The microbial succession in indigenous fermented maize products

[摘要] Several aspects related to cereal fermentations were reviewed in the literature section of this study. These aspects included among others, the history of indigenous cereal fermentation, factors that affect cereal fermentation, potential microbiological hazards of cereal fermentation, recent advances in related industry, and the future of fermented foods. A wide variety of recipes exists across the African continent and the beers are known by many local names. In particular this study focussed on mahewu and umqombothi, both made from a combination of maize and sorghum, fermented beverages consumed in South Africa. Improved process technologies such as the use of starter cultures can lead to improved product characteristics and consequently better health attributes for the consumer of these indigenously fermented products. During the fermentation processes for umqombothi and mahewu, yeasts, lactic acid bacteria, moulds and enterobacteriaceae were present at the start of the process but as fermentation progressed yeasts and lactic acid bacteria were the dominant microorganisms. This was over a 48 h, and 3 day, fermentation period for the umqombothi and mahewu respectively. Home-, township-, and laboratorymade samples of umqobothi were compared while for mahewu, the comparison was between the home- and laboratory-made samples. Results from different production sites were not significantly different although there were instances that called for improved hygiene as contaminants were found in some samples. Yeasts isolated from umqombothi were identified and these included; Candida ethanolica, C. haemuloni, C. sorbophila, Dekkera anomala, Dekkera bruxellensis, Saccharomycopsis capsularis and Saccharomyces cerevisiae. The yeasts isolated from mahewu were identified and the predominant strains were Candida haemuloni, Candida sorbophila, Debaryomyces hansenii, Saccharomyces capsularis and Saccharomyces cerevisiae. Confirmation of the yeast identity was done using sequence analysis of the D1/D2 domain using primer pairs NL-1(5'-GCATATCAATAAGCGGAGGAAAAG) and NL-4(5'- GGTCCGTGTTTCAAGACGG). Scanning electron microscopy was performed on the interior surface of a pot used for indigenous cereal fermentation. The images obtained confirmed the presence of biofilm on the surface and the microorganisms present in this biofilm were predominantly yeasts and bacteria. The observed proximity of yeasts to the bacterial cells lent further support to the suggestion of a symbiotic relationship existing between these microorganisms in indigenous cereal fermentations. Biofilms are not homogenous in composition but are complex matrices composed of microcolonies interspersed with channels allowing the movement of fluids and nutrients. It therefore follows that a combination of different techniques that are available may be required to give the most accurate picture of the true biofilm structure and organisation. Indigenous cereal fermented products are an integral part of the diet of many African households. Several advantages do arise from the fermentation of cereals and improvement of this process will not only lead to better health attributes but also the production of fermented beverages with guaranteed and consistent quality. This augurs well for the producers of fermented products as more consumers become aware of the health properties of fermented products and this trend is only likely to improve in the future.

[发布机构] University of the Free State