Development of Intelligent Composite Materials from Polyvinyl Alcohol (PVA) and Clitoria ternatea L. Anthocyanin Extract for Shrimp Freshness Monitoring

The development of bioplastic films represents an alternative to conventional plastics and an opportunity for applications in intelligent packaging. The present study aimed to develop a smart material based on poly (vinyl alcohol) (PVA) incorporated with <i>Clitoria ternatea</i> L. extract, capable of monitoring shrimp freshness through colour changes associated with pH variations. The films were prepared using the casting method and characterised in terms of their physical, mechanical, structural, and functional properties. The incorporation of the anthocyanin extract (EAC) significantly intensified the colouration of the films, decreasing lightness (L*) from 88.7 to 37.1 and modifying the chromatic parameters (b from -0.16 to -22.34). Thickness increased from 109.5 μm to 184 μm as the extract concentration was raised, while water vapour permeability ranged from 0.77 to 1.79 g·m/m²·s·Pa, evidencing modifications in the structure of the polymeric matrix. From a mechanical standpoint, tensile strength decreased from 26.0 MPa to 15.2 MPa, and the elastic modulus was reduced by approximately 75.0 MPa, whereas the percentage elongation at break increased from 75.2% to 92.4%, confirming the plasticising effect of the extract. Functionally, the films exhibited a visible transition from blue to green during the refrigerated storage of shrimp, corresponding to increases in pH from 6.6 to 9.2 and total volatile basic nitrogen (TVB-N) values from 3.92 to 67.7 mg N/100 g. The formation of TVB-N followed first-order kinetics (R² = 0.997), confirming the sensitivity of the system as a freshness indicator. These results demonstrate the potential of PVA-anthocyanin films as intelligent colorimetric sensors for monitoring the freshness of protein-rich foods.