'Celeste' cuticles were richer in triterpenes and fatty acids than those isolated from 'Somerset', thus showing some cultivar-related differences in the chemical composition of cuticular waxes.