ABSTRACT We present transparent anthocyanin‐poly(vinyl alcohol) (PVA) films that enable rapid pH sensing with a real‐time freshness readout. 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 exposure to acidic or alkaline vapors, the membranes undergo rapid, reversible color changes while preserving optical transparency. The 2% 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 increasing acidity (milk) and alkalinity (squid), demonstrating in‐package atmosphere applicability for shelf‐life assessment. These results outline design rules for clear‐film colorimetry—maintaining optical clarity, minimizing haze, and tuning thickness to control response time—and support RedC@PVA as a safe, sustainable, consumer‐friendly platform for on‐package monitoring.
Benvenuto et al. (Wed,) studied this question.