Bioactive peptides are organic substances formed by amino acids joined by covalent bonds known as amide or peptide bonds. Although some bioactive peptides exist 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.

Nutraceuticals 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.

Considering that most functional peptides are present in complex matrices containing a large number of hydrolysed protein fractions, their separation and purification are required. Conventional pressure-driven processes can be used for amino acids and peptides separation but are limited by their fouling problems and their low selectivity when separating similar sized biomolecules.

Processes combining an electrical field as a driving force and porous membranes have been developed for the separation of biopeptides to obtain better-purified products. More recently, electrodialysis using ultrafiltration membranes has been developed to fractionate simultaneously acidic and basic peptides using a conventional electrodialysis cell, in which some ion exchange membranes are replaced by ultrafiltration ones.

After separation and identification of bioactive peptides in three hypoallergenic infant milk formulas, the identity of 24, 30, and 38 bioactive peptides was confirmed in each of the three infant milk formulas. A significant number of these peptides were reported as inhibitors of ACE. However, the presence of sequences with other biological activities such as antihypertensive, anti-thrombotic, hypocholesterolemic, immunomodulation, cytotoxicity, antioxidant, antimicrobial, antigenic or opioid was also confirmed.

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.

For instance, the effects of Allium sativum on total phenolic content, proteolysis by o-phthaldialdehyde assay, antioxidant activity by radical inhibition and capacity to inhibit a-amylase and a-glucosidase activities in vitro were higher in camel milk yogurt than cow milk yogurt.

The tendency to confer new functional properties to fermented dairy products by supplementation with bioactive peptides to develop health promoting foods is steadily increasing. One approach exploits the proteolytic system of lab or food grade enzymes, or the combination of both, to release the functional peptides from the milk proteins directly in the fermented milk products.

In another strategy, the bioactive peptides are obtained outside of the product through the hydrolysis of the purified proteins by the same enzyme sources. Finally, in the last procedure the bioactive peptides, initially identified from the milk proteins, are produced by microorganisms using recombinant DNA technology.

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.

On the other hand, some bioactive peptides have been identified in fermented dairy products, and there are already a few commercial dairy products enriched with blood pressure-reducing milk protein peptides. However, there still is a need to develop methods to optimise the activity of bioactive peptides in food systems and to enable their optimum utilisation in the body.

The separation and purification of bioactive peptides involving the development of automated and continuous systems is an important field for food chemists. Much effort has been devoted to developing selective column chromatography methods that can replace batch methods of salting out or using solvent extraction to isolate and purify bioactive peptides. These developments will allow the recovery of bioactive peptides with minimal destruction to guaranty their incorporation into functional foods or for specific nutraceuticals applications.

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.

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. The type, amount and activity of the peptides produced depend on the particular cultures used. Douchi, also a soybean product fermented by fungal cultures, contains antioxidant peptides released by microbial enzymes.

Chemical organic synthesis is an indispensable tool to obtain organic molecules displaying particular physicochemical properties. The use of in silico protocols as well as established experimental approaches, in solution or solid phase allow the design and construction of molecules with various molecular complexities that can be used for biological studies.

In recent years, there has been a growing interest in de novo design and construction of novel synthetic peptides that mimic protein secondary structures to develop potent peptide analogs and peptidomimetics displaying unique pharmaceutical properties.

Despite the significant progress in the isolation and purification of bioactive peptides from several natural sources, as well as the assessment of their bioactivities, there still are several obstacles to overcome, particularly from the technological viewpoint to produce them at large scale without losing activity.

The increasing interest of the scientific community in the identification, purification, chemical synthesis and uses of bioactive peptides active and the food industry to use bioactive peptides in commercial products will contribute to improving human health.