Impact of hydrothermal treatment on denaturation and aggregation of water-extractable quinoa (Chenopodium quinoa Willd.) protein

Abstract

The extent of hydrothermally induced denaturation and aggregation of native quinoa protein depends on the process conditions. Proteins in quinoa extracts containing water-extractable albumins and dilute salt-extractable globulins aggregate when heated at pH 5.0 to 7.0. An I-optimal experimental design was used to investigate the impact of heating temperature (45–100 °C), time (1–15 min), pH (5.0–7.0) and protein content (25.0–100.0 mg/ml) on the total and covalent aggregation of aqueous quinoa extracts. These were evaluated by determining protein solubility losses in water and a sodium dodecyl sulfate containing medium, respectively, using size separation chromatography. Both protein solubility loss types were independent of the protein content during the treatment. While heating time only had an impact on the intensity of protein aggregation, temperature and pH also influenced the type of aggregates formed. Non-covalent protein aggregation was important when heating at temperatures not exceeding 70 °C and when the pH was close to the iso-electric point (pH 5.0). Covalent protein aggregation was maximal (ca. 25%) after heating 15 min at 100 °C and pH 7.0. Under these conditions, oligomeric protein structures (ca. 100–500 kDa) had been formed already after 1 min of heating which further had polymerized to larger ones (>500 kDa) after 5 min of heating. Mainly 7S and 11S globulins aggregated (predominantly by disulfide cross-links), while 2S albumins were not involved in covalent protein aggregation. Furthermore, intact 11S globulin monomers were most prone to covalently aggregate. The new insights allow tailoring quinoa protein aggregation by adjusting the hydrothermal treatment conditions.