Abstract: The surface of citrus peel is covered with a layer of wax, exerting multiple important physiological functions. The qualitative and quantitative analysis of cuticular components in the fruit peel of Satsuma mandarin (Citrus unshiu Marc.) and Bingtang sweet orange (Citrus sinensis Osbeck) were carried out by gas chromatography-mass spectrometry (GC-MS). Scanning electron microscopy (SEM) was used to observe the difference in the cuticle microstructure of Satsuma mandarin and Bingtang sweet orange. GC-MS results showed that the epicuticular wax contents of Satsuma mandarin and Bingtang sweet orange were 3.7 and 2.2 μg/cm2, respectively, and the intracuticular wax contents were 13.9 and 18.4 μg/cm2, respectively. The major aliphatic components of epicuticular and intracuticular wax in two citrus cultivars were identical, including alkanes, fatty acids, and primary alcohols, but their proportions and carbon number distribution were dependent on cultivars. Farnesol was found to be exclusively present in the epicuticular wax of Bingtang sweet orange. Moreover, triterpenoid compounds were detected only in the intracuticular wax. The cutin contents of Satsuma mandarin and Bingtang sweet orange were 44.00 and 70.00 μg/cm2, respectively, being significantly different. SEM showed irregular platelet flattened platelet waxes to be deposited on the surface of Satsuma mandarin and Bingtang sweet orange, respectively. The removal of epicuticular wax could cause a significant increase of water loss rate in Satsuma mandarin and Bingtang sweet orange (P < 0.05). Compared with fatty acids, alkanes played a more significant role in water retention in fruits. The differences in the chemical composition and microstructure of cuticle between citrus varieties may contribute to the differences in postharvest storage characteristics, which will provide important evidence for improving the storage quality of different citrus varieties.

Key words: citrus fruits, cuticle, scanning electron microscopy, gas chromatography-mass spectrometry, water loss