A BSH volumetric activity dependent method for determination of coprecipitated cholesterol and the assimilation/coprecipitation proportion of cholesterol removal by Lactobacillus plantarum

Abstract

The in vitro removal of cholesterol by probiotics has been categorized into two phases: assimilation by bacterial cells, and coprecipitation with deconjugated bile salts. Bile salt hydrolase (BSH) produced by probiotics catalyzes the deconjugation reaction of bile salts. A novel method that depends on the BSH volumetric activity (μg min-1 ml-1 bacteria culture) was developed to evaluate the cholesterol coprecipitation in MRS culture supplemented with synthetic human bile and cholesterol. Six probiotic Lactobacillus plantarum strains from the healthy youth intestinal tract were screened. The amount of cholesterol coprecipitation that occurred in each L. plantarum culture was then determined according to the method developed here and verified by a modified redissolution method. Next, the assimilation/ coprecipitation proportion of cholesterol removal for each strain was deduced. The results revealed that after 12 h of incubation, all six strains of L. plantarum removed a larger amount of cholesterol by assimilation (63.45-81.62%) than by coprecipitation (18.38-36.55%). Finally, we investigated the effects of synthetic human bile on BSH specific activity (μg min-1 mg -1 protein) and found that the BSH specific activity of all strains showed a rapid, limited and reversible decrease in response to synthetic human bile stress. We also found that variations in the BSH specific activity were related to the growth phases and that the maximum emerged after approximately 8 h (middle exponential phase) of growth.