Zayadi, R. A., N. Abdul Rahim, and F. Abu Bakar. “Determination of Flavonoid and Caffeine Content in Black and Oolong Teas”. Journal of Science and Technology, Vol. 8, no. 2, Nov. 2016, https://publisher.uthm.edu.my/ojs/index.php/JST/article/view/1747.