Sample preparation
Two g of crude RJ was placed in a 10 mL volu- metric flask, and a water/methanol solution (3:1) was added to make a final volume in the flask of no more than 9 mL, Flask contents were mixed. To weigh the RJ sample directly in the small 10 mL flask, a 5 mL plastic pipette tip was used: part of the bottom end of the pipette tip was cut away and the top end inserted in a rubber pipette filler. Then the RJ sample, already homogenized with a metal spat- ula, was drawn into the pipette tip and easily deliv- ered into the volumetric flask. Alternatively, a 3 mL polyethylene disposable Pasteur pipette can be used, after cutting away part of the tip.
Optionally, to include a surrogate standard, 0.2 mL of a solution composed of 5 g of xylose and 25 mL of a 3:1 solution of water/methanol was added. This gave a final xylose concentration of 4 mg/mL.
A 0.2 mL volume of Carrez I reagent (distilled water solution of potassium hexacyanoferrate(II), K4Fe(CN)6·3H2O, 15 g/100 mL) was added and mixed. Subsequently, a 0.2 mL volume of Carrez II reagent (distilled water solution of zinc acetate, Zn(CH3COO)2·2H2O, 30 g/100 mL) was added and mixed. The flask was then filled to 10 mL volume with the water/methanol solution and mixed. The solution was transferred to a 10 mL glass centrifuge vial and centrifuged at 4000 rpm for 15 minutes to remove the protein fraction.
An aliquot of 5 mL of the supernatant was trans- ferred to a 10 mL glass vial (provided with cap) that had been pre-washed with dichloromethane. Four to 5 mL of dichloromethane was added, the vial was capped and shaken and then vortexed vigorously for at least two minutes. The two layers were allowed to separate and the upper layer (containing the sugar fraction) was collected with a Pasteur pipette. Two additional extractions were performed on this sugar fraction as described above. Following the third extraction, the sugar fraction was filtered through a 0.45 μm disposable syringe filter (e.g. Whatman Puradisc 25AS, polysulfone filter media). The sam- ple was refrigerated and used for HPLC injection within 3 days.