Prior to secretion in the intestine, conjugation with taurine or glycine takes place in liver cells to form conjugated bile acids (Figure 1). Only conjugated bile acids are able to act efficiently as an emulsifier. The unconjugated forms are insoluble in water due to their specific molecular structure and subsequent acidbase properties. They will be excreted in the faeces.
Some intestinal bacteria are capable of hydrolysing the amide bond and removing glycine and taurine. Clostridium perfringens, for example, has been shown to express high levels of the bile salt hydrolase enzyme. When hydrolysed, the bile salt is in its unconjugated form and loses its ability to act as an emulsifier, resulting in decreased fat digestion.
Imbalanced microflora and its effect on fat digestibility
The influence of microbiota, antibiotics and conjugated bile acid concentration on the adsorption of fat was investigated in broilers (Table 1).
The group without antibiotics showed high numbers of Clostridium perfringens in the small intestine and lower amounts of conjugated bile acids. Lower amounts of conjugated bile acids reduced the absorption of fatty acids and fat-soluble compounds (α-tocopherol).
Lipase activity was also assessed, and shown to be decreased in antibioticfree birds, suggesting an effect of the conjugated bile salts on the activity of lipase.