Abstract Composite casein-pectin gels are key to dairy products like yoghurts, yet the nanoscale interactions governing their microstructure remain incompletely understood. This study employs atomic force microscopy (AFM) to visualize and quantify casein micelles, pectin conformations, and their composites at neutral (pH = 7) and acidified (pH = 4.5) conditions. AFM imaging with tip-broadening correction reveals casein micelles averaging 160 nm diameter and 50% flattened upon immobilization. Pectin imaging and skeletonization analysis show that high-methoxyl pectin (HMP) chains are longer (169 nm) and more tortuous ( = 2.66) than low-methoxyl pectin (LMP) chains (105 nm, = 1.94). At pH = 7, HMP exhibits apparent depletion zones around casein micelles, whereas LMP shows markedly closer surface-associated localization around the micelles. Under acidified conditions (pH = 4.5), AFM reveals more compact local casein aggregates in the presence of pectin, with the strongest effect observed for LMP. Together, the results highlight the importance of pectin methylation in governing nanoscale organization in casein-pectin composites and provide a framework for the formulation of dairy-plant food systems based on direct imaging of pectin-casein interactions.
Mishra et al. (Wed,) studied this question.