pH-Responsive Color Indicator of Saffron (Crocus sativus L.) Anthocyanin-Activated Salep Mucilage Edible Film for Real-Time Monitoring of Fish Fillet Freshness

Abstract

Researchers have been focusing increasingly on preparing innovative packaging films made from renewable and biodegradable materials in recent years. This research set out to fabricate and analyze pH-sensitive edible films based on salep mucilage combined with anthocyanin from saffron (Crocus sativus L.) (SAAs). A casting technique was developed with varying concentrations of SAAs (0, 2.5, 5, 7.5, and 10%v/v) pH-sensitive edible films. The surface morphology, physicochemical, barrier, and mechanical properties, as well as the pH sensitivity of films, were investigated. The results showed SAAs increased thickness, water solubility, moisture content, and oxygen permeability (O2P) up to 199.03 µm, 63.71%, 14.13%, and 47.73 (cm3 µm m−2 day−1 kPa−1), respectively, of the pH-sensitive salep mucilage edible indicator films. As expected, the SAAs concentration from 0% to 10%v/v decreased tensile strength, transparency, and contact angle to 11.94 MPa, 14.27%, and 54.02°, respectively. Although achieving the highest elongation at the break (108%) and the lowest water vapor permeability (WVP) (1.39 g s−1 m−1 Pa−1 × 10−11), the pH-sensitive edible indicator film containing 5 %v/v of SAAs showed the best results. An investigation of pH sensitivity revealed that the solution’s pH variation altered the SAAs color. When the pH was raised from 3 to 11, the SAAs’ color shifted from pink to brown. The SAAs-halochromic salep mucilage edible indicator film was employed as a label in an experiment to track the degradation of fish fillets stored at 4 °C, revealing that the halochromic indicator changed color from yellow to brown as the fish was stored. Our findings show that SAAs-loaded salep mucilage indicator films help monitor real-time food deterioration.