Quinoa Protein Isolates Research Articles

Modulation of physico-chemical and technofunctional properties of quinoa protein isolate: Effect of precipitation acid

The typically low solubility and gelation capacity of plant proteins can impose challenges in the design of high-quality plant-based foods. The acid used during the precipitation step of plant protein isolate extraction can influence protein functionality. Here, acetic acid and citric acid were used to extract quinoa protein isolate (QPI) from quinoa flour, as these acids are more kosmotropic than the commonly used HCl, promoting the stabilisation of the native protein structure. While proximate analysis showed that total protein was similar for the three isolates, precipitation with kosmotropic acids increased soluble protein, which correlated positively with gel strength. Microstructure analysis revealed that these gels contained a less porous protein network with lipid droplet inclusions. This study shows that the choice of precipitation acid offers an opportunity to tailor the properties of quinoa protein isolate for application, a strategy that is likely applicable to other plant protein isolates.

Dual decoration of quinoa protein isolate by different dietary polyphenols with covalent and noncovalent approaches: Structure characterization, conformational changes and functional properties

Naringenin (Nar) showed diverse biological activities as well as limited stability and bioavailability. In this study, polyphenol-grafted quinoa protein isolate (QPI) nanoparticles were synthesized and utilized for encapsulating Nar to improve its stability and enhance its antioxidant capacity. Initially, the study investigated the effects of different types of polyphenols (dihydrocaffeic acid [DA] and dihydromyricetin [DHM]) and different QPI/polyphenol mass ratios (10:1, 10:2.5, 10:5, 10:7.5, 10:10) on the structural properties and conformational changes of the conjugates. Results from polyphenol binding equivalents, SDS-PAGE analysis, and reactive group changes confirmed the covalent binding between QPI and polyphenols, with DHM showing higher reactivity and binding strength to QPI. Subsequently, Nar was encapsulated in QPI-polyphenol nanoparticles (Nar@conjugates), with Nar@DHMgQ displaying a spherical structure and higher EE (82.33%) and LC (8.98%). Furthermore, Nar@conjugates exhibited superior thermal stability, free radical scavenging ability, and controlled release characteristics. Nar@conjugates effectively maintained cell viability, reduced reactive oxygen species (ROS) levels, and restored intracellular antioxidant enzyme activity under oxidative stress conditions. These findings suggested a promising approach for delivering hydrophobic bioactive compounds like Nar in functional foods and pharmaceuticals.

Co-assembly of quinoa protein isolate and shellac as nano-vehicles for naringenin: Characterization, formation mechanism, release behavior and cellular uptake

Naringenin (Nar) is a natural flavonoid with diverse health-promoting benefits. However, the bioavailability of Nar is significantly restricted due to its poor water-solubility, instability under physiological conditions, and limited absorption profile. In this study, a shellac-quinoa protein isolate (QPI) binary nanocomplex (SQP) was fabricated using the pH-shifting method for effectively delivering Nar. Isothermal titration calorimetry (ITC) and analysis of inner interactive forces revealed that the complexation between QPI and shellac was primarily driven by electrostatic and hydrophobic forces. Subsequently, Nar was successfully encapsulated within the stable and uniform SQP nanocomplex (Nar@SQP), achieving a high encapsulation capacity (94.52 % encapsulation efficiency and 14.68 % loading capacity). Meanwhile, the Nar@SQP nanoparticle exhibited excellent stability against pH, ionic strength, and long-term storage. Moreover, it also demonstrated sustained and slow-release characteristics during simulated gastrointestinal digestion. Compared to free Nar, the safe Nar@SQP nanoparticle effectively facilitated the cellular uptake of encapsulated Nar by Caco-2 cells, suggesting that Nar@SQP has a good potential to improve the bioavailability of Nar. Hence, these findings indicated that the developed Nar@SQP nanoparticle might hold significant promise as a nano-delivery system for hydrophobic bioactive nutrients, like Nar.

