Antimicrobial activity of D-3-phenyllactic acid produced by fed-batch process against Salmonella enterica

Five lactic acid bacteria (LAB) were studied for the ability to produce 3-phenyllactic acid (PLA), a novel antimicrobial compound derived from the metabolism of phenylalanine (Phe). The highest amount of PLA (1.38 +/- 0.048 mM) was produced by Lactobacillus plantarum CECT-221. A 3**(2-0) full factorial design studding different initial Phe and glucose concentrations revealed the inhibitory effect of high starting glucose concentrations in spite of being the most significant variable. Fed-batch methodologies were assessed since no product inhibition was observed with PLA concentrations lower than 6 mM. Fed-batch fermentations of L. plantarum in Erlenmeyer Flasks without pH-control were unsuccessful; however fed-batch fermentations in a 2 L Biorreactor with pH-control improved considerably the stoichiometric parameters. Starting with 0.6 g L-1 Phe, PLA was continuously accumulated reaching a maximum amount of 4.25 +/- 0.18 mM after 158 h of fermentation (Q(p) = 0.00258 g L-1 h(-1)). A GC-FID analysis of the metabolites obtained in the Phe metabolism by LAB showed the presence of small amounts of benzaldehyde and phenylacetaldehyde. Exhausted broths containing mixtures of PLA and other organic acids resulted to be an effective antimicrobial against the pathogen Salmonella reducing his growth in 63.2% in 24 h of incubation, thus, opening new perspective to preserve foods and feedstuffs with natural antimicrobials, avoiding food-borne diseases caused by Salmonella. (C) 2011 Elsevier Ltd. All rights reserved.