The defatted fiber samples were extracted with 25 ml of cold, slightly alkaline water (pH 7.0 - 7.5) for 2 h at 20°C. The samples were then centrifuged at 1500 g or 3000 rpm for 10 min. The supernatants were removed and collected, and the procedure was repeated twice. Residues were extracted with 0.01 M EDTA solution for 2 h to bind cations and solubilize
the more pectic substances. The mixtures were filtered and the extraction repeated twice. After extraction, the residue was washed twice with 15 ml 80% ethanol and three times with 20 ml distilled deionized water. The washed residue was freeze-dried and kept for further analysis. This residue was called non-purified insoluble residue (NPIR).