pH conditions. Additionally, histamine was produced at all temperatures
and pH. Histamine production started during the exponential
proliferation stage, and continued during the stationary
phase.
For the cultures grown at 5 C (and at a pH > 5.5), the bacterial
count after 3 days was >107 CFU/mL, and the amount of histamine
exceeded 500 ppm. Additionally, after culturing for 5 days, the bacterial
count exceeded 108 CFU/mL under all pH conditions, and the
corresponding histamine levels exceeded 1500 ppm (Fig. 1a and b).
For the cultures at 10 C, the bacterial count exceeded 107 CFU/
mL under all pH conditions after hour 36, and the corresponding
amount of histamine exceeded 500 ppm. Additionally, following
culture for 48 h, the amount of histamine exceeded 1000 ppm at
pH 6.5 (Fig. 2a and b).