Super resolution microscopy imaging of pH induced changes in the microstructure of casein micelles

Acidification of milk destabilizes casein micelles (CMs) and results in network formation. This process is fundamental during the manufacturing dairy gels such as cheese yoghurts. Understanding structural alterations CMs this aids to predict physicochemical sensory properties gels. Herein we utilize direct Stochastic Optical Reconstruction Microscopy (dSTORM) visualize individual hydrated characterize pH-dependent changes CM size distributions. were immobilized, fixed, labelled with caseins-specific primary antibodies, imaged by dSTORM using Alexa Fluor 647 conjugated secondary antibodies. While antibodies specific κ- β-casein used stain CMs, only enabled reproducible imaging across entire chosen pH window. Furthermore, CM’s evolution was studied at acidic values representing conditions acid gel formation three elevated values. aggregates 4.5, below isoelectric point caseins, showed that distribution throughout protein resolved nano-sized pores within structure. Moreover, automated quantitative image analysis revealed average increased upon alkalization 7.5 8.3, whilst narrow distributions found acidification 5.5.