| V.spinulosa Yan is submerged grass vegetation which belongs to Hydrocharitaceae. Its rhizome was edible. The browning occurred in storage and processing, which would effect on its merchandise appearance and edible quality. But the study on browning of rhizome of V.spinulosa Yan was rarely reported in the literature. Therefore, the changes of browning-related components of rhizome, browning substrates, purification and characterization of polyphenol oxidase from rhizome of V.spinulosa Yan were studied. The main results were as follows:1. The rhizome of V. spinulosa Yan showed that it contains 76.05%Water, 2.6%Protein, 0.9% Ash,0.4%Reducing sugar,7.7%Amylum,0.2%Sucrose, 7.9mg/100g Vc.2. The changes of reducing sugar and TP were the same as the PPO activity, which rose during storage and descended till15 day during storage, while it was different to the change of BD and POD activity, which rose during storage. Vc descended during storage. The browning in rhizome of V. spinulosa Yan were mainly due to the oxidation of phenols. Meanwhile, nonenzymatic factors have contributed to browning.3. The qualitative analysis of browning substrates by the thin layer chromatography, absorption spectrum showed that the chiorogenic acid was one of the main enzymatic browning substrates.4. The polyphenol oxidase in rhizome of V.spinulosa Yan was purified to 10.66 fold with a recovery of 21.25% though ammonium sulfate fractionation with saturation 30% and 80%, DEAE Sephadex A-50 and Sephadex G-75. The analysis revealed a single band on the SDS–PAGE which corresponded to a molecular weight of 33 kD.5. The experimental characterization results showed that the optimal pH and temperature were 6.0 and 50℃respectively, and the Km and Vmax value with catechol substrate were 0.0344 mol/L and 0.094U/min respectively, and PPO had good thermal stability. Ascorbic acid, NaHSO3, oxalic acid, sodium pyrophosphate, citric acid, malic acid and cycloheptaamylose were effective inhibitors. |
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