Steviol glycosides obtained from Stevia rebaudiana leaves are increasingly used in the food industry as natural lowcalorie sweeteners. Among them, the sweetness of major glycosides composed of glucose residues (e.g., stevioside and rebaudioside A) has been widely studied. However, the properties of minor natural products containing rhamnose or xylose residues are poorly investigated. In this study, five unreported steviol glycosides containing rhamnose or xylose were extracted from our developing stevia leaves, and their sweetness was evaluated. The highly glycosylated steviol glycosides were identified, and their structures were examined by fragmentation analysis using mass spectrometry. Chemical synthesis of these glycosides confirmed their structures and allowed sensory evaluation of minor steviol glycosides. Our study revealed that a xylose-containing glycoside, rebaudioside FX1, exhibits a well-balanced sweetness, and thus, it is a promising candidate for natural sweeteners used in the food industry.

Steviol glycosides are found in the leaves of Stevia rebaudiana Bertoni plants and have been used as natural, high-intensity sweeteners. Rebaudioside D (RebD) is a steviol glycoside derivative that has a similar sweetening profile to that of sugar; however, it is poorly soluble in water. Therefore, in this study, polymorphs of RebD showing greater solubility were investigated. We identified at least two novel polymorphs using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). We identified the transition to one polymorphic form of RebD (named "form α") by desolvation at about 50 ℃, and the other (named "form β") at about 70 ℃. Both forms exhibited greater water solubility compared to untreated RebD. This is the first report of RebD polymorphs with improved solubility, which may contribute to the production of RebD with both a sugar-like taste profile and high-solubility property.

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