Beckman scintillation counter

Fatty acid consumption of Lactobacillus strains, L. rhamnosus GG (ATCC 53103), L. acidophilus (ATCC 4356), and L. gasseri (ATCC 33323) in bacterial growth medium was evaluated quantitatively using radioactive tracers, [¹⁴C]-OA and [¹⁴C]-palmitic acid (PA) (PerkinElmer, Waltham, MA). The glucose concentration in each bacterial medium was measured using a GM9 glucose analyzer (Analox Instruments, London, UK). Overnight cultures of Lactobacillus were diluted 100-fold (v/v) and subcultured three times to achieve viability, as described previously^{27 (link)}. [¹⁴C]-OA (1 µci) was added to 10 ml of MRS growth medium at 20 g/l, and three Lactobacillus strains (1x10⁸ cfu of each strain) were cultured for 6 h with shaking (37 °C at 220 rpm). For L. rhamnosus GG, 1 μci of [¹⁴C]-OA and [¹⁴C]-PA were further tested. One milliliter of cultured broth was aliquoted every 3 h and centrifuged (10 min, 4000×g), and the supernatant was collected. The pellet was resuspended and washed three times in MRS broth (10 min, 4000×g). ¹⁴C radioactivity was measured in both the supernatant and pellet of each aliquoted sample using a β-counter (Beckman scintillation counter, PerkinElmer, Waltham, MA).