Ten gram of sample and 1 g of PVPP (polyvinylpyrolidone)
were homogenized with 20 ml of cold (4 C) 0.2 M sodium
phosphate buffer (pH 6.5). After blending for 1 min, the homogenate
was filtered through 2 layers of cheesecloth; and
then the solution was centrifuged (4 C) at 14.000 rpm for
30 min. The supernatant was filtered through Whatman #1
paper and kept on ice until analyzed. Two independent
extractions per treatment were performed in triplicate.