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 by Pseudomonas fragi. 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-degrees-C and 150 RPM than at 15, 20 or 25-degrees-C and 200 or 250 RPM. The development off-aromas was observed at high temperatures and at high agitation speeds.