Investigation of carotenoids and C13-norisoprenoids dynamics in developing grapes of Vitis vinifera cv. Blaufränkisch under varying sunlight exposure

This study investigates the evolution of carotenoids and C13-norisoprenoids in whole berries of Blaufränkisch grapes during ripening. The concentrations of these compounds were compared between the east- and west-facing sides of a north-south oriented vineyard canopy, corresponding to morning and afternoon sun exposure. Grapes were sampled at nine developmental stages, including three potential harvest times: preripeness, ripeness, and overripeness. Results demonstrated significant interactions between ripening stage and canopy side (morning vs afternoon sun exposure), indicating that sunlight exposure dynamically modulated carotenoid accumulation and degradation patterns as well as C13-norisoprenoid formation during berry development. In overripe grapes, higher β-damascenone concentrations were found on the morning sun side, whereas higher β-ionone concentrations occurred on the afternoon sun side. At ripeness, grapes exposed to the morning sun have a significantly higher carotenoid content than grapes exposed to the afternoon sun. From ripeness to overripeness, carotenoid levels declined substantially in berries exposed to the morning sun, while they remained stable in berries exposed to the afternoon sun. Regarding C13-norisoprenoids, a rapid accumulation was observed across the first five developmental stages, followed by a plateau during ripening. Interestingly, the substantial late-stage degradation of carotenoids on the morning side did not yield an increase in C13-norisoprenoids. Conversely, afternoon-exposed grapes showed a sharp terminal spike in specific volatiles, such as vitispiranes and TDN, at overripeness, despite stable precursor levels. These results highlight the impact of canopy orientation on grape secondary metabolism and suggest that, under dry autumn conditions and moderate ripening temperatures, delayed harvest could enhance the aromatic profile of Blaufränkisch by accumulating specific volatile norisoprenoids.