 Potatoes, avocados, broccoli, and Brussels sprouts may also contain dopamine at levels of 1 part per million or more; oranges, tomatoes, spinach, beans, and other plants contain measurable concentrations less than 1 part per million.The dopamine in plants is synthesized from the amino acid tyrosine, by biochemical mechanisms similar to those that animals use.It can be metabolized in a variety of ways, producing melanin and a variety of alkaloids as byproducts.