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Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 119-127).

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Não consta resumo na publicação. / Abstract not available.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 198-219).

Master of Science / Food Science Institute - Animal Sciences & Industry / Jayendra K. Amamcharla / High-protein dairy powders are added to a variety of products to improve nutritional, functional, and sensory properties. To have the intended properties, the powder must be soluble. The solubility is effected by processing storage, and dissolution conditions, as well as the type of powder. Various tests are used to determine solubility, but they are time-consuming and subjective. Literature has shown that ultrasound spectroscopy can characterize the solubility of high-protein dairy powders, but it requires expensive equipment and skilled technicians. An economical alternative is to use an ultrasonic flaw detector, which is commonly used in the construction industry. For this study, an ultrasonic flaw detector based method was developed to characterize the solubility of high protein dairy powders. To evaluate the method, commercially available milk protein concentrate (MPC) was obtained and stored at 25°C and 40°C and stored for four weeks to produce powders with different dissolution properties. To test the powders, a 5% (w/w) concentration of powder was added to water. A focused beam reflectance measurement (FBRM) and solubility index were used as a reference method. After powder addition, data was collected at regular intervals for 1800s. The FBRM and solubility index showed that the powders lost solubility as the storage time and temperature increased. From the ultrasound data, one parameter was extracted from the relative velocity and three parameters were extracted from the attenuation data. A soluble powder had a low relative velocity standard deviation from 900-1800s, high area under the attenuation curve, low peak time, and high peak height. The ultrasonic flaw detector detected differences in solubility before the solubility index. When testing MPC with protein contents ranging from 85% to 90% and at a dissolution temperature of 40°C and 48°C, data from the ultrasonic flaw detector and FBRM showed that the solubility decreased as the protein content increased and increasing the dissolution temperature improved the solubility of the powder. Overall, the ultrasonic flaw detector can characterize the solubility of high-protein dairy powders.

Não consta resumo na publicação. / Abstract not available.

Whey proteins have restricted use in many food applications because of limited functional properties. Whey proteins' relatively high content of disulfide bonds may be responsible for their lack of functionality, especially in extrusion applications. To determine the effect of disulfide bond content on functional properties and extrudate performance, whey protein concentrate was treated with sodium sulfite to achieve four levels of disulfide bond sulfonation (0, 31, 54, and 71%). Sulfonated whey protein functional properties, extrusion-expanded snack properties (32% total protein), and extrusion-textured fibrous product properties (48% protein) were determined. Correlation analysis was performed to determine relationships between functional properties and extrudate performance. Sulfonation of whey protein concentrate (80% protein) increased foaming and emulsion properties and decreased melt temperatures. These changes were largely attributed to increased protein unfolding and flexibility. Sulfonation decreased gel strength and increased resolubilization after heat treatment. These changes were likely the result of increased electric charge on the proteins, limiting protein-protein interactions during heating. Snack products extruded from the 31 and 71% sulfonated samples were less expanded and released less protein and carbohydrate during extrudate solubilization. Sulfonation may have promoted protein unfolding, thereby exposing interaction sites and increasing the formation of insoluble protein-starch aggregates . In support of this suggestion, negative correlation s were found between extrusion performance and protein functional properties related to flexibility , including emulsification activity index, foam stability, and melt onset temperature. The anomalous behavior of the 54% sulfonated sample may be the result of significant structural and functional changes of a-Lb that are predicted to occur at approximately 50% sulfonation. Although the textured extrudate produced from all levels of sulfonation (including the control) did not possess typical fibrous texture, sulfonation at 31% and higher decreased stability after hydration . Decreased stability and fibrous texture may have resulted from decreased protein-protein interactions caused by the repulsion of electric charges contributed by sulfite groups. In conclusion, sulfonated whey protein functional and extrudate properties were influenced by disulfide bond content. Changes in these properties were attributed primarily to increased protein unfolding and flexibility. Increased electric charge on proteins also played a role where protein-protein interactions were important.

There is considerable interest among food manufacturers to incorporate protein into food products in both developed and developing countries. Dairy proteins are excellent choices for many different applications, as they are known to have several nutritional and functional benefits. Membrane filtration techniques are often utilized as the preferred method of fractionation, due to the high throughput and continuous nature of the process. One such product produced from membrane filtration of skim milk is called milk protein concentrate. This product is valued for its high protein content, but it has historically exhibited poor solubility when reconstituted into water, which severely restricts the food applications for which it is suitable. There is some existing evidence that milk protein concentrates which contain elevated levels of sodium exhibit higher solubility upon reconstitution into water. The main objective of this thesis project was to demonstrate the effect of sodium chloride, added to diafiltration (DF) water utilized during the manufacturing process, on the solubility of milk protein concentrate. It was observed that the addition of sodium chloride into diafiltration water at levels of 50 mM, 100 mM, and 150 mM had a beneficial effect on the solubility of milk protein concentrate across a variety of reconstitution conditions. For example, when milk protein concentrate was mixed for 1 h on a stage mixer at 23 °C ± 1 °C, a significant increase (p < 0.001) in mean solubility was observed when at least 50 mM NaCl had been incorporated into DF water. The incorporation of 50 mM NaCl into DF water significantly increased (p < 0.001) the mean solubility of milk protein concentrate from 59.81 % to between 64.34 % and 71.78 %. The addition of 100 mM NaCl significantly increased (p < 0.001) the solubility to between 88.80 % and 96.24 %, and the addition of 150 mM NaCl significantly increased (p = 0.005) the solubility to between 92.79 % and 100 %. Minerals analysis of dry powders revealed a significant increase (p < 0.001) in levels of sodium. The addition of 50 mM NaCl into DF water was associated with a significant increase (p < 0.001) in powder Na content to between 2.48 mg/g and 7.44 mg/g. The addition of 100 mM NaCl into DF water was associated with a significant increase (p = 0.002) in powder Na content to between 5.80 mg /g and 10.75 mg/g, and the addition of 150 mM NaCl into DF water was associated with a significant increase (p = 0.001) in powder Na content to between 9.57 mg/g and 14.53 mg/g. A significant difference (p < 0.001) in magnesium level was also detected. Differences in calcium content were not found to be statistically significant (p = 0.016) at α = 0.01. Preliminary observations of milk protein concentrate upon reconstitution were made using a confocal laser scanning microscopy method. This method showed evidence of possible differences in powder particle rehydration and affinity for lipid association between powder particles manufactured at different treatment levels. As the level of NaCl incorporated into DF water increased, particle structures upon rehydration appeared more porous, and the incidence of lipid material that was not associated with powder particles appeared to increase. Overall, this study demonstrates the importance of sodium content in determining the solubility of milk protein concentrate.

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