Volatile compounds of the traditional sorghum beers “ikigage” brewed with Vernonia amygdalina “umubirizi”

Abstract

Volatile compounds in traditional sorghum beer ikigage brewed with Vernonia amygdalina were investigated using Headspace-Solid Phase Micro Extraction (HS-SPME) and gas chromatography–mass spectrometry (GC/MS). A total of 75 volatile compounds were identified in the traditional ikigage made by Rwandese peasants (using V. amygdalina leaves during the preparation of traditional leaven) and pilot ikigage brewed with and without addition of V. amygdalina in the boiling kettle (instead of hops). Traditional sorghum beer brewed with V. amygdalina was characterized by the presence of higher levels of esters, alcohols and fatty acids. Ethyl acetate, ethyl caprylate, ethyl caproate and ethyl caprate are the main ester components with higher concentrations. Higher alcohols were mainly composed of propan-1-ol, 2-methyl propan-1-ol, 3-methylbutan-1-ol, 2-methylbutan-1-ol and 2-phenylethanol. Acetic, caproic and caprylic acids were the most important fatty acids. Volatile phenols such as 2-methoxy-4-vinylphenol, 4-vinylphenol and 2-methoxyphenol were also detected in the sorghum beer ikigage and may contribute to its phenolic note. V. amygdalina provides the terpenes compounds (δ-3-carene, β-farnesene, farnesol, β-citronellol and linalool), methyl salycilate and beta-damascenone in the sorghum beer. Like in hopped beers, these compounds might play a significant role in the overall flavor and aroma of the sorghum beer ikigage. V. amygdalina leaves emerge as an interesting hops substitute for tropical beers, but complementary data are still needed to understand which volatile compounds or precursors preexist in V. amygdalina.