G. Huether et al., Tryptophan, Serotonin, and Melatonin: Basic Aspects and Applications, 29012, p. 754 ([Internet, 2019-12-16](https://books.google.ch/books?id=K1LxBwAAQBAJ&pg=PA754&lpg=PA754&dq=%22GMO+additive%22&source=bl&ots=V_9YiIIhGU&sig=ACfU3U3pchvIql2wXmknS2GgJxzfrnn_Xg&hl=de&sa=X&ved=2ahUKEwjOl4rgmrrmAhVjxoUKHSexBo0Q6AEwBXoECAoQAQ#v=onepage&q=%22GMO%20additive%22&f=false))