Acid and Bile Tolerance and The Cholesterol Removal Ability of Bifidobacteria Strains

Abstract

Five strains of bifidobacteria were studied for their acid and bile tolerance, and their cholesterol removal ability from nutrient medium incorporated with cholesterol. All strains showed varying levels of tolerance at pH2.0 for 2 h, retaining viability ranging from 42.49 to 72.74% after 1 h. Most strains showed greatest tolerance to cholic acid and oxgall, and greatest inhibition by taurocholic acid. Cholesterol assimilation was determined by a difference in cholesterol content in the medium before and after the incubation period. All bifidobacteria strains were able to assimilate cholesterol, ranging from 4.17 to 27.14 μg/ml. Cholesterol assimilation patterns suggested that cholesterol removal was associated with growth of organisms. Binding of cholesterol to cells as determined using heat-killed cells and resting-cells in phosphate buffer indicated that a small level of cholesterol was removed by binding, ranging from 1.11 to 3.35 mg/g dry weight. Fatty acid compositions were compared between cells grown in the presence or absence of cholesterol. Changes in the fatty acid composition, especially tetradecanoic, hexadecanoic, octadecanoic, total saturated and unsaturated acids suggested that cholesterol removed was incorporated into the cellular membrane. Our findings suggest that bifidobacteria could remove cholesterol in vitro via assimilation, binding to cells and incorporation into cellular membrane, hence they may be potential candidates as dietary adjunct to lower serum cholesterol in vivo.