Biodiversity of Saccharomyces cerevisiae isolated from a survey of pito production sites in various parts of Ghana

Identification of non-Saccharomyces yeast strains isolated from local traditional sorghum beer produced in Abidjan district (Côte d'Ivoire) and their ability to carry out alcoholic fermentation

Studies on yeasts involved in traditional sorghum beer fermentation in several African countries revealed the presence of two groups: Saccharomyces and non-Saccharomyces. If Saccharomyces strains were reputed for their fermentation performances, the non-Saccharomyces yeast strains have been recognized for their contribution towards the improvement of the beverage's organoleptic quality, justifying their use as aromatic starter. In spite of this contribution, most studies were focused only on Saccharomyces strains as starter. In this work, the non-Saccharomyces yeast strains found in the inoculum of traditional sorghum beer was investigated. Identification of non-Saccharomyces yeast strains by PCR-RLFP followed sequencing of D1/D2 domain revealed the presence of 2 species: Issatckenkia orientalis and Pichia kudriavzevii with Issatckenkia orientalis predominating. Out of the two species, fermentation characteristics showed that Issatckenkia orientalis seemed suitable for sorghum beer production.

Sustainable Production of African Traditional Beers With Focus on Dolo, a West African Sorghum-Based Alcoholic Beverage

Spontaneously fermented sorghum beers remain by far the most popular traditional cereal-based alcoholic beverages in Africa. Known under various common names (traditional beers, sorghum beers, opaque, native or indigenous beers) they are also recognized under various local names depending on the region or ethnic group. Dolo and pito are two similar traditional beers popular in West African countries including Burkina Faso, Mali, Ghana, Benin, Togo, Nigeria and Ivory Coast. These low-alcoholic beers are nutritious and contribute to the nutritional balance of local populations, as well as to their socio-cultural and economic well-being. The production of African traditional beers remains one of the major economic activities, creating employment and generating substantial income that contributes to livelihoods as well as the countries' economic systems. Their processing (malting and brewing) is still artisanal, based on traditional family know-how. The brewing process involves either an acidification and an alcoholic fermentation phases, or a mixed fermentation combining LAB and yeasts. Saccharomyces cerevisiae has been identified as the dominant yeast species involved in the alcoholic fermentation, with a biodiversity at strain level. LAB involved in the processing belong to the genera of Limosilactobacillus, Lactobacillus, Pediococcus, Leuconostoc, Lactococcus, Streptococcus, and Enterococcus. Molds (Aspergillus, Penicillium, Rhizopus, Geotrichum), and acetic bacteria are often associated with the malting and brewing processes. Challenges for sustainable production of African sorghum beer include inconsistent supply of raw materials, variability in product quality and safety, high energy consumption and its impact on the environment, poor packaging and short shelf-life. For sustainable and environmentally-friendly production of African sorghum beers, there is the need to assess the processing methods and address sustainability challenges. Strategies should promote wider distribution and adoption of improved sorghum varieties among farmers, prevent losses through the adoption of good storage practices of raw material, promote the adoption of improved cook stoves by the brewers, develop and adopt starter cultures for controlled fermentation, regulate the production through the establishment of quality standards and better valorize by-products and wastes to increase the competitiveness of the value chain. Appropriate packaging and stabilization processes should be developed to extend the shelf-life and diversify the channels for sustainable distribution of African cereal-based alcoholic beverages.

Volatile compounds of traditional sorghum beer (tchapalo) produced in Côte d'Ivoire: comparison between wild yeasts and pure culture of Saccharomyces cerevisiae

In recent years, there had been growing demand for distinctive high quality beer. Fermentation management has a fundamental role in beer quality and the levels of aroma compounds. Use of non-conventional yeast has been proposed to enhance beer flavor. In this study, the bioflavor of traditional sorghum beer from Côte d'Ivoire was investigated. The flavor profile of two beers fermented with wild yeasts and with pure culture of Saccharomyces cerevisiae respectively were studied. The main flavor components of the beer fermented by pure culture of Saccharomyces cerevisiae were different from those of the beer fermented with wild yeasts. The total level of esters and higher alcohols were (173.51 and 128.85 mg/L) respectively in the beer fermented with wild yeasts. These levels were significantly higher than those in the beer fermented with pure culture of Saccharomyces cerevisiae which were 13.08 and 78.26 mg/L for higher alcohols and esters respectively. On the other hand, the beer fermented with pure culture of Saccharomyces cerevisiae had an acid content higher than beer fermented with wild yeasts, i.e. 9.3 mg/L and 7.53 mg/L respectively.

