Abstract
The research was carried out to determine the effect of adding fermentable sugars that could be utilized by the indigenous fermenting microorganisms to the ferment, with the aim of producing a sustained low pH level. Type, concentration and time of adding sugar at the beginning (Day 0) and during (Day 3) fermentation of orange-fleshed sweet potato were evaluated. Addition of fermentable sugars, which are intrinsically present in orange-fleshed sweet potato, such as sucrose, glucose and fructose at Day 0 and Day 3 of the fermentation, resulted in a decrease in pH level that was not sustained in the natural (control) fermentation. More importantly, the experiment identified that 5 or 8% w/v fructose were the optimum concentrations that resulted in pH level falling to 3.5, which was the minimum pH level recorded. It was also discovered that addition of 5 or 8% w/fructose at the beginning of fermentation resulted in a greater fall in pH level than adding the sugar on Day 3 of the fermentation. The findings suggest that in the traditional fermentation the fermentable substrate is a limiting factor and once used up the pH starts to rise.

Key words: Orange-fleshed sweet potato traditional, fermentation, sucrose, glucose, fructose, pH, Nigeria