Biotransformation of blueberry anthocyanins to bioavailable phenolic compounds by Lactobacillus

Abstract

Blueberries are one of the most anthocyanin-rich fruits, containing more than 25 forms of anthocyanins. This high anthocyanin content may contribute to the health benefits of blueberries against cardiovascular diseases, diabetes and cancers. However, the bioavailability of anthocyanins is relatively low, meaning that intact anthocyanins are unlikely to act as local antioxidants. Anthocyanin metabolites, such as phenolic acids, are easier to absorb, and are thus more bioavailable. This study has investigated the biotransformation of blueberry anthocyanins and a standard anthocyanin, malvidin-3-glucosides, into metabolites in the presence of Lactobacillus plantarum and Lactobacillus sakei at pH 3.4, 4.2, 5.9 & 7.0 and incubated anaerobically at 37oC for up to 24h. Samples were centrifuged and the supernatants were analysed using semi-preparative liquid chromatography. The metabolites were identified using high performance liquid chromatography-mass spectrometry (LC-MS). Malvidin glycosides were found to completely hydrolyse at pH 4.2 and 5.9 after 24h of incubation. The anthocyanins were quite stable under acidic conditions (pH 3.4) but were highly unstable at neutral pH and disappeared after 8h at pH 7.0 by both chemical and microbial degradation. Similar results were obtained when testing the same strains with blueberry samples, although most of the anthocyanins were not fully transformed due to their high initial concentrations. The primary metabolites were phenolic acids and aldehydes such as syringic acid, gallic acid and protocatechuic acid (Figure 1). These metabolites showed a greater antioxidant capacity than the anthocyanins themselves as the antiradical power was found to increase in the order, malvidin-3-glucoside < syringic acid < protocatechuic acid < gallic acid. Thus, the metabolites of blueberry anthocyanins may be mainly responsible for the antioxidant activity of blueberries against chronic diseases, which then contribute to a healthy heart.