Integrated process for a new sequential valorization of corn ethanol production by-products: Production of fermented solid with lipase activity, ethyl esters, and animal feed

Abstract

The use of co-products from corn ethanol production such as distillers’ dried grains with solubles (DDGS) and distillers’ corn oil (DCO) to produce a crude extract with lipolytic activity and fatty acid ethyl esters was studied in an integrated process. The dry fermented solid (DFS) with lipase activity was produced from the fermentation of the filamentous fungus Rhizomucor miehei in DDGS in tray-type reactors and column systems. The DFS was used to catalyze esterification reactions between oleic acid and ethanol, with conversions of 72% and 80% (within 4 h) for the biocatalyst produced in tray-type and fixed bed systems, respectively. The biocatalyst also converted glycerides from DCO into FAEE, with an ester yield higher than 70% after three consecutive reactions. By introducing 2 wt% of a commercial preparation (Novozym 435) in the system with the DFS, ester contents of 81% were obtained and, the yield was higher than 95% after three consecutive reactions. The biocatalyst could be reused 6 consecutive times in the esterification reactions, after washing with ethanol and 5 times after washing with hexane. In DCO transesterification reactions, reuse was less efficient with a loss of activity after the second reuse. Bromatological analysis showed that the fermented material maintained the main properties of the in natura DDGS, with a reduction in the oil and grease and an increase in protein content. The chemical composition was maintained after its use in the corn oil ethanolysis (used DFS). These findings show the potential for developing novel pathways to diversify the use and enhance the value of co-products derived from the large-scale corn ethanol industry, in a biorefinery concept.