PROTEIN SEPARATION FROM CORN ENDOSPERM BY SOLVENT EXTRACTION
Abstract
The two major classes of corn endosperm protein, zein and glutelin, were extracted by using the solvents ethanol and sodium hydroxide. For each class, the primary phenomena responsible for the rate of protein dissolution and extraction were quantitatively evaluated and modeled. Maximal extractions of zein from corn endosperm were obtained by using 55%-65% (w/w) enthanol and solvent:endosperm ratios of 20 m1:1 cm('3) or greater, allowing recovery of 97% of the total zein. No significant effect of stirring speed was observed in separate batch extractions of zein and glutelin, implying that mass transfer across the fluid boundary layer was not a major factor governing the overall solubilization process. The apparent rate of zein solubilization, determined with 100 micron endosperm particles, was best described as a first order reaction. The apparent activation energy was 3.9 kcal/mole suggesting that pore diffusion may have influenced the observed rates. The extraction of zein from larger endosperm particles appeared to be controlled by pore diffusion with the calculated value of De King 3.7 x 10('-10) cm('2)/s (average). This value, together with pore size distribution data suggested that the diffusional process was one of Knudsen diffusion with substantial wall effects. The initial rate of glutelin solubilization varied linearly with N(,2)OH concentration and was found to have an activation energy of 6.2 kcal/mole, again indicating probable diffusional influence on the measured kinetics. The overall rate of glutelin solubilization was modeled with reaction-rate-limited shrinking core kinetics by assuming that the rate of glutelin solubilization was proportional to the rate of disulfide bond cleavage. Two-step sequential extractions of zein and glutelin were found to result in overall solubilization of approximately 90% of the total protein in corn endosperm. In large scale extractions, it appears to be sufficient to use only enough ethanol to wet the endosperm before adding sodium hydroxide to solubilize the remaining portion. This method should result in 80%-85% protein recoveries for pilot plant scale operations.
Degree
Ph.D.
Subject Area
Chemical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.