Interactions of whey proteins with milk fat globule membrane proteins during heat treatment of whole milk

Abstract

International audienceThe association of $\beta$-lactoglobulin ($\beta$-Lg) and $\alpha$-lactalbumin ($\alpha$-La) with milk fat globule membrane (MFGM), when whole milk was heated in the temperature range 60-95 °C, was investigated using one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and non-reducing conditions. In SDS-PAGE under reducing conditions, $\beta$-Lg was observed in MFGM material isolated from milk heated at $\geq$60 °C for 10 min; small amounts of $\alpha$-La and $\kappa$-casein were also observed in the MFGM material of milk heated at $\geq$65 °C for 10 min and $\geq$75 °C for 10 min, respectively. However, these proteins were not observed in SDS-PAGE under non-reducing conditions. Two-dimensional SDS-PAGE of MFGM material isolated from heated milk showed that the protein complexes that remained at the top of the non-reducing gel (first dimension) were resolved into $\beta$-Lg, $\alpha$-La and the major original MFGM proteins in the reducing gel (second dimension). These results indicate that $\beta$-Lg and $\alpha$-La associated with MFGM proteins via disulfide bonds during the heat treatment of whole milk. The amounts of $\beta$-Lg and $\alpha$-La that associated increased with an increase in the temperature up to 80 °C, and then remained almost constant. These maximum values for $\beta$-Lg and $\alpha$-La were ~1.0 mg*g-1 fat and ~0.2 mg*g-1 fat, respectively. Of the major original MFGM proteins, xanthine oxidase and butyrophilin were not affected by the heat treatment of whole milk, whereas PAS 7 was heat labile and PAS 6 decreased to some extent during heating.Interactions des protéines sériques avec les protéines de la membrane des globules gras induites par le traitement thermique du lait entier. Les interactions de la $\beta$-lactoglobuline ($\beta$-Lg) et de l'$\alpha$-lactalbumine ($\alpha$-La) avec les composants de la membrane des globules gras (MFGM), contenues dans le lait entier, chauffé entre 60 et 95 °C, ont été étudiées par électrophorèse mono ou bi-dimensionnelle, en gel de polyacrylamide et dodécyl sulfate de sodium (SDS-PAGE) en conditions réductrices ou non. En conditions réductrices, les gels de SDS-PAGE indiquaient la présence de $\beta$-Lg dans les MFGM isolés du lait chauffé dans des conditions $\geq$ à 60 °C - 10 min ; de faibles quantités d'$\alpha$-La étaient également détectées dans les MFGM pour ce même traitement thermique. Un traitement thermique plus intense ($\geq$ à 75 °C - 10 min) montrait la fixation de caséine $\kappa$. Aucune de ces interactions n'était observée en conditions SDS-PAGE non réductrices. La caractérisation en SDS-PAGE bi-dimensionnelle des MFGM isolés du lait chauffé montrait que les complexes protéiques qui restaient au sommet des gels non réducteurs (1e dimension) étaient résolus en $\beta$-Lg, $\alpha$-La et composants protéiques majeurs des MFGM en conditions réductrices (2e dimension). Ces résultats confirment l'association de la $\beta$-Lg et de l'$\alpha$-La avec les protéines d...

Effect of cream pasteurization, microfiltration and enzymatic proteolysis on in vitro cholesterol-lowering activity of buttermilk solids

“…This may be due to modifications of the MFGM composition following heat treatment. It is well known that heatinduced complexes can be formed between whey proteins (β-LG and α-LA) and MFGM via thiol/disulphide interchange [24,28,29]. In fact, it has been reported that a new membrane can result from these new interactions and modify the functional properties of buttermilk [2].…”

“…It is known that heat processing of cream modifies the composition and structure of MFGM to a considerable extent [8,24]. Heat treatment denatures whey and MFGM proteins, resulting in the formation of various complexes with caseins [3,5,8,29]. These heat-induced interactions are likely to modify the bioactivity and functional properties of MFGM.…”

Composition, Properties and Nutritional Aspects of Milk Fat Globule Membrane – A Review

“…First, cream can be separated from milk by a laboratory centrifuge or in a large scale, bench-top cream separator. Next, the separated cream is washed two [Ye et al, 2002], three [Fong et al, 2007;Kanno & Kim, 1990] or more number of times [Asker, 1974;Mangino & Brunner, 1975] in 3-15 fold volumes of distilled or deionized water [Kanno & Kim, 1990;Newman & Harrison, 1973], sucrosesaline solution with [Erickson et al, 1964;Mather et al, 1977;Nejjar et al, 1986;Snow et al, 1977] or without [Dowben et al, 1967] pH buffering, pH buffered sucrose solution [Khodaparast-Sharifi & Snow, 1989], isotonic phosphate buffer solution [Nielsen & Bjerrum, 1977], phosphate-saline buffer [Innocente et al, 1997], or simulated milk ultrafiltrate [Ye et al, 2004]. In some cases, detergents [Diaz-Maurino & Nieto, 1976;Mather et al, 1977] or dissociating agents [Ye et al, 2002] are added to facilitate the washing.…”

“…Therefore, collecting the membrane material from both buttermilk and butter serum without separating the supernatant and the pellet -e.g., by lyophilization of the combined solution -is necessary to have a representative evaluation of MFGM characteristics. Three washing steps are sufficient to remove virtually all milk serum components [Nejjar et al, 1986;Ye et al, 2004]. However, three washes already cause a loss of MFGM components [Anderson & Brooker, 1975;Nejjar et al, 1986].…”

“…A native fat globule may act as an inert filler (structure breaker) in milk-based gels [Michalski et al, 2002a], while the newly formed MFGM (mainly casein and some serum proteins) in homogenized fresh milk or recombined milk would cross-link (structure promoter) with the protein network and reinforce it in both rennet and acid gels [Lopez & Dufour, 2001;Lucey et al, 1998;Michalski et al, 2002b]. Heat treatment induces disulfide bridges formation between κ-casein and β-lactoglobulin [Dalgleish, 1990] which is in turn absorbed to MFGM [Cano-Ruiz & Richter 1997;Houlihan et al, 1992;Ye et al, 2004].…”