Butyribacterium methylotrophicum has been grown on carbon monoxide as its carbon and energy source in the presence of various surfactants that are capable of forming microbubble dispersions for the screening of surfactants for use in microbubble-sparged synthesis gas fermentations. In the range of 0-3 times the critical micelle concentration, the presence of Tween surfactants was not significantly inhibitory to growth, final cell density, and fermentation stoichiometry, although some of the Brij surfactants caused significant inhibition. As the batch fermentations entered the stationary phase both the pH and the ratio of acetate to butyrate decreased.
The actual and potential keeping quality of milk from 50 Pennsylvania processing plants was determined by comparing Standard Plate, coliform, and psychrophilic counts on commercially processed and laboratory pasteurized portions held at 4.4 C and 7.2 C. Examinations were made on the day of processing and after 5 and 10 days storage at each temperature.
Bacterial data on fresh commercially pasteurized milk were of little or no value in predicting shelf life. As shown by previous studies, laboratory pasteurization destroys or inactivates coliform and psychrophilic organisms usually responsible for spoilage of commercially processed milk. Some laboratory pasteurized milk exhibited increases in counts when held 5 or 10 days at 7.2 C, even though freshly pasteurized portions were free of the psychrophilic or coliform organisms often found in commercially processed milk. The need for low temperature storage of pasteurized milk is clearly shown.
The most important fact illustrated by this study is that Standard Plate, coliform, or psychrophilic counts on fresh commercially processed milk are poor criteria of potential keeping quality. Even though this has been pointed out by others, official regulatory methods, as usually applied, have not recognized the need for new procedures to measure milk quality, especially at the consumer level.
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