Title
Soy glycinin Influence of pH and ionic strength on solubility and molecular structure at ambient temperatures
Author
TNO Voeding
Lakemond, C.M.M.
de Jongh, H.H.J.
Hessing, M.
Gruppen, H.
Voragen, A.G.J.
Publication year
2000
Abstract
This study describes the relationship between the solubility of glycinin, a major soy protein, and its structural properties at a quaternary, tertiary, and secondary folding level under conditions representative for food products. When the ionic strength is lowered from 0.5 to 0.2 or 0.03, the basic polypeptides shift more to the exterior of the glycinin complex, as determined at pH 7.6 by labeling solvent-exposed lysines, supported by the study of the proteolytic action of clostripain on glycinin. This structural reorganization caused the pH of minimal solubility to shift to higher values. Ultracentrifugational analysis shows that at pH 7.6 and an ionic strength of 0.5 glycinin forms hexameric complexes (11S), whereas at pH 3.8 and at anionic strength of 0.03 glycinin exists as trimers (7S). Intermediate situations are obtained by modulation of pH and ionic strength. The observed quaternary dissociation correlates with an increased amount of nonstructured protein at a secondary level and with changes in tertiary folding as determined using circular dichroism. Tryptophan fluorescence shows no significant structural changes for different ionic strengths but demonstrates a more tightly packed fluorophore environment when the pH is lowered from 7.6 to 3.8. Chemicals / CAS glycinin, 9007-93-6; soybean protein, 9010-10-0; Globulins; Plant Proteins; Soybean Proteins; glycinin, 9007-93-6.
Subject
Glycinin
Ionic strength
PH
Soy
soybean protein
vegetable protein
chemistry
circular dichroism
food processing
nonhuman
osmolarity
protein denaturation
protein quaternary structure
structure analysis
Globulins
Hydrogen-Ion Concentration
Osmolar Concentration
Plant Proteins
Protein Folding
Protein Structure, Quaternary
Protein Structure, Secondary
Protein Structure, Tertiary
Solubility
Soybean Proteins
Soybeans
Thermodynamics
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DOI
https://doi.org/10.1021/jf9908695
TNO identifier
953482
ISSN
0021-8561
Source
Journal of Agricultural and Food Chemistry, 48 (48), 1985-1990
Document type
article