Enzyme Catalyzed Dissasembly of Corn Kernels

David Orrego, Purdue University

Abstract

In this dissertation, we introduce a novel process to fractionate corn kernels into its identifiable components: starch, germ (oil), protein, pericarp (fiber), using proteases and cellulases, without addition of chemicals or cooking steps. Early stages of the research focused on proving the concept of the fractionation using enzymes and testing different types of activities including cellulases, hemicelulases, pectinases, proteases, and other enzyme compoents carried in these preartions. These enzymes were mixed and incubated with corn kernels with and without exposed endosperm. Results showed that the combination of cellulases and proteases yielded the highest starch recoveries from grains with exposed endosperm while minimal recoveries were obtained with whole kernels. At this point, all experiments had been carried out in flasks agitated in shaker incubators; however, it was desired to evaluate a new mixing pattern able to be reproduced at higher scales. Hence, an upward flow in a cone-bottom reactor was tested, and resulted in a finding a significant enhancement in starch recovery at shorter times, thanks to the axial movement of the kernels which induced gentle rotational motion for release of starch particles from the body of the kernal fragments. Knowing the type of enzymes and mixing conditions that favored the fractionation, after tests in shaking flask and cone-bottom reactor, the process was taken to a scalable configuration consisting of 1L stirred tanks. The up-ward flow in the new vessels was recreated using a right-hand propeller. Maximum starch recovery in the reactors was similar to that in the cone-bottom reactor, when all conditions remained constant between scales, but with a considerable reduction in time. Successful results under the new configuration allowed testing of other variables and continued optimization of the technology. Reduction of enzyme concentration, increment in solid loading, a commercially available corn shape, and use of water as liquid phase were evaluated in the 1 L reactors. Results showed the feasibility to carry out the fractionation using 10 times less enzyme (1.4 mg enzyme/ g corn), higher corn loadings (from 25% to 35% w/v) with commercial cracked corn, and water instead of buffer. An expected reduction in starch recovery and longer process time were observed under these new conditions; however, modifications during the scaling up were expected to improve results. At this point, a scalable configuration and feasible process conditions (enzyme loading, no buffer) were reached, narrowing the gap between laboratory result and an economically and technically viable fractionation, supported by a preliminary economic analysis. As a natural next step, the fractionation was scaled up to a 10 L reactor geometrically similar to the 1 L reactors. For this new vessel, an approximation to the particle Reynolds number and specified scaling criteria were used to select an impeller able to reproduce mixing conditions used in previous scales. Additionally, given the dimensions of the new tank, a dual impeller configuration was tested, finding a measureable improvement in the productivity of the process. Best recovery yields for starch, protein, germ and pericarp, obtained in the reactor, were used in model developed in Aspen Plus to simulate the fractionation at higher scales and present a preliminary economic analysis. (Abstract shortened by ProQuest.)

Degree

Ph.D.

Advisors

Ladisch, Purdue University.

Subject Area

Agricultural engineering|Chemical engineering

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