| Lotus is an important resource in China. Jiangxi province is one of the domainproduction area in China, while Guangchang known as the "the hometown of lotusseeds", has become a large exporting and distributing center. Fresh lotus seedsharvested in summer, large amounts of output made storage even more difficult. Toenhance the additional value of fresh lotus seeds, change the traditional and relativelysingle pattern, which is essential to discuss the factors affecting the storage of freshlotus seeds. Lotus seed polyphenol oxidase (PPO) plays a main role in fresh lotusseeds browning change, which is one of the important factors that affect the sensoryand nutritional value. Therefore, the properties of both polyphenol oxidase andbrowning change during storage should be studied. At the same time, to develop anew type of drink with fresh lotus seeds as raw material. The main results are asfollows:1．Establish the methods of polyphenol oxidase purification from lotus seeds.Lotus seed PPO was extracted by phosphate buffer (including1%PEG and1%Triton X-100, pH6.8) in ice-bath, lotus seed PPO was precipitated by saturationammonium sulfate, purified by DEAE-Sepharose Fast Flow and Sephadex G-75gelcolumn, and gained freeze dry lotus seed PPO enzyme powder, then compared withthe standard protein molecular weight, the SDS-PAGE showed that lotus seed PPO’smolecular weight was about26kD.2．The enzymatic properties and structure characterization of PPO from lotus seeds.With catechol as lotus seed PPO substrate, results showed that PPO had thehighest activity at45-50℃and pH6.5-7.0. Calcium, manganese and ferric ions wereeffective in promoting PPO activity. Copper ion was highly effective in inhibitingPPO activity. PPO activity was inhibited by reductants, such as sodium bisulfate andsodium sulfite.The lotus seed PPO’s amino acid composition was analysised. The content ofnon-polar amino acids (Ala, Val, Leu, lle, Pro, Met, Phe, Trp), polar amino acids (Gly,Ser, Thr, Cys, Tyr, Asp, Glu, Lys, Arg, His), acidic amino acids (Asp, Glu), basic amino acids (Lys, Arg, His) were about31.2%,52.8%,18.4%and16.8%respectively.The conformation of lotus seed PPO was studied by circular dichroism. The resultsshowed that lotus seed PPO’s α-helix conformation and β-sheet conformationaccounted for24.35%and39.02%, while β-corner conformation content was16.67%,irregular curly conformation content was19.96%.3．Lotus seed physicochemical changes during storage at different temperature.Lotus seeds were stored at4℃and room temperature (27±3℃) for14days. Thecontents of moisture, vitamin C, total phenol, total soluble protein and reducing sugar,as well as the activity of polyphenol oxidase and browning degree were compared.The results showed that browning degree was on the rise, moisture and vitamin Ccontent were on the decline, soluble protein content, total phenol content and PPOactivity showed a trend of decline after rising first, reducing sugar content hadsignificant differences at different temperatures. Compared with room temperaturestorage, lotus seed browning degree and PPO activity were lower, while total solubleprotein, vitamin C and reducing sugar content were higher in lower temperature.4．The processing technologies of lotus seed beverage.Fresh lotus seed juice by enzyme hydrolysis technologic conditions as follows:4%material proportion of lotus seeds mix with25u/g dry powder of amylase enzymeunder72℃enzymolysis for60min. Then add multiplex emulsifiers with0.15%CMC,0.10%xanthan gum and0.05%carrageenan to obtain a better stability of lotusseed beverage. |
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