ENZYMATIC-HYDROLYSIS OF HIGH-MOISTURE CORN FIBER PRETREATED BY AFEX AND RECOVERY AND RECYCLING OF THE ENZYME COMPLEX

Corn fiber is a grain-processing residue containing significant amount s of cellulose, hemicellulose, and starch, which is collected in facil ities where fuel ethanol is currently manufactured. Preliminary resear ch has shown that corn fiber (30% moisture dry weight basis [dwb]) res ponds well to ammonia-fiber explosion (AFEX) pretreatment. However, an important AFEX pretreatment variable that has not been adequately exp lored for corn fiber is sample moisture. In the present investigation, we determined the best AFEX operating conditions for pretreatment of com fiber at high moisture content (150% moisture dwb). The optimized AFEX treatment conditions are defined in terms of the moisture content , particle size, ammonia to biomass ratio, temperature, and residence time using the response of the pretreated biomass to enzymatic hydroly sis as an indicator. Approximate optimal-pretreatment conditions for u nground corn fiber containing 150% (dwb) moisture were found to be: te mperature, 90 degrees C; ammonia: dry corn fiber mass ratio, 1:1; and residence time 30 min (average reactor pressure under these conditions was 200 pounds per square inch [psig]). Enzymatic hydrolysis of the t reated corn fiber was per formed with three different enzyme combinati ons. More than 80% of the theoretical sugar yield was obtained during enzymatic hydrolysis using the best enzyme combination after pretreatm ent of corn fiber under the optimized conditions previously described. A simple process for enzyme recovery and reuse to hydrolyze multiple portions of AFEX-treated corn fiber by one portion of enzyme preparati on is demonstrated. Using this process, five batches of fresh substrat e (at a concentration of 5% w/v) were successfully hydrolyzed by repea ted recovery and reuse of one portion of enzyme preparation, with the addition of a small portion of fresh enzyme in each subsequent recycli ng step.