Enzyme assaysThe effect of hydrogen peroxide and phenolic compounds on the decolorization of betanin and a betaxanthin preparation by horseradish peroxidase (HRP) was examined. Betanin was decolorized at a greater rate than the betaxanthm pigments and both reactions were HzOz-dependent. Betaxanthin was more prone to oxidatic decolorization than beta&. 2,4-Dichlorophenol, resorcinol and o-toluidine stimulated the decolorization of both pigments. Guaiaco1 enhanced the peroxidatic decolorization of both pigments to a small extent, but inhibited the oxidatic breakdown of betaxanthin. Possible implications of these results are discussed.The standard 1 ml assay mixture contained approximately 12 PM betanin (As38 = 0.8-1.1; E = 65,000 L-cm-l-M-') or 20 PM betaxanthin (A476 = 0.5-0.6; E = 25,000 L-cm-'*M-i) in 100 PM citrate-phosphate buffer, pH 3.4, and 0 or 10 PM H202. In assays containing phenolics, final concentrations are given with individual results. Reactions were initiated by the addition of HRP and absorbance losses measured at 25°C using a Gilford 2600 spectrophotometer. Rates of nonenzymic pigment loss were negligible.

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The red beet root cell wall betanin decolorizing enzyme was solubilized by digestion of tissue slices with cellulase, pectinase and glusulase. The cell wall hydrogen peroxide generating system was inactivated by the digestion process. Lysis of released protoplasts demonstrated the presence of a soluble intracellular decolorizing enzyme. The intracellular form, representing approximately 25% of the total activity, appears to have become ionically bound to cell wall fragments when intact tissue was homogenized and could be released by washing with 1M NaCl.