Betaine is a by product in the production of sugar, that is extracted from the molasses of the beet root (Beta Vulgaris). It is a secondary plant material that occurs in many wild harvested plants but also occurs in shellfish and seafood, such as crayfish and mussels. Betaines are a group of substances, however, it is not identical to the cocamidopropyl betaine that is often found in cosmetic products.
Betain is used in skin care to condition, lessen irritations and protect the skin against dryness. In surfactant products, it stabilized the foam, and when included in shampoos and hair care products, it increases the hair's strength and body.
see Heike Käser 2010, "Naturkosmetische Rohstoffe", Linz, Verlag Freya, 3. Edition 2012