| Euryale ferox Salisb.is the mature seed of aquatic floating leaf herb belonging the familiy Nymphaea,which is widely planted in the north and south of China.It has been recognized as a high nutritional value of tonics due to its multi-medicinal properties.Euryale ferox protein(EP)accounts for about 8%-10% of the dry weight of Euryale ferox seed kernel,much higher than that of wheat,rice and other cereals,and its essential amino acids are much higher than standard amino acids,so it is a source of high-quality dietary protein.However,the researches on Euryale ferox mainly focus on the cultivation of the plant and the pharmacological activities of its polysaccharides and polyphenols,and there are few researches on EP.Therefore,in this study,divergent ultrasound and energy-gathered ultrasound were used to extract EP,and the differences in structure,function and antioxidant activity of EP prepared by different ultrasonic modes were compared.Based on this,the EP extracted by optimized ultrasonic parameters was selected for enzymolysis,and the in vitro antioxidant activity of hydrolysates was evaluated,which may lay a theoretical and scientific basis for the resource utilization and product development of Euryale ferox protein.The main research contents and results are as follows:(1)Optimization of ultrasonic-assisted extraction process of EP under different ultrasonic modes.The temperature,solid-liquid ratio,power and time were optimized by orthogonal tests,and the optimal conditions for divergent ultrasound-assisted extraction of EP(SEP)were as follows: ultrasonic frequency 40 k Hz,power 300 W,temperature 40℃,30 min,p H 10.0,liquid-solid ratio 35:1(m L:g),the yield of EP was62.64% and the protein purity was 85.43g/100g;The optimal EP extraction parameters of energy-gathered ultrasound(PEP): ultrasonic frequency 28 k Hz,power 240 W,temperature 40℃,20 min,p H 10.0,liquid-solid ratio 45:1(m L:g).Under these conditions,the extraction rate of EP was 48.64%,and the protein purity was74.32g/100 g.The extraction rate of DEP extracted by divergent dual-frequency ultrasound was 52.44%,and the protein purity was 76.20g/100 g.Compared with traditional alkaline extraction method(TEP),the extraction rate of ultrasonic assisted extraction EP increased by 84.94%-138.08%.(2)Study on the structure and functional properties of EP by different ultrasonic treatmentsThe EP obtained by different ultrasonic mode assisted alkali extraction and traditional alkali extraction were respecytively SEP,DEP,PEP,TEP,the structure,functional properties and antioxidant activity were compared.The results showed that the structure,functional properties and antioxidant activity of EP were significantly improved by ultrasound with different modes.The β-folding relative content,hydrophobicity index,maximum UV and endogenous fluorescence absorption intensity of SEP were significantly higher than those of TEP,DEP and PEP(p<0.05),and their values were 31.82%,1382.63,1.02,117.56,respectively;Compared with TEP,DEP and PEP,SEP had the best oil retention,solubility and foaming properties,with the values of 7.85%,2.95mg/m L and 4.59%,the order of thermal stability and antioxidant activity of the four proteins were SEP>DEP>PEP>TEP.Therefore,SEP was selected as the sample for further study.(3)Antioxidant activity of hydrolysates of EP in vitroAfter ultrafiltration,three peptides,Mw<3kDa,3kDa<Mw<5kDa and Mw>5kDa,and the antioxidant activities of the hydrolysates with different molecular weights were evaluated by chemical system and cell system.The results showed that the scavenging power of DPPH·,ABTS+· and total reducing power of hydrolysates in each group were higher than those of SEP.Enzyme hydrolysates in each group could reduce ROS level and MDA content in oxidized HepG2 cells,and increase SOD activity,thus preventing oxidative damage of liver cells.The antioxidant activity of Mw<3kDa hydrolysates in cell system was higher than that of 3kDa<Mw<5kDa and Mw>5kDa hydrolysate. |
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