Bacterial growth was measured spectrophotometrically as optical
density at 600 nm (Shimadzu, UV 1203 model) after centrifugation of culture samples at 16,000g for 5 min. Optical density
data was converted to cell dry weight (expressed in grams per
litre) using the corresponding previously obtained calibration
curve. The lactobionic acid, lactose, gluconic acid, glucose and glycerol
contents of cell-free culture samples were measured by high
performance liquid chromatography as previously reported by
Alonso et al. (2011).