High loading of anthocyanin on chitosan films by acrolein for sensitive monitoring of meat freshness.

As a natural pigment, anthocyanins show different colours in a wide pH range and can be used to prepare pH-responsive smart packaging films. However, free anthocyanins have obvious disadvantages, including easy degradation under light and easy migration into foods. This study used acrolein (ACR), a highly reactive β-unsaturated aldehyde, to cross-link anthocyanin and chitosan (CS). This technique enabled loading of up to 26.18 mg/g of anthocyanin on CS, increasing the stability and preventing migration. Furthermore, acrolein substantially enhanced the mechanical strength of the film while reducing its swelling ability, water-vapour transmission and water contact angle. The film exhibited a broad range of colour shifts across pH levels ranging from 2 to 13. In ammonia simulation experiments, the film demonstrated exceptional sensitivity and quick response to volatile ammonia, exhibiting a 48.5 % colour change within 1 min. Pork freshness test also showed that when the total volatile basic nitrogen content is below 15 mg/100 g (indicating meat deterioration), the film undergoes a substantial colour change (S > 40 %). Concurrently, the cross-linked anthocyanins improved the antioxidant and antibacterial activities of the membrane. Therefore, it can be concluded that the CSAP-2 film can detect pork freshness and has great application prospects in the field of smart meat packaging films.