Food processing increases casein resistance to simulated infant digestion

Effect of processing on nutritive values of milk protein

Milk is an essential source of nutritionally excellent quality protein in human, particularly in vegan diet. Before consumption, milk is invariably processed depending upon final product requirement. This processing may alter the nutritive value of protein in a significant manner. The processing operations like thermal treatment, chemical treatment, biochemical processing, physical treatments, nonconventional treatments, etc. may exert positive or negative influence on nutritional quality of milk proteins. On one side, processing enhances the nutritive and therapeutic values of protein while on other side intermediate or end products generated during protein reactions may cause toxicity and/or antigenicity upon consumption at elevated level. The review discusses the changes occurring in nutritive quality of milk proteins under the influence of various processing operations.

Protein Digestion of Baby Foods: Study Approaches and Implications for Infant Health

Protein digestion is critical for infants. Dissimilarities between infants and adults in food intake and digestive physiology lead to distinct patterns of proteolysis between individuals. However, such differences are not well represented in many studies on protein digestion of baby foods. The complex biological structures of baby foods and the physiology of the infant digestive system are key factors affecting proteolysis during the first two years of life. Well-controlled in vitro studies have demonstrated that varying digestion conditions alter the specificity, rate, and extent of proteolysis of baby foods. Nonetheless, these models do not completely replicate in vivo proteolysis or the complex biogeography of the gastrointestinal tract. Animal and clinical studies have revealed the fate of dietary proteins along the digestive tract and the overall health impact on subjects. Building comprehensive and annotated datasets from human infants will require innovative and standardized measurement. Now, more systematic evaluations of digestion are emerging to advance the knowledge and its translation as food design for effective diet and health management in infants.

Personalizing protein nourishment

Proteins are not equally digestible-their proteolytic susceptibility varies by their source and processing method. Incomplete digestion increases colonic microbial protein fermentation (putrefaction), which produces toxic metabolites that can induce inflammation in vitro and have been associated with inflammation in vivo. Individual humans differ in protein digestive capacity based on phenotypes, particularly disease states. To avoid putrefaction-induced intestinal inflammation, protein sources, and processing methods must be tailored to the consumer's digestive capacity. This review explores how food processing techniques alter protein digestibility and examines how physiological conditions alter digestive capacity. Possible solutions to improving digestive function or matching low digestive capacity with more digestible protein sources are explored. Beyond the ileal digestibility measurements of protein digestibility, less invasive, quicker and cheaper techniques for monitoring the extent of protein digestion and fermentation are needed to personalize protein nourishment. Biomarkers of protein digestive capacity and efficiency can be identified with the toolsets of peptidomics, metabolomics, microbial sequencing and multiplexed protein analysis of fecal and urine samples. By monitoring individual protein digestive function, the protein component of diets can be tailored via protein source and processing selection to match individual needs to minimize colonic putrefaction and, thus, optimize gut health.

Comparative analysis of human milk and infant formula derived peptides following in vitro digestion

It has long been recognised that there are differences between human milk and infant formulas which lead to differences in health and nutrition for the neonate. In this study we examine and compare the peptide profile of human milk and an exemplar infant formula. The study identifies both similarities and differences in the endogenous and postdigestion peptide profiles of human milk and infant formula. This includes differences in the protein source of these peptides but also with the region within the protein producing the dominant proteins. Clustering of similar peptides around regions of high sequence identity and known bioactivity was also observed. Together the data may explain some of the functional differences between human milk and infant formula, while identifying some aspects of conserved function between bovine and human milks which contribute to the effectiveness of modern infant formula as a substitute for human milk.

Peptide profiling and the bioactivity character of yogurt in the simulated gastrointestinal digestion

This study investigated the relationship between peptide profiles and the bioactivity character of yogurt in simulated gastrointestinal trials. A total of 250, 434 and 466 peptides were identified by LC-MS/MS analyses of yogurt, gastric digest and pancreatic digest. Forty peptides of yogurt survived in gastrointestinal digestion. κ-CN and β-CN contributed the diversity of peptides during the fermentation process and gastrointestinal digestion, respectively. The favorite of κ-CN by lactic acid bacteria complemented gut digestion by hydrolyzing κ-CN, the low abundance milk proteins. The potential bioactivities were evaluated by in vitro ACE and DPP-IV inhibition assays. The ACE inhibition rate of the pancreatic digests was ~4 - and ~2 - fold greater than that of yogurt and the gastric digests. The ACE inhibitory peptides generated during gastrointestinal digestion improved the ACE inhibitory activity of the gastric and pancreatic digests. The DPP-IV inhibition rate of the pancreatic digest was ~6 - and ~3 - fold greater than that of yogurt and the gastric digest. The numbers of potential DPP-IV inhibitory peptides were positively correlated to the DPP-IV inhibitory activity of the gastric and pancreatic digests.

