Spatial arrangement of casein micelles and whey protein aggregate in acid gels: Insight on mechanisms
Résumé
Skim milk used for the yoghurt manufacture contains 2 main colloidal particles, the native micellar
casein (NMC) and the heat-induced whey protein aggregates (WPA). The aim of this study was to understand
how these 2 colloids organize in space to form binary acid gels. While acid milk gels were
considered homogeneous for scales typically above ~10 mm, shorter length scales were examined to
investigate the early stages of particle aggregation. The NMC and WPA were dispersed in milk permeate
at different protein concentrations, separately or in an 80/20 w/w mixture (MIX). Acidification was
performed at 35 C with glucono-d-lactone to achieve a final pH at ~4.5 in 6 h. Acid gelation was studied
by rheology, while the microstructure of the gels at pH 4.5 was studied by confocal scanning laser microscopy
and transmission electron microscopy (TEM). Using Shih et al.'s (1990) model on the rheological
data, it seemed that aggregation in the NMC and MIX mixtures was driven by the casein micelles and
therefore differed from that of the WPA suspension. The different organizations were confirmed using
image analysis of confocal or TEM images. The differences in gel formation were discussed in terms of the
different interactive properties of the surface of these 2 colloids, together with their different internal
structure.
Origine : Accord explicite pour ce dépôt
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