ABSTRACT
Surface active agents are present in nature and intervene in the biological processes of plants, animals, and humans. Saponins are glycosides occurring primarily in plants but also in starfish and sea cucumbers. Properties generally shared by this group of natural products are surfactant activity, haemolytic action, steroid complexing ability, and biocidal capability. The use of saponins as cleaning agents probably predates recorded history. They were certainly mentioned with different names in Egyptians, Greek, and Roman writings. Their use was already common in France and Germany in the 10th century (where it remained in use until the 19th century) and presumably across other countries in Europe in the late Middle Ages. Phospholipids play an important role in lung functions. The surface active material in the alveolar lining of the lung is a mixture of phospholipids, neutral lipids, and proteins. The lower surface tension in this surfactant system and the surface elasticity of the surface layers assist with alveolar expansion and contraction. Bile acids are essential for human and animal metabolism. They are converted to their sodium salts in the alkaline pH of the intestine and emulsify the food fats, thus facilitating their digestion.
