Effect of film forming solution pH on antibacterial, antioxidant and structural characteristics of edible films from modified quinoa protein

Abstract

The active packaging films were developed from the ultrasound or heat modified quinoa protein (QP) infused with lysozyme, by varying the pH of film forming solution (FFS). It was observed that, due to the increase in the solubility of ultrasonicated or heat-treated QP at higher pH, there was a decrease in the moisture content, light transmittance, solubility, and water vapor permeability of the prepared films. On the other hand, increasing the pH of FFS, an increase in the thickness, tensile strength, elongation at break, color, total phenolic content (TPC), and antioxidant activity (AA) was observed. Morphological analysis revealed that there developed the rough and irregular surfaces in the films when the pH of FFS was lowered. In the antibacterial activity, the film prepared at pH 7.5 had shown the highest inhibitory zones of 27.70 mm, 25.48 mm, and 24.90 mm for Staphylococcus spp , Streptococcus agalactiae and Enterococcus faecalis , respectively, It was noteworthy that the pH of FFS was detrimental in TPC and hence the AA. The FTIR analysis indicated that the higher pH of FFS had induced favorable structural changes, stable intermolecular interactional compatibility, and higher ordered molecular structure in the QP films, The X-ray diffraction analysis showed a decrease in the film intensity and an increase in the crystallinity, whereas the thermal analysis indicated an increase in T g up to 43.88 °C at higher pH. Hence the films developed at higher pH, while portraying an enhanced physicochemical and structural characteristic had also shown the lowered antibacterial and antioxidant characteristics. • An active packaging films has been developed using variable pH of film forming solution (FFS). • Lysozyme infused film at pH 7.5 showed highest solubility and bioactivity. • Higher pH of FFS induced structural integrity as depicted by FTIR analysis. • Film prepared at lower FSS pH were less smooth with irregular surface than higher pH. • Higher pH values were detrimental in antimicrobial and antioxidant potential of films.