Multi-color composite films constructed by natural colorants and carbon dots: manipulation of color, property characterization, and application in food anti-counterfeiting packaging

Abstract

Food packaging plays a vital role by protecting food from environmental hazards, prolonging shelf life, and signaling freshness. Our manuscript introduces a multi-colored composite film, showcasing a spectrum of colors sourced from natural colorants. Additionally, these colorants impart gas barrier, antioxidant and antibacterial benefits to the film. The film's anti-counterfeiting feature is enabled by the fluorescence characteristics of white carbon dots (WCDs), which are increasingly utilized in food packaging. The multi-color composite film is cross-linked by polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC), exhibiting a tensile strength of 8.81 MPa and elongation at a break of 91.72 %. A series of stable natural colorants, including gardenia yellow, gardenia blue, and amaranth, are incorporated into the PVA-CMC-based packaging films. By employing the mixing principle of colorant colors, a diverse range of packaging films characterized by vibrant colors (Lab value) and opacity (O), different “Transmittance%-λ” (T%-λ) spectra have been gained. Films produced in shades of red, orange, yellow, green, blue, and purple retain their color stability when exposed to acetic acid, ammonia, and ethanol, fulfilling the stability standards set for food packaging materials. Conversely, the color difference (ΔE) of composite films made with anthocyanins exhibits “red→ purple→ green→ brown yellow” colors changes when subjected to buffer solution form pH 1.0 to 14.0, highlighting the characteristics of responsive films. The multi-color composite films constructed by natural colorants have demonstrated superiority in preserving cherry tomatoes. In contrast, the anthocyanin composite food packaging film indicated color changes related to the freshness of beef during preservation. By improving the control of dosage and refining the coating methods for the WCDs solution, researchers have successfully developed a composite anti-counterfeiting film utilizing WCDs. The WCDs enable the embedding of fluorescent encrypted information that can be revealed under UV light, thereby ensuring food safety. • Formulated multi-color composite films incorporating natural colorants and CDs. • Incorporated natural colorants into the film and performed color analysis. • Studied color changes in anthocyanin films across different pH to detect fresh beef. • The CDs enhance the anti-counterfeiting features of the composite films.

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