Saponins are a diverse class of amphiphilic glycosides found in many plants, consisting of a hydrophobic aglycone (triterpenoid or steroid sapogenin) covalently linked to one or more hydrophilic sugar chains. Their surfactant properties enable stable foam formation in aqueous solutions. Present in legumes, spinach, and quinoa, they exhibit cholesterol-lowering, antimicrobial, and anti-inflammatory activities but may act as antinutrients by chelating minerals or causing hemolysis at high doses. Over 1000 structures are known; specific extracts like Quillaja are used as food additives and vaccine adjuvants. Biological effects and solubility vary widely with structure.