Production of volatile aroma compounds by kefir starter cultures

Production of carbonyl compounds by single-strain cultures, kefir starter (Lactobacillus delbrueckii subsp. bulgaricus HP1+ Lb. helveticus MP12+ Lactococcus lactis subsp. lactis C15+ Streptococcus thermophilus T15+ Saccharomyces cerevisiae A13) and kefir grains during fermentation and storage of kefir was studied. The content of carbonyl compounds produced by kefir starter was greater than that produced by kefir grains. The maximum acetaldehyde concentration (18.3 mug.g(-1)) in kefir with starter culture was mainly due to the metabolic activity of Lb. delbrueckii subsp. bulgaricus HP1 isolated from kefir grains. The highest diacetyl production activity was recorded in the starter culture (1.87 mug.g(-1)) and the single-strain culture St. thermophilus T15 (1.62 mug.g(-1)), followed by Lb. helveticus MP12 (0.85 mug.g(-1)) and Lc. lactis subsp. lactis C15 (0.42 mug.g(-1)). The lactobacilli Lb. delbrueckii subsp. bulgaricus HP1 and Lb. helveticus MP12 produced acetone, which was not found in the cocci cultures. The presence of 2-butanone was related to the production ability of Lb. helveticus MP12. In comparison, Lc. lactis subsp. lactis C15 synthesized ethyl acetate more actively than the other single-strain cultures included in the starter. S. cerevisiae A13 produced ethanol and CO2 in amounts (3975 mug.g(-1); 1.80 gL(-1)) that lent cultured kefir distinctive flavour and aroma characteristic of authentic kefir. (C) 2003 Elsevier Science Ltd. All rights reserved.