Structural properties of quinoa protein isolate: Impact of neutral to high alkaline extraction pH
Abstract
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.
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Higher extraction pH and harsher treatments increase void-volume aggregates, which is consistent with irreversible association and altered solubility and interfacial behavior.
“Higher extraction pH and harsher treatments increase void-volume aggregates, which is consistent with irreversible association and altered solubility and interfacial behavior”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
These treatments also increase ζ-potential magnitude and hydrophobic exposure while maintaining recognizable globulin structures.
“These treatments also increase ζ -potential magnitude and hydrophobic exposure while maintaining recognizable globulin struc tures”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Quinoa often shows modest neutral-pH solubility with a sharp rise under alkaline pH, but harsh extraction pH can also drive irreversible aggregation that limits solubility recovery despite increased extractability.
“Quinoa often shows modest neutral-pH solubility with a sharp rise under alkaline pH, but harsh extraction pH can also drive irreversible aggregation that limits solu bility recovery despite increased extractability”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Higher extraction pH, from 9 to 11, and thermal treatments tend to increase void-volume aggregates and β-associated aggregation.
“Higher extraction pH, from 9 to 11, and thermal treatments tend to increase void-volume aggregates and β -associated aggregation.”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
A treatment that improves solubility and molecular emulsification may weaken gel-network formation, whereas a treatment that promotes aggregation may impair interfacial adsorption but improve particle stabilization or gelation.
“For example, a treatment that improves solubility and molecular emulsification may weaken gel-network formation, whereas a treatment that promotes aggregation may impair interfacial adsorption but improve particle stabilization or gelation”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Thermal and alkaline treatments tend to increase β-sheets, β-turns and decrease α-helix, consistent with enhanced β-aggregation and cross-linking.
“Thermal and alkaline treatments tend to increase β -sheets, β -turns and decrease α -helix, consistent with enhanced β -aggregation and cross-linking”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Controlled aggregation, unfolding, and junction formation are often associated with higher storage modulus, stronger holding capacity.
“Controlled aggregation, unfolding, and junction formation are often associated with higher storage modulus, stronger”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al. (2023)
Conventional alkaline solubilization-isoelectric precipitation can generate relatively high-purity protein isolates, but it can also alter secondary structure, aggregation state, digestibility, and antinutritional-factor profiles.
“Conventional alkaline solubilization-isoelectric pre cipitation can generate relatively high-purity protein isolates, but it can also alter secondary structure, aggregation state, digestibility, and antinutritional-factor profiles (Liu et al., 2023; Manzanilla-Valdez et al., 2024).”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Lack of harmonized datasets for ML across amaranth, buckwheat, and quinoa protein studies is the main limitation, not absence of modelling algorithms.
“At present, the main limita tion is not the absence of modelling algorithms, but the lack of harmo nized datasets for ML across amaranth, buckwheat, and quinoa protein studies.”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Larger aggregates or microgels may support network formation even when solubility is low.
“Larger aggregates or microgels may support network formation even when solubility is low”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al. (2023)
A single descriptor cannot be used for prediction without recording its preparation history.
“indicating that a single descriptor cannot be used for prediction without recording its prepara tion history (Liu et al., 2023).”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Extraction pH altered quinoa protein extractability, particle size, ζ-potential, surface hydrophobicity, solubility, and gelation behavior.
“extraction pH altered quinoa protein extractability, particle size, ζ -potential, surface hydro phobicity, solubility, and gelation behavior”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Extreme alkaline extraction, such as pH 11, can accelerate formation of high-MW aggregates; these aggregates reduce solubility and slow interfacial rearrangement, often weakening emulsification despite more unfolding.
“However, extreme alkaline extraction, such as pH 11, can accelerate formation of high-MW aggregates. These aggregates reduce solubility and slow interfacial rearrangement, which often weaken emulsification despite more unfolding (Cui et al., 2025; Liu et al., 2023; Wang et al., 2025a).”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Reported data differ substantially in extraction route, pH trajectory, protein purity, fraction composition, co-component retention, processing intensity, and analytical endpoints, which makes direct pooling of values unreliable.
“Reported data differ substantially in extraction route, pH tra jectory, protein purity, fraction composition, co-component retention, processing intensity, and analytical endpoints, which makes direct pooling of values unreliable (Liu et al., 2023; Luo et al., 2022; Yan & Zhu, 2025).”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al., 2023
Water extraction, ultrasound-assisted extraction, and homogenization show that extraction route affects yield, purity, co-component retention, particle state, and functionality.
“Water extraction, ultrasound- assisted extraction, and homogenization show that extraction route affects yield, purity, co-component retention, particle state, and”
From Structure-function design of amaranth, buckwheat and quinoa proteins as hydrocolloids for emulsion and gel structuring (2027) · cites this paper as Liu et al. (2023)
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Quinoa protein: Composition, structure and functional properties
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Cited by
Sorted by citations
Yan, X., & Zhu, F. (2027) · Food Hydrocolloids · doi:10.1016/j.foodhyd.2026.113137
- Authors
- Liu, S., Xie, Y., Li, B., Li, S., Yu, W., Ye, A., & Guo, Q.
- Affiliations
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
- Riddet Institute, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand
- Shandong Wonderful Biotech Co., Ltd., Dongying 257500, China
- ORCID
- Venue
- Foods
- Publisher
- MDPI AG
- Published
- 2023-07-03
- Volume
- 12
- Issue
- 13
- Pages
- 2589
- ISSN
- 2304-8158
- PMC
- PMC10340486
- Cited by
- 40
- References
- 3
- Language
- en
- Funders
- National Key Research and Development Program of China (2021YFE0193600)
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