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Link between goat milk lipolysis and sensorial quality of lactic goat cheeses made from raw or pasteurised milk. There is an important variability of the lipolysis level in goat milk, due to various physiological and breeding factors. The aim of this study was to evaluate the impact of these natural variations on the sensorial quality of fresh and ripened lactic goat cheeses. The effect of milk pasteurisation was also studied. The results show that the variation of the lipolysis level of goat milk do not have any significant effect on the sensorial quality of ripened cheeses. On the contrary, the sensorial quality of fresh cheeses is linked to the lipolysis level of milk. These results allowed us to recommend some means of controlling the sensorial quality of goat cheeses. For ripened cheeses, a satisfying sensorial quality could be obtained via the control of the technological parameters, notably the moisture in non-fat cheese at the demoulding. For fresh cheeses, the lipolysis level of milk should be checked before cheesemaking, and milks with high lipolysis levels should not be used. Pasteurisation of milk induced a decrease in the lipolysis level of cheeses. The use of pasteurisation led to a limitation of the appearance of organoleptic defects in rip- ened cheeses, but the overall flavour and odour of ripened cheeses made from pasteurised milk was also reduced compared to cheeses made from raw milk. goat milk / lipolysis / goat cheese / sensorial quality / pasteurisation

Compositional factors involved in the variable acidification capacity of goat milk by lactic starters. This study was designed to define the factors involved in the variable acidification capacity of goat milk by lactic starters. Acidification capacity and compositional parameters of 28 goat milk samples were determined. The influences of the period of production and of some tech- nological treatments (cold storage and heating) were also investigated. The results point out the influ- ence of milk composition, and notably the role of the buffering components such as proteins and minerals. An improved activity of lactic starters is observed in milks with a high level of proteins and minerals. The lactation period, through its effect on the protein concentration, affects the acidification capacity of goat milk. Cold storage does not exert any major influence on the acidification process. However, the results indicate that heating of milk lead to an improved activity of lactic starters at the beginning of the acidification period. goat milk / acidification / lactic starter / composition

The first months of life correspond to a key period in human life where dramatic physiological changes (establishment of microbiota, development of the immune system, etc.) occur. In order to better control these changes it is necessary to understand the behaviour of food in the gastrointestinal tract of the newborn. Infant formula is the only food for the newborn when breast-feeding is impossible. The kinetics of digestion of milk proteins and the nature of the peptides liberated in the small intestine throughout infant formula digestion have never been extensively investigated so far and were therefore studied using the piglet as a model of the newborn child. Piglets were fed infant formula by an automatic delivery system during 28 d, and slaughtered 30, 90 and 210 min after the last meal. Contents of stomach, proximal and median jejunum and ileum were collected and characterised. The extent of β-lactoglobulin (β-lg), α-lactalbumin (α-la) and casein proteolysis was monitored by inhibition ELISA, SDS-PAGE, immunoblotting and MS. At 30 min after the last meal, caseins were shown to be extensively hydrolysed in the stomach. Nevertheless, peptides originating mainly from β-caseins (from 509 to 2510 Da) were identified in the jejunum and ileum of the piglets. β-Lg partially resisted gastric digestion but completely disappeared in the stomach after 210 min. α-La had a similar behaviour to that of β-lg. Two large peptides (4276 and 2674 Da) generated from β-lg were present in the ileum after 30 and 210 min and only one (2674 Da) after 90 min.

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 aw 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 aw 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., 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 dépendant du rapport protéine/lactose dans les CPL.

The effect of glycation with lactose on the association behavior and conformational state of bovine β-lactoglobulin (β-LG) was studied, using size exclusion chromatography, polyacrylamide gel electrophoresis, proteolytic susceptibility, and binding of a fluorescent probe. Two modification treatments were used, i.e., aqueous solution glycation and dry-way glycation. The results showed that the latter treatment did not significantly alter the nativelike behavior of the protein while the former treatment led to important structural changes. These changes resulted in a specific denatured β-LG monomer, which covalently associated via the free thiol group. The homodimers thus formed and the expanded monomers underwent subsequent aggregation into a high molecular weight species, via noncovalent interactions. The association behavior of glycated β-LG is discussed with respect to the known multistep denaturation/aggregation process of nonmodified β-LG. Keywords: β-Lactoglobulin; glycation; denaturation; aggregatio...

The solubility of lactose-beta-lactoglobulin conjugates at pH 4.6, after heating near neutral pH in phosphate buffer/0.116 M NaCI, was investigated by size exclusion chromatography and compared with unmodified protein. Heated conjugates in the temperature range 65-90 degrees C showed greater solubility at pH 4.6. The proportion of soluble protein increased with the number of bound lactose molecules. Total solubility was obtained for conjugates with nine lactose residues attached per monomer of beta-lactoglobulin. The protective effect of bound sugar toward precipitation was associated with the formation of soluble disulfide cross-linked dimers, highly accessible to trypsin digestion. These results suggested that bound lactose, through steric hindrance and high surface hydrophilicity, prevents the thiol-disulfide exchange reactions of the polymerization-aggregation process of lactose-beta-lactoglobulin conjugates.