Designing of a wheat gluten/montmorillonite based system as carvacrol carrier: Rheological and structural properties

An antimicrobial delivery system was designed from film-forming solutions containing wheat gluten 20% (wt/vol) (WG) as matrix, montmorillonites (Mmt) as structuring agent and carvacrol as active agent (15% wt/wt dry WG). The objectives of this work were to understand how the addition of montmorillonites (0–10% wt/wt dry WG) affects the carvacrol retention capacity of both the film forming solution and the resulting film obtained by casting. For this purpose, structural, granulometric and rheological changes that occurred in the film-forming solutions were studied. The introduction of carvacrol in a WG solution containing increasing amounts of Mmt resulted in dramatic changes in its rheological behaviour. Depending on the Mmt amount added (<or ≥ 5%), the viscosity evolved in different ways indicating an unexpected and specific effect of Mmt on the WG solutions that contain carvacrol. In the presence of a sufficiently high Mmt content (≥5%), particles size measurements and microscopic observations pointed out large aggregated structures. These aggregated structures were supposed to result in an entrapment of carvacrol molecules that could be responsible for a higher carvacrol retention exhibited by both WG film-forming solutions and cast films. Further indications of this assumption were provided by XRD measurements that confirmed the establishment of specific interactions between Mmt, carvacrol and WG. The investigated delivery system based on a WG matrix reinforced by high content of Mmt fillers (≥5%) was clearly efficient to retain and protect an antimicrobial active agent such as carvacrol during the processing stage.