Folate is synthesized from its precursors PABA, glutamate and GTP. PABA is obtained from the shikimate pathway and
GTP is produced through the purine biosynthetic pathway.
The folate production by Lactococcus lactis was found to be dependent on the concentration of PABA in the culture medium (Sybesma et al. 2003b). Our results were also in accordance to this.
The addition of varying concentration of PABA into the skim milk medium increased the folate production.
Maximum of 31.93±2.8 μg/L extracellular folate was obtained when 100 μmol/L PABA was supplemented (Fig. 3).
The elevated PABA levels in the medium could result in the inactivation of folylpolyglutamate synthetase, the enzyme
responsible for the elongation of the polyglutamate tail of the folate molecule thereby increasing the amount of secreted
folate (Wegkamp et al. 2007).
The intracellular retention of polyglutamyl folates is higher than the monoglutamyl folates.
Similarly, the addition of glutamate also resulted in an increase in the released folate.
The cumulative effect of PABA and glutamate resulted in 37.56±1.8 μg/L extracellularfolate (Fig. 4).