Suliman, Abdallah M.A., et al. “A Comparative Study on Red and White Karkade (Hibiscus Sabdariffa L.) Calyces, Extracts and Their Products”. Pakistan Journal of Nutrition, vol. 10, no. 7, June 2011, pp. 680–683, https://doi.org/10.3923/pjn.2011.680.683.