PHYSICAL FACTORS INFLUENCING THE PRODUCTION OF STRAWBERRY AROMA BY PSEUDOMONAS FRAGI GROWN IN SKIM MILK

The influence of temperature, agitation speed, pH and biomass on the synthesis of 19 metabolites contributing to a strawberry aroma was followed over a 72 h fermentation of skim milk byPseudomonasfragi. Amongst the major odor-active metabolites were ethyl butyrate, ethyl hexanoate, ethyl 2-hexenoate, ethyl crotonate, ethyl isovalerate and ethyl 2-methyl hexanoate. Up to 17 ppm of some of these metabolites were detected at 60 h of fermentation, approximately 36 h after the beginning of the stationary growth phase. The production of most odor-active metabolites was higher at 11°C and 150 RPM than at 15, 20 or 25°C and 200 or 250 RPM. The development of off-aromas was observed at high temperatures and at high agitation speeds.