Bioactive peptides, or BP, refer to specific protein fragments that have a positive impact on a variety of body functions and may influence one's health in a number of ways. Presently, it is estimated that there are more than 1500 bioactive peptides, and these are well documented in a database known as Biopep. You can also think of bioactive peptides as organic substances that arise when amino acids are joined by covalent bonds known as amide or peptide bonds.
Proteins, on the other hand, refer to a polypeptide that has greater molecular weight. Both proteins and bioactive peptides have a significant role to play in a variety of metabolic functions of living organisms and, by extension, human health. They are believed to have hormone or drug-like tendencies and this makes it possible for them to be classified according to their mode of actions such as anti-thrombotic, immunomodulatory, antioxidative, mineral binding, and opioid.
The composition, as well as the sequence of the amino acid, are the characteristics that are responsible for determining the nature of the activity of the peptides once they are released from their parent protein. The interaction between specific amino acids is responsible for the modulation of certain natural processes of the body.
As far as classification goes, it is possible to classify proteins as endogenous if they came from amino acids through the synthesis that occurs within an organism. They can also be classified as exogenous if they resulted from diet or if they were obtained from a source that is external to the organism. Proteins obtained from both plants and animals are viewed as potential sources of a wide range of bioactive peptides.
Bioactive peptides are being viewed as the new generation of biologically active regulators that have the ability to inhibit processes such as oxidation and microbial degradation in food substances. Currently, there are many studies exploring their potential for use as treatments for a variety of medical conditions and, as such, they are potential agents that could be deployed in improving and increasing the quality of life.
In the recent past, nutraceuticals and functional foods have received a lot of attention, especially as a result of their ability to impact human health as well as their ability to be used in the prevention of a variety of diseases. As a result, there is a lot of work and interest that is currently being devoted to the research and production of bioactive peptides.
Presently, it is not possible to predict the relationship between the chemical structure and the activity of a peptide. It is, however, known that the activity of a peptide is a factor of its structure which in turn depends on factors such as the composition of the amino acid, the types of amino acids found in the N and C terminals, the length of the peptide chain, the net charge of the amino acids forming the peptide, and the hydrophobic characteristics of the amino acid among other factors.
For example, peptides that tend to have higher ACE inhibitory activities have always been found to possess basic or aromatic N-terminal amino acids, positively charged amino acids on the C-terminals, and higher amounts of hydrophobic features. For a dietary component to be considered to be bioactive, the component must be able to impart a considerable biological effect at a physiological level. Also, the bioactivity must be potent enough to affect health in a positive way. This excludes the ability to potentially possess damaging effects such as mutagenicity, allergenicity, and toxicity. Below is a detailed look at some of the most desirable benefits as well as the pharmacological properties of bioactive peptides.
Bioactive peptides obtained from protein sources such as milk tend to have antioxidant properties which make them effective in preventing the peroxidation of essential fatty acids. For example, when you add Pro or Leu residues to the N-terminus of a His-His, there will be enhanced antioxidant activities of the dipeptide and this will further facilitate the synergy between the non-peptide antioxidants. On the other hand, studies have shown that the digestion of casein can produce phosphorylated peptides with properties of both lipophilic and hydrophilic antioxidant activities. This is because of both the metallic ion sequestering of ROS.
In the fish industry, it is estimated that nearly 60% of the products normally become waste. To put this waste to good use, and also to add more value to various underutilized species of fish, enzymes are currently being used to prepare protein hydrolysates. The protein hydrolysates obtained from fish have small quantities of bioactive peptides that are rich in antioxidant activities. This antioxidant potential of these hydrolysates is a factor of the amino acid composition as well as the ability to disrupt the tertiary structure of the parent protein through a variety of enzymatic hydrolysis that leads to an increase in the solvent accessibility of the amino acid residues.
The peptide obtained from a Spanish dry-cured ham extract obtained through size-exclusion chromatography has been extensively studied and found to possess water-soluble antioxidant activities. Some of the fractions showed great 1-diphenyl radical-scavenging activities, suggesting the presence of peptides with antioxidant activities. Peptides obtained from soy have also been shown to have exceedingly increased antioxidant activities whenever they are compared to intact proteins. For example, soy protein hydrolysates obtained from heated and native soy protein isolates display a variety of enzymes as well as a varying degree of hydrolysis and antioxidant activities.
The enzymatic hydrolysates obtained from wheat germ protein and lactoglobulin have free-radical scavenging and antioxidant properties. These properties have also been observed to be strongly present in hydrolysates obtained from gelatin, potatoes, and eggs. The detection or discovery of antioxidant peptide segment in proteins may be useful in helping the research world provide more elaborate explanations as to why it is believed that the intake of dietary protein may help in promoting animal and human health past the standard nutritional benefits that are already known. Digestion studies conducted in vitro tend to suggest that a mixture of peptides obtained from certain food proteins with the help of human digestive enzymes may have highly potent antioxidant activities.
