FOAM FRACTIONATION OF PEA (PISUM SATIVUM L.) PROTEINS & INTERACTIONS WITH RED BEET EXTRACT (BETA VULGARIS L.) TO IMPROVE STABILITY & FUNCTIONAL PROPERTIES

Abstract

Peas (Pisum sativum) are a valuable source of vegan protein in Canada. They are preferred for their low production cost, good digestibility, low allergenicity, and gluten-free character. Common extraction methods can limit the functional performance of pea proteins by reducing their structural flexibility during processing, hence limiting their application in food systems. Red beets (Beta vulgaris L.) are also a valuable source of ingredients for the food industry. An example is betanin which is the main natural colorant in red beet extract (RBE), however it is susceptible to degradation under environmental and processing conditions. Herein, this thesis investigates the potential of foam fractionation to enhance the functional properties of pea proteins, and their subsequent interaction with compounds in RBE to enhance the stability, functional, antioxidant and antimicrobial properties of the complexes. Two-stage foam fractionation was used to recover and concentrate proteins from dilute pea protein flour (PPF) solution. With the first stage aimed for recovering the proteins, recovery percentage (R) of 86.66 ± 3.55 was attained, at the initial protein concentration (C) of 1.05 g/L, pH 4.5, air flow rate (V) of 800 mL, and liquid loading volume (L) of 4000 mL. The second stage was focused on the concentration of the PPF proteins, which resulted in the enrichment (E) of 5.83 ± 0.14 at pH 4.5, V of 300 mL and L of 1500 mL. Of all separated fractions, the second stage foamate showed most significant improvement of functional properties, such as solubility, foaming, emulsification, oil and water holding capacities. Interactions between pea protein isolate (PPI) and betanin in RBE on the stability of betanin were studied. Among the several pH levels investigated (pH 3-7), pH 3 exhibited an increased betanin retention of 55.53% at room temperature (21 ± 2 ℃) storage in PPI-RBE complex compared to the RBE control with a betanin retention rate of 4.31%. Under elevated thermal conditions (80 ℃), betanin retention rate in the PPI-RBE complex (12.5%) at pH 3 was higher than that of the RBE control, which exhibited a retention rate of 6.5%. The results showed that PPI-RBE interaction changed the PPI conformation, transitioning its structure from α-helical to β-sheets. Compared to the RBE control, the PPI-RBE complexes exhibited enhanced antioxidant activity and enhanced betanin retention following one-year of refrigeration storage. Foam-fractionated (foamed) PPF proteins and non-foamed PPF proteins were mixed with RBE to facilitate their complex formation. Molecular assessment analysis showed that non-foamed PPF proteins possess an α-helical structure, which is more pronounced in foam-fractionated PPF proteins. The interaction of non-foamed and foam-fractionated PPF protein with betanin in RBE resulted in transitions from α-helical to β-sheet structures. The foam-fractionated PPF-RBE complexes had a greater prevalence of β-sheets. The improvement of functional properties, stability, and antioxidant properties was likely due to the increase in β-sheets and legumin αβ disintegration in the foam-fractionated proteins. In general, the antimicrobial activity of these foam-fractionated PPF complexes was higher than RBE control with most inhibiting and bactericidal activity against gram-negative bacteria, specifically Escherichia coli. Thus, these complexes have the potential to be used as enhanced functional ingredients in food systems.