Survival rate of lactobacilli during digestion. An in vitro study

Abstract

Various fermented milk products are recommended by physicians to restore the lactobacilli in an altered GI-flora. It is, however, not known which fermented milk type is best suited to the purpose or whether lactic starters used by the dairy industry have the ability to survive in gastric juices during digestion in the stomach. Fermented milk types investigated were: 1) buttermilk (filmjolk). containing Streptococcus lactis. Streptococcus cremoris, Streptococcus diace-tylactis, and Leuconostoc citrovorum (cremoris); 2) yogurt containing Lactobacillus bulgaricus and Streptococcus thermophilus; and 3) acidophilus milk containing Lactobacillus acidophilus. In vitro digestion was carried out using a homogenized breakfast mixture consisting of orange juice, cheese sandwich and coffee in amounts supplied in a hospital menu. Human gastric juice (pH = 1.5 to 1.8) was added in proportions normally secreted in the stomach during digestion. The mixture was divided into three samples, to which buttermilk, yogurt or acidophilus milk was added. The pH was noted and a zero time sample was taken immediately, diluted (10-3,10-5,10-7) and cultivated. The homogenized mixtures with fermented milks added were incubated in a water bath and samples were taken at 1,2, and 3 hr. Samples were cultivated anaerobically at 37 C for 24 hr. The results indicate that the lactobacilli in buttermilk were the first to decrease. After I hr digestion only a few colony forming units were found. The bacteria in yogurt had a higher survival rate than those in buttermilk. However, at the end of the 3rd hr only a few colony forming units were found. The microbes used in acidophilus milk showed the highest survival rate in this investigation; appreciable numbers of colony forming units were found after 3 hr digestion. These results suggest that the microbes of acidophilus milk may pass the stomach barrier in greater number than those of yogurt or buttermilk.