Comparison of Some Preparations, Obtained from Waste Yeast Cells for their Ability to Stimulate Microorganism Growth

ABSTRACTSeveral preparations, aimed as additives to microbial broth media were obtained from waste yeast cells usually discarded by two Bulgarian breweries. The products were assessed with respect to their ability to stimulate microbial growth, simplicity of obtaining, maximal yield of soluble substances from the starting material, necessity of expensive equipment, expenditure of materials, chemicals, and time. It was established that the preparation, obtained by usual autolysis at elevated temperatures, filtration through two sheets of gauze, vacuum concentration, addition of starch, drying, grinding and sieving is the preferable one because of its high ability for stimulating bacterial growth and easiness of obtaining. The turbidity, caused by the starch and some dead yeast cells is no obstacle since they remain blocked in the agar layer. When clear liquid media is necessary to be prepared, these particles are easily eliminated before the sterilisation step of the media by filtration through ordinary fi...