Antioxidant activity and oxalate content of selected Thai herbal teas

Abstract

The extracts of 20 Thai herbal teas were evaluated for antioxidant activity by ferric reducing antioxidant power (FRAP) assay, total phenolic compounds using a modified Folin-Ciocalteu method, and calcium and oxalate contents using atomic absorption spectrophotometry. The results showed that the highest level of antioxidant activity was found in the tea extract of Phyllanthus emblica Linn., followed by Momordica charantia Linn. and Pluchea indica (L.) Less., respectively. The herbal extract that had the highest phenolic compounds was also Phyllanthus emblica Linn. A positive linear relationship between the antioxidant activity and total phenolic content of tea extracts (r value = 0.92) was found, indicating that phenolic compounds were the dominant antioxidant components in the studied herbal teas. Although the strong antioxidant effects present in herbal teas, high levels of calcium and oxalate can increase the risk of renal stone formation, leading to kidney stone disease. Therefore, from this present study, the recommended tea to consume is Phyllanthus emblica Linn. because of its low levels in calcium and oxalate and high levels of natural antioxidants.