Sample preparation: Ten grams minced pineapple
was homogenized with 40 ml methanol in a Sorvall
Omnimixer at 2°C. The homogenized was refluxed for
30 min at 50°C on a water bath. The mixture was filtered
through a ~atman No. 1 filter paper on a
Biichner funnel and the residue was washed with
methanol. The filtrate was evaporated under vacuum at
50°C in a Biichi rotavapor and the residue redissolved in
50 ml distilled water. This solution was filtered through
glass wool, cleaned up through a Sep-pak Cl8 cartridge
(Waters Associates) and filtered through a 0.45 pm
Millipore filter. The injection volume was 10 ~1.