Bioactive Peptides, simply known as BP, refer to certain specific protein segments that display positive impacts on certain body functions or conditions that may ultimately impact health. At the moment, it is believed that there are over 1500 bioactive peptides that have already been reported in the Biopep Database – the database dedicated to keeping the records of all discovered bioactive peptides in the world. Bioactive peptides can also be viewed as organic substances formed by amino acids which have been joined by covalent bonds.
Proteins, on the other hand, are organic peptides or polypeptides with greater molecular weight. Both bioactive peptides and proteins have significant roles when it comes to regulating the metabolic functions of living organisms, and consequently, they also play important roles in regulating human health. They demonstrate to have therapeutic potential, and this makes it possible to classify them based on their modes of operation such as anti-thrombotic, anti-microbial, antihypertensive, mineral binding, immunomodulatory, and anti-oxidative.
The composition of the amino acid, as well as the sequence of the proteins, is responsible for determining the kind of activity of the peptides after they have been released from their precursor proteins. Certain natural processes within the body are normally regulated by the interaction of certain specific amino acid sequences responsible for forming part of the protein. If the proteins are obtained from amino acids through the process of synthesis, then the proteins can be classified as endogenous, but if they are obtained through diet or from external sources, then they are classified as exogenous proteins. Proteins obtained from plants and animals are regarded as potential sources of a wide variety of bioactive peptides.
Although the relationship between the structure and the functions of the proteins have not been well defined, many bioactive peptides tend to share the same structural features and these include peptide residues with lengths between two and 20 amino acids, and the presence of arginine and lysine groups, and hydrophobic amino acids. Bioactive peptides have also been shown to be resistant to the actions of digestion enzymes such as peptidase.
Currently, bioactive peptides are being considered as the new generation of biologically active regulators with the ability to prevent processes such as microbial degradation in foods. It is possible for them to be used as treatments for a variety of medical conditions, hence, contributing towards improving the quality of life.
In the recent past, nutraceuticals, as well as functional foods, have received a lot of attention, especially regarding the impact of bioactive peptides on human health, including their potential application in preventing as well as treating certain diseases and conditions. As a result, much effort and interest has been invested in the product and the properties of antimicrobial peptides have been studied in detail.
Though bioactive peptides have been identified and obtained from a variety of natural sources, and their properties and activities have also been explored in many disciplines, the focus of this text is on bioactive peptides present within various types of food matrices.
Sources of Bioactive Peptides
Of all the macronutrients found in foods, proteins and peptides are among the most important of them all. This is because they are responsible for supplying the body with all the required raw materials and because they also form a very good source of energy. Additionally, they form part of a complex series of organic transformations that usually take place during the process of food storage. Apart from their nutritional benefits, proteins and peptides also have distinct biological effects.
While we explore the sources of bioactive peptides, it should be noted that they are predominantly encrypted inside bioactive proteins. Currently, there is a lot of effort to develop on a commercial scale bioactive peptides and nutraceutical proteins designed for improving human health through the prevention or alleviation of certain medical conditions such as cardiovascular diseases, cancer, obesity, hypertension, strokes, and diabetes. Below is a brief overview of some of the sources of the bioactive peptides.
Bioactive peptides obtained from animal sources
Bioactive peptides obtained from animal sources have been attributed to a variety of health benefits. Blood has always been a vital source of proteins, and it has always been seen as a great source of bioactive peptides. Although the process of disposing of blood has always been a huge challenge for meat processors worldwide, the main blood protein known as serum albumin has not always received the kind of attention it deserves as far as bioactive protein sources are concerned.
In recent research, after serum albumin was hydrolyzed using trypsin of various concentration levels of trypsin, it was observed that it possessed activities such as an angiotensin-converting enzyme, antioxidation properties, and DPP-IV inhibition which is exceedingly necessary for glucose regulation.
Blood from the slaughterhouse is usually considered part of the meat production food chain that is yet to be fully exploited. In yet another recent study involving blood from the slaughterhouse, bovine hemoglobin was subjected to in vitro GI digestion. During this process, it was possible to identify close to 75 unique peptides with the help of low-resolution liquid chromatography.
With the help of high-resolution liquid chromatography, on the other hand, it was possible to identify up to 950 unique peptides. Hemoglobin fragments are known to portray vital physiological functions. For example, the α- and β- globin chains of this substance have the ability to potentially increase the length of the peptides to up to thirty amino acids.
Bioactive peptides from vegetal sources
Vegetal sources can also be excellent sources of peptides and such are being explored in a variety of studies currently. Bioactive peptides produced during the digestion of soy milk and soybean seeds have been extensively investigated in recent studies. Following the analysis of extracted protein samples from soybean seeds and milk, it was observed that soybean protein showed signs of degradation along the GI tract, leading to the generation of a large number of bioactive peptides, some of which had firmly established activity, while other had predictive microbial activity.
