Abstract
In tropical and subtropical regions, the overall production cost of Baker's yeast is highly influenced by the prices of raw materials (mainly the carbon source) and cooling cost during fermentation. In the present work, a process for the production of thermotolerant yeast in molasses medium is described. Cultivations were carried out in cane molasses based medium in stirred tank bioreactor at different agitation speeds. The increase of agitation speeds from 200 to 600 rpm almost doubled both volumetric production and specific yield of baker's yeast. The maximal dry cell mass of about 16.2 g l(-1) with yield coeffecient [Y-X/S] 0.62 g g(-1) (g biomass per g carbohydrates consumed) was obtained in 600 rpm agitated culture. Based on these data, fed batch cultivation was designed to obtained higher cell mass using intermittent addition of growth limiting substrates (molasses and yeast extract). The volumetric production of cell mass in fed batch culture increased up to 40.4 g l(-1) after about 72 h cultivation. On the other hand, during the fed-batch cultivation process at high agitation speed of 600 rpm neither oxygen limitation nor ethanol production was observed. This allowed also obtaining a high yield coefficient [Y-X/S] 0.54 g g(-1) in fed-batch cultures.