Development of konjac glucomannan-based active-intelligent emulsion films loaded with different curcumin-metal chelates: Stability, antioxidant, fresh-keeping and freshness detection properties

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The aim of this study was to develop konjac glucomannan (KGM)-based active-intelligent emulsion films loaded with different curcumin-metal chelates, where six types of films were prepared and their corresponding properties were investigated. The FTIR and XRD results showed that curcumin chelated with metal ions successfully. Moreover, curcumin-Ca chelate had the best thermal stability and antioxidant activity with the DPPH and ABTS radical-scavenging activity values of 38.28 % and 22.79 %, respectively. Furthermore, the results of microstructure and contact angle showed that chelation with metal ions improved the interfacial interactions between curcumin-metal chelates and film matrix. Interestingly, KGM-based active-intelligent emulsion films loaded with curcumin-Ca chelate (Type IV film) displayed the best thermal stability with the highest temperature of maximum weight loss at 380 °C, the best mechanical property, the highest total phenol content (17.31 mg gallic acid/g film), as well as the best antioxidant activity with DPPH and ABTS radical-scavenging activity values of 69.24 % and 58.66 %, respectively, and the best antibacterial activity. Consequently, Type IV film was used for the fresh-keeping and freshness detection of pork. The results showed that the pork packaged with Type IV film displayed excellent fresh-keeping properties, including reducing the increase rate of volatile basic nitrogen (TVB-N) and pH values and the decrease rate of hardness and elasticity of pork during storage time. Meanwhile, the color of Type IV film gradually changed from yellow to red. Therefore, this study suggested that KGM-based active-intelligent emulsion films have great potential application in the fresh-keeping and freshness detection of fresh meat.