In Vitro Digestion of Proteins and Growth Factors in a Bovine Whey Protein Extract as Determined Using a Computer-Controlled Dynamic Gastrointestinal System (TIM-1)

Digestion-resistant whey peptides promote antioxidant effect on Caco-2 cells

Enteric endothelial cells are the first structure to come in contact with digested food and may suffer oxidative damage by innumerous exogenous factors. Although peptides derived from whey digestion have presented antioxidant potential, little is known regarding antioxidant pathways activation in Caco-2 cell line model. Hence, we evaluated the ability to form whey peptides resistant to simulated gastrointestinal digestive processes, with potential antioxidant activity on gastrointestinal cells and associated with sequence structure and activity. Using the INFOGEST method of simulated static digestion, we achieved 35.2% proteolysis, with formation of peptides of low molecular mass (<600 Da) evaluated by FPLC. The digestion-resistant peptides showed a high proportion of hydrophobic and acidic amino acids, but with average surface hydrophobicity. We identified 24 peptide sequences, mainly originated from β-lactoglobulin, that exhibit various bioactivities. Structurally, the sequenced peptides predominantly contained the amino acids lysine and valine in the N-terminal region, and tyrosine in the C-terminal region, which are known to exhibit antioxidant properties. The antioxidant activity of the peptide digests was on average twice as potent as that of the protein isolates for the same concentration, as evaluated by ABTS, DPPH and ORAC. Evaluation of biological activity in Caco-2 intestinal cells, stimulated with hydrogen peroxide, showed that they attenuated the production of reactive oxygen species and prevented GSH reduction and SOD activity increase. Caco-2 cells were not responsive to nitric oxide secretion. This study suggests that whey peptides formed during gastric digestion exhibit biological antioxidant activity, without the need for previously hydrolysis with exogenous enzymes for supplement application. The study's primary contribution was demonstrating the antioxidant activity of whey peptides in maintaining the gastrointestinal epithelial cells, potentially preventing oxidative stress that affects the digestive system.

Understanding protein digestion in infants and the elderly: Current in vitro digestion models

The last decades have witnessed a surge of interest in the fate of dietary proteins during gastrointestinal (GI) digestion. Although several in vitro digestion models are available as alternatives to clinical experiments, most of them focus on the digestive conditions of healthy young adults. This study investigates the static/dynamic models used to simulate digestion in infants and the elderly and considers the related in vivo conditions. The in vitro digestive protocols targeting these two groups are summarized, and the challenges associated with the further development of in vitro digestion models are discussed. Static models rely on several factors (e.g., enzyme concentration, pH, reaction time, and rotation speed) to differentiate digestive conditions depending on age. Dynamic models can more accurately simulate the complex digestion process and allow the inclusion of further parameters (sequential secretion of digestive fluids, gradual changes in pH, peristaltic mixing, GI emptying, and the inoculation of luminal microbiota). In the case of infants, age or growth stage clarification and the differentiation of digestive protocols between full-term and preterm infants are required, whereas protocols dealing with various health statuses are required in the case of the elderly, as this group is prone to oral cavity and GI function deterioration.

Dietary Whey Protein Supplementation Increases Immunoglobulin G Production by Affecting Helper T Cell Populations after Antigen Exposure

Whey protein is a by-product of cheese and casein manufacturing processes. It contains highly bioactive molecules, such as epidermal growth factor, colony-stimulating factor, transforming growth factor-α and -β, insulin-like growth factor, and fibroblast growth factor. Effects of whey protein on immune responses after antigen (hemagglutinin peptide) injection were evaluated in rats. Experimental diets were formulated based on NIH-31M and supplemented with 1% amino acids mixture (CON) or 1% whey protein concentrate (WPC) to generate isocaloric and isonitrogenous diets. Rats were fed the experimental diets for two weeks and then exposed to antigen two times (Days 0 and 14). Blood was collected on Days 0, 7, 14, and 21 for hematological analysis. The WPC group showed decreased IgA and cytotoxic T cells before the antigen injection (Day 0) but increased IgG, IL-2, and IL-4 after antigen injection due to increased B cells and T cells. Helper T cells were increased at Days 14 and 21, but cytotoxic T cells were not affected by WPC. WPC may activate adaptive immunity (IgG) against antigen by modulating helper T cells. Bioactive molecules might contribute to the immune-enhancing effects of whey protein concentrate.

Invited review: Dairy proteins and bioactive peptides: Modeling digestion and the intestinal barrier

Dairy products are one of the most important sources of biologically active proteins and peptides. The health-promoting functions of these peptides are related to their primary structure, which depends on the parent protein composition. A crucial issue in this field is the demonstration of a cause-effect relationship from the ingested protein form to the bioactive form in vivo. Intervention studies represent the gold standard in nutritional research; however, attention has increasingly been focused on the development of sophisticated in vitro models of digestion to elucidate the mechanism of action of dairy nutrients in a mechanistic way and significantly reduce the number of in vivo trials. On the other hand, the epithelial intestinal barrier is the first gate that actively interacts with digestion metabolites, making the intestinal cells the first target tissue of dairy nutrients and respective metabolites. An evolution of the in vitro digestion approach in the study of dairy proteins and derived bioactive compounds is the setup of combined in vitro digestion and cell culture models taking into consideration the endpoint to measure the target organism (e.g., animal, human) and the key concepts of bioaccessibility, bioavailability, and bioactivity. This review discusses the relevance and challenges of modeling digestion and the intestinal barrier, focusing on the implications for the modeling of dairy protein digestion for bioactivity evaluation.

Digestibility of transglutaminase cross-linked caseinate versus native caseinate in an in vitro multicompartmental model simulating young child and adult gastrointestinal conditions

Aim of this study was to investigate the digestion of transglutaminase cross-linked caseinate (XLC) versus native caseinate (NC) in solution and in cheese spread under digestive conditions for adults and children mimicked in a gastrointestinal model. Samples were collected for gel electrophoresis and nitrogen analysis. The results showed no relevant differences between XLC and NC for total and α-amino nitrogen in digested fraction under adult and child conditions. However, the rate of digestion was depending on the food matrix. Gel electrophoresis showed the gastric breakdown of XLC without formation of pepsin resistant peptides larger than 4 kDa. NC was slowly digested in the stomach with formation of pepsin resistant fragments and was still detectable in the stomach after 90 min. In the small intestine the proteins were rapidly digested. XLC was digested to small peptides, while NC was resistant against pepsin digestion under gastric conditions of adults and children.