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Kinetics of Racemization of Amino Acid Residues in Casein
Author(s) -
FRIEDMAN MENDEL,
MASTERS PATRICIA M.
Publication year - 1982
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/j.1365-2621.1982.tb12709.x
Subject(s) - racemization , chemistry , amino acid , aspartic acid , casein , phenylalanine , alanine , alkali metal , organic chemistry , medicinal chemistry , biochemistry
Exposing casein to alkali (0.1N NaOH at 65°C) partly racemized the amino acid residues. A plot of D/L ratios for seven amino acids versus time of treatment shows fast initial racemization rates that decrease after about 1 hr. A linear free energy relationship exists between racemization rates and inductive effects of amino acid side chains or R‐substituents (σ*). Kinetic studies over the temperature range 25–75°C yields activation energies (in Kcal/mole) for aspartic acid (20.8), phenylalanine (28.7), glutamic acid (32.5), and alanine (32.4). Racemization rates increase with hydroxide ion concentration but not with protein concentration. Acetylation of amino groups prevents lysinoalanine formation but not racemization, permitting studies which distinguish between effects of these two alkali‐induced reactions. Understanding principles that govern racemization should help in designing food processes that minimize undesirable, deteriorative changes in food proteins.