Occurrence and Importance of Yeasts in Indigenous Fermented Food and Beverages Produced in Sub-Saharan Africa

Indigenous fermented food and beverages represent a valuable cultural heritage in sub-Saharan Africa, having one of the richest selections of fermented food products in the world. In many of these indigenous spontaneously fermented food and beverages, yeasts are of significant importance. Several factors including raw materials, processing methods, hygienic conditions as well as the interactions between yeasts and other commensal microorganisms have been shown to influence yeast species diversity and successions. Both at species and strain levels, successions take place due to the continuous change in intrinsic and extrinsic growth factors. The selection pressure from the microbial stress factors leads to niche adaptation and both yeast species and strains with traits deviating from those generally acknowledged in current taxonomic keys, have been isolated from indigenous sub-Saharan African fermented food products. Yeasts are important for flavor development, impact shelf life, and nutritional value and do, in some cases, even provide host-beneficial effects. In order to sustain and upgrade these traditional fermented products, it is quite important to obtain detailed knowledge on the microorganisms involved in the fermentations, their growth requirements and interactions. While other publications have reported on the occurrence of prokaryotes in spontaneously fermented sub-Saharan food and beverages, the present review focuses on yeasts considering their current taxonomic position, relative occurrence and successions, interactions with other commensal microorganisms as well as beneficial effects and importance in human diet. Additionally, the risk of opportunistic yeasts is discussed.

Candida species in tchapalo and bangui, two traditional alcoholic beverages from Côte d'Ivoire

The increase of infections due to non-Candida albicans species made it very necessary to conduct adequate characterization to be able to identify the species of Candida isolated from traditional fermented foods. In this study, based on their hue on Candida Chromogenic Agar medium, a total of 136 yeast strains were isolated from tchapalo and bangui. Molecular identification based on PCR-RFLP of internal transcribed spacers of rDNA (ITS) and sequencing of the ITS and the D1/D2 regions allowed us to assign these isolates to seven species: Candida tropicalis, Candida inconspicua, Candida rugosa, Saccharomyces cerevisiae, Kluyveromyces marxianus, Hanseniaspora guilliermondii, Trichosporon asahii. With the respect to each beverage, six species were found among with four species are regarded as opportunistic pathogens. From these, C. tropicalis, C. inconspicua and K. marxianus were the most commonly encountered. The enzyme activities of the potential pathogens assessed using API ZYM system showed that almost strains had esterase, esterase lipase, valine and cystine arylamidase, alpha chymotrypsin, alkaline phosphatase and naphthol phosphohydrolase activities. The activity of α-glucosidase was found only in C. tropicalis and C. inconspicua strains isolated from tchapalo while β-glucosidase activity was found in all strains from tchapalo and only in C. inconspicua isolated from bangui.

Biochemical and Microbiological Changes during the Ivorian Sorghum Beer Deterioration at Different Storage Temperatures

In order to extend shelf life of traditional sorghum beers, it is of importance to evaluate their spoilage characteristics. Therefore, the microbiological, biochemical, and sensory changes of the Ivorian sorghum beer tchapalo during storage at ambient temperature (28 to 30 °C) for four days and at 4 °C for six days were assessed. The aerobic mesophilic bacteria and the yeast counts remained stable during the storage time. However, variations were observed in the lactic acid bacteria and acetic acid bacteria counts. The deteriorating tchapalo acidity did not show significant variations. In contrast, the total soluble solids decreased at ambient temperature and remained stable at 4 °C. Lactic acid was a major compound during storage, and acetic acid was found at a detectable level of 1.26 mg/mL after the third day at ambient temperature. The ethanol contents increased significantly at ambient temperature after two days and then decreased but showed a fair decrease at 4 °C. Evaluating the beer’s appearance, odor, and taste, a panel considered the beers to be spoiled after two days when stored at 28 to 30 °C and after three days when stored at 4 °C.

