High Antioxidant and Phenolic Contents Related to Antibacterial Activity against Gastrointestinal Pathogenic Bacteria of Some Thai Medicinal Plants

Objective: Thai medicinal plants were used as the traditional medicines and as part of everyday plants diet. Plants contain a mixture of phytochemical and exhibit a lot of functional food and medicinal properties. This project aims to investigate the potential of selected Thai medicinal plants according to the properties of their antioxidant and antibacterial activities. Methods: The eighteen plants were extracted using maceration method with 95% ethanol. The antioxidant activity was evaluated by DPPH and FRAP assay. The total phenolic content was evaluated by Folin-Ciocalteu phenol reagent. The antibacterial activity was evaluated by agar disc diffusion method. The extract which exhibited high antioxidant and antibacterial activity was selected to observe morphological changes by the scanning electron microscope (SEM). Results: The extract of Caesalpinia sappan showed the highest activities on both antioxidant assayed by FRAP method and total phenolic contents, however, exhibited high antioxidant assayed by DPPH compared to Bauhinia strychnifolia extract. Moreover, the extract of C. sappan showed the excellent antibacterial activities against six pathogenic bacteria in Gastro-intestinal tract. The morphological change by SEM was selected for further investigation antibacterial activities of C. sappan extract. The results showed that the inhibitory effect to those bacterial strains could be caused by the disruption of the cell membrane and decrease biofilm formation after treatment with the extract. Conclusion: The ethanol extract of C. sappan exhibited strong antioxidant and antibacterial activities against the six pathogenic bacteria. This result suggested that C. sappan could be applied to use for medicinal purpose and functional products.