Characteristics of Quinoa Protein Isolate Treated by Pulsed Electric Field.

The aim of this study was to investigate the impact of a pulsed electric field (PEF) on the structural and functional properties of quinoa protein isolate (QPI). The findings revealed a significant alteration in the secondary structure of QPI following PEF treatment, converting the random coil into the β-sheet, resulting in an improvement in structure orderliness and an enhancement of thermal stability. The PEF treatment led to a reduction in particle size, induced structural unfolding, and increased the surface hydrophobicity, resulting in a statistically significant enhancement in the solubility, foaming, and emulsifying properties of QPI (p < 0.05). Specifically, PEF treatment at 7.5 kV/cm for 30 pulses was identified as the optimal condition for modifying QPI. This study provides a basis for the precision and range of application of pulsed electric field treatment and offers the possibility of improving the physical and chemical properties of quinoa protein.

PH-shifted quinoa protein isolate-based nanocarriers for naringenin: Structure characterization and stability evaluation

Naringenin (Nar) is an important natural flavonoid compound with multiple health functions, but stability issues and poor solubility greatly limit its bioavailability. To enhance the water-solubility, chemical stability and bioavailability of Nar, quinoa protein isolate (QPI)-Nar and pH-shifted QPI (PQPI)-Nar nanoparticles were constructed in this study. The results of ultraviolet–visible and fluorescence spectra showed there existed the interactions between QPI or PQPI and Nar, with stronger interaction between PQPI and Nar. Thermodynamic analysis indicated the molecular interactions between QPI or PQPI and Nar were mainly driven by hydrogen bonds. Circular dichroism (CD) and surface hydrophobicity results revealed that the binding of Nar changed the secondary structures and reduced surface hydrophobicity of QPI and PQPI. The measured DLS, LC and EE results suggested that PQPI-Nar nanoparticles formed a more stable system with higher encapsulation capacity. Additionally, PQPI-Nar nanoparticles exhibited higher antioxidant activity, superior slow-release property and biocompatibility, as well as better thermal and ultraviolet stability than QPI-Nar nanoparticles. These results indicated that PQPI-Nar nanoparticles could effectively improve the bioavailability of Nar. This study may provide a theoretical basis for the promising application of PQPI-Nar nanoparticle delivery systems in the food industry.

Effect of Starch on the Solubility of Quinoa Protein Isolates during Heat Treatment.

There is increasing interest in developing quinoa products due to their unique nutritional value. Starch and protein are the primary components in quinoa, and the interaction between them affects the quality of quinoa products. This study extracted the starch and protein from quinoa and simulated the thermal processing of quinoa to investigate the effects of starch on the solubility and structure of quinoa protein isolates during heat treatment. The structure of quinoa protein isolates was characterized by fluorescence spectroscopy, Fourier transform infrared spectroscopy, laser particle size analysis, and scanning electron microscopy. The results showed that starch decreased protein solubility, and the maximum solubility was obtained after heating for 5 min. After starch addition during heat treatment, the surface charge distribution of protein changed, the degree of protein aggregation increased, the particle size of proteins increased, the thermal stability increased, and the β-sheet ratio of the proteins increased, suggesting that the protein structure is more ordered, which is the structural foundation of protein solubility decreasing. The research about the interaction between starch and protein and the effects on the solubility of protein could provide a reference for quinoa products processing.

Influence of extraction method on inherent properties and techno‐functional behavior of quinoa protein ingredients

