Anthocyanins-encapsulated 3D-printable bigels: A colorimetric and leaching-resistant volatile amines sensor for intelligent food packaging

Anthocyanins-based colorimetric volatile amines sensors have recently received great attention for monitoring meat and fish freshness. However, most of the sensors suffered from anthocyanins leaching problems in humid packaging environments, severely limiting their indication ability. The present study developed a hydrogel-in-oleogel bigel to protect anthocyanins from leaching. The internal hydrogel was composed of water, agar and purple sweet potato anthocyanins (PSPA), and the external oleogel was made up of sunflower oil, beeswax and glyceride monooleate (GMO). The agar concentration and water-to-oil-phase volume ratio (W/O) were optimized to be 1.0% and 2:8, respectively. The optimal pH value of hydrogel was determined to be 6.50, taking into consideration of the gas sensitivity and color stability of the bigel. The bigel was extruded onto polyvinylidene fluoride (PVDF) film through a 3D printing method to form the composite film. The results of the study revealed that PVDF-bigel composite film showed good stability in water, indicative of strong anti-leaching properties. Meanwhile, the PVDF-bigel film was sensitive to trimethylamine (TMA) with a limit of detection of 2.52 μM. The PVDF-bigel film was subjected to in-situ and real-time monitor beef and salmon freshness. The film exhibited a red-to-purple color change upon reacting with volatile amines generated from beef and salmon. Henceforth, this study presented a new method to develop anthocyanins-based colorimetric gas sensors for intelligent food packaging.