Improving Stability of Effervescent Products by Co-Crystal Formation: A Novel Application of Crystal Engineered Citric Acid

The major concern of the physical and chemical instability of effervescent products during manufacturing and storage is addressed through a co-crystallization strategy. Citric acid (CA) and sodium bicarbonate (SBC) are the essential components of effervescent products. CA is hygroscopic and led to an uncontrollable autocatalytic chain reaction with SBC in the presence of a small amount of moisture, causing product instability. The acid···amide dimer bond and layered structure of the citric acid-nicotinamide co-crystal restricts interaction of moisture with CA, making it nonhygroscopic, and improves the stability of effervescent products. The comparative study of effervescent products containing CA in its free form and as a co-crystal suggests a significant advantage of the use of co-crystal in effervescent products. This finding is supported by the mechanistic understanding developed through GAB and Y&N models obtained from moisture sorption data along with the computational investigations into moisture interactions with different crystal surfaces.