Fermentation of yogurt is one of the oldest methods practiced by human beings in order to transform milk into products. Its beneficial influence on human health and nutrition has existed in many civilizations and has been known for thousands of years.

Yogurt is one of the best-known of the foods that contain lactic bacteria. It is defined as a coagulated milk product that results from the fermentation of lactic acid in milk by Lactobacillus delbrueckii subspecies bulgaricus (L. bulgaricus) and Streptococcus salivarius subspecies thermophilus (S. thermophilus). Indeed, fermentation of the sugar found in milk (lactose) by these bacteria produces lactic acid, which acts on milk proteins to give yogurt its texture and its characteristics. Other lactic acid bacteria species, such as probiotic bacteria belonging to the Bifidobacterium and Lactobacillus genera, are also used to give yogurt unique characteristics.

As starter cultures for yogurt production, lactic acid bacteria species display symbiotic relations during their growth in milk. Thus, a carefully selected mixture of bacteria species is used to complement each other and to achieve a remarkable efficiency in health benefits.

The benefits of yogurt and lactic acid-producing bacteria such as yogurt species have been investigated in numerous studies in recent years. Studies showed promising health benefits for certain gastrointestinal conditions, including lactose intolerance, constipation, diarrheal diseases, colon cancer, inflammatory bowel disease, Helicobacter pylori infection, and allergies. Patients with any of these conditions could possibly benefit from the consumption of yogurt. The benefits of yogurt consumption to gastrointestinal function are related to effects mediated through the gut microflora, bowel transit, and enhancement of immune responses.