Sugar analyses were performed on suitably diluted (typically 2,500-fold) culture medium in 100 mM potassium phosphate, pH 7.0, containing 10 mM MgSO4, 1 mM NAD+, 1.5 mM ATP and 20 U mL−1Leuconostoc mesenteroides glucose-6-phosphate dehydrogenase (Worthington Biochemical Corporation). Concentrations of glucose, fructose, sucrose and fructan were determined from the changes in absorbance at 340 nm following sequential addition of 20 U mL−1
S. cerevisiae hexokinase (Worthington Biochemical Corporation), 20 U mL−1E. coli phosphoglucose isomerase (Megazyme International Ireland Ltd), 1.5 U mL−1
S. cerevisiae sucrase/maltase (Megazyme International Ireland Ltd) and 10 U mL−1 fructanase from Aspergillus niger (Megazyme International Ireland Ltd), respectively. Standards of glucose, fructose, sucrose and chicory inulin were used to calibrate the assay.
Ethanol determinations were made using a spectrophotometric ethanol assay kit (K-ETOH 11/06; Megazyme Ltd) according to manufacturer’s instructions. All samples were diluted 1,000-fold with distilled water prior to analysis.