Reconstituted skimmed milk (RSM; 8 %w/v) was inoculated with 1 % (v/v) inoculum and fermented for 20 h at 37 °C
with continuous shaking at 100 rpm. Fermented RSM was
then centrifuged at 10,000 g for 15 min at 4 °C. The
supernatant (extracellular extract) were filtered (pore size,
0.22 μm) and stored at −20 °C prior to analysis. The sediment was suspended in sterile phosphate buffer saline
(PBS), sonicated (2 rounds of 15 min each, duty cycle
50 %, on ice) and recentrifuged at 10,000 g for 15 min at
4 °C. The supernatant (intracellular extract) were filtered
(pore size, 0.22 μm) and stored at −20 °C prior to analysis.
The cell wall-containing sediment was resuspended into
sterile PBS. Samples were stored at −20 °C prior to analysis