(+)-Dihydrorobinetin: a Marker of Vinegar Aging in Acacia (Robinia pseudoacacia) Wood

The use of acacia wood for the aging of vinegars is increasing because the efficient air transfer through the pores permits a good acetification rate. In this study, vinegars aged in acacia (Robinia pseudoacacia) wood barrels were analyzed and found to contain a characteristic compound, which increased during the aging process. This so far unknown compound was isolated by semipreparative LC and structurally identified by NMR spectroscopy. H-1 and C-13 NMR chemical shifts and optical rotation revealed its structure to be (+)-dihydrorobinetin, a dihydroflavonol identified for the first time in vinegars as a marker of aging in this kind of wood. This study also reports for the first time the complete assignment of C-13 NMR data for this compound. Moreover, it revealed a longer contact time with acacia wood results in higher concentrations of (+)-dihydrorobinetin found in vinegars. Another finding was that the vinegars aged with nontoasted acacia chips showed significantly higher concentrations of (+)-dihydrorobinetin than found in vinegars aged with toasted acacia chips (384.8 and 23.5 mg/L, respectively). The in vitro antioxidant activity (DPPH center dot and ORAC assays) of (+)-dihydrorobinetin was also determined. (+)-Dihydrorobinetin is reported here for the first time as a chemical marker of vinegars aged in acacia wood and can be used for authenticity purposes.