Lactic acid is an organic acid which has a wide range of application in food, pharmaceutical, leather and textile industries. Lactic acid is produced via chemical synthesis and also fermentative processes. In microbial fermentation, lactic acid is produced by lactic acid bacteria. The aim of present research was to investigate the effect of lactose concentration in production of lactic acid from cheese whey using Lactobacillus bulgaricus (ATCC 8001, PTCC 1332) in a batch culture. Fermentation media was inoculated, stirred at 180 rpm and incubated at 32°C. Substrate consumption and lactic acid production were determined. Four defined lactose concentrations were used in fermentative lactic acid production. Maximum lactic acid production of 24.57 g.lG1 was achieved with initial lactose concentration of 40 g.lG1. As the concentrations of lactose in the fermentation media was reduced from 40 to 10 g.lG1, the yield of lactic acid production from 0.69 to 0.81 g lactic acid per g lactose was improved.

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