Chitosan-gelatin composite film with Rhus chinensis fruit extracts-loaded silver nanoparticles for food preservation

Microbial contamination and the oxidation process contribute significantly to food spoilage. The use of synthetic preservatives in packaging raises concerns due to their toxicity. In contrast, phytochemicals derived from medicinal plants extracts are less toxic and have fewer side effects than their synthetic counterparts. Therefore, this study aims to fabricate bioactive composite films using chitosan/gelatin (CG) incorporated with plant extracts and silver nanoparticles (AgNPs) for enhanced biological activities and promote eco-efficient packaging. The study evaluates the effectiveness of bioactive compounds extracted from two types of medicinal plants, Rhus chiensis Mill fruit (RCM) and Acacia concinna (Willd.) DC pods (AC), using aqueous, 80% ethanol, and 80% methanol. From this study, RCM 80% ethanol extract exhibited optimal minimum bactericidal concentration (MBC) values for E.coli (1.563 mg/ml) and S.aureus (0.391 mg/ml). The antioxidant activities of RCM 80% ethanol revealed a total phenol content of 461.36 ± 13.26 mg GAE/g, IC50 values of 26.21 ± 0.09 μg/ml for ABTS radical scavenging, and 16.08 ± 0.06 μg/ml for DPPH radical scavenging. Gas chromatography-mass spectrometry (GCMS) identified the phytochemical components as malic acid, pyrogallol, 2, 5-Furandione, 3-methyl, palmitic acid, and linoleic acid. In the second stage, the optimal conditions for RCM 80% ethanol extract mediated synthesis of RCM-AgNPs was achieved at pH 7 and a temperature of 80 °C. UV-Vis spectroscopy confirmed RCM-AgNPs formation with a plasmon band around 430 nm. Dynamic light scattering (DLS) demonstrated the stability of the AgNPs with a zeta potential value of −25.56 ± 2.1 mV and Polydispersity Index (PDI) value of 0.5 ± 0.019. Transmission electron microscopy (TEM) analysis revealed spherical nanoparticles sized 7-30 nm. Meanwhile, the MBC values of RCM-AgNPs against E.coli and S.aureus were 39 μg/ml and 156 μg/ml, respectively. Cytotoxicity analysis using the 3T3 cell line indicated that RCM-AgNPs showed no toxic effects at concentrations up to 20 μg/ml. Subsequently, CG composite films were developed with varying ratios of RCM 80% ethanol extract and RCM-AgNPs using ultrasound treatment. Among the CG-RCM films, CG-RCM-4 (0.8%) exhibited the lowest value of water vapour permeability (WVP) of 2.76 ± 0.45×10-12 g m-1 s -1Pa-1 and the highest effectiveness activity against S.aureus. Addition of AgNPs enhanced the thickness without significantly affecting the WVP value and CG-RCM-AgNPs-4 (0.08%) had the highest inhabitation zone of S.aureus and E.coli. Over 14 days, the cumulative silver migration for CG-RCM-AgNPs-4 was 7 ± 0.2 μg/L, which is below the European Food Safety Authority’s (EFSA) limit. Scanning electron microscopy (SEM) revealed a dense and compact structure of CG-RCM-4 and CG-RCM-AgNPs- 4 composite films, even in the presence of particles agglomeration. Considering the physicochemical and biological properties of CG-RCM-4 and CG-RCM-AgNPs-4, these composite films can serve as antioxidant and antimicrobial active films. Furthermore, chicken meat inhibited growth with these bioactive composite films demonstrated that CG-RCM-4 and CG-RCM-AgNPs-4 can improve chicken meat quality by minimising colour variation, slowing pH increment, and maintaining a total plate count below 7 log CFU/g at 4°C for 14 days when compared to the control CG film. Finally, these findings suggest RCM 80% ethanol extract and RCM-AgNPs as promising alternatives to chemical antioxidants and antibacterial agents in sustainable food packaging.

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