Quancheng, Zhou, et al. “Optimization of Xanthophylls Extraction from Marigold Extractum With Supercritical CO2 by Response Surface Methodology”. International Journal of Agricultural and Biological Engineering, vol. 3, no. 2, June 2010, pp. 58-63, https://ijabe.migration.pkpps06.publicknowledgeproject.org/index.php/ijabe/article/view/137.