Assessment of cyanogenic glucoside (cyanide) residues in Mbege: an opaque traditional Tanzanian beer

Abstract

Levels of cyanide in two varieties of malted millet, spent grain (Machicha) and opaque beer (Mbege) were determined. Protein content and amino acid composition of the malt, Mbege and Machicha were determined. Mbege was made in the laboratory using an improved method. The cyanide content of millet, malt, spent grain and Mbege were 40.6, 513.4, 18.9 and 8.1 ppm, respectively for the Moshi local millet variety. For Sumbawanga-2 millet variety the cyanide content was found to be 41.2, 489.2, 17.8 and 6.8 ppm for the millet, malt, spent grain and Mbege, respectively. The cyanide content increased linearly as the number of days of germination of the millet grain increased and the highest values of cyanide were attained on the third day of germination. Cyanogenic glucosides in the millet were enzymetically hydrolysed to respective cyanohydrins and volatile hydrogen cyanide due to low pH level of the Mbege which was 4. Malting of the millet increased the protein content by 5%. Lysine, the most limiting amino acid in millet, increased by 20%. It was concluded that the fermentation process of the millet malt into Mbege is efficient in reducing the levels of cyanogenic glucosides below levels considered toxic and therefore rendering the product safe.