Proteins are composed of 20 different amino acids that are arranged in different ways and give each protein molecule its unique structure and function. Amino acids can be cleaved in certain places on proteins to produce peptide sequences of different sizes. Bioactive peptides are considered protein fragments that, after hydrolysis by proteolytic enzymes or fermentation, create positive functions or conditions that affect human health. The activity of peptides is based on their inherent amino acid composition and sequence.
The activity of peptides is based on their inherent amino acid composition and sequence. The size of active sequences may vary from two to twenty amino acid residues, and many peptides are known to exhibit multifunctional properties. Milk proteins are considered the most important source of bioactive peptides, and currently, more than 200 biologically active peptide sequences have been identified from caseins and whey proteins of most dairy animals. Best features include antihypertensive, antithrombotic, antimicrobial, antioxidant, immunomodulatory, and opioid peptides.
The excellent nutritional value and versatile functional properties of milk proteins are well established. The main protein fractions of milk are caseins and whey proteins, which show great differences in terms of functional and physiological properties. Compared to caseins, whey proteins are biochemically a more diverse group and include α-lactalbumin, β-lactoglobulin, immunoglobulins, lactoferrin, lactoperoxidase, and growth factors. Most of these proteins are found in abundance in colostrum, which shows their importance in the growth and development of a newborn baby.
Today, all these compounds can be enriched and purified on an industrial scale from bovine colostral whey or cheese whey.
Bioactive peptides are encrypted as inactive within the amino acid sequence of their parent protein molecule and can be released in the following ways:
1- Hydrolysis by digestive enzymes
2- Milk fermentation with proteolytic starter cultures
3- Proteolysis by microbial or plant-derived enzymes
In many studies, these methods have been successfully used in combination to generate novel functional peptides. The gastrointestinal enzymes pepsin, trypsin, and chymotrypsin have been shown to cleave a large number of antihypertensive peptides, casein phosphopeptides, antibacterial, antioxidant, immunomodulatory, and opioid peptides from caseins and whey proteins α-LA, β-LG, and GMP. Also, commercial proteolytic enzymes, such as alcalase, Flavourzyme, thermolysin subtilisin, and other proteases, have been employed to release various bioactive peptides from both caseins and whey proteins.
Many lactic acid bacteria (LAB) and probiotic strains have high proteolytic activity, and the release of different bioactive peptides from milk proteins by means of microbial fermentation is now well documented. The bioactive peptides released depend on the strain used and the fermentation time and conditions. A large number of starter cultures and probiotic strains have been used to study the release of such peptides, but Lactobacillus helveticus strains have been particularly prominent in the release of antihypertensive peptides. Starter cultures of yogurt, cheese, and commercial probiotic bacteria have also been shown to produce antihypertensive, antioxidant, antimicrobial, and immunomodulatory peptides in milk during fermentation.
Therefore, the improvement of the health quality of fermented liquid or semisolid dairy foods may be enhanced by the addition of bioactive peptides. For enrichment and isolation of bioactive peptides from the hydrolysates of milk proteins, membrane filtration systems, chromatographic methods, and selective precipitation have been developed in recent years and many companies now produce specific peptide concentrates.
It is now well established that bioactive peptides are formed in the production and ripening processes of various fermented dairy products as a result of proteolytic action by added starter cultures. In screening studies, a wide variety of bioactive peptides have been found in fermented dairy products, such as yogurt, sour milk, dahi, kefir, quark, and various types of cheese, for example, Cheddar, Edam, Emmental, Gouda, and many types of Italian cheese. The presence, specific activity, and number of bioactive peptides in fermented dairy products depend on many factors such as the type of starter cultures used, the type of product, fermentation time, and storage conditions.
The formation of peptides can be regulated to some extent by starter cultures and adjunct cultures. Still, it seems difficult to control the stability of the desired peptides during the dairy product storage period. For example, ACE-inhibitory activity increases during cheese ripening but decreases when proteolysis exceeds a certain level. Apart from the production during the ripening period, more bioactive peptides are likely to be formed in the gastrointestinal tract upon consumption of a fermented dairy product.
Commercial products containing bioactive peptides derived from milk protein are now available in many countries. These products include dairy and fruit-based drinks, sweets, gums, pastilles and capsules. They are claimed to have anti-hypertensive, anti-cariogenic, mineral-binding or stress-relieving properties.
Many preparations based on casein hydrolysates have been commercialized for various purposes such as dental care (Recaldent). Other interesting uses of bioactive peptides include lactium, Vivinal Alpha and Cysteine peptides, which claim to deliver stress-relieving effects.
PeptoPro is targeted to improve athletic performance and recovery after exercise.
Insulvital™ is a casein hydrolysate and is claimed to help regulate blood sugar peaks when taken with food.
Tegricel™ is a product made from milk peptides and other bioactive substances from milk and is claimed to reduce inflammation and promote healing in the digestive system.
Immunel™ is a combination of milk peptides recommended to support and balance total immunity.
Apart from cow's milk, bioactive proteins or peptides from other domesticated dairy animals are currently being used industrially to a very limited extent. The reason is that relatively little research has been done on these components and there is no suitable technology to separate and purify these components from colostrum or milk of species other than cows. This situation is expected to change in the future with increasing demand for bioactive substances derived from other species. In particular, such special applications can be considered in the fields of clinical and medical nutrition, biomedical, and sports nutrition.
The current global interest in developing functional foods provides a timely opportunity for the wide exploitation of native bioactive components of milk to improve human nutrition and health. This approach has been facilitated by the rapid increase in knowledge about the biological properties and mechanism of action of the main milk proteins, bioactive peptides, and growth factors. Commercial applications based on these components can be developed using more advanced industrial or semi-industrial fractionation and separation techniques. Biomining of specific milk molecules and their sale is now emerging as a new profitable business for the dairy and specialized bio industries. Examples of product development include specific casein and whey protein hydrolysates and products enriched with LF or bioactive peptides.
Apart from cow and colostrum, the milk of other animals, for example, buffalo, goat, sheep, mare, and camel, may be a good source of specific ingredients with targeted use to promote health or reduce the risks of certain diseases. Mare's milk is traditionally used in some countries as a substitute for human milk or to treat patients suffering from conditions such as tuberculosis, peptic ulcer, or chronic hepatitis. There is a new field of research called nutrigenomics, which can focus on studying the effects of milk proteins and peptides on the function of animal and human genomes and susceptibility to diseases. Research in this field may open new opportunities for optimal utilization of milk proteins from different species for human nutrition and well-being in the future.
Nielsen, S.D.H., Liang, N., et al., 2023. Bioactive milk peptides: an updated comprehensive overview and database. Critical Reviews in Food Science and Nutrition, pp.1-20.
Park, Y.W. and Haenlein, G.F. eds., 2013. Milk and dairy products in human nutrition: production, composition and health. John Wiley & Sons.