Mostafa Ghasemi - School of Chemical Engineering, Noushirvani University of Technology, Babol, Iran
Ghasem D Najafpour - School of Chemical Engineering, Noushirvani University of Technology, Babol, Iran
Habibollah Younesi - Department of Environmental Science, Tarbiat Modares university, Noor, Iran

The disposal of whey, the liquid remaining after the separation of milk fat and casein from whole milk is a major problem for dairy industry which demands simple and economical solutions.Ultra filter whey with different nutritional and process parameters was used as a substrate for lactic acid production by different strains of homofermentative lactobacilli.In this research different concentration of yeast extract (0,5,10,15 g/l) was used in media for lactic acid production. Batch process with retention time of 72 hours for lactic acid production was obtained. For batch process 10 g/l yeast extract was found to be optimal. The initial lactose concentration in whey was 50 g/l and the final lactose concentration was 4 g/l. At this amount of yeast extract the lactose consumption and conversion to lactic acid and biomass was 92 percent ، yield was 42 percent and productivity was 0.6 g.l-1.h-1. When the yeast extract concentration increases to 15 g/l inhibition effect occured.

Whey, Batch process, Lactobacillius bulgaricus, Lactic acid, Yeast extract