Preparation of alginate oligosaccharide and its effects on decay control and quality maintenance of harvested kiwifruit

•Alginate oligosaccharide (AOS) was prepared and characterized.•AOS inhibited postharvest decay and maintained quality of kiwifruit.•AOS inhibited pectin solubilization, and induced antifungal compounds.•AOS repressed cell-wall-degrading gene expression and enzyme activity in kiwifruit.•AOS elevated antioxidant gene expression and enzyme activity in kiwifruit. Alginate oligosaccharide (AOS) is a biological carbohydrate formed from the degradation of sodium alginate. AOS used in this study was enzymatically prepared and had varying degrees of polymerization (2–8). AOS applied to harvested kiwifruit stored at 25 °C inhibited gray mold, blue mold, and black rot. AOS inhibited pectin solubilization, gene expression of pectin methylesterase and polygalacturonase, and the corresponding enzyme activity of their encoded proteins in kiwifruit. In contrast, AOS induced antioxidant gene expression and enzyme activity, including catalase and superoxide dismutase. The level of total phenols and flavonoids in kiwifruit was also elevated. AOS treatment also had a beneficial effect on fruit quality. Collectively, the results indicate that postharvest treatment with AOS inhibits postharvest decay and prolongs fruit quality by suppressing cell wall degradation and eliciting antioxidants in harvested kiwifruit. AOS has the potential to be used to preserve and extend the postharvest quality of kiwifruit.