Characterization of normal and waxy corn starch for bioethanol production
The uncertainty of future oil supply and growing concerns of the energy security of the United States have boosted the investment in alternative energy carriers, including biofuels. Bioethanol, made from bio-renewable resources, has gained the mainstream usage in the USA. Ethanol is almost exclusively made from corn in the USA. The objectives of the study were: 1) To compare the differences of ethanol production between the normal and waxy corn using a cold-fermentation process; 2) To understand the effects of starch structure and properties on the ethanol production. Ethanol yields of the waxy corn ranged from 33.1% (33.1g/ 100g dry grain) to37.6% for 2009 grown corn, and ranged from 34.8 to 37.9% for 2010 grown corn. Ethanol yields of the normal corn ranged from 34.2 to 37.2% (2009) and from 34.3 to 37.5% (2010). Ethanol yields positively correlated with the kernel starch contents of both normal and waxy corn. Average starch-ethanol conversion efficiency of the waxy corn (93.2%, 2009; 93.0%, 2010) was substantially greater than that of the normal corn (88.0%, 2009; 88.4%, 2010). This could be attributed to the greater starch hydrolysis rate of the waxy corn than that of the normal corn. Starch hydrolysis of uncooked dry-grind corn showed that more than 90% of starch in the waxy corn was hydrolyzed, whereas less than 80% of starch in the normal corn was hydrolyzed to glucose. It indicated that normal corn contained a significant portion of starch that was less readily hydrolyzed by the enzymes, which reduced the conversion efficiency. There were differences in starch physicochemical properties between the corn grown in 2009 and 2010 crop years. This was likely caused by the changes in the growing conditions (e.g. growing temperatures) between the two crop seasons.