Microbiological Effect of Fermented Mexican Oregano (Lippia berlandieri Schauer) Waste

Purpose The antimicrobial properties of Mexican oregano (Lippia berlandieri Schauer) essential oil have been well documented; but its extraction process generates large amounts of agro-industrial wastes. This material can be used as support-substrate in solid-state fermentation, to release and/or accumulate molecules with industrial application. Therefore, the aim of this work was to evaluate the microbial effect of products derived from solid state fermentation of Mexican oregano waste by Aspergillus niger PSH. Methods Microbial activity was tested by well diffusion test of aqueous and non-polar extracts from solid state fermentation, against fungi, foodborne pathogens and spoilage bacteria, as well as Lactic Acid Bacteria. Further, growth curves were done with Listeria monocytogenes and Lactobacillus lactis to describe the possible effect of extracts on bacterial growth. Results Polar and non-polar extracts from solid state fermentation had no deleterious effect against tested fungi and food-borne pathogenic bacteria (Escherichia coli O157: H7, Staphylococcus aureus, Salmonella enterica subgroup enterica subsp. Tiphymurium). Aqueous extract, at concentrations higher than 2.5 % had a bacteriostatic effect on L. monocytogenes. Lactic acid bacteria showed a growth increment in culture medium complemented with aqueous extracts, and this effect was confirmed by microbial growth curves. Conclusions Non polar extracts had no antimicrobial effect. Aqueous extracts had a bacteriostatic effect in L. monocytogenes and promote the lactic acid bacteria growth; this extracts can be used as prebiotic or growth-enhancing supplement for lactic acid bacteria, but further research is needed.