Study On The Enzymatic Browning Mechanism Of Fresh-cut Lotus Roots

The mechanical wounding by cuts led to the cell rupture lotus roots tissue, which accelerated enzymatic browning and the quality deterioration.. The reason of browning and its main substrates were analyzed, the enzymatic characteristics of PPO were measured, and the best combination containing four inhibitors at different levels was selected according to the orthogonal test. The main results were as follows:1. The changes of FP and BD had significantly negative relationship, while Vc and reducing sugar showed slight one to BD, which deduced that the browning in fresh-cut lotus roots were mainly due to the oxidation of phenols. The newly synthetic phenolic substances were mainly the FP which were the primary phenols catalyzed by PPO in lotus roots tissue after cuts. The FP and PPO activity changed synchronously and both reached the peak on day 6. The qualitative and quantitative analysis of browning substrates by the thin layer chromatography, absorption spectrum and HPLC showed that the catechol was the main phenols in lotus root tissue and its contents decreased significantly after browning, which is consistent with FP, so the catechol was identified as the enzymatic browning substrate and the main composition of FR2.The folds of PPO purification by precipitation of acetone and (NH4)2S04 were 3.2 and 7.8, respectively. The Km of PPO on catechol was 1.69mmolIL. The PPO had two optimum pH 5.0 and 8.0, and the optimum temperature was 30 c. PPO was relatively steady when pH was among 5.0 and 8.0 or3Thesis for Master抯 Degree~~k~眫tZ ~ (2001)temperature under 35 C. The different substrates showed the different combining capabilities to PPO. The combining capabilities of several substrates to PPO from lotus roots was in the following order: catechol>chlorgenic acid~pyrogal1ol pyrogallic acid>guaiacol>tyrosine. The PPO could be inhibited by NaHSO3, EDTA-2Na, Zn(Ac)2, CA, AA, L-Cys, NaC1 and Thi in varying degrees, and CA, L-Cys, NaC1 and Zn(Ac)2 were more effective than others.3.The most effective combination of inhibitors based on the L9(34) experiment was 0.1 %L-Cys+O.2%Zn(Ac)2+0.5%NaC1+0. 1 50/oCA and the order of inhibition to browning was CA>L-Cys>NaC1>Zn(Ac)2. The selected combination had almost the same inhibition to browning in fresh-cut lotus roots and was more economical, compared to the combination containing different chemicals obtained earlier by our laboratory.