AbstractThis study investigated the structural modification and functional properties of quinoa protein ingredients using dry and wet fractionation techniques. Alkali extraction at pH 9.0 produced a quinoa protein isolate (QPI) with 76.2% wt/wt protein (dry basis) and a concentrate (QPC) with 55.9% protein. However, the protein separation efficiencies (PSE) were 32.1% and 58.5%, respectively. In contrast, dry fractionation produced a quinoa protein rich fraction (QPRF) containing 24.7% wt/wt protein, but higher PSE at 69.9%. Despite varying final protein concentrations, SDS‐PAGE showed similar relative abundance of 11S, 7S, and 2S proteins among the ingredients and quinoa whole meal. Mass spectrometry revealed different levels of oxidative modifications to proteins, with QPI showing more pronounced oxidation. In starch pasting experiments, QPRF exhibited significantly higher viscosity than QPI and QPC, attributed to low starch content and the formation of protein–starch and protein–lipid complexes in QPI and QPC. Solubility over pH 2.0–9.0 followed a U‐shaped trend for all ingredients, with QPC showing lower solubility at pH &gt;7.0. Furthermore, foaming capacity and stability of foams converged at high ingredients concentration (3% wt/vol), while increasing protein refinement gave high foam stability at lower concentration (0.5–1% wt/vol). Similarly, emulsion activity index was favored at high purity (QPI), while emulsion stability was promoted at low protein purity (QPRF). This study demonstrated that dry fractionation enabled the retention of techno‐functional properties of the protein while enhancing quinoa bioresource recovery.

Impact of Ultrasound Emulsification on the Physicochemical Properties of Emulsions Stabilised by Quinoa Protein Isolates at Different pHs

Ultrasonication (20 kHz, 19.9 W/10 mL sample) was used to form O/W emulsions stabilised by quinoa protein isolate (QPI) particles at 3 wt%. Effects of pH (3, 5, 7, 9) and oil volume fractions (20%, 40%, and 60%) on rheological properties and microstructural characteristics of emulsions were investigated. All emulsions show viscoelastic behaviours and form a network structure comprising aggregated oil droplets and QPI particles. Emulsions stabilised by QPI at pH 5 showed largest droplet sizes and lowest gel strength due to extensive aggregation of proteins around the isoelectric point (pI ~ 4.5). The gel strength (G´(1 Hz)) were enhanced when the oil volume fraction increased and reached ~ 1100–1350 Pa at 60% oil volume fraction at different pH. This could be attributed to a tighter packing of oil droplets at 60% oil. Confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) revealed that interdroplets bridging and voids filling of QPI particles between oil droplets are critical in formation of aggregated emulsions network. Emulsions stabilised by QPI at pH 7 and 9 possessed thinner interfacial layers compared to those at pH 3 and 5. Finally, this study shows a potential of using ultrasonication to prepare gel-like emulsions stabilised by QPI, broadening applications of quinoa proteins in making dairy substitutes with semi-solid textural characteristics.

Controlled oxidation and digestion of Pickering emulsions stabilized by quinoa protein and (-)-epigallocatechin-3-gallate (EGCG) hybrid particles

In this study, we prepared Pickering emulsions stabilized by quinoa protein isolate (QPI) and (-)-epigallocatechin-3-gallate (EGCG) non-covalent hybrid particles using ultrasonic emulsification technique and demonstrated lipid oxidation and in vitro digestion process of Pickering emulsions. The interaction forces between QPI and EGCG were characterized using fluorescence spectroscopy, isothermal titration calorimetry, and Fourier transform infrared spectroscopy. Results indicated that the non-covalent QPI/EGCG hybrid particles were formed mainly via hydrophobic interactions, hydrogen bonds, and electrostatic interactions at pH 5. Then, the QPI/EGCG non-covalent hybrid particles were applied to modify the Pickering emulsion with ultrasonic homogenization. The rheological experimental results showed that the energy storage modulus (G′) was higher than the loss modulus (G″), indicating that the emulsion had solid-like properties. As a physical barrier, interfacial layer fabricated by antioxidant QPI/EGCG hybrid particles limited lipid oxidation at 60 °C for 15 days. At 37 °C, the QPI/EGCG hybrid particles stabilized Pickering emulsions with robust antioxidant interfacial structure limited the lipid digestion under simulated gastrointestinal tract (gastric, small intestine phases). Thus, EGCG and quinoa proteins were more resistant to free radical oxidation and gastrointestinal digestion with the assistance of ultrasound. It provides a basis for better development of food and drug delivery systems by fully utilizing the antioxidant properties of plant polyphenols.

