Development of Bioactive Quinoa Protein Hydrolysate-based Emulsion Gels: Evaluation of Their Antioxidant and Rheological Properties

This study aimed to develop oil-in-water emulsion gels based on quinoa protein hydrolysates, alginate, and high-oleic sunflower oil, to assess their antioxidant activity, and to evaluate their viscoelastic properties. Quinoa protein concentrate (QPC) was hydrolyzed using alcalase. The resulting quinoa protein hydrolysates (QPH) (DH: 30 ± 4%) were evaluated for their iron-chelating activity and reducing power. The antioxidant capacity of emulsion gels based on QPC or QPH was determined using the ABTS and DPPH methods, and rheological analysis was also performed. The QPH exhibited higher ability to chelate ferrous ions and greater reducing power than QPC. The ABTS and DPPH free radical scavenging activity of the QPH-based emulsion gels was higher than that obtained from QPC-based emulsion gels. Furthermore, QPH was more effective in reducing lipid oxidation. After 30 days of storage, QPH-based emulsion gels showed lower levels of malondialdehyde compared to those obtained from QPC-based emulsion gels. The rheological behavior of the emulsion gels revealed that the storage modulus (Gʹ) was greater than the loss modulus (Gʺ) throughout the entire frequency range, thus deformation in the linear region was mainly elastic. The strain recovery occurred because of the good viscoelastic properties of the samples. Although the strengthening of QPH-based emulsion gels was less than that of the QPC-based gels, the gel structure remained stable through the entire temperature range. Overall, this evidence strongly suggests that quinoa protein hydrolysates can be effectively employed in the development of soft-solid food acting as natural antioxidant sources and preventing lipid oxidation.