Diffusion of lactic acid in a buffered gel system supporting growth of Lactobacillus curvatus

Diffusion of lactic acid in a buffered gel system was investigated using fluorescent ratio imaging. The range of pH studied was from 5.5 to 3.8, which included the minimum pH of growth of Lactobacillus curvatus (4.26). Diffusion of lactic acid in this pH range was found to be Fickian and the estimated effective diffusion coefficient of lactic acid at 20 °C was 2.81 x 10-10 m2 s-1 with a standard deviation of 0.21 x 10-10 m2 s-1. This effective diffusion coefficient was estimated by fitting the one-dimensional solution of the Fickian diffusion equation for infinite systems to a transformed experimental data set. The original data set as recorded by the fluorescent microscope consisted of concentration-distance curves at specific time intervals. This was transformed by realigning the distance scale of all the concentration-distance curves.