Enzymatic modification and fractionation of corn protein
Mannheim, Adie
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https://hdl.handle.net/2142/23261
Description
Title
Enzymatic modification and fractionation of corn protein
Author(s)
Mannheim, Adie
Issue Date
1991
Doctoral Committee Chair(s)
Cheryan, Munir
Department of Study
Food Science and Human Nutrition
Discipline
Food Science and Human Nutrition
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Food Science and Technology
Chemistry, Biochemistry
Language
eng
Abstract
The overall objective of this research was to enhance the utilization of corn refining by-products by improving the functional properties of corn proteins.
Methods were developed to modify zein and glutelin, present in corn gluten meal (CGM), using controlled enzymatic hydrolysis and membrane technology. Since zein is soluble only in organic solvents and glutelin in alkaline solutions, several enzymes were screened for their activity and stability in aqueous and organic solvents. Alcalase$\sp\circler$ (a serine endo-peptidase made from Bacillus licheniformis) was found suitable for this purpose.
Pre-treatment of CGM to reduce disulfide bonds present in its matrix, significantly improved hydrolysis rates. Sodium sulfite was found to be effective at 0.4 mg/mL. For zein hydrolysis, a two-phase sequential hydrolysis process was developed: the first reaction conducted in 60% isopropanol (37$\sp\circ$C, pH 9), followed by a second aqueous phase reaction at 50$\sp\circ$C and pH 9.
The modified and native corn proteins were fractionated using 10,000 and 30,000 molecular weight cut-off hollow fiber membranes. Almost all fractions showed two major peaks with size-exclusion HPLC: one at $>$70,000 daltons and another at 5,500 daltons. The smaller fraction was not affected by the degree of hydrolysis or membrane pore size.
Nitrogen solubility index (NSI) of CGM and zein increased dramatically by enzymatic treatment and membrane fractionation from an average of 8% in the unmodified protein to 99%, at a pH range of 3 to 9. NSI was also affected by degree of hydrolysis (DH) and membrane pore size, increasing with the former and decreasing with the latter.
Foam volume and stability increased with DH and pH. Membrane filtration of hydrolyzates decreased foam stability but increased foam volume.
Moisture sorption characteristics of corn protein hydrolyzates were superior to unmodified protein. At a water activity of 0.97, moisture sorption of sulfite-treated CGM (10% DH) was 380 gm water/100 gm solids, compared to 30 for the unmodified CGM. Values for zein (12-20% DH) were 275 and 245 gm water/100 gm solids, respectively.
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