Role of the food matrix in gastrointestinal survival of probiotic microorganisms using in vitro digestion of model cheese

Several kinds of cheese naturally contain live microorganisms which may also have probiotic potential. These strains must first survive within the gastrointestinal environment to mediate any health promoting activity. This study aimed to examine the ability of a model cheese to protect probiotic lactic acid bacteria from pH and bile stress in the gastrointestinal tract using an in vitro digestive model. Nineteen bacteria strains from Trentino cheeses were tested for their capacity to inhibit the growth of important human gastrointestinal pathogens. Nine strains showing to inhibit at least one pathogen were chosen for acid and bile tolerance tests. Two strains were highly resistant to the pH stress and their viability changed by only one log after 2 hours at pH 2.5. Under the same conditions, the other 7 strains showed a decreased viability of 4-6 log. Bile acid affected the growth rate of 5 bacteria strains at 0.2%. while 0.4% affected the growth rate of 3 strains, and 1 strain appeared not affected by the presence of bile acids. This latter strain was characterized by a low growth rate overall. Three strains belonging to the genus Lactobacillus were studied in vitro gastrointestinal model both as pure culture and in cheese. The combined stress of low pH and bile acid diminished bacterial viability however the cells survived better in the cheese matrix: their viability in the in vitro gastrointestinal model was 4 log higher in cheese compared to pure culture after passing. This study identified putative probiotics within the lactic microbiota of Trentino cheeses. Moreover, it appears that the cheese matrix itself may aid in the survival of probiotic lactic acid bacteria within the gastrointestinal tract, suggesting that cheese with diverse and abundant lactic microbiota may have potential as natural probiotic foods.