The authors would like to thank Universiti Sains Malaysia for providing the research facilities for carrying out the experiment and for making this research work possible, and the Division of Oleochemicals, PT. Bakri Sumatera Plantation Tbk., Medan, 20362, Sumatera Utara, Indonesia, for supplying the RBDPS. One of the authors (Indra Surya) is grateful to the Directorate General of Higher Education (DIKTI), Ministry of Education and Culture (Kemdikbud) of the Republic of Indonesia, for the
award of a scholarship under the fifth batch of the Overseas Postgraduate Scholarship Program.