Role of protein aggregation in heat-induced heat stability during milk powder manufacture

Abstract

-Although the inherent heat stability and the processes leading to the heat-induced coagulation of milk and reconstituted milk powders have been studied extensively, the processes that lead to heat-induced heat stability are less well established. An investigation has been undertaken into the effects of standardization with milk permeate or lactose and the heat-stabilization of milk powders. Standardized and unstandardized milk powders were produced in spring and autumn to determine seasonal effects on their heat stability. Other standardized powders were produced using a range of preheat treatments (85 • C/1800 s, 120 • C/120 s, and 140 • C/5 s) to evaluate the effects of preheat treatment and standardization on the heat stability of milk powders. Micelle size and the soluble aggregates formed during the preheat treatment were characterized by a combination of size-exclusion chromatography and SDS-PAGE. The heat stability of the powders was evaluated in a bench-scale model of retorted recombined evaporated milk manufacture. As has been generally accepted, the heat stability may be mediated by the way in which the milk responds to the preheat treatment given during milk powder manufacture. However, we have found that causing the denaturation of the whey proteins in itself, as is indicated by analytical measures such as the whey protein nitrogen index (WPNI) is not sufficient to impart heat stability. Our work suggests that milks with good heat stability are achieved by heating to give a low WPNI and a balance of moderately sized soluble aggregates and a decrease in the proportion of smaller micelles. The formation of these aggregates is influenced by the heating regime applied and varies at different times of year.heat stability / milk protein aggregation / micellar integrity Résumé -Rôle de l'agrégation des protéines dans la stabilité thermique thermo-induite au cours de la fabrication de poudre de lait. Bien que la stabilité thermique inhérente et les processus conduisant à la coagulation thermo-induite du lait et des poudres de lait reconstituées aient été largement étudiés, les processus qui conduisent à la stabilité thermique thermo-induite sont moins bien établis. Une étude a été entreprise concernant les effets de la standardisation avec du perméat de lait ou du lactose et la stabilisation thermique des poudres de lait. Des poudres de lait, standardisé et non standardisé, ont été produites au printemps et en automne pour déterminer l'effet saison sur leur stabilité thermique. D'autres poudres standardisées ont été produites en appliquant différents prétraitements thermiques (85 • C/1800 s, 120 • C/120 s et 140 • C/5 s) pour évaluer les effets du pré-traitement et de la standardisation sur la stabilité thermique des poudres de lait. La taille des micelles et les agrégats solubles formés au cours du prétraitement thermique ont été caractérisés en combinant chromatographie d'exclusion de taille et électrophorèse SDS-PAGE. La stabilité thermique des poudres était évaluée à l'aide d'un modèle simulant...

Casein polymorphism heterogeneity influences casein micelle size in milk of individual cows

“…Using this technique, further resolution of the distribution of the particles in milk was obtained, allowing separation of 6 differently sized populations within the sample. These are indicated in Figure 1 as follows: peak 1 = large casein micelles with diameters >200 nm; peak 2 = small casein micelles with diameters in the range 160 to 80 nm; peak 3 = small protein aggregates and very small micelles with diameters 80 to 37 nm; peak 4 = whey proteins; peak 5 = small peptides; and peak 6 = small aromatic molecules (Williams et al, 2008).…”

Controlling milk protein interactions to enhance the reconstitution properties of whole milk powders – A minireview

“…These heat treatments cause a number of competitive and often interdependent reactions in milk proteins, and many reactions also involve the non-protein constituents of milk. The heat-induced changes in milk have been the subject of many reviews and books [9,13,[21][22][23][24]27].…”

Sensitivity analysis of a small‐volume objective heat stability evaluation test for recombined concentrated milk

“…Williams et al . () suggested that different aggregation processes are involved at different time–temperature combinations resulting to the creation of discretely differently sized populations of aggregates.…”

“…Williams et al . () very nicely described the effect of different heat treatments on the degree of dissociation and size of the formed soluble aggregates. The authors suggested that upon heating milk containing a mixture of casein micelles and whey proteins at 85 °C for 1800 s, a considerable dissociation of the whey protein/casein complexes from the micellar surface takes place, resulting in large soluble aggregates and hence only a slight increase of the micelle size.…”