Delaying the aging process of pears by maintaining cuticular waxes under high humidity storage conditions

Cuticular wax is an important factor that affects storage quality and commercial value of fruits and vegetables after postharvest. Previous studies have shown that cuticular wax of pears undergoes significant changes during storage. However, there are few studies on the effects of different humidity environments storage on the wax changes and the correlation with storage quality. In this paper, the total wax content, chemical composition and the relationship between the wax and storage quality of Korla pear stored at different relative humidity (40% - 45%, 60% - 65%, 80% - 85%) were determined. After extracting cuticular wax by chloroform extraction, chemical compositions were determined by gas chromatography-mass spectrometry (GC-MS). Eight quality parameters (e.g. qualified fruits percentage, weight loss, apparent colour, hardness, soluble solids content, titratable acidity content, ethylene evolution rate and respiratory intensity) were measured and correlation analysis were performed between total wax content, chemical compositions and storage parameters. The results showed that the compositions of fruit wax under different humidity environments were quite similar, mainly including alkanes, olefins, fatty acids, aldehydes, alcohols and esters. Nevertheless, the amount and type of each composition varied. The substances of the primary components with higher contents were nonacosane, hentriacontane, (9Z)-9-tricosene, palmitic acid, oleic acid, docosanol, 1,1-dimethoxydodecane and lanosterin. At the end of storage, the highest cuticular wax content was observed in 80%-85% relative humidity storage and the lowest in 40%-45% relative humidity storage. Compared with the control, high humidity environment delayed the aging process of pear, reduced the decrease of weight loss, hardness, soluble solids content, titratable acid content, and qualified fruits percentage, postponed the peak of respiratory and ethylene release, the 80%-85% treatment was remarkable. Different humidity environment had certain influence on wax content and chemical composition of postharvest pear. The relative humidity of 80%-85% could better maintain the total wax content, alkane and aldehydes, and delay the increase rate of fatty acids and alcohols. Among the components, esters and terpenoids have the greatest influence on storage parameters, followed by alkanes and alcohols. The results showed that the chemical composition of cuticular wax were changed under different humidity environments during storage, at the same time, there was significant correlation(P<0.01) between total wax content, chemical composition and postharvest senescence. In summary, most of the aging process were delayed due to the total wax content and chemical composition were maintained in high humidity environment, manifesting that stable chemical composition of cuticular wax play an important role in keeping good quality of postharvest pear. Overall, to understand the changes of cuticular wax in different humidity environment could provide sufficient information for further study on the effect of cuticular wax on postharvest storage performance. In this paper, the effect of storage in different humidity on the cuticular wax of Korla pear was studied. The change of cuticular wax during shelf life period of pear fruits after storage and control measures to regulate cuticular wax compositions need to be further explored. In addition, the molecular mechanism between cuticular wax chemical compositions and storage quality of Korla pear is not clear, which needs further study.