Bioactive peptides are defined as the fragments of AA sequences in a protein that confer biological functions beyond their nutritional value [ 25 ]. They have antimicrobial, antioxidant, antihypertensive, and immunomodulatory activities. Many of them exhibit common structural properties, such as a relatively small number of AAs, a high abundance of hydrophobic AA residues, and the presence of Arg, Lys, and Pro residues [ 24 ]. In animals, endogenous peptides fulfil crucial physiological or regulatory functions.
Additionally, many intestinal peptides secreted by Paneth cells have an anti-microbial function [ 27 ]. Furthermore, the brain releases numerous peptides to regulate endocrine status, food intake, and behavior in animals [ 28 ]. In the small intestine, peptide transporter 1 PepT1 is responsible for the proton-driven transport of extracellular di- and tri-peptides through the apical membrane of the enterocyte into the cell [ 29 ].
However, due to the high activity of intracellular peptidases in the small intestine [ 2 ], it is unlikely that a nutritionally significant quantity of peptides in the lumen of the gut can enter the portal vein or the lymphatic circulation.
It is possible that a limited, but physiologically significant, amount of peptides particularly those containing an imino acid may be absorbed intact from the luminal content to the bloodstream through M cells, exosomes, and enterocytes via transepithelial cell transport [ 30 , 31 ].
Diet-derived peptides can exert their bioactive e. The first food-derived bioactive peptide, which enhanced vitamin D-independent bone calcification in rachitic infants, was produced from casein [ 32 ].
To date, many angiotensin-I converting enzyme ACE -inhibitory peptides have been generated from milk or meat Table 2. There is evidence that these two proline-rich peptides may partially escape gastrointestinal hydrolysis and be transported across the intestinal epithelium into the blood circulation [ 35 ]. Similarly, the hydrolysis of proteins from meat [ 36 ] and egg yolk [ 37 ] also generates potent ACE inhibitors.
Adapted from Ryan JT et al. Many small peptides from animal products e. These small peptides can reduce the production of oxidants by the small intestine, while enhancing the removal of the oxidants, resulting in a decrease in their intracellular concentrations and alleviating oxidative stress Fig.
Many of the bioactive peptides have both ACE-inhibitory and anti-oxidative effects [ 36 , 37 ]. Additionally, some peptides from animal Table 4 and plant protein-hydrolysates [ 25 ] also have antimicrobial effects, as reported for certain endogenous peptides in the small intestine [ 27 ]. These antimicrobial peptides exert their actions by damaging the cell membrane of bacteria, interfering with the functions of their intracellular proteins, inducing the aggregation of cytoplasmic proteins, and affecting the metabolism of bacteria [ 42 — 44 ], but the underlying mechanisms remain largely unknown [ 27 ].
Adapted from Ryder et al. Inhibition of cellular oxidative stress by dietary small peptides in the small intestine. The small peptides, which are supplemented to the diets of animals particularly young animals , can reduce the production of oxidants by the small intestine and enhance the removal of the oxidants, leading to a decrease in their intracellular concentrations and alleviating oxidative stress.
Antimicrobial peptides generated from the hydrolysis of animal proteins or synthesized by intestinal mucosal cells. Adapted from Lima et al. The hydrolysis of certain proteins [e. This can be performed in vitro by using digestive enzymes from the small intestine of mammals e. Opioid peptides are oligopeptides typically 4—8 AA residues in length that bind to opioid receptors in the brain to affect the gut function [ 46 , 47 ], as well as the behavior and food intake of animals Table 5.
Furthermore, the protein hydrolysates containing opioid-like peptides may be used as feed additives to alleviate stress, control pain and sleep, and modulate satiety in animals. Opioid peptides generated from the enzymatic hydrolysis of animal and plant proteins in the gastrointestinal tract. A major goal for animal agriculture is to enhance the efficiency of feed utilization for milk, meat and egg production [ 48 ].
This approach requires optimal nutrition to support the function of the small intestine as the terminal site for the digestion and absorption of dietary nutrients [ 49 ]. To date, peptides generated from the hydrolysis of plant and animal proteins are included in the diets for feeding pigs, poultry, fish, and companion animals. The outcomes are positive and cost-effective for the improvement of intestinal health, growth and production performance [ 50 ].
The underlying mechanisms may be that: a the rate of absorption of small peptides is greater than that of an equivalent amount of free AAs; b the rate of catabolism of small peptides by the bacteria of the small intestine is lower than that of an equivalent amount of free AAs; c the composition of AAs entering the portal vein is more balanced with the intestinal transport of small peptides than that of individual AAs; e provision of functional AAs e.
In swine nutrition research, most of the studies involving the addition of peptides to diets have been conducted with post-weaning pigs to improve palatability, growth, health, and feed efficiency [ 53 — 58 ].
This is primarily because young animals have immature digestive and immune systems and weanling pigs suffer from reduced feed intake, gut atrophy, diarrhea, and impaired growth. Moreover, peptide products have been supplemented to the diets of calves [ 59 ], poultry [ 60 , 61 ], fish [ 62 , 63 ], and companion animals [ 64 ] to improve their nutrition status, gut function, and abilities to resist infectious diseases.
