Trehalose-water-salt interactions related to the stability of β-galactosidase in supercooled media

The conservation of desirable properties in foods and ingredients is often based on the maintenance of the amorphous metastable properties of the systems. Enzymes may be stabilized by drying in saccharide matrices, but a second excipient is generally required to improve sugar protective effects. The effect of electrolytes on the thermophysical properties of sugar systems is of special interest because of their major influence on water structure and their possible interactions with biomolecules. Salts affect the kinetics of very important changes in sugar systems such as crystallization. The purpose of the present work was to analyze fungal beta-galactosidase stability in supercooled systems of trehalose-containing electrolytes (water soluble acetates, citrates, and chlorides of magnesium and potassium). The degree of sugar crystallization was also related to enzyme stability. Potassium citrate and acetate improved enzyme stability during freeze-drying and thermal treatment of samples at water activity (a(w)) of 0.22. However, trehalose crystallization inhibition at a(w)=0.43 (which was about 50-60%, related to the system without salt) impaired enzyme protection. Certain salts may act retarding sugar crystallization, but in the presence of salts, trehalose crystallization is even more critical because the enzyme is confined in a highly salt-concentrated region. Thus, crystallization inhibition by sugar-salt combinations should be carefully conducted.