Study On Extraction And Antioxidant Activitiy In Vitro And Others Of Polyphenols,Flavonoids From Onion Skin

The onion epidermis is rich in polyphenols and flavonoids,and its content is 2 to 6 times that of the internal bulbs.China is a major producer of onion,and most of the onion skin is discarded during onion processing and consumption.In order to make full use of the resources of onion skin,this paper studied the effect of different solvents on the extraction of total polyphenols,flavonoids and quercetin,and the anti-oxidation,inhibition of?-glycosidase and antibacterial activity of different concentrations of ethanol extracts.Screening for the appropriate solvent,and further based on the single factor test,through the second response surface design,optimizing the process conditions when extracting total flavonoids and quercetin onion,the main results found are as follows:?1?Ultrasonic-assisted extraction was used to extract total polyphenols and flavonoids from onion skin with ethyl acetate,petroleum ether,water,40%,60%,80%,95%and anhydrous ethanol as solvents.The extraction yield and purity of quercetin showed that the extraction rates of total polyphenols,flavonoids and quercetin from onion skin were significantly higher than those of petroleum ether and ethyl acetate.With the increase of ethanol concentration,the extraction yield and purity of the main active ingredients both increased first and then decreased.Among them,the highest polyphenols,flavonoids,and quercetin extractable rates in 60%ethanol extracts were up to 5.5 g/100 g,9.87 g/100 g,3.25 g/100 g,respectively;40%,60%ethanol extract quercetin purity is significantly higher,respectively 202.8 mg/g,195.6 mg/g;60%ethanol extract total polyphenols,flavonoids purity is significantly higher than other solvent extracts,reaching 331.2 mg/g and 594.4 mg/g,respectively.Taking into comprehensive consideration the extraction efficiency and purity of the main active ingredients of onion skin with different solvents,40%⁶0%ethanol solution has the best effect.?2?Through the vitro activity tests to study the anti-oxidation,inhibition of?-glycosidase and antibacterial activity of water and different concentrations of ethanol onion skin extracts,the results indicates:the total reducing power of 40%to 80%ethanol extracts was strong;40%⁶0%ethanol extract had better ability to scavenge free radicals;40%ethanol extracts clearDPPH·,ABTS⁺·,and O₂^?·IC₅₀0 values were 64±0.12,54±1.26,146±1.12?g/mL,respectively;The 60%ethanol extracts were64±0.22,60±0.88,and152±0.74?g/mL,respectively;The 40%ethanol extract inhibited the?-glycosidase activity better than other solvent extracts,and its IC₅₀0 was 329±3.12?g/mL;Anhydrous ethanol extract had a good inhibitory effect on Staphylococcus aureus,cabbage soft rot fungus,Bacillus subtilis,and its minimum inhibitory concentrations were 1.6,0.8,and 0.4 mg/mL,respectively.Considering the different concentrations of ethanol on the extraction of the main active ingredients of onion skin and its anti-oxidation,inhibition of?-glycosidase activity,using 40%⁶0%ethanol as the extraction solvent is better.?3?The correlation analysis shows that the contents of total polyphenols,flavonoids and quercetin of onion skin extracts were significantly or extremely significantly correlated with their antioxidant activity in vitro,and their correlations with in vitro antibacterial activities were not significant;The content of quercetin was also significantly or extremely significantly related to the inhibition of?-glycosidase activity.The correlation between polyphenol content and its inhibition of?-glycosidase activity was not significant.Amid them,the correlation coefficient between the content of quercetin in the extract and its scavenging free radicals and inhibition of?-glycosidase activity,in comparison to total flavonoids and polyphenols,was higher.Therefore,through the comprehensive analysis,total flavonoids and quercetin,especially quercetin,in the onion skin extract are the main active ingredient of its anti-oxidation,inhibition of?-glycosidase activity.?4?Based on the single factor test with factors of extraction temperature,ethanol concentration,solid-liquid ratio,and extraction time,the extraction process of total flavonoids and quercetin from onion skin is optimized through the secondary response surface design.The order of the factors affecting the extraction rate of total flavonoids is:extraction temperature>ethanol concentration>extraction time>ratio of solid to liquid;the order of the factors affecting the extraction rate of quercetin is:extraction temperature>ethanol concentration>solid-liquid ratio>extraction time.The optimal extraction conditions are as follows:material-liquid ratio 1:30 g/mL,extraction time 41 min,extraction temperature 88 ^oC,and ethanol concentration 49%.The extraction yields of total flavonoids and quercetin are 10.71%and 3.22%,respectively,close to theoretical values of 10.82%and 3.37%.