Effect of mill type and mechanical kneading conditions on fermentation kinetics of tef dough during injera making and phytate to mineral molar ratio of injera

Abstract

Injera is Ethiopian traditional fermented flatbread which is made mostly from tef flour. Tef grain is milled and the flour kneaded to have batter-like dough which will ferment before injera baking. The influence of mill type: hammer mill (HM), disc mill (DM) and blade mill (BM) and mechanical kneading speed-time combinations (K1, K5, and K9) on fermentation kinetics was investigated. Phytate to mineral molar ratio (Fe, Zn and Ca) of tef injera was also investigated as affected by mill type and different kneading conditions. In both milling and kneading levels, maltose was the highest sugar concentration initially, followed by glucose and fructose. As fermentation continued, a similar trend in maltose breakdown was seen among HM, DM, and BM. However, different patterns of glucose and fructose breakdown were seen on HM than DM and BM. Similarly, HM had a different pattern in increment of lactic acid concentration than DM and BM. Similar trend in maltose concentration was seen between K1, K5, and K9. Again glucose breakdown and the increment of lactic acid in K9 were different than that of K1 and K5. Phytate/mineral molar ratio of BM was significantly different (p<0.05) from HM and DM. There was also a significant difference (p<0.05) in phytate/mineral molar ratio between K1, K5, and K9. Decreased phytate/mineral molar ratio was seen with increasing of kneading speed (rpm) for a longer period of time. The effect of mill type and kneading speed and time combinations on fermentation kinetics and phytate/mineral molar ratio were significant.