Budiastra, I Wayan, and Fila Rodotul Jannah. “Non Destructive Determination of Soursop Firmness and Sweetness With Ultrasonic Method”. Jurnal Teknik Pertanian Lampung (Journal of Agricultural Engineering) 11, no. 2 (June 30, 2022): 253–265. Accessed October 18, 2025. https://jurnal.fp.unila.ac.id/index.php/JTP/article/view/5865.