EFFECTS OF CULTURE CONDITIONS ON PECTINATUS-CEREVISIIPHILUS AND PECTINATUS-FRISINGENSIS METABOLISM - A PHYSIOLOGICAL AND STATISTICAL APPROACH

The genus Pectinatus has been often reported in beer spoilage with off -flavours. The bacteria are strictly anaerobic, Gram-negative rods. Pr opionate and acetate are the main fermentation products from glucose i n the two species belonging to the genus, P. cerevisiiphilus and P. fr isingensis. Amino acids routinely present at a high level in beer were not growth substrates for both species, and a significant accumulatio n of succinate was observed with lactate as growth substrate. Both Pec tinatus ssp. showed almost identical fermentation balances on glucose. Growth kinetics of both glucose-grown species were unchanged under a N-2, H-2 or 20% CO2-containing atmosphere. Combinations of culture med ium pH values from pH 3 . 9 to pH 7 . 2, of glucose levels between 5 a nd 55 mmol l(-1), and of lactate concentrations varied from 4 to 40 mm ol l(-1) demonstrated that biomass and volatile fatty acids production were proportional to glucose concentration for both Pectinatus specie s. A significant increase of volatile fatty acid production was measur ed for both species at the lowest pH values with a lactate or a glucos e concentration increase. The maximum biomass production was observed at pH 6 . 2 for P. cerevisiiphilus, and between pH 4 5 and pH 4 . 9 fo r P. frisingensis. Glucose and lactate or pH value were dependent with regard to propionate and acetate production in P. frisingensis. On th e other hand, the variations of these three parameters were independen t with regard to biomass production for both strains, and to volatile fatty acids production for P. cerevisiiphilus. Addition of ethanol to glucose-grown cultures completely inhibited growth at 1 . 3 mol l(-1) ethanol for P. cerevisiiphilus, and at 1 . 8 mol l(-1) for P. frisinge nsis.