Phenolic Acids Content and Antioxidant Capacity of Fruit Extracts from Thailand

In this study, soluble and insoluble phenolic acids (SPA and IPA) in selected Thai fruit such as orange, banana, guava and mango using isocratic HPLC-UV method were determined. Results showed that the predominant compounds of all fruit studied were IPA (80.2-99.5%). Gallic and hydroxybenzoic acids were identified as major SPA in guava and orange, respectively. Gallic, hydroxybenzoic, vanillic, caffeic, syringic and ferulic acids were identified as major IPA in all fruit samples. Ferulic acid was the dominant IPA in orange and banana extracts (335.8 +/- 13.38 and 219.5 +/- 18.47 mu g/g dry weights, respectively). Whilst, gallic acid was the dominant IPA in mango extract (542.5 +/- 6.80 mu g/g dry weight) and hydroxybenzoic acid was the dominant IPA in guava extract (50.5 +/- 8.12 mu g/g dry weight). The antioxidant capacity of all fruit extracts was also evaluated using a Folin-Ciocalteu's assay and DPPH free radical-scavenging assay. The phenolics in bound form of orange extract contained the highest total phenolic content (2.6 +/- 0.02 mu g GAE/ml). Its antioxidant capacity was 94.9%. Whereas insoluble phenolic content of guava extract had the least antioxidant capacity (22.0%).