1. Introduction

Breast milk is an unbeatable food that alone meets the requirements of babies up to 6 months of age. The exclusively breastfed infants tend to have a satisfactory nutritional status. But the advantages of breastfeeding go beyond nutrition and are unanimously defended by all health establishments ^[1]. Among the innumerable benefits we can mention, in the neonatal period: lower mortality rates among breastfed infants exclusively during the first six months of life and improvement in the most prevalent pathologies in the first months of life (otitis media, asthma). As in the future life of the infant: babies who are breastfed have a reduction in dental malocclusion, lower risk of obesity, and even higher intelligence ratios ^[2].

According to the European Consensus on “Scientific Concepts of Functional Foods” ^[3] a food can be considered as functional if it is satisfactorily demonstrated to affect beneficially one or more target functions in the body, beyond adequate nutritional effects, in a way that is relevant to either improved stage of health and well-being and/or reduction of risk of disease. A functional food must remain food and it must demonstrate its effects in amounts that can normally be expected to be consumed in the diet. It is not a pill or a capsule, but part of the normal food pattern. The almost indisputable evidence scientist endorse breast milk as the best functional food, source of benefits for the infant and for the mother [4,5]^[4][5].

2. Composition of Breast Milk

Knowledge of the composition of breast milk has highly increased and this will help understand the health benefits associated with breast feeding and to bring the composition of the infant formulas as close as possible to this “gold standard” ^[6]. Omics technologies, capable of detecting and identifying the set of molecules that exist in breast milk, have improved the understanding of their composition. This helps us to explain their physiological importance and their advantages from the point of view of infant health ^[7]. Moreover, the results of epidemiological studies and the growing knowledge of epigenetics allow us to understand the possible lifelong effects of breastfeeding ^[8]. Preventive medicine could also benefit from knowledge of the mechanisms by which human milk improves human development.

Breast milk is a complex matrix that contains a large number of bioactive components, with a distribution and organization that is not accidental. The excellent tolerability and absence of side effects of compounds derived from human milk is an obvious advantage. However, the difficulty of isolating and producing these bioactive substances on an adequate scale slows down the progress towards preclinical-clinical research and their nutraceutical application. Dairy components isolated from milk of other species such as bovines, transgenic cattle, or microbial cultures are used.

The study of specific structures with clear functional activity that are present in breast milk, allows the development and / or improvement of infant formulas. To bring them as close as possible to breast milk, attempts are made to reproduce the microstructure of functional MFG emulsions. Also, formulas are enriched with components of breast milk such as b-palmitate, ARA, DHA, taurine or carnitine. In addition, dairy fractions have been isolated from bovine milk with bioactive components and are now commercially available. Among these components are MFGM, a-lactalbumin, lactoferrin, and osteopontin. Chemoenzymatic processes have been used in these by-products of the dairy industry to approximate the oligosaccharides of the cow and goat serum permeate to HMOs, especially in terms of fucosylated oligosaccharides. Furthermore, engineered microbial systems are currently used to produce HMO in sufficient quantities. Some strains of Bifidobacterium and Lactobacillus present in breast milk are added to artificial formulas. However, we are still a long way from replicating the complexity of human milk and many questions about its clinical implications remain unanswered. The research findings in this field should serve, above all, as another compelling reason to encourage and support breastfeeding as the “gold standard” in infant nutrition.

Apart from infant formula, breast milk bioactive compounds can be used in other food products, nutritional supplements, nutraceuticals, or they can even lead to opportunities for translational medicine. Thus, 2'FL and LNnT HMOs are included in nutritional supplements to improve intestinal flora in adults with irritable bowel syndrome. Some casein-derived peptides are incorporated into nutraceuticals to help patients with pathologies as diverse as hypertension or cognitive impairment. Bovine α-lactalbumin is used in older adults or in athlete supplements to protect muscle mass and to modify neurological or behavioral outcomes such as sleep and mood. Microbial cultures and transgenic animals are used for the large-scale production of HAMLET (α-lactalbumin lethal to tumor cells), which is used in pharmaceutical formulations against cancer. Recombinant human lactoferrin and lysozyme are used in nutraceutical preparations as antimicrobial agents with clinical efficacy in the treatment of infectious diseases in humans. HBC has been used successfully for specific antimicrobial prophylaxis in healthy adults and to treat diarrhea in children. Adding recombinant human BSSL to pasteurized breast milk or infant formula improves growth rate and absorption of long-chain PUFAs in premature infants. The TGF-β present in human milk improves the nutritional and inflammatory pat-terns of Crohn's disease. But also, exosomes from bovine milk are used as drug delivery systems. Finally, we must not forget the probiotic strains isolated from breast milk that are used in the prevention and treatment of diarrhea and mastitis.