Probiotika skal passere gennem maven og gå ind i tarmen, hvis de vil spille en probiotisk effekt. PH -værdien af gastrisk juice under faste er mellem 0,9 og 1,8, og den svinger mellem 1,8 og 5,0 under spisning og opretholdes normalt ca. 3,0. At være i stand til at tolerere et surt miljø er en vigtig tilstand for overlevelse af probiotika.
In artificial gastric juice with a pH of 1.5, Lactobacillus helveticus cannot survive; at a pH of 2.0, the survival rate of Lactobacillus helveticus is very low. The sampling time is 1.0 to 1.5 hours, and the number of viable bacteria drops by one order of magnitude. After 3 hours, it decreased by 2 orders of magnitude; artificial gastric juice with a pH value of 3.0 to 3.5 had little effect on Lactobacillus helveticus, and compared with pH = 7.0, there was no significant difference (P>0,05), der viser, at schweizisk mælkbacillus har stærk syrebestandighed