Potassium sorbate diffusion in multilayer polymer films: Effects of water activity and pH

Abstract

The main aim of this study was to estimate the effect of acidity and water activity (aw) on the diffusion of potassium sorbate (PS) into model aqueous systems at 25 °C from an industrially produced multilayer active film (LPDE/polyamide/LPDE containing 2%PS). The releases of PS from films were set according to two factors face-centered central composite design of the response surface method (RSM). The ANOVA, 3D response surface, and 2D contour plots showed that pH and aw were effective factors in the diffusion coefficient (D) of PS from the films, and these two variables had an important interaction between them. Film samples within the liquid medium with low aw and pH values had the highest D. This might have occurred owing to the swelling of films within the solution with lower aw and high solubility of PS, and within the solution having lower pH, the faster diffusion of PS might have occurred. Practical applications In this study, the diffusion kinetic of potassium sorbate was observed under various conditions, such as pH and water activity. These conditions are the most important physico-chemical properties for food products. Moreover, the efficiency of the sorbate depends on the pH of the medium; with increasing pH, the efficiency is decreased, and above pH = 6.5, sorbic acid loses its antimicrobial property. Thus, the pH level is very important for the application of such films. Furthermore, these properties can affect both food product specialists and antimicrobial agent release. The pH and water activity were found to be very effective in diffusion kinetics of potassium sorbate. The results showed that antimicrobial diffusion from an active packaging film should be evaluated according to the food properties. We also observed adverse changes in the film structure, especially at lower water activity values. It was possible to relate the effect of aw on diffusion with the characteristics of film, the incorporated agents, and the used system. Depending on the diffusion medium, the film structure might change, and this could accelerate or limit the migration.