Melatonin Treatment Affects Wax Composition and Maintains Storage Quality in ‘Kongxin’ Plum (Prunus salicina L. cv) during Postharvest

Abstract

Cuticular wax is an essential barrier against biological and abiotic stress and is also an important factor affecting fruit storage quality. This paper investigated the effect of melatonin treatment on cuticular wax and the storage quality of plum fruit at low temperature storage of 4 ± 1 °C. ‘Kongxin’ plum was treated with 150 μmol·L−1 melatonin, dried overnight at room temperature 25 ± 1 °C, and then stored at 4 ± 1 °C for 40 d. The microstructure of the fruit epidermis was examined after 0, 20, and 40 d of storage, and the wax composition and fruit storage quality were measured at 10 d intervals. The results demonstrated that melatonin promoted the disintegration and thickening of rod-shaped waxy crystals of ‘Kongxin’ plum fruit and inhibited the combination of disintegrated wax and inner wax. Melatonin maintained fruit firmness and decreased the correlation between fruit firmness and other storage quality parameters. The correlation between firmness and wax composition was enhanced. Melatonin promoted long-chain alkanes that were positively correlated with firmness and water retention and strengthened the correlation between the length of the alkane chain and storage quality parameters but reduced the difference between alkane isomers and storage quality parameters.

The Relationships between Waxes and Storage Quality Indexes of Fruits of Three Plum Cultivars

“…Therefore, the firmness of plum fruit was significantly positively correlated with TSS content TA content ( Figure 7 ), which has been illustrated in grape [ 45 ] and apricot [ 50 ]. There was a negative correlation between firmness and soluble sugar content, which was consistent with the findings of Lin et al [ 26 ]. Weight loss had a negative correlation with TA content and positive correlation with the soluble sugar content, which showed that weight loss and soluble sugar increased as TA was consumed as a respiratory substrate [ 45 ].…”

“…Cuticular wax extraction was performed using the method proposed by Lin et al [ 26 ]. Cuticular wax was extracted from three varieties of plum fruits stored for 0, 10 and 20 d. Fruits of the same shape and size ( n = 10) were selected, and each fruit was extracted in three 500 mL beakers for 30 s in turn so that all the fruits were immersed and agitated for 30 s in chloroform/methanol ( v / v : 4/1) under a fume hood, which ensured that the fruit epidermis was not damaged.…”

“…Values were expressed as percentages (%). The values of firmness, respiration rate, TSS and TA were determined in triplicate [ 25 , 26 ].…”

“…It is a local excellent plum cultivar produced in Liuma Town, Zhenning County, Anshun City, Guizhou Province [ 25 ]. Prunus salicina ‘Kongxin’ (KXL) is named after the natural division of the fruit stone and flesh at maturity and enjoys the reputation of ‘Maotai in plum’ and is mainly cultivated in Yanhe County, Tongren City, Guizhou Province [ 26 ]. Prunus salicina ‘Cuihong’ (CHL) is a late-mature variety selected from the fruiting offspring of Chinese prunus which is named for its red skin and crisp, sweet flesh and is primarily planted in Sichuan, Chongqing, Guizhou and other southwest regions [ 27 ].…”

Impact of Pre-Storage Melatonin Application on the Standard, Sensory, and Bioactive Quality of Early Sweet Cherry

“…According to these authors, melatonin activates the accumulation of abscisic acid and, in turn, also regulates the transport of water across the membrane and cuticle. Nije et al [ 41 ] and Lin et al [ 42 ] also observed maintenance of firmness and weight in the treated fruit due to melatonin-promoted synthesis of long-chain alkanes that were positively correlated with water retention and firmness.…”