Glucose syrup and corn steep liquor as alternative to molasses substrates for production of baking-quality yeast

In the present study the possibility of substituting molasses with glucose syrup produced from corn starch and supplemented with corn steep liquor (CSL) (a by-product of corn-starch extraction process) as a source of proteins, vitamins and oligo-elements was investigated. For this purpose, fed-batch fermentations with constant volume were carried out to evaluate the influence of molasses sugars replacement (0-30-60-100%) by glucose syrup on biomass growth, yield coefficient (YX/S) for substrate conversion into biomass, nitrogen and phosphorus (as P2O5) content of final biomass. A mixture of cane and beet molasses was used, and integrations of nitrogen, phosphorus, biotin, thiamin, inositol, nicotin amide, nicotinic acid, piridoxin and zinc were supplied For fermentations with 100% of sugars as glucose, addition of corn steep was considered and calculated on the basis of CSL and molasses composition. A substitution of molasses sugars up to 60% led only to a slight reduction in biomass nitrogen content. Complete replacement of molasses sugars brought to reduced biomass yield (partly due to the absent buffering power of molasses and then to an excessive pH reduction of medium during fermentation), YX/S, nitrogen content, and higher phosphorus content. In this case, addition of CSL could partly compensate the negative effects.