Probiotici moraju proći kroz želudac i ući u crijeva ako žele igrati probiotički učinak. PH vrijednost želučanog soka tijekom posta je između 0,9 i 1,8, a tijekom prehrane fluktuira između 1,8 i 5,0, a obično se održava na oko 3,0. Mogućnost 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 snažnu otpornost na kiselinu