Preparation and characterization of Polysaccharide based pH sensitive colorimetric new antimicrobial nanocomposite bioindicator films

In this study, the behavior as pH sensitive indicator and antimicrobial properties of nanocomposite films, which are widely used in smart food packages, were investigated. The starch-based film (N) prepared using oak tree acorns was doped with quercetin (KUE) extracted from red onion peel and pH sensitive starch-based quercetin doped film (N-KUE) was obtained. Nano-zinc oxide (ZnO) was added to the obtained film in order to give it antimicrobial properties. Thus, a starch-based quercetin and nano-ZnO added film (N-KUE-ZnO) that is both pH sensitive and antimicrobial was obtained. The properties of these films were compared with the obtained methyl cellulose based (MC) and 50% starch-50% methyl cellulose based (NMC) films. Optimum extraction conditions were determined for the extraction of quercetin from red onion peel. In order to determine the pH sensitivity of the quercetin extract, the color change of the extract in different pH solutions was investigated by Ultraviolet-visible (UV-Vis) spectroscopic method. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), opacity, color, mechanical strength, thermal gravimetric analysis (TGA) and water vapor permeability analyzes were performed on the obtained bioplastic film samples. In the morphological images of the films, it was observed that 5% KUE doping increased the roughness on the N-KUE and MC-KUE film surfaces. It was determined that there was no change in the morphological structure of the NMC-KUE film with 5% KUE doping. It was observed that 3% ZnO doping formed a heterogeneous structure on the surfaces of all films. It was determined that the opacity (O) value of the film increased from 5.22 to 5.52 with the addition of 5% KUE to the N film matrix, and the O value increased from 5.52 to 9.65 when 3% ZnO was added to the film containing quercetin. The lightness (L) value of the N-KUE film decreased by 61.84%, the color difference (∆E) value increased by 800.71% and the whiteness index (WI) value decreased by 71.28% compared to the pure N film. When the mechanical properties of the films are compared; It was determined that the maximum tensile stress and maximum tensile strain values of N and MC films increased in KUE doped films. Compared to N film, the maximum tensile stress and maximum tensile strain values of the N-KUE film increased by 93.34% and 296.56%, respectively. In NMC film, the addition of KUE caused a decrease in the maximum tensile stress value and increased the maximum tensile strain value. Maximum tensile stress and maximum tensile strain values decreased in all nano-ZnO doped films. When the thermal properties of the films are examined; It was determined that the thermal stability of all films increased with the addition of KUE and decreased with the addition of nano-ZnO. The thermal decomposition temperature of the N film, which was 206°C, increased to 226.4°C in the N-KUE film, while it decreased to 188.33°C in the N-KUE-ZnO film. The addition of KUE and nano-ZnO to the film matrix decreased the water vapor transmission rate (WVTR), permeance and water vapor permeability (WVP) values of the films. The food application tests of the films on the poultry meat were carried out in two stages and the color change in the films over time was observed. In the first stage, the films were placed on the inner surface of the lids of the petri dishes so that they would not come into contact with the food, and change in the color of the placed films was observed depending on the pH change of the poultry meat in the petri dishes, and it was determined that the color change rate was slow in the nano-ZnO doped films. In the second stage, the poultry meat samples were vacuum packed with N, N-KUE and N-KUE-ZnO films and they were provided to contact with the food. Color change over time was observed in N-KUE and N-KUE-ZnO films, and it was determined that the color change occurred more slowly in N-KUE-ZnO films. Experimental results revealed that low-cost and nature-friendly N-KUE and N-KUE-ZnO bioplastic films are pH sensitive and have a great potential to be used in packaging of poultry meat as smart food packaging.