Reference Number: 170
Eighty-seven strains (15 species) of sourdough lactic acid bacteria (homo- and hetero-fermentative) and yeasts were characterized and statistically discriminated on the basis of volatile compounds produced during sourdough fermentation. The species differed and, in general, the strains differed within the species. Heterofermentative LAB mainly produced ethylacetate with some alcohols and aldehydes, and homofermentative LAB synthetized diacetyl and other carbonyls, while iso-alcohols were produced by yeast fermentation. Lactobacillus brevis subspecies, lindneri and Lactobacillus plantarum were the LAB with the most complete profiles. Sourdoughs started with bacterial associations were characterized by a more complete profile (integrations of hetero- and homo-fermentative volatile compounds) and by a decrease of the percentage amounts of the main products individually synthetized. In association with yeasts (with the exception of L. plantarum DC400 –Saccharomyces exiguus M14 association) both hetero- and homo-fermentative LAB enhanced the formation of the yeast volatile compounds. Mixed sourdough starters (L. brevissubsp, lindneri CB1, L. plantarum DC 400 and Saccharomyces cerevisiae 141 or S. exiguus M14) were selected to produce sourdoughs with different volatile compound profiles.
SIGNIFICANCE OF THIS STUDY
In the current study, sourdough LAB (homo and hetero-fermentative) and yeasts were characterized and discriminated on the basis of the volatile compounds produced during sourdough fermentation. The paper shows that hetero- fermentative LAB produce various concentrations of lactic and acetic acids and ethanol and contributed differently to the synthesis of the volatile flavour components from wheat. For example sourdoughs started with L. fructivorans and L. fermentum strains mainly contained ethylacetate with smaller amounts of octanal and nonanal. L. brevis (subspecies lindneri-synonimus with L. sanfrancisco) cotributed largely to 2-methyl pentanol and Ethylacetate. 2 methyl pentanol is responsible for the fresh, aldehydic, floral, green, overipe fruit, fruity, roasted, malty smell associated with sourdough starters as well as the baked breads. Ethylacetate on the other hand is mainly responsible for the smell of nail varnish or acetone in sourdough starters. Iso-alcohols such as 2-methyl-1-propanol and 2/3-methyl- 1-butanol, with their respective aldehydes and ethyla- cetates, were also the characteristic volatile compounds of sourdoughs started with fermentative yeasts (Saccharomyces and Hansenula genus). Overall, the contributions of both LAB species and yeasts are responsible for the unique flavours and aromas of sourdough starters and breads.