Zhu, Mingming, Hongju He, Mingtao Fan, Hanjun Ma, Haiwei Ren, Jie Zeng, and Haiyan Gao. 2018. “Application and Optimization of Solid-State Fermentation Process for Enhancing Polygalacturonase Production by Penicillium Expansum”. International Journal of Agricultural and Biological Engineering 11 (6). Beijing, China:187-94. https://ijabe.org/index.php/ijabe/article/view/3673.