Characterization of three polyphenol oxidase isoforms in royal dates and inhibition of its enzymatic browning reaction by indole-3-acetic acid

Abstract

In this study, Polyphenol oxidases (PPO) from royal dates fruit was purified and characterized. These procedures led to 8-fold purification with 14.72% recovery. Three isoenzymes of royal dates PPO exhibited a molecular weight of 20.,45 and 64 kDa. The royal date PPOs had maximum activity at pH 4.6 and 8, 3.6-5.6 and 5.6 with pyrogallol, 4-methylcatechol and pyrocatechol substrates, respectively. The enzyme showed high stability in the temperature range of 30-60 °C.4-Methylcatechol was the most suitable substrate, due to the lowest Km and the biggest Vmax/Km values. The kinetic of thermal inactivation were performed in a temperature range of 60-75 °C. A biphasic model provided a good description of dates PPO thermal inactivation. Indole-3acetic acid markedly inhibited Royal dates PPO activity. Its Anti-browning effect on dates was investigated. IAA-treatment reduced weight loss, pericarp decay, browning index and membrane electrolyte leakage. Thus, a higher total anthocyanins contents and total phenolic contents was correlated with higher DPPH scavenging activity and lower MDH contents Such effect was accredited to maintain of membrane integrity and inhibition of oxidative enzymes by IAA. In conclusion, IAA could be used as a potent inhibitor of fruits enzymatic browning reaction.

Keywords: Characterization; Enzymatic browning; Indole-3-acetic acid; Inhibition; Polyphenol oxidase; Royal dates.