Effect of heat on antioxidant activity of Ati-ati Hijau (Plectranthus amboinicus) leaves extracts

Nowadays, there are a variety of antioxidants in the market, but most of them are thermolabile. Their antioxidant capacity decreases during processing and storage or value-chain distribution. Thus, it is necessary to discover a heat stable antioxidant to ensure their effectiveness for scavenging the free radical. Hence, the aim of this research is to determine the presence of heat stables antioxidant in Plectranthus amboinicus leaves. The fresh leaves of Plectranthus amboinicus were dried at 45 ºC and powdered. The leaves powdered were boiled in distilled water at 100 °C for 0, 30, 60, 90 and 120 minutes respectively. The water extracts were separated from leaves biomass by centrifugation and filtration. Then, the biomass is then sequential soaked in ethanol and ethyl acetate solvent to produce ethanol and ethyl acetate fraction respectively. The antioxidant activities of the extracts were determined by using 2,2- diphenyl-1-picryhydrazyl (DPPH), 2,2’-azinobis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) and Ferric ion reducing antioxidant power (FRAP). Total phenolic content (TPC) and total flavonoid content (TFC) were determined using Folin-Ciocalteu method and aluminium chloride colorimetric method, respectively. Profile of extracts was determined with Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC). Results indicated that heating increased the antioxidant activity in water, ethanol, ethyl acetate extracts when compared to the unheated sample. TPC and TFC showed the presence of phenolic and flavonoid compound in all extracts, and directly proportional to the antioxidant activity. TLC analysis showed the presence of alkaloids, phenolic, flavonoid, terpenoids, aldehydes and ketones. HPLC analysis showed the presence of caffeic acid and rosmarinic acid in some of the extracts, mainly in ethanol fractions. In conclusion, this study revealed the presence of heat stable antioxidant metabolites in Plectranthus amboinicus leaves that might be contributed by the phenolic compound. The discovery is beneficial knowledge for researchers who possibly will further study on this plant in the future which is useful for industry sector of functional food, cosmetic and pharmaceutical field.