Comparison of the pH- and NH3-sensitivity of chitosan/polyvinyl alcohol smart films containing anthocyanins or betacyanins for monitoring fish freshness

In the Persian Gulf and Oman Sea, where silver pomfret ( Pampus argenteus ) is widely consumed, monitoring its freshness is highly important to guarantee its safety, quality, and economic value. Traditional methods of assessing seafood freshness are usually subjective or involve complicated lab analyses that can hardly be viable within a supply chain environment. This comparative study addresses the gap by developing smart halochromic films using chitosan (CS) and polyvinyl alcohol (PVA), incorporated with different contents of Sambucus nigra L. anthocyanins (SNA; 4, 6 and 8%) or red beetroot betacyanin (RBB; 10, 20 and 30%). SEM images and FTIR spectra revealed that both SNA and RBB were uniformly distributed within the biopolymeric matrix, demonstrating significant molecular interactions such as hydrogen and electrostatic connections. However, the films rich in RBB exhibited irregular and rough surfaces with small pores. Both SNA/RBB-rich films displayed effective antioxidant activity and pH/ammonia-sensitivity; in addition, SNA-rich films outperformed the others. Under simulated supply chain conditions, PVA/CS indicators reliably indicated the freshness of fish fillets stored at 4 and 25 °C, correlating with the accumulation of ammonia gases and pH changes in the package's headspace. The SNA-rich indicators had more pronounced visual color changes.