VOLATILE ORGANIC-COMPOUNDS PRODUCED BY THERMOPHILIC AND MESOPHILIC SINGLE STRAIN DAIRY STARTER CULTURES

The potential of different commercially used starter cultures to form volatile organic compounds were determined. Special interest was laid on the so-called minor constituents compounds that al-e present in the low mu g/kg-range in the end-product aroma of the investigated starter cultures. The variability of the tested single sti-ain cultures was very wide within the investigated species. It was not possible to group the strains according to the species by applying statistical procedures such as principal component analysis or cluster analysis on the GC-MS-data of the samples. Applying the concept of odour unit values to all cultures tested, it was possible to estimate the impact of each volatile organic compound investigated on the resulting aroma of the end product. Of 32 quantified compounds only 2,3-butanedione (odour unit values between 6 and 362), 2,3-pentanedione (between 0 and 363), and to a lesser extent demethyl sulfide (between 6 and 12), and benzaldehyde (between 0 and 3) are supposed to have such an impact. Mixed cultures were formed, using three strains of Lb. delbruckii sap. bulgaricus and S. salivarius ssp. thermophilus, respectively, to produce yogurt. The most interesting finding was that 2,3-pentanedione is produced by all mixed strain cultures in three to five times the amount of the sum produced by the respective single strains.