Phenolic compounds, antioxidant and antibacterial activity of extract from leaves and bark of Stryphnodendron adstringens (Mart.) Coville

ABSTRACT There is currently growing interest in the investigation of bioactive compounds from natural sources. In this context, this study investigated the phenolic content, antioxidant capacity, and antimicrobial activity of the hydroalcoholic extract (EHA) of the stem barks and leaves of Stryphnodendron adstringens. Plant parts were extracted with ethanol:water (1:1) and filtered in a vacuum to obtain the crude extract. Phenolic content was determined by the Folin-Ciocalteu method. Antioxidant activity was measured using the DPPH test. The antimicrobial activity of extracts was evaluated against Gram-positive cocci: Staphylococcus aureus (ATCC 25923) and Staphylococcus epidermidis (strain isolated from a patient); and Gram-negative bacilli: Escherichia coli (ATCC 25922) and Pseudomonas aeruginosa (ATCC 27853). The zone of inhibition and the minimum inhibitory concentration (MIC) of the plant extracts were evaluated by the agar diffusion disc method and broth microdilution, respectively. Total phenolic content of the EHAs was higher in stem barks (970.4 mg GAE/g) than in leaves (693.8 mg GAE/g). In the DPPH assay, all extracts showed high antioxidant activity, above 75% at the concentration of 100 μg/mL. About antimicrobial activity, all the EHAs showed effects against Gram-positive bacteria S. aureus andS. epidermidis, whose MIC ranged from 7.81 μg/mL to 62.5 μg/mL. This finding is important since these pathogens are generally resistant to a variety of widely known antibiotics. Therefore, these results are promising and indicate the use of S. adstringens (Mart.) Coville as a natural antioxidant in foods, medicines and also point to its use in antimicrobial therapy.

摘要：当前，从天然来源中挖掘生物活性成分的研究日益受到学界关注。在此背景下，本研究针对收涩铁木（Stryphnodendron adstringens）茎皮与叶片的水醇提取物（hydroalcoholic extract, EHA）的酚类物质含量、抗氧化能力及抗菌活性开展了系统探究。采用乙醇-水（体积比1:1）对植物组织进行提取，经真空过滤获得粗提物。酚类物质含量采用福林-乔凯特法（Folin-Ciocalteu method）测定；抗氧化活性通过DPPH试验（1,1-二苯基-2-苦基肼试验，DPPH test）检测。提取物的抗菌活性评价菌株包括：革兰氏阳性球菌——金黄色葡萄球菌（Staphylococcus aureus, ATCC 25923）、从患者体内分离的表皮葡萄球菌（Staphylococcus epidermidis）；以及革兰氏阴性杆菌——大肠埃希菌（Escherichia coli, ATCC 25922）与铜绿假单胞菌（Pseudomonas aeruginosa, ATCC 27853）。分别采用纸片琼脂扩散法与微量肉汤稀释法，测定植物提取物的抑菌圈直径与最低抑菌浓度（minimum inhibitory concentration, MIC）。结果显示，水醇提取物的总酚类物质含量在茎皮中（970.4 mg 没食子酸当量（gallic acid equivalent, GAE）/g）高于叶片（693.8 mg GAE/g）。在DPPH试验中，所有提取物均表现出较强的抗氧化活性，在100 μg/mL浓度下的自由基清除率均高于75%。抗菌活性方面，所有水醇提取物均对革兰氏阳性细菌金黄色葡萄球菌与表皮葡萄球菌具有抑制作用，其最低抑菌浓度范围为7.81 μg/mL至62.5 μg/mL。该结果具有重要学术与应用价值，因为此类病原菌通常对多种临床常用抗生素存在耐药性。综上，本研究结果具有良好的应用前景，表明收涩铁木（Stryphnodendron adstringens (Mart.) Coville）可作为天然抗氧化剂应用于食品与医药领域，同时也提示其可用于抗菌治疗。