Probiotics and Prebiotics in Fermented Dairy Products

Abstract

The microbiota of the large intestine is thought to account for 95% of the total cells in the human body, to have a population of approximately 1011-1012 CFU/g of intestinal content, and it represents approximately 1012 cells/g dry weight feces. A lot of metabolic activity is carried out by the intestinal microbiota to support the constant elimination through feces. The intestine of the human baby is sterile at birth; the composition of the intestinal microbiota is relatively simple in infants but becomes more complex in adults. The intestinal microbiota is thought to derive from the microbiota of the own mother (vagina, skin, and mother milk) and from the environment. With regard to bacterial species and strains, there is a high degree of variability among human subjects, and this variability depends on age, diet, immune status, stress factors, and many other factors not yet completely known. Indeed, the normal intestine microbiota is as yet an unexplored organ of host defense (Isolauri et al. 2004). The main genera or species found within the intestinal microbiota include Bacteroides, Eubacterium, Ruminococcus, Clostridium, and Bifidobacterium, and, as subdominant microbiota, Escherichia coli, Veillonella, Staphylococcus, Proteus, Streptococcus, and Lactobacillus (Tannock 2003). New paragraph The metabolic activities of the intestinal microbiota are very diverse: for example the formation of short-chain fatty acids that act as carbon source for colonocytes, the synthesis of vitamins, and the activation or inactivation of bioactive food components. Its function is crucial for the development of the host gut mucosal immune system, for the anatomy of the intestine (Moreau and Gaboriau-Routhiau 2000), and it also has many implications in health and disease (Blaut and Clavel 2007). In general, it is possible to categorize the gut microbiota components on the basis of whether they exert potentially pathogenic activities, a mixture of potentially pathogenic and health-promoting activities, or exclusively potentially health-promoting aspects (Gibson et al. 2003). Species from the genera Bifidobacterium and Lactobacillus, commonly found among the human intestinal microbiota in healthy subjects, have a long tradition of being considered health-promoting bacteria, and it is from these genera that the most studied probiotic bacteria come from.