As noted previously, plant-source protein ingredients often contain allergenic proteins and other anti-nutritional factors which can limit their practical use, particularly in the diets of young animals [ 50 ] and companion animals [ 64 ].
For example, soybeans can be processed to manufacture soybean meal and soybean protein concentrates for the elimination of some anti-nutritional substances. However, the soy products still contain considerable amounts of protein-type allergens e. Fermentation of soybeans by the commonly used microorganism e. Likewise, 4.
The inclusion of plant-protein hydrolysate in diets is important in aquaculture because fish meal is becoming scarce worldwide. Furthermore, as a replacement of the expensive skim milk powder, the hydrolysate of soy protein isolate Finally, acidic hydrolysates of plant proteins e. There was a carry-over effect on enhancing growth performance during weeks 3—5 postweaning in piglets that were previously fed the SDPI [ 56 ], which was likely due to an increased area of the intestinal villus as well as improved digestion and absorption of dietary nutrients [ 57 ].
Similarly, Stein reported that piglets weaned at 20 days of age fed a weanling diet containing 1. Of note, these effects of the SDPI supplementation were dose-dependent. Likewise, the inclusion of 2. Thus, SDPI or other hydrolysates of animal proteins hold promise for animal production. Thus, the global annual volume of total animal by-products generated by the processing industries is approximately 60 billion kg annually.
Thus, protein hydrolysates from the by-products of pigs or poultry and from plant ingredients hold great promise in sustaining the animal agriculture and managing companion animals worldwide. Potential scale and economic values for the global use of animal and plant protein hydrolysates PH in animal feeding. The nutritional value of protein hydrolysates as flavor enhancers, functional ingredients, and precursors for protein synthesis depends on the composition of free AAs, small peptides and large peptides in the products, as well as their batch-to-batch consistence.
At present, such data are not available for the commercially available products of animal or plant hydrolysates and should be obtained with the use of HPLC and mass spectrometry. Only when the composition of protein hydrolysates is known, can we fully understand their functionally active components and the mechanisms of their actions.
In addition, the net rates of the transport of small peptides across the small intestine are not known for all the protein hydrolysates currently used in animal feeding. This issue can be readily addressed with the use of Ussing chambers [ 71 ]. There is also concern that some animal protein hydrolysates, which contain a high proportion of oligopeptides with a high abundance of basic AAs, have a low palatability for animals particularly weanling piglets , and, therefore, the inclusion of the protein hydrolysates in animal feeds may be limited.
Such a potential problem may be substantially alleviated through: a the addition of exopeptidases and a longer period of hydrolysis to remove basic and aliphatic AAs from the C- and N-terminals of the polypeptides; and b appropriate supplementation with glycine, monosodium glutamate and inosine.
Furthermore, the role of animal and plant protein hydrolysates in the signaling of intestinal epithelial cells and bacteria and metabolic regulation in these cells should be investigated to better understand how these beneficial products improve gut integrity, immunity, and health.
Finally, the potential of protein hydrolysates as alternatives to dietary antibiotics should be explored along with studies to elucidate the underlying mechanisms.
All these new lines of research will be particularly important for animals with compromised intestinal structure and function e. Plant- and animal-protein hydrolysates provide highly digestible peptides and bioactive peptides, as well as specific AAs e.
The industrial production of these protein hydrolysates involves: a strong acidic or alkaline conditions, b mild enzymatic methods, or c fermentation by microorganisms. The degree of hydrolysis is assessed by the number of peptide bonds cleaved divided by the total number of peptide bonds in a protein. Chemical hydrolysis is often employed to generate savory flavors, whereas microbial fermentation not only produces peptides but also removes anti-nutritional factors in protein ingredients.
In addition to their nutritional value to supply AAs, bioactive peptides usually 2—20 AA residues in length have antimicrobial, antioxidant, antihypertensive, and immunomodulatory roles.
These peptides exert beneficial effects on improving intestinal morphology, function, and resistance to infectious diseases in animals including pigs, calves, chickens, companion animals, and fish , thereby enhancing their health and well-being, as well as growth performance and feed efficiency. GW conceived this project.
YQH and GW wrote the manuscript. GW had the primary responsibility for the content of the paper. All authors read and approved this manuscript. None of the authors have any competing interests in the manuscript. This article reviews published studies and does not require the approval of animal use or consent to participate.
Yongqing Hou, Email: moc. Zhenlong Wu, Email: moc. Zhaolai Dai, Email: moc. Genhu Wang, Email: moc. Guoyao Wu, Phone: , Email: ude. National Center for Biotechnology Information , U. J Anim Sci Biotechnol. Published online Mar 7. Author information Article notes Copyright and License information Disclaimer.
Corresponding author. Received Oct 4; Accepted Feb This article has been cited by other articles in PMC. Abstract Recent years have witnessed growing interest in the role of peptides in animal nutrition.
