Preparation and characterization of a novel polyvinyl alcohol/pectin film containing bromocresol green-alizarin mixed indicator label for monitoring mushroom freshness

From the paper

Abstract

Intelligent indicator labels offer significant potential for real-time shelf-life assessment and quality preservation during perishable food logistics. This study developed a novel bromocresol green-alizarin (BGA) indicator-embedded polyvinyl alcohol (PVA)/pectin (P) composite film for visual freshness monitoring of Lentinula edodes (shiitake mushrooms). The performance of the films was evaluated based on parameters including thickness, puncture resistance, opacity, moisture content, water solubility, and water vapor permeability. The optimal PVA/P mass ratio of 3:1 in films was determined through a fuzzy comprehensive evaluation, which effectively balanced mechanical strength, water sensitivity, and optical barrier properties. Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) confirmed that BGA incorporation strengthened intermolecular interactions within the polymer matrix, resulting in superior thermal and color stability. For freshness evaluation, the BGA-3 (the ratio of BG:A=1:3) indicator label displayed distinct color transitions from green (pH 7.0) to yellow-green (pH ≈5.0) and finally to orange (pH ≈4.0), corresponding precisely to the freshness stages of L. edodes. Notably, the total color difference (ΔE) of the BGA-3 label showed significant correlations with the accumulated CO₂ concentration within the package and key mushroom quality parameters, including sensory evaluation, total aerobic plate counts, weight loss, hardness, and respiration intensity. The colorimetric response was directly triggered by CO₂-induced pH changes. This intelligent film provides a convenient, non-destructive method for real-time mushroom quality monitoring, demonstrating high application potential within the fresh produce supply chain.