Integrated valorization of agro-byproducts and functional ingredients for nutritional enhancement of Teff Injera

Injera is a traditional Ethiopian fermented flatbread with important cultural and dietary roles. However, increasing teff cost and limited availability may affect its sustainability and affordability. This study evaluated composite flour incorporation into teff injera using rice flour, cassava flour, mango seed flour, and fenugreek to improve its nutritional, functional, bioactive, glycemic, microbial, and sensory properties. A four-component Simplex Lattice Mixture Design (SLMD) was applied to optimize composite formulations consisting of teff flour (50–70%), rice flour (15–25%), cassava flour (10–20%), and mango seed flour (5–15%), with constant supplementation of 2.5% fenugreek and 10% maize absit. Fermentation was conducted for 48 h at 25°C. Proximate composition, bioactive compounds, in-vitro starch digestibility, microbial stability, and sensory evaluation were analyzed. Quadratic Scheffé models showed significant fit (p < 0.05), with high predictive performance (R² = 0.93–0.99). The optimized formulation (55% teff, 20% rice, 15% cassava, 10% mango seed flour) showed the highest desirability index. Protein (7.66%), dietary fiber (4.17%), and energy (362.8 kcal/100 g) were obtained. Total phenolic content ranged from 185 to 298 mg GAE/100 g, and flavonoid content ranged from 74 to 120 mg QE/100 g. Antioxidant activities (DPPH, FRAP, and H₂O₂ scavenging) increased across formulations. In-vitro starch digestibility showed reduced rapidly digestible starch (58.4% to 47.9%) and estimated glycemic index (74.2 to 64.8), with increased slowly digestible starch (28.6% to 38.6%) and resistant starch (8.2% to 13.4%). Microbial analysis indicated the absence of coliforms and controlled microbial growth throughout the 7-day storage period under ambient room-temperature conditions. Among all formulations, MR3 exhibited the highest overall acceptability (8.6 ± 0.2), indicating favorable consumer acceptance. Overall, composite flour incorporation with fenugreek improved the nutritional, functional, microbial, and sensory quality of Injera. The Simplex Lattice Mixture Design (SLMD) approach was effective for optimizing fermented cereal-based products with improved health-related properties.