Bifidobacteria are normal inhabitants of the human gastrointestinal tract throughout lift, starting just days after birth, and are one of several predominant species of the colonic microflora, along with Peptostreptococcus, Eubacteria, Clostridia, and Bacteroides. Bifidobacteria differ from lactic acid bacteria in that they produce not only lactic acid but also acetic acid as major fermentation products. The classification of bifidobacteria has changed numerous times since they were discovered in 1899 in the feces of breast-fed infants. Since 1994, three additional species have been included in the list (B. lactis, B. inopinatum, and B. denticolens), with a current total of 32 species. A variety of probiotic effects of bifidobacteria are currently being investigated. Research reports suggests several potential probiotic advantages, in particular antimicrobial effects, immune-modulation reduction of the cancer risk, and modulation of gastrointestinal flora. As technological challenges related to viability and enumeration are being overcome, milks fermented with these anaerobic microorganisms(alone or in combination with lactic acid bacteria) are more able to provide consistently satisfying with large numbers of viable microorganisms. Over 70 products containing bifidobacteria are currently offered around the world, including fermented milks, cheese, buttermilk frozen desserts, candy, and pharmaceutical preparations.