The improvement of milk by cultivation with ciliates

The exceptional nutritional values of milk have long been recognized. Howev er, important drawbacks of milk and dairy products are their relatively hig h cholesterol contents and their low proportion of polyunsaturated fatty ac ids. Hypersensitivity to milk proteins can also draw the public away from f luid milk consumption. The nonpathogenic ciliate Tetrahymena thermophila ha s a unique set of enzymes that converts cholesterol into provitamin D-3 and related compounds. It also contains Delta 12 fatty acid desaturases and re leases various hydrolases, including proteases, lipases, and phospholipases . We investigated the potential use of these peculiar traits to improve mil k by short-term incubation with live ciliate suspensions. We found that cho lesterol can be reduced to 50% of its initial content in whole milk by a 12 -h period of incubation with T. thermophila cells, mostly by conversion to Delta7-desaturated cholesterol derivatives, including provitamin D-3. In ad dition, a considerable increase in gamma -linolenate (18:3, n-6) takes plac e. The protein profile is markedly changed by proteolysis, with a striking reduction of casein and enhancement in total amino acid content. Despite th ese changes, no marked alterations in flavor or odor were observed at the e nd of 12 h of incubation. Thus, Tetrahymena appeared ideally suited to corr ect for milk drawbacks, making this important source of nutrients more acce ptable to the health-conscious public.