Comparative study of the antioxidant activity and the α-glucosidase inhibitory activity of the ethanol extracts from different parts of jaboticaba plant

Abstract:【Objective】The study compared the antioxidant activity, α-glucosidase inhibitory activity, and the contents of total polyphenols and flavonoids in ethanol extracts from different parts (peel, pulp, seed, young leaf, old leaf, root, stem) of jaboticaba plant, and analyzed the relationships of the contents of total polyphenols and flavonoids with the antioxidant activity and α-glucosidase inhibitory activity.【Methods】The plants of‘Sabah'jaboticaba were provided by Huichang Farmer Specialized Cooperative Society of Jaboticaba, Longhai, Fujian. Different plant parts of jaboticaba were crushed in 70% ethanol at a mass ratio of 1∶10 for 1 min with a shredder. Then the mixed liquor was shaken at 180 r· min-1, 28 ℃ for 16 h and centrifuged for 15 min at 6 000 r· min-1. The supernatant was collected and applied to determine the scavenging effects on DPPH·, · OH and ABTS+free radicals, the inhibition effect on α-glucosidase activity, and the contents of total polyphenols and flavonoids. Correlation analysis between the content of active substances (polyphenols and flavonoids) and antioxidant and α-glucosidase inhibi-tory activities were analyzed by SPSS 19.0 software.【Results】The extracts of different plant parts of jaboticaba exhibited obvious difference in contents of polyphenols and flavonoids, antioxidant capacity and α-glucosidase inhibitory activity. The contents of polyphenols and flavonoids of the extracts ranged from 1.51 to 274.72 mg· g-1 and from 0.66 to 111.94 mg· g-1, respectively. The content of polyphenols was in the order of young leaf > peel > old leaf > root > stem > seed > pulp, while that of flavonoids was in the order of young leaf >old leaf>peel>root>stem>seed>pulp. Thus, young leaves had the highest contents of polyphenols and flavonoids, whereas pulp had the lowest. The results of all tested samples showed a linear relationship between the capacities of scavenging DPPH ·, · OH and ABTS+free radicals and the concentration in a certain range of concentrations. According to the IC50 values obtained from linear regression equation, the capacity of scavenging DPPH free radicals was in the order of young leaf > peel>root> old leaf> stem> seed> pulp; the order of the capacity of scavenging hydroxyl radicals was in the order of young leaf> peel> old leaf> root> stem> seed> pulp; the ability of scavenging ABTS+radicals was in the order of young leaf > peel> root> stem> old leaf > seed> pulp. Thus, the3 antioxidant tests exhibited that the extract of young leaf showed the highest antioxidant activity, followed by peel. The pulp extract exhibited the lowest antioxidant activity. Except for pulp extract, the capacity of scavenging · OH of all extracts with an IC50 in the range of 127.80-1 060.80 mg· L-1 were much higher than the positive control of vitamin C (IC50=2 658.62 mg· L-1) . The inhibitory rate on α-glucosidase was linearly correlated with the logarithm values of extract concentration within certain range in all the tested samples. The IC50 value reflecting α-glucosidase inhibitory activity of 6 samples ranged from 1.99 to 39.04 mg· L-1. The inhibitory activity of all extracts from different plant parts in this study was much higher than that of acarbose (IC50=3 133.47 mg· L-1) , and in the order of young leaf > root>stem> peel> old leaf> seed. Similar to the antioxidant activity, the α-glucosidase inhibitory activity was the highest in young leaf extract, followed by root extract and stem extract, and seed extract was the lowest (pulp extract was not detected) . Correlation analysis revealed that the contents of polyphenols were significantly and positively correlated with the scavenging ability towards DPPH ·, · OH and ABTS+free radicals (P < 0.01, 0.983 2 < r < 0.996 7) and with the inhibitory activity on α-glucosidase (P < 0.01, r = 0.938 6) . Similarly, the contents of flavonoids were significantly and positively correlated with the antioxidant capacity (P < 0.01, 0.910 0 < r < 0.911 3) and with α-glucosidase inhibitory activity (P < 0.05, r = 0.851 6) .【Conclusion】The results indicated that there were obvious differences in the contents of total polyphenols and flavonoids, antioxidant activity and α-glucosidase inhibitory activity among the ethanol extracts from different parts of jaboticaba plant. The contents of polyphenols had the most significant positive correlation with the two bioactivities. The contents of flavonoids had the strongest positive correlation with antioxidant activity, and also a significant positive correlation with α-glucosidase inhibitory activity. The contents of total polyphenols and flavonoids, the antioxidant activity and α-glucosidase inhibitory activity in young leaves were the highest.