Whey protein isolate and kraft lignin multifunctional films for potential food packaging application: UV block and antioxidant potential

Abstract

Kraft lignin (KL) is a promising additive for obtaining multifunctional biodegradable packaging. However, the hydrophobic properties of lignin hinder its dispersion in hydrophilic matrices. The prior alkaline solubilization of lignin before adding it to the filmogenic dispersion could be an alternative to overcome this limitation. In this sense, this study aimed to produce whey protein isolate (WPI) multifunctional films incorporated with different concentrations of KL, ranging from 0% to 8%, previously solubilized in alkaline solution, and characterize them in terms of morphological, molecular, mechanical, optical, hydrophobicity, thermal, sealability, antioxidant, and UV-blocking properties. The prior solubilization of KL allowed the obtainment of homogeneous films of a dark color with greater resistance to fracture, higher hydrophobicity, higher glass transition temperature than the control film, and a slightly greater thermal stability: the initial and maximum degradation temperature of 166.1 °C and 305.3 °C, respectively. Lignin presence in the matrix also gave the films functionalities compared to the control: the films added with 2% of KL blocked 95% of UVA and 100% UVB radiation without impairing the passage of visible light, and the films with 8% of KL showed 34.69% of antioxidant activity in DPPH analysis. However, the films were not heat sealable, which was an undesirable outcome. Nevertheless, lignin solubilization in alkali proved to be an efficient methodology for producing multifunctional WPI films, with potential application on foods susceptible to oxidation.