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

Rôle de l’agrégation des protéines dans la stabilité thermique thermo-induite au cours de la fabrication de poudre de lait

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Dairy Science & Technology

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.

Abstract

(85 °C/1800 s 120 °C/120 s 140 °C/5s) SDS-PAGE (WPNI) WPNI

Résumé

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 prétraitement 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 à l’échelle de la paillasse la fabrication de lait en poudre recombiné. On considère en général que la stabilité thermique dépend de la façon avec laquelle le lait répond au prétraitement thermique appliqué au cours de la fabrication de poudre. Cependant, nous avons trouvé que la dénaturation des protéines de lactosérum, comme indiquée par des mesures analytiques tel que l’indice d’azote des protéines de lactosérum (WPNI), n’est pas en soi un critère suffisant pour dire qu’il y a stabilité thermique. Notre travail suggère que des laits de bonne stabilité thermique s’obtiennent par chauffage donnant un WPNI bas et un équilibre entre agrégats solubles de taille modérée et une diminution de la proportion des plus petites micelles. La formation de ces agrégats est influencée par le chauffage appliqué et varie au cours des périodes de l’année.

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Authors and Affiliations

  1. Werribee Laboratory, Food Science Australia, 671 Sneydes Rd, 3030, Werribee, Victoria, Australia

    Roderick P. W. Williams & Lynette D’Ath

  2. Dairy Innovation Australia, 671 Sneydes Rd, 3030, Werribee, Victoria, Australia

    Bogdan Zisu

Authors
  1. Roderick P. W. Williams
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  2. Lynette D’Ath
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  3. Bogdan Zisu
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Correspondence to Roderick P. W. Williams.

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Williams, R.P.W., D’Ath, L. & Zisu, B. Role of protein aggregation in heat-induced heat stability during milk powder manufacture. Dairy Sci. Technol. 88, 121–147 (2008). https://doi.org/10.1051/dst:2007048

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