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A294、褐变程度和游离氨基含量的测定结果证实乳清分离蛋白与葡聚糖在干热处理条件下确实发生了以美拉德反应为机理的接枝反应。使用傅里叶变换红外光谱技术研究了接枝反应对乳清分离蛋白分子结构的影响。与原蛋白相比,乳清分离蛋白-葡聚糖接枝物在3700~3200 cm-1范围内出现一宽峰及在1260~1000 cm-1范围内吸收增强;接枝物在酰胺Ⅰ带(1600~1700 cm-1)和酰胺Ⅱ带(1500~1600 cm-1)内的峰形发生变化,峰强增加,对应的吸收峰位发生红移。结合去卷积和二阶导数处理,对酰胺Ⅰ带进行曲线拟合,定量分析了接枝反应前后蛋白质分子二级结构的变化。结果显示,由于大分子葡聚糖的接入,WPI的二级结构遭到破坏,β-转角和无规则卷曲含量增加,α-螺旋和β-折叠含量减少,蛋白质分子结构有序性减弱。
A294, the degree of browning and the content of free amino groups confirmed that whey protein isolate and dextran indeed did the Maillard reaction grafting reaction under the conditions of dry heat treatment. The effect of grafting reaction on the molecular structure of whey protein isolate was studied by Fourier transform infrared spectroscopy. Compared with the original protein, the whey protein-glucan graft showed a broad peak in the range of 3700 ~ 3200 cm-1 and the absorption increased in the range of 1260 ~ 1000 cm-1. (1600-1700 cm-1) and amide II band (1500-1600 cm-1), the peak intensity increased and the corresponding absorption peak shifted red. The curve of amide Ⅰ band was fitted by deconvolution and second derivative treatment, and the changes of the secondary structure of protein molecules before and after grafting reaction were quantitatively analyzed. The results showed that the secondary structure of WPI was destroyed due to the attachment of macromolecular dextran, the content of β-turn and irregular curl increased, the content of α-helix and β-sheet decreased, and the orderliness of protein molecular structure decreased.