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

Resumen

Injera is Ethiopian traditional fermented flatbread which is made mostly from tef flour. Tefgrain is milled and the flour kneaded to have batter-like dough which will ferment beforeinjera 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 fermentationkinetics was investigated. Phytate to mineral molar ratio (Fe, Zn and Ca) of tef injera wasalso investigated as affected by mill type and different kneading conditions. In both millingand kneading levels, maltose was the highest sugar concentration initially, followed byglucose and fructose. As fermentation continued, a similar trend in maltose breakdown wasseen among HM, DM, and BM. However, different patterns of glucose and fructosebreakdown were seen on HM than DM and BM. Similarly, HM had a different pattern inincrement of lactic acid concentration than DM and BM. Similar trend in maltoseconcentration was seen between K1, K5, and K9. Again glucose breakdown and the incrementof lactic acid in K9 were different than that of K1 and K5. Phytate/mineral molar ratio of BMwas 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/mineralmolar ratio was seen with increasing of kneading speed (rpm) for a longer period of time. Theeffect of mill type and kneading speed and time combinations on fermentation kinetics andphytate/mineral molar ratio were significant.