Opportunities in African Countries to Use Vernonia amygdalina as a Local Hop Substitute for Improving Beer Antioxidant Activity, Bitterness, Aroma, and Spoilage Resistance

Vernonia amygdalina, an Asteraceae-family plant used in the preparation of leaven for traditional red sorghum beer in Africa, exhibits exceptional antioxidant activity (Oxygen Radical Absorbance Capacity > 3000 μmol Trolox equivalents/g), even higher than hop, in spite of its similar total polyphenol content (up to 27000 mg/kg). This study investigated the potential of V. amygdalina for use as a local hop substitute. Although this plant lacks humulones, its leaves can bring bitterness to beer, thanks to alkaloids (caffeine up to 0.3 mg/kg), chlorogenic acids (1,5-dicaffeoylquinic acid up to 760 mg/kg), sesquiterpene lactones, and saponins. Solvent-Assisted Flavor Evaporation – Gas Chromatography – Mass Spectrometry data confirmed the absence of most hop terpenes and terpenoids, while Gas Chromatography – Pulsed-Flame Photometric Detector results evidenced three hoppy/grapefruit-like polyfunctional thiols as primary aromatic determinants: 3-methylbut-2-ene-1-thiol (Odor Activity Value/OAV = 348), 3-sulfanylhexan-1-ol (OAV = 652), and 3-sulfanyl-4-methylpentyl acetate (OAV = 3591). Moreover, ethanolic V. amygdalina extracts exhibited potent antibacterial activity (Minimum Inhibitory Concentration: 2 mg/mL) against both Gram-positive and Gram-negative bacteria, without any effect on S. cerevisiae performance. Despite a very distinct chemistry for most secondary metabolites, V. amygdalina leaves thus emerge as a serious candidate for improving traditional beer quality.