Olive fermentations using lactic acid bacteria isolated from olive phylloplane and olive brines

Two-hundred lactic acid bacteria identified as Lactobacillus plantarum, Leuconostoc mesenteroides subsp. mesenteroides, Leuconostoc spp., Enterococcus faecium and Enterococcus spp. were isolated from olive phylloplane and olive brines in Apulia. The isolates were analyzed for their several physiological properties related to the olive fermentation process such as acidification properties, lipolytic activity, synthesis of exopolysaccharides, production of antimicrobial substances, and hydrolysis of the bitter glucoside oleuropein. Individual strains of L. plantarum, E. faecium and L. m. subsp. mesenteroides were selected on the basis of the above characteristics among 193 isolates. Fermentations were carried out with the above strains (single or mixed cultures) on green and black table olives using brines containing 3% NaCl and 1% saccharose. Olives brined in 13% NaCl and 1% saccharose were used as controls. During fermentation processes, microbial populations were monitored by using microbiological and molecular techniques. In mixed cultures, L. plantarum developed and persisted until the end of fermentation, while E. faecium and L. m. subsp. mesenteroides survived for about 20 days. Moreover, the use of mixed cultures was essential to obtain a rapid decrease of pH in the first stage of fermentation. Low pH levels are necessary to prevent natural contaminants mostly when low concentrations of NaCl are used.