BIOLOGICAL SIGNIFICANCE

The present study describes the characters and bioactivities of peptides from yogurt in a simulated gastrointestinal digestion. The number of peptides identified from yogurt and gastrointestinal digests by LC-MS/MS increased in the simulated gastrointestinal trials. The in vitro ACE and DPP-IV inhibition bioactivities revealed that the bioactivity of yogurt was enhanced during gastrointestinal digestion. The correlation between peptides and bioactivity in vitro indicated that not only the peptides amount but also the proportion of peptides with high bioactivities contributed to increased bioactivity during gastrointestinal digestion. The study of peptides identified from yogurt and digests revealed that the number of released peptides was not determined by the abundance of the parent proteins but by whether the enzymes favored the protein. In summary, peptide profiling and bioactivities of yogurt in simulated gastrointestinal digestion helped to elucidate the health benefits of yogurt peptides. The results further revealed that pre-digestion of milk by lactic acid bacteria are complementary to generate bioactive peptides and to provide particular yogurt functions.

Designing food delivery systems: challenges related to the in vitro methods employed to determine the fate of bioactives in the gut

This review discussesin vitroavailable approaches to study delivery and uptake of bioactive compounds and the associated challenges.

In vitro digestion of infant formulations with hydrolysed and non-hydrolysed proteins from dairy and soybean

Digestion of hydrolysed and non-hydrolysed dairy (casein and whey proteins) and soy proteins commonly used in infant formulations was studied underin vitrogastrointestinal (without lipases) conditions for 60 and 120 minutes in the stomach and small intestine, respectively.

Specificity of infant digestive conditions: some clues for developing relevant in vitro models

Digestion of nutrients is an essential function of the newborn infant gut to allow growth and development and understanding infant digestive function is essential to optimize nutrition and oral drug delivery. Ethical considerations prohibit invasive in vivo trials and as a consequence in vitro assays are often conducted. However, the choice of in vitro model parameters are not supported by an exhaustive analysis of the literature and do not mimic precisely the digestive conditions of the infant. This review contains a compilation of the studies which characterized the gastroduodenal conditions in full-term or preterm infants of variable postnatal age from birth up to six months. Important data about healthy full-term infants are reported. The enzymatic (type of enzymes and level of activity) and nonenzymatic (milk-based diet, frequency of feeding, bile salt concentrations) conditions of digestion in infants are shown to differ significantly from those in adults. In addition, the interindividual and developmental variability of the digestive conditions in infants is also highlighted.

Effects of different industrial heating processes of milk on site-specific protein modifications and their relationship to in vitro and in vivo digestibility

Heating processes are applied to milk and dairy products to ensure their microbiological safety and shelf lives. However, how differences in "industrial" thermal treatments affect protein digestibility is still equivocal. In this study, raw milk was subjected to pasteurization, three kinds of ultra-high-temperature (UHT) treatment, and in-can sterilization and was investigated by in vitro and in vivo digestion and proteomic methods. In-can sterilized milk, followed by UHT milk samples, showed a rapid decrease in protein bands during the course of digestion. However, protein digestibility determined by a Kjeldahl procedure showed insignificant differences. Proteomic analysis revealed that lactulosyllysine, which reflects a decrease in protein digestibility, in α-lactalbumin, β-lactoglobulin, and caseins was higher in in-can sterilized milk, followed by UHT milk samples. Thus, industrial heating may improve the digestibility of milk proteins by denaturation, but the improvement is likely to be offset by heat-derived modifications involved in decreased protein digestibility.

