A Review of Anthocyanin‐Based pH‐Sensitive Composite Films for Food Freshness Monitoring

ABSTRACT With the increasing global demand for food safety and quality, pH‐responsive intelligent composite films have become a pivotal innovation in the packaging sector. Anthocyanins, as natural plant pigments, possess excellent biocompatibility and environmental friendliness and exhibit significant colour changes under different pH conditions: appearing red at pH < 3.0, purple at pH 4.0–6.0 and blue‐green at pH > 7.0. This colour difference (ΔE > 3.0) enables anthocyanins to visually reflect changes in the acid–base environment of foods, making them widely applicable in pH‐sensitive films. By combining anthocyanins with polysaccharides, proteins or lipid‐based materials, pH‐responsive intelligent films can be prepared for real‐time monitoring of the freshness of perishable foods such as meat, seafood, dairy products, fruits and vegetables. When spoilage induces pH changes in food, the resulting colour difference in the film (typically ΔE > 5.0) becomes detectable by the naked eye. This article systematically reviews recent advances in anthocyanin‐based pH‐sensitive films, covering their botanical sources, physicochemical properties, extraction methods and applications in food quality detection. The preparation processes of relevant films are further analysed, and their effectiveness in freshness monitoring is evaluated. Finally, current technological limitations are summarized, and future development directions are discussed.