Lactic acid bacteria decarboxylates hydroxycinnamic acids under acidic environments

Some lactic acid bacteria (LAB) enzymatically decarboxylate hydroxycinnamic acids (HCAs) as a detoxification mechanism, yielding 4-vinylphenols. These compounds can in turn react with anthocyanins to form more stable chromophores, called pyranoanthocyanins, which are potential candidates as food colorants. However, LAB growth conditions differ from the ones needed for pyranoanthocyanin production. This study aimed to determine if Lactiplantibacillus plantarum, Enterococcus mundtii and Pediococcus pentosaceus strains could perform decarboxylation under acidic conditions that favor pyranoanthocyanin formation. Decarboxylation efficiencies towards p-coumaric, caffeic, and ferulic acids were tested at pH 4.1 and 6.0 for up to 24 h. The reaction was monitored by HPLC-PDA, concentrations were calculated with standard curves, and reaction kinetics were evaluated. The 3 LAB decarboxylated HCAs at pH 4.1, but at lower rates than at pH 6.0. For L. plantarum, 4-vinylphenol, 4-vinylcatechol, and 4-vinylguaiacol formation rates were higher at pH 6.0 (1.5 h^-1, 0.38 h^-1, and 0.08 h^-1) than at pH 4.1 (0.24 h^-1, 0.34 h^-1, and 0.05 h^-1), with similar trends among bacteria. Decarboxylation yields of p-coumaric and caffeic acids were ∼80 and ∼58 %, respectively, regardless of the strain and pH. Ferulic acid decarboxylation yields with L. plantarum (∼88 %) were similar at pH 4.1 and 6.0, but yields were lower at pH 4.1 when incubated with E. mundtii and P. pentosaceus (∼25 %). Reduced bacterial activity may have impacted the final decarboxylation yields obtained.