Impedance evaluation of coatings from biobased material

Abstract

The authors propose a modification of sodium caseinate edible coating for foodstuff protection. The aim was to improve the film’s barrier properties. It was achieved by the addition of propolis, which is a natural, environmentally friendly product known from its intrinsic sealing action. In the next step, propolis-admixed sodium caseinate films were exposed to elevated temperature for 10 min. This approach was meant to improve the barrier effect of propolis. Electrochemical impedance spectroscopy was used to evaluate the performance of the control and modified samples upon immersion in water. Atomic force microscopy-based measurements visualised the sealing effect of propolis by means of topographical images, local direct-current maps and local impedance spectra of the control and modified films. From the obtained results the authors drew the conclusion that the proposed modifications improved the barrier properties of the sodium caseinate films. Applied combination of the investigation methods, electrochemical impedance spectroscopy and atomic force microscopy, allowed successful characterisation of protective properties of sodium caseinate coatings. The proposed atomic force microscopy measurement modes can be employed for evaluation of modifications implemented into biobased coatings, particularly when there is a need for electrolyteless tests.