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The Interactions between Exopolysaccharides Produced by Lactic Acid Cultures and Milk Proteins, and Their Impact on the Texture of Milk Gel

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Title: The Interactions between Exopolysaccharides Produced by Lactic Acid Cultures and Milk Proteins, and Their Impact on the Texture of Milk Gel
Author: Miao, Zhu Tuan
Department: Department of Food Science
Program: Food Science
Advisor: Corredig, Milena
Abstract: The use of bacterial cultures producing polysaccharides is widespread, but the details of the interactions between these molecules and casein micelles during aggregation are still unclear. The objective of this research was to produce, isolate, and characterize selected exopolysaccharides (EPS), and study their interactions in model dairy systems. In addition, the effect of their presence during milk coagulation was studied in situ. Different EPS isolation procedures were compared, and it was concluded that ethanol precipitation followed by TCA precipitation was the best method to obtain high EPS yields. It was also shown that sugar composition and molecular weight of the isolated EPS varied depending on the isolation procedure. The interactions between the isolated EPS produced by S. thermophilus (CHCC-5086) depended on pH. The EPS associated with both-lactoglobulin and sodium caseinate when these proteins were present at the interface of emulsion droplets. The addition of isolated EPS (200mg/L) caused a higher gelation pH in unheated milk, during glucono delta lactone (GDL) induced gelation. On the other hand, this was not the case for heated milk. The presence of the isolated EPS significantly increase the storage modulus of the acid gel and the ability of the gel to recover after shearing. The effect of the presence of exopolysaccharide during natural fermentation was also evaluated, via in situ production of EPS by S. thermophilus strains, stopping fermentation at pH 6.2, and then studying the casein micelles aggregation, under controlled conditions, using either GDL or rennet. There was a significant delay in rennet-induced coagulation of the micelles in the presence of EPS producing strains. Acid induced gelation was also affected. This research showed novel approaches to the study of the interactions between EPS and proteins in milk, and provided new information about how the presence of EPS may affect the structure formation of dairy products.
Date: 2015-03
Rights: Attribution-NonCommercial-ShareAlike 2.5 Canada
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Attribution-NonCommercial-ShareAlike 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-ShareAlike 2.5 Canada