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Heat‐induced gelation of whey protein at high pH studied by combined UV spectroscopy and refractive index measurement after size exclusion chromatography and by in‐situ dynamic light scattering
Author(s) -
Bauer Rogert,
Rischel Christian,
Hansen Steen,
Øgendal Lars
Publication year - 1999
Publication title -
international journal of food science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.831
H-Index - 96
eISSN - 1365-2621
pISSN - 0950-5423
DOI - 10.1046/j.1365-2621.1999.00322.x
Subject(s) - chemistry , absorbance , size exclusion chromatography , radius of gyration , dynamic light scattering , molar mass , analytical chemistry (journal) , chromatography , whey protein , light scattering , refractive index , ionic strength , gel permeation chromatography , scattering , materials science , polymer , aqueous solution , optics , organic chemistry , physics , optoelectronics , nanoparticle , enzyme , nanotechnology
Summary The interactions between β‐lactoglobulin and α‐lactalbumin involved in gelation at 67.5 °C at high pH and low salt concentration were studied by size exclusion chromatography, followed by UV and refractive index measurements, and by in‐situ dynamic light scattering. This was achieved by choosing whey protein samples with different proportions of the two proteins. The ratio of absorbance at 280 nm to the refractive index was used to demonstrate that α‐lactalbumin was incorporated in aggregates and gels and drastically changed the properties of the gel, making them much more turbid than the transparent gels formed by β‐lactoglobulin alone at the same pH and ionic strength. At a ratio of 1:2 for α‐lactalbumin relative to β‐lactoglobulin in the samples, the gel consisted of a 1:1 mixture of the two proteins. The aggregates present after 10 min of heating at 67.5 °C had molar mass of about 6.10 6 g/mol and a radius of gyration of about 40 nm. After gel formation the field autocorrelation function could be described as a power law over many decades of lag time for all samples, demonstrating selfsimilarity of the gel structure. The only exception to this was for the gel with high content of α‐lactalbumin which showed an oscillatory behaviour of the autocorrelation function. Significant amounts of glycosylated caseino‐macro‐peptide were observed in many of the samples at the position of β‐lactoglobulin. However it did not affect gelation as it remains in solution.