Abstract: The relationship between browning degree (BD)and relative ingredients in fresh-cut yams was analyzed during storageperiod. The characteristice of polyphenol oxidase enzyme (PPO) were assayed.The main browning substrate which led to enzymaticbrowning in fresh-cut yams was identified by thin-layer chromatography, HPLC and absorption spectrum. The results were:Thechanges of PPO activity and free phenol concentration in fresh-cut yams during storage were simultaneous and significantly related.This result indicated that the browning in fresh-cut yams was mainly due to the oxidation of phenols.The optimal temperature forfresh-cut yams was mainly due to the oxidation of phenols. The optimal temperature for fresh-cut yam PPO was 45℃,and theoptimal pH was 5.0 or 6.8. The capability of the PPO combining with various substrates was in the following order: chlorgenic acid>catechol> tyrosine>pyrogallol>pyrogallic acid> guaiacol> benophenol.The PPO activity could be inhibited by NaHSO3,EDTA-2Na,Zn(Ac)2,VC,L-Cys and NaCl at varying degrees.Among the inhibitors,NaHSO3 was the most effective,and its inhibition levelcould reach 92%.The main substrate identified for enzymatic browning in yam was chlorgenic acid.

Key words: fresh-cut yams, PPO characteristics, browning substrates