Endocyclic double bond isomers and by-products from rebaudioside A and stevioside formed under acid conditions

The hydrolysis reaction of rebaudioside A and stevioside was studied under mild and strong acidic conditions at different temperatures and times. Exposure of rebaudioside A to vigorous acid conditions yielded three different aglycone cores which were purified by silica gel chromatography: compound 1 (isosteviol), 2 (steviol) and 3 (endocyclic isomer of steviol). Four new glucoside degradation products with an ent-kaur-15-en-19-oic acid skeleton together with three known compounds were obtained after mild acid hydrolysis from rebaudioside A and stevioside. Compounds were identified based on extensive 1D and 2D NMR measurements and/or MS/MS fragmentation: compound 4 (Endo-steviolmonoside), compound 5:(Endo-rebaudioside G(1)), compound 6 (Endo-steviolbioside) and compound 7 (Endo-rubusoside) while compounds 8-10 were identified as iso-rebaudioside A (Endo-rebaudioside A) (8), iso-rebaudioside B (Endo-rebaudioside B) (9) and iso-stevioside (Endo-stevioside) (10). Crystal structure determination of compound 3 and 6 allowed confirmation of their structures by X-ray diffraction. Acidic beverages based on steviol glycosides as sugar substitutes should be properly storage for avoiding the loss of their organoleptic properties by formation of these or other hydrolysis products.