Puteh, Abdul Quddus, et al. “Comparative Study of Carotenoids Content in Ripe and Unripe Oil Palm Fresh Fruit Bunches”. International Journal of Integrated Engineering, vol. 14, no. 9, Dec. 2022, pp. 240-6, https://publisher.uthm.edu.my/ojs/index.php/ijie/article/view/11933.