Production, Stability, and Antioxidative and Antimicrobial Activities of Two l-Ascorbate Analogues from Phycomyces blakesleeanus: d-Erythroascorbate and d-Erythroascorbate Glucoside

d-Erythroascorbate (d-EAA), a five-carbon analogue of l-ascorbate (l-AA), and d-erythroascorbate monoglucoside (d-EAAG) are accumulated in Phycomyces blakesleeanus grown on glucose (99.5 and 1084 μg/g mycelial dry weight, respectively) and also excreted into the culture medium. Both compounds showed UV spectral properties and ionization constants similar to those of l-AA. d-EAAG was much more stable to aerobic oxidation than d-EAA and l-AA at acidic pH. d-EAAG is synthesized from d-erythroascorbate by a mycelial glucosyltransferase activity that uses UDP-glucose as glucose substrate donor with K m = 2.5 mM and 41.3 μM for d-EAA. This glucosyltransferase activity was maximal in the stationary growth phase in parallel with maximal production of d-EAAG. The presence of d-arabinose or d-arabinono-1,4-lactone in the culture medium produces the maximal accumulation of d-EAA and d-EAAG (about 30- and 4-fold with respect to that obtained in glucose culture). Both compounds showed greater antioxidant activity than l-AA and other standard antioxidants, with a capacity similar to that of l-AA to inhibit the growth of Escherichia coli.