Acid-catalyzed hydrolysis of alcohols and their beta-D-glucopyranosides

The hydrolysis, in model wine at pH 3, of the allylic, homoallylic, and pro pargylic glycosides, geranyl-beta-D-glucopyranoside, [3'-(1 "-cyclohexenyl) -1'-methyl-2'-propynyl]-beta-D-glucopyranoside, (3'RS,9'SR)-(3'-hydroxy-5'- megastigmen-7-yn-9-yl)-beta-D-glucopyranoside, (3',5',5'-trimethyl-3'-cyclo hexenyl)-beta-D-glucopyranoside, E-(7'-oxo-5',8'-megastigmadien-3'-yl)-beta -(3-hydroxy-beta-damascone-beta-D-glucopyranoside), and their corresponding aglycons has been studied. In general, aglycons were more rapidly converte d to transformation products than were the corresponding glucosides. Glycoc onjugation of geraniol in grapes is a process that reduces the flavor impac t of this compound in wine, not only because geraniol is an important flavo r component of some wines but also because the rate of formation of other f lavor compounds from geraniol during bottle-aging is reduced. However, when flavor compounds such as beta-damascenone are formed in competition with f lavorless byproducts, such as 3-hydroxy-beta-damascone, by acid-catalyzed h ydrolytic reactions of polyols, then glycoconjugation is a process that cou ld enhance as well as suppress the formation of flavor, depending on the po sition of glycosylation. (3'RS,9'SR)-(3'-Hydroxy-5'-megastigmen-7'-yn-9'-yl )-beta-D-glucopyranoside hydrolyzed more slowly but gave a higher proportio n of beta-damascenone in the products than did the aglycon at 50 degrees C. Reaction temperature also effected the relative proportion of the hydrolys is products. Accelerated studies do not parallel natural processes precisel y but only approximate them.