Structural Properties of Quinoa Protein Isolate: Impact of Neutral to High Alkaline Extraction pH.

In this work, we extracted proteins from white quinoa cultivated in the northeast of Qinghai-Tibet plateau using the method of alkaline solubilization and acid precipitation, aiming to decipher how extraction pH (7-11) influenced extractability, purity and recovery rate, composition, multi-length scale structure, and gelling properties of quinoa protein isolate (QPI). The results showed that protein extractability increased from 39 to 58% with the increment of pH from 7 to 11 whereas protein purity decreased from 89 to 82%. At pH 7-11, extraction suspensions and QPI showed the similar major bands in SDS-PAGE with more minor ones (e.g., protein fractions at > 55 or 25-37 kDa) in suspensions. Extraction pH had limited effect on the secondary structure of QPI. In contrast, the higher-order structures of QPI were significantly affected, e.g., (1) emission maximum wavelength of intrinsic fluorescence increased with extraction pH; (2) surface hydrophobicity and the absolute value of zeta-potential increased with increasing extraction pH from 7 to 9, and then markedly decreased; (3) the particle size decreased to the lowest value at pH 9 and then increased to the highest value at pH 11; and (4) denaturation temperature of QPI had a large decrease with increasing extraction pH from 7/8 to 9/10. Besides, heat-set QPI gels were formed by loosely-connected protein aggregates, which were strengthened with increasing extraction pH. This study would provide fundamental data for industrial production of quinoa protein with desired quality.

A new approach to enhance quinoa protein nano-aggregates: Combined pH shifting - High pressure homogenization.

The physicochemical characteristics of soluble nano-sized quinoa protein isolates prepared by combined pH shifting and high-pressure homogenization were studied. Commercial quinoa protein isolates were exposed to pH shifting at acidic (pH 2-6) or alkaline (pH 8-12) conditions followed by high-pressure homogenization earlier than neutralizing of pH to 7.0. The pH method under pH 12 followed by high-pressure homogenization was found as the most efficient treatment in the reduction of protein aggregate sizes and transparency, improving soluble protein content and surface hydrophobicity. Quinoa protein isolates treated with pH 12 and high-pressure homogenization increased the solubility from 7.85% to 78.97%, creating quinoa protein isolate nanoaggregates with an average size around 54nm. The quinoa isolate aggregates were used to produce oil-in-water nanoemulsions, which demonstrated the good stability for 14 d at 4°C. This new approach might present an effective technique for the modification of functional features of quinoa protein isolates.

Ultrasonic treatment influences the compactness of quinoa protein microstructure and improves the structural integrity of quinoa protein at the interfaces of high internal phase emulsion

For native quinoa protein with a loose disordered structure and low structural integrity, once the protein is absorbed to the oil–water interface, the stress of interfacial tension and hydrophobic interaction can easily trigger the conformation change and denaturation of quinoa protein, leading to the instability of high internal phase emulsion (HIPE). Ultrasonic treatment can induce the refolding and self-assembling of quinoa protein microstructure, which is expected to frustrate the disruption of protein microstructure. The particle size, tertiary structure, and secondary structure of quinoa protein isolate particle (QPI) were investigated by multi-spectroscopic technology. The study demonstrates that QPIs prepared with ultrasonic treatment of 5 kJ/mL exhibit more robust structural integrity compared with native QPIs. The relatively loose structure (random coil, 28.15 ± 1.06 %∼25.10 ± 0.28 %) transformed to a more ordered and compact form (α-helix, 5.65 ± 0.07 %∼6.80 ± 0.28 %). Through the addition of QPI-based HIPE as an alternative for commercial shortening, the specific volume of white bread was increased (2.74 ± 0.35 ∼ 3.58 ± 0.04 cm3/g).

