2.4. HPLC
High performance liquid chromatography (HPLC) of the sugars
and citric acid was performed on Waters 484 system, connected
to a refractometric Waters R401 detector and Aminex HPX – 87H
column (300 7.8 mm, BioRad), eluent 0.004 mol/l H2SO4, flow
0.5 ml/min, temperature 23 C. The standard compounds were purchased
from Sigma–Aldrich (Steinheim, Germany).