Probing early-stage casein micelle aggregation during milk acidification with differential dynamic microscopy

Area of Science:

• Colloid and Surface Science
• Food Science and Technology
• Biophysics

Background:

• The sol-gel transition of casein micelles is crucial for dairy manufacturing.
• Milk's turbidity impedes traditional methods for studying early gelation events.
• Understanding microscopic dynamics is key to controlling acid-induced milk gelation.

Purpose of the Study:

• To apply Differential Dynamic Microscopy (DDM) for in situ analysis of casein micelle dynamics during milk acidification.
• To overcome the limitations of light-scattering methods in turbid colloidal systems.
• To quantify micellar aggregation and network formation during acid gelation.

Main Methods:

• Utilized Differential Dynamic Microscopy (DDM) for time-resolved measurements of skim milk subjected to acid-induced gelation.
• Quantified casein micelle diffusion coefficients and aggregate growth without sample dilution or tracer particles.
• Compared gelation dynamics in heated versus unheated milk samples.

Main Results:

• DDM successfully monitored casein micelle dynamics and aggregation in real-time.
• A decrease in micellar diffusion and the formation of fractal aggregates were observed, leading to gel network formation.
• Heat treatment subtly influenced the relationship between aggregate size and mobility, shifting aggregation onset to higher pH.

Conclusions:

• DDM provides a powerful and accessible method for studying gelation in turbid colloidal systems like milk.
• The study offers quantitative, multi-scale insights into the microstructural changes during acid milk gelation.
• DDM can be a valuable tool for optimizing dairy manufacturing processes reliant on milk gelation.