Yeast dynamics during spontaneous fermentation of mawè and tchoukoutou, two traditional products from Benin

Mawè and tchoukoutou are two traditional fermented foods largely consumed in Benin, West Africa. Their preparations remain as a house art and they are the result of spontaneous fermentation processes. In this study, dynamics of the yeast populations occurring during spontaneous fermentations of mawè and tchoukoutou were investigated using both culture-dependent and -independent approaches. For each product, two productions were followed. Samples were taken at different fermentation times and yeasts were isolated, resulting in the collection of 177 isolates. They were identified by the PCR-DGGE technique followed by the sequencing of the D1/D2 domain of the 26S rRNA gene. The predominant yeast species identified were typed by rep-PCR. Candida krusei was the predominant yeast species in mawè fermentation followed by Candida glabrata and Kluyveromyces marxianus. Other yeast species were detected in lower numbers. The yeast successions that took place during mawè fermentation lead to a final population comprising Saccharomyces cerevisiae, C. krusei and K. marxianus. The yeast populations dominating the fermentation of tchoukoutou were found to consist of S. cerevisiae, almost exclusively. Other yeast species were detected in the early stages of fermentation. For the predominant species a succession of biotypes was demonstrated by rep-PCR for the fermentation of both products. The direct analysis at DNA and RNA levels in the case of mawè did not reveal any other species except those already identified by culture-based analysis. On the other hand, for tchoukoutou, four species were identified that were not detected by the culture-based approach. The spontaneous fermentation of mawè and tchoukoutou in the end were dominated by a few autochthonous species.

Genotypic characterization and safety assessment of lactic acid bacteria from indigenous African fermented food products

Background

Indigenous fermented food products play an essential role in the diet of millions of Africans. Lactic acid bacteria (LAB) are among the predominant microbial species in African indigenous fermented food products and are used for different applications in the food and biotechnology industries. Numerous studies have described antimicrobial susceptibility profiles of LAB from different parts of the world. However, there is limited information on antimicrobial resistance profiles of LAB from Africa. The aim of this study was to characterize 33 LAB previously isolated from three different African indigenous fermented food products using (GTG)₅-based rep-PCR, sequencing of the 16S rRNA gene and species-specific PCR techniques for differentiation of closely related species and further evaluate their antibiotic resistance profiles by the broth microdilution method and their haemolytic activity on sheep blood agar plates as indicators of safety traits among these bacteria.

Results

Using molecular biology based methods and selected phenotypic tests such as catalase reaction, CO₂ production from glucose, colonies and cells morphology, the isolates were identified as Lactobacillus delbrueckii, Lactobacillus fermentum, Lactobacillus ghanensis, Lactobacillus plantarum, Lactobacillus salivarius, Leuconostoc pseudomesenteroides, Pediococcus acidilactici, Pediococcus pentosaceus and Weissella confusa. The bacteria were susceptible to ampicillin, chloramphenicol, clindamycin and erythromycin but resistant to vancomycin, kanamycin and streptomycin. Variable sensitivity profiles to tetracycline and gentamicin was observed among the isolates with Lb. plantarum, Lb. salivarius, W. confusa (except strain SK9-5) and Lb. fermentum strains being susceptible to tetracycline whereas Pediococcus strains and Lb. ghanensis strains were resistant. For gentamicin, Leuc. pseudomesenteroides, Lb. ghanensis and Ped. acidilactici strains were resistant to 64 mg/L whereas some W. confusa and Lb. plantarum strains had a MIC value of 16 mg/L and 32 mg/L respectively. No β-haemolytic activity was observed, however, α-haemolytic activity was observed in 27% (9) of the strains comprising Lb. salivarius (6), W. confusa (2) and Lb. delbrueckii (1) isolates.

