Harvest maturity modulates light-induced anthocyanin biosynthesis in postharvest cranberry (Vaccinium macrocarpon) fruit

Postharvest light treatments can enhance anthocyanin accumulation in berry fruit, but the extent to which these responses depend on developmental stage at harvest remains poorly understood. This study evaluated the effects of blue, red, and wide-spectrum white light applied for 7 or 14 days to cranberry ( Vaccinium macrocarpon ) fruit harvested at the green, white, and turning stages. Anthocyanin accumulation was strongly influenced by harvest maturity and light spectrum. Blue light induced the greatest anthocyanin accumulation in fruit harvested at the green and white stages and was accompanied by increased expression of the late anthocyanin biosynthetic genes ANS (anthocyanidin synthase) and UFGT (UDP-glucose:flavonoid 3-O-glucosyltransferase). In turning-stage fruit, all light treatments enhanced anthocyanin accumulation relative to darkness. Changes in skin color closely mirrored anthocyanin accumulation across treatments. Metabolite profiling further revealed contrasting responses among phenolic subclasses: anthocyanins responded strongly to postharvest illumination, whereas proanthocyanidins were influenced primarily by harvest maturity and showed limited responsiveness to light treatments. Flavonols exhibited intermediate, compound-specific responses. In contrast, total phenolics, soluble solids, and titratable acidity were only minimally affected by postharvest illumination and largely followed developmental trends. Ethylene evolution was stimulated by all light treatments in green fruit, showed a transient increase under blue light in white fruit, and was unaffected in turning fruit. These findings demonstrate that the effects of postharvest spectral illumination on cranberry fruit are strongly dependent on harvest maturity and differ among flavonoid subclasses.