During this study, endogenous protease was also used to conduct the analysis in the presence of the peptides. It was observed that the peptides found in soymilk could also be formed during the processes of food processing.
There are certain cereal grains that have formed part of the human diet for decades, and which have been currently discovered to be incredible sources of bioactive peptides. Some of these cereal grains include rye, oat, rice, barley, corn, sorghum, and millet. Through scientific studies, it has been shown that there are many health benefits that accompany the consumption of whole grains, including the prevention of diseases such as cancer, cardiovascular diseases, and diabetes.
Oat and wheat have also been shown to have a very strong presence of ACE inhibitory peptides, as well as anti-thrombotic, antihypertensive, antioxidant, and opioid activities. Wheat and rice, on the other hand, have proteins whose peptidic sequences have anti-cancer activities. Barley and wheat, have also been studied as a source of bioactive peptides, and they have been found to have the greatest diversity and abundance of peptides with potential biological activities of all the cereal proteins. Additional research, is, however, needed to help in understanding the mechanism for releasing the active peptide sequences from the cereals.
Still, on the vegetal sources of bioactive peptides, it is worth considering the incredible amount of waste generated through the processing of food and vegetables. This is known to generate a significant amount of waste, the residues of which are mostly discarded or used for animal feeding. It should be noted that certain components of this waste are rich in proteins and can be potent sources of bioactive peptides.
A good example of such is the stones of fruits such as plums. Since it is cheap and a potential source of bioactive peptides, it can be a great ingredient in both the food and pharmaceutical industries. One method that can be used for extracting proteins from residual material such as the stone of plums may be through the use of high-intensity focused ultrasound.
Bioactive peptides obtained from milk
Dairy products, cheese, and bovine milk are known to be some of the greatest sources of bioactive proteins as well as peptides derived from foods in the world. This is possibly one of the major reasons why milk is such a vital nutritional component during the first months of the life of a newborn.
Milk protein possesses an incredible range of biological activities. For example, immunoglobulins have very good immunoprotective effects while lactoferrin present in milk has powerful antibacterial activities. The low concentration of growth factors and growth hormones mainly witnessed in colostrum may also have powerful roles to play in post-natal development in babies and infants.
The major significance of milk proteins is to provide nitrogen and amino acids to young mammals and also to immensely contribute to the protein dietary requirements in adults. The proteins obtained from milk are rich in biologically active peptides that are usually released within the GI system during the normal digestion and processing of foods. A good example is the opioid peptides found in dairy products which are rich in pharmacological properties just like those found in morphine and is also known to play a vital role in regulating the central nervous system.
Through the process of liquid chromatography-mass spectrometry, a considerable number of medium and low bioactive peptides were found to be present in human milk obtained from mothers with pre and full-term infants. The presence of many peptides is a confirmation that human milk is more susceptible to casein proteolysis compared to bovine milk. When the peptide sequence obtained from the human milk was characterized, it was possible to establish the pathway of casein hydrolysis which then facilitates the formation of small peptides. It was also discovered that the activities of plasma-like enzymes acting on certain specific lysine residues are the major step when it comes to casein degradation. This is then followed by endopeptidase-mediated cleavage of the oligopeptide to produce a multiplicity of short peptides that are different from one another by one or two amino acids.
Bioactive peptides obtained from eggs
Eggs are another great source of protein vital for human nutrition. Over the years, they have come to be known as vital sources of bioactive peptides which have made them very strong candidates in the formulation of a variety of diets and medicines. It has been possible to identify and characterize the biologically active peptides present in egg proteins and with these results, eggs are currently being viewed as a new source of biologically active ingredients for formulating functional foods that confer certain nutritional benefits to humans as well as for treating and preventing certain forms of diseases.
It has now been confirmed that eggs contain numerous substances with potential and already demonstrated therapeutic benefits in addition to providing the basic nutritional benefits. The bioactive peptide Arg-Val normally found in the egg white, after being chemically synthesized and assayed, showed to have ACE inhibitory activities and they showed great stability in a simulated GI digestion.
Bioactive peptides obtained from meats
Meat and meat products have, for years, been associated with increased risks of cancer, heart diseases, and obesity among other diseases. However, this has always been in total disregard of some of the vital health benefits that accompany the consumption of meat. The bioactive peptides obtained from meat products have the potential for inclusion in not just nutraceuticals, but also functional foods.
Fish and meat-derived peptides tend to have anti-hypertensive properties in in vivo studies, where they have also been observed to have anti-microbial activities. The potential benefits of these products are not in doubt, though there is still a need for more conclusive studies regarding the negative effects of meat on the human diet. With such, there will be a proper understanding as well as a compromise as to whether the risks of ingesting the meats outweigh the benefits that can be obtained from tapping into the bioactive peptides obtained from the meats.