Characterization of changes in composition and physicochemical properties of casein micelles from raw milk to buttermilk

• Main Author: Looney, Melissa Ann
• Format: Others
• Published: DigitalCommons@CalPoly 2014
• Online Access: https://digitalcommons.calpoly.edu/theses/1162; https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=2255&context=theses

It is well-documented that buttermilk has poor coagulation properties due to changes that occur to the casein micelles during the butter-making process. These modifications are generally attributed to the pasteurization of the cream upon which interactions between the proteins are promoted. It was hypothesized that churning is also a critical step for the changes that occur in composition of the casein micelles. The objective of this work was to learn more about the interactions that occur between casein micelles and MFGM components during the butter making process. Raw cream was processed using a rotary churn at 18°C for approximately 30 minutes, and buttermilk was collected for analysis. Raw milk was skimmed at 10°C by centrifuging at 3000 x g for 20 minutes. Cream, skim milk and buttermilk were centrifuged at 60,000 x g for 40 minutes twice using imidazole buffer at pH 6.8 in order to isolate the micellar content in the pellet. Variation in physical properties of the casein micelles was determined using a Malvern Zetasizer. Protein profiles of UP cream, skim milk, and buttermilk were analyzed using one and two-dimensional gel electrophoresis technique. Experiments were performed using three different batches of UP cream, skim milk and buttermilk. Statistical analyses showed that processing the buttermilk significantly increased the surface charge (P0.05). Our results also indicate that churning of cream promoted interactions between casein micelles and MFGM proteins as shown by the more complex 2D-gel electrophoresis pattern obtained for casein micelles sedimented from buttermilk. This work is significant in its focus of better understanding the functionality changes of valuable milk components during the churning of cream.