Effect of varying processing methods (optimal conditions) on chemical properties of herbal leaf tea produced from “Voi” (Syzygium nervosum) leaves

Abstract

Tea is one of the most preferred food-drink due to its antioxidant potential benefit for human health. Syzygium nervosum leaves contain numerous bioactive components with different functional properties. Syzygium nervosum leaves can be processed into dried tea convenient for daily consumption. This research evaluates the effect of various thermal treatments like blanching, convective drying, roasting and steeping to the anti-nutritional factors, phenolics and antioxidant capacities in the S. nervosum dried leaf tea. Raw S. nervosum leaves were treated under different conditions of blanching (100/5, 95/10, 90/15, 85/20, 80/25oC/s), convective drying (65/10, 60/12, 55/14, 50/16, 45/18oC/hrs), roasting (150/2, 145/3, 140/4, 135/5, 130/6oC/mins), and steeping (100/2, 90/3, 80/4, 70/5, 60/6oC/mins). In each processing step, samples were taken to analyze tannin content, phytate content, oxalate content, total phenolic content, diphenylpicrylhydrazyl (DPPH) free radical scavenging and Ferric reducing antioxidant power (FRAP). Results show that S. nervosum leaves should be blanched at 90/15oC/s, convective drying at 55/14oC/hrs, roasting 140/4oC/mins, steeping in hot water at 80/4oC/mins to remove anti-nutrients while preserving the highest phenolics and antioxidants in the S. nervosum dried leaf tea. Results of this research will contribute important scientific data for processors and consumers in the exploitation of this medicinal plant as a healthy food drink.