Determination of hydro-colloidal characteristics of milk protein aggregates using Asymmetrical Flow Field-Flow Fractionation coupled with Multiangle Laser Light Scattering and Differential Refractometer (AF4-MALLS-DRi)
Résumé
During heat treatment, whey proteins (WP) are denatured and form different kinds of whey protein
aggregates (WPA) depending on the physico-chemical conditions. In the presence of casein micelles,
mixed aggregates (MA), resulting from the interaction of k-casein and WP, are formed. The aim of this
study is to understand the effect of pH on the WPA structure and the impact of the casein/whey proteins
(Cas/WP) ratio on MA morphology. In this work, WP solutions were heated at pH 5.8 or 7 to produce
WPA. On the other hand, aqueous mixtures containing three Cas/WP ratios (82/18, 56/44 and 30/70)
were heated at 80 C during 1 h at pH 6.3 to obtain MA. Milk protein aggregates were analyzed by
Transmission Electron Microscopy (TEM) and Asymmetrical Flow Field-Flow Fractionation coupled with
Multiangle Laser Light Scattering and Differential Refractometer (AF4-MALLS-DRi). Dense and spherical
WPA were formed at pH 5.8 whereas branched and fractal aggregates were obtained at pH 7. Regarding
MA, results suggested that they were mainly produced with the 82/18 Cas/WP ratio whereas a majority
of WPA was obtained with the 30/70 ratio. At intermediate ratio, the mixture was composed of small MA
and WPA that did not interact with k-casein. Moreover, WP seem to interact preferentially with larger
casein micelles. Thereby, AF4-MALLS-DRi proved to be a powerfull technique to characterize the complex
structure of milk protein aggregates and an interesting alternative to size exclusion chromatography
especially for MA and casein micelles which interact with the stationary phase and are retained in the
column
