Some factors influencing carbon dioxide production by Leuconostoc citrovorum Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/mw22v8324

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  • This study was undertaken to determine the role Leuconostoc citrovorum may play in carbon dioxide production in milk. The ability of L. citrovorum strains to produce gas was studied by two methods. A qualitative method used visual measurement of gas where an agar plug was forced up the neck of a volumetric flask. It demonstrated that 0.25 percent yeast extract in a milk medium stimulated L. citrovorum to produce at least ten ml of gas at 30°C. Studies using a Gilson Differential Respirometer revealed that L. citrovorum produced 500-900 μl of CO₂ in milk and 800-1500 μl of CO₂ in nonfat milk containing 0.33 percent yeast extract. Cell extracts of Streptococcus cremoris, Streptococcus lactis, Lactobacillus lactis, Lactobacillus casei, and Lactobacillus helveticus also enhanced gas production of L. citrovorum 20 to 70 percent. Autolysates of these bacteria present during ripening or aging of certain cheeses may stimulate L. citrovorum, a common organism in starter cultures, to produce gas causing, for example, the slit-open defect of Cheddar cheese. Yeast extract caused an increase in acid and gas production per cell, but did not cause an increase in growth as measured by counting the cells. Experiments indicated that one metabolic source of the carbon dioxide was the decarboxylation of pyruvate produced during catabolism of citric acid; yeast extract stimulated this reaction 16 percent.
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  • File scanned at 300 ppi using Capture Perfect 3.0 on a Canon DR-9050C in PDF format. CVista PdfCompressor 5.0 was used for pdf compression and textual OCR.
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