**1. Introduction**

Pseudocereal grains are considered as good sources of protein with a balanced amino acid profile. Proteins from pseudocereal grains have recently gained increasing popularity due to their nutritional, functional, and biological properties. Proteins from quinoa, amaranth, and chia are among the most extensively studied pseudocereal proteins in terms of characterization of physicochemical, functional, and biological properties. The functionality of proteins from other less known pseudocereals, such as kiwicha and cañihua, still remains to be explored. Although proteins from pseudocereal grains are indicated to show good functionality, some processes may be required to modify the structure and improve the functionality of pseudocereal proteins. Structural and functional properties of various pseudocereal proteins are recently reviewed [1–3]. This chapter presents an overview of the structural and functional properties of pseudocereal proteins, the effects of methods used for protein extraction and fractionation on protein functionality, and several methods applied for modification of structure and optimizing the functionality of pseudocereal proteins.

## **2. Quinoa protein**

Quinoa (*Chenopodium quinoa* Willd) contains ∼13–16% protein with major fractions of albumins (29–50%) and globulins (7–37%) classified based on the extraction methodology [2, 4–6]. Structural and functional properties of quinoa protein were recently reviewed by Dakhili et al. [2]. Quinoa seed protein is reported to contain a balanced essential amino acid profile, with relatively higher amounts of lysine and methionine compared to cereals and legumes [5]. Physicochemical and functional properties of quinoa protein were investigated in recent studies to elucidate its potential for utilization as an ingredient in various food applications. It has been indicated that the method used for protein extraction has a significant effect on the composition and functionality of quinoa protein [2]. Moreover, inert physical barriers in the seed are indicated to hinder a significant portion of protein in quinoa from being extracted [6]. Van de Vondel et al. [6] recently investigated heat-induced protein denaturation and aggregation during protein extraction from quinoa using denaturing agent sodium dodecyl sulfate (SDS) and reducing agent dithiothreitol (DTT) with an aim to maximize extraction yield. The maximum protein extraction yield obtained using SDS, DTT, and/or various pretreatments was reported to be 82%, which indicated that physical barriers hinder the extraction of ∼20–25% of the protein in quinoa [6].

Various physical, chemical, and biological modification methods are applied to pseudocereal proteins to improve functionality. Enzymatic hydrolysis is a commonly applied strategy to improve not only the functional but also the bioactive properties of plant-based proteins. Guo et al. [7] recently reviewed the biological activities of quinoa protein hydrolysate and peptides. In a recent study, Daliri et al. [8] applied enzymatic hydrolysis to quinoa protein concentrate with pancreatin and investigated the changes in emulsifying, foaming, and antioxidant properties. Quinoa protein concentrate was obtained from defatted quinoa flour with alkaline extraction followed by the isoelectric precipitation method. Hydrolysis with pancreatin at 40°C for 180 min was reported to result in the highest degree of hydrolysis (∼19%). Fouriertransform infrared spectroscopy analysis revealed that different functional groups, such as free regions of hydroxylic amino acids, aromatic amino acids, and free amino groups, originated in the hydrolysate due to the hydrolyzing action of pancreatin. The obtained hydrolysate was reported to show better antioxidant properties in terms of 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity. Solubility, emulsifying and foaming activities of the hydrolysate were found to be higher than that of the native protein. On the other hand, the native protein showed better emulsion and foam stabilizing properties [8].

Maillard reaction is used as a tool to modify structural properties and improve the functionality and biological activity of proteins. In a recent study, Teng et al. [9] investigated the effect of glycosylation with xylose on the structural and functional properties of quinoa protein. Quinoa protein isolate (96% protein) was obtained from defatted quinoa flour with alkaline extraction followed by an isoelectric precipitation method. Glycosylation via Maillard reaction was performed by mixing quinoa protein isolate with mannose or xylose with varying proportions in phosphate buffer and heating at 60°C for 4 h. The optimum ratio of quinoa protein to monosaccharide was determined to be 2:1 based on the degree of grafting and browning index analyses. The electrophoretic profile of samples revealed that glycosylation had significant effects on the depolymerization and remodeling of molecular aggregates of quinoa protein. The specific surface area and absorption capacity of quinoa protein were indicated to increase after glycosylation. Solubility, water and fat absorption capacities, emulsifying activity, and stability of glycosylated quinoa protein were reported to be significantly higher than that of the native protein. Moreover, anti-inflammatory and anti-proliferative activities of quinoa protein were indicated to increase after the glycosylation reaction [9].
