Betaine, also known as trimethylglycine or glycine betaine, is a naturally occurring zwitterionic quaternary ammonium compound derived from the amino acid glycine. It is abundant in sugar beets, spinach, and whole grains. Betaine serves as an important osmoprotectant in plants and microorganisms, helping cells maintain fluid balance under stress conditions. In human biochemistry, it functions as a methyl donor in the methionine cycle, converting homocysteine to methionine via betaine-homocysteine methyltransferase. This supports cardiovascular health by regulating homocysteine levels. In the food industry, betaine is used as a dietary supplement, flavor enhancer, and functional ingredient. It is highly stable under various pH and temperature conditions and exhibits hygroscopic properties.