A Method for Improving the Nutritional Value of Food Proteins: Covalent Attachment of Amino Acids

  • Antoine J. Puigserver
  • Lourminia C. Sen
  • Andrew J. Clifford
  • Robert E. Feeney
  • John R. Whitaker
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 105)


Casein was modified by use of a series of active N-hydroxysuccinimide esters of amino acids in order to study the effects of new covalently linked hydrophobic or hydrophilic groups on its physical and nutritional properties. Tryptophan was used to determine the best conditions for the chemical reaction and to study the stability of the newly formed amide linkage (isopeptide bond). Casein was also modified with glycine, alanine, methionine, Nacetyl-methionine and aspartic acid. In vitro hydrolysis studies using bovine chymotrypsin, pancreatin and rat bile-pancreatic juice indicated that digestibility of the modified casein derivatives was lower than that of the untreated protein. Since solubility was not significantly changed (except for tryptophylcasein), the decreased in vitro digestibility is probably due to other factors such as steric hindrance as well as to decrease in lysine residues available to trypsin in pancreatin and rat pancreatic juice. Plasma amino acid patterns for rats fed a 10% protein diet of highly modified glycyl-casein or methionyl-casein suggest that the ε-aminolysyl derivatives are readily hydrolyzed in vivo. This was confirmed by the growth response of rats fed the following isonitrogenous diets (protein source listed only): casein, casein + free methionine, methionyl-casein, casein + free N-acetyl-methionine, N-acetyl-methionyl-casein. Covalently attached methionine appeared to be as readily available as the free amino acid; bound N-acetyl-methionine was also available but to a slightly lower extent. Although this study is preliminary, the covalent attachment of amino acids to proteins appears to be a promising method for improving the biological value of food proteins.


Food Protein Covalent Attachment Soybean Trypsin Inhibitor Isopeptide Bond Reductive Alkylation 
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Copyright information

© Plenum Press, New York 1978

Authors and Affiliations

  • Antoine J. Puigserver
    • 1
  • Lourminia C. Sen
    • 2
  • Andrew J. Clifford
    • 3
  • Robert E. Feeney
    • 2
  • John R. Whitaker
    • 2
  1. 1.Centre de Biochimie et de Biologie Moléculaire (C.N.R.S.)MarseilleFrance
  2. 2.Department of Food Science and Technology and Department of NutritionUniversity of CaliforniaDavisUSA
  3. 3.Department of NutritionUniversity of CaliforniaDavisUSA

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