EFFECT OF HIGH-PRESSURE TREATMENT ON THE STABILITY OF QUINOA PROTEIN-CANOLA OIL NANOEMULSIONS IN TERMS OF DROPLET SIZE AND LIPID OXIDATION

The stability characteristics of soluble nano-sized quinoa protein isolates prepared by different high-pressure homogenization in terms of droplet size and lipid oxidation were studied. Commercial quinoa protein isolates (QPI) were exposed to high-pressure homogenization (HPH) at various pressure (50, 100 and 200 MPa) and pressure cycles (one-cycle and two cycles). The quinoa isolate aggregates were utilized to produce oil-in-water nanoemulsions, which demonstrated the good stabile characteristics for 28 day of storage at 4 oC. While quinoa protein / canola oil nanoemulsions (QPCON) produced with untreated QPI and QPI samples by other HPH treatments were shown a significant increase in terms of droplet size and lipid oxidation in 28 days of storage, QPI samples treated with HPH at 100 MPa for a cycle (100 MPa-1) was found as the most efficient treatment in the stability of protein aggregate sizes and less oxidation level. The sample showed a slight increase from 98 nm to 117 nm for droplet size and from 58 to 102 mmol/kg for lipid oxidation from day 0 to day 28.

Impacts of sonication and high hydrostatic pressure on the structural and physicochemical properties of quinoa protein isolate dispersions at acidic, neutral and alkaline pHs.

Herein, 1wt% quinoa protein isolate (QPI) was exposed to sonication using a 20kHz ultrasonicator equipped with a 6mm horn (14.4W, 10mL, up to 15min) or high hydrostatic pressure (HHP, up to 600MPa, 15min) treatments at pH 5, pH 7, and pH 9. The changes to physicochemical properties were probed by SDS-PAGE, FTIR, free sulfhydryl group (SH), surface hydrophobicity (H0), particle size and solubility. As revealed by SDS-PAGE, substantial amounts of 11S globulin participated in the formations of aggregates via SS bond under HHP, particularly at pH 7 and pH 9. However, protein profiles of QPI were not significantly affected by the sonication. Free SH groups and surface hydrophobicity were increased after the sonication treatment indicating protein unfolding and exposure of the embedded SH and/or hydrophobic groups. An opposite trend was observed in HHP treated samples, implying aggregation and reassociation of structures under HHP. HHP and sonication treatments induced a decrease in ordered secondary structures (random coil and β-turn) accompanied with an increase in disordered secondary structures (α-helix and β-sheet) as probed by FTIR. Finally, the sonication treatment induced a significant improvement in the solubility (up to ∼3 folds at pH 7 and ∼2.6 folds at pH 9) and a reduction in particle sizes (up to ∼3 folds at pH 7 and ∼4.4 folds at pH 9). However, HHP treatment (600MPa) only slightly increased the solubility (∼1.6 folds at pH 7 and ∼1.2 folds at pH 9) and decreased the particle size (∼1.3 folds at pH 7 and ∼1.2 folds at pH 9). This study provides a direct comparison of the impacts of sonication and HHP treatment on QPI, which will enable to choose the appropriate processing methods to achieve tailored properties of QPI.

Atypical phase behaviour of quinoa protein isolate in mixture with maltodextrin

Consumers are increasingly looking for new plant-based alternatives to substitute animal proteins in their diets but for some applications it can be difficult to achieve the desired product microstructure using only plant proteins. One approach to facilitate structuring is to mix these plant-based ingredients with a polysaccharide. Here, the phase behaviour and microstructure of quinoa protein isolate (QPI) in mixture with maltodextrin (MD) of two dextrose equivalents (DE 7 and 2) were investigated. The binodals of both QPI-MD phase diagrams showed an atypical shape, where the concentration of MD in the QPI-rich phase and of QPI in the MD-rich phase increased with overall biopolymer concentration. Molecular weight distribution and microstructure analyses revealed that both maltodextrins fractionated between the phases and were probably entrapped within the volume-spanning protein network in the QPI-rich phase, indicating a depletion flocculation mechanism of phase separation. The pre-heating of QPI and the removal of salt from the systems resulted in similarly atypical phase diagrams. The approach presented contributes to our understanding of the phase behaviour of mixtures between plant proteins and polysaccharides, while the results suggest that the formulation of plant-based products of predictable properties may be more challenging than anticipated.

