Tim M. Cogan

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Microorganisms are an essential component of all natural cheese varieties and play important roles during both cheese manufacture and ripening. They can be divided into two main groups; starters and secondary flora. The starter flora, Lactococcus lactis, Streptococcus thermophilus, Lactobacillus helveticus and Lactobacillus delbrueckii used either(More)
The relationship between acetoin production and citrate utilization in Leuconostoc lactis NCW1 was studied. In a complex medium the organism utilized citrate at neutral pH (initial pH, 6.3) and at acid pH (initial pH, 4.5) but produced nine times more acetoin at the latter pH. In resting cells the utilization of citrate was optimum at pH 5.3. Production of(More)
C nuclear magnetic resonance (C-NMR) was used to investigate the metabolism of citrate plus glucose and pyruvate plus glucose by nongrowing cells of Lactococcus lactis subsp. lactis 19B under anaerobic conditions. The metabolism of citrate plus glucose during growth was also monitored directly by in vivo NMR. Although pyruvate is a common intermediate(More)
A simple gas-liquid chromatographic procedure for analyzing ethanol, acetic acid, acetoin, and racemic and meso-2,3-butylene glycol in broth media is described. Overnight broth cultures were filtered or centrifuged, and the filtrate or supernatant was treated with formic acid to aid separation of volatile fatty acids. Samples were then directly analyzed by(More)
Mesophilic Lactobacillus spp. are the dominant organisms in mature Cheddar cheese. The heat resistance of broth grown cultures of Lactobacillus plantarum DPC1919 at temperatures between 50 and 57.5 degrees C, Lact. plantarum DPC2102 at temperatures between 48 and 56 degrees C and Lact. paracasei DPC2103 at temperatures between 50 and 67.5 degrees C was(More)
The effect of citrate on production of diacetyl and acetoin by four strains each of heterofermentative and homofermentative lactic acid bacteria capable of utilizing citrate was studied. Acetoin was quantitatively the more important compound. The heterofermentative bacteria produced no acetoin or diacetyl in the absence of citrate, and two strains produced(More)
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