Biodegradation Studies and Material Properties of Quercetin Incorporated Soy Protein Isolate Films

ABSTRACT The study aims to evaluate the effects of different contents of quercetin (1%–3%) on structural and morphological characteristics of soy protein isolate (SPI) based films fabricated by the solution casting method. Prior to the preparation of the modified SPI film, quercetin incorporated SPI suspension was characterised for molecular weight distribution, particle size, and zeta potential. Addition of quercetin affected the charge distribution on the surface of protein and made it a more stable entity, as evident from more negative ζ‐ potential values. The as‐prepared film was structurally and thermally characterised by x‐ray diffraction, Raman spectroscopy, and thermogravimetric analysis. The results revealed the changes in the secondary conformation of the protein structure with a simultaneous decrease in the crystallinity of the conjugated films and an increase in the thermal stability of quercetin incorporated SPI films. Quercetin incorporated SPI film was also subjected to morphological, antioxidant, and biodegradation studies. The antioxidant activity of the modified films in terms of scavenging free radicals like 2,2′‐azino‐bis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) increased significantly due to the native antioxidative ability of quercetin. The initial phase of biodegradation was rapid, followed by a slower rate of degradation phase. FTIR studies were used to structurally characterise biodegraded samples, and the results revealed the formation of carboxyl dimer during fragmentation and disruption of peptide bonds.