Polyphenol-based intelligent food packaging has emerged as a promising approach for real-time freshness monitoring, driven by the natural pH-sensitivity and antioxidant properties of plant-derived pigments such as anthocyanins. This review summarizes recent advances in extraction methods, stabilization strategies, and polymer matrices used to incorporate polyphenols into biodegradable films capable of visually detecting food spoilage through distinctive color changes. Studies consistently report strong correlations between chromatic shifts and spoilage indicators such as pH, total volatile basic nitrogen (TVB-N), and microbial activity, while highlighting ongoing challenges related to pigment stability, leaching control, and environmental durability. Overall, the findings indicate that polyphenol-based smart films offer a sustainable and low-cost alternative to conventional sensors, with significant potential for future development in active and intelligent packaging applications.