Tracing Phenolic Metabolism in Vitis vinifera Berries with ¹³C₆‑Phenylalanine: Implication of an Unidentified Intermediate Reservoir

Abstract

Understanding the regulation of phenolic compounds in agricultural products has been a topic of great interest. In V. vinifera berries, phenolics are responsible for important sensory and functional characteristics. To elucidate the ripening profile of phenolic compounds in Cabernet Sauvignon berries, the stable-isotope tracer l-phenyl-¹³C₆-alanine (Phe¹³) was incorporated in situ, and the development of labeled and unlabeled phenolics was tracked in the vineyard at different stages of maturity over two vintages. Phenolic profiles during ripening were consistent with previous research. However, individual anthocyanins accumulated with different profiles during ripening; malvidin species continually climbed in concentration, whereas other anthocyanins tended to plateau or drop near the end of the growing season. The isotopic label was predominantly incorporated into anthocyanins, presumably because of their dominant accumulation during ripening. Notably, the incorporation of label continued long after levels of Phe¹³ had dropped to below 1 nmol/berry, preventing an accurate assessment of the hypothesized turnover of anthocyanins. Although our tracer did not perform exactly as we had expected, the results of this study suggest the presence of a previously unreported pool of substrate in the phenolic pathway