Wheat gluten, a bio-polymer layer to monitor relative humidity in food packaging: Electric and dielectric characterization

Thin wheat gluten protein film, largely investigated as eco-friendly material for food packaging, is investigated as a relative humidity monitoring polymer deposited on designed and manufactured interdigital capacitor (IDC) systems, on the frequency range from 30 MHz to 1000 MHz. The ability of wheat gluten to interact with water molecules was characterized and assessed in terms of electrical and dielectric properties with the IDC technique. When relative humidity increases from 20% to 95% RH at 25 °C, the dielectric permittivity and loss change from 5.01 ± 0.04 to 9.79 ± 0.06 and from 0.39 ± 0.01 to 1.48 ± 0.02 respectively. The dielectric permittivity and loss are very sensitive to relative humidity and increase exponentially due to the comparable exponential increase of wheat gluten water content versus relative humidity. The accessibility of water molecules and the plasticization of wheat gluten results in an increase in the water absorbed by the protein from 3.6% (at 20% relative humidity) reaching up to 33.6% (at 95% relative humidity) of the dry weight. The dependence of both dielectric permittivity and dielectric loss of wheat gluten on relative humidity offered the possibility to use the protein for monitoring relative humidity in packed food products. For this purpose, wheat gluten is foreseen to be coupled with Ultra High Frequency (UHF) Radio Frequency Identification (RFID) systems, giving a cost-effective, low-energy consuming and reliable solution for traceability and monitoring of food packed products.