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Journal Articles Food Hydrocolloids Year : 2022

Atomic force microscopy to assess the mechanical properties of individual casein micelles

Abstract

Casein micelles (CMs) are ~100 nm natural colloids found in milk resulting from the complex and unresolved association of casein monomers, phosphorus, and calcium; the latter being either directly bound to the phosphoserine residues of caseins or present as nanoclusters of insoluble micellar calcium phosphate (MCP). Dairy products such as cheese or yogurt are colloidal gels formed by CMs destabilization, for which texture and ability to be processed are essentially determined by rheological properties. Those properties depend on the physicochemical conditions used during gel formation (e.g., pH, temperature, ionic content). However, questions remain about the origin of this dependence at the microscopic scale. In particular, we still do not have a clear picture of the specific contributions of the rigidity of the elementary bricks (CMs) in comparison with the interparticles interactions or their spatial distribution. In this work, Atomic Force Microscopy (AFM) is used to evaluate changes in the nanomechanical properties of single CMs following physico-chemical modifications that are known to affect the MCP content and the rheology of the enzymatic milk gel (i.e. decrease of pH and CaCl 2 addition). AFM is used as a direct indenter that assesses the CMs' elastic deformation and gives an estimate of their Young modulus. We show that for a ±18-24% w/w depletion or enrichment in MCP content, the Young modulus of CMs significantly decreases or increases, respectively. This correlation suggests that variations in the modulus of individual CMs could explain the changes in the macroscopic properties of the enzymatic milk gel upon variations of physico-chemical conditions.
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hal-03622993 , version 1 (29-03-2022)

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Julien Bauland, Antoine Bouchoux, Thomas Croguennec, Marie-Hélène Famelart, Fanny Guyomarc'H. Atomic force microscopy to assess the mechanical properties of individual casein micelles. Food Hydrocolloids, 2022, 128, pp.107577. ⟨10.1016/j.foodhyd.2022.107577⟩. ⟨hal-03622993⟩
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