Chitosan-phytic acid-metal ion emulsifier for long-term stable carvacrol emulsion: from characterization, stability to strawberry preservation

Chitosan colloidal particle-stabilized Pickering emulsions have shown potential in sterilization and food preservation, but limited by insufficient antibacterial properties of low-concentration colloidal particles and poor emulsion stability. To address this issue, we aimed to develop a new type of low-concentration, antibacterial emulsifier to replace traditional fungicides and emulsifiers. Through polyelectrolyte complexation and ion cross-linking strategies, chitosan, phytic acid (PA) and metal ions (Ag + , Cu 2+ and Zn 2+ ) self-assembled hand in hand to fabricate antibacterial emulsifiers CPA-Ag, CPA-Cu and CPA-Zn. CPA-Ag and CPA-Cu exhibited excellent antibacterial properties, destroying cell membranes through the adhesion of chitosan and release metal ions to synergistically kill bacteria. In the surgical knife disinfection experiment, the sterilization rate of CPA-Ag (400 μg/mL) reached 99.8%, comparable to that of 3% hydrogen peroxide (100%) and significantly superior to 75% ethanol (89.3%), CPA-Cu (85.5%) and 400 ppm sodium hypochlorite (72.4%). Subsequently, CPA-Cu and CPA-Ag emulsified carvacrol to form multifunctional Pickering emulsions (CCE and CAE series) with stronger antibacterial properties, excellent antioxidant performance and storage stability (1-3 months). Additionally, the application of CPA-Cu, CPA-Ag and emulsions on strawberries could kill and inhibit the growth of microorganisms within 24 hours. In particular, CPA-Cu (400 μg/mL) and emulsions could extend the shelf life from 3 days to 5 days, reducing the rot rate of strawberries and slowing down the change in total phenol content. This research provides a new idea for the development of green, safe and low-concentration new emulsifiers and fruit preservation sprays based on natural components and non-covalent interactions.