Effects of microwave heating, steaming, boiling and baking on the structure and functional properties of quinoa ( Chenopodium quinoa Willd.) protein isolates

Summary The effects of microwave heating (MW), steaming (SM), boiling (BL) and baking (BK) on the structure and functional properties of quinoa protein isolates (QPI) were investigated. SDS‐PAGE showed the 20–30 kDa band strength of QPI‐BL was enhanced, which indicated the disulphide bond was broken and protein molecules dissociated. Due to the recombination of subunits, some large molecular weight or insoluble polymer components of QPI‐SM and QPI‐BK did not pass through the gel. Microwave heating and boiling showed negative effects for α‐helix and positive effects for β‐sheet, which implied the molecular structure was transformed from ordered to disordered, the secondary structure became loose. The reduction of free SH (sulfhydryl) and surface hydrophobicity implied that aggregation and cross‐linking of protein molecules for QPI‐SM and QPI‐BK. QPI, QPI‐MW and QPI‐BL exhibited better solubility, which was related to the water holding capacity (WHC) and emulsification. For QPI‐SM and QPI‐BK, functional properties (including solubility, WHC and gel‐forming ability) decreased due to molecular aggregation. Heat treatments significantly affect the structure and functional properties of QPI, the current research showed that microwave heating and boiling might be better heat treatment methods for QPI and would help the development of quinoa protein products.