Unraveling antimicrobial efficacy variability in controlled-release packaging across food surfaces: Roles of adsorption and post-adsorption activity

Antimicrobial efficacy of controlled-release packaging (CRP) often varies across food surfaces, yet the mechanisms responsible for this variability remain poorly understood. This study investigated how food surface properties influence carvacrol adsorption and contribute to differences in CRP efficacy. Carvacrol antimicrobial activity against Escherichia coli O157:H7 Sakai was evaluated on food surfaces with distinct physicochemical properties, and adsorption behavior was quantified using a mechanistic model. The results demonstrated that differences in antimicrobial efficacy among food surfaces could not be explained by headspace concentrations alone but were strongly influenced by adsorption behavior, highlighting the role of food-surface interactions in CRP performance. Although efficacy generally increased with the amount of carvacrol adsorbed onto the surface, the adsorbed amount alone could not fully account for the differences in efficacy among food surfaces. To address this limitation, post-adsorption activity ( δ ), a new parameter adapted from water activity, was developed to describe the relative availability of adsorbed carvacrol on food surfaces. Adsorption isotherms revealed that strong antimicrobial efficacy generally occurred when δ approached approximately 0.1, despite substantial differences in the adsorbed amounts required to reach this value. The results further showed that variations in δ explained the contrasting effects of surface saturation on efficacy, with persistently low δ values on blueberry surfaces associated with declining antimicrobial activity. Taken together, these observations suggest that adsorption, surface saturation, and post-adsorption activity jointly contribute to CRP efficacy and support δ as a promising mechanistic descriptor for understanding antimicrobial performance across food surfaces.