Improvement in the functional properties of quinoa (Chenopodium quinoa) protein isolates after the application of controlled heat-treatment: Effect on structural properties

Abstract

Quinoa protein isolates (QPIs) were subjected to controlled heat-treatment (80−100 °C) at variable time (15−30 min). Results showed that heat-treatment induced structural changes in QPIs. Circular dichroism showed loss of secondary structure of QPIs, particularly α-helix and β-sheet. Total and exposed SH groups were significantly (p ≤ 0.05) lower in heat-treated QPIs. SDS-PAGE profile showed formation of soluble protein aggregates with smaller particle size. Particle size decreased when QPIs were heated at 80 °C for 30 min. Solubility and turbidity of heat-treated QPIs improved significantly. Decline in crystallinity was due to denaturation of protein molecules by heat-treatment. Water binding capacity, oil binding capacity, emulsifying activities and stabilities were found lower in QPIs heat-treated at higher thermal temperatures for longer time. This might be due to decline in total and exposed SH contents, accelerated conversion of SH groups into disulfide bonds and formation of large molecular weight polymers or protein aggregates due to polymerization reactions. Higher foaming capacity (89.99 %) and foaming stability values of 167.80 % (10 min) and 124.15 % (20 min) were found in QPIs heated at 80 °C for 30 min. The results thus suggests that heat-treatment carried out at lower heating temperatures had improved the functional properties of QPIs.