Relationship between fruit fresh-keeping effect with cold storage and peel wax content, chemical composition and surface micro-morphological structure in 'Gonggan' mandarin (Citrus reticulate)

Abstract: 【Objective】The present study was carried out to reveal the relationship between fruit freshkeeping effect with cold storage and peel wax content, chemical composition and the surface micro-morphological structure in'Gonggan'mandarin(Citrus reticulate), and to provide scientific support for the optimizations of postharvest physiological regulation and storage technology aming at this famous specialty citrus cultivar in Zhaoqing, Guangdong Province.【Methods】Mature'Gonggan'mandarin fruits(280 d after full blossom, the surface was fully yellow) were harvested in mid-December and packed in plastic film air-conditioned bags(100 cm × 60 cm) with micropores(Φ 3 mm, 18 pores per bag). Then the fruits were divided into two groups randomly and stored for 90 d under natural room temperature(Control, 14.2± 2.8 ℃) and cold storage temperature(cold storage, 6.5 ± 0.5℃), respectively. During the storage period, the fruit weight loss rate and decay incidence, contents of ethanol and acetaldehyde,malondialdehyde(MDA) content and electrolyte leakage of plasma membrane were tested and analyzed, and the responses was analyzed to peel wax content, chemical composition as well as surface micro-morphological structure at storage for 30, 60 and 90 d.【Results】During the 90-day storage period,with the fruits stored at cold temperature, the content of vitamin C and organic acid contents were significantly lower than those of the control, soluble sugar content changed very little, and there was no significant difference in fruit sugar/acid ratio compared with those stored for 0 d, the accumulation of ethanol and acetaldehyde was significantly inhibited, and the daily average weight loss rate, malondialdehyde content and the electrolyte leakage of plasma membrane were significantly smaller than those of the control. Electron microscopy observations showed that the peel cerotegument of'Gonggan'mandarin fruits degraded rapidly under room temperature storage, while that of the fruits under cold storage was effectively protected, but also persevered the surface micro-morphological structure of the fruit in an excellent status, which was significantly different from the control. The results of Gas Chromatography-Mass Spectrometer analysis showed that cold storage significantly inhibited the decrease of wax content of'Gonggan'mandarin fruits, and the total wax content and the contents of four mamajor components—long-chain fatty aldehydes, long-chain fatty acids, long-chain aliphatic hydrocarbons, and long chain fatty primary alcohols were all higher than those of the control. The contents of branched alkanes, alkenes and alkenals in peel of'Gonggan'mandarin fruits were still notable under cold storage for 90 d.【Conclusion】The excellent fresh-keeping effect of'Gonggan'mandarin fruits under cold storage was closely related with the effective protection to the surface micro-morphology, wax content as well as the chemical composition of fruits in storage.