Effect of Hydrothermal Treatment on the Structure and Functional Properties of Quinoa Protein Isolate.

The aim of this study was to investigate the effects of hydrothermal treatment at different temperatures and times on the structure and functional properties of quinoa protein isolate (QPI). The structure of QPI was investigated by analyzing changes in the intrinsic fluorescence spectrum, ultra-violet (UV) spectrum, and Fourier transform infrared spectrum. The solubility, water/oil-holding capacity, emulsifying activity, and emulsion stability of QPI were studied, as were the particle size and the thermogravimetric properties of QPI. The results showed that the average particle size of QPI gradually increased with the increase in hydrothermal treatment time and temperature, and reached a maximum value of 121 °C for 30 min. The surface morphology also became rough and its thermal stability also increased. The endogenous fluorescence and UV spectral intensity at 280 nm decreased gradually with increasing hydrothermal treatment time and temperature, and reduced to the minimum values at 121 °C for 30 min, respectively. After hydrothermal treatment, the secondary structure of QPI tended to be disordered. The functional properties of QPI after treatment were all superior to those of the control. The results of this study might provide a basis for the processing and utilization of QPI.

Structural, functional, and anti-cancer properties of conjugates of quinoa protein isolate and olive leaf polyphenolic extract: Application in production of bread

Plant-based proteins are of growing interest in the food industry as an alternative to replace animal based ones, however, their functional properties are limited and research is needed in order to improve emulsifying, foaming, solubility properties. The objectives of the present study were to investigate the impacts of complexation between quinoa protein isolate (QPI) and different concentrations of olive leaf polyphenolic extract (OLE) (0.1 %, 0.2 %, 0.3 %, 0.4 %, and 0.5 %) on the structural changes, functional properties, and in-vitro gastric digestion of QPI. The cytotoxicity of the hydrolyzed QPI/OLE complex, in which proteins turn to bioactive peptides, was evaluated using human stomach cancer cell lines. Additionally, bread using optimum QPI/OLE complex was produced and textural, sensorial, and color properties were evaluated. Fluorescence quenching and surface hydrophobicity measurements showed that QPI and OLE were complexed mainly through hydrophobic interactions. SDS-PAGE revealed that the complexation between the protein and phenolic compounds was appropriate and also complexes were highly digestible in stomach-like conditions. Additionally, OLE could enhance solubility, foaming as well as emulsification properties of QPI significantly. The rate of lipid hydroperoxide formation in QPI/OLE samples containing greater amounts of OLE was also reduced significantly. QPI/OLE complexes also exhibited a large potential to scavenge free radicals. In-vitro digestion experiment showed that the addition of OLE to the QPI solution promoted the production of bioactive peptides. According to the anti-cancer results, hydrolyzed QPI/OLE complexes exhibited a greater cell survival reduction in comparison to the OLE alone. Analysis of produced bread also revealed that the hardness of samples decreased with addition of QPI/OLE complexes. This study demonstrated that QPI/OLE complex shows the potential to be developed by food industry as a tailor-made functional food with health benefits. • Hydrophobic interactions were the main interaction mechanism between QPI and OLE. • Addition of OLE improved the solubility of QPI, significantly. • Complexation with OLE promoted the production of bioactive peptides during digestion. • Digested QPI/OLE complex exhibited a greater human stomach cancer cell survival reduction in comparison to the OLE alone. • Bread with QPI/OLE complexes was made without negative changes in bread’s properties.

