Abstract: To explore the effect of different processing methods on quinoa proteins, the structural and functional properties of the proteins extracted from cooked, germinated or extruded quinoa were investigated. Results showed that the solubility at pH 7.0 of the proteins from germinated quinoa increase by 14.12% compared to the quinoa proteins from the control group (powder passing through a 100 mesh screen, prepared by drying at 45 ℃ followed by crushing), while a significant reduction in protein solubility was found for the other treatments at all pHs. The three treatments caused a 7.09%–21.28% reduction in the emulsifying capacity of quinoa proteins, but a 1.08–2.03-fold increase the emulsion stability relative to the untreated group. Foaming ability (69.58%) and foam stability (67.86%) of the proteins from germinated quinoa were the highest, while heat treatments (cooking and extrusion) generally significantly reduced foaming ability and foam stability of quinoa proteins (P < 0.05). Differential scanning calorimetric (DSC) analysis showed that the denaturation temperature of quinoa proteins was slightly increased by the three treatments. Free sulfhydryl group content was not changed significantly by germination (P > 0.05), but reduced by cooking due to oxidation and increased to 33.20 μmol/L by extrusion. Spectral analysis revealed that all treatments caused protein denaturation; the proportion of random coil was reduced by 1.96% by germination, while the proportion of β-sheet was increased from 58.17% to 89.42% and 100.00% by cooking and extrusion, respectively. Quinoa proteins with molecular masses of 48–63 and < 15 kDa were identified by sodium dodecyl sulfonate polyacrylamide gel electrophoresis (SDS-PAGE), and it was deduced that quinoa proteins as well as their aggregates and small subunits may interact by disulfide bonds. Germination increased the number of subunits, while heat treatment led to the formation of aggregates. In conclusion, the three processing methods show different effects on the structure and consequently functional properties of quinoa proteins.

Key words: quinoa; protein; processing methods; structure; functional properties