African sorghum opaque beers play a vital role in the diet of millions of consumers. In the current study we investigated the growth profiles of yeast strains isolated from kpete-kpete, a traditional starter used to produce tchoukoutou, an opaque sorghum beer in Benin. 10 yeast strains were isolated from sorghum beer starters and cultivated under both liquid and solid media for phenotypic growth characterization. All yeast isolates were able to grow both on solid and liquid media. Based on their growth profiles, the isolates were clustered into three groups: (i) the aggressive growth pattern (30%), (ii) the moderate growth pattern (50%), and (iii) the slow growth pattern (20%). Based on gene expression pattern, absorbance (A(600 nm)) and diameter of growth in both liquid and solid media respectively, yeast strains YK34, YK15 and YK48 were clustered in the first group, and referred to as the most aggressive growth strains, followed by group 2 (YK24, YK5, YK12, YK20, YK2) and group 3 (YK37, YK41). This growth pattern was confirmed by Invertase gene expression profiling of the yeasts showing group 1 with high level of Invertase gene expression followed by group 2 and group 3 respectively. Our results suggest that YK34, YK15 and YK48 and YK2 yeast strains constitute the best candidates in fermentation of sorghum beer production based on growth rate and assimilation of carbon and nitrogen sources.

Opaque sorghum beers are the most consumed African alcoholic beverages. Tchoukoutou is one of the Benin opaque sorghum beers. Its fermentation process is carried out using a traditional starter called kpete-kpete. The present study characterized and identified the yeasts isolated from kpete-kpete. A total of 24 samples of kpete-kpete were collected from eight different commercial processing sites in Northern Benin. The mean values of the pH, titrable acidity, dry matter content and refractive index for all samples were respectively 3.58; 0.07% as lactic acid; 16.61% and 7.0. The mean counts of yeasts was 9.24 log cfu/ml. Based on their phenotypic characters and their assimilation profiles, 49 yeasts were isolated and found to belong to five genera with seven species. Seventy one percent (71%) of the isolates were identified as Saccharomyces cerevisiae.

Tchoukoutou is a traditional sorghum opaque beer produced and consumed in Benin. It is obtained from an uncontrolled fermentation of sorghum wort using a traditional starter called "kpete-kpete". The present study assessed the effects of storage duration on the physicochemical and microbiological characteristics as well as on the functional properties of the heat stabilized starter produced from "kpete-kpete". The physicochemical characteristics of the stabilized starter were not significantly affected by the storage duration. After 60.0 days of storage, the dry matter, pH and titratable acidity were stable with mean values of 92.5%, 4.76 and 1.33 g/kg, respectively. However, the microbial characteristics of the product were significantly affected by the storage duration. Yeasts, lactic acid bacteria (LAB) and total mesophilic aerobic counts were modified following three phases: a latency phase (between 0 and 10 days), an exponential growth phase (between 10 and 40 days) and the decline phase (between 40 and 60 days). As compared to the stabilized starter, the physicochemical characteristics of "kpete-kpete'' were extensively modified after 15 days of storage. In the traditional "kpete-kpete'', all the major groups of microorganisms, reached their maximum growth phase after 10 days of storage suggesting that they would have lost their fermentation power afterwards. The fermentation test performed using stabilized starter sampled at different growth phases, revealed that the starter of 25 days of storage possesses better fermentation capacity. In these conditions, the fermentation duration was reduced to 16 instead of 24 h.