Thermal Processing Effects on Bioactive Composition and Physicochemical Parameters of Citrus grandis Juices: A Cultivar-Specific Study

Conventional thermal pasteurization is widely applied to ensure the safety of fruit juices, although its impact on bioactive compounds and functional properties may vary according to cultivar. This study evaluated the effects of conventional pasteurization on physicochemical parameters, bioactive composition, antioxidant capacity, and enzyme inhibitory activities of juices obtained from five Sicilian Citrus grandis cultivars (Todarii, Maxima, Pyriformis, Chadock, and Terracciani). Total polyphenols, flavonoids, and carotenoids were quantified, while flavanone profiles were characterized by means of HPLC analysis. Antioxidant activity was assessed using DPPH, ABTS, FRAP, and β-carotene bleaching assays, and in vitro inhibitory activities against α-amylase, α-glucosidase, and pancreatic lipase were determined. Pasteurization led to cultivar-dependent reductions in total polyphenols (up to ~40%), flavonoids (up to ~45%), and carotenoids (up to ~25%), accompanied by decreased radical scavenging capacity and reducing power. Naringin was identified as the predominant flavanone, with thermal processing inducing both degradation and release phenomena depending on the cultivar. Fresh juices exhibited stronger enzyme inhibitory activities, particularly against α-amylase and α-glucosidase. Multivariate analysis discriminated against fresh and pasteurized juices, identifying phenolics as the main contributors to antioxidant capacity. Despite bioactive reductions, functional quality was partially preserved, supporting targeted cultivar selection for optimized industrial processing.