Abstract
Freeze-drying is a well-known dehydration method widely used to preserve microorganisms. In order to produce freeze-dried yeast starter culture for the brewing purpose of African sorghum beer, we tested protective agents (sucrose, glucose, glycerol) in combination with support materials (millet, maize, sorghum, and cassava flours) at 1:1 ratio (v/v). The yeast strains Saccharomyces cerevisiae F 12-7 and Candida tropicalis C 0-7 previously isolated from sorghum beer were used in a mixed culture at a ratio of 2:1 (C.tropicalis/S.cerevisiae). After the freeze-drying, the residual water contents were between 0.78 -2.27%, 0.55 -4.09%, and 0.40-2.61%, respectively, with sucrose, glucose and glycerol. The dried yeasts viabilities were between 4.0% and 10.6%. Among the protective agents used, sucrose was found to be the best protectant giving cell viabilities of 8.4-10.6%. Considering the support materials, millet flour was the best support after drying. When the freeze-dried yeast powders were stored at 4°C and room temperature (25-28°C) for up to 3months, the survival rates were the highest with cassava flour as the support material.
Highlights
Sorghum beer is a traditional fermented beverage from most of West African countries where sorghum is produced
Sucrose, glucose, and glycerol were tested in mixtures with maize, sorghum, millet and cassava flours
Our study was focused for the first time on freeze-drying preservation of yeast strains, potential starter culture for tchapalo production
Summary
Sorghum beer is a traditional fermented beverage from most of West African countries where sorghum is produced. It is known as tchapalo in Côte d’Ivoire and by various other names in other African countries. The beers are consumed at various festivals and African ceremonies (e.g., marriage, birth, baptism, the handing over of a dowry, etc.) and constitute a source of economic return for women beer producers. The fermentation of these beverages is uncontrolled and the microorganisms involved come from the raw materials, equipment and local environments or from residues of previous fermentation batches. Various investigations for this purpose have been done
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