Effect of process parameters on the production and drying of Leuconostoc mesenteroides cultures.

Abstract

Leuconostoc mesenteroides BLAC was grown on MRS broth or on a carrot juice medium, and the effects of sugar concentration, type of pH control, aeration and fermentor size on viable counts were examined. The effect on viability of the type of centrifuge used to concentrate the bacterial culture was also examined. When the MRS broth had the traditional 110 mM glucose, pH control did not increase the final population. However, using a zone pH control mode, increasing the glucose content of MRS both from 110 to 220 mM almost doubled the population. In MRS broth, the amount of acetic acid produced was the same for all treatments, and was proportional to the amount of citrate consumed. There was a significantly lower cell yield in the carrot juice medium when the pH was not regulated. In the carrot juice medium, pH had a more pronounced effect on the final population level than did aeration, even though the quantity of viable cells was greater when the culture was aerated. In MRS broth, glucose was completely consumed during fermentation, but this was not the case in carrot juice medium. Aeration resulted in increased acetic acid content of the fermented medium. Viable counts were not affected by scaling the volume of the fermentation from 2 to 15 l,or by the type of centrifuge used to concentrate the cells. Cells were concentrated by a factor of 10, but in both centrifuge types, viable counts showed only an eightfold average increase. However, freeze-dried powders obtained from the continuous pilot-plant-centrifuged cultures had, on the average, 33% lower populations than those obtained from the laboratory unit.