Liquid droplet-like behaviour of whole casein aggregates adsorbed on graphite studied by nanoindentation with AFM

AFM study of casein micelles cross-linked by genipin: effects of acid pH and citrate

“…However, the control CMs were ∼fourfold wider than high, which reflected in a low value for the apparent θ determined namely ∼40°. These results support the fact that CMs could be deformed on adsorption (Helstad et al 2007;Ouanezar et al 2012). Although CMs are physically stable lyophilic colloids (Walstra et al 2010), the lack of covalent bonds in their core makes them susceptible to destructuration regarding the chemical environment.…”

“…Estimation of the apparent contact angle (θ) By using AFM, it is possible to estimate the apparent contact angle (θ) between a particle and the solid surface from the height (h) and width (w) of the individual particle as the following equation: θ=cos −1 (1−h/w) (Nguyen et al 2003;Helstad et al 2007). Here, the concept of apparent contact angle θ was used to estimate the deformation of spherical particles upon adsorption onto a flat surface, which has been shown to relate to the elastic modulus of polymer particles (Evangelopoulos et al 2012).…”

Atomic force microscopy of food assembly: Structural and mechanical insights at the nanoscale and potential opportunities from other fields

“…With this approach, the effect of pressure, fouling or enzymatic coagulation on the morphology of casein micelles layers could be visualized on dessicated concentrated samples spread onto mica, glass or silicon nitride (Freitas et al, 2019;Gebhardt, Doster, Friedrich, & Kulozik, 2006, 2011Regnault, Thiebaud, Dumay, & Cheftel, 2004). To identify individual casein micelles, they need more specialized immobilization, e.g., on freshly cleaved graphite (Helstad, Rayner, van Vliet, Paulsson, & Dejmek, 2007), glass (Freitas et al, 2019), self-assembled monolayers (Christensen, Rasmussen, & Simonsen, 2015;Ouanezar et al, 2012;Silva, Bahri, Guyomarc'h, Beaucher, & Gaucheron, 2015;Uricanu, Duits, & Mellema, 2004, Fig. 2 B) or substrates coated with casein-specific monoclonal antibody (Bahri et al, 2017(Bahri et al, , 2018.…”

“…In this pioneer study, the measurement of local structural features, such as fibrils, was linked with the bulk mechanics of the heterogeneous sample. AFM has also been used to evaluate the Young's modulus of small objects such as the milk's casein micelles (Bahri et al, 2017(Bahri et al, , 2018Helstad et al, 2007;Uricanu et al, 2004). When the tip is properly positioned at the apex of the micelles, values of hundreds of kPa order Fig.…”

“…Instead of force measurements, AFM imaging may help predict the Young's modulus of polymer particles using their deformation upon adsorption onto a surface (Evangelopoulos, Glynos, Madani-Grasset, & Koutsos, 2012). Similarly, the calculation of a "contact" angle is used to evaluate stiffness changes of casein micelles as a consequence of chemical crosslinking, demineralization, acidification (Helstad et al, 2007;Silva et al, 2015) or heating in the presence of whey proteins (Micleusanu et al, unpublished results; Fig. 6).…”