Abstract
Black spots are often developed on the surface of frozen pie sheets during refrigeration before using. Investigation on the nature and the mechanism of the appearance of the black spots showed the following results: no typical microorganisms were observed, but wheat bran was observed in every black spots by an electron microscope, and inhibitors of polyphenol oxidase enriched in wheat bran could delay or inhibit the appearance of the black spots. These results show that polyphenols and polyphenol oxidases contained in the bran contaminated in wheat flour are the cause of the black spot formation. Furthermore, one isozyme of polyphenol oxidases in the bran was determined as a causative enzyme from the inhibitory pattern of various inhibitors on polyacrylamide gel electrophoretic analysis of bran extracts. Several inhibitors containing cysteine and an extract of garlic were efficient for use in inhibiting the formation of black spots without impairing taste and texture of baked pies.
