Production and purification of tagatose with its evaluation in cookie formulations

Abstract

Tagatose is a rare sugar with significant potential as a low-calorie, low-glycemic alternative to conventional sweeteners. The large-scale application of tagatose remains limited by challenges in efficient production and downstream processing. This thesis investigates the production, purification, and functional application of tagatose-rich syrups derived from CaO-promoted isomerization of galactose. In Chapter 1, a literature review is presented covering the properties, production, and food applications of tagatose. The chapter examines both enzymatic and chemical isomerization routes for converting galactose to tagatose, with particular focus on CaO-promoted alkaline isomerization via the Lobry de Bruyn-van Ekenstein transformation. Downstream purification is reviewed alongside the functional role of tagatose in baked food systems, including its enhanced participation in Maillard browning and its effects on dough rheology and cookie texture. Key knowledge gaps in process integration and food-system performance for tagatose-rich syrups are identified, providing the scientific rationale for the subsequent experimental chapters. In Chapter 2, the impacts of neutralization strategy (CO2 vs. H2SO4) and ion-exchange resin processing on the purification of tagatose-rich syrups were evaluated. Results demonstrated that neutralization chemistry strongly influences the ionic composition of the feed syrup and, consequently, deionization efficiency. CO2-neutralized systems exhibited lower initial conductivity and improved ion-exchange performance compared to H2SO4-neutralized systems, where residual sulfate ions hindered effective removal. Sequential cation-anion exchange achieved significant reductions in conductivity and divalent ions (Ca2+ and Mg2+), producing syrups suitable for food applications. Empirical regression models were developed to relate resin dosage and contact time to conductivity reduction, providing predictive capability for bench-scale process optimization. In Chapter 3, the functional performance of the purified tagatose-rich syrup was evaluated in shortbread cookie formulations and compared with sucrose and commercial high fructose corn syrup (HFCS). Tagatose-containing formulations exhibited distinct physicochemical behaviors, including increased Maillard browning, altered dough rheology, and differences in moisture retention and texture. Cookies prepared with tagatose syrup showed darker color development, comparable or higher hardness, and modified adhesiveness relative to sucrose-based systems. This work establishes a systematic framework linking upstream reaction chemistry, downstream purification, and final food functionality. The findings provide critical insights into process optimization, demonstrate the feasibility of producing tagatose-rich syrups, and highlight their potential as functional sugar alternatives in bakery applications.