The fresh melon fruit were cut into trapezoids, cubes and slices and then stored at 10 ℃ for up to 72 h. The effects of different cutting methods on the quality, and total phenol and γ-aminobutyric acid (GABA) contents of fresh-cut Hami melon were investigated. The results indicated that fresh-cut processing promoted the decrease in the color parameters L, a and b values, firmness, total soluble solid (TSS) and ascorbic acid contents, and the increase in total bacterial count and transparency, and higher wounding intensity resulted in greater changes in these indicators. Meanwhile, fresh-cut processing significantly induced the increase in L-phenylalanine ammonialyase (PAL) and glutamate decarboxylase (GAD) activity, total phenolic and GABA contents and 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) radical scavenging capacity (P < 0.05), and slicing, casuing the greatest wounding intensity, resulted in the highest PAL and GAD activity, DPPH radical scavenging capacity and total phenolic and GABA contents. These results implied that although fresh-cut processing accelerated deterioration in the quality of fresh-cut cantaloupe, it could also promote the accumulation of bioactive compounds including phenolic compounds and GABA, thus improving antioxidant capacity.

The effects of calcium chloride treatments on the storage quality and γ-aminobutyric acid (GABA) metabolism of fresh-cut lettuce were studied. Fresh-cut lettuce shreds were treated with 0%, 0.5%, 1.0%, 1.5% or 2.0% calcium chloride solution for 10 min and stored at 10 ℃ for 48 h. The quality parameters and GABA content were measured to determine the optimum treatment conditions and the mechanism by which calcium regulates GABA synthesis. The results showed that calcium chloride at different concentrations delayed the increase of mass loss rate, aerobic plate count and browning index, retarded the decrease of ascorbic acid and chlorophyll contents, and promoted GABA accumulation in fresh-cut lettuce, with 1.0% calcium chloride treatment being most effective in delaying the quality deterioration and promoting GABA synthesis. Furthermore, calcium chloride treatment increased the activities of glutamate decarboxylase (GAD), diamine oxidase (DAO), polyamine oxidase (PAO) and 4-aminobutyraldehyde dehydrogenase (AMADH), and promoted the decomposition of glutamic acid and polyamine, thus inducing the formation of GABA in fresh-cut lettuce. These results indicated that calcium chloride treatment could not only effectively maintain the quality, but also promote the synthesis of GABA and improve the nutritional value of fresh-cut lettuce during storage.

Adenosine triphosphate (ATP) treatment effects on the quality maintenance of fresh-cut cucumber and the contents of bioactive compounds such as total phenolic and γ-aminobutyric acid (GABA) in fresh-cut cucumber were studied. Fresh-cut cucumber was soaked separately in 0, 0.8, 1.2, 1.6 and 2.0 mmol/L ATP solution for 10 min. To determine the appropriate concentration of ATP treatment, fruit quality parameters, and total phenol and GABA contents were measured during storage at 10 ℃ for 72 h. Furthermore, the regulatory mechanism of ATP treatment at the appropriate concentration on total phenol and GABA accumulation. The results indicated that compared with the control group, ATP treatment maintained better color quality and lower total bacterial count (TBC), delayed the decrease in firmness and ascorbic acid content, and promoted an increase in the accumulation of total phenols and GABA in fresh-cut cucumber, the effect being most pronounced at an ATP concentration of 1.6 mmol/L. Furthermore, compared with the control group, 1.6 mmol/L ATP treatment increased the activities of phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4CL), cinnamate-4-hydroxylase (C4H), glutamate decarboxylase (GAD), diamine oxidase (DAO), polyamine oxidase (PAO) and 4-amino aldehyde dehydrogenase (AMADH), and promoted the synthesis of phenolic substances and the decomposition of glutamate (Glu) and polyamine to produce GABA, thus increasing total phenol and GABA contents in fresh-cut cucumber. These results indicated that ATP treatment could not only delay quality deterioration, but also increase total phenol and GABA contents, thereby improving the antioxidant capacity and nutritional value of fresh-cut cucumber.

This study aimed to investigate the effect of ultrasound (US) treatment on the quality maintenance of freshcut broccoli during storage. Fresh-cut broccoli was treated ultrasonically at 40 kHz and different power levels (200, 250, 300, 350 and 400 W) for 10 min and then stored at 10 ℃ for up to 96 h. The changes of appearance and microbial load were measured to determine the optimum parameters of US treatment for fresh-cut broccoli. Furthermore, the effect of the optimum US treatment on chlorophyll degradation and the changes in bioactive components in fresh-cut broccoli was studied. The obtained data indicated that US treatments at all power levels tested delayed the increase of yellowing index, L^* value, total mold and yeast count and total bacterial count, and inhibited the decrease of H value, the 300 W power being the most effective in maintaining the appearance and microbial quality of fresh-cut broccoli. US treatment at 300 W effectively inhibited the activities of chlorophyllase and Mg-dechelatase, contributing to maintaining higher contents of chlorophyll a, chlorophyll b and total chlorophyll of fresh-cut broccoli. Meanwhile, this treatment maintained higher contents of bioactive ingredients such as vitamin C, total phenols, total glucosinolates and sulforaphane, and improved the scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radicals. Therefore, these results indicated that US treatment could not only effectively slow down the yellowing of fresh-cut broccoli, but also maintain higher contents of bioactive compounds, thus playing a fresh-keeping role.

The protective effect and underlying mechanism of melatonin (MT) treatment against Rhizopus stolonifer in postharvest peach fruit (Prunus persica (L.) Batsch cv ‘Xiahui 8’) were studied. Freshly harvested peaches were inoculated with R. stolonifer following pretreatment with different concentrations of MT (0, 0.05, 0.10, 0.50 and 1.00 mmol/L) and then stored at 20 ℃ for up to 60 h. Disease development was measured to determine the most effective MT concentration. Subsequently, the effects of MT treatment on quality parameters, total phenol and lignin contents, disease resistance-related enzyme activity and gene expression in peaches during postharvest storage, and the in vitro growth of R. stolonifer were investigated. The results showed that 0.50 mmol/L MT treatment could most significantly reduce the occurrence of Rhizopus rot and maintain postharvest fruit quality. Furthermore, compared with either of them alone, R. stolonifer inoculation after MT treatment exhibited stronger disease resistance response, resulting in a marked increase in the activities of chitinase (CHI), β-1,3-glucanase (GLU), phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), peroxidase (POD) and polyphenol oxidase (PPO), the contents of total phenols and lignin, and the expression levels of defense-related genes such as those encoding CHI (PpCHI), GLU (PpGLU), PAL (PpPAL) and POD (PpPOD). Moreover, MT treatment had no significant inhibitory effect on the growth of R. stolonifer in vitro. Taken together, these results indicate that MT can initiate defense responses to pathogenic infection indirectly by priming defense, thereby reducing the occurrence of peach postharvest diseases.