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This study was conducted to investigate the effects of magnesium (Mg) supplementation on the growth performance, muscle fiber development and flesh quality of Megalobrama amblycephala fed a high-carbohydrate (CHO) diet. In vivo, six experimental diets, a control diet (30% CHO, C), and five Mg supplementation levels (0 (HC1), 200 (HC2), 400 (HC3), 800 (HC4) and 1200 (HC5) mg kg−1, respectively) of high-CHO diet (45% CHO), were formulated and then fed to M. amblycephala (initial weight 43.15 ± 0.43 g) for 13 weeks. Results showed that the HC1 diets remarkably decreased weight gain rate (WGR), specific growth rate (SGR), water holding capacity (WHC), pH 24 h postmortem, collagen content, textural properties (hardness, tenderness, chewiness and resilience), muscle fiber density, succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) activities, as well as transcriptions of ampkα2, pgc-1α, mrf-4, myf-5 and myf-6 compared with the C group, but muscle AMP/ATP ratio, ATPase activities and mstna and mstnb transcription showed an opposite trend. The HC3 group of fish obtained relatively high values of WGR, SGR, muscle lipid and protein content, collagen content, textural properties (hardness, tenderness, chewiness and resilience), fiber density, SDH and MDH activities, AMP/ATP ratio as well as transcriptions of ampkα1, pgc-1α, myod, myog and myf-5 compared with other HC groups. In vitro, the isolated primary hepatocytes from M. amblycephala were assigned into four experimental groups: a control group (5.5 mM glucose, Control), a high glucose group (30 mM glucose, HG), an AICAR group (30 mM glucose + 250 μM AICAR, HGA) and an MgSO4 group (30 mM glucose + 2 mM MgSO4, HGM). Results showed that MgSO4 treatment remarkably increased p-Ampk/t-Ampk ratio, Pgc-1α protein content and transcriptions of ampkα1, ampkα2 and pgc-1α compared with the HG group. Overall, based on regression analysis for SGR, the optimal Mg level of M. amblycephala fed high-CHO diets was 366.67 mg kg-1, which was consistent with the above results that fish fed HC3 diets displayed higher the growth performance, muscle fiber density and flesh quality of M. amblycephala.

The Yali pear (Pyrus bretschneideri Rehd.) is susceptible to superficial scald during prolonged cold storage and at shelf life. This study investigated the effects of 1-methylcyclopropene (1-MCP) and modified atmosphere packaging (MAP) on changes of fruit quality and superficial scald during cold storage and at shelf life in Yali pear. Compared with MAP, the combination of MAP and 1-MCP (MAP+1-MCP) treatment reduced the carbon dioxide and ethylene content inside the packaging bag. The 1-MCP, MAP, and MAP+1-MCP treatments reduced the superficial scald index, malondialdehyde content, O2−· production rate and relative conductivity and inhibited the accumulation of α-farnesene and conjugated trienes in the peel. 1-MCP and MAP+1-MCP treatments maintained a higher phenolic content and enhanced the catalase and superoxide dismutase activities in the fruit, while reduced activities of lipoxygenase and polyphenol oxidase in the peel preceding the onset of superficial scald. Comprehensive analysis indicated that the MAP+1-MCP treatment is the most effective method tested for improving the quality of Yali pears during cold storage and at shelf life.

According to synthetic pathway of plant chlorogenic acid (CGA), the expression patterns of genes encoding enzymes that are associated with CGA synthesis were studied in normally developed Xuehua pear fruit. The study demonstrated that CGA content in peel and flesh of Xuehua pear decreased as fruit development progressed, with a higher level in peel. The expression levels of PbPAL1, PbPAL2, PbC3H, PbC4H, Pb4CL1, Pb4CL2, Pb4CL6, PbHCT1 and PbHCT3 genes decreased in fruit, which was consistent with the pattern of variation in CGA content. That indicated that these genes might be key genes for influencing fruit CGA synthesis in Xuehua pear. However, Pb4CL7 gene expression profile is not consistent with variation of CGA content, hence, it may not be a key gene involved in CGA synthesis.