Alginic acid (alginate) is extracted from brown seaweeds (Phaeophyta, especially Macrocystis, Laminaria, Ascophyllum). It is a polysaccharide used as a gelling, thickening, and stabilising agent in food, pharmaceuticals, and biotechnology. Carrageenan is also produced from red seaweeds and is an option, but alginic acid is the most characteristic seaweed product. Gelatin is animal-derived (collagen); biotoxins are harmful substances, not commercial products.