Exploring the Multifunctional Roles of Betaine: Traditional Applications, Emerging Technologies, and Green Chemistry Innovations

Betaine, a simple natural zwitterion, is currently attracting widespread attention. Although historically labeled as an osmoregulator in agriculture and a methyl donor in animal nutrition, the molecule is now being repositioned at the forefront of green chemistry and materials science due to its unique physicochemical structure. This review critically explores the expanding horizon of betaine applications, bridging the gap between its established biological functions and its emerging roles in recently reported technologies, such as deep eutectic solvents (DESs), cocrystal engineering, and sustainable polymer synthesis. Beyond summarizing its versatile functionality across biomedicine, food science, and industrial formulations, we provide a comprehensive bibliometric analysis to map the evolution of research trends, identifying a clear focus toward industrial ecology and advanced materials. By synthesizing current advancements and discussing potential future directions, this work highlights betaine not merely as a supplement, but as a versatile molecular component with potential applications in sustainable materials and chemical engineering processes.