Ethyl butanoate formation by dairy lactic acid bacteria

The formation of ethyl butanoate by non-growing cells of 22 starter and 49 non-starter dairy lactic acid bacteria (LAB) varied widely (0.4-310 units 100 mg(-1) dry weight cells) and was both species and strain dependent. Strains of the thermophilic starter Streptococcus salivarius subsp. thermophilus produced the highest levels of ethyl butanoate (an average of 156 units 100 mg(-1) dry weight cells), while strains of the mesophilic starters Lactococcus lactis subsp. cremoris and Lactococcus lactis subsp. lactis gave a more moderate production of the ester (averages of 39 and 27 units 100 mg(-1) dry weight cells, respectively). Non-starter LAB (lactobacilli, pediococci and leuconostocs) and propionibacteria varied widely in their ability to produce ethyl butanoate (0.4-160 units 100 mg(-1) dry weight cells). The effect of physicochemical factors (pH, NaCl, water activity (a(w)) and temperature) on ethyl butanoate production was also investigated using Lactococcus lactis subsp. cremoris 2272 and Lactobacillus rhamnosus 2615. For both strains, ester formation increased by up to 175% when the pgi was lowered from 5.8 to 4.0, but was drastically inhibited by up to 99% in the presence of NaCl and at reduced a(w). Lowering the temperature from 30 to 13 degrees C decreased ester production by 25% for both strains. The findings suggest that the normal cheese pH (similar to 5.0) and ripening temperature (similar to 13 degrees C) are not critical factors in ester formation, but NaCl concentration and a(w) level are pivotal in determining ester formation. (C) 1998 Elsevier Science Ltd. All rights reserved.