Fermentation-Driven Changes in Microbial Dynamics, Physicochemical Characteristics, and Proximate Composition of Yam (Dioscorea spp.) in Southwestern Ethiopia

Abstract

Yam (Dioscorea spp.) is a widely consumed root-tuber crop across Africa and holds cultural significance as a prestige food among rural communities in southwestern Ethiopia. Despite its importance, traditional processing methods, particularly boiling, do not effectively extend the shelf life of yam, resulting in considerable post-harvest losses. This study was conducted to

evaluate the effects of natural fermentation on the physicochemical properties, microbial dynamics, and proximate composition of yam. Mature tubers of white (T1) and brown (T2) yam varieties were collected, processed, and fermented in micro-silo jars under laboratory conditions for seven days. Physicochemical parameters, microbial dynamics, and proximate composition were subsequently analyzed throughout the fermentation period. The results showed a consistent increase in titratable acidity, ranging from 0.45 to 1.74, as fermentation progressed. In contrast, pH and moisture content significantly decreased (p < 0.05), with pH values declining from 6.73 to 3.89 and moisture content from 61.3% to 54%. Microbial analysis revealed a reduction in yeast

and mold counts from 5.34 to 4.57 CFU/ml and the complete elimination of Enterobacteriaceae (<1.00 CFU/ml) by the fifth day of fermentation. Total viable counts remained relatively high throughout the fermentation period, while lactic acid bacteria populations increased until day five, followed by a slight decline. Proximate composition analysis indicated that crude protein

and total carbohydrate contents increased during fermentation, whereas crude fat, crude fiber, and ash contents decreased. These findings suggest that fermentation not only enhances the nutritional quality of yam but also significantly reduces microbial spoilage, thereby extending shelf life and minimizing post-harvest losses. Overall, the study highlights the potential of fermentation as an effective post-harvest technology for yam preservation. Further research is recommended to develop suitable starter cultures and to investigate the effects of fermentation on anti-nutritional factors under varying fermentation duration.