Tracing
Phenolic Metabolism in Vitis
vinifera Berries with <sup>13</sup>C<sub>6</sub>‑Phenylalanine:
Implication of an Unidentified Intermediate Reservoir
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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-<sup>13</sup>C<sub>6</sub>-alanine (Phe<sup>13</sup>) 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 Phe<sup>13</sup> 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