Litchi (Litchi chinensis Sonn.) fruit deterioration occurs rapidly after harvest and is characterized by pericarp browning, pulp softening, and decay. In this study, we found that calcium chloride (CaCl₂) treatment (5 g L⁻¹ CaCl₂ solution vacuum infiltration for 5 min) affected the cell wall component contents and cell wall-degrading enzyme activities of litchi fruit during storage at room temperature. CaCl₂ treatment significantly increased the contents of Ca²⁺ and cellulose, while it decreased the water-soluble pectin content, and the activities of polygalacturonase, β-galactosidase, and cellulase in the litchi pericarp. Meanwhile, the treatment resulted in significantly increased contents of Ca²⁺, water-soluble pectin, ionic-soluble pectin, covalent-soluble pectin and hemicellulose, and upregulated activities of pectinesterase and β-galactosidase, while significantly decreasing the activities of polygalacturonase and cellulase in litchi pulp. The above results indicate that CaCl₂ treatment strengthened the cell wall structure of litchi fruit. More importantly, the enzymatic browning of the pericarp, softening of the pulp, and disease incidence were delayed. The treatment had a more pronounced effect on the pericarp than on the pulp. We consider CaCl₂ treatment to be a safe and effective treatment for maintaining the postharvest quality of litchi fruit.

Pericarp browning and fruit decay severely reduce the postharvest quality of litchi. Improving the antioxidant capacity of the fruit is an effective way to solve these problems. In our study, the appropriate zinc oxide nanoparticles (ZnO NPs) treatment and its mechanism of action on the storability of litchi was investigated. Litchi fruit was soaked in a 100 mg·L⁻¹ ZnO NPs suspension, water, and 500 mg·L⁻¹ prochloraz for 2 min, respectively. The results showed that the ZnO NPs treatment delayed pericarp browning and decay in litchi fruit and was more effective than prochloraz treatment. The ZnO NPs-treated fruit showed significantly increased contents of total anthocyanin, total phenols, and activities of DPPH scavenging, superoxide dismutase, and glutathione peroxidase, as well as the lowest activities of polyphenol oxidase and laccase. ZnO NPs generated hydrogen peroxide and superoxide anion radicals, which were beneficial in slowing down the decay and inducing antioxidant capacity. However, these reactive oxygen species also consumed catalase, peroxidase, glutathione, and glutathione peroxidase. This means that litchi should be treated with an appropriate concentration of ZnO NPs. We concluded that treatment with a 100 mg·L⁻¹ ZnO NPs suspension could induce antioxidant capacity, which is a promising and effective method to maintain the postharvest quality of litchi.

Although the effects of phytohormones (mainly salicylic acid) on the storability of longan fruit have been reported, the relationship between postharvest hormone variation and signal transduction and storability remains unexplored. The basis of physiology, biochemistry, hormone content and signalling for the storability difference at room-temperature between ‘Shixia’ and ‘Luosanmu’ longan fruit were examined. ‘Luosanmu’ longan exhibited faster pericarp browning, aril breakdown and rotting during storage. ‘Luosanmu’ pericarp exhibited higher malondialdehyde but faster decreased total phenolics, flavonoid, glutathione, vitamin C, catalase activity and gene expression. Higher H₂O₂ and malondialdehyde but lower glutathione, glutathione-reductase and peroxidase activities, while higher activities and gene expressions of polygalacturonase, β-galactosidase and cellulose, lower covalent-soluble pectin, cellulose and hemicellulose but higher water-soluble pectin were observed in ‘Luosanmu’ aril. Lower abscisic acid and methyl jasmonate but higher expressions of LOX2, JAZ and NPR1 in pericarp, while higher abscisic acid, methyl jasmonate and salicylic acid together with higher expressions of ABF, JAZ, NPR1 and PR-1 in ‘Luosanmu’ aril were observed. In conclusion, the imbalance between the accumulation and scavenging of active oxygen in ‘Luosanmu’ longan might induce faster lipid peroxidation and senescence-related hormone signalling and further the polymerization of phenolics in pericarp and polysaccharide degradation in aril.

Litchi downy blight, caused by Peronophythora litchii, is a major postharvest disease that leads to severe pericarp browning and fruit decay, significantly reducing market quality. Strengthening the fruit’s innate defense systems represents a promising strategy for minimizing these losses. This study investigated the efficacy and underlying mechanisms of ethephon treatment in controlling postharvest litchi downy blight. The results showed that treatment with 400 mg·L⁻¹ ethephon solution via a 2-min immersion significantly suppressed P. litchii infection, reduced the disease index and pericarp browning index, and enhanced the rate of ethylene production. Ethephon application notably increased 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, and the activities of key antioxidant and defense-related enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), chitinase (CHI), β-1,3-glucanase (GLU), and phenylalanine ammonia lyase (PAL). Concurrently, it up-regulated the expression of corresponding genes LcCAT, LcAPX, LcCHI, LcGLU, LcPAL. In contrast, ethephon treatment reduced the accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA). In summary, ethephon treatment suppresses postharvest litchi downy blight likely through the enhancement of both antioxidant and pathogen defense capacities. These findings provide valuable insights into the potential application of ethephon for maintaining postharvest quality in litchi fruit.

Longan fruit generally undergoes rapid quality deterioration during the postharvest stage, with the manifestation of flavor loss as well as pronounced off-odor production. Nevertheless, the unapparent aroma makes people ignore the odor change in postharvest longan. Sensory analysis serves as an indispensable method combining instrumental detection and the perceptibility of human sensation in a comprehensive evaluation of quality during production and consumption. In this study, we established the evaluating data of the appearance, flavor, taste substances, volatile profiles, and deterioration of ‘Shixia’ longan throughout room-temperature storage using instrument assessment and descriptive measurements. Our results indicated that both the appearance state and the taste condition notably engendered confusion or trouble for consumers to judge under the quality transition period. Conversely, the development of odor was highly consistent with that of quality deterioration. Some unpleasant volatile substances including alcohol (ethanol), acid (acetic acid), and esters (acetic acid methyl ester and ethyl acetate) were probably the cause of off-odor during the storage. The result of the sensory evaluation also presents a more significant relevance between the overall quality and the odor. Generally, the work paved the way to reveal the importance of odor profiles for assessing the comprehensive quality condition of postharvest room-temperature stored longan.