Fermentation kinetics of finger millet-based Injera dough recipes: Implications for raffinose hydrolysis, amino acid content and other metabolites

Finger millet is a nutritious, gluten-free cereal crop commonly consumed as whole flour. Despite its nutritional benefits, it contains antinutritional factors such as raffinose, which can cause intestinal distress and affect nutrient absorption and digestion. Fermentation is one of the methods that can be employed to reduce antinutrients in cereals. However, detailed studies on raffinose hydrolysis as well as changes in sugar profiles, amino acid content and other metabolites during the traditional fermentation of finger millet based Injera dough (typically 4–7 days) are limited. This study investigated the fermentation kinetics and its implication in changes in raffinose levels and levels of other metabolites in finger millet-based dough recipes used to prepare Injera, a staple Ethiopian flatbread. Over a seven-day fermentation period, samples from finger millet and finger millet-maize composite dough recipes were analyzed at 24-hour intervals for pH, titratable acidity (TA), microbial growth, raffinose content, amino acids and levels of other metabolites following standard procedures. A decrease in pH and an increase in TA was observed across all recipes at the later stages of fermentation. LAB counts increased from 2.55 to 9.86logcfu/g and yeast counts increased from 1.13 to 6.41logcfu/g from the initial stage to 168 h of fermentation. A two-step fermentation process involving both lactic acid and alcoholic fermentation was observed, resulting in lactic acid and mannitol as the main end products. Fermentation significantly enriched the metabolite profile of fermented dough recipes (p < 0.05) including mono and disaccharides, sugar alcohols, organic acids, while reducing the raffinose content with a decrease ranging from 77.83 % to 99.83 % for the various dough recipes. Both essential and non-essential amino acids also increased (increment ranging from 30.9 % to 140.5 %) across all dough recipes with an increase in fermentation time. In conclusion, the seven-day fermentation process significantly decreased the raffinose content while increasing the levels of amino acids and other beneficial metabolites across all dough recipes. The reduction in raffinose suggests improved digestibility, while the increased amino acids and metabolites further support the use of finger millet as a nutritious staple food option in Ethiopia.