Tucker Melvin P, Nagle Nicholas J, Jennings Edward W, Ibsen Kelly N, Aden Andy, Nguyen Quang A, Kim Kyoung H, Noll Sally L
National Renewable Energy Laboratory, National Bioenergy Center, Bioprocess Engineering Group, 1617 Cole Boulevard, Golden, CO 80401, USA.
Appl Biochem Biotechnol. 2004 Spring;113-116:1139-59. doi: 10.1385/abab:115:1-3:1139.
Over the past three decades ethanol production in the United States has increased more than 10-fold, to approx 2.9 billion gal/yr (mid-2003), with ethanol production expected to reach 5 billion gal/yr by 2005. The simultaneous coproduction of 7 million t/yr of distiller's grain (DG) may potentially drive down the price of DG as a cattle feed supplement. The sale of residual DG for animal feed is an important part of corn dry-grind ethanol production economics; therefore, dry-grind ethanol producers are seeking ways to improve the quality of DG to increase market penetration and help stabilize prices. One possible improvement is to increase the protein content of DG by converting the residual starch and fiber into ethanol. We have developed methods for steam explosion, SO2, and dilute-sulfuric acid pretreatment of DG for evaluation as a feedstock for ethanol production. The highest soluble sugar yields (approximately 77% of available carbohydrate) were obtained by pretreatment of DG at 140 degrees C for 20 min with 3.27 wt% H2SO4. Fermentation protocols for pretreated DG were developed at the bench scale and scaled to a working volume of 809 L for production of hydrolyzed distiller's grain (HDG) for feeding trials. The pretreated DG was fermented with Saccharomyces cerevisiae D5A, with ethanol yields of 73% of theoretical from available glucans. The HDG was air-dried and used for turkey-feeding trials. The inclusion of HDG into turkey poult (as a model non-ruminant animal) diets at 5 and 10% levels, replacing corn and soybean meal, showed weight gains in the birds similar to controls, whereas 15 and 20% inclusion levels showed slight decreases (-6%) in weight gain. At the conclusion of the trial, no negative effects on internal organs or morphology, and no mortality among the poults, was found. The high protein levels (58-61%) available in HDG show promising economics for incorporation of this process into corn dry-grind ethanol plants.
在过去三十年中，美国的乙醇产量增长了10倍多，到2003年年中达到约29亿加仑/年，预计到2005年乙醇产量将达到50亿加仑/年。同时每年联产700万吨酒糟（DG），这可能会压低作为牛饲料补充剂的DG价格。将剩余的DG出售给动物饲料是玉米干磨乙醇生产经济的重要组成部分；因此，干磨乙醇生产商正在寻求提高DG质量的方法，以增加市场渗透率并帮助稳定价格。一种可能的改进方法是通过将残留的淀粉和纤维转化为乙醇来提高DG的蛋白质含量。我们已经开发了蒸汽爆破、二氧化硫和稀硫酸预处理DG的方法，以评估其作为乙醇生产原料的可行性。用3.27 wt% H2SO4在140℃下预处理DG 20分钟可获得最高的可溶性糖产量（约占可利用碳水化合物的77%）。在实验室规模上开发了预处理DG的发酵方案，并扩大到809升的工作体积，用于生产水解酒糟（HDG）以进行喂养试验。预处理的DG用酿酒酵母D5A发酵，乙醇产量为可利用葡聚糖理论产量的73%。HDG经风干后用于火鸡喂养试验。在火鸡幼雏（作为典型的非反刍动物模型）日粮中加入5%和10%的HDG来替代玉米和豆粕，结果显示幼雏的体重增加与对照组相似，而加入水平为15%和20%时体重增加略有下降（-6%）。试验结束时，未发现对内脏器官或形态有负面影响，幼雏也没有死亡。HDG中高含量的蛋白质（58 - 61%）表明将此工艺纳入玉米干磨乙醇工厂具有可观的经济效益。
