The surface properties of milk fat globules govern their interactions with the caseins: Role of homogenization and pH probed by AFM force spectroscopy

Sameh Obeid (1) , Fanny Guyomarc'H (1) , Gregory Francius (2) , Herve Guillemin (3) , Xiaoxi Wu (1) , Stéphane Pezennec (1) , Marie-Hélène Famelart (1) , Chantal Cauty (1) , Frédéric Gaucheron (4) , Christelle Lopez (1)

1 STLO - Science et Technologie du Lait et de l'Oeuf
2 LCPME - Laboratoire de Chimie Physique et Microbiologie pour les Matériaux et l'Environnement
3 GMPA - Génie et Microbiologie des Procédés Alimentaires
4 CNIEL - Centre National Interprofessionnel de l'Economie Laitière

The surface of milk fat globules consists of a biological membrane rich in polar lipids and glycoproteins. However, high shear stress applied upon homogenization disrupts the membrane and leads to the adsorption of casein micelles, as the major protein fraction of milk. These changes in the interface properties could affect the interactions between native or homogenized milk fat globules and the surrounding protein matrix, at neutral pH and upon acidification. In this study, macroscale rheometry, microscopic observations, nanoscale AFM-based force spectroscopy and physico-chemical analysis were combined to examine the interfacial composition and structure of milk fat globules and to evaluate their interactions with casein micelles. We showed that the surface properties of milk fat globules (biological membrane vs. caseins) and pH govern their interactions with casein micelles. The adhesion between individual fat globules and casein micelles was higher upon homogenization, especially at acid pH where the work of adhesion increased from 3.3 x 10-18 to 14 x 10-18 J for native and homogenized fat globules, respectively. Consequently, casein-coated homogenized fat globules yield stiffer milk acid gels. These findings cast light on the importance of colloidal particle’s surface properties and pH on their connectivity with the surrounding matrix, which modulates the bulk microstructure and rheological properties with potential functional consequences, such as milk lipid digestion.

Mots clés: émulsion; milk fat globules

Mots clés: matière grasse du lait; gouttelette lipidique; micelle de caséine; propriété interfaciale; adhésion; microscopie à force atomique

Domaines: Alimentation et Nutrition; Ingénierie des aliments

Sameh Obeid, Fanny Guyomarc'H, Gregory Francius, Herve Guillemin, Xiaoxi Wu, et al.. The surface properties of milk fat globules govern their interactions with the caseins: Role of homogenization and pH probed by AFM force spectroscopy. Colloids and Surfaces B: Biointerfaces, 2019, 182, pp.110363. ⟨10.1016/j.colsurfb.2019.110363⟩. ⟨hal-02215870⟩