*Corresponding author. Email: mkhairi@umt.edu.my eISSN: 2550-2166 / © 2019 The Authors. Published by Rynnye Lyan Resources Food Research 4 (1) : 175 - 183 (February 2020) Journal homepage: http://www.myfoodresearch.com FULL PAPER Effect of steaming time on antioxidant properties of Napier grass herbal tea by green tea processing method 1 Ng, K.S., 1,2 Mohd Zin, Z., 1 Mohd Maidin, N., 3 Abdullah, M.A.A. and 1* Zainol, M.K. 1 School of Food Science and Technology, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu, Malaysia. 2 Centre for Fundamental and Liberal Education, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu, Malaysia. 3 School of Fundamental Science, Universiti Malaysia Terengganu, Kuala Nerus, Terengganu, Malaysia Article history: Received: 21 July 2019 Received in revised form: 30 August 2019 Accepted: 1 September 2019 Available Online: 10 September 2019 Keywords: Napier grass, Antioxidant properties, Herbal green tea, Steaming DOI: https://doi.org/10.26656/fr.2017.4(1).263 Abstract This study aimed to determine the effect of steaming time on antioxidant properties of Napier grass green tea. Napier grass was subjected to steaming for 1, 2, 3, 4, 6, 8 and 10 mins. Fresh and dried samples were extracted in water (95°C, 30 mins) and the extracts were then analysed by total phenolic content (TPC) assay, total flavonoid content (TFC) assay, diphenyl-picryl-hydrazyl (DPPH) assay, Ferric reducing antioxidant potential (FRAP) assay, ferric thiocyanate (FTC) method and thiobarbituric acid (TBA) method. Sample steamed for 8 mins showed the highest TPC (18.32±0.26), TFC (152.71±5.74) and 109.88±5.44 in FRAP assay. High antioxidant activity was found in sample steamed for 3 to 10 min (81.63±1.19 to 83.50±1.10) in DPPH which were not significantly different with the fresh sample indicating steaming can retain the phytochemical compounds. Samples undergone 6 to 10 mins steaming time were found to have high lipid peroxidation in ferric thiocyanate (75.02±2.96 to 81.01±6.68) and thiobarbituric acid (85.99±1.56 to 86.21±1.44) assays. The results suggested that 8 mins of steaming time is suitable for Napier grass green tea as it exhibited the greatest antioxidant properties. 1. Introduction Fruits, herbs, vegetables and various plants are natural sources of antioxidants (Balasundram et al., 2006; Andres-Lacueva et al., 2008; Brito et al., 2014). Numerous previous studies and reviews had reported the benefits of the intake of foods with high contents of natural antioxidants in disease prevention (Duthie and Bellizzi, 1999; Young and Woodside, 2001; Bennett et al., 2012; Hashemi et al., 2014; Sadowska-Bartosz and Bartosz, 2014; Zhang et al., 2015; Rani, 2017; Khan et al., 2018). The major compounds that contribute to the antioxidant activity in plants are phenolic compounds such as flavonoids and phenolic acids (Lin et al., 2016). Various plants are considered as resources of traditional remedies, foods and beverages in Asia Pacific. Malaysia is one of the countries of the Asia- Pacific region which is rich in plant species. Although many plant species have been used for food, industrial, cultural and medicinal purposes, there are still many underutilised plants (Arora, 2014). Napier grass (Pennisetum purpureum) is one of the underutilised plants. In Malaysia, it is commonly used as silage for animal feeds due to its high yield potential and drought tolerance (Lowe et al., 2003; Nyambati et al., 2011). Studies showed that high flavonoids content is found in Napier grass and it is a potential source of minerals, vitamins and dietary protein (Akah and Ani, 2014; Akah and Onweluzo, 2014; Ukpabi et al., 2015). Similarly, tea which is a common drink all over the world is also rich in various nutrients such as antioxidants, amino acids and vitamins (Hui et al., 2004; Mondal, 2007). Although there are studies reported on the high nutrient contents of Napier grass, the usage of Napier grass is restricted by limited knowledge regarding the processing technique in food production. Therefore, it is interesting to explore the potential of Napier grass in the production of herbal tea by tea processing method. In tea processing, steaming helps to retain the antioxidant components, appearance and texture of the products. It is also one of the important steps in tea making process because over steaming can damage the leaves while insufficient steaming can initiate the onset of the fermentation (Singh et al., 2014). When tea fermentation occurs, organoleptic and antioxidant properties of the tea could be affected (Rodrigues et al.,