Lactic and acetic acids are generated inside the cell via carbohydrate catabolism and exported out through the membrane by citrate transporter to maintain cell homeostasis (Magni et al.1999). Lactobacilli metabolize carbohydrates either homofermentatively or heterofermentatively to produce lactic acid and acetic acid as predominant endproducts, with at least 50–85 % lactic acid. Bifidobacteria,on the other hand, metabolize carbohydrates via the bifidus pathway to produce more acetic acid than lactic acid. However, our results showed that bifidobacteria produced more lactic acid than acetic acid. Bifidobacteria have been reported to alter their metabolic pathways,depending on the availability of carbon sources, and thus may result in higher production of lactic acid than acetic acid (Palframan et al. 2003). In this study, all strains of
lactobacilli and bifidobacteria were able to produce lactic acid at total concentrations ranging from 3.50 to 4.75 mg/mL.
Beneficial effects of lactic acid on skin such as improving skin barrier function, hydration and lightening have been extensively reported. It is also reported that topical application of lactic acid at low concentrations of 0.1–1 % could exhibit
antibacterial activity against most dermal pathogenic bacteria(Pasricha et al.1979). Our current study also showed that
strains of lactobacilli and bifidobacteria were able to produce acetic acid at total concent rations ranging from 1.84 to 3.32 mg/mL. Nagoba et al. (2008) reported that topical application of acetic acid at a low concentration of 0.5 % successfully eliminated Pseudomonas aeruginosa from burns and soft tissue wounds of 14 out of 16 patients within 2 week