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[摘要]：The molecular motion of water was studied in glucono-delta-lactone-acidified skim milk powder (SMP) solutions with various values and dry matter contents. NMR relaxometry measurements revealed that lowering the pH in SMP solutions affected (17)O and (1)HT(2) relaxation rates almost identically. Consequently, the present study indicates that the proteins present in the samples do not affect the (1)H relaxation behavior markedly, even at relatively high SMP concentrations (15-25%). Comparison of rheological measurements and NMR measurements suggested that the collapse of kappa-casein during acidification could contribute to the initial decrease in (17)O and (1)H 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 (17)O and (1)H 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. |
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