Effect of two mulberry (Morus alba L.) leaf polyphenols on improving the quality of fresh-cut cantaloupe during storage

Mulberry leaf polyphenols (MLP) with good biological activities have not been applied to the preservation of fresh-cut (FC) fruits and vegetables. In present study, MLPs (Jialing20 and Naxi) were firstly used as natural preservatives in FC cantaloupe to improve its quality. FC cantaloupes were treated with 5 mg mL−1 MLPs (Naxi and Jialing20) and stored at 25 °C for four days. MLP-treated samples exhibited significantly better retention in color, firmness, soluble solids content, titratable acidity, total phenolic content and weight compared with samples treated by sterile distilled water (p < 0.05). The ranking of antioxidant activity was: Naxi MLP-treated FC cantaloupes > Jialing20 MLP-treated FC cantaloupes > untreated FC cantaloupes, indicated by higher DPPH radical-scavenging activity and reducing power. MLP treatment inhibited bacterial growth, contributing to improving the safety of FC cantaloupes. The antibacterial activity of Jialing20 MLP was significantly higher than that of Naxi MLP, but the total phenolic content of Naxi MLP was significantly higher than that of Jialing20 MLP (p < 0.05). Five major monomers (gallic acid, chlorogenic acid, caffeic acid, rutin and isoquercitrin) were detected in Naxi and Jialing20 MLP by HPLC. Moreover, p-coumaric acid was detected only in Jialing20. The monomers of different contents in MLP could account for different antibacterial activities between Naxi and Jialing20 MLP. These results indicated that Naxi MLP could be valorized as a promising natural antioxidant and Jialing20 MLP as a natural antimicrobial agent inhibited foodborne bacterial pathogens growth. Hence, MLP improved the quality of stored FC cantaloupe and can be applied to preserve minimally processed fruit.