94 Comparison of methods used to measure polyphenol oxidase in wheat.

D. VAZQUEZ (1,2), B. Watts (1), F. Townley-Smith (3), O. Lukow (3), and N. Ames (3). (1) Dept. Foods and Nutrition, University of Manitoba, Winnipeg, MB, Canada; (2) INIA, La Estanzuela, Uruguay; (3) Cereal Research Center, Winnipeg, MB, Canada.

Polyphenol Oxidase (PPO) has been implicated in enzymatic browning of wheat end products during processing or storage. This discoloration makes products less acceptable to consumers. The aim of this research was to identify a rapid, reliable method of measuring PPO activity for application in wheat breeding experiments. Methods for PPO activity were tested on two sets of white wheats, one set consisting of 27 samples of 6 classes, the second of 56 double haploid lines obtained from a cross of a white by red wheats, and 8 checks, grown in four locations. PPO activity was measured by an oxygen consumption rate method, and by two absorbance assay methods. One spectrophotometric assay method used an aqueous extract; the other the whole kernel. Catechol and tyrosine were used as substrates. Results for the oxygen consumption method and for assays performed using whole kernels, showed better results than for assays carried out on extracts. Correlation coefficients between PPO methods were determined for each set of samples. Results were correlated with dough discoloration data.