Conclusions

The resistance to kanamycin and vancomycin is probably an intrinsic feature since similar observations were reported in the literature for LAB. Low prevalence of pathogenicity indicator traits were observed among the isolates especially with the presence of poor haemolytic activities and they could therefore be considered as interesting candidates for selection of starter cultures or probiotics for different applications.

Identification of yeasts during alcoholic fermentation of tchapalo, a traditional sorghum beer from Côte d'Ivoire

This study investigated the diversity and dynamics of yeasts involved in alcoholic fermentation of a traditional sorghum beer from Côte d'Ivoire, tchapalo. A total of 240 yeast strains were isolated from fermenting sorghum wort inoculated with dry yeast from two geographic regions of Côte d'Ivoire (Abidjan and Bondoukou). Initial molecular identification to the species level was carried out using RFLP of PCR-amplified internal transcribed spacers of rDNA (ITS1-5.8S-ITS2). Ten different profiles were obtained from the restriction of PCR products with the three endonucleases HaeIII, CfoI and HinfI. Sequence analysis of the D1/D2 domain of the 26S rDNA and the ACT1 gene allowed us to assign these groups to six different species: Saccharomyces cerevisiae-like, Candida tropicalis, Pichia kudriavzevii, Pichia kluyveri, Kodamaea ohmeri and Meyerozyma caribbica. The most frequent species associated with tchapalo fermentation was S. cerevisiae-like (87.36%), followed by C. tropicalis (5.45%) and M. caribbica (2.71%). S. cerevisiae-like strains were diploid heterozygotes and exhibited three to four nucleotides divergence from the type strain in the D1/D2 domain and several indels in the more discriminant sequence of the intron of the ACT1 gene. During the process, the yeast species isolated and their frequencies varied according to the geographic origin of the dry yeast. The occurrence of some species was sporadic and only two non-Saccharomyces species were found in the final product.

Genetic analysis of Saccharomyces cerevisiae strains isolated from palm wine in eastern Nigeria. Comparison with other African strains

AIMS

To study the yeast diversity of Nigerian palm wines by comparison with other African strains.

METHODS AND RESULTS

Twenty-three Saccharomyces cerevisiae strains were obtained from palm wine samples collected at four locations in eastern Nigeria, and characterized using different molecular techniques: internal transcribed spacer restriction fragment length polymorphism and sequence analysis, pulsed field gel electrophoresis, inter delta typing and microsatellite multilocus analysis. These techniques revealed that palm wine yeasts represent a group of closely related strains that includes other West African isolates (CBS400, NCYC110, DVPG6044). Population analysis revealed an excess of homozygote strains and an allelic richness similar to wine suggestive of local domestication. Several other African yeast strains were not connected to this group. Ghana sorghum beer strains and other African strains (DBVPG1853 and MUCL28071) displayed strikingly high relatedness with European bread, beer or wine strains, and the genome of strain MUCL30909 contained African and wine-type alleles, indicating its hybrid origin.

CONCLUSIONS

Nigerian palm wine yeast represents a local specific yeast flora, whereas a European origin or hybrid was suspected for several other Africa isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study presents the first genetic characterization of an autochthonous African palm wine yeast population and confirms the idea that human intervention has favoured yeast migration.

The biodiversity of predominant lactic acid bacteria in dolo and pito wort for the production of sorghum beer

AIM

To quantify and identify the predominant lactic acid bacteria (LAB) in dolo and pito wort processing, and to examine their biodiversity at strain level.

