Bioactive peptides are organic substances formed by amino acids joined by covalent bonds known as amide or peptide bonds. Although some say it exists free in its natural source, the vast majority of known bioactive peptides are encrypted in the structure of the parent proteins and are released mainly by enzymatic processes.
Some bioactive peptides have been prepared by chemical synthesis. Bioactive peptides play a significant role in human health by affecting the digestive, endocrine, cardiovascular, immune, and nervous systems. Bioactive peptides are considered the new generation of biologically active regulators; they can prevent oxidation and microbial degradation in foods and also improve the treatment of various diseases and disorders, thus increasing the quality of life.
The growing interest in bioactive peptides has incentivised the scientific community and the food industry to exploring the development of new food additives and functional products based on these peptides. The present review highlights the recent findings on the identification, bioassays, and use of bioactive peptides, as well as their potential use as food additives and in the development of functional products.
The fish processing industry produces more than 60% by-products as waste. To use these wastes, and to add value to several underutilised fish species, protein hydrolysates from fish proteins are being prepared using enzymes. These fish protein hydrolysates contain small bio active peptides with antioxidant activity.
Antimicrobial peptides (AMPs) are an abundant and diverse group of molecules that are produced by many tissues and cell types in a variety of invertebrate, plant, and animal species. Their amino acid composition, amphipathicity, cationic charge and size allow them to attach to and insert into membrane bilayers. These peptides are involved in the inhibition of cell growth and in the killing of several microorganisms, such as bacteria and fungi. Antimicrobial peptides are usually below a MW of 10 kDa and encoded within the sequences of native protein precursors, may also be generated in vitro by enzymatic hydrolysis.
Immunomodulatory peptides derived from hydrolysates of rice and soybean proteins act to stimulate reactive oxygen species (ROS), which triggers non-specific immune defence systems.
Peptides derived from milk proteins have also shown antioxidant activity to prevent peroxidation of essential fatty acids. The addition of a Leu or Pro residue to the N-terminus of a His-His, dipeptide will enhance antioxidant activity and facilitate further synergy with non-peptide antioxidants (e.g., BHT).
Proteins and peptides from egg, milk, soy, and plant sources have shown anti-inflammatory properties. Ovotransferrin is an egg white protein well known for its antibacterial activity.
Antihypertensive peptides, also known as ACE inhibitors have been derived from milk, corn, and fish protein sources.
A large number of proteins and peptides of plant and animal origin are known to exhibit cytotoxic effects. There is evidence that many cytotoxic compounds described in the literature exclusively affect malignant cells leading to the assumption that a cancer protective effect could exist for such bioactive proteins and peptides.
The endogenous ligands for opioid receptors are peptides, also known as endorphins. These peptides share the common N-terminal sequence of Tyr-Gly-Gly-Phe-(Met or Leu), which has been termed the opioid motif; this is followed by various C-terminal extensions yielding peptides ranging from 5 to 31 residues in length.
A potential target for food protein-derived bioactive peptides is calmodulin (CaM), a protein that plays important roles in maintaining physiological functions of cells and body organs.
Metabolic syndrome consists of a deadly quintet of factors, namely diabetes, centripetal obesity, hypertension, dyslipidemia (elevated triglycerides, dense low-density lipoproteins, and low high-density lipoproteins), and alterations in the thrombotic potential that are related to hyperinsulinemia and insulin resistance.
Applications and production in food industry
Nutraceuticals
These are substances of natural origin that can be extracted from various sources (e.g., fruits, plants, lignocellulosic biomass and algae) and that have important health benefits when incorporated into food or pharmaceutical formulations. In recent years, functional foods and nutraceuticals have attracted much attention, particularly for their impact on human health and prevention of certain diseases.
Functional ingredients
Peptides derived from the milk of cow, goat, sheep, buffalo and camel exert multifunctional properties on human health. Additionally, medicinal plants are a rich source of natural antioxidants that are increasingly used in food manufacturing, because they provide valuable nutritional and therapeutic properties and retard oxidative degradation of lipids thus improving, the quality and nutritional values of foods regarded as functional.
Production
There is an increasing commercial interest in the production of bioactive peptides from various sources (Figure). Industrial-scale production of such peptides is, however, hampered by the lack of suitable technologies which retain or even enhance the activity of bioactive peptides in food systems.
Enzymatic hydrolysis
Enzymatic digestion is the most efficient and reliable method to produce peptides with target functionalities, including antioxidant activity. A broad range of antioxidant peptides and peptide mixtures (hydrolysates) have been produced from soy, corn, potato, peanut, milk, whey, egg, and meat proteins. The antioxidant efficacy of protein hydrolysates and peptides depends on the source of proteins, the protein substrate pretreatment, the type of proteases used, and the hydrolysis conditions applied. Both pure and crude enzymes can be used to produce antioxidative peptides. However, to reduce the production cost, crude protein mixtures are preferred.
Microbial fermentation
The production of antioxidant peptides by microbial fermentation rather than using purified enzymes is an integral part of healthy food production in many countries. Natto and tempeh are fermented soybean products that contain antioxidant peptides by the action of fungal proteases.
Chemical synthesis
Chemical organic synthesis is an indispensable tool to obtain organic molecules displaying particular physicochemical properties.
Bioactive peptides from foods are valuable functional agents in healthy diets that can prevent and treat diseases. Consumer awareness of the effects of functional foods on health is a strong drive for the search and production of bioactive peptides in foods. Milk derived tripeptides the most studied food derived antihypertensive peptides and have shown positive effects in human studies.
(The author is junior scientific officer, Hi-Tech Laboratory, DTL, Drugs Control Department, Bangalore . He can be contacted at dtlsbcs@gmail.com)