Studies on roles of lactic acid bacteria and yeast in the flavor of bakery products Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gq67jt520

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  • Roles of lactic acid bacteria in flour pre-ferment and white bread were investigated. Volatile compounds produced by the organisms were identified using gas-liquid chromatography (GLC). Lactic acid bacteria were isolated from domestic commercial compressed yeast and active dry yeast. Numbers per gram of sample were 10⁸ to 10⁹ in compressed yeast and 10⁴ in active dry yeast. These lactic acid bacteria were identified by physiological and fermentation characteristics. Commercial yeast preparations were found to contain both homo- and heterofermentative lactobacilli, and Leuconostoc mesenteroides. Breads with or without lactic acid bacteria were prepared and analyzed by GLC for volatile compounds present. Lactic acid bacteria in compressed yeast were found to contribute at least to the production of acetic acid. Dough like-preparations for conversion to pre-ferments were inoculated with combinations of yeast and different types of lactic acid bacteria to investigate the behaviors of these organisms. The pre-ferments were considered useful flavor enhancers for bakery products. From results of GLC analyses, it was found that by adding certain lactic acid bacteria to the pre-ferment with yeast, the content of volatile compounds produced was changed dramatically. Pre-ferments inoculated with different lactic acid bacteria but without yeast also were examined for volatile compounds produced. Each strain produced characteristic metabolites in the pre-ferment. Lactococcus diacetylactis 18-16, which produced an elevated amount of diacetyl in the pre-ferment without yeast, did not produce a significant amount of the compound in pre-ferment with yeast. Cells of the bacterium added directly to sponge dough of bread increased the concentrations of acetoin and acetic acid present, but not diacetyl. Since the column packing material used in this study was found to be very suitable for the analysis of volatile compounds, direct injection of cultures on GLC column was carried out to determine the compounds produced by Leuconostoc strains. Most citrate-utilizing strains of Leuconostoc did not produce diacetyl or acetoin in modified MRS or acidified milk cultures, but did in citrate solutions. When the citrate-utilizing strains did produce diacetyl and acetoin, the amounts of ethanol produced by them were always small.
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