Bioefficacy of tea catechins encapsulated in casein micelles tested on a normal mouse cell line (4D/WT) and its cancerous counterpart (D/v-src) before and after in vitro digestion

Numerous studies have demonstrated that tea catechins form complexes with milk proteins, especially caseins. Much less work has been conducted to understand the metabolic conversions of tea-milk complexes during gastro-duodenal digestion. The objective of this study was to determine the significance of this association on the digestibility of the milk proteins and on the bioaccessibility of the tea polyphenol epigallocatechin gallate (EGCG). An in vitro digestion model mimicking the gastric and duodenal phases of the human gastrointestinal tract was employed to follow the fate of the milk proteins during digestion and determine the bioefficacy of EGCG isolated or encapsulated with the caseins. The samples, before and after digestion, were tested using two parallel colonic epithelial cell lines, a normal line (4D/WT) and its cancerous transformed counterpart (D/v-src). EGCG caused a decrease in proliferation of cancer cells, while in normal cells, neither isolated nor encapsulated EGCG affected cell proliferation, at concentrations <0.15 mg ml(-1). At higher concentrations, both isolated and encapsulated produced similar decreases in proliferation. On the other hand, the bioefficacy on the cancer cell line showed some differences at lower concentrations. The results demonstrated that regardless of the extent of digestion of the nanoencapsulated EGCG, the bioefficacy of EGCG was not diminished, confirming that casein micelles are an appropriate delivery system for polyphenols.

Influence of heat and shear induced protein aggregation on the in vitro digestion rate of whey proteins

Protein intake is essential for growth and repair of body cells, the normal functioning of muscles, and health related immune functions.

The impact of the Maillard reaction on the in vitro proteolytic breakdown of bovine lactoferrin in adults and infants

The impact of the Maillard reaction on proteolysis of the bioactive bovine lactoferrin is comparedin vitrobetween adults and infants for the first time, coupling proteomics to elucidate bioactive peptide formation.

In vivo digestion of bovine milk fat globules: effect of processing and interfacial structural changes. I. Gastric digestion

The aim was to study the in vivo gastric digestion of fat globules in bovine cream from raw, pasteurised or pasteurised and homogenised milk. Fasted rats were gavaged once and chyme samples were collected after 30, 120 and 180 min post-gavage. Proteins from raw (RC) and pasteurised (PC) creams appeared to be digested faster and to a greater extent. Free fatty acids (FAs) increased throughout the 3h postprandial period. Short and medium chain FAs were released more rapidly than long chain FAs which were hydrolysed to a greater degree from PC. The size of the fat globules of all creams increased in the stomach. Protein aggregates were observed in pasteurised and homogenised cream chyme. Protrusions, probably caused by the accumulation of insoluble lipolytic products, appeared at the surface of the globules in RC and PC chyme. Overall, PC proteins and lipids appeared to be digested to a greater extent.

In vitro digestibility of bovine β-casein with simulated and human oral and gastrointestinal fluids. Identification and IgE-reactivity of the resultant peptides

Stability during digestion is considered an important feature in determining the allergenicity of food proteins. This study aimed to provide an immunological characterisation of the digestion products of the major cow's milk allergen β-casein (β-CN) produced by in vitro orogastrointestinal hydrolysis with simulated and human digestive fluids. β-CN was unaffected by oral digestion, but quickly broke down during the early stages of gastric digestion. The degradation with human fluids was faster than that with commercial enzymes. There were similarities in the peptide patterns of the hydrolysates produced in both models, showing 20 peptides in common after gastric digestion. After gastroduodenal digestion, the human fluids gave less numerous and shorter peptides. The IgE binding of most of the individual sera used to the hydrolysates produced with simulated and human fluids increased at the end of the gastric phase and decreased when the duodenal digestion was completed. Two IgE-binding synthetic peptides: β-CN (57-68) and β-CN (82-93), which matched fragments released by β-CN following in vitro digestion with simulated and human fluids, consisted of the most immunoreactive areas of the protein. The similarities found between the in vitro simulated digestion system and that using human digestive fluids suggest that the former would provide a reasonably good estimation of the potential allergenicity of protein digests.

Transport across Caco-2 monolayers of peptides arising from in vitro digestion of bovine milk proteins

The entire panel of peptides produced from caseins (CN) and whey proteins (WP) that survive in vitro sequential gastro-pancreatic digestion and translocate across monolayers of Caco-2 cells, used as a model of the intestinal epithelium, has been characterised by HPLC and mass spectrometry. Among the milk-derived bioactive peptides, only minor amounts of mono-phosphorylated peptides arising from αs1- and β-CN were detected. The absorption behaviour of two resistant β-lactoglobulin (β-Lg) domains, β-Lg 125-135 and β-Lg 40-60, was studied in detail using synthetic peptides. The IgE-binding properties of the digests recovered from the apical and basolateral monolayer compartments were evaluated by dot-blot, using the sera of milk allergic children (N=5). Outcomes indicated β-Lg 127-135 as a possible "immune sensitising factor"in vivo. The almost complete loss of the IgE-affinity of CN and WP after digestion points out the need to design in vivo experiments to track the metabolic fate of dietary proteins.