3. Results and discussion
3.1. The decrease and control of pH during biofilm formation
incubation
To simulatemilk or milk residueswhich remained onmilk contact
surface after washing procedure, three dilutions of skim milk (0.1%,
1.0% and 5.0%) were prepared for single-strain inoculations of
B. licheniformis and L. paracasei. The changes of pH during incubation
were shown in Fig. 1. In unadjusted samples, pH decreased due to
bacterial development and acid production through proteolysis and
glycolysis pathway. B. licheniformis (Fig. 1A, B and C) had a weaker
ability to lower pH than L. paracasei (Fig. 1D, E and F). The lowest pH
values of 4.3 and 5.5 were attained at 5.0% skim milk solution by
L. paracasei and 1.0% skim milk by B. licheniformis, respectively.