Protein ingredient quality of infant formulas impacts their structure and kinetics of proteolysis under in vitro dynamic digestion.

Infant formula (IF) is a complex matrix requiring numerous ingredients and processing steps. The objective was to understand how the quality of protein ingredients impacts IF structure and, in turn, their kinetics of digestion. Four powdered IFs (A/B/C/D), based on commercial whey protein (WP) ingredients, with different protein denaturation levels and composition (A/B/C), and on caseins with different supramolecular organisations (C/D), were produced at a semi-industrial level after homogenization and spray-drying. Once reconstituted in water (13 %, wt/wt), the IF microstructure was analysed with asymmetrical flow field-flow fractionation coupled with multi-angle light scattering and differential refractometer, transmission electron microscopy and electrophoresis. The rehydrated IFs were subjected to simulated infant in vitro dynamic digestion (DIDGI®). Digesta were regularly sampled to follow structural changes (confocal microscopy, laser-light scattering) and proteolysis (OPA, SDS-PAGE, LC-MS/MS, cation-exchange chromatography). Before digestion, different microstructures were observed among IFs. IF-A, characterized by more denatured WPs, presented star-shaped mixed aggregates, with protein aggregates bounded to casein micelles, themselves adsorbed at the fat droplet interface. Non-micellar caseins, brought by non-micellar casein powder (IF-D) underwent rearrangement and aggregation at the interface of flocculated fat droplets, leading to a largely different microstructure of IF emulsion, with large aggregates of lipids and proteins. During digestion, IF-A more digested (degree of proteolysis + 16 %) at 180 min of intestinal phase than IF-C/D. The modification of the supramolecular organisation of caseins implied different kinetics of peptide release derived from caseins during the gastric phase (more abundant at G80 for IF-D). Bioactive peptide release kinetics were also different during digestion with IF-C presenting a maximal abundance for a large proportion of them. Overall, the present study highlights the importance of the structure and composition of the protein ingredients (WPs and caseins) selected for IF formulation on the final IF structure and, in turn, on proteolysis. Whether it has some physiological consequences remains to be investigated.

Transmembrane Pressure and Recovery of Serum Proteins During Microfiltration of Skimmed Milk Subjected to Different Storage and Treatment Conditions.

Milk pre-processing steps-storage at 4 °C (with durations of 48, 72 or 96 h) and methods for microbiological stabilization of milk (1.4 µm microfiltration, thermization, thermization + bactofugation, pasteurization) are performed industrially before 0.1 µm-microfiltration (MF) of skimmed milk to ensure the microbiological quality of final fractions. The objective of this study was to better understand the influence of these pre-processing steps and their cumulative effects on MF performances (i.e., transmembrane pressure, and transmission and recovery of serum proteins (SP) in the permeate). Results showed that heat treatment of skimmed milk decreased ceramic MF performances, especially after a long 4 °C storage duration (96 h) of raw milk: when milk was heat treated by pasteurization after 96 h of storage at 4 °C, the transmembrane pressure increased by 25% over a MF run of 330 min with a permeation flux of 75 L.h-1.m-2 and a volume reduction ratio of 3.0. After 48 h of storage at 4 °C, all other operating conditions being similar, the transmembrane pressure increased by only 6%. When milk was 1.4 µm microfiltered, the transmembrane pressure also increased by only 6%, regardless of the duration of 4 °C storage. The choice of microbiological stabilization method also influenced SP transmission and recovery: the higher the initial heat treatment of milk, the lower the transmission of SP and the lower their recovery in permeate. Moreover, the decline of SP transmission was all the higher that 4 °C storage of raw milk was long. These results were explained by MF membrane fouling, which depends on the load of microorganisms in the skimmed milks to be microfiltered as well as the rate of SP denaturation and/or aggregation resulting from pre-processing steps.

Impact of food consumption habits on the pesticide dietary intake: comparison between a French vegetarian and the general population.

This study aims to compare the pesticide residue dietary intake of the French general population and the vegetarian population, separated into five specific diets: omnivorous (OMN), lacto-vegetarian (LV), ovo-lacto-vegetarian (OLV), pesco-lacto-vegetarian (PLV) and vegan (VG). Theoretical Maximum Daily Intakes (TMDIs) based on Maximum Residue Levels (MRLs) were calculated as a percentage of the Acceptable Daily Intake (ADI). Among the 421 pesticides studied, only 48 had TMDI above ADI for at least one population subgroup. An excessive exposure was noticed for 44, 43, 42, 41 and 30 pesticides in the OLV, VG, OMN, LV and PLV groups, respectively, versus 29 in the general population. Meat and egg products consumption was responsible for higher intakes of organochlorine pesticides in the general population than in the vegetarian population (TMDI = 348% versus 146-183% ADI for aldrin). However, as the limited consumption of animal-origin commodities was largely offset by a higher fruit, vegetable and cereal intake in the vegetarian diets, vegetarians appear to be preferentially exposed to pesticides, for which fruit, vegetables and cereals are the main contributors, such as tri-allate, chlorpyrifos-methyl and diazinon. This study illustrates that consumption habits have a real impact on pesticide exposure in terms of intake levels, number and type of pesticides, representing a potential risk of dietary exposure. Except for organochlorine compounds, the vegetarian population may be more exposed to pesticide residues than the general population due to specific dietary habits. Thus, this population should be considered for risk assessment of pesticide residues.

Diversity in prion protein oligomerization pathways results from domain expansion as revealed by hydrogen/deuterium exchange and disulfide linkage.

The prion protein (PrP) propensity to adopt different structures is a clue to its biological role. PrP oligomers have been previously reported to bear prion infectivity or toxicity and were also found along the pathway of in vitro amyloid formation. In the present report, kinetic and structural analysis of ovine PrP (OvPrP) oligomerization showed that three distinct oligomeric species were formed in parallel, independent kinetic pathways. Only the largest oligomer gave rise to fibrillar structures at high concentration. The refolding of OvPrP into these different oligomers was investigated by analysis of hydrogen/deuterium exchange and introduction of disulfide bonds. These experiments revealed that, before oligomerization, separation of contacts in the globular part (residues 127-234) occurred between the S1-H1-S2 domain (residues 132-167) and the H2-H3 bundle (residues 174-230), implying a conformational change of the S2-H2 loop (residues 168-173). The type of oligomer to be formed depended on the site where the expansion of the OvPrP monomer was initiated. Our data bring a detailed insight into the earlier conformational changes during PrP oligomerization and account for the diversity of oligomeric entities. The kinetic and structural mechanisms proposed here might constitute a physicochemical basis of prion strain genesis.