Febrianto, N., and T. Wahyudi. “Optimization Study of Ultrasound-Assisted Polyphenol Extraction from Cocoa Powder and Utilization of Its Grounds Using Papain Solution.”. Pelita Perkebunan (a Coffee and Cocoa Research Journal), Vol. 32, no. 1, Apr. 2016, pp. 22-33, doi:10.22302/iccri.jur.pelitaperkebunan.v32i1.209.