MATERIALS AND RESULTS

The processing of dolo and pito wort was studied at four production sites in Burkina Faso and Ghana. The succession of dominant micro-organisms, pH and titratable acidity were determined from sorghum malt through mashing and acidification to final wort. In the sorghum malt and during mashing, the LAB counts were 5.7-7.5 log CFU g(-1). Similar levels of yeasts and gram-negative, catalase-positive bacteria were observed. These levels decreased to 3.7-4.5 log CFU g(-1) and<or=2-3 log CFU g(-1), respectively, at the end of mashing, including a mild heat treatment. During acidification at ambient temperature (30-33 degrees C) lasting for 12-16 h, LAB counts increased to 8.8-9.9 log CFU g(-1), pH decreased from 5.55+/-0.12 to 3.72+/-0.24, and the titratable acidity calculated as lactic acid, increased from 0.13% to 0.61%. The gram-negative, catalase-positive bacteria and yeasts observed in the malt and during mashing were no longer detected. A total of 556 strains of LAB were isolated and purified. The LAB isolates were characterized and identified by a polyphasic approach based on phenotypic and genotypic methods, such as carbohydrate fermentation patterns using API 50 CHL, intergenic transcribed spacers-polymerase chain reaction/restriction fragment length polymorphism (ITS-PCR/RFLP), pulsed-field gel electrophoresis (PFGE) and 16S rRNA gene sequencing. Lactobacillus fermentum was identified as the dominant LAB species in the malt during mashing and during acidification. The other species observed during acidification were Lactobacillus delbrueckii ssp. delbrueckii, Lact. delbrueckii ssp. bulgaricus and Pediococcus acidilactici. These bacteria comprised a minor fraction of the bacterial population and no distinct microbial succession was observed for the LAB. At species level, the LAB profiles were similar for the four production sites; however, a pronounced diversity was observed at strain level. For one site, which had implemented a cleaning procedure between batches only, Lact. fermentum was found.

CONCLUSION

Lact. fermentum was found to be the dominant LAB species throughout the entire process to final dolo and pito wort, including the acidification. Lact. delbrueckii ssp. delbrueckii, Lact. delbrueckii ssp. bulgaricus and P. acidilactici occurred in low numbers. At strain level, a high diversity based on PFGE-RFLP was observed for Lact. fermentum within and between sites.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study for the first time gives details of the involvement of LAB in the production of dolo and pito wort, for West African traditional sorghum beer production. One species, Lact. fermentum was predominant throughout the process, and seems to harbour potential starter cultures to be selected according to technological characteristics determined at strain level.

Surface binding of aflatoxin B1 by Saccharomyces cerevisiae strains with potential decontaminating abilities in indigenous fermented foods

Saccharomyces cerevisiae constitutes one of the most important microorganisms involved in food fermentations throughout the world. Aflatoxin B(1) binding abilities of S. cerevisiae strains isolated from indigenous fermented foods from Ghana, West Africa were tested in vitro. Results show that aflatoxin binding was strain specific with 7 strains binding 10-20%, 8 strains binding 20-40% and 3 strains binding more than 40% of the added aflatoxin B(1) when grown and incubated under standard conditions. Binding by two of the strains was further characterized. Highest binding capacity was seen with cells collected at the exponential growth phase with the strains A18 and 26.1.11 binding 53.0 and 48.8% of the total toxin respectively and the binding reduced towards the stationary phase. Aflatoxin B(1) binding increased steadily when the cells were incubated with 1 to 20 microg/ml of aflatoxin B(1). Binding was not affected by the cells grown at temperatures ranging from 20 to 37 degrees C, but was significantly reduced at 15 degrees C. Binding seems to be a physical phenomenon with cells treated at 52, 55 and 60 degrees C for 5 and 10 min or 120 degrees C for 20 min binding significantly higher quantities (more than 2-fold in 120 degrees C treated cells) of aflatoxin B(1) than their viable counterpart. Similarly, when the cells were treated with 2 M HCl for 1 h, up to 2-fold increase in binding was observed. The results obtained show that some strains of S. cerevisiae, viable or non-viable, are effective aflatoxin binders and these properties should be considered in the selection of starter cultures for relevant indigenous fermented foods where high aflatoxin level is a potential health risk.