Effect of fermentation processes on proanthocyanidins in sorghum during preparation of Mahewu, a non-alcoholic beverage

Abstract

Grain samples from four sorghum cultivars ( Sorghum bicolor (L) Moench) were steeped and germinated for a period of 84 h and changes in their proanthocyanidin (PA), total phenol, reducing sugar, amylase enzyme and free α amino nitrogen (FAN) contents determined. During malting of the grain cultivars DC-75 and Mutode, decreases in soluble PAs were 48 and 59%, respectively, while initial PA levels were very low, becoming negligible for Chihumani and SV-2 cultivars. Total phenol contents of DC-75, Mutode and SV-2 were reduced during malting. In contrast, the total phenol content of Chihumani increased marginally during malting. Accumulation of reducing sugars, FAN and amylase enzyme activities were considerably higher for DC75 and Mutode as compared to Chihumani and SV-2 during the germination period, suggesting that the development of these constituents were not correlated with total phenol levels. Germinated grains were kilned and milled to produce a malt which was used to produce an improved variant of the traditional non-alcoholic beverage mahewu. Decreases in water soluble PAs during fermentation were 54 and 63% for cultivars DC-75 and Mutode, respectively. Differences in fermentation characteristics were observed between red and white sorghum cultivars.