Potentiality of amylolytic yeasts for direct fermentation of starchy substrates to ethanol

This review article contains a comprehensive survey of types of starchy substrates and their digestion, potentiality of amylolytic yeasts in ethanol production, production and characterization of yeast amylases, ethanol fermentation from starch, factors impairing starch fermentation and genetic manipulation of amylolytic yeasts. The cost of production of ethanol from starch increases if commercial amylases are used. In order to reduce the cost (15–20%) of production of ethanol from starchy substrates, there is a need to find suitable microorganisms especially yeasts that can directly ferment starch to ethanol in a single step process. The amylolytic yeasts are the potential candidates that can reduce not only the cost of production, but also yield valuable byproducts like Single Cell Protein (SCP). Raw starch digesting enzymes of amylolytic yeast can reduce energy requirement for glucose production. Because of the developing economic interest in using ethanol as a blending agent with petroleum, the overall demand for the former has been increasing in recent years. Since molasses, the basic raw material used in the production of ethanol, is in short supply, the use of appropriate alternate substrates like starchy materials with single-step (direct) fermentation for the purpose is gaining economic importance at present.