Citrate utilization and production of diacetyl among lactobacilli has been extensively studied over the past few
decades, and these studies showed that homofermentative
species produced diacetyl more readily and in larger volumes than the heterofermenters (Christensen and Pederson
1958). Interestingly, our results showed that the heterofermenter, L. casei BT 1268 strains produced higher amounts
of diacetyl than the homofermenter, L. gasseri FTDC 8131. Østlie et al. (2003) reported that the production of diacetyl
through citrate metabolism was dependent on the genus of
bacteria and the growth conditions, while Christensen and
Pederson (1958) has reported that the production of diacetyl
was dependent on the different strains within the same
species. The difference in concentrations of diacetyl in extracellular and intracellular extracts has been attributed to
different efficiencies of transport across the cellular membrane. It has been reported that the limiting step for the
utilization of citrate is the requirement for specific transporters, which facilitate its intake into the cells prior to
production of diacetyl (Quintans et al. 2008). Also, this
limiting step and transport efficiency vary between microorganisms, which support the varying concentrations among
the strains studied, for both intracellular and extracellular
extracts. Our results showed that all strains were able to
produce diacetyl at total concentrations ranging from 6.70 to
31.31 mg/mL. It has been reported that diacetyl exhibited
antimicrobial activity against Gram-positive skin pathogens
such as Staphylococcus aureus at concentrations as low as
3 mg/mL (Lanciotti et al. 2003), indicating that the amount
of diacetyl produced by our current strains of lactobacilli
and bifidobacteria have the potential to exhibit dermal antimicrobial activities.