Effect of Heating Condition and pH on Stability of Total Phenolic Content and Antioxidant Activities of Samui (Micromelum minutum) Extract

: Samui ( Micromelum minutum ) leaf, commonly consumed in southern Thailand has a high potential of antioxidant. In this study, this plant was extracted with three various solvents; water, ethanol (95%) and acetone (60%), freeze-dried and then, re-dissolved in water. The factorial design was applied to evaluate the effect of pH (ranged from 5-7) and heat condition (60-80°C) on the stability of bioactive activity. The total phenolic content (TPC), DPPH radical scavenging, ABTS radical scavenging, ferric ion reducing antioxidant power (FRAP) and antioxidation by TBARs method were determined. The result indicated the influence of the solvent. Acetone extract seemed to be more effective compared to ethanolic and aqueous extracts. In addition, pH and heat conditions significantly affected the stability of TPC and antioxidant capacities (p ≤ 0.05). Generally, the TPC and antioxidant capacities were higher at higher pH. On the other hand, increasing heat conditions significantly deteriorated the TPC and antioxidant capacities. In conclusion, all studied factors influenced the stability of bioactive compounds and their activities which need to be considered when applying the extract into food.