Chemical and enzymatic modification of whey proteins
Lakkis, Jamileh M.
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Permalink
https://hdl.handle.net/2142/20530
Description
Title
Chemical and enzymatic modification of whey proteins
Author(s)
Lakkis, Jamileh M.
Issue Date
1991
Doctoral Committee Chair(s)
Artz, William E.
Department of Study
Food Science and Human Nutrition
Discipline
Food Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Food Science and Technology
Language
eng
Abstract
"Chemical and enzymatic modifications of whey proteins and their effects on the protein's structural and functional properties were studied. Chemical modification by acylation improved the surface properties of the proteins. Succinylation, in particular, imparted a significant resistance against browning development upon storage in an intermediate moisture system. Enzymatic deamidation, via trypsin and chymotrypsin, resulted in proteins with improved solubility and enhanced in vitro digestibility. Enzymatic hydrolysis of whey proteins was performed using six different enzymes, namely, trypsin, chymotrypsin, papain, bromelin, pepsin and pronase. Efficiency of the hydrolytic process was evaluated by monitoring parameters such as temperature, pH, substrate concentration, enzyme to substrate ratio and ionic composition. Correlation of the enzymes' mode of action on whey proteins to their hydrolytic power was studied in comparison to other proteins with different molecular structures. Separation and recovery of the hydrolyzed fractions was achieved using two hollow fiber membranes of different molecular weight cut-offs arranged in series. Physicochemical characterization of the recovered whey protein fractions showed that this treatment affected the secondary structure of the proteins to various degrees as evidenced by their circular dichroic profiles. Interactions of the modified proteins with other proteins, lipids and mineral ions were compared to those of the native whey protein. Interaction of the modified proteins with gluten took place by two different mechanisms, namely, hydrophobic interaction and disulfide-sulfhydryl groups interchange. The improved performance of the modified proteins with gluten enhanced foaming power as shown in the reduction of foam drainage volume and prolonged life-time of the foams. Gels from modified whey proteins with gluten exhibited smoother texture, improved strength and unique ultrastructural properties as evidenced by scanning electron microscopy. Protein modification improved binding ability to calcium as detected by the fluorescence probe Quin-2. Upon heating, the modified proteins showed a delay in flocculation at various pH values implying increased thermal stability. Evaluation of the nutritional value of the enzyme-treated proteins was studied in terms of the effect of enzyme to substrate ratio on the rates of rupturing peptide bonds and release of free amino acids. Whey proteins and their modified counterparts followed the ""variable ratio effect"" mechanism of enzyme digestibility."
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