Carvacrol release from PLA to a model food emulsion: Impact of oil droplet size

The effect of food structure on the release of a volatile antimicrobial from an active packaging (AP) was investigated by measuring the migration of carvacrol from a polylactic acid (PLA) film to a model food system, namely, an oil-in-water (O/W) emulsion. We aimed to understand the influence of the oil droplet size on the kinetics of carvacrol migration from the PLA film to the emulsions, on its final partitioning and antimicrobial activity. Five model systems were prepared: they had the same composition, i.e., an oil fraction of 20 wt% and an aqueous phase containing 1.5 wt % whey protein isolate, but different structures. Emulsions with the smallest oil droplets (d_3,2 = 0.27 μm) absorbed a higher amount of carvacrol than emulsions with large oil droplets (d_3,2 = 0.34 μm and d_3,2 = 0.51 μm). Despite the higher overall carvacrol concentration, inhibition of bacterial growth was less effective in emulsions with the smallest droplet (d_3,2 = 0.27 μm). This can be explained by the highest log K of carvacrol in this emulsion indicating that carvacrol partitioned more into the oil droplet phase than in the continuous phase. The current study suggests that the spatial distribution of carvacrol in the emulsion determines its actual antimicrobial effect. The combined findings of antimicrobial distribution and activity highlight the need for tailoring active packaging systems based on the physical characteristics of multiphase food matrices.