Reference Number: 132
Profiles of volatile organic compound (VOC) produced by nine individual lactic acid bacteria (LAB) during rye sourdough fermentation were compared by automated SPME and GC ? MS-Tof. The dough samples were inoculated with individual strains, placed inside the headspace vials and incubated during next 24 h. Volatile profiles differed among LAB species and divided LAB into two main groups – hetero- and homofermentative. Hetrofermentative LAB (Lactobacillus brevis; Leuconostoc citreum; Lactobacillus vaginalis, Lactobacillus panis) showed high production of acetic acid, CO2, ethanol, ethylacetate, producing also hexyl acetate, ethyl hexanoate and isopentyl acetate. Whereas homofermentative LAB species (Lactobacillus helveticus; Lactobacillus casei; Lactobacillus sakei; Lactobacillus curvatus) produced a considerable amount of 2,3-butanedione. Production of l-leucine methyl ester was unique for Lb. sakei, Lb. casei and Lb. curvatus strains. Lb. helveticus was the only LAB that produced benzaldehyde.
SIGNIFICANCE OF THIS STUDY
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.