Water states associated with skim milk components quantitated by NMR
Padua, Graciela Wild
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Permalink
https://hdl.handle.net/2142/22996
Description
Title
Water states associated with skim milk components quantitated by NMR
Author(s)
Padua, Graciela Wild
Issue Date
1989
Doctoral Committee Chair(s)
Steinberg, Marvin P.
Department of Study
Food Science
Discipline
Food Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Food Science and Technology
Language
eng
Abstract
The water states associated with the skim milk components whey protein, rennet casein, lactose and with other sugars were characterized and quantitated by pulsed NMR spectroscopy. The relation between the water states and the rheological properties of these materials was also investigated.
Proton longitudinal relaxation rates were determined for whey protein powders and suspensions of solids concentrations between 0.01 and 2.90 g solids/g water. These data showed three hydration regions. The application of the two-state model with fast exchange to the dilute suspension data allowed the identification of polymer and free water states in this region. The same model was used to identify polymer and capillary water in the high solids region. For the intermediate solids, a three-state model was developed. These models enabled the calculation of the quantity of each water state in a whey protein-water system.
The same approach was used to determine the water states in casein-water mixtures over a concentration range of 0.4 to 6 g casein/g water. A plot of relaxation rate against solids content showed four linear regions which indicated the presence of four water states. The NMR two-state model with fast exchange was applied to Regions III and IV, and two extended forms of this model were developed for Regions I and II.
Proton relaxation rates were determined for lactose, sucrose, dextrose and fructose solutions of about 0.5 to 2 g sugar/g water. The log of relaxation rate against concentration was linear throughout the concentration range for all sugars. Each line showed the same intercept but a different slope. Variation of log viscosity with concentration for the same solutions was also linear; and the semi-log plots fell in the same relative order as they did for the relaxation rate. This finding showed that the viscosity of a sugar solution depends on the mobility of the water phase.
Viscosity was determined for whey protein suspensions up to 0.48 g solids/g water. Correlation of viscosity data with proton relaxation rate determinations yielded two linear relations. This correlation was interpreted in terms of the effect of water states on the viscosity of the system. Within a hydration region, viscosity was linearly dependent on the amount of free water in the sample.
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