According to previous studies, L. acidophilus possesses several
mechanisms to counteract acid stress (Altermann et al., 2005;
Azcarate-Peril, Altermann, Hoover-Fitzula, Cano, & Klaenhammer,
2004). Kullen and Klaenhammer (1999) reported that the F1F0-
ATPase system maintaining the pHi was an important mechanism
for promoting survival in the presence of accumulating organic
acids.