Preharvest Water Restriction Improves Physicochemical and Nutraceutical Postharvest Attributes of Actinidia chinensis cv. Gold3

This study investigated the effects of three irrigation regimes (120, 90, and 75 L plant−1 day−1) on the postharvest morphometric, physicochemical, colorimetric, and nutraceutical attributes of Actinidia chinensis (Planch.) ‘Gold3’ grown under Mediterranean conditions. Fruit morphometry was not influenced by irrigation level, as fresh weight, polar and equatorial diameters, and weight loss showed no significant differences among treatments. In contrast, several qualitative traits responded sensitively to water availability after cold storage. Reduced irrigation increased flesh firmness by 33–37%, enhanced total soluble solids by 4–6%, and elevated titratable acidity by 4–7%, resulting in a slightly lower TSS/TA ratio. The lowest water supply yielded DMC values approximately 8.6% higher than the fully irrigated control, while the intermediate treatment showed a 4.4% increase. Colorimetric parameters were modulated by irrigation level, with reduced water availability decreasing L*, b, Chroma, and Hue (2–9%) and increasing a* (20–35%), indicating a shift toward less bright and less yellow pulp coloration. From a nutraceutical perspective, total antioxidant capacity increased by approximately 14–17% under reduced irrigation, whereas total phenolic content remained unchanged. Principal Component Analysis revealed a dominant quality-related axis integrating compositional, structural, and colorimetric traits, while morphological variables contributed minimally to overall variance. Considering the combined effects on water saving and fruit quality, particularly the higher dry matter content and antioxidant capacity observed under the lowest irrigation level, the 75 L plant−1 day−1 regime can be recommended as the most effective treatment, as it maximizes qualitative improvements without compromising fruit morphology. These findings demonstrate that moderate irrigation reduction enhances several desirable postharvest attributes without compromising fruit size or commercial morphology, supporting the adoption of controlled deficit irrigation as a sustainable strategy to improve kiwifruit quality in Mediterranean environments.