A review on recent advancement in lactulose: From synthesis to application

Lactulose is a nondigestible disaccharide widely used in functional foods and pharmaceuticals. This review links advances in lactulose production with purification requirements and applications. Alkaline isomerization remains the most mature chemical route, while complexation and electrochemical methods modify product equilibria or regulate reaction conditions. Enzymatic routes involve transgalactosylation or cellobiose 2-epimerase-catalyzed lactose isomerization, with distinct substrate requirements and product profiles. These differences guide enzyme engineering and immobilization to improve selectivity, stability, and catalyst reuse. Reaction mixture composition also determines the roles of membrane separation, ion exchange, decolorization, and crystallization in product recovery. Product composition and quality subsequently influence pharmaceutical and food applications, discussed alongside physiological effects, matrix interactions, and processing and storage behavior. This process-wide perspective integrates catalyst and reactor development with purification and application-specific requirements, using productivity, catalyst lifetime, resource consumption, waste generation, and lactulose recovery to evaluate industrial feasibility and guide scale-up.