Lactic acid is considered to be a very important organic acid, which used in
different food, dairy and other pharmaceutical industries. Therefore, the aim of this
work focused on the production of lactic acid with free and cc-lrnrnobillzed mixed
cultures which revealed that: starch hydrolyzate medium gave the highest lactic acid
co~nlraliOl'\. However, oeproleinizeo whey was found in the third order 01 lactic acid
production. Deprolelnized whey was used for further studies as a by-product from
cheese manufacture. 96 hours and 10% yeast extract Induced the production Of lactic
acid. The increase of lactic acid production in the fermentation media, as end
product, repressed Ihe production of lactic acid. 37°C was found as the optimum
temperature {Of lactic acid production. Lactic acid production was increased gradually
by increasing of inoculum size up to 3.0% (vlv, inoculum size to the producticn
media), Higher production of lactic acid was obtained by co-immobll1zed mixed
culture of L. de/bflJec1cii subsp. bulgaricus and S. saJiverius subsp. fhermophilus,
Increasing the Incubation time of co-irnrncbilaed mixed cultures, increased the
oevelopment of lactic acid concentration up to the end of fermentation time.