Metabolic and Isotopic Correlations between D-Glucose, L-Ascorbic Acid and L-Tartaric Acid

Abstract L-Ascorbic acid in fruit juices is enriched in 13C by 4.8 δ-units relative to its precursor glucose, and this enrichment is mainly located in position C-1. On the other hand, biotechnologically produced L-ascorbic acid preserves the pattern as expected from glucose. In grapes L-tartaric acid is synthesized from glucose via L-ascorbic acid and it is one of its main products. It preserves C-atoms 1 to 4 from glucose and the measured δ13C-value is identical to that calculated from this precursor. The findings are interpreted as overlapping influences of isotope discriminations after metabolic branching and relative turnover rates leading to isotopic balances. The results can also be used to distinguish between identical products by different synthetic processes.