Microbiological quality and safety of the Zambian fermented cereal beverage: Chibwantu
Mwale, Mercy Mukuma
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Fermentation has been used for over three thousand years as an effective and inexpensive means to preserve the quality and safety of foods. In Africa most of the traditional foods are fermented at household level before consumption. The cereals are fermented, and then cooked prior to consumption and this offers added safety advantages because pathogenic microorganisms are inactivated thereby increasing shelf life of product. However, some cereals are cooked first and then other sources of fermentable carbohydrates and amylase such as other cereals (malts) or roots from Rhynchosia spp. (generally called munkoyo roots) are added and then fermented prior to consumption. Chibwantu and munkoyo beverages, Zambia‟s important cereal based fermented foods are prepared in such a way. The substrates added after cooking of cereals are a major concern in terms of product quality and safety. In literature there is limited information on munkoyo roots. Knowledge on quality of these roots, their effect on quality and microbiological safety of the fermented food products prepared by their use is essential for the development of improved products for increased consumption, commercial production and marketing. The present research work aimed at contributing to closing up this knowledge gap by evaluating the microbiological quality and safety of chibwantu. This was done by first gathering information on the production and utilisation of indigenous cereal based fermented food products in Lusaka and Chongwe districts of Lusaka province, Zambia with special emphasis on chibwantu and munkoyo beverages prepared using munkoyo roots. Second to isolate and characterize the microorganisms associated with the munkoyo roots and maize grit used during the preparation of chibwantu and to establish whether the same microorganisms are involved during the fermentation process of the beverage. Third to study the survival of selected food borne enteropathogenic microorganisms during fermentation of chibwantu beverage and finally to investigate the effect of munkoyo roots on growth of selected microorganisms. From the information gathered during this study, it was found that different types of indigenous cereal based fermented foods especially the beverages are prepared in Zambian households. The foods contribute to the nutritional, economical and medical needs of the consumers, thereby making them relevant to the consumers and the country at large. The raw materials; maize grit and munkoyo roots, used in the preparation of the beverage chibwantu are associated with coliforms, lactic acid bacteria (LAB), yeasts and moulds, particularly the munkoyo roots. The groups of microorganisms; coliforms, LAB, Yeasts and moulds, associated with the raw materials used in the preparation of the beverage chibwantu, particularly from the roots, were also responsible for the fermentation of the beverage. Some microorganisms that could not be identified from the raw materials were also encountered during the fermentation process of chibwantu. Staphylococcus aureus, E. coli, Salmonella and Shigella species were not encountered during natural fermentation of chibwantu and growth of selected enteropathogenic microorganisms was significantly suppressed during the fermentation process and storage. Both the yellow and white munkoyo roots possess some antimicrobial activity against some enteropathogenic microorganisms as well as microbial growth stimulatory activity. This study forms basis for further studies on the active components of the roots for possible use in preservation for improved food quality and safety. The quality of the beverage is varied due to different methods of preparation and the microorganisms involved during fermentation which are dependent on the quality of the munkoyo roots. There is still a lot of work needed on the munkoyo roots and the fermented products prepared from them to be able to establish their safety convincingly. However, fermented foods generally have a very good safety record and chibwantu should be relatively safe to consume.