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Effect of microfiltration on heat stabiity of milk concentrates

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Title: Effect of microfiltration on heat stabiity of milk concentrates
Author: Renhe, Isis Rodrigues Toledo
Department: Department of Food Science
Program: Food Science
Advisor: Corredig, MilenaHill, Arthur
Abstract: Heat stability of milk concentrates may increase by removal of whey proteins. In this thesis, physico-chemical changes caused by partial whey protein removal by microfiltration (MF) were evaluated. The impact of these changes on the processing properties of retentates, especially heat stability, was also assessed. Ultrafiltration (UF) and MF were compared to establish the effect of protein composition, while maintaining the same protein concentration in the milk dispersions. Results demonstrated that changes on heat coagulation time (HCT) were due to the reduction of whey proteins. However, all treatments showed better stability than what is reported in the literature. It was hypothesized that the differences were due to the processing history and reconstitution conditions of the concentrates used in previous works. Diafiltration (DF) using water or permeate (PF) was also tested, to determine if a further increase in the ratio of protein to other solids may have an impact on the heat stability of the milk concentrates. At the same concentration factor, DF had a major impact on retentates composition when compared to UF and MF; however, this difference could not only be attributed to a decrease in lactose and ions, but also to an increase in pH. The analysis of the heat-induced complexes residual in the unsedimented fraction after UHT reinforced the positive impact of DF on heat stability, with the sample presenting fewer aggregates and with smaller sizes compared to UF or MF milk concentrates. Because calcium chelators are important in obtaining shelf stable products in protein concentrates subjected to high heat treatments, the impact of these salts at different concentrations and pH on the stability of a fresh microfiltered concentrate was evaluated. As the original sample was quite stable, no major changes were observed in short period of time. The results stressed, once again, the effect of processing history, and the difference in processing functionality between fresh and reconstituted concentrates. Indeed the present results were in contrast with literature reports. The work in this thesis contributes to a better understanding of the differences in processing functionality between milk protein concentrates depending on their processing history. This is critical to improved utilization of the concentrates in high protein nutritional beverages.
Date: 2017-01
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