Colorimetric measurement of water activity based on Bouligand-structured cellulose nanocrystal film

In this study, a new method for water activity (Aw) measurement based on the colorimetric response of Bouligand-structured cellulose nanocrystal (CNC) films was developed and evaluated. Three composite films with different CNC/glycerol mass ratios (9/1, 8/2 and 7/3) were fabricated, and their responses to Aw were investigated. Evaluation of the method was performed with various foods, and Conway's diffusion method as the reference. The results showed that the color parameters a*, b* and ΔE of the films exhibited good quadratic relationships (R² > 0.96) with Aw. The models for the film with a CNC/glycerol ratio of 9/1 provided the highest measurement accuracy for foods with Aw >0.4, with relative errors <5%; while they gave unreliable results with relative errors >70% for foods with Aw <0.4. The findings of this study demonstrated the great potential of the CNC-based method for Aw measurement in the range above 0.4.