Document Detail

Factors affecting organic acid production by sourdough (San Francisco) bacteria.
MedLine Citation:
PMID:  5042265     Owner:  NLM     Status:  MEDLINE    
Previous workers from this laboratory observed considerable variation in the proportions of acetic and lactic acids produced in pure broth culture as compared to consistently high proportions of acetic acid produced in the sourdough and flour suspension systems. In the latter the proportion of acetic acid was always in the range of 20 to 35% of the total, whereas in pure broth culture frequently less than 5% acetic acid was produced. In the natural environment, the sourdough bacteria, tentatively identified as lactobacilli, coexist with a yeast, Saccharomyces exiguus, and this study was undertaken to determine whether this yeast or flour ingredients including glucose or other factors were involved in this variable production of acetic acid. The proportion of acetic acid produced in broth culture on maltose, the preferred carbohydrate source, was found to depend almost entirely on the degree of aeration. Essentially anaerobic conditions, as obtained by thorough evacuation and flushing with CO(2) or N(2), resulted in very low (5% or less) proportions of acetic acid. Aerobic conditions, achieved by continuous shaking in cotton-plugged flasks, yielded high levels (23 to 39% of the total) of acetic acid. Similar effects of aeration were observed with glucose as the substrate, although growth was considerably slower, or in nonsterile flour suspension systems. It is theorized that, under aerobic conditions, the reduced pyridine nucleotides generated in the dissimilation of carbohydrate are oxidized directly by molecular oxygen, thereby becoming unavailable for the reduction of the acetyl phosphate intermediate to ethyl alcohol, the usual product of anaerobic dissimilation of glucose by heterofermentative lactic acid bacteria. Comparative studies with known strains of homo- and heterofermentative lactobacilli showed similar effects of aeration only on the heterofermentative strains, lending additional support to the tentative grouping by previous workers from this laboratory of the sourdough bacteria with the heterofermentative lactobacilli.
H Ng
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Applied microbiology     Volume:  23     ISSN:  0003-6919     ISO Abbreviation:  Appl Microbiol     Publication Date:  1972 Jun 
Date Detail:
Created Date:  1972-09-13     Completed Date:  1972-09-13     Revised Date:  2010-09-13    
Medline Journal Info:
Nlm Unique ID:  7605802     Medline TA:  Appl Microbiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1153-9     Citation Subset:  IM    
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MeSH Terms
Acetic Acids
Bacteria / classification,  metabolism*
Culture Media
Food Microbiology*
Glucose / metabolism
Lactobacillus / classification,  metabolism*
Maltose / metabolism
Species Specificity
Time Factors
Reg. No./Substance:
0/Acetic Acids; 0/Butanones; 0/Culture Media; 0/Lactates; 50-99-7/Glucose; 69-79-4/Maltose

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