Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2003
Publication Date: 11/1/2003
Citation: HOJILLAEVANGELIST, M.P., JOHNSON, L.A. SEQUENTIAL EXTRACTION PROCESSING OF HIGH-OIL CORN. CEREAL CHEMISTRY. 2003.
Interpretive Summary: The Sequential Extraction Process (SEP) is a promising new approach to fractionating corn for ethanol production. SEP produces value-added co-products like corn oil and protein products, potentially making ethanol production more economical. SEP appears to be well-suited for high-oil corn (HOC) hybrids. HOC is preferred over normal dent corn in livestock feed because its greater oil content imparts higher energy value to the feed. HOC also has higher protein content and better protein quality. Other possible uses of HOC have not been widely adopted because of processing problems associated with the high oil content. Such problems are not likely to become major factors in SEP. In fact, we anticipate that HOC will be a better starting material for SEP than normal dent corn because it would produce greater oil yields for the same amount of extracting solvent (ethanol) and better-quality protein products. We, therefore, evaluated the performance of HOC in SEP and compared the yields and properties of HOC co-products with those of normal soft dent corn (SDC). SEP extracted more than 90% of the oil from both HOC and SDC, but, as expected, the oil yield of HOC was almost double that of SDC. Crude oil from HOC had better color (less red) and lower estimated refining loss than SDC oil. Zein, which is used in film-coating and fiber-spinning industries, was recovered from HOC in reasonable yield and quality. The glutelin-rich protein fractions (GRF), extracted by using a mixture of ethanol and dilute alkali, from both HOC and SDC had very high protein purity (90% protein content), which classifies the GRF as protein isolates. HOC GRF protein isolate had functional properties that were similar to those observed in SDC GRF. The high solubility in water at pH 7 (found in most food systems), good foaming and emulsifying properties, and excellent heat stability of corn GRF are traits that are highly desired by the food industry. When SEP is used to fractionate HOC, oil and value-added protein products such as zein and GRF isolate can be produced in addition to ethanol, thus making ethanol production more cost-effective.
Technical Abstract: The Sequential Extraction Process (SEP), a process that uses ethanol to fractionate corn, was evaluated as an approach to recover oil and other co-products from high-oil corn (HOC). Oil and protein recoveries, ethanol-drying capability, and oil and protein properties were compared with those of normal soft dent corn (SDC). Moisture adsorption capacities (ca. 24 g water/kg corn) and oil recoveries (>95%) were nearly identical for both corn types, however, oil yield from HOC (7.1 g oil/100 g corn) was nearly double that of SDC (4.3 g oil/100 g corn). HOC crude oil was less red and contained less free fatty acids and phosphatides than did SDC oil. HOC zein contained higher crude protein content (86% dry basis, db) than did SDC zein (79%, db). The freeze-dried glutelin-rich fractions from both types of corn contained 90% (db) crude protein, which classified the protein extracts as protein isolates. SEP protein isolates had >85% protein solubilities in water at pH>7. Both protein isolates from HOC and SDC were heat-stable, had good emulsifying capacities, and produced highly stable emulsions. They also had substantial foaming capacities, but HOC protein isolate foam was significantly more stable than was the SDC protein isolate foam. SEP is a suitable process for recovering oil and protein products from HOC corn and HOC is a preferred feedstock to SDC.