Chemical imaging of protein hydrogels undergoing alkaline dissolution by CARS microscopy

Hydrogels swell, shrink and degrade depending on the solution they are in contact which, strongly affecting their performance. The minimum information needed to validate many published simulations would be the spatial quantification of the solute material with time. In this study we develop a simple methodology to quantify the protein content in heat induced protein hydrogels using a commercial Coherent anti-Stokes Raman Spectroscopy (CARS) microscope. The system is used to quantify the whey protein isolate (WPI) concentration in hydrogels undergoing dissolution at alkaline pH. Quantitative measurements were performed in hydrogels up to depths of ∼600 µm, with an average accuracy of ∼1 wt%. Results show that the protein concentration within the swollen layer is constant with time, confirming the existence of steady state conditions during dissolution. The methodology presented can easily be implemented to other biopolymer hydrogels and foods.