Selective fractionation of carbohydrate complex mixtures by supercritical extraction with CO2 and different co-solvents

Nowadays consumers hold high standards for the foods they consume and they also demand for products that can provide added healthful benefits; two of these products with an observed prebiotic activity, tagatose and lactulose, are the core of our study. These two carbohydrates are ketoses and have important biological activities, such as the stimulation of the growth of beneficial microorganisms in the colon. They are currently produced by alkaline isomerization of the corresponding aldose, followed by several purification steps to remove carbohydrate by-products and the unreacted aldose (around 30%).In this work, the possibility of using supercritical fluid extraction (SFE) technology to fractionate complex carbohydrate mixtures is analyzed. The study is based on previous results obtained for the fractionation of solid binary carbohydrate mixtures such as lactulose–lactose and tagatose–galactose. The appropriate selection of the co-solvent employed, together with the most suitable extraction conditions (including temperature, pressure and co-solvent flow rate) allows the selective extraction of the prebiotic ketose with high selectivity and recovery. The fractionation by SFE of a complex commercial carbohydrate mixture, containing around 74 wt.% of lactulose and 24 wt.% of different aldose carbohydrates, was carried out at the optimal extraction conditions attained in the study of binary mixtures. The selective extraction of the ketosugar lactulose was also observed in this case, obtaining an extract with 81 wt.% lactulose and around 67% yield.