Prevalence and impact of single-strain starter cultures of lactic acid bacteria on metabolite formation in sourdough.

Flavour of type II sourdoughs is influenced by the ingredients, processing conditions, and starter culture composition. It is, however, not fully clear to what extent different sourdough lactic acid bacteria (LAB) contribute to flavour. Therefore, two types of flour (rye and wheat) and different LAB starter culture strains were used to prepare sourdoughs, thereby leaving the yeast microbiota uncontrolled. All LAB starter culture strains tested were shown to be prevalent and to acidify the flour/water mixture to pH values between 3.1 and 3.9 after 24h of fermentation. Multiple aldehydes, alcohols, ketones, and carboxylic acids were produced by the sourdough-associated microbiota throughout the fermentation period. Based on the organoleptic evaluation of breads produced with these sourdoughs, five LAB strains were selected to perform prolonged wheat and rye fermentations as to their capacity to result in an acidic (Lactobacillus fermentum IMDO 130101, Lactobacillus plantarum IMDO 130201, and Lactobacillus crustorum LMG 23699), buttermilk-like (Lactobacillus amylovorus DCE 471), or fruity flavour (Lactobacillus sakei CG1). Upon prolonged fermentation, higher metabolite concentrations were produced. For instance, L. sakei CG1 produced the highest amounts of 3-methyl-1-butanol, which was further converted into 3-methylbutyl acetate. The latter compound resulted in a fruity banana flavour after 48h of fermentation, probably due to yeast interference. Rye fermentations resulted in sourdoughs richer in volatiles than wheat, including 3-methyl-1-butanol, 2-phenylethanol, and ethyl acetate.

The application of staphylococci with flavour-generating potential is affected by acidification in fermented dry sausages.

Differences in the production of bacterial metabolites with potential impact on fermented sausage flavour were found in meat simulation medium when comparing different strains of Staphylococcus xylosus and Staphylococcus carnosus as starter cultures. Overall, higher levels of 3-methyl-1-butanol and acetoin were found for S. xylosus, with some intraspecies variability. In addition, sausage fermentation parameters affected staphylococcal growth and metabolism. Strong acidification, as in Northern-European types of fermented dry sausage, inhibited S. xylosus 3PA6 but not S. carnosus 833. During a milder, Southern-European type of acidification, both strains displayed survival over time. During in situ sausage trials, variations in the degree of acidification and the choice of starter microorganisms were of importance, whereas modifications in fat and salt contents had no effects. Staphylococcus sciuri alphaSg2, Staphylococcus succinus 4PB1, and S. xylosus 3PA6 were unable to survive the fermentation of a Northern-European type of fermented dry sausage, characterized by low or no 3-methyl-1-butanol and acetoin production. Inoculation with S. sciuri alphaSg2, S. succinus 4PB1, or S. xylosus 3PA6 led to 3-methyl-1-butanol and acetoin production in Southern-European type of fermented dry sausages, which was not observed with S. carnosus 833.

Competitiveness and antibacterial potential of bacteriocin-producing starter cultures in different types of fermented sausages.

Application of bacteriocin-producing starter cultures of lactic acid bacteria in fermented sausage production contributes to food safety. This is sometimes hampered by limited efficacy in situ and by uncertainty about strain dependency and universal applicability for different sausage types. In the present study, a promising antilisterial-bacteriocin producer, Lactobacillus sakei CTC 494, was applied as a coculture in addition to commercial fermentative starters in different types of dry-fermented sausages. The strain was successful in both Belgian-type sausage and Italian salami that were artificially contaminated with about 3.5 log CFU g(-1) of Listeria monocytogenes. After completion of the production process, this led to listerial reductions of up to 1.4 and 0.6 log CFU g(-1), respectively. In a control sausage, containing only the commercial fermentative starter, the reduction was limited to 0.8 log CFU g(-1) for the Belgian-type recipe, where pH decreased from 5.9 to 4.9, whereas an increase of 0.2 log CFU g(-1) was observed for Italian salami, in which the pH rose from 5.7 to 5.9 after an initial decrease to pH 5.3. In a Cacciatore recipe inoculated with 5.5 log CFU g(-1) of L. monocytogenes and in the presence of L. sakei CTC 494, there was a listerial reduction of 1.8 log CFU g(-1) at the end of the production process. This was superior to the effect obtained with the control sausage (0.8 log CFU g(-1)). Two commercial antilisterial cultures yielded reductions of 1.2 and 1.5 log CFU g(-1). Moreover, repetitive DNA sequence-based PCR fingerprinting demonstrated the competitive superiority of L. sakei CTC 494.