No abstract

This article details recent research conducted on the complexation between milk proteins and polysaccharides and the properties of the complexes, and the application of such relationships to the food industry. Complexation between proteins and polysaccharides through electrostatic interactions gives either soluble complexes in a stable solution or insoluble complexes, leading to phase separation. The formation and the stability of these complexes are influenced by pH, ionic strength, ratio of protein to polysaccharide, charge density of protein and polysaccharide as well as processing conditions (temperature, shearing and time). The functional properties of milk proteins, such as solubility, surface activity, conformational stability, gelforming ability, emulsifying properties and foaming properties, are improved through the formation of complexes with polysaccharides. These changes in the functional properties provide opportunities to create new ingredients for the food industry.

No abstract

International audienceThe association of $\beta$-lactoglobulin ($\beta$-Lg) and $\alpha$-lactalbumin ($\alpha$-La) with milk fat globule membrane (MFGM), when whole milk was heated in the temperature range 60-95 °C, was investigated using one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and non-reducing conditions. In SDS-PAGE under reducing conditions, $\beta$-Lg was observed in MFGM material isolated from milk heated at $\geq$60 °C for 10 min; small amounts of $\alpha$-La and $\kappa$-casein were also observed in the MFGM material of milk heated at $\geq$65 °C for 10 min and $\geq$75 °C for 10 min, respectively. However, these proteins were not observed in SDS-PAGE under non-reducing conditions. Two-dimensional SDS-PAGE of MFGM material isolated from heated milk showed that the protein complexes that remained at the top of the non-reducing gel (first dimension) were resolved into $\beta$-Lg, $\alpha$-La and the major original MFGM proteins in the reducing gel (second dimension). These results indicate that $\beta$-Lg and $\alpha$-La associated with MFGM proteins via disulfide bonds during the heat treatment of whole milk. The amounts of $\beta$-Lg and $\alpha$-La that associated increased with an increase in the temperature up to 80 °C, and then remained almost constant. These maximum values for $\beta$-Lg and $\alpha$-La were ~1.0 mg*g-1 fat and ~0.2 mg*g-1 fat, respectively. Of the major original MFGM proteins, xanthine oxidase and butyrophilin were not affected by the heat treatment of whole milk, whereas PAS 7 was heat labile and PAS 6 decreased to some extent during heating.Interactions des protéines sériques avec les protéines de la membrane des globules gras induites par le traitement thermique du lait entier. Les interactions de la $\beta$-lactoglobuline ($\beta$-Lg) et de l'$\alpha$-lactalbumine ($\alpha$-La) avec les composants de la membrane des globules gras (MFGM), contenues dans le lait entier, chauffé entre 60 et 95 °C, ont été étudiées par électrophorèse mono ou bi-dimensionnelle, en gel de polyacrylamide et dodécyl sulfate de sodium (SDS-PAGE) en conditions réductrices ou non. En conditions réductrices, les gels de SDS-PAGE indiquaient la présence de $\beta$-Lg dans les MFGM isolés du lait chauffé dans des conditions $\geq$ à 60 °C - 10 min ; de faibles quantités d'$\alpha$-La étaient également détectées dans les MFGM pour ce même traitement thermique. Un traitement thermique plus intense ($\geq$ à 75 °C - 10 min) montrait la fixation de caséine $\kappa$. Aucune de ces interactions n'était observée en conditions SDS-PAGE non réductrices. La caractérisation en SDS-PAGE bi-dimensionnelle des MFGM isolés du lait chauffé montrait que les complexes protéiques qui restaient au sommet des gels non réducteurs (1e dimension) étaient résolus en $\beta$-Lg, $\alpha$-La et composants protéiques majeurs des MFGM en conditions réductrices (2e dimension). Ces résultats confirment l'association de la $\beta$-Lg et de l'$\alpha$-La avec les protéines d...

