The investigation of structural conversion of Mogrosides, a group of triterpene-glycosides from Siraitia grosvenorii, in acid and yeast model systems using HPLC-ESI-tandem mass spectrometry

Mogrosides are major triterpenoidal saponins in fruits of Siraitia grosvenorii, Lo Han Kuo, with intensive sweetness and many biological activities. To establish an analytical protocol of mogrosides for food quality control, a liquid chromatography- electron spray ionization- tandem mass spectrometric method, LC-ESI-MS/MS, was developed to investigate the structural conversion of the mogrosides in acid and yeast model systems. A commercial extracted and concentrated product was used as studying material. The major component of the mogrosides was found to be the penta-glucosyl saponin, mogrosides V, in the commercial product. Its content was as high as 25.56% of the weight of the product studied. All types of mogrosides could be enriched by using reversed phase C-18 solid-phase-extraction cartridges in the fraction eluted out with 45-80% of methanol and separated by a reversed phase C-18 analytical HPLC column in a water/methanol gradient elution with 45-75% methanol ratio (V/V). Eleven different mogrosides differing in glucosly numbers and glycosidic linkages could be obtained from acid hydrolysis model system using 2N hydrocholoric acid solution with heating in 60°C for 3 hours and be distinguished through their molecular weight and specific fragment patterns in the positive ion mode of electrospray-ionization by a linear ion-trap mass spectrometric analysis, respectively. These glucopyranosyl units could be lost sequentially in the negative collision-induced dissociation (CID) mode on mass spectrometric analysis. In the yeast model system, Saccharomyces cerevisiae BY4741 wild type converted majority of mogrosides V into siamenoside I (with 4 glucosyl moieties), mogroside IV (with 4 glucosyl moieties) and mogroside III (with 3 glucosyl moieties) without substantial amount of mogrosides with one or two glucosyl moieties and aglycone. The structures of mentioned three mogrosides were further confirmed by nuclear magnetic resonance (nmr) analysis.he results indicated that the enzyme system of the yeast used could selectively hydrolyze the (1, 6)-beta-glycosidic linkage of mogrosides but not (1, 2)-beta-glycosidic linkage on the mogrosides. According the literature, the remaining mogrosides, siamenoside I, mogroside IV and mogroside III, still presents 195 ~ 465 times sweetness higher than sucrose. These results imply that the mogrosides can be used as a sweetener in the yeast fermented food system.