Effects of Corn Quality and Storage on Dry Grind Ethanol Production

摘要

Corn dry grind industry is the major contributor of ethanol production in the US. Ethanol plants incur economic losses due to seasonal variations in ethanol yields. Ethanol yields typically are low during the first month after harvest, increase for the next six to seven months and decrease again three to four months before next harvest. There is little published information on factors causing variation in dry grind ethanol concentrations. One possible cause associated with ethanol yield variability is incoming grain quality. The main objectives of this study were to quantify ethanol yield variation over time at a dry grind facility, evaluate relationships among corn quality attributes and ethanol yields and determine physiologic changes in corn protein quality during storage and its effects on ethanol yields.;Corn from a Midwestern ethanol plant (commodity corn) and an identity preserved corn hybrid from a seed company (control corn stored at 4° C) were used to study the effects of incoming corn on ethanol concentrations. Ethanol concentrations were determined every two weeks for one year using conventional dry grind procedure. Variations in ethanol concentrations were significant and variability patterns for commodity and control corn followed the same trend. Highest ethanol concentrations were seen in the month of January. Variation with control corn suggested that storage time is a significant factor affecting ethanol concentrations. Effects of different enzyme treatments on mean ethanol concentration over a year were evaluated. Two liquefaction enzymes (optimum pH -- 5.8 and 5.1, respectively), two saccharification enzymes (optimum pH -- 5.0) and one protease were used in five enzyme treatments (I, II, III, IV and V). Final ethanol concentration with enzyme treatment V was (17.5 +/- 0.486)% v/v. This was 0.6% higher than enzyme treatment I resulting in an additional ethanol production of 600,000 gallons/year in a 100 million gallon/year ethanol plant. Using effective enzymes increases overall dry grind ethanol production and ethanol plant profitability.;Commodity corn samples were analyzed for physical quality parameters (test weight, kernel weight, true density, percent stress cracks and moisture content) and composition (starch, protein, oil and soluble sugars contents). There were variations in corn quality parameters and ethanol concentrations. Correlation coefficients were significant but low (-0.50< r < 0.50) between starch content and final ethanol concentrations (72 hr) and total soluble sugar content and ethanol concentrations at 72 and 48 hr. Ethanol concentrations (at 24, 48 and 72 hr) were predicted as a function of a combination of grain quality factors using multiple regression methods; however, the R2 values obtained were low. Ethanol concentration variations were not related to physical and chemical composition quality factors.;Physiologic changes in corn protein quality (soluble protein contents, initial free amino nitrogen (FAN) content and susceptibility to enzyme hydrolysis) during storage at refrigerated and ambient conditions were investigated. Albumin, prolamin, glutelin contents and initial FAN contents of corn slurry varied with storage time; however, there were no effects of storage temperatures (ranging from -7 to 23°C) on soluble protein and FAN contents. Albumin content decreased; whereas, prolamin content increased from wk 8 to 40. Susceptibility to enzyme hydrolysis was affected during storage; highest rate of protein hydrolysis was observed during wk 20. Variation in ethanol yields for corn stored at ambient and refrigerated conditions followed similar trends. Final ethanol yields (72 hr) had no correlations with protein quality attributes; however, ethanol yields at 24 hr correlated with glutelin (r = -0.76) and prolamin (r = +0.74) content.