Corn solvent milling process, using ethanol solutions as extracting solvents
Abstract
An alternative corn milling process to current corn wet milling was developed to efficiently recover corn oil, and corn proteins in the corn kernels with no intensive energy input step involved. Three major components, corn oil, proteins, and crude starch could be sequentially recovered in the column mode by using different ethanol solutions as solvents. The corn solvent milling process included two major extraction steps besides the subsequent process of corn starch recovery: oil extraction and protein solubilization. Both extractions were carried out in a column reactor operated at 68$\sp\circ$C with a flowrate of 100 mL/h. Extraction of oil from dried ground corn by using 95% ethanol (w/w) resulted a rapid simultaneous dehydration of the extracting ethanol. The oil extraction recovered approximately 90% of the total crude oil and 500 mL of 99.3% ethanol per kg of bone dry corn. Protein extraction was achieved by using an alkaline ethanolic solvent containing 0.08N NaOH in 50% aqueous ethanol (w/w). About 90% of proteins was recovered and starch was not gelatinized The phenomena of column extraction were further examined through evaluation of thermodynamic and kinetic quantities in three individual studies: oil extraction, ethanol dehydration, and protein solubilization. The rate of oil extraction and ethanol dehydration were modeled. The oil extraction rate of finely ground corn using absolute ethanol as a solvent was very fast, reaching completion in 10 min, whereas the rate of large corn particles was limited by the slow diffusion of ethanol into the particles. The limitation could be overcome by wetting the dried ground corn with ethanol at 68$\sp\circ$C for 18h. The dehydration rate of 95% ethanol by dried corn flour was fast, reaching completion in 30 min. In large corn particles, the dehydration rate was slow and was found to correlate with the oil extraction rate. Protein solubilization by the alkaline ethanolic solvent was governed by the rate of disulfide bond cleavage of glutelin proteins and was not correlated to the deamidation of proteins. The rate of disulfide cleavage was found to be second order with respect to the sulfide concentration of the unextracted proteins.
Degree
Ph.D.
Advisors
Chen, Purdue University.
Subject Area
Food science
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