Effects of polysaccharide-based edible coatings on the postharvest quality and shelf life of peeled lychee fruit
摘要
Peeled lychee fruit is highly susceptible to enzymatic browning, tissue softening, moisture loss, and microbial proliferation because of the removal of its natural peel barrier, which markedly compromises its postharvest commercial value. This study systematically evaluated the preservation efficacy of three polysaccharide-based edible coatings, namely konjac glucomannan (KGM), guar gum (GG), and sodium alginate (SA), on peeled lychee fruit stored at 4 °C for 14 days. All coating treatments mitigated quality deterioration to varying degrees, with the 1% (w/v) KGM coating treatment (KGM1) showing the most consistent performance across color stability, moisture retention, firmness, antioxidant preservation, enzyme inhibition, and microbial control. Compared with the control on day 14, KGM1 maintained higher lightness (39.89 vs. 35.81) and firmness (0.45 vs. 0.37 kg/cm²), limited weight loss to 11.62% compared with 26.49% in the control, and lowered the total bacterial count to 2.9 × 10⁴ CFU/g. KGM1 also retained higher total phenolic content (77.43 µg GAE/g FW) and total flavonoid content (4.37 mg RE/g FW), together with stronger antioxidant capacity, as indicated by DPPH radical scavenging activity of 71.95% and FRAP reducing power of 72.07 µg FeSO₄/g FW. The retention of phenolic and flavonoid compounds, together with enhanced antioxidant activity, may have contributed to the suppression of browning-related oxidative reactions, as reflected by lower polyphenol oxidase (0.189 U/g FW) and peroxidase (0.308 U/g FW) activities. In addition, KGM1 reduced polygalacturonase activity to 0.400 U/g FW, suggesting delayed cell wall degradation and tissue softening. These findings indicate that KGM1 effectively delayed the deterioration of peeled lychee by integrating physical barrier protection, antioxidant preservation, enzymatic browning suppression, and microbial growth inhibition, providing a feasible sulfur-free strategy for extending the shelf life of high-value peeled fruit.