Natural pigment-based smart packaging films for real-time food spoilage monitoring: Compositions, color-changing mechanisms, applications, and challenges

Real-time monitoring of food spoilage remains a significant challenge, driving the urgent demand for smart packaging solutions. Natural pigments like anthocyanins, curcumin, alizarin, shikonin, and betalains demonstrate robust bioactivity and excellent pH sensitivity. Notably, these compounds serve a dual function: inhibiting bacterial growth and dynamically indicating food freshness. Therefore, their integration as freshness indicators in smart packaging films has garnered substantial research interest. This review consolidates current studies to analyze the structural composition, color-changing mechanisms (particularly the formation processes of volatile substances), and the application prospects of natural pigment pH-sensitive films. More importantly, it critically discusses limitations and challenges in existing research, including the barriers hindering their transition from laboratory-scale development to industrial production, while proposing actionable strategies to overcome these obstacles. By synthesizing these insights, this review aims to advance the development of natural pigment-based smart packaging films and address existing challenges and research limitations.