Development and evaluation of sumac (Rhus coriaria) incorporated guar gum films as colorimetric pH indicator with antioxidant and antimicrobial potential

Sumac (Rhus coriaria) is a natural source of phenolic compounds especially anthocyanins and tannins which makes it a potential active agent and colorimetric indicator. This work aimed to prepare simultaneously antioxidant, antimicrobial, and pH-responsive guar gum (GR) films by incorporating sumac. Moisture content, water vapor permeability (WVP), opacity, color, thermal, antioxidant, antimicrobial properties, and pH-response of the films were analyzed. Sumac addition resulted in WVP and higher opacity values when compared to GR films. Guar gum sumac (GR_S) films showed strong antioxidant activity (up to 99%). Sumac incorporation bestowed the guar gum films with antimicrobial function against Staphylococcus aureus. When the films were immersed in buffer solutions at different pH values, the color of the films changed from pink to brown which proved the GR_S films' colorimetric sensitivity to pH change. Thus, this study demonstrated that GR_S films have the potential to be promising active and pH-sensitive food packaging materials.