Sustainable Production of Low-Calorie Tagatose via CaO-Promoted Galactose Isomerization with CO2 Neutralization under Ambient Conditions

Tagatose is a low-calorie sweetener with comparable sweetness to sucrose. This study presents a green process for tagatose production via galactose isomerization using CaO at room temperature, followed by neutralization with CO₂, H₂SO₄, or H₃PO₄. At a CaO/galactose molar ratio of 1/1 and 0.5 M galactose, 86.7% galactose conversion and 43.7% tagatose yield were achieved when CO₂ was used for neutralization. Replacing CaO with CaCl₂, triethylamine, or arginine significantly reduced galactose conversion. Neutralization with H₃PO₄ resulted in higher galactose conversion (89.1%) but lower tagatose selectivity (53.6%) than H₂SO₄ (69.1%, 73.2%). Techno-economic analysis showed tagatose minimum selling prices of $0.80/kg (H₂SO₄), $0.81/kg (CO₂), and $0.85/kg (H₃PO₄). Sensitivity analysis identified plant capacity, IRR, and galactose price as key cost drivers. Life cycle assessment found CO₂ neutralization had the lowest environmental impacts. This work provides a sustainable approach to tagatose production and offers insights into nonenzymatic green sugar isomerization.