Characteristics and Inhibition of Polyphenol Oxidase from Fuji Apples

후지 사과 Polyphenol Oxidase의 특성 및 활성억제

As a basic research for inhibition of enzymatic browning of apples during dehydration or processing, polyphenol oxidase was extracted from Fuji apples to investigate heat inactivation, chemical inhibition and other properties. Polyphenol oxidase showed the highest activity at $20^{\circ}C$ and pH 5.5 with catechol as substrate, and the Michaelis constant of 0.14 M under the same condition of substrate and pH. The thermal inactivation followed pseudo first-order kinetics to have activation energy of 23.0 kcal/mol and z value of $19.7^{\circ}C$. As for substrate specificity the polyphenol oxidase showed high affinity toward the o-diphenolic compounds, particularly chlorogenic acid. Neither the m- and p-dihydroxy phenols nor monophenols were attacked. Browning by polyphenol oxidase was completely inhibited at the concentrations of 10mM for potassiummetasulfite and thiourea and 1mM for L-cysteine, ascorbic acid and sodium diethyldithiocarbamate.

사과의 건조, 가공 중의 갈변을 방지하기 위한 기초 조사로서 후지 사과로부터 추출한 crude polyphenol oxidase의 특성과 열에 대한 저항성, 갈변 저해제의 저해 효과 등을 조사하였다. Catechol을 기질로 사용하였을 때 polyphenol oxidase의 최적 pH는 5.5, 최적온도는 $20^{\circ}C$, $K_m$ 값은 0.14M이었고, 열불활성화는 유사일차반응을 보였으며 이때 활성화에너지$(E_a)$와 Z값은 각각 23.0cal/kmol, $19.7^{\circ}C$였다. 기질에 따른 친화력은 o-diphenol, 특히 chlorogenic acid에 대하여 높았고, monophenol과 m-diphenol, p-diphenol에 대해서는 나타나지 않았다. Polyphenol oxidase에 의한 갈변은 thiourea와 potassium metabisulfite는 10mM에서, L-cysteine과 ascorbic acid, sodium diethyldithiocarbamate는 1mM에서 현저하게 저해되었다.