2024 Nouvelle approche de fractionnement des composés protéiques du babeurre à l'aide d'hydroxyapatite à des fins de valorisation
Authors:
Jean Lung
Journal:
Dissertation
Institute:
Université Laval
Abstract:
Buttermilk is the co-product obtainedfrom churning cream into butter. As butter consumption continues to rise in Quebec and Canada, significant quantities of buttermilk, produced in the same mass ratios as butter, need to be valorized. Although buttermilk shares a similar composition to skimmilk, its technological use is limited due to certain characteristics. Apart from its emulsifying power, its techno-functional properties are often inferior to skim milk. These differences are attributed, among other factors, to the release of milk fat globule membrane (MFGM) fragments into buttermilk during cream churning. However, MFGM contains several high-value compounds,such as phospholipids and membrane proteins, possessing nutritional and health properties. Thus, separating MFGM from buttermilk could yield two fractions: a delipidated fraction usable as skim milk and a lipid-rich fraction containing MFGM phospholipids usable as a bioactive compound. However, separating buttermilk components remains a significant challenge, especially on an industrial scale. This study focuses on implementing a technique for separating buttermilk components using their affinity for an adsorbent, hydroxyapatite (HA).
As part of this thesis, an initial study was conducted to determine if it was possible to adsorb MFGM fragments from pasteurized and non-pasteurized cream buttermilk onto HA. This study confirmed that both types of MFGM could interact with HA, with MFGM from pasteurized cream buttermilk showing greater affinity for HA than MFGM from raw cream. Moreover, MFGM proteins tended to adsorb onto the surface of HA, while phospholipids (PL) adsorbed internally. However, they adsorbed in equal proportions and at the same rate, indicating complete adsorption of MFGM fragments initially. Subsequently, aggregation of HA was observed during MFGM adsorption, suggesting that MFGM fragments adsorbed in multilayers on HA surfaces. This aggregation created interparticle spaceswhere additional MFGM fragments could intercalate. This first part verified that MFGM, composed of proteins and PL, could interact with and adsorb onto HA. Furthermore, no proportion or adsorption rate differenceswere observed between PL and MFGM proteins, only in their adsorption location within HA.
In a second study, the affinitiesof major buttermilk proteins,such as caseins(CN), α-lac(α-lac), and β-lg(β-lg),and MFGMfragmentsfor HA were individually determined under physicochemical parameterschanges(pH, ionic strength, and temperature). It was found that caseins exhibited the highest affinity for HA, followed by α-lac and β-lg, which had similar affinities for HA, and then MFGM. Subsequently, a study on the influence of physicochemical parameters on the adsorption of each buttermilk component onto HA was conducted. Changes in pH, ionic strength, and temperature only affected casein (CN) adsorption. Specifically, MFGM and β-lgadsorbed completely regardless of the parameters, while α-lac adsorbed at 90%,irrespectiveof the studied conditions.
The third study aimed to validate these observations for each component but in a model mixture. This time, changes in physicochemical parameters influenced the adsorption of each component in the mix, resulting in the predominant adsorption of CN(90%) and minor adsorption of whey proteins (11% α-lac and 37% β-lg) and MFGM (7%). It was then proposed to fix theCNvia HA, allowing subsequent separation of MFGM from the remaining whey proteins based on their solubility differences at varying pH levels. By adjusting the physicochemical parameters determined in the model mixture, it was possible to recover 90% of the CNin a diluted buttermilk solution through HA adsorption. Subsequently, MFGM was separated from the unadsorbed whey proteins by selective precipitation. Adjusting the pH to approximately 4.0 led to complete MFGM precipitation compared to whey proteins, which remained mostly soluble. Only 30% of β-lgwas co-precipitated, attributed to its interaction with MFGM following cream pasteurization. Thus, the majority of β-lg(70%) and α-lac (100%), being more thermally stable, were entirely recovered in the soluble phase. Ultimately, this sequence of processes (HA and selective precipitation) yielded three fractions from diluted buttermilk: one enriched in CN, another in MFGM, and a third in whey proteins and the remaining buttermilk components (lactose and minerals).
This thesis project has contributed new insights into the HA-based separation of buttermilk components and the influence of physicochemical parameter changes on their interactions. The knowledge gained regarding the behavior of buttermilk proteins and MFGM with HA particles, combined with selective precipitation of MFGM, has led to the development of a novel and straightforward technique for fractionating buttermilk components, generating fractions enriched in CN, whey proteins, and notably MFGM. This has addressed two identified challenges in the literature: isolating MFGM from other buttermilk components to valorize these distinct fractions (MFGM and delipidated buttermilk), and separating MFGM from whey proteins. These new insights suggest potential applications for fixing proteins and PL via HA for other dairy fluids, as well as using selective precipitation by pH adjustment to separateMFGM from whey proteins.