IN VITRO BIODEGRADATION OF OLEUROPEIN BY LACTOBACILLUS PLANTARUM FSO175 IN STRESS CONDITIONS (pH, NaCl AND GLUCOSE)

The objective of this work is to study the oleuropein (OLP) biodegradation by a strain of Lactobacillus plantarum FSO175 under conditions (pH 4.5, NaCl 5% and glucose 1%), during 7 days of incubation at 30 °C, in modified MRS broth containing OLP as carbon source. The results obtained, by HPLC analyses, showed that the biodegradation of OLP by L. plantarum FSO175, is accompanied with increase of hydroxytyrosol (HT) content and acidity values. The yields of OLP degradation and HT accumulation are depending on carbon sources, stress conditions and time of incubation. So that, the drastic reduction in OLP biodegradation, obtained at pH 6.7 (trial B), decreased significantly (p <0.05) in presence of NaCl 5% (trial D) and with glucose 1% (trial C). Indeed, the OLP biodegradation rate was maximal at pH 4.5 (trial E) and was higher even with NaCl 5% (trial F). In contrast, in presence of combined stress conditions (glucose 1%, pH 4.5 and NaCl 5%: trial G), the biodegradation of OLP decreased significantly (p <0.05). The effectiveness of the strain L. plantarum FSO175 in OLP biodegradation leading to variable yields of HT production, revealed its promising perspectives as starter culture, under controlled stress conditions of pH 4.5 and NaCl 5%, allowing the production of green table olives rich of HT, the main antioxidant highly desired in foods.