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.
