Chikezie, P. “Extraction and Activity of Polyphenol Oxidase from Kolanuts (<i>Cola nitida</i> and <i>Cola acuminata</i>) and Cocoa (<i>Theobroma cacao</I>)”. Journal of Agriculture and Food Sciences, vol. 4, no. 2, May 2008, pp. 115-24, doi:10.4314/jafs.v4i2.41598.