Fermentation Kinetics and Changes in Levels of Antinutrients in Pearl Millet and Pearl Millet-Maize Composite Dough Recipes Used to Prepare Injera

Abstract

While pearl millet is rich in important nutrients with potential health and nutrition benefits, it contains antinutrients that limit the bioavailability of minerals and the digestibility of starches and proteins; however, fermentation is believed to reduce these antinutrient levels. The objective of this work was to determine the fermentation kinetics and its implications for changes in the levels of antinutrients in pearl millet and pearl millet-maize composite dough recipes used to prepare Injera, a traditional fermented flatbread consumed in Ethiopia. Three dough recipes identified through focus group discussion with women from the Dangeshita sub-district, Dangila District, Ethiopia, were investigated: pure pearl millet dough (P), a 1:1 mixture of pearl millet and maize (P1M1) and a 1:2 mixture of pearl millet and maize (P1M2) doughs. Significant decreases in pH were observed for all dough recipes at the later stages of fermentation. This drop in pH was accompanied by a rapid increase in titratable acidity. Counts of aerobic mesophilic bacteria and molds decreased (with molds reaching zero), while counts of yeasts and lactic acid bacteria (LAB) increased at the later stage of fermentation across all dough recipes. A two-step fermentation process characterized by both lactic acid and alcoholic fermentation was identified, yielding lactic acid and mannitol as primary end products. Phytate was degraded by 91.3% in pearl millet (P) dough, by 98.2% in P1M1 dough, and by 72.7% in P1M2 dough after 168 h (7 days) fermentation. All fermented dough recipes resulted in reduced levels of raffinose at the later stages of fermentation, with the highest degradation noted in pearl millet (P) dough (95%) followed by P1M1 dough (87.7%) and P1M2 (80.8%) dough. In conclusion, 7 days fermentation resulted in significant reductions of phytate and raffinose levels in all dough recipes.