Another potential source for the production of antioxidant peptides is the gut of shellfish. During a study, the GI digestion of oysters produced an active 1.6kda peptide whose amino acid sequences were discovered to be Leu-Lys-Glu-Asp. It was observed that this peptide had the capability necessary for the peroxidation of lipids and superoxide radicals. Alaska Pollock frame protein is a common waste in the industrial procession of fish.
The frame protein hydrolysate was fractioned and discovered to have APH-V which was shown to have extremely high antioxidative activities. In another study, it was observed that the peptide Leu-Val-Gly-Asp-Glu with potent antioxidant activity was isolated from the gastrointestinal tract of mussel muscle protein. During the studies, it was observed that the peptide had very high protective activity on lipid peroxidation compared to ascorbic acid and tocopherol when administered in similar doses. In yet another study, it was observed that another peptide with 16 amino acid residues had a very strong activity of lipid peroxidation when they are isolated from the peptic hydrolysate of Hoki frame protein.
Endogenous Antioxidant Peptides
One of the leading causes of pathogenesis and diseases in human beings is a process known as oxidation. Glutathione, which is a tripeptide is known to be very effective in protecting cells from the actions of free radicals. The dipeptide carnosine and belentine are known to have very high antioxidant and pH-buffering properties in the muscles of the cells. Several studies have suggested that melatonin may have the ability to protect cells from the effects of oxidation.
The endogenous peptide known as cyclo is normally found in high concentration in the central nervous system as well as several body fluids and the gastrointestinal tract plays a vital neuroprotective role in protecting a variety of body cells. In vitro studies conducted on rats have shown that cyclo may have the ability to enhance the cellular antioxidant capacity and the expression of small heat shock proteins. Also, there is a lot of evidence to suggest that cyclic peptides may have a role in ameliorating diabetes.
Antioxidant activities of peptides in a variety of food systems
As already mentioned, peptides obtained from milk proteins have antioxidant activities that may prevent the peroxidation process of essential fatty acids. When Pro or Leu residues are added to the N-terminus of His – His, it is observed that the dipeptide has improved antioxidant activities and may promote the synergy between non-peptide antioxidants. Several studies have also suggested that most of the peptide and protein hydrolysates obtained from plant sources have very high antioxidant activities. For example, peptides from whey proteins, soy proteins, casein, potato protein, corn protein muscle protein, and egg protein showed very powerful antioxidant properties.
Antioxidant peptide fragments that have methionine and tyrosine have significant radical scavenging activities and it is believed that they have a vital role to play in the overall antioxidant activity of the protein hydrolysates. The antioxidant properties of a variety of peptide mixtures as well as protein hydrolysates have been tested in situ studies and it was observed that some of them are already being used as part of the ingredient in the commercial processing of some foods.
Yolk, casein, whey, potato, and soy proteins have been showing in a variety of studies that they have the ability to inhibit lipid oxidation in muscle foods. During a study, a total of 21 peptides were identified and isolated from hydrolysate of bivalve mollusks. A sequence was then established with the help of MS/MS fragmentation data. After the peptides were chemically synthesized, it was observed that they had very high activity in radical scavenging assays. Through this strategy, it became possible to quickly, sensitively, and accurately analyze complex protein hydrolysates through the use of the techniques deployed in this study.
In yet another study, the proteins obtained from goat milk were hydrolyzed by pepsin to give caseins, whey proteins as well as protein fractions that had multiple soluble peptides. Proteins and peptides obtained from goat milk have also gotten a lot of attention, especially the bioactive peptides released from parent proteins of digestive enzymes. These peptides have shown reduced allergenicity compared to peptides derived from bovine milk. The peptides were also screened for radical scavenging activities and it was observed that casein and whey proteins had potent superoxide anion that had very strong scavenging activities. This is a subtle indication that soluble peptides obtained from digestion then subjected to pepsin processes have a powerful ability to scavenge superoxide radicals and as such, they present interesting opportunities for use as antioxidants in bioactive peptides.
Antimicrobial peptides, also known as AMPs, are a diverse group of molecules produced by a variety of tissues and body cells in plants, mammals, and other various animal species. The composition of the amino acids, their cationic charge, amphipathicity, and their size make it possible for them to attach to, as well as insert themselves into the membrane bilayers. The peptides are involved in a number of activities, including inhibiting the growth of cells and causing the death of various microorganisms like fungi and bacteria.
Most of the antimicrobial peptides have molecular weights of 10kda and they are usually encoded within the sequence of the parent protein precursors. Within the research world, antimicrobial peptides are currently being viewed as promising alternatives to therapeutic agents that can be used against a wide variety of pathogenic microbes. Due to the robustness of the antimicrobial peptides, there are more than 58 peptide drugs that have already hit the market and which are currently benefitting a large number of patients suffering from a variety of microbial ailments and conditions.
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