The Impact of Canopy Position on the Biochemical, Nutritional, and Nutraceutical Quality Characteristics of Grapefruit Cultivars During Fruit Growth and Development

Citrus fruit quality traits are governed by canopy position, harvest maturity, and cultivar, influencing nutritional and nutraceutical profiles. Grapefruit (Citrus paradisi Macf.) is recognized for its antioxidant-rich, health-promoting properties; however, limited information exists on how canopy microclimate interacts with developmental stages to affect nutritional-quality attributes. In a two-year study, four grapefruit cultivars (Rio Red, Star Ruby, Shamber, and Flame) were evaluated to determine the effects of canopy position (outer vs. inner) and harvest time on biochemical characteristics, antioxidant potential, and pigment accumulation under subtropical conditions in Pakistan. Fruits were collected monthly from August to December (6–10 months after anthesis; MAA). The results demonstrated that canopy position and harvest time had pronounced effects on fruit quality. Outer canopy fruits presented higher total soluble solids, ripening index, sugars, pigment accumulation, and antioxidant compounds across development stages. Fruit quality improved with maturity, and peaked in mid-December with maximal total soluble solids, ripening index, sugars, and pigment content accumulation. Overall, all the cultivars showed similar profiles in the change in fruit quality traits during growth and development. Rio Red and Star Ruby outperformed Shamber and Flame across most traits, highlighting cultivar-specific differences in metabolite accumulation. Together, canopy microclimate, harvest maturity, and cultivar are key determinants of bioactive–nutritional quality traits in grapefruit. In practice, managing canopy exposure and harvest windows with cultivar choice enhances health-promoting metabolites and nutritional quality, with added gains in commercial value and tree productivity.