Effects of drying method and particle size on the antioxidant properties of leaves and teas of Morus alba, Lagerstroemia speciosa and Thunbergia laurifolia

Abstract

Antioxidant properties (AOP) of leaves and teas of Morus alba L., Lagerstroemia speciosa (L.) Pers. and Thunbergia laurifolia Lindl. as affected by microwave, oven and freeze drying were assessed. Total phenolic content (TPC), radical scavenging ability expressed as ascorbic acid equivalent capacity (AEAC) and ferric reducing power (FRP) were screened using the Folin-Ciocalteu, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and potassium ferricyanide assays, respectively. The effects of particle size were also investigated. Microwave drying resulted in enhanced AOP in M. alba and T. laurifolia. Oven drying resulted in declined AOP in T. laurifolia with M. alba and L. speciosa relatively unchanged. Significant increase in AOP was observed in freeze-dried leaves of M. alba with L. speciosa and T. laurifolia showing no change or slight increase. TPC, AEAC and FRP of ground microwave-, oven- and freeze-dried leaves of M. alba extracted with 50% methanol were significantly higher than shredded leaves. For tea infusions extracted with hot water, three categories were recognised, i.e. species with shredded leaves yielding stronger AOP (M. alba), species with ground leaves yielding stronger AOP (L. speciosa), and species with ground and shredded leaves yielding comparable AOP (T. laurifolia).