Upcycling of non-pomace residue of grape juice in the functionalization of polyelectrolyte complexes for biodegradable freshness indicators development.

Non-pomace residue of grape juice powder (NPG) was employed for the first time as source of anthocyanins and fibers, as the indicator compounds and reinforcing material of the polymeric matrix, respectively, to produce freshness indicators by polyelectrolyte complexation. NPG addition affected the stability and the rheological behavior of the alginate-gelatin (AG) and alginate-chitosan (ACH) complexes, which presented predominantly viscous and viscoelastic characteristics, respectively, evidenced by their creep-recovery behavior. The complexes dispersions were dried by the casting method. NPG content affected the water-related properties of the indicators, decreasing their moisture content and increasing their solubility and water vapor permeability, whose values ranged from 26.4 to 40.4% and 0.33–0.79 g mm h−1 kPa−1 m−2, respectively. The morphology and the mechanical and optical properties were also affected, with more heterogeneous and rigid films' formation with lower light transmission. Lowest mass losses up until 100 °C were found for the ACH complex indicators, which showed the highest storage and loss modules in dynamic mechanical analysis. A new method, by area loss assessment through digital image analysis, was proposed to evaluate the films' biodegradability. NPG addition decreased their biodegradability, whose area losses ranged from 90.02 to 27.76% after 30 days under indoor soil conditions. Colorimetric efficiency tests of the indicators in acid lactic and ammonia as model systems for the deterioration of dairy and meat products, respectively, demonstrated that lower NPG contents were more efficient for color differentiation by the viewer, showing potential for application in food packaging. [Display omitted] • Food freshness indicator films were developed by polyelectrolyte complexation. • Non-pomace residue of grape juice was applied for the first time in indicator films. • Grape residue addition improved the mechanical and optical properties of the films. • Area loss evaluation was efficient in the films' biodegradation degree assessment. • Lower residue content was better for color differentiation in buffer solutions tests. [ABSTRACT FROM AUTHOR]