By the method of two-dimensional paper chromatography of the polyphenolic substances in apple fruit, three spots were detected, i.e., L-epi-catechin which was epimerized to L-cate-chin by heating, D-catechin which gave a small spot and was epimerized to D-epi-catechin, and chlorogenic acid which was hydrolized to caffeic acid (Fig. 1).
In these, L-epi-catechin and chlorogenic acid were isolated in crystalline form from fresh apple fruit (Kokko). These were expectedly oxidized by polyphenol oxidase of apple fruit (Fig. 2).
Catechins were estimated by nephelometry (Fig. 4), and chlorogenic acid was estimated by cdlorimetry (Fig. 4), and the relation was studied between the contents of these polyphenols and the quality of apple fruit, but no evidence was obtained (Table 2).