Fabrication of smart film based on fish gelatin incorporating phycoerythrin and cellulose nanofibrils to monitor fish freshness

Phycoerythrin (PE) extract from red algae Laver (Pyropia dentata) was used in the fabrication of a smart packaging film. The PE showed pH sensitivity, implying unique color shifts at different pH. The film colors altered from red through purple-brown to colorless with increasing pH. The smart packaging films were prepared by casting method composed of gelatin (GE), sodium alginate (SA), and cellulose nanofibrils (CNF). The films were coded as GE/SA (control), GE/SA/PE, and GE/SA/CNF/PE. The thickness of the films ranged from 0.24 ± 0.02 mm to 0.33 ± 0.01 mm. The mechanical properties tensile strength (TS) (12.24 ± 0.30 MPa to 17.65 ± 0.33 MPa) and elongation at break (EAB) (79.34% ± 1.02% to 93.36% ± 0.69%) significantly increased after addition of CNF. The synthesized films showed water contact angle ranged from 84.55 ± 2.12 to 69.41 ± 1.21, suggesting that films were hydrophobic. The Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis demonstrated strong interaction among PE, CNF, and biopolymers. The film with GE/SA/CNF/PE exhibited higher thermal stability compared with control film. Then, the films were applied for checking real time application for the freshness of salmon fish. The significant color change of the film occurred and the number of bacterial colony and TVB-N were increased from 3.81 Log CFU/g to 6.94 Log CFU/g and from 4.78 mg/100 g to 32.27 mg/100 g after incubation for 48 hours. Therefore, the film with PE and CNF was intended as an excellent candidate for smart packaging film.