Comparative study of the biological activities of different commercial Stevia extracts from local market in Malaysia

Abstract

An increased awareness on consuming healthy food and beverages worldwide has led to an upsurge of interest in functional food, which includes the use of natural sweetener, the Stevia rebaudiana Bertoni extract. Nevertheless, limited data has been available on the biological activities of commercial Stevia extract available in Malaysia. Hence, the present study aims to evaluate the biological activities of commercial Stevia extract from local market in Malaysia, by evaluating its total phenolic (TPC) and total flavonoid content (TFC), as well as its antioxidant and anti-diabetic activities. Three independent Stevia extracts (Samples A, B and C) sourced from local market in Malaysia were evaluated, in comparison to the freshly prepared Stevia extract. The results showed a significantly lower amount of TPC in commercial Stevia extracts when compared to the freshly prepared Stevia extract (7.077 mg GAE/100 g), with sample A containing the highest TPC (6.359 mg GAE/100 g), followed by sample C (1.496 mg GAE/100 g) and sample B (0.624 mg GAE/100 g). Similar trend was observed with TFC, with sample A containing 0.937 mg QE/100 g, followed by sample C (0.264 mg QE/100 g) and sample B (0.029 mg QE/ 100 g) as compared to the freshly prepared Stevia extract (1.684 mg QE/100 g). Sample A showed the highest antioxidant activity (DPPH: 48.84%, FRAP: 2.589 μmole Fe2+/g, ABTS: 28.48%), albeit lower to the freshly prepared Stevia extract. The commercial samples showed a higher α-amylase inhibition activity compared to the freshly prepared Stevia extract, but no inhibition was observed in the α-glucosidase activity. Fundamentally, the results highlight the biological activities of Stevia extract for functional food applications, but caution has to be exercised as all three commercial extracts have significantly different biological activities.