Background A protein is a macromolecule usually consisting of twenty different amino acids AAs linked via peptide bonds. Definitions of amino acids, peptides, and protein Amino acids are organic substances that contain both amino and acid groups. For example, tryptophan is destroyed during the reaction, while sulfur-containing amino acids e.
Furthermore, amino acids such as tyrosine, serine, and threonine may have lower recoveries due to the nature of acid hydrolysis. However, some of the sulfur amino acids e. To accurately quantify these amino acids, the sample can be oxidized or alkylated prior to acid hydrolysis by HCl. For oxidation, typically with performic acid, the sulfur-containing amino acids are oxidized prior to acid hydrolysis by HCl.
This results in accurate quantitation of these amino acids in their oxidized forms. Alkylation alternatively allows for preservation of the sulfur- containing amino acids cysteine for accurate quantitation in their alkylated forms. Two of the most common alkylating reagents produce cysteine in either of two forms, pyridylethyl cysteine or carboxymethyl cysteine.
An added advantage of this alkylation process is that it does not impact other amino acids. Lastly, given the challenges quantifying some amino acids by HCl hydrolysis, there are alternative acid hydrolysis techniques that can be applied for specific amino acids.
One technique uses sulfonic acids, such as methanesulfonic acids MSA to quantify tryptophan and methionine in the sulfoxide form. While this reagent is non-volatile, it does preserve tryptophan and methionine sulfoxide for quantitation.
While acid hydrolysis using HCl is by far the most common technique to hydrolyze proteins and peptides, alkaline or base hydrolysis is often used to measure tryptophan. Because tryptophan is stable under basic conditions, this technique gives accurate quantitation of tryptophan and is widely used for a variety of samples, from foods and feeds to peptides and proteins.
However, alkaline hydrolysis cannot replace acid hydrolysis for the quantitation of all amino acids. Under alkaline conditions, arginine, cysteine, serine, and threonine are destroyed and cannot be quantified. Turns out, faster absorption may mean faster recovery, too. Because hydrolyzed protein powder contains smaller peptides than non-hydrolyzed protein, it's more rapidly absorbed in the GI tract and more readily available for use by the body, making recovery post-workout more efficient, says Blakely.
This can potentially improve recovery time and reduce muscle soreness," she says. A little extra background: When you work out, you create small tears in your muscles, which results in the breakdown of protein. Amino acids are needed to help repair those tissues. There are non-essential amino acids, which your body can make on its own, and then there are essential amino acids, which you need to get from food or supplements.
Certain essential amino acids called branched-chain amino acids BCAAs —leucine, valine, and isoleucine—are stored in the muscles for energy and play a significant role in muscle recovery. Because hydrolyzed protein has faster absorption, it might supply BCAAs to your muscles more quickly. This all makes sense in theory, but what does science say about hydrolyzed protein?
The short answer is that there isn't enough research. Moreover, research hasn't delved into the differences between hydrolyzed whey, casein, collagen , soy, and other plant-based proteins and their effectiveness for recovery compared to their non-hydrolyzed counterparts.
A small study in the Journal of Science and Medicine in Sport compared the recovery effects of hydrolysate whey protein versus whey protein isolate. In the study, 28 participants consumed either 25 grams of hydrolysate whey protein in flavored water or 25 grams of whey protein isolate in flavored water. Results showed that the participants who consumed the hydrolysate whey protein powder recovered their muscle power better and faster than those who consumed the flavored water with whey protein isolate after an intense workout.
However, there was no difference in muscle soreness between the two whey proteins. Research has shown that hydrolyzed protein powder can also help with restoring glycogen post-workout. FYI, your body uses glycogen for energy, which is stored in your liver and muscles. According to a small study in The American Journal of Clinical Nutrition , adding protein hydrolysate to a carbohydrate drink provides the same glycogen-replenishing benefits as drinking a higher-carb drink.
Participants drank their beverages every 30 minutes, and five hours post-exercise, muscle biopsies were taken. This study backs up previous research that adding protein to low-dose carbs can promote faster glycogen synthesis, aka the process of restoring glycogen, says Spano.
That's because the majority of the carbs you eat are converted into glucose for fuel and when you aren't using it, it's converted into glycogen. For glucose to convert into glycogen, insulin is needed to direct glucose from your blood to your liver and muscles. And hydrolyzed protein has been shown to have a faster insulin response than non-hydrolyzed proteins because the proteins are already broken down and it's absorbed into the body so quickly, says Michels.
An October review in the World Journal of Diabetes suggests that hydrolysate whey protein stimulates insulin secretion at a greater rate than intact whey protein and whey isolate.
If hydrolyzed protein might help you repair muscles and recover glycogen faster, it makes sense that it can give you an athletic edge over non-hydrolyzed protein, right? The body cannot make all the amino acids required to build different proteins.
It relies on protein intake from our diet to supply the essential amino acids. Amino acids can then be used in sequence to build up protein in the body.
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