In this study, we present and discuss the technical benefits of using nanoclays as a promising property enhancer in organic polymers for food and beverage packaging. The incorporation of nanoclays can improve the thermal, mechanical, and barrier properties of a host polymer. Both natural hydrophilic and modified organophilic nanoclays provide unique characteristics to the host polymer depending on the selected applications. Besides the advantage of polymer reinforcement, various novel applications of nanoclays in food packaging have been suggested recently, such as control and release for active ingredients, antimicrobial agent, and carrier for the colorimetric indicator system. The existing migration studies discussing the transition from plastic to nanoclay packaging revealed that the diffused level of aluminum and silicon in the nanoclay packaging are within the limitation proposed in Council Directive 90/128/EEC (1990). Therefore, until now, there is no safety restriction in the use of clay nanocomposite films in food packaging applications.

The market and the future trends of smart packaging show a tendency towards a continuous increase. Several reports have revealed about the increase of consumer concern for food quality and safety, which gives rise to the demand of intelligent packaging. Nano-enabled food packaging has attracted considerable interest and driven a variety of potential applications in the intelligent packaging. The presence of nanomaterials as nanodevices or nanosensors has been recognized as a part of the modern intelligent packaging for monitoring the condition of packaged food or the environment surrounding the product. Among of nanosensors, optical indicator has been widely applied in the market due to the convenient and easy to use. The utilization of nanomaterial such as metal nanoparticles or photonic nanocrystals shows superior performance in novel communicative functions than the traditional colorimetric indicator because of their unique optical properties and high surface reactivity. This review focuses exclusively on ongoing scientific research and recent technological breakthroughs related to nanotechnology-derived colorimetric indicators. The challenges of their application are highlighted and discussed to provide adequate information for future development. Open image in new window

In this study, a colorimetric freshness indicator based on cellulose nanocrystal-silver nanoparticles (CNC-AgNPs) was successfully fabricated to offer a convenient approach for monitoring the quality of packaged food. AgNPs were directly synthesized and embedded in CNC via a one-pot hydrothermal green synthesis, and CNC-AgNP composited indicator films were prepared using a simple casting method. The AgNPs obtained were confirmed by UV-Vis diffuse reflectance spectroscopy and X-ray diffraction. The ability of the as-prepared CNC-AgNP film to indicate food quality was assessed in terms of the intensity of its color change when in contact with spoilage gases from chicken breast. The CNC-AgNP films initially exhibited a yellowish to dark wine-red color depending on the amount of AgNPs involved. They gradually turned colorless and subsequently to metallic grey. This transition is attributed to the reaction of AgNPs and hydrogen sulfide (H₂S), which alters the surface plasmon resonance of AgNPs. Consequently, the color change was suitably discernible to the human eye, implying that the CNC-AgNP composite is a highly effective colorimetric freshness indicator. It can potentially serve as an accurate and irreversible food quality indicator in intelligent packaging during distribution or storage of products that emit hydrogen sulfide when deteriorating, such as poultry products or broccoli.