Lactic Acid Fermentation Enhances Microbial Safety and Iron Bioavailability of Common Beans Under Ambient Storage in Rwanda

Background In Rwanda and across Sub-Saharan Africa, Phaseolus vulgaris L. serves as an important source of essential proteins and micronutrients. However, its nutritional benefits are compromised by post-harvest spoilage and the limited bioavailability of iron, which is affected by antinutritional factors in environments with scarce resources. Methods: In Kamonyi District, Rwanda, common beans of the RWR 10 variety were subjected to fermentation in airtight, sterile glass containers at a temperature of 30±1 °C for durations of 0, 12, 24, and 36 hours. The microbiological assessments conducted included total plate count (TPC), lactic acid bacteria (LAB) enumeration on MRS agar, and Salmonella spp. detection following ISO standards. Iron bioavailability and physicochemical properties were evaluated through in vitro gastrointestinal digestion using atomic absorption spectrophotometry. Statistical analysis was performed using one-way ANOVA and the Tukey HSD post-hoc test with a significance level of α=0.05. Findings: Fermentation caused acidification with pH reducing between 6.2+-0.1 and 4.1+-0.1 (p<0.001), forming an acidic environment preventing pathogenic and spoilage microorganisms. The total plates reduced from 6.8+-0.2 to 3.7+-0.1 log CFU/g, equivalent to 54.4% microbial reduction at 36 hours. The lactic acid bacteria showed an increase from 2.1+-0.1 to 7.4+-0.2 log CFU/g, serving as competition exclusion and biopreservation. No Salmonella spp. was found during the study. Iron bioavailability increased (8.5+-0.4% to 15.1+-0.7%, p<0.001) due to phytate breakdown by microbial phytases and Bornu mineral acid chelation. A 24-hour fermentation provided optimal balance between microbial safety (TPC: 4.2+-0.1 log CFU/g), nutritional fortification (iron bioavailability: 13.4+-0.6%), and sensorial acceptability. Conclusion : Fermentation-preconditioning is a sustainable, low-cost intervention that improves microbial safety and iron bioavailability in common beans during storage. The technology can enhance food security and iron deficiency anemia in Sub-Saharan Africa by extending shelf-life and nutritional quality.