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Title: THE USE OF PROTEASES TO REDUCE STEEP TIME AND SO2 EMISSION IN A CORN WET- MILLING PROCESS

Author
item Johnston, David
item SINGH, VIJAY - UNIVERSITY OF ILLINOIS

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2001
Publication Date: 4/1/2001
Citation: N/A

Interpretive Summary: The processing of corn by wet milling to obtain starch is done by first soaking (steeping) the corn for 24-36 hours in a chemical solution (sulfur dioxide dissolved in water). The corn is then ground and the products separated using physical techniques (screening, centrifuging, washing, etc.). The long processing times due to the soaking step and the quantities of chemicals required make this a costly process having significant environmental concerns. In this study, we develop and demonstrate (at a laboratory scale) an enzymatic process that substantially shortens the corn processing time and decreases and possibly eliminates the need for sulfur dioxide addition.

Technical Abstract: To eliminate the diffusion barriers associated with enzyme addition during conventional steeping, we have developed a two-stage procedure to evaluate the effects of enzyme addition on corn wet-milling. The current study compares the effects of the addition of commercially available enzymes during conventional steeping to their addition in the developed two-stage procedure. Results are presented in terms of yields of fiber, starch, germ and gluten. The results demonstrate that the application of enzymes to the normal steeping step of wet milling is not an effective means of decreasing the steeping time or sulfur dioxide usage. Only when specific enzymes are added to the hydrated ground corn, using the modified two-stage procedure, are enzymes effective in decreasing the steeping time and sulfur dioxide requirements. This approach removes the diffusion barriers and allows the enzymes to interact with the endosperm associated proteins that encapsulat the starch granules. The overall steeping time with the two-step modified procedure will range from 6 to 8 hours, representing a 67-83% reduction over the conventional process. The modified process greatly decreases and possibly eliminates the need for sulfur dioxide addition and gives starch yields and quality equivalent to that from the conventional process. The reduced steep time and sulfur dioxide requirements will have a significant effect on reducing energy consumption and environmental pollution.