No abstract

Background: The traditional dairy-cattle-based industry is becoming increasingly diversified with milk and milk products from non-cattle dairy species. The interest in non-cattle milks has increased because there have been several anecdotal reports about the nutritional benefits of these milks and reports both of individuals tolerating and digesting some non-cattle milks better than cattle milk and of certain characteristics that non-cattle milks are thought to share in common with human milk. Thus, non-cattle milks are considered to have potential applications in infant, children, and elderly nutrition for the development of specialized products with better nutritional profiles. However, there is very little scientific information and understanding about the digestion behavior of non-cattle milks. Scope and Approach: The general properties of some non-cattle milks, in comparison with human and cattle milks, particularly focusing on their protein profile, fat composition, hypoallergenic potential, and digestibility, are reviewed. The coagulation behaviors of different milks in the stomach and their impact on the rates of protein and fat digestion are reviewed in detail. Key findings and Conclusions: Milk from different species vary in composition, structure, and physicochemical properties. This may be a key factor in their different digestion behaviors. The curds formed in the stomach during the gastric digestion of some non-cattle milks are considered to be relatively softer than those formed from cattle milk, which is thought to contribute to the degree to which non-cattle milks can be easily digested or tolerated. The rates of protein and fat delivery to the small intestine are likely to be a function of the macro- and micro-structure of the curd formed in the stomach, which in turn is affected by factors such as casein composition, fat globule and casein micelle size distribution, and protein-to-fat ratio. However, as no information on the coagulation behavior of non-cattle milks in the human stomach is available, in-depth scientific studies are needed in order to understand the impact of compositional and structural differences on the digestive dynamics of milk from different species.

We determined seasonal variations in the composition and characteristics of bovine milk, as well as heat-induced changes in the physicochemical properties of the milk, in a typical seasonal-calving New Zealand herd over 2 full milking seasons. Fat, protein, and lactose contents varied consistently during the year in patterns similar to those of the lactation cycle. Seasonality also had significant effects on milk calcium, ionic calcium, fat globule size, buffering capacity, and ethanol stability, but not on casein micelle size. The ratio of casein to total protein did not vary significantly over the season, but late-season milk had the highest content of glycosylated κ-casein (G-κ-CN) and the lowest content of α-lactalbumin in both years. We observed significant between-year effects on protein, total calcium, ionic calcium, pH, and casein: total protein ratio, which might have resulted from different somatic cell counts in the 2 years. Compared with heating at 90°C for 6 min, UHT treatment (140°C for 5 s) induced greater dissociation of κ-casein, a similar extent of whey protein denaturation, a lower extent of whey protein-casein micelle association, and a larger increase in casein micelle size. Indeed, UHT treatment might have triggered significant dissociation of G-κ-CN, resulting in aggregation among the casein micelles and increased apparent mean casein micelle diameter. Seasonality had significant effects on the partitioning of G-κ-CN between the micelle and the serum phase, the extent of whey protein-casein micelle association under both heating conditions, and the casein micelle size of the UHT milk.

20The objective of this study was to understand quantitatively the role that bile salts 21 play in the digestion of emulsified lipids. The behaviours of digestion by pancreatin (1.6 22 mg/mL) of sodium-caseinate-stabilized emulsions (0.5 wt% protein) and bile-extract-23 stabilized emulsions (0.2 5 mg/mL) as influenced by the addition of aqueous bile extract 24were studied under simulated intestinal conditions (37 °C; pH 7.5; 39 mM K2HPO4, 150 mM 25 NaCl; with continuous agitation at ~ 150 rev/min for 3 h). The droplet characteristics (size 26 and -potential) of the sodium caseinate-and bile extract-stabilized droplets were evaluated 27 by light scattering techniques. The kinetics of the total fatty acids released by hydrolysis of 28 the emulsified lipids was monitored by the pH-stat method with or without the presence of 29 continuous phase bile extract. The results suggested that the presence of unadsorbed bile 30 extract markedly enhanced the rate and the extent of lipid digestion. This could be attributed 31 to considerable removal of lipolysis products (free fatty acids, mono-and/or di-acylglycerols) 32 in mixed micelles, which are known to inhibit lipid digestion, by the unadsorbed bile salts. 33This study provides new insights for the lipid digestion of food formulations. 34 35