Because of its high content of lactose (4.5%), unprocessed whey was a very polluting waste and because of its very low percentage of dry matter whey was expensive and difficult to move. In spite of the existence of many valorization processes (concentration,' drying,2 and constituent extraction3',, whey is still causing very important pollution problems especially in mountainous areas. As far as the industrial production of yeast proteins from deproteinized whey is concerned, it could not take place in the mountains because dairies are spread about which entails high transportation costs, and because they are small business they can't afford drying systems. Finally, the value of sweet whey is more difficult to entrance than acid whey. For all these reasons, the setting up of a yeast production process able to be integrated in a small dairy (10,000 L milk/day) was considered, This process has to be as economical and as reliable as possible.
This present work is concerned with the yeast culture from crude whey towards the complete lactose use and the maximum biomass production. The soluble proteins of whey must be harvested after fermentation in order to be added to the yeast proteins to make an animal food of a very high nutritional value. Although many works have been concerned with the cultures of the yeast strains as Khyvero- myces fragilis, Candida pseudotropicalis, and Candida intermedia5-8 on deproteinized whey the use of crude whey as a culture medium has not been developed until now."
MATERIALS AND METHODS
Culture Medium
Crude (nondeproteinized, nondiluted, nonsterilized) and sweet (pH 5.5-6.2) whey was used as culture medium. This whey contained 4.5% of lactose and was supplemented with 0.45% of ammonium sulfate [(NH4)2 SO,], 0.1% of yeast extract (Difco), and with a trace element solution" containing (1 mL/L): CuSO, -5H20, 0.3; MnSO, -HzO, 0.8; Na2M00, * 2 H 2 0 , 0 . 4 ; ZnSO, * 7 H 2 0 , 3.0; FeCl, * 6H,O, 4.0 made up with distilled water to 1 L.