GLUCOSE AND FRUCTOSE ADSORPTION ON SUCROSE CRYSTALS - THEIR ROLE AS HABIT-MODIFIERS

Experimental evidences show that alpha-D-glucose and beta-D-fructose w ork as habit-modifiers of sucrose crystals grown from aqueous solution s at high concentration only. Their ability to affect the sucrose habi t is examined from structural point of view, through stereochemical an alysis of both additive molecules and surface sites on some significan t polar and non-polar forms of sucrose crystal. We referred to the cla ssical TLK (terraces, ledges, kinks) model and restricted the adsorpti on interactions to the H-bondings only. Notwithstanding the simple qua litative model we adopted, our method of analysis appears satisfactory to interpret analogies and differences in selectivity between glucose and fructose. However, it is not able to explain why the additive con centrations, needed to induce macroscopic effects, are so high. To cle ar this aspect, we assumed a behaviour as ''disruption tailor-made add itives'' for both monosaccharides. Finally, sucrose crystals grown in the presence of equimolecular mixture of glucose and fructose (50 + 50 g/100 g H2O), examined by X-ray powder diffractometry, show the syste matic splitting of main diffraction peaks; the systematic effect revea ls the influence of both impurities on the bulk structure of sucrose c rystal.