Effects of Phosphorus Fertilization on Physico-mechanical Properties of Citron Watermelon Rind and Biochemical Properties of Fruit Pulp

Abstract

The combined effects of phosphorus fertilization (applied as triple superphosphate, TSP; Ca(H₂PO₄)₂·H₂O, 43 to 44% P₂O₅) and storage duration were studied relative to the physico-mechanical and biochemical properties of citron watermelon (Citrullus lanatus var. citroides). Five phosphorus application rates and three storage durations under ambient conditions were evaluated. Storage duration significantly impacted both quality and mechanical traits. Moisture content decreased progressively during storage, accompanied by increases in rind lightness (L*), yellowness (b*), and chroma (C*). After two months of storage, cutting force and deformation increased significantly, reflecting storage-induced modifications in tissue structure and viscoelastic behavior. Prolonged storage was also associated with a general decline in antioxidant-related biochemical parameters, suggesting degradation of bioactive compounds over time. Phosphorus fertilization did not significantly affect (P > 0.05) fruit weight, dimensional characteristics, color attributes, puncture resistance, or cutting-related mechanical parameters. In contrast, increasing phosphorus doses significantly enhanced total phenolic and flavonoid contents, total antioxidant activity, and chlorophyll contents, indicating the effect of phosphorus on secondary metabolism and antioxidant capacity. Overall, storage duration was the dominant factor influencing the structural and mechanical behavior of citron watermelon rind, whereas phosphorus fertilization primarily governed biochemical composition and antioxidant potential.