Metabolism of ferulic acid by two lactic acid bacteria

Lactic acid fermentation of vegetable products, which are a rich source of phenolic acids, is a technique to prolong the shelf-life. It has been known that phenolic acids not only influence growth of Lactobacillus sp. but also that different Lactobacillus strains are able to metabolise the phenolic compounds. Ferulic acid (FA) is a major phenolic acid present in vegetable products and was chosen to use in the fermentation experiments. In this study, it was aimed to investigate the effect of different FA concentrations (0, 0.5, 1.5 and 3 mM) on the growth as well as to quantify the conversion products of FA of two lactobacillus strains. The two lactic acid bacteria were Lactobacillus plantarum (LMG6907) and Lactobacillus collinoides (LMG9194). The strains were grown until end-stationary phase in MRS medium at 30 °C. Inoculation was done at 1 %. Also samples were taken to identify and quantify FA and its conversion products. Quantification was done by LC-DAD, while identification was performed by UPLC-HDMS-Q-TOF. From the fermentation experiments, it was observed that none of the FA concentrations clearly affected the growth of both lactobacilli. However metabolism of FA by these bacteria was different, and was dependent on the added FA concentration. Lactobacillus plantarum converted FA into 4-vinylguaiacol and hydroferulic acid. These conversion products appeared in different stages of the growth phase, and were formed depending on the added FA concentration. Lactobacillus collinoides converted FA only into 4-vinylguaiacol, and to a much lesser extent than Lactobacillus plantarum. Also, a clear effect of the added FA concentration on the extent of conversion to 4-vinylguaiacol was observed for Lactobacillus collinoides fermentations. From the results it can be suggested that metabolic pathways on phenolic acids between the different lactic acid bacteria are different.