Formation of a structured clot during the gastric digestion of milk: Impact on the rate of protein hydrolysis

Food Matrix Design for Effective Lactic Acid Bacteria Delivery

The range of foods featuring lactic acid bacteria (LAB) with potential associated health benefits has expanded over the years from traditional dairy products to meat, cereals, vegetables and fruits, chocolate, etc. All these new carriers need to be compared for their efficacy to protect, carry, and deliver LAB, but because of their profusion and the diversity of methods this remains difficult. This review points out the advantages and disadvantages of the main food matrix types, and an additional distinction between dairy and nondairy foods is made. The food matrix impact on LAB viability during food manufacturing, storage, and digestion is also discussed. The authors propose an ideal hypothetical food matrix that includes structural and physicochemical characteristics such as pH, water activity, and buffering capacities, all of which need to be taken into account when performing LAB food matrix design. Guidelines are finally provided to optimize food matrix design in terms of effective LAB delivery.

Gastric digestion of milk protein ingredients: Study using an in vitro dynamic model

The coagulation behavior and the kinetics of protein hydrolysis of skim milk powder, milk protein concentrate (MPC), calcium-depleted MPC, sodium caseinate, whey protein isolate (WPI), and heated (90°C, 20 min) WPI under gastric conditions were examined using an advanced dynamic digestion model (i.e., a human gastric simulator). During gastric digestion, these protein ingredients exhibited various pH profiles as a function of the digestion time. Skim milk powder and MPC, which contained casein micelles, formed cohesive, ball-like curds with a dense structure after 10 min of digestion; these curds did not disintegrate over 220 min of digestion. Partly calcium-depleted MPC and sodium caseinate, which lacked an intact casein micellar structure, formed curds at approximately 40 min, and a loose, fragmented curd structure was observed after 220 min of digestion. In contrast, no curds were formed in either WPI or heated WPI after 220 min of digestion. In addition, the hydrolysis rates and the compositions of the digesta released from the human gastric simulator were different for the various protein ingredients, as detected by sodium dodecyl sulfate-PAGE. Skim milk powder and MPC exhibited slower hydrolysis rates than calcium-depleted MPC and sodium caseinate. The most rapid hydrolysis occurred in the WPI (with and without heating). This was attributed to the formation of different structured curds under gastric conditions. The results offer novel insights about the coagulation kinetics of proteins from different milk protein ingredients, highlighting the critical role of the food matrix in affecting the course of protein digestion.

Influence of food structure on dairy protein, lipid and calcium bioavailability: A narrative review of evidence

Beyond nutrient composition matrix plays an important role on food health potential, notably acting on the kinetics of nutrient release, and finally on their bioavailability. This is particularly true for dairy products that present both solid (cheeses), semi-solid (yogurts) and liquid (milks) matrices. The main objective of this narrative review has been to synthesize available data in relation with the impact of physical structure of main dairy matrices on nutrient bio-accessibility, bioavailability and metabolic effects, in vitro, in animals and in humans. Focus has been made on dairy nutrients the most studied, i.e., proteins, lipids and calcium. Data collected show different kinetics of bioavailability of amino acids, fatty acids and calcium according to the physicochemical parameters of these matrices, including compactness, hardness, elasticity, protein/lipid ratio, P/Ca ratio, effect of ferments, size of fat globules, and possibly other qualitative parameters yet to be discovered. This could be of great interest for the development of innovative dairy products for older populations, sometimes in protein denutrition or with poor dentition, involving the development of dairy matrices with optimized metabolic effects by playing on gastric retention time and thus on the kinetics of release of the amino acids within bloodstream.

Digestion of milk proteins: Comparing static and dynamic in vitro digestion systems with in vivo data

In the frame of the COST action INFOGEST, a static in vitro digestion protocol has been elaborated aiming at the improvement of data comparability by harmonizing the experimental conditions. The success in harmonization was confirmed with inter-laboratory trials using skim milk powder as a standardized model food. Moreover, the physiological relevance of the gastric and intestinal endpoints of the static digestion protocol was demonstrated in a pig in vivo trial, with the same skim milk powder and samples collected from different sections of the digestive tract, as well as in a human study with from jejunal effluents. In vivo, digestion is a dynamic process influenced by peristalsis and by the gradual secretion of enzymes and juices and the dwell time of the food. To mimic these physiological mechanisms, dynamic in vitro digestion protocols are widely used. Until now, the differences of protein hydrolysis taking place during dynamic and static in vitro digestion have not been investigated. In this study, the gradual hydrolysis of the main milk proteins present in skim milk powder was digested with the dynamic DIDGI®-system using adult digestion protocol and the static harmonized INFOGEST method. Protein hydrolysis was analyzed by gel electrophoresis, peptide patterns were measured with mass spectrometry, and free amino acids with high pressure liquid chromatography. The peptide patterns at the gastric and intestinal endpoints of in vitro digestion showed a good approximation to the in vivo results from pigs. Moreover, gradual peptide generation was comparable in both in vitro digestion conditions. However, the dynamic protocol reflected the physiological situation better at the level of free amino acid release. Nonetheless, in both in vitro digestion protocols, absorption of free amino acids is not simulated, and they are therefore limited in reflecting the in vivo situation at this level.

Re-assembled casein micelles improve in vitro bioavailability of vitamin D in a Caco-2 cell model

The pandemic of vitamin D (VD) deficiency, and the global rise in obesity stimulate a need for staple low-fat foods and beverages enriched with VD. In light of consumer demand for a clean label, the use of natural endogenous food ingredients as delivery vehicles is of great interest. To this end, re-assembled casein micelles (rCM) have been shown to help retain VD during processing and shelf life and provide high bioavailability in low-fat milk and non-fat yoghurt. This follow-up study focused on the performance of VD-loaded rCM after drying and reconstitution, considering VD retention during simulated digestion, and the subsequent in vitro bioavailability of the vitamin. rCM conferred great protection to VD₃ during simulated digestion with a significant increase in vitamin retention for 1 h under gastric conditions. This observation is believed to arise from the vitamin-casein binding and the system's natural gelation (curd formation) near the casein isoelectric point that seclude the vitamin from environmental stressors and couple its release with digestive proteolysis of the rCM matrix. Vitamin absorption by Caco-2 cells from digested rCM was not significantly different from the absorption of the digested free VD. However, thanks to the highly protective effect of the rCM, against VD gastric degradation, the overall effect of the rCM was a 4-fold higher bioavailability, compared to the free VD.

Use of imaging techniques to identify efficient controlled release systems of Lactobacillus rhamnosus GG during in vitro digestion

Complementary microscopy techniques were used to highlight the importance of matrix formulation on lactic acid bacteria delivery system efficiency.