Impact of high-pressure homogenization on physico-chemical, structural, and rheological properties of quinoa protein isolates

The impact of high pressure homogenisation (HPH) on physico-chemical, microstructural, and rheological properties of quinoa protein isolate (QPI) suspensions were studied. Individual protein bands kept unchanged with HPH treatment up to 50 MPa, as revealed by SDS-PAGE. After HPH treatment at 50 MPa, large protein aggregates were disrupted, and particle size was substantially reduced from ~8.2–0.5 µm. Concurrently, water solubility, emulsifying, and foaming capability were significantly enhanced. QPI molecules after HPH treatment became more flexible with increased surface hydrophobicity and absorbed at the air-water and oil-water interfaces faster, resulting in a more rapid decrease of surface tension and interfacial tension. The secondary structure of QPI proteins was not significantly altered after HPH treatment as probed by FTIR. All QPI suspensions formed weak gels after thermal treatment (85 °C, 30 min), and HPH treated QPI suspensions resulted in a stronger gel strength with a more compact and homogeneous protein network microstructure. These results show that HPH treatment could be an excellent processing technique to modify the physico-chemical, techno-functional, and microstructural properties of QPI suspensions.

Processing Condition and Properties of Protein Isolates from Mung Bean (Vigna radiata) and Quinoa (Chenopodium quinoa Willd)

Mung bean and quinoa are good sources of protein from legumes and pseudo cereals respectively. Both sources have relatively high protein content and acceptable amino acids composition. The potential and application of mung bean and quinoa as protein isolates have been discovered in some studies. Several isolation techniques such as wet fractionation (acid-base extraction), micellization, dry fractionation, aqueous separation or combination of some techniques can be used to isolate protein. This review summarized different methods and processing conditions applied during production of mung bean and quinoa protein isolates. Extracting protein from different sources may require different conditions, which results in different compositions and functional properties. Acid-base extraction is the most common method applied in mung bean and quinoa and results in high protein purity and yields. Micellization is an alternative method used in mung bean to produce higher protein content. Dry fractionation is a sustainable option used in quinoa to concentrate protein fractions. Purification methods such as ultrafiltration and aqueous phase separation can be used. Different methods and processing conditions affect functional properties, including solubility, water and oil absorption, emulsification, foaming, thermal properties of isolates, which also affect the suitable application for isolates.&#x0D; Keywords: Protein isolates; Quinoa; Mung bean; Wet fractionation; Dry fractionation

Ultrasonic Assisted Extraction of Quinoa (Chenopodium quinoa Willd.) Protein and Effect of Heat Treatment on Its In Vitro Digestion Characteristics.

To extract and utilise the protein in quinoa efficiently, we investigated the effect of rate of quinoa protein isolate (QPI) extraction by ultrasound-assisted alkaline extraction and traditional alkaline extraction methods using single-factor experiments and Box-Behnken design. The effect of different heat treatment temperature and time on QPI functional properties and in vitro digestion characteristics were also investigated. The results showed that the optimal conditions of ultrasound- assisted alkaline extraction process were: ultrasonic time 99 min, solid-liquid ratio 1:20 w:v, ultrasonic temperature 47 °C, and pH 10, and its extraction rate and purity were 74.67 ± 1.08% and 87.17 ± 0.58%, respectively. It was 10.18% and 5.49% higher than that of the alkali-soluble acid precipitation method, respectively. The isoelectric point (pI) of QPI obtained by this method was 4.5. The flexibility and turbidity of QPI had maximum values at 90 °C, 30 min, and 121 °C, 30 min, which were 0.42 and 0.94, respectively. In addition, heat treatment changed the 1.77–2.79 ppm protein characteristic region in QPI’s nuclear magnetic resonance hydrogen spectroscopy (1H NMR). After heating at 90 °C and 121 °C for 30 min, the hydrolysis degree and total amino acid content at the end of digestion (121 °C, 30 min) were significantly lower than those of untreated QPI by 20.64% and 27.85%. Our study provides basic data for the efficient extraction and utilisation of QPI.