Prediction of the sweetening effect of Siraitia grosvenorii (luo han guo) fruits by two-dimensional quantitative NMR
During the last decade, dried fruits of Siraitia grosvenorii (luo han guo), also known as monk fruit, have become popular food ingredients. Luo han guo extracts, which are promoted as non-caloric natural sweeteners, are now incorporated into dietary supplements, soft drinks, and energy shakes. The compounds responsible for the sweetening effect are glycosylated cucurbitane-type triterpenoids, the so-called mogrosides. However, of the more than 40 known mogroside compounds, only 11-α-hydroxy-mogrosides exhibit a sweetening effect, whereas the other triterpenoids are non- or bitter-tasting. We have used two-dimensional quantitative NMR to determine selectively the content of 11-α-hydroxy-mogrosides in these dried fruits and thus to predict their sweetening potential. Homonuclear (H,H COSY) and heteronuclear (HSQC) methods were developed, validated, and compared. Both techniques were found suitable for the quality control of luo han guo fruits and extracts, the COSY experiment being advantageous with regard to accuracy, precision, and limit of quantification.