Journal Articles
Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915
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Item Impact of Ultrasound Emulsification on the Physicochemical Properties of Emulsions Stabilised by Quinoa Protein Isolates at Different pHs(Springer Science+Business Media, LLC, 2024-03) Yang Z; Cheng LUltrasonication (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.Item Limited Alcalase hydrolysis improves the thermally-induced gelation of quinoa protein isolate (QPI) dispersions(Elsevier BV, 2022-11-01) Wang X; Cheng L; Wang H; Yang ZGelation is critical in many food applications of plant proteins. Herein, limited hydrolysis by Alcalase was used to promote thermally induced gelation of quinoa protein isolates (QPI). Mechanical properties of various QPI gels were characterised by small and large oscillatory shear deformation rheology while the microstructural features were observed by confocal laser scanning microscopy (CLSM). Both the gel strength and microstructure are strongly related to the hydrolysis time. The maximum gel strength (∼100 Pa) was achieved after Alcalase hydrolysis for 1 min, which was ∼20 folds higher than that of untreated QPI. Extended hydrolysis up to 5 min progressively decreased the gel strength. A string-like interconnected protein network was formed after proteolysis. The change of gel strength with hydrolysis time correlated well to the Gʹ 20°C/Gʹ 90°C value and results of intrinsic fluorescence and surface hydrophobicity. The Gʹ 20°C/Gʹ 90°C value is sensitive to hydrogen bonds formation while the intrinsic fluorescence and surface hydrophobicity are associated with protein unfolding and exposure of hydrophobic groups. Therefore, both hydrogen bonding and hydrophobic interactions are critical in improving the gel strength of QPI hydrolysates. Finally, FTIR analysis revealed that protein secondary structures are affected by the proteolysis and formation of inter-molecular hydrogen bonds between polypeptides. This study provides an efficient strategy for improving thermally induced gelation of QPI and enables a deep understanding of QPI gelation mechanism induced by Alcalase hydrolysis.Item Impacts of sonication and high hydrostatic pressure on the structural and physicochemical properties of quinoa protein isolate dispersions at acidic, neutral and alkaline pHs(Elsevier BV, 2022-12) Luo L; Yang Z; Wang H; Muthupandian A; Hemar YHerein, 1 wt% quinoa protein isolate (QPI) was exposed to sonication using a 20 kHz ultrasonicator equipped with a 6 mm horn (14.4 W, 10 mL, up to 15 min) or high hydrostatic pressure (HHP, up to 600 MPa, 15 min) 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 Ssingle bondS 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 (600 MPa) 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.Item Impact of incorporations of various polysaccharides on rheological and microstructural characteristics of heat-induced quinoa protein isolate gels(Springer Science+Business Media, LLC, 2022-09) Patole S; Cheng L; Yang ZThis study aimed to investigate the properties of heat-induced gels (85 °C for 30 min) of quinoa protein isolate (QPI) in the presence and absence of various polysaccharides including guar gum (GG), locust bean gum (LBG), and xanthan gum (XG) at pH 7. For this purpose, samples with three gum concentrations (0.05, 0.1, and 0.2 wt%) at a fixed QPI concentration (10 wt%) and a fixed ionic strength (50 mM NaCl) were studied in terms of their gelation behaviour, small and large deformation rheological properties, water holding capabilities, and microstructural characteristics. Rheological measurements revealed that all polysaccharides incorporation could improve gel strength (complex modulus, G*) and breaking stress, accelerate gel formations, and more stiffer gels were obtained at greater polysaccharide concentrations. The XG exhibited the most gel strengthening effect followed by LBG and GG. Incorporation of 0.2 wt% XG led to a 15 folds increase in G* compared to the control. Confocal laser scanning microscopy observation revealed that the polysaccharides also altered gel microstructures, with the gels containing XG showing the most compact gel structures. The findings of this study may provide useful information for the fabrication of novel QPI based food gel products with improved texture.