Composite films containing red onion skin extract as intelligent pH indicators for food packaging

• Smart biodegradable packaging was designed using red onion extract as a pH sensor. • Salicylate-loaded halloysite-layered double hydroxide filler provides active function. • The filler stabilizes the extract enhancing its reliability in reporting pH changes. • Biodegradability is ensured by a potato starch matrix. • Spectroscopic, mechanical and antimicrobial properties of the films were examined. A multifunctional and sustainable packaging was developed based on a potato starch matrix loaded with a cyanidin-rich freeze-dried onion extract (OE) anchored on a halloysite-layered double hydroxide filler. Due to a distinct colour change that varies according to the environmental pH, the extract acts as a visual sensor of food quality and it is stabilised by the filler which can be loaded with antibacterial agents, providing the active component of the film. In this work, the physical, mechanical and antimicrobial properties of films prepared with only extract or containing both extract and filler are examined and compared. In addition, the real-time sensing capability of the films was tested by monitoring their colour changes when applied in meat and milk storage.