采用 17O 和 1H 核磁共振和流变学研究酸化过程中脱脂奶粉溶液的分子水运动。

Molecular water motions of skim milk powder solutions during acidification studied by 17O and 1H nuclear magnetic resonance and rheology.

机构信息

Department of Food Science, Faculty of Science and Technology, Aarhus University, Research Centre Aarslev, Kirstinebjergvej 10, DK-5792 Årslev, Denmark.

出版信息

J Agric Food Chem. 2011 Sep 28;59(18):10097-103. doi: 10.1021/jf202258h. Epub 2011 Aug 31.

DOI:10.1021/jf202258h

PMID:21854070

Abstract

The molecular motion of water was studied in glucono-δ-lactone-acidified skim milk powder (SMP) solutions with various pH values and dry matter contents. NMR relaxometry measurements revealed that lowering the pH in SMP solutions affected 17O and 1H T2 relaxation rates almost identically. Consequently, the present study indicates that the proteins present in the samples do not affect the 1H relaxation behavior markedly, even at relatively high SMP concentrations (15-25%). Comparison of rheological measurements and NMR measurements suggested that the collapse of κ-casein during acidification could contribute to the initial decrease in 17O and 1H relaxation rate in the pH range between 6.6 and 5.5 for 15% SMP and in the pH range between 6.6 and 5.9 for 25% SMP. However, below pH 5.5 the viscosity and 17O and 1H NMR relaxation rates did not correlate, revealing that the aggregation of casein micelles, which increases viscosity below pH 5.5, does not involve major repartitioning of water.

摘要

采用 NMR 弛豫法研究了不同 pH 值和干物质含量的葡萄糖酸-δ-内酯酸化脱脂乳粉（SMP）溶液中的水分子的分子运动。研究表明，降低 SMP 溶液的 pH 值几乎对 17O 和 1H T2 弛豫速率产生相同的影响。因此，本研究表明，即使在相对较高的 SMP 浓度（15-25%）下，样品中的蛋白质也不会显著影响 1H 弛豫行为。流变学测量和 NMR 测量的比较表明，酸化过程中κ-酪蛋白的塌陷可能导致 15% SMP 在 pH 值为 6.6 至 5.5 之间以及 25% SMP 在 pH 值为 6.6 至 5.9 之间时，17O 和 1H 弛豫速率的初始降低。然而，在 pH 值低于 5.5 时，粘度和 17O 和 1H NMR 弛豫速率不再相关，这表明在 pH 值低于 5.5 时，由于酪蛋白胶束的聚集而导致粘度增加，但不会涉及水的主要重新分配。