Effect of blanching and convective drying on phytochemical constituents of dried tea from white mulberry (Morus alba) leaf

Abstract

White mulberry (Morus alba) leaf is highly valued due to its health-promoting attributes. It is specified by a great content of phytochemical constituents with excellent antioxidant properties. This research was conducted at STNanotech Laboratory in 2021 to evaluate the dried tea production from the white mulberry leaf. The total phenolic content, total flavonoid content, DPPH free radical scavenging, FRAP ferric reducing antioxidant and beta-carotene bleaching activity in the raw white mulberry leaf were primarily analyzed. The raw white mulberry leaf was blanched in different conditions (100/5, 95/10, 90/15, 85/20 and 80/25 oC/s) to inactivate enzymes. The blanched leaves were cut into small pieces with dimension of 0.5 × 3.5 cm. The cut mulberry leaves were then convective-dried at different conditions (50/18, 55/15, 60/12, 65/9, and 70/6 oC/h) by a convective dryer. Dried tea was left to cool and ready for testing of total phenolic content, total flavonoid content, DPPH free radical scavenging, FRAP ferric reducing antioxidant and beta-carotene bleaching activity. Results showed that raw mulberry leaves should be blanched in hot water at 95/10 (oC/s) and convective-dried at 60/12 (oC/h) to maintain the highest bioactive contents and antioxidant properties. The dried mulberry leaf tea still retained the most valuable ingredients in raw material.