Flavour production in ewe's milk and ewe's milk yoghurt, by single strains and combinations of Streptococcus thermophilus and Lactobacillus delbrueckii subsp bulgaricus, isolated from traditional Greek yoghurt

The f1avour production in ewe's milk by 5 Streptococcus thermophilus and 4 Lactobacillus delbrueckii subsp bulgaricus strains as weil as by their 20 combinations in ewe's milk yoghurt was studied. Samples for analysis were taken alter 24 h and 5 days of storage at 4C. The flavour compounds (acetaldehyde, acetone, diacetyl and ethanol) were extracted by ether microsteam distillation and were identified and quantitatively estimated by gas chromatography. The concentrations of flavour compounds varied considerably among the single strains and their combinations. Acetaldehyde was recognized as the major flavour component, while acetone, diacetyl and ethanol were produced in lower concentrations. The Lb bulgaricus strains produced, generally, higher concentrations of acetaldehyde th an the Str thermophilus orres. In the 24 h as weil as in the 5-days ewe's milk yoghurt, the combination ACA-OC 116/ACA-OC 232 was found to produce the highest acetaldehyde concentration (13.14 mg kg-1 ). Changes in the concentrations of flavour compounds were also observed between the 24 h and 5-days sarnples.