Transparent Anthocyanin–PVA Indicator Films for Real‐Time pH Sensing and Food Freshness Monitoring

We present transparent anthocyanin-poly(vinyl alcohol) (PVA) films that enable rapid pH sensing with a real-time freshnessreadout. The extract was quantified for phenolic content, antioxidant activity, and photostability, then embedded at 1% and 2%(w/w) in PVA to yield free-standing, flexible membranes. Profilometry and SEM confirm uniform, defect-free films. Upon exposureto acidic or alkaline vapors, the membranes undergo rapid, reversible color changes while preserving optical transparency. The2% RedC@PVA film responds in 21.10±0.11 s and retains about 91% of visible-band absorbance after 3 months of outdoor sunlight,outperforming lower loading and drop-cast controls. Studies on fresh milk and thawed squid correlate color shift with increasingacidity (milk) and alkalinity (squid), demonstrating in-package atmosphere applicability for shelf-life assessment. These resultsoutline design rules for clear-film colorimetry—maintaining optical clarity, minimizing haze, and tuning thickness to controlresponse time—and support RedC@PVA as a safe, sustainable, consumer-friendly platform for on-package monitoring.