Formation of 2,6-DMBQ in anthocyanin-rich foods

The naturally occurring 2,6-dimethoxybenzoquinone (DMBQ) has anti-bacterial, anti-fungal and anti-cancer activities. As it is probably formed in plants via oxidative degradation of the anthocyanin malvidin and its glycosides, a targeted analysis of the DMBQ concentration of different wines and grape juices was performed. Whereas no DMBQ was detected in white wines, concentrations between 28 and 137 μg/l were measured in red wines. In vivo formation kinetics in crushed anthocyanin-rich fruits were monitored, and up to 2.84 mg/kg DMBQ were found showing that its formation was triggered by cell disruption and catalysed by intrinsic oxidases. Ethanolic extraction of grape pomace, a cheap and sustainable source of malvidin-3-O-glucoside, yielded around 1.3 g/l corresponding to 272 mg/100 g dry matter. Solid phase purification of malvidin on XAD7HP resulted in the separation of 229 mg malvidin/100 g dry matter. A basidiomycetous laccase converted the purified malvidin to DMBQ with a yield of 94% followed by adsorption on XAD16N separating 65 mg DMBQ/100 g dry grape pomace under full food-grade conditions. DMBQ may contribute to the shelf life of malvidin-rich foods and is a promising candidate as a natural alternative to other food preservatives.