A SAXS and USAXS study of the influence of pH on the casein micelle structure

• Published in: Food chemistry 2024-06, Vol.443, p.138606-138606, Article 138606
• Main Authors: Takagi, Hideaki, Nakano, Tomoki, Aoki, Takayoshi, Tanimoto, Morimasa
• Format: Article
• Language: English
• Subjects: Bovine milk; Casein micelle; Colloidal calcium phosphates; Small-angle X-ray scattering
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2024.138606

•The pH dependence of the casein micelle was investigated using SAXS and USAXS.•SAXS profiles were analyzed using a structure model including water domains.•The size of a micelle and CCP were changed in response to changes in pH.•pH affected the voluminosity and other physical properties in a micelle.•The structure of the casein micelles varied sensitively with pH changes. Changes in milk pH significantly influence the behavior and physical properties of casein micelles; however, the effects of these changes on casein micelle structures are still unclear. The aim of this study was to elucidate the effect of changes in pH range from 5.9 to 7.1 on the structure of casein micelles in milk using small-angle X-ray scattering (SAXS) and ultra small-angle X-ray scattering (USAXS). The casein micelles formed one-dimensional aggregates. The micelle radius decreased with decreasing pH, whereas the size of the water domain increased. The distance between colloidal calcium phosphates (CCP) remained unchanged, whereas the CCP radius decreased with decreasing pH. Voluminosity, which was calculated from scattering intensities, increased at increased pH. In conclusion, the micelle structure changed significantly in response to changes in pH. Our findings help to understand the changes in the physical properties of milk at various pH levels in terms of the microscopic structure.