132 - ‘Analysis of volatile compounds produced by different species of lactobacilli in rye sourdough using multiple headspace extraction’. International Journal of Food Science and Technology. 46, 1940–1946

The generation of odorants occures in sourdough mainly because of enzymatic and microbial processes during sourdough fermentation but some of these volatile compounds may already be present in rye flour. As shown by other researchers, LAB liberate aroma precursors such as free amino acids and their  concentrations are increased significantly during flour hydration and sourdough fermentation. Some of the amino acids that are liberated get degraded via a special pathway called the Ehrlich pathway leading to formation of volatile compounds such as aldehydes or corresponding alcohols. In addition, the increased amounts of esters, such as acetates, propionates, hexanoates, lactates and octanoates, have been also been reported.  Interestingly, the number of aldehydes was lower in rye sourdoughs fermented by heterofermentative LAB (such as Lb. sakei, Lb. casei, Lb. curvatus, Lb. helveticus  and Lb. helveticus), whereas the production of esters like ethyl acetate, isopentyl acetate, hexyl acetate, ethyl hexanoate was specific only to heterofermentative species (such as Lb. bre- vis, Ln. citreum, Lb. panis, Lb. vaginalis). This is because of the higher production of ethanol and acetate by the heterofermentative species. The volatile flavour compound specific to the homofermentative species is  2,3-butanedione (particularly Lb. casei). The current study therefore provides some interesting facts about the type of lactic acid bacteria present in rye sourdough and the volatile flavour compounds that are unique to them.