Search

Trabajo presentado al: 73rd Annual Meeting of the European Federation of Animal Science (EAAP). Oporto (Portugal), 5-9 de septiembre.

Milk lipids supply 50-60 % of the calories necessary for newborn growth under the form of maternal milk or infant formulas. Infant formulas have been optimized in terms of chemical composition but not with regards to the structure of the emulsion. An important difference remains between the native emulsions of milk fat globules (4 µm) as opposed to the processed submicronic emulsions (0.5 µm) of infant formulas. This structural difference may modify the kinetics of digestion and disintegration of the emulsion in the digestive tract of the newborns. Indeed the native emulsions develop an interfacial surface of 1.8 m2/g of lipid stabilized by a natural trilayered membrane based of phospholipids and proteins, whereas infant formulas present a much higher neoformed interfacial surface (30 m2/g of lipid) stabilized by dairy proteins. This higher interfacial surface is supposed to increase infant formula susceptibility to lipolysis but also to proteolysis through the higher accessibility of proteases to adsorbed proteins. To check this hypothesis, 3 matrices were formulated: M1 containing raw bovine milk fat globules dispersed in an infant formula-type serum phase, M2 similar to M1 with an additional high pressure homogenization treatment and M3 similar to M2 with the addition of a pasteurization treatment. The matrices were subjected to the semi-dynamic gastric phase of an in vitro digestion mimicking the conditions reported in newborns. The disintegration and the kinetics of lipolysis and proteolysis were monitored during the 180 minutes of digestion. The initial structure affected both the kinetics of the hydrolysis and the disintegration of the matrices. The initial rate of lipolysis of M1 was ~ 55 times lower than for M2 or M3 which was partially explained by its lower specific surface. Total proteolysis of caseins was observed at 30 minutes on M3 whereas it only occurred after 120 minutes for M1. The initial structure impacted the gastric destabilization with the formation of larger aggregates for M1 (mode at 190 µm at 30 min) than on the two other matrices. Since the free fatty acids and amino acids liberated in the gastric phase can act as second messenger and modulate the gastric emptying, this effect of structure may have important physiologic consequences. The gastric in vitro semi-dynamic model allowed rapid screening of matrices and limitations of consumption of digestive enzymes. In the future, it will be employed on maternal milk to determine the additional effect of the endogenous lipase on the digestion.

Dry heating is intensively used in pharmaceutical and food industry for viral and microbial decontamination of thermosensible proteins. It is rapidly developing as a pre-texturization process in food ingredient industry because it constitutes a means for improving the food proteins functionalities.[1] In this study, we investigated the chemical and structural changes that occur during dry heating under controlled physicochemical conditions and their consequences on the gelling properties of whey proteins. The water activity of the powder before dry heating and heat intensity (temperature/times) strongly accelerate the kinetic of denaturation/aggregation of whey proteins. The proteins composition and pH are the major factors that affect the structure of denatured and aggregated proteins. The kinetic of denaturation/aggregation of whey proteins was enhanced at pH 2.5 as compared to pH 6.5.[2] However, the presence of traces of lactose, as in case of commercially available WPI powders, modifies such kinetic order. At pH 2.5 the protein molecules were mainly linked together by intermolecular disulfide bonds, while at pH 6.5, covalent cross-links other than disulfide bonds were also involved in the formed aggregates. Stable non-native monomeric species of β-Lg and α-La exhibiting mass loss of 18 Da were generated during the course of dry heating, the proportion of which depends on pH. This mass loss has been attributed to N-term cyclisation for α-La and to an internal cyclic imide formation for β-Lg. Interestingly, the gelling properties were found to be highly dependent on the relative proportion of non-native monomers, soluble and insoluble aggregates that can be controlled by dry-heating pH. These results give new insight into the complex dry-heat induced modifications and aggregation pathways of whey proteins. They also give indications for a better control of physicochemical parameters of the powders at the industry to maintain the reproducibility of functionality of dry heated proteins ingredient.

International audience

b-lactoglobulin/linoleic acid complexes - Formation, binding stoichiometry and cytotoxic capability

International audience; Monolayers on a Langmuir trough constitute a great biomimetic model to characterize protein-protein or protein-lipid interaction, where the physical state of the interfacial layer is completely controlled. We present here three studies performed on monolayers, with a wide panel of experimental (optical, spectroscopical, rheological) techniques. i) Surface properties and conformation of Nephila clavipes Spider recombinant silk proteins (MaSpI and MaSp2) was studied at the air-water interface: we show that the mechanism of assembly of both proteins is different, although both proteins share the same sequence pattern and a close hydrophobicity. They both exhibit a certain propensity to form b-sheets that may be important for the efficiency of the natural spinning process. ii) The dystrophin molecular organization and its anchoring in a lipidic environment depend on the rod fragment used and on the lipid nature. Moreover the interaction is guided by the lateral surface pressure. This lipid packing variation is essential to understand the role of the dystrophin during compression-extension cycle of the muscle membrane. iii) We evidence that non additive behavior of mixtures of food globular proteins leads to enhanced foaming properties or to self assembled objects.

International audience