CULTURE OF SACCHAROMYCES-CEREVISIAE ON HYDROLYZED WASTE CASSAVA STARCH FOR PRODUCTION OF BAKING-QUALITY YEAST

A fermentation medium based on waste cassava starch hydrolysate and a four-phase feeding strategy for a fed-batch culture of Baker's yeast S accharomyces cerevisiae are presented. Cassava starch isolated from th e wastewater produced in processing of cassava mash into gari was liqu efied with a thermostable 1,4-alpha-D-glucanohydrolase (EC 3.2.1.1) in the presence of 100 ppm Ca2+ at 80 degrees C and pH 6.1-6.3 for one h . The liquefied material was saccharified with 1,4-alpha-D-glucan gluc ohydrolase (EC 3.2.1.3) at 55 degrees C and pH 5.5 for two h. Over 98% of the starch was hydrolyzed; about 80.7% of the hydrolysate was gluc ose. The fermentation feeding profile ,which was based on a desired sp ecific growth rate range of 0.18-0.23 h(-1), a biomass yield coefficie nt of 0.5 g g(-1), and a feed substrate concentration of 200 g l(-1) w as implemented manually using the cassava hydrolysate feed in test exp eriments and glucose feed in control experiments. The fermentation off -gas was analyzed on-line by mass spectrometry for the calculation of the oxygen uptake rate, the carbon dioxide evolution rate, and the res piratory quotient. Off-line determinations of biomass, ethanol, and gl ucose were done, respectively, by dry weight, gas chromatography, and spectrophotometry. Cell mass concentrations of 50-58 g l(-1) were achi eved in all experiments within 28 h of which the last 15 h were in the fed-batch mode. The average biomass yields for the cassava mid glucos e media were identical at 0.49 g g(-1). No significant differences wer e observed between the leavening activities of the products of the tes t, the control media, and a commercial preparation of instant active d ry yeast. Waste cassava starch hydrolysate was established as a suitab le low cost replacement for glucose in the production of baking-qualit y yeast.