Fermentation activity, biomass yield, and productivity in skimmilk and whey permeates by 10 lactose fermenting yeasts as influenced by pH, lactose and ash levels were reported. Aerobic fermentations by the three most active yeasts were conducted in whey permeates at 30°C and pH 5.6 during 120 hr. Low ash levels, approximately OS%, in permeates above 15% lactose accelerated complete sugar fermentation and high aeration rates led to significant increases in biomass. Maximum biomass yields at greatest efficiencies were attained with K. frugilis ATCC 8582. It gave 8 and llg biomass (dry wt)/liter in 5 and 12% lactose permeates. Biomass production decreased markedly when the lactose concentration in permeates rose above 15%.

This review pertains the current knowledge concerned with the application of SCP in human and animal nutrition. General factors limiting the utilization of microbial proteins in human nutrition, such as toxicological barriers, nutritive value and functional properties, are discussed. Special attention is paid to several modern procedures of protein extraction from microbial cells, reduction of nucleic acids level as well as preparation of protein isolates. According to the data presented the latter can be considered as valuable protein substitutes. Significantly less nutritive problems are being concerned with the application of SCP in animal nutrition. Successful feeding experiments with chicken and pigs are discussed. Under these experimental conditions 10-20% of the protein in the feedstuff can be replaced by SCP. Moreover, several in Poland obtained protein-vitamin preparations are described. These originated from selected yeast and propionic acid bacteria grown in whey and its ultrafiltrates and can be considered as valuable food and feed supplements.

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The nutritive values o f propionic acid bacteria (Pb) grown in whey media as mixed cultures and as a 2-stage fermentation with a lactosefermenting yeast (Y-Pb) were determined. Yields were 14 g o f cells per liter f o r Pb cultures and 16 g/liter for Y-Pb fermentations. When the fermentation medium and cells were dried together, total solids equalled 28 glliter. The BOD of the whey was reduced over 90% in both fermentations. Adequate yields o f vitamins, particularly B1 , were obtained in both fermentations. The in vitro enzymatic digestibility of the cultures was increased by mechanical disruption o f cells; however, this cell breakage did not affect Biological Value (BV). The essential amino acid composition was equal to or better than the F A 0 Standard Reference Protein. The BV o f the Y-Pb was 25% higher than Pb and 10-40% higher than other microbial cell masses, including Torula yeast, commercial yeast and BP yeast from n-para f f in.