Bioconversion of Pinot noir anthocyanins into bioactive phenolic compounds by lactic acid bacteria

Abstract

There has been increasing interest in red wine anthocyanins in relation to changes brought about by lactic acid bacteria in the human digestive system. Anthocyanins are modified multiple times prior to being absorbed, so that intact anthocyanins are unlikely to survive the process, although the parent compounds may still act as local antioxidants within the digestive system. Metabolites such as phenolic acids are easier to absorb, and are thus more bioavailable. This study has investigated the biotransformation of the representative Pinot noir anthocyanin, malvidin-3-glucoside, into metabolites by Lactobacillus plantarum at pH 3.4, 4.2, 5.9 and 7.0 incubated anaerobically at 37°C for up to 24 hours. The metabolites were identified by HPLC-MS. Anthocyanin glycosides were found to be completely hydrolyzed by all selected strains at pH 5.9 after 24 h of incubation. The anthocyanins were quite stable under acidic conditions (pH 3.4) but were highly unstable at neutral pH due to both chemical and microbial degradation. The main metabolites were phenolic acids such as gallic acid and protocatechuic acid. They showed greater antioxidant activity than the parent anthocyanins, as indicated by radical scavenging assays and through an assessment of reducing strength using cyclic voltammetry.