(E)-2-Decenoic acid is an interesting fatty acid isolated from royal jelly secretions of honey bees. In Vitro: (E)-2-Decenoic acid is isolated along with 10-hydroxy-trans-2-decenoic acid, a fatty acid unique to royal jelly. (E)-2-Decenoic acid and 10-hydroxy-trans-2-decenoic acid are both described to demonstrate estrogenic activity, where the fatty acids demonstrate inhibition of 17β-estradiol binding to estrogen receptor-β.