Whey protein isolate biodegradable films: Influence of the citric acid and montmorillonite clay nanoparticles on the physical properties

•Whey protein isolate nanocomposites as a potential for active food packaging.•MMT nanoparticles and citric acid improve the thermal stability of the films.•The combination of MMT and citric acid reduced water vapor permeability.•The GAB model describes the isothermal behavior of water vapor adsorption.

Innovative technologies for the incorporation of nanoparticles into packaging systems are being studied in order to improve performance properties. The objective of this study was to evaluate the influence of the addition of citric acid (CA) and sodium montmorillonite clay nanoparticles (MMT) on the physical properties and thermodynamic equilibrium with water vapor in films from whey protein isolate (WPI). WPI nanocomposites (6% w/v), glycerol (40 g/100 g of WPI), montmorillonite (3 g/100 g of WPI) and citric acid (5 g/100 g of WPI), were developed by the casting technique. The GAB model adequately described the water adsorption isothermal behavior (E ≤ 6.08%), the curves were sigmoidal. The combined addition of MMT and CA reduced the adsorption capacity, the moisture content of the monolayer (Xm), permeability to water vapor and moisture in relation to the control film. It was also verified that the combination increased the decomposition temperature and showed less mass loss variation. Thus, the interaction between MMT and CA enabled to obtain nanocomposites with good thermal and barrier properties and higher storage stability for application as packaging materials.

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