Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Identification of crucial factors in viability retention during passage of GI tract

During the consumption probiotics are exposed to various conditions in the upper GI-tract which may affect detrimentally their viability. The single most detrimental factor to probiotic viability in the GI-tract is the low pH of the stomach. In addition, e.g. bile secreted to the upper part of the small intestine has antimicrobial properties.

VTT: Influence of various test parameters on the acid and bile tolerance test result was evaluated to optimise the testing protocol: the parameters studied (strain and test) were cell density (L. rhamnosus E800, acid and bile tolerance), different bile reagents (B. animalis subsp. Lactis Bb-12), sterilisation technique for the bile solution (B. animalis subsp. lactis Bb-12 L. rhamnosus E800 and GG), molarity of the buffer solution (B. animalis subsp. lactis Bb-12; acid and bile tolerance), growth conditions (fermenter vs. test tube grown B. animalis subsp. lactis Bb-12, bile tolerance).Influence of processing conditions on acid and bile tolerance of B. animalis subsp. lactis Bb-12 was studied by using fermenter grown (15 and 22 h) cells prior and after freeze-drying with different cryoprotectants (sucrose and RSM as carriers for non-neutralised and neutralised cells). From the same freeze-dried preparations influence of food matrix storage on acid and bile tolerance of B. animalis was studied after harvesting the cells from milk, fruit juice or PBS (control) at baseline or after two weeks storage in milk and PBS. Kinetic changes in the membrane functions during acid treatment of B. animalis were further investigated by using a membrane potential-sensitive fluorochrome, DiBAC4(3), in conjunction with a fluorometer.

VTT: B. animalis subsp. lactis Bb-12 fresh cells tolerated well pH3.0 and poorly pH 2.5; pepsin supplementation had clearly protective effect against the pH of 2.5. The same phenomenon was observed with sucrose- and RSM-protected freeze-dried cells. Different freeze-drying conditions or fermentation times did not affect the acid tolerance of the cells. Milk showed clearly protective effect of the cells against low pH and some protection against bile acids. No significant differences in the bile tolerance of differently produced fresh or freeze-dried B. animalis cells were detected. However, the type of bile used had a large impact, bile extract being much more detrimental to the cells than bile acids. The DiBAC4(3) fluorescence measurements showed a rapid decrease of fluorescence during the acid exposure of the cells (more profound in pH 2.5 treated cells). This change in the membrane integrity suggests hyperpolarisation of the cell membrane during acid stress which can be associated to the activity of proton pumps.

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