Curcumin‑sodium alginate-polyvinyl alcohol pH-indicating composite film for shrimp freshness monitoring.

Abstract

Intelligent food packaging, as an innovative direction for enhancing food quality monitoring capabilities, has garnered extensive attention among consumers and in the research community in recent years. This study constructed composite film materials using sodium alginate (SA) and polyvinyl alcohol (PVA) as the matrix, loaded with the natural active ingredient curcumin to evaluate the potential of the composite film as an indicator of shrimp freshness. The results revealed that the composite film had a thickness of less than 0.1 mm and could effectively block ultraviolet-visible light. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) analyses indicated that curcumin was uniformly distributed within the film matrix. This composite film exhibited strong antioxidant activity (ABTS scavenging rate: 82 %; DPPH scavenging rate: 47.9 %) and reliable pH-responsive characteristics, turning purple or reddish-brown when the pH exceeded 10. This property provides a simple and intuitive method for detecting changes in food quality. In terms of monitoring shrimp freshness, the composite film effectively indicated spoilage. The SA-PVA-CUR30 film changed from light yellow to purple on the fourth day, with a significant increase in the ΔE value (from 34.52 to 51.89), demonstrating optimal indicating performance. In conclusion, this pH-sensitive composite film offers new insights for innovation in food packaging and lays a foundation for the precise control of food quality.