Essential for the reductive metabolism of L-phenylalanine, L-tyrosine and L-tryptophan (PubMed:29168502). Catalyzes the reduction of phenylacrylic acid to phenylpropionic acid, 4-hydroxy-phenylacrylic acid to 4-hydroxy-phenylpropionic acid, and indoleacrylic acid to indolepropionic acid (PubMed:29168502). 3-phenylpropanoate + H(+) + oxidized [electron-transfer flavoprotein] = (E)-cinnamate + reduced [electron-transfer flavoprotein] H(+) + oxidized [electron-transfer flavoprotein] + phloretate = (E)-4-coumarate + reduced [electron-transfer flavoprotein] 3-(1H-indol-3-yl)propanoate + H(+) + oxidized [electron-transfer flavoprotein] = (E)-3-(indol-3-yl)acrylate + reduced [electron-transfer flavoprotein] Amino-acid degradation. Mutants are deficient in reductive metabolism of phenylalanine, tyrosine and tryptophan, and exhibit growth defects when cultured with amino acids as the sole carbon source. Belongs to the acyl-CoA dehydrogenase family.