Producing Single Cell Protein By Yeasts Fermentation Of Corn Steep Water And Molasses

Corn steep water and molasses are mainly byproducts in producing crystallized glucose by corn. It is very important to use these byproducts to produce edible foods and animal feeds in corn processing industry. Corn steep water and molasses are ideal culture medium for microorganisms because it contains abound protein, carbohydrates, vitamins and minerals. The yeasts are fermented in the mixture of steep water and molasses, and to be used to produce a quantity of yeast which is called single cell proteins (SCP). SCP is a kind of high quality protein animal feeds. Therefore, the paper focuses on the producing SCP by yeasts fermented in the mixture of corn steep water and molasses.Three yeast strains, Candida utilis yeast, Geotrichum candidum and Candida tropicalis, were choose to fermentation in the mixture of corn steep water and molasses. Based on the growth properties of three yeasts in the mixture, the dry weight and crude protein were 5.61 g/100mL and 1.29 g/100mL which was fermented by Candida utilis yeast (48h), and the dry weight and crude protein were 5.61 g/100mL and 1.37 g/100mL which was fermented by Geotrichum candidum (44 h), and the dry weight and crude protein were 5.78 g/100mL and 1.25 g/100mL which was fermented by Candida tropicalis (44h).According to the results of single yeast fermentation, the maximum dry weight and crude protein were 5.87 g and 1.78 g/100mL when corn steep water and molasses were fermented by two yeast strains (Geotrichum candidum and Candida tropicalis).Based on the basic composition of corn steep water and molasses and the single factor test of yeast fermentation, the optimum fermentation of single cell protein was that 10% Geotrichum candidum and Candida tropicalis (1:1) were inoculated into the mixture of corn steep water and molasses (15% w/w, pH3.5) and urea (3.5 g/100mL), and then it was fermented 48h at 30℃. The final dry weight and crude protein in fermentation mixture were 8.07 g/100mL and 5.27 g/100mL, respectively. Finally, the dried fermented mixture (SPC) was constituted by 70.18% crude protein and abounded of minerals (P, Ca, Fe, Zn and so on) and amino acids. Therefore, the SPC is nutritional animal feed.