Nonpolluting Conversion of Whey Permeate to Food Yeast Protein

Abstract

By using concentrated whey permeate as substrate, food grade yeast (Kluyveromyces fragilis) was grown continuously in the fermentor to very high cell densities (total broth dry weight of over 140 g/L). The high ash content in whey permeate was not inhibitory to cell growth. Cell mass yield remained about constant at pH range 3.9 to 5.1, temperatures between 31 to 37C, with 6 to 30% whey permeate solids in the feed. Dilution rate (.1 to .3 h -I) had little effect on the cell mass yield. At temperatures higher than 38C, yield decreased. The high cell density fermentation broth was directdried without centrifugation and washing and the composition of the direct-dried product was determined. Amino acid profile, vitamin content, and fatty acid composition indicated a quality protein product suitable for food or feed supplementation. Ash content of the product was higher than other dried yeasts because of the high mineral content in whey permeate. Ash content could be significantly reduced by the addition of a small portion of another inexpensive fermentable sugar to the whey permeate feed. With this addition, cell mass yield, productivity, and protein content of the product increased. Because this high cell density, direct-dry process did not require preconcentration of the fermentor broth to dry the product economically, it did not generate a waste stream that required further treatment. This process converts waste whey permeate to useful food protein and essentially eliminates potentially polluting waste streams.