Scientific interest is continuously increasing towards new biomolecules with beneficial effects on human health. These include bioactive peptides, short fragments of proteins consisting of 2-20 amino acids. There are different food sources from which bioactive peptides can be obtained, however the most important and most numerous studies have been performed in milk (Sánchez & Vázquez, Food Quality and Safety, 2017; Karami & Akbari-adergani, J Food Sci Technol, 2019).
Milk has always been considered a complete food, much important for the first stages of life as it contains all the essential components for growth such as high quality proteins, essential amino acids, minerals and vitamins. The two main protein fractions in milk are casein and whey protein. Caseins are phosphoproteins which they accounts for about 80% of all milk proteins. Whey proteins (which instead represent 20% of milk protein content) are mainly composed of β-lactoglobulin, α-lactalbumin, immunoglobulins, lactoferrin and lactoperoxidase, which support and stimulate the immune system.
Bioactive peptides in the milk can derive from both whey proteins and caseins and can originate through different mechanisms, such as enzymatic hydrolysis, microbial fermentation, food processing processes and gastrointestinal digestion. The main site of production of bioactive peptides is the intestine, where their physiological function can be exercised.
It is therefore very important to consider that not all types of milk have the same nutritional value. Indeed, different factors influence both positively and negatively the presence of bioactive peptides. The main factors are animal nutrition, lactation duration and also animal maintenance and health conditions. If these conditions are best managed, the quality of the milk obtained is optimal, with a high nutritional value and bioactive peptides content (Pecka-Kiełb et al., Mljekarstvo, 2018).
Furthermore, even thermal, chemical or physical processes during protein extraction and the entire production chain can influence the nutritional value. To maintain optimal milk quality, antibiotic residues used in animals for prophylactic and therapeutic purposes must also be controlled to avoid harm to human health. (Priyanka et al., Journal of Environment and Life Sciences, 2017).
The importance of bioactive peptides in human health is strongly emerging, and they can also cross the intestinal barrier and, through the bloodstream, reach the digestive, cardiovascular, immune or nervous systems. In these organs the bioactive peptides in milk exert numerous beneficial biological activities including anti-hypertensive, antidiabetic, immunomodulatory, antimicrobial and antioxidant (Sánchez & Vázquez, Food Quality and Safety, 2017; Park, Bioactive components in milk and dairy products, 2009; Korhonen & Pihlanto, Curr Pharm Des, 2003).
Regarding food supplementation with whey protein or milk, it is therefore clear that the protein content and the amino acid profile present on the label represent only a part of the nutritional value of a protein in powder form. It is in fact very important to be aware also of the origin of the milk and of all those factors that can affect, positively or negatively, the presence of the bioactive peptides so important for our health.