Abstract
Heat-denaturation of quinoa protein isolate (QPI) at alkali pH and its influence on the physicochemical and cold gelation properties was investigated. Heating QPI at pH 8.5 led to increased surface hydrophobicity and decreases in free and bound sulfhydryl group contents. Heating at pH 10.5 caused a lesser degree of changes in sulfhydryl groups and surface hydrophobicity, and the resulting solutions showed drastically increased solubility. SDS PAGE revealed the presence of large aggregates only in the sample heated at pH 8.5, suggesting that any aggregates present in the sample heated at pH 10.5 were non-covalently bound and disintegrated in the presence of SDS. Reducing conditions partially dissolved the aggregates in the pH 8.5 heated sample indicating the occurrence of disulphide bonding, but caused no major alterations in the separation pattern of the pH 10.5 heated sample. Denaturation pH influenced the cold gelation properties greatly. Solutions heated at pH 8.5 formed a coarse coagulum with maximum G’ of 5 Pa. Heat-denaturation at 10.5 enabled the proteins to form a finer and regularly structured gel with a maximum G’ of 1140 Pa. Particle size analysis showed that the pH 10.5 heated sample contained a higher level of very small particles (0.1–2 μm), and these readily aggregated into large particles (30–200 μm) when pH was lowered to 5.5. Differences in the nature of aggregates formed during heating may explain the large variation in gelation properties.
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Abbreviations
- ANS:
-
1-anilino-8-naphthalene sulfonate
- GDL:
-
D-Gluconic acid δ-lactone (GDL)
- QPI:
-
Quinoa protein isolate
- SDS PAGE:
-
Sodium dodecyl sulphate polyacrylamide gel electrophoresis
- TNB:
-
5,5′-dithio-bis-(2-nitrobenzoic acid)
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Acknowledgments
Outi Mäkinen was funded by the Food Institutional Research Measure administered by the Department of Agriculture, Fisheries and Food (Ireland). The authors wish to express their sincere gratitude to Walter von Reding, Uwe Schill and Uncas Roukema from Bühler AG for the fractionation of quinoa.
Conflict of Interest
Outi E. Mäkinen has no conflict of Interest.
Emanuele Zannini has no conflict of interest.
Elke K. Arendt has no conflict of Interest.
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Mäkinen, O.E., Zannini, E. & Arendt, E.K. Modifying the Cold Gelation Properties of Quinoa Protein Isolate: Influence of Heat-Denaturation pH in the Alkaline Range. Plant Foods Hum Nutr 70, 250–256 (2015). https://doi.org/10.1007/s11130-015-0487-4
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DOI: https://doi.org/10.1007/s11130-015-0487-4