EVALUATION OF INDIGENOUS LACTIC ACID STRAINS ISOLATED FROM NATURAL FERMENTATION OF GREEN OLIVES

DE LA FUENTE A C; FONT DE VALDEZ G; GARRO M S

San Miguel de Tucumán – Tucumán, Argentina

Simposio; III Simposio Internacional de Bacterias Lácticas; 2009

CERELA-CONICET

The microflora in the brines of green olives is very complex, lactic acid bacteria (LAB) and yeasts being predominant. During natural fermentation process leuconostocs, pediococci, enterococci, and lactobacilli were mainly found. These microorganisms are able to survive the harsh environmental conditions such as high NaCl concentrations, changes in pH, and nutrients limitations. The objectives of the study were: a) To evaluate the performance of 13 indigenous strains under extreme culture conditions, b) To study the effect of the carbon source on cell growth. In the first trial, the tolerance of the strains to NaCl (0, 4, 6, 8, 10, and 12%, w/v) at initial pH (pHi) of 6.5 was evaluated. In a second trial, the pHi was 3.5, 4.5, 5.5, 6.5, 7.5 and 8.5, and NaCl was fixed to 4% (w/v). The medium used MRS broth containing 1% (w/v) glucose instead of 2%. Each LAB strain was inoculated separately and incubated at 30°C. The parameters measured were: Optical Density (OD), pH and colony counts (cfu/ml) for 7 days. During the first two days of incubation, OD and pH were measured every 6 h; the following days every 24 h. The colony counts were determined at 0, 24 h, and 7 days. For the second objective, six Lactobacillus strains were grown in MRS broth (pHi = 6.5) added with NaCl (4%, w/v) and 1% (w/v) of each sugar (glucose, sucrose, and fructose). Cultures were incubated at 30°C for 24 h. The parameters measured were OD, pH, cfu/ml, and organic acids (lactic acid, acetic acid, malic acid). The results of the first test evinced that all the strains tested were able to grow in most of the conditions (pH / NaCl), the most critical being pH 3.5/4% NaCl, and 6.5/10% NaCl. At pH 6.5/12% NaCl no viable cells were obtained. Conditions: pH 6.5/8% NaCl, and pH 4.5/4% NaCl were the most suitable for growing. Only six strains of lactobacilli showed ability for adapting to stress conditions, three of them (identified as L. pentosus) were able to use glucose, fructose and sucrose similarly. These trials allowed a better knowledge on the behaviour of wild lactic acid bacteria (isolated from natural olive fermentations) under single or combined stress environmental conditions. From the data obtained, L. pentosus strains were selected for further studies. The formulation of a starter culture to be used in controlled fermentations processes in a factory of La Rioja, Argentina, is undergoing.