Rheological Properties of Concentrated Skim Milk: Influence of Heat Treatment and Genetic Variants on the Changes in Viscosity During Storage

Heat treatment during manufacturing of milk powder is one of the most important tools for manipulation of its functional properties, and it is the basis of the classification of these proteins into low-, medium-, and high-heat types. Slight differences in the sequences of the major proteins in milk (genetic variants) seem to have also a significant effect in milk powder processing (U.S. patent). Therefore, the effects of high-temperature storage and heat treatment on skim milk of defined genetic variants of β-lactoglobulin (β-LG) were measured. The samples had 45% total solids, the temperature of aging was 50°C, and the heat treatment was 90°C for 10 min prior to evaporation. Measurements on shear rate and on apparent viscosity were determined for each sample. During storage of the concentrated milk, the apparent viscosity and yield values increased markedly, and the age-dependent increase in viscosity in heat-treated concentrated skim milks was much more pronounced than in those prepared from unheated skim milks. The increase in apparent viscosity and yield value with storage time was notably different for milks containing different genetic variants. Unheated concentrated milks containing the B variant of β-LG showed the most rapid increase in apparent viscosity with storage time, whereas the viscosity increase was slowest in the concentrate containing the A variant. In contrast, heat-treated concentrated milks containing the A variant of β-LG showed the most rapid increase in viscosity with storage time, whereas the viscosity increase was slowest in the concentrate containing the AB variant. The changes in apparent viscosity of concentrated milk were largely reversible under high shear during the early stages of storage, but samples stored for a long time showed irreversible changes in apparent viscosity. Particle size analysis confirmed irreversible aggregation and fusion of casein particles during storage

Heat-Induced Reactions Involving β-Lactoglobulin and Other Milk Proteins in Milk, Whey, and Model Systems

Abstract of paper presented at the 2002 Joint Annual Meeting of the American Dairy Science Association & the American Society of Animal Science

Disulfide Bonding Patterns Between β-Lactoglobulin and κ-Casein in a Heated and Spray-Dried Milk-Model

Abstract of paper presented at the 2002 Joint Annual Meeting of the American Dairy Science Association & the American Society of Animal Science

Heat-Induced Redistribution of Disulfide Bonds in Milk Proteins. 2. Disulfide Bonding Patterns Between Bovine β-Lactoglobulin and κ-Casein

Heat treatment of milk causes the heat-denaturable whey proteins to aggregate with κ-casein (κ-CN) via thiol-disulfide bond interchange reactions. The particular disulfide bonds that are important in the aggregates are uncertain, although Cys121 of β-lactoglobulin (β-LG) has been implicated. The reaction at 60°C between β-LG A and an activated κ-CN formed small disulfide-bonded aggregates. The tryptic peptides from this model system included a peptide with a disulfide bond between a Cys residue in the triple-Cys peptide [β-LG(102-124)] and κ-CN Cys88 and others between κ-CN Cys88 or κ-CN Cys11 and β-LG Cys160. Only the latter two novel disulfide bonds were identified in heated (90°C/20 min) milk. Application of computational search tools, notably MS2Assign and SearchXLinks, to the mass spectrometry (MS) and collision-induced dissociation (CID)-MS data was very valuable for identifying possible disulfide-bonded peptides. In two instances, peptides with measured masses of 4275.07 and 2312.07 were tentatively assigned to β-LG(102-135): κ-CN(11-13) and β-LG A(61- 69): κ-CN(87s97), respectively. However, sequencing using the CID-MS data demonstrated that they were, in fact, β-LG(1-40) and β-LG(41-60), respectively. This study supports the notion that reversible intramolecular disulfide-bond interchange precedes the intermolecular interchange reactions

Heat-Induced Redistribution of Disulfide Bonds in Milk Proteins. 1. Bovine β-Lactoglobulin

Changes in the structure and chemistry of β-lactoglobulin (β-LG) play an important role in the processing and functionality of milk products. In model β-LG systems, there is evidence that the aggregates of heated β-LG are held together by a mixture of intermolecular non-covalent association and heat-induced non-native disulfide bonds. Although a number of non-native disulfide bonds have been identified, little is known about the initial inter- and intramolecular disulfide bond rearrangements that occur as a result of heating. These interchange reactions were explored by examining the products of heat treatment to determine the novel disulfide bonds that form in the heated β-LG aggregates. The native protein and heat-induced aggregates were hydrolyzed by trypsin, and the resulting peptides, before and after reduction with dithiothreitol, were separated by high-performance liquid chromatography and their identities confirmed by electrospray ionization mass spectrometry. Comparisons of these peptide patterns showed that some of the Cys160 was in the reduced form in heated β-LG aggregates, indicating that the Cys160-Cys66 disulfide bond had been broken during heating. This finding suggests that disulfide bond interchange reactions between β-LG non-native monomers, or polymers, and other proteins could occur largely via Cys160

La teneur en iode du sel de cuisine consommé à Lubumbashi et le statut iode des personnes vulnérables: cas de femmes enceintes de milieux défavorisés

INTRODUCTION: Consumption of low iodine salt can cause different types of disorders associated with iodine deficiency. This study aims to determine iodine content in table salt consumed in Lubumbashi and iodine status of pregnant women who are the main target of iodine deficiency.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

La teneur en iode du sel de cuisine consommé à Lubumbashi et le statut iode des personnes vulnérables: cas de femmes enceintes de milieux défavorisés

Introduction: la consommation du sel faiblement iodé peut engendrer des troubles divers liés à la carence iodée Ce travail a pour objectif d'évaluer la teneur en iode du sel consommé à Lubumbashi et de déterminer le statut iodé des femmes enceintes, cible privilégiée de la carence iodée. Méthodes: une étude transversale descriptive a été consacrée à une analyse iodométrique d'iode dans 739 échantillons de sel collectés dans les ménages et marchés de Lubumbashi en 2014. Précédemment, l'iode urinaire a été déterminé par la technique de minéralisation au persulfate d'ammonium chez 225 femmes enceintes reçues en consultation du 15 mars 2009 au 25 avril 2011. Résultats: notre enquête a révélé 47,5% des échantillons de sels de cuisine adéquatement iodés (15 à 40 ppm), 36,9% d'échantillons faiblement iodés, 7,4% d'échantillons trop riches en iode et 8,1% des échantillons non iodés. La disponibilité en iode du sel de cuisine analysé était globalement de 54,9%, se trouvant nettement en dessous des normes OMS (90%). En mesurant l'iode urinaire chez la femme enceinte, la carence iodée (iode urinaire <150 µg/l) a été observée dans une proportion de 52%. Conclusion: la faible disponibilité en iode du sel consommé à Lubumbashi pourrait être responsable d'une grande proportion de la carence iodée observée chez la femme enceinte, ce qui expose celle-ci aux risques majeurs des troubles dus à la carence en iode.The Pan African Medical Journal 2016;2