EFFECT OF VARYING GRILLED SORGHUM CONCENTRATION ON PHYSICO-CHEMICAL QUALITY PARAMETERS OF URWAGWA AND IDENTIFICATION OF INDIGENOUS YEASTS INVOLVED IN ITS FERMENTATION Munezero Emmanuel

Abstract

The alcoholic beverage called Urwagwa in Rwanda is one of the most popular drinks traditionally processed from banana. Besides being a popular beverage during various social gatherings, it is also a primary source of income for farmers in some of the banana producing agricultural zones in Rwanda. Due to limited information on the aspect of microorganisms involved in the fermentation process and the effect of grilled ground sorghum vulgaris sp on physico-chemical changes that take place during fermentation. This study was carried out to determine how varying grilled sorghum concentration affected both proximate composition of banana juice-sorghum composite mixture before fermentation and the physico-chemical quality parameter of Urwagwa. The study also sought to identify the indigenous yeasts involved in the spontaneous fermentation of this alcoholic beverage. Both proximate composition of banana juice-sorghum composite mixtures and physico-chemical characteristics of urwagwa were determined include the protein, pH, sugar content, ethanol and titratable acidity in natural fermentation. Identification of indigenous yeast involved in fermentation was carried out using both the conventional (morphological identification) and the molecular (PCR) techniques. The results obtained at the end of fermentation indicated that the ethanol content in all fermenters ranged from 10.3-12.2% v/v, total soluble solids 8.1-9.7°Brix, pH 4.0-4.3 and titratable acidity 0.64-0.93%. The highest fermentation rate was observed in fermenters containing ground grilled sorghum compared to the control (0% sorghum added). The highest total soluble solid at the completion of fermentation was found in banana-based alcoholic beverage with zero percent of sorghum while highest pH xvi was generally found in fermenters with sorghum combinations. High titratable acidity was observed in fermenter with zero percent of sorghum. The concentration of 5% of ground grilled sorghum was found to result to the most desirable banana-based alcoholic beverage as it gave the best quality parameters of banana-based alcoholic beverage. The morphological characteristics of the isolates recovered from urwagwa matched those of yeast (circular, umbonate, smooth and white to cream color). Molecular identification through BLAST analysis of partial sequences of isolates showed that they were from genus Saccharomyces cerevisiae with 97 to 100% similarities of previously known sequences in GenBank database. These findings seem to suggest that a sorghum concentration of 5% would give the best quality urwagwa under the study conditions reported here and can therefore be recommended for adoption by traditional urwagwa producers. The study has also confirmed that yeast species Saccharomyces cerevisiae is involved in the spontaneous fermentation of this alcoholic beverage. Saccharomyces cerevisiae strain 1000 (LC269108.1) identified in fermenter with 0%, 2%, 5% and 15% of sorghum was found to be the best strain which can be used in banana-based alcoholic beverage production.