Javier Rúa

Chicken meat and its derivatives are easily alterable. They are a nutritionally healthy food, and their consumption has seen a remarkable increase worldwide in recent years. At the same time, consumer demand for the use of natural products to control microbial growth is increasing. In this context, the antimicrobial capacity of a commercial extract of the lemon verbena (Lippia citriodora) plant, (LCE) was tested in binary combination with gallic acid or octyl gallate against two strains of lactic acid bacteria (LAB) of meat origin: Carnobacterium divergens ATCC 35677 and Leuconostoc carnosum ATCC 49367. First, the antimicrobial potential was evaluated by the checkerboard microdilution method at the optimal growth temperature of each and at 4 °C, pH 5.7 and 6.7, in culture medium. Octyl gallate was the most effective antimicrobial against the two bacteria under all study conditions. At 4 °C, the combination of LCE with octyl gallate had a similar antimicrobial effect on the two LAB, being bactericidal at pH 6.7. In chicken breast, this effective combination was tested in normal or modified atmosphere and refrigerated (4–8 °C) for 9 days. LCE + OG in modified atmosphere reduced the different microbial groups studied, including the lactic acid bacteria as the main microorganisms responsible for the spoilage of fresh meat. Further research could pave the way for the development of novel strategies contributing to the technological stability, security, and functional properties of chicken meat.

The antimicrobial activity of a commercial Lippia citriodora extract (LCE) at 2,500 μg mL−1 (maximum sensory acceptable level) and vanillin (MIC and 2 MIC) alone and in combination were analyzed in four strains of Escherichia coli (two nonverotoxigenic and two verotoxigenic) in cation-adjusted Mueller-Hinton medium and in Piel de Sapo melon juice (MJ) stored under refrigeration (4°C) for 7 days. The bacterial counts of the four strains together in untreated samples were higher (≈4 log CFU/mL) in cation-adjusted Mueller-Hinton medium than in stored MJ. LCE showed higher antimicrobial activity in MJ than in standard culture broth, but vanillin showed a higher effect in broth. The verotoxigenic strain E. coli O146:H stx2 was the most sensitive to LCE in refrigerated MJ. Combinations of vanillin (at MIC and 2 MIC) with LCE were very effective in reducing E. coli counts either in broth or in refrigerated MJ to undetectable levels. Bactericidal effects were observed for the combinations in all strains in broth and in MJ. Also, these combinations showed an antimicrobial synergistic effect after day 3 of storage in MJ in three of the bacterial strains tested. These results indicate that the combination of LCE (at maximum sensory acceptable levels) and vanillin (at low concentrations) could be considered as a promising natural antimicrobial agent to inhibit verotoxigenic E. coli growth in refrigerated MJ and improve its quality.HIGHLIGHTSVanillin was a better antimicrobial agent for E. coli strains in CA-MHB than in melon juice.LCE showed higher antimicrobial activity in melon juice than in CA-MHB.Verotoxigenic E. coli O146 was the most sensitive to LCE in melon juice.Combinations of vanillin and LCE were the most effective treatments.Bactericidal effects were observed for the combinations in CA-MHB and melon juice.

Partial sequencing of 16S ribosomal RNA (rRNA) gene is commonly used for the identification of lactic acid bacteria (LAB). The present study evaluated the performance in the identification of dairy LAB of two universal (515FPL-13B and 91E-13) and one Lactobacillus group-specific (S-D-Bact-0011-a-S-17-S-G-Lab-0677-a-A-17) primer pairs. After amplification, the 16S rRNA gene portions were sequenced, and sequences were analysed using the Ribosomal Database Project (RDP-II) and Basic Length Alignment Search Tool (BLAST) programs. The primers were used with three reference strains and eight isolates from Oaxaca cheese. The 515FLP-13B primer misled the identification of one reference strain and two isolates. Five among the eight isolates were identified as Lactococcus lactis by at least two of the primers, and the specific primer showed higher RDP-II identity scores than the universal primers. The specific primer was successfully used for the identification of other 24 cheese isolates. The joint use of the two programs (RDP-II and BLAST) allowed to confirm the identification results.

This study investigated the antimicrobial activity of 3 natural (thymol, carvacrol, and gallic acid) and 2 synthetic [butylated hydroxyanisole (BHA) and octyl gallate] phenolic compounds, individually and in binary combinations, on 4 dairy isolates of Enterococcus faecalis with different virulence factors (β-hemolytic, gelatinase, or trypsin activities; acquired resistance to erythromycin or tetracycline; and natural resistance to gentamicin). A checkerboard technique and a microdilution standardized method were used. All compounds individually tested exhibited antimicrobial activity against E. faecalis, with minimal inhibitory concentrations (MIC) ranging from 30 μg/mL (octyl gallate) to 3,150 μg/mL (gallic acid), although no significant differences were detected among strains to each phenolic compound. Carvacrol in combination with thymol or gallic acid, and gallic acid combined with octyl gallate showed partial synergistic inhibition of all E. faecalis strains. The most effective combinations were thymol+carvacrol and gallic acid+octyl gallate, as the MIC for each of these compounds was reduced by 67 to 75% compared with their respective individual MIC. These results highlight the possibility of using combinations of these phenolic compounds to inhibit the growth of potential virulent or spoilage E. faecalis strains by reducing the total amount of additives used in dairy foods.