Antioxidative activity and α-glucosidase inhibitory activity of ethanol ex⁃tracts of leaves of different cultivars of jaboticaba

Abstract:【Objective】The study compared the antioxidant activity, α-glucosidase inhibitory activity,and the contents of total polyphenols and flavonoids of ethanol extracts from young and old leaves in 4 dif⁃ferent cultivars of jaboticaba, and to analyze their correlations.【Methods】The fresh young and old leavesof 4 cultivars of jaboticaba,‘Sabah’‘Sijizaosheng’‘Fukuoka’and‘Argentina’, were collected from Fujian-Taiwan Jiyong Cooperative Farm of Fruits and Vegetables, Longhai, Fujian. Leaves were crashed in70% ethanol at a mass ratio of 1∶10 for 1 min by a shredder. The liquor was shaken for 16 h at 28 ℃ and180 r·min^-1 and centrifuged for 15 min at 6 000 r·min^-1. The supernatant was collected and applied to de⁃termine the scavenging effects on DPPH·, ·OH and ABTS+ free radicals, the inhibition effect on α-gluco⁃sidase activity, as well as the contents of total polyphenols and flavonoids. Difference significance and thecorrelations between the content of active substances (polyphenols and flavonoids) and antioxidant activi⁃ty, α-glucosidase inhibitory activity were analyzed using SPSS19.0 software.【Results】Extracts of youngand old leaves from different cultivars had different levels of antioxidant capacity and a strong α-glucosidase inhibitory activity. The results of all tested samples showed a linear relationship between the abilityof scavenging DPPH·, ·OH and ABTS+ free radicals and the concentrations the components. According tothe IC50 values obtained from linear regression equation, the scavenging ability towards DPPH· free radi⁃cals was in the order of young leaves of‘Sabah’(ySa) > young leaves of‘Sijizaosheng’(ySi) > youngleaves of‘Argentina’(yAr) > young leaves of‘Fukuoka’(yFu) > old leaves of‘Sijizaosheng’(oSi) > oldleaves of‘Sabah’(oSa) > old leaves of‘Argentina’(oAr) > old leaves of‘Fukuoka’(oFu); the order ofthe ability of scavenging hydroxyl radicals was ySa > ySi > yAr > oSi > yFu > oSa > oAr > oFu; the abilityof scavenging ABTS+ radicals is in the order of ySa > ySi > yAr > oSi > yFu > oAr > oSa > oFu. Thus, thethree antioxidant tests exhibited the highest antioxidant activity in the extract of ySa, followed by that ofySi and yAr. The extract of oFu exhibited the lowest antioxidant activity. The capacity of scavenging ·OHof all extracts with an IC50 in the range of 127.80-960.63 mg·L^-1, was much higher than the positive control of ascorbic acid (VC, IC50=2 658.62 mg·L^-1). The α-glucosidase inhibitory rate was linearly correlat⁃ed with the logarithm values of extract concentration for all the tested samples. The IC50 value of α-gluco⁃sidase inhibitory activity of the 8 samples ranged from 1.99 to 38.71 mg·L^-1. The inhibitory activity of allextracts from jaboticaba leaves in this study was much higher than that of acarbose (IC50=3 133.47 mg·L^-1),and was in the order of ySa > ySi > oSi > yFu > yAr > oSa > oAr > oFu. Similar to the antioxidant activity,ySa showed the strongest α-glucosidase inhibitory activity, followed by ySi, and oFu had the lowest activi⁃ty. The contents of polyphenols and flavonoids of extracts ranged from 53.92 to 274.72 mg·g-1 and 49.84to 214.82 mg·g- 1, respectively. The content of polyphenols was in the order of ySa > ySi > yAr > oSi >yFu > oAr > oSa > oFu, but the content of flavonoids was in the order of yAr > ySi > oSa > yFu > ySa >oAr > oSa > oFu. The contents of polyphenols and flavonoids in the young leaves were significantly higher than those in the old leaves of the same cultivar (P<0.01). Correlation analysis revealed that theDPPH·,·OH and ABTS+ free radicals scavenging abilities were highly, significantly and positively correlated with the contents of polyphenols (P<0.01, 0.933 1α-glucosidasewas also significantly and positively correlated with the contents of polyphenols (P=0.009 6，r=0.836 5).However, the antioxidant capacity and α-glucosidase inhibitory activity had no significant correlationwith flavonoids (P>0.05).【Conclusion】The results indicated that there were significant differences in an⁃tioxidant activity, α-glucosidase inhibitory activity, and the contents of total polyphenols and flavonoidsamong the ethanol extracts from young and old leaves of different cultivars of jaboticaba. The antioxidantactivity, α-glucosidase inhibitory activity, and the contents of total polyphenols and flavonoids in theyoung leaves were obviously higher than in the old leaves for each cultivar in this study. These bioactivities had a significant positive correlation with the content of polyphenols. The extract of ySa had the highest antioxidant activity, α-glucosidase inhibitory activity, and content of total polyphenols among the 4cultivars, followed by ySi.