The food industry is constantly looking for new natural antimicrobials to prevent food spoilage and to respond to consumer demands for high quality minimally processed foods. Among the natural preserving systems, lactic acid bacteria (LAB) have been shown to improve the shelf-life of several food products, including bakeries. In our study, the ability of several LAB strains isolated from sourdoughs to prevent fungal contamination of bakery products was assessed, and the culture filtrates of two strains of Lactobacillus plantarum (ITM21B and ITM20B) resulted able to inhibit almost completely a variety of fungal species namely Aspergillus, Penicillium, Eurotium, Endomyces, Monilia and Fusarium spp., which are responsible for contamination of bakery products. Purification of the culture filtrate of strain ITM21B was then carried out and resulted in the identification of two novel antifungal compounds that is 4-hydroxy-phenyllactic acid (OH-PLA) and phenyllactic acid (PLA) to which most of the antifungal activity of the strain should be attributed (1). The inhibitory activity of PLA was evaluated against 23 fungal strains isolated from bakery products, flours and cereals and a fungicidal effect against 19 strains at levels ? 10 mg/ml was observed. Interestingly, less than 7.5 mg/ml of PLA was required to obtain at least 90% of growth inhibition for all strains including some potential toxigenic species such as Aspergillus ochraceus, A. flavus, Penicillium roqueforti, P. verrucosum and P. citrinum (2). The fungicidal activity of PLA indicates a clear advantage of the application of PLA to reduce fungal mass in food systems. For these reasons the ability of LAB to produce PLA was evaluated by HPLC analysis in 29 strains belonging to 12 species widely used in the production of fermented foods. Metabolite production was demonstrated for all strains of the species Lactobacillus plantarum, L. alimentarius, L. rhamnosus, L. sanfranciscensis, L. hilgardii, Leuconostoc citreum, and for some strains of Lactobacillus brevis, L. acidophilus and Leuconostoc mesenteroides subsp. mesenteroides. The improvement of PLA production was investigated in L. plantarum ITM21B: the increase of phenylalanine concentration in the presence of low amounts of tyrosine resulted in a higher level of the metabolite (3). Starting from these observations we can suppose that the antimicrobial activity of L. plantarum ITM21B could not be ascribed only to PLA, therefore investigations are in progress to establish all the potential of the metabolite pool by exploiting the ability of the strain to inhibit food contaminants and human pathogens, both bacteria and yeasts. For example, a 100% growth inhibition of Candida albicans was obtained by using the pool metabolite of the selected strain. Interesting results were also obtained by using a particular procedure of bread-making, patented in Italy (4), which allowed to obtain a complete inhibition of Bacillus spore's germination. The same procedure was used to reduce mould contamination: in this case fungal spores of Aspergillus niger were inoculated after baking on bread slices. The ability of PLA as well as of L. plantarum ITM21B to inhibit or to delay the growth of a variety of microbial contaminants offers new perspectives for the application of these antimicrobials in bakery products and other foods.
Antimicrobial activity of lactic acid bacteria isolated from sourdough
Valerio F;Lavermicocca P
2005
Abstract
The food industry is constantly looking for new natural antimicrobials to prevent food spoilage and to respond to consumer demands for high quality minimally processed foods. Among the natural preserving systems, lactic acid bacteria (LAB) have been shown to improve the shelf-life of several food products, including bakeries. In our study, the ability of several LAB strains isolated from sourdoughs to prevent fungal contamination of bakery products was assessed, and the culture filtrates of two strains of Lactobacillus plantarum (ITM21B and ITM20B) resulted able to inhibit almost completely a variety of fungal species namely Aspergillus, Penicillium, Eurotium, Endomyces, Monilia and Fusarium spp., which are responsible for contamination of bakery products. Purification of the culture filtrate of strain ITM21B was then carried out and resulted in the identification of two novel antifungal compounds that is 4-hydroxy-phenyllactic acid (OH-PLA) and phenyllactic acid (PLA) to which most of the antifungal activity of the strain should be attributed (1). The inhibitory activity of PLA was evaluated against 23 fungal strains isolated from bakery products, flours and cereals and a fungicidal effect against 19 strains at levels ? 10 mg/ml was observed. Interestingly, less than 7.5 mg/ml of PLA was required to obtain at least 90% of growth inhibition for all strains including some potential toxigenic species such as Aspergillus ochraceus, A. flavus, Penicillium roqueforti, P. verrucosum and P. citrinum (2). The fungicidal activity of PLA indicates a clear advantage of the application of PLA to reduce fungal mass in food systems. For these reasons the ability of LAB to produce PLA was evaluated by HPLC analysis in 29 strains belonging to 12 species widely used in the production of fermented foods. Metabolite production was demonstrated for all strains of the species Lactobacillus plantarum, L. alimentarius, L. rhamnosus, L. sanfranciscensis, L. hilgardii, Leuconostoc citreum, and for some strains of Lactobacillus brevis, L. acidophilus and Leuconostoc mesenteroides subsp. mesenteroides. The improvement of PLA production was investigated in L. plantarum ITM21B: the increase of phenylalanine concentration in the presence of low amounts of tyrosine resulted in a higher level of the metabolite (3). Starting from these observations we can suppose that the antimicrobial activity of L. plantarum ITM21B could not be ascribed only to PLA, therefore investigations are in progress to establish all the potential of the metabolite pool by exploiting the ability of the strain to inhibit food contaminants and human pathogens, both bacteria and yeasts. For example, a 100% growth inhibition of Candida albicans was obtained by using the pool metabolite of the selected strain. Interesting results were also obtained by using a particular procedure of bread-making, patented in Italy (4), which allowed to obtain a complete inhibition of Bacillus spore's germination. The same procedure was used to reduce mould contamination: in this case fungal spores of Aspergillus niger were inoculated after baking on bread slices. The ability of PLA as well as of L. plantarum ITM21B to inhibit or to delay the growth of a variety of microbial contaminants offers new perspectives for the application of these antimicrobials in bakery products and other foods.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
