Variation of sorghum phenolic compounds during the preparation of opaque beer

Phenolic compounds affect the rate of fermentation, quality and stability of opaque beer produced from sorghum. The levels of proanthocyanidins (PAs) were determined photometrically at various stages during the preparation of opaque beer from high polyphenol sorghum. Decreases in the levels of proanthocyanidins were 52 and 34% during the lactic and second alcoholic fermentation stages, respectively. Quantitative and qualitative changes in the low molecular weight phenolic compounds of sorghum during the preparation process of opaque beer were determined by gas chromatography coupled with mass spectrometric detection. The main low molecular weight phenolic compounds detected in sorghum malt were p-hydroxybenzoic acid, p-hydroxybenzaldehyde and p-hydroxybenzoyl alcohol. Levels of p-hydroxybenzaldehyde decreased during both lactic acid and alcoholic fermentation while the levels of p-hydroxybenzoic acid and p-hydroxybenzoyl alcohol increased during alcoholic fermentation. Protocatechuic acid, caffeic acid and p-coumaric acid were detected at relatively low levels at various stages of opaque beer preparation.