Onion skin extract immobilized on Halloysite-layered double hydroxide filler as active pH indicator for food packaging

Abstract

This work reports the use of potato starch films embedded with a cyanidin-rich freeze-dried onion extract as a sensor for food quality. The cyanidin in the extract reacts via color change to pH alterations caused by food spoilage and can therefore replace synthetic pigments to monitor food freshness. The extract was stabilized by anchoring it on the surface of a filler consisting of halloysite nanotubes coated with layered double hydroxide nanocrystals. Filler-extract interactions were studied in-depth using ATR and Raman spectroscopy. The filler, synthesized through a sustainable and solvent-free method, also serves as a carrier of active species that can be released to increase the shelf-life of the product. These compounds were incorporated into a starch-based film and the efficiency of pH detection was assessed in both alkaline and acidic environments by simulating the conditions of food items that produce volatile amines or acidic compounds during degradation.