Lactose crystallisation and early Maillard reaction in skim milk powder and whey protein concentrates

Abstract

-Lactose crystallisation and Maillard reaction are two major modifications occurring in milk and whey powders during processing and storage. In this work, the aim was first to monitor the solid-state early Maillard reaction (EMR) in whey protein concentrates (WPC) heated at 60 °C and various water activities, and then, to characterise the physical changes that occur as a consequence of heat treatment in skim milk powder (SMP) and WPCs. After a w adjustment, SMP and WPC were heated at 60 °C in hermetic conditions to induce an amino-sugar reaction. Furosine analysis (% of blocked lysine) was used to monitor the progress of EMR. The results showed that the kinetic of EMR was linked to the initial a w of the powders. Heating of SMP may lead to the crystallisation of lactose in humidified powders, without apparently affecting the progress of EMR. Surprisingly, lactose crystallisation -monitored by micro-Differential Scanning Calorimetry -was easily induced in heated SMP, whereas it was delayed or even inhibited in WPC. The results showed that this effect was dependent on the protein/lactose ratio in WPCs.lactose crystallisation / early Maillard reaction / whey protein concentrate / water activity Résumé -Cristallisation du lactose et réaction de Maillard précoce dans les poudres de lait écrémé et les concentrés de protéines du lactosérum. La cristallisation du lactose et la réaction de Maillard sont deux modifications importantes survenant au cours de la production et du stockage des poudres de lait et de lactosérum. L'objectif de ce travail était dans un premier temps de suivre la réaction de Maillard précoce (RMP) dans des concentrés de protéines de lactosérum (CPL) chauffés à 60 °C à différentes activités d'eau et, dans un deuxième temps, de caractériser les modifications physiques consécutives au traitement thermique (comparaison poudres de lait écrémé et CPL). Les poudres de lait écrémé et les CPL -équilibrés à différentes activités d'eau -étaient chauffés à 60 °C dans des conditions hermétiques pour induire la RMP (suivie par l'analyse de la furosine). Les résultats indiquaient que la cinétique de la RMP était liée à l'activité d'eau initiale de poudres. Dans les poudres de lait écrémé humidifiées et chauffées, la cristallisation du lactose ne semblait pas avoir d'impact sur l'évolution de la RMP. La microcalorimétrie différentielle à balayage permettait d'observer que la cristallisation du lactose, induite facilement dans les poudres de lait écrémé, était retardée voire inhibée dans les CPL. Les résultats indiquent que cet effet était dépen-dant du rapport protéine/lactose dans les CPL. cristallisation du lactose / réaction de Maillard précoce / concentré de protéines du lactosérum / activité de l'eau

Maillard reaction kinetics in milk powder: Effect of water activity at mild temperatures

“…Although, at 50 and 60 C and at the same RH, faster crystallization could be expected, there were no significant differences between the rate constant values of samples equilibrated at a w 0.33 and 0.43 at 50 and 60 C. Apparently, in this study crystallization of lactose had no effect on the reactivity of lysine. Similar results were reported by other authors (Morgan, Appolonia Nouzille, Baechler, Vuataz, & Raemy, 2005;Vuataz, 1988) who suggested that, despite the fact that an increase of a w could accelerate NEB, crystallization immobilizes lactose and thus less dissolved lactose is available for reaction with proteins. It should be noted that a w could also rise during storage, as water is a product of Maillard reaction.…”

Effects of Protein Conformational Modifications, Enthalpy Relaxation, and Interaction with Water on the Solubility of Milk Protein Concentrate Powder

“…Lactose crystallization may depend on the lactose protein ratio in milk powder. Crystallization is easily induced in skim milk powder (SMP), whereas it is delayed or even inhibited in whole milk powder (WMP) (Morgan et al 2005). Thomas et al reported that interactions between β-lactoglobulin and lactose resulted in stabilization of β-lg-lactose (90:10) powder against lactose crystallization and the lactose crystallization was delayed (Thomas et al 2005).…”

“…The nonenzymatic reaction can occur progressively during storage. The nature and extent of the Maillard reaction depend on numerous factors, including water activity, pH, temperature, and physicochemical state of the component (Morgan et al 2005). In milk products, the Maillard reaction begins by lactose condensation on some amino acid residues (lactosylation) and involves a wide range of subsequent reactions (Thomas et al 2004).…”

Effect of water activity, temperature and pH on solid state lactosylation of β-lactoglobulin

“…Even for the dry-state lactosylation, the water activity is a major determinant for the reaction, the rate of reaction being maximal at intermediate water activities (0.4e0.8) due to the dual effect of water acting as a reaction product (mass-law retardation) and increasing the mobility of the reactants ( van Boekel, 2001;Labuza & Baisier, 1992;Morgan, Nouzille, Baechler, Vuataz, & Raemy, 2005;Saltmarch, Vagnini-Ferrari, & Labuza, 1981).…”

“…The authors therefore speculated that the attachment of one lactose molecule to b-LG may make the protein less prone to react with the next lactose molecule. Despite the very small structural changes induced by the dry-state lactosylation (Medranoa et al, 2009), this might also be the case for dry-state lactosylation of b-LG, since the lactosylation reaction between b-LG and lactose in whey protein concentrate in the dry-state (a w 0.2e0.4) proceeded non-linearly with time at both 35 and 60 C, as measured by the percentage of blocked lysine residues (Morgan et al, 2005). Therefore, there is a need to study the kinetics of the initial steps in the lactosylation process in more detail.…”