Wang Xueyang, Cheng Lirong, Wang Haifeng, Yang Zhi
School of Food and Advanced Technology, Massey University, Auckland, 0632, New Zealand.
The Riddet Institute, Massey University, Palmerston North, 0745, New Zealand.
Curr Res Food Sci. 2022 Nov 1;5:2061-2069. doi: 10.1016/j.crfs.2022.10.027. eCollection 2022.
Gelation 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 / value and results of intrinsic fluorescence and surface hydrophobicity. The / 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.
凝胶化在植物蛋白的许多食品应用中至关重要。在此，利用碱性蛋白酶进行有限水解以促进藜麦分离蛋白（QPI）的热诱导凝胶化。通过小振幅和大振幅振荡剪切变形流变学表征各种QPI凝胶的力学性能，同时通过共聚焦激光扫描显微镜（CLSM）观察微观结构特征。凝胶强度和微观结构均与水解时间密切相关。碱性蛋白酶水解1分钟后达到最大凝胶强度（约100 Pa），这比未处理的QPI凝胶强度高约20倍。延长水解至5分钟会使凝胶强度逐渐降低。蛋白水解后形成了丝状相互连接的蛋白质网络。凝胶强度随水解时间的变化与/值以及内在荧光和表面疏水性的结果密切相关。/值对氢键形成敏感，而内在荧光和表面疏水性与蛋白质展开和疏水基团暴露有关。因此，氢键和疏水相互作用对于提高QPI水解产物的凝胶强度都至关重要。最后，傅里叶变换红外光谱（FTIR）分析表明，蛋白质二级结构受蛋白水解以及多肽之间分子间氢键形成的影响。本研究为改善QPI的热诱导凝胶化提供了一种有效策略，并有助于深入了解碱性蛋白酶水解诱导QPI凝胶化的机制。
