DEVELOPMENT OF A REAL-TIME INTELLIGENT pH SENSITIVE COLOUR CHANGE FRESHNESS INDICATOR USING ANTHOCYANIN-BIOPOLYMER FILM FOR FOOD APPLICATIONS

Abstract

Food spoilage represents a critical challenge in the global food supply chain, necessitating innovative solutions for real-time freshness monitoring. This study successfully developed a biodegradable intelligent packaging film that provides visual indication of food freshness through pH-dependent colour transitions, addressing the limitations of conventional passive packaging systems. Anthocyanins extracted from purple cabbage were selected as the natural colourimetric indicator due to their pH sensitivity, non-toxicity, biodegradability, and sustainability advantages over synthetic indicators. Anthocyanin extraction was optimized using ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) techniques, with UAE yielding significantly higher anthocyanin content (21.8 mg/L) compared to MAE (15.3 mg/L). The extracted anthocyanins exhibited excellent pH responsiveness across pH 1–14, displaying distinct colour transitions from red in acidic conditions to purple at neutral pH and yellow-green under alkaline conditions, confirming their suitability as natural colourimetric sensors. Biodegradable films were fabricated using carboxymethyl cellulose (CMC) and chitosan as polymer matrices through solvent casting methodology. Comprehensive characterization revealed that CMC-based films demonstrated superior properties: higher thickness (0.36 mm), enhanced flexibility (33 mm elongation), better colour uniformity, and superior pH-responsive behaviour compared to chitosan films. Advanced analytical techniques including UV-Visible spectroscopy, FTIR, XRD, DSC, and SEM confirmed successful anthocyanin incorporation with excellent structural integrity and thermal stability. Storage studies on fresh mackerel fish and paneer over 12 days in refrigerated condition demonstrated that the anthocyanin-incorporated CMC film exhibited progressive colour changes from purple (fresh) to dark red (intermediate) to green (spoiled), accurately correlating with microbiological analysis and Total Volatile Base Nitrogen (TVB-N) values, thereby confirming its effectiveness as an intelligent freshness indicator. This study established that anthocyanin-biopolymer films represent a promising sustainable alternative to synthetic packaging, effectively combining environmental responsibility with functional freshness monitoring capability for highly perishable foods.