Post-consumer polymers (PCR) for color retention of delicatessen meats and elucidation of the light blocking mechanism

Abstract

Increased light blocking properties of extruded films can be realized by sustainable, post-consumer recycled (PCR) polymers. This study elucidates the light blocking mechanism of these films within the ultraviolet-visible region (UV–Vis) via a novel optical measurement and electron microscopy analysis. A spectrometer and integrating sphere were mounted on a translational stage opposite a light source to measure the apparent absorbance as a function of distance. It was determined that a mixed scattering/reflection mechanism is present for virgin/PCR high density polyethylene (HDPE) blends with increased scattering in the ultraviolet and both scattering and reflection in the blue-visible. An electron microscopy study further suggests that the unique optical properties may be due to the well-dispersed nano-domains of aluminum, oxygen, and silica with increasing PCR content in addition to changes in crystalline domains reported previously. This inspired the application of the material as a light fixture filter for preserving light sensitive products. The preservation efficiency of light sensitive specimens under light emitting diode (LED) illumination was evaluated quantitatively (CIE L*a*b* color space) and qualitatively (digital imaging) as a function of time. Using roast beef as a model system, the maximum red color change (a*) of non-filtered roast beef specimens was realized approximately 55% faster than the filtered (Δa* = 7.1) in simulated retail display conditions. The improved color retention under filtered light can be attributed to increased light scattering across the blue wavelength range (440–485 nm) reducing light exposure near the maximum absorption band of myoglobin. Reduction of blue light exposure inhibits metmyoglobin production and meat discoloration. Data presented in this study suggest that PCR polymers can tune light blocking properties, providing a means to increase the color retention of light sensitive foods while simultaneously diverting food and plastic waste from landfills.