Effect of Plant Water Deficit Irrigation on the Postharvest Nutritional Quality Parameters and Antioxidant Pathway of ‘Soreli’ Kiwifruits

This study investigated the effects of regulated deficit irrigation on quality and postharvest characteristics of ‘Soreli’ kiwifruit (Actinidia chinensis Planch.). Plants were irrigated at 100% (control), 80%, and 60% of the standard water supply. Fruit quality was monitored by assessing weight loss (WL), firmness, soluble solids content (SSC), and color stability. Bioactive compounds, such as polyphenols (POL), flavonoids (FLAV), ascorbic acid (AA), β-carotene (Car), and chlorophyll (Chl) content and antioxidant enzyme activities, including ascorbate peroxidase (APX), superoxide dismutase (SOD), and catalase (CAT), and the 2,2-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assay were also evaluated. Results indicated that reduced irrigation at 60% of water supply enhanced antioxidant enzyme levels, without negatively affecting fruit quality parameters: greater resistance to firmness loss, higher soluble solids accumulation, and better color stability. In the early stages of cold storage, fruits under the 60% irrigation treatment showed higher POL, FLAV, and ABTS values, with polyphenols exceeding 200 mg GAE 100 g−1 FW and FLAV content ranging from 4.69 to 5.53 mg CE 100 g−1 FW. The 80% irrigation treatment showed a moderate biochemical response without altering quality. Controlled water deficit can enhance antioxidant activity and bioactive compounds, improving fruit quality and the environmental and commercial value of ‘Soreli’ kiwifruit.