Smart packaging containing red poppy anthocyanins for fish freshness monitoring

New eco-friendly packaging materials are essential for improving food quality, safety, nutritional value, shelf-life, and sustainability. Whey protein isolate (WPI) and chitin nanofiber (CNF) were applied as the matrix models to construct freshness indicators. The natural anthocyanin was obtained from red poppy (RPAs, 3%) and acted as the color-sensing agent in the indicator. Utilizing SEM, FTIR, and colorimetry teste, knowledge about the chemical, structural, and optical characteristics of these indicators was gained. The anthocyanin was uniformly dispersed in the biopolymer matrix to produce an indicator with smooth surfaces. The incorporation of RPAs into the indicator increased the flexibility (from 23.21 to 24.63%), and strength (from 28.30 to 32.60 MPa), and decreased the water vapor permeability (from 3.65 to 3.25 × 10^− 11 g.m/m².s.Pa), water solubility (from 73.03 to 61.24%), and swelling index (from 94 to 86%). The WPI/CNF/RPAs indicator had the highest sensitivity for acid, base, and ammonia. Meanwhile, WPI/CNF/RPAs indicator showed obvious color changes from brownish-yellow to gray at 4 °C to reflect the spoilage of fish. Simulated tests indicate pH-sensitive intelligent indicators can be used to determine the freshness of fish in real-time and visually before the point of consumption.