(+)-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. 1H and 13C 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 13C 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• 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.