Production of high-quality edible protein from Candida yeast grown in continuous culture

Candida utilis NRRL Y-900 was grown in aerobic continuous culture with cane molasses as the source of the growth-limiting carbon. At 1% reducing sugar in the chemostal (10 liter working volume) feed medium, addition of Zn (25μM) to a minimal salts medium resulted in an increase in the biomass productivity of the chemostat from 1.7 to 2.6 g/liter/hr with a growth yield of 0.55 g dry biomass/g reducing sugar utilized at D_max. On the average, the yeast biomass was 50–55% protein. At S_R > 2% sugar, the biomass productivity was limited by the oxygen supply. With O₂-supplemented aeration (at S_R = 4.2%)the maximum biomass productivity Was 7.25 g/liter/hr. Aerobic ethanol production was not observed. A highquality undenatured protein fraction was isolate from the yeast homogenate by isoelectric precipitation at pH 4.5. Contaminating nucleic acid was removed as an insoluble complex by chelation with an organic cation (cetavlon). The final protein product contained about 3% RNA (DWB) and was suitable for use as a food additive.