Mechanism of the Suppressive Effect of NaCl on the Polyphenol Oxidase Activity of Vegetables

  • OBA Kazuko
    Nagoya Women's University, Department of Food Science and Nutrition
  • YAMAMOTO Atsuko
    Nagoya Women's University, Department of Food Science and Nutrition
  • ITO Sachiko
    Nagoya Women's University, Department of Food Science and Nutrition
  • FUJIE Ayumi
    Nagoya Women's University, Department of Food Science and Nutrition
  • TAKEUCHI Wakako
    Nagoya Women's University, Department of Food Science and Nutrition

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  • 食塩によるポリフェノールオキシダーゼ活性の阻害メカニズム
  • ショクエン ニ ヨル ポリフェノール オキシダーゼ カッセイ ノ ソガイ メカニズム

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Abstract

NaCl inhibited the activity of polyphenol oxidase (PPO) isozymes in apples, potatoes and mung bean sprouts. To elucidate the mechanism for the suppressive effect of NaCl on PPO activity in vegetables, we purified PPO from mung bean sprouts by means of ammonium sulfate fractionation and 2 column chromatographies. Six isozymes of PPO from mung bean sprouts were detected by means of SDS-polyacrylamide gel electrophoresis and chromatofocusing. The PPO isozyme of highest activity was pI 6.7. The PPO isozyme was purified as a single protein and the molecular mass was found to be 40 kDa by means of SDS-polyacrylamide gel electrophoresis. The enzyme showed an apparent Km value of 1.3 mM for chlorogenic acid. The enzyme was inhibited non-competitively by NaCl with a Ki value of 0.22M (1.27%). These results suggest that NaCl inhibits PPO activity non-competitively, and results in preventing the enzymatic browning of vegetables.

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