Improving the flavor of fermented foods: Biotransformation of hydroxycinnamic acids into volatile aroma compounds by lactic acid bacteria from dairy products

The sensory characteristics of foods are significantly impacted by the presence of 4-vinylphenols, volatile aroma compounds with very low-perception thresholds, produced by decarboxylation of hydroxycinnamic acids (HCAs) ubiquitous in nature. In foods produced by bacterial fermentation of HCA-rich materials, like sourdough bread and pickled vegetables, strain-selection is key to produce the desired sensory properties. Our goal was to screen the ability of lactic acid bacteria (LAB) isolated from dairy products to produce 4-vinylphenols. The decarboxylating activity of LAB strains from the OSU–Parker Endowed Chair collection with potential to produce phenolic acid decarboxylase (22 strains) was evaluated after incubation with HCAs for 36 hr at 32°C in the dark. Decarboxylation was monitored using a novel high-throughput spectrophotometric method based on hypsochromic shifts when HCAs are transformed into 4-vinylphenols and compared to uHPLC-DAD-ESI-MS, monitoring for longer retention times, shorter λ230-500 max than their precursor, and characteristic m/z. Enterococcus mundtii, Lactobacillus plantarum and Pediococcus pentosaceus decarboxylated p-coumaric, caffeic and ferulic acids producing their respective 4-vinylphenol derivatives. Other 7 strains only decarboxylated p-coumaric and caffeic acids, while 1 decarboxylated only caffeic acid and 1 decarboxylated only p-coumaric acid. Ten strains were not able to biotransform any HCA. p-Coumaric acid had the highest biotransformation efficiency, followed by caffeic acid and lastly ferulic acid. To our knowledge, this is the first study showing decarboxylating activity by Enterococcus mundtii strain. This work can help improve LAB strain selection for the design of fermentation starters for food applications, ultimately improving the sensorial characteristics of fermented HCA-rich foods.