**4. Bulgarian dairy products as functional foods**

For more than a decade, the focus of nutritional science aims toward optimal nutrition, the objective of which is the optimization of the daily diet regarding nutrients, non-nutrients, and other food ingredients that favor the maintaining of good health [57]. The increased lifestyle diseases, in combination with the high healthcare costs, are the reasons for the rising research to formulate and produce foods with functions that could improve health and well-being and lower the risk of or delay ongoing major diseases [58]. Within this context, the concept of functional foods has arisen.

A functional food must have health benefits and can be classified as one if it enhances target functions or reduces the risk of specific diseases, has to provide benefits beyond the basic nutritional functions, should be or look like a traditional food, and should have a dietary pattern and be a part of the normal daily diet. From this baseline, the most complete definition of functional foods was proposed by the EC Concerted Action on Functional Food Science in Europe (FUFOSE). It states that a functional food is one that beneficially affects one or more target functions in the human body beyond normal nutritional effects, relevant to improved health state and well-being and/or reduced risk of disease, and it is consumed as a normal food pattern, not in the form of a pill, capsule, or any other dietary supplement (European Commission, 2010) [59].

Dairy products have a special place in Bulgarian diet. After Stamen Grigorov's discovery, extensive research has begun on the unique nutritional characteristics of Bulgarian yoghurt. In 1909, the Russian biologist and Nobel Prize winner Elie Metchnikoff developed a theory regarding the prolongation of life. He proposed that there is a relationship between the increased life expectancy of Bulgarians and the daily consumption of yoghurt [60]. Then, it was suggested that the consumption of yoghurt is connected with the increased number of Bulgarian centenarians. Metchnikoff's main research was on lactic acid, which is proven to reduce the number of putrefactive microorganisms [61, 62]. Then, he further proposed another hypothesis that the inhibition of pathogens and the harmful fermentation of food in the gut can slow down the process of aging.

Studies report that *L. bulgaricus* possess high antimicrobial properties and are able to colonize the human intestines, which suggests its probiotic functions [63, 64]. More studies describe that regular consumption of yoghurt that contains viable *L. delbrueckii* and *Str. thermophilus* can improve decreased lactose intolerance and the overall digestion of lactose [65, 66]. From intensive research, Bulgarian yoghurt could be considered a dairy product with functional characteristics, as scientific results state that functional probiotic foods can modulate the microbial composition in the gut, thereby improving intestinal health [67, 68].

Our achievements clearly showed that products with a century-old tradition of production and consumption in the Balkans are a promising source of beneficial LAB microbiota with the capacity to transfer them into new safety food with functional properties.
