Probiotici moraju proći kroz želudac i ući u crijeva ako žele igrati probiotski efekat. PH vrijednost želučanog soka za vrijeme post je između 0.9 i 1.8, a ona fluktuira između 1,8 i 5,0 za vrijeme jela i obično se održava oko 3.0. Biti u stanju tolerirati kiselo okruženje važan je uvjet za opstanak 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), što pokazuje da švicarski mliječni bacillus ima jaku otpornost na kiselinu