Abstract
Soybean meal (SBM) is commonly used as a livestock feed due to its high protein content (45%) and desirable balance of amino acids. Unfortunately SBM contains several oligosaccharides that are poorly digested or even considered anti-nutritional. Alcohol extraction of SBM is commonly used to remove these carbohydrates and produce soy protein concentrate (SPC), which contains 65% protein. An alternative to alcohol extraction would be to convert the carbohydrates to ethanol that could be recovered as a valuable co-product. In this project we investigate the first step of this process—conversion of oligosaccharides into fermentable sugars—by comparing mixtures, dosages, and operating conditions for several hydrolytic enzymes. The goal was to generate the maximum amount of fermentable sugars so that the residual solids, following subsequent fermentation, would contain comparable protein levels to SPC. Extruded soybean white flakes were hydrolyzed using five different enzyme combinations to identify the enzyme combination that achieved the highest sugar recovery. Dosages of the oligosaccharide-degrading enzyme Novozyme 960 and the cellulose-degrading enzyme Cellic CTec were then varied to identify the best dosage based on effectiveness and usage rates. The influence of hydrolysis temperature (50°C or 55°C) was then evaluated. After these variables had been optimized, extruded white flake (extrusion at 50°C, 75 rpm, and 15% wb moisture) was hydrolyzed with Novozyme 960 (0.5 inulinase units (INU)/g), Cellic CTec (6% based on cellulose), and Cellic HTec (0.3% of total solids) at 55°C. The resultant residue was analyzed for protein content and then subjected to double ethanol washing to remove sugars. Sugar recovery was 4 times higher than that of non-treated white flake, and the protein content increased from 46% to 69%, which would increase the value of the product by at least $0.375/kg.
Get full access to this article
View all access options for this article.