Effect of Vernonia amygdalina (bitter leaf) extract on brewing qualities and amino acid profiles of stout drinks from sorghum and barley malts

The brewing qualities and amino acid profiles of barley and sorghum-derived stout drinks produced with a hop substitute, ‘bitter leaf’ (Vernonia amygdalina) extract and residue (BLE & BLR), were analysed. The alcoholic contents, original gravities and apparent extracts of the stout drinks were essentially the same as those of a commercial stout. Seventeen free amino acids were found in the stout samples. Isoleucine (2.91 mg/100 ml), leucine (3.74 mg/100 ml), alanine (2.16 mg/100 ml), phenylalanine (3.18 mg/100 ml), tyrosine (2.56 mg/100 ml) histidine (2.05 mg/100 ml), glutamine (2.20 mg/100 ml) and proline (7.0 mg/100 ml) were the major free amino acids. All stout samples were rated the same as a commercial barley stout in terms of flavour, bitterness, colour and foam formation. The stout samples had a slightly sweet and bitter taste which was probably due to the high contents of bitter amino acids (isoleucine, leucine, histidine) and proline.