evaluated
factors (pH, NaCl concentration, temperature, and lactose availability)
influencing HdcA activity. The hdcA was mostly active at pH 4.5
but reduced activities were observed at higher pH (pH 8.0). In the
presence of salt concentration up to 5% (w/v) no significant differences
were observed in comparison with the control HdcA group.
For higher NaCl concentrations, the histamine amount decreased.
The optimum thermal stability of hdcA of S. thermophilus was
50 C but increasing temperate reduces activity. The addition of
lactose as carbon source caused only slight induction in hdcA
expression (Calles-Enriquez et al., 2010). The present molecular
studies indicated that the presence of hdcA gene was not correlated
with histamine production. Occurrence of BA production should be
taken into consideration rather than presence of genes.