ENZYMATIC BROWNING OF MODEL SOLUTIONS AND APPLE PHENOLIC EXTRACTS BY APPLE POLYPHENOLOXIDASE

Model solutions containing chlorogenic acid (CG) and (-)-epicatechin (EP), and phenolics from nine apple cv., were oxidized with apple polyphenoloxidase (PPO). Browning was determined by absorbance at 380-700 nm, and transformed into CIE L*, a* and b*. Multilinear correlations were established between initial and degraded amounts of each phenolic. In model solutions of CG and EP, color values and A(400) correlated strongly with initial and oxidized CG and EP. Both phenolics contributed to decrease in L* and increase in A(400). Increase in CG increased a*, but EP had little effect. The impact of increased EP on b* was two to three times higher than for CG. In each phenol class (hydroxycinnamic (HD), flavan-3-ol (FA), flavonol (FO) and dihydrochalcone (DC) derivatives), degraded amounts were increased or decreased by increasing amounts of other classes. Besides major phenolics, HD (mainly CG) and FA (mainly EP and procyanidin B2), FO and DC, appeared to affect color development.