4种龙眼核提取物的总黄酮含量、体外抗菌活性与抗氧化活性

以聚酰胺吸附-硝酸铝显色法测定龙眼核水提取物、95%乙醇提取物、丙酮提取物、乙酸乙酯提取物等4种不同极性提取物的总黄酮含量，同时采用管碟法、最小抑菌浓度(MIC)法测定比较4种提取物的抗菌活性，并测定评价在二苯代苦肼自由基(DPPH自由基)体系、羟自由基体系、超氧阴离子自由基体系及抗脂质体过氧化体系中各提取物的抗氧化活性。结果表明：95%乙醇提取物的总黄酮含量最高，为(3.90±0.12)%，其抗菌活性也强于其他3种提取物，在质量浓度100mg/mL时，对大肠杆菌、普通变形杆菌、枯草芽孢杆菌、藤黄八叠球菌、金黄色葡萄球菌、白菜软腐菌、甘蓝黑腐菌7种菌的抑菌圈直径均达15mm以上，对各菌的MIC均≤100mg/mL；在不同的自由基体系中，4种提取物均对超氧阴离子自由基的清除作用相对较弱，但对清除DPPH自由基、清除羟自由基、抗脂质体过氧化均表现出较强的效果；以清除率达50%时所对应的样液质量浓度IC50作为指标比较发现4种提取物对3种自由基的的抗氧化作用由强到弱依次是水提取物、95%乙醇提取物、丙酮提取物、乙酸乙酯提取物，其中水提取物对这3种自由基的IC50分别为0.20、0.15、2.69mg/mL。可见，龙眼核的95%乙醇提取物适宜作为植物源抗菌剂，水提取物则适宜作为植物源抗氧化剂以深度开发利用。

Total Flavonoid Contents,Antibacterial Activities and Antioxidant Activities of Four Extracts from Dimocarpus longan Seeds

Four extracts including water extract, 95% ethanol extract, acetone extract and ethyl acetate extract from Dimocarpus longan seeds were determined for their total flavonoid contents by polyamide adsorption-aluminum nitrate color reaction method. Meanwhile, their antibacterial activities were evaluated by cylinder-plate method and minimal inhibitory concentration (MIC) method. In addition, the abilities of these extracts were tested to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, hydroxyl radicals and superoxide anion radicals and inhibit lipid peroxidation. The results showed that the 95% ethanol extract had the highest content of total flavonoids, which was (3.90 ± 0.12)% among the four extracts. Its antibacterial activities against Escherichia coli, Proteus vulgaris, Bacillus subtilis, Sarcina lutea, Staphylococcus aureus, Erwinia carotorora and Xanthomonas campestris were stronger than the other extracts. Its inhibition zones were more than 15 mm at the concentration of 100 mg/mL. The MICs of the four extracts against all tested bacteria were not higher than 100 mg/mL. The four extracts superoxide anion radicals had a relatively weak scavenging effect on superoxide anion radicals but could strongly scavenge DPPH and hydroxyl free radicals and resist lipid peroxidation. In terms of IC50 (the concentration required for 50% inhibition), the scavenging effects of the four extracts against DPPH, hydroxyl and superoxide anion radicals ranked in the following sequence: the water extract, the 95% ethanol extract, the acetone extract and the ethyl acetate extract. The IC50 values of the water extract were 0.20, 0.15 mg/mL and 2.69 mg/mL, respectively. Therefore, it can be clearly seen that the 95% ethanol extract is a suitable source of botanical antibacterial agent, and the water extract is more suitable to be deeply developed and utilized as a source of botanical natural antioxidant.