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PHYSICOCHEMICAL VERIFICATION OF NONEXISTENCE OF α s1 ‐CASEIN‐ κ ‐CARRAGEENAN INTERACTION IN CALCIUM‐FREE SYSTEMS
Author(s) -
SKURA B. J.,
NAKAI S.
Publication year - 1980
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.1365-2621.1980.tb04106.x
Subject(s) - chemistry , casein , chromatography , sedimentation coefficient , ionic strength , analytical ultracentrifugation , carrageenan , elution , analytical chemistry (journal) , sedimentation equilibrium , viscosity , ultracentrifuge , aqueous solution , thermodynamics , biochemistry , organic chemistry , physics , enzyme
The interaction between α s1 , ‐casein and K‐carrageenan was investigated by sedimentation velocity and sedimentation equilibrium ultra‐centrifugation, frontal chromatography, fluorescence polarization, viscosity, and turbidity experiments. Schlieren patterns of α s1 ‐casein‐K‐carrageenan mixtures during sedimentation velocity ultracentrifugation experiments (pH 6.6, μ= 0.08) revealed a large α s1 ‐casein containing peak followed by a slower sedimenting peak which was thought to be residual, uncomplexed k‐carrageenan. The S 2 0, w of the interaction peak was greater than the S 2 0, w of α s1 ‐casein alone under identical conditions. The effects of pH, ionic strength, temperature and 6.OM urea suggested that the interaction observed during sedimentation velocity ultracentrifugation and viscometry of α s1 ‐casein and K‐carrageenan was mediated by hydrogen bonding. Fluorescence polarization, frontal chromatography, and molecular weight distributions calculated from sedimentation equilibrium data, however, showed that α s1 ‐casein and K‐carrageenan did not interact in calcium‐free systems (pH 6.6, μ= 0.08). DNS‐α s1 ‐casein and DNS‐K‐carrageenan were employed as the labelled components during the fluorescence polarization experiments. α s1 ‐Casein‐K‐car‐rageenan mixtures eluted from a controlled pore glass column (170 Å pore diameter) as the individual components with elution volumes identical to those obtained when α s1 ‐casein and K‐carrageenan were chromatographed separately. The molecular weight distributions of α s1 ‐casein‐K‐carrageenan mixtures (pH 6.6, μ= 0.08), subjected to sedimentation equilibrium ultracentrifugation, contained a major peak in the molecular weight range corresponding to unreacted α s1 , ‐casein. Thus the “interaction” revealed by sedimentation velocity and viscosity data was not a chemical interaction but, rather a physical entrapment of α s1 ‐casein by K‐carrageenan. Fluid flow through the capillary during viscosity measurements and the intense gravitational fields generated during sedimentation velocity ultracentrifugation probably induced physical entanglement of the K‐carrageenan. Under these conditions, α s1 ‐casein‐K‐carrageenan mixtures flowed as a “porous‐plug” where α s1 ‐casein, larger than the pores of the K‐carrageenan network, was trapped giving rise to the observed “interaction” peak. Physical entanglement of α s1 ‐casein within the K‐carrageenan system which causes a pseudo‐interaction was not detected during frontal chromatography, sedimentation equilibrium, and fluorescence polarization measurements. Thus, α s1 ‐casein and K‐carrageenan do not chemically interact in calcium‐free systems.