chapter  8
Bioethanol from Starchy Biomass: Part II Hydrolysis and Fermentation
Pages 16

Bioethanol, which is derived from starchy and cellulosic biomass, is becoming important as an alternative fuel due to diminishing petroleum resources and environmental impacts. Acid and enzymatic methods have been developed for the hydrolysis of starchy biomass in order to release fermentable sugars. Acid hydrolysis results in the production of unnatural compounds that have adverse effects on yeast fermentation. In enzymatic hydrolysis of starch, the biomass has to be cooked at high temperatures and large amounts of amylolytic enzymes have to be added to hydrolyze the starchy biomass prior to fermentation. Recent advances in yeast cell surface engineering developed the strategies to genetically immobilize amylolytic enzymes like

Abstract .................................................................................................................. 105 8.1 Introduction................................................................................................... 106 8.2 Yeast Cell Surface Engineering: A Tool for Direct Ethanol Production from Starch ................................................................................................... 106 8.3 Ethanol Production from Soluble Starch ...................................................... 108

8.3.1 Displayed Glucoamylase ................................................................... 108 8.3.2 Co-Displayed Glucoamylase and Amylase ...................................... 109

8.4 Ethanol Production from Low-Temperature Cooked Corn Starch ............... 111 8.5 Ethanol Production from Raw Corn Starch ................................................. 113 8.6 Evaluation of Surface Engineered Yeast Strains .......................................... 117 8.7 Conclusions ................................................................................................... 117 References.............................................................................................................. 118

α-amylase and glucoamylase on the yeast cell surface. As a means of reducing the cost of ethanol production, occulent and nonocculent yeast strains co-displaying amylolytic enzymes have been developed and used successfully for direct ethanol production from raw starch. Hence, the cell surface engineered yeast appears to have great potential in industrial application.