The pHs of single or combined antimicrobial substances are listed in Table 6. The pHs of the single EOs were 5.81, 5.45 and 5.01 for carvacrol, thymol, and eugenol, respectively. The pHs of two of the EOs were slightly lower than those of the single formulas, such as 4.31, 4.13 and 4.12 for carvacrol + thymol, carvacrol + eugenol, and thymol + eugenol, respectively. The pH of three EO substances combination was 5.26. The pHs of combinations with organic acid were 2.5–3.1, and combinations with acetic acid were little higher than those with lactic acid.