Microbiological activity in stored olive oil.

The disappearance of the bitter taste of newly produced olive oil during storage is due to the enzymatic hydrolysis of the bitter-tasting secoiridoid compound known as oleuropein. Current knowledge attributes the enzymatic hydrolysis of the oleuropein to the beta-glucosidase present in the olives. The present study, however, has demonstrated for the first time that oleuropein present in olive oil can be hydrolysed by beta-glucosidase from the yeasts Saccharomyces cerevisiae and Candida wickerhamii. The enzymatic analyses carried out directly on the untreated olive oil and on sterilized olive oil inoculated with the above-mentioned yeasts proved the beta-glucosidase activity through the hydrolysis of both the synthetic substrate p-nitrophenyl-beta-D-glucopyranoside (PNPG) and the oleuropein. The absence of lipases in the isolated S. cerevisiae and C. wickerhamii examined lead us to believe that the yeasts contribute in a positive way towards the improvement of the organological quality of the oil without altering the composition of the triglycerides.