The brown filtrate was mixed
with 5% activated carbon (Aldrich) for 2 h to remove protein, color,
and cell debris, and the mixture was again clarified by centrifugation
and filtration as described above. The solution was then
passed through an ion-exchange resin column (Amberlite IR
120H+, £ 2 cm 40 cm) at 5 mL min1 to protonate the acids.
The eluent (pH 2) was vacuum distilled at 70–80 C, filtered
(0.45 lm nylon), to obtain a concentrated solution of LA.