ISOLATION AND CHARACTERIZATION OF BLACKSPOT PIGMENTS FROM POTATO-TUBERS

Blackspot related pigments were partially purified from bruised tubers of two commercial potato cultivars (cv. Bildstar and cv. Lady Rosetta ). Chemical characterization showed that these pigments consisted of p rotein and a relatively small amount of covalently bound constituents. These polymeric structures absorbed light throughout the visible spec trum without any maximum. They did not contain eumelanin. Quinic acid was detectable in hydrolysates of the pigments from Bildstar, but not in those of Lady Rosetta, which indicated that chlorogenic acid may ta ke part in blackspot formation, but is not essential for the discolora tion. The results support the hypothesis that blackspot pigments are p roducts of non-regulated reactions between nucleophilic amino acid res idues in proteins, and quinones, which are derived from endogenous sub strates of polyphenol oxidase. This means that blackspot formation mos t probably takes place in disintegrated cells.