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

Abstract

Yam (Dioscorea spp.) is an important root and tuber crop in several African communities and has particular cultural value as a prestigious food in southwestern Ethiopia. Although it is widely consumed, traditional processing, mainly boiling, provides limited opportunities for shelf-life extension and contributes to postharvest losses. The present investigation assessed the influence of natural fermentation on the physicochemical characteristics, microbial dynamics, and proximate composition of yam. Mature white (T1) besides brown (T2) yam tubers were processed and fermented for seven days in laboratory micro-silo jars. Changes in physicochemical properties, microbial populations, and nutrient composition were examined during fermentation. Titratable acidity increased progressively from 0.45 to 1.74, whereas pH and moisture declined significantly (p < 0.05), from 6.73 to 3.89 and from 61.3% to 54%, respectively. Yeast and mold counts declined from 5.34 to 4.57 CFU/ml, and Enterobacteriaceae fell below the detection threshold (<1.00 CFU/ml) by fermentation day five. Total viable counts remained comparatively elevated, while lactic acid bacteria increased initially before a subsequent decline. The proximate analysis indicated increases in crude protein and total carbohydrate content, accompanied by reductions in crude fat, crude fiber, and ash. These findings suggest that yam fermentation may enhance nutritional characteristics and restrict spoilage-associated microbial populations, thereby supporting improved preservation and reduced postharvest losses. Further work should assess appropriate starter cultures and the effects of different fermentation periods on antinutritional compounds.