Stevia Underlying the Sweetness: An Analysis via Mass Spectrometry of the Diterpene Glycosides Occurring in Stevia Leaves

A large part of the nutritional and dietary social and technological revolution that has been occurring since the middle of the twentieth century has focused on the issue of sugar and other sweeteners, and the various health problems that these can cause -- especially when consumed in abundance. The caloric content of sugar and most other naturally derived sweeteners has caused worries concerning the growing obesity epidemic in the Western world, and the United States especially, but many zero-calorie artificial sweeteners that have been developed have been shown to be carcinogenic. It is for this reason that naturally-derived yet zero-calorie sweeteners have been sought as dietary alternatives.

The leaves of the Stevia plant have been known to be naturally sweet by certain peoples for quite some time, and recently this plant and its potential to provide a sweetener that is healthy -- or at least is not detrimental to human health -- both in terms of its nutritional content and its carcinogenic potential (or lack thereof) on a more widespread and even industrial scale have come to wider attention. Determining the actual molecular and chemical properties of the Stevia leaf that provide the sensation of sweetness -- that is, determining the precise mechanisms that make this plant of interest to the nutritional and food sciences industries -- has been the matter of ongoing research and experimentation conducted from a variety of perspectives and with differing methods. This paper develops an understanding of the glycosides that produce the taste of sweetness in the Stevia plant as they have been identified using the method of mass spectrometry.

Methods

This paper does not itself represent the conducting of any primary or direct empirical research, but rather engages in a review of current literature published on the subject. The published research results incorporated in this review all examine the molecular structure of the Stevia leaf, and especially the existence of glycosides in the leaves, utilizing mass spectrometry as a tool for direct analysis. It is the hope of the author that a combined examination of the results of this technique as repeated in currently available literature will lead to more detailed, valid, and reliable understandings of the issue.

In some studies, minimal to no preparation of the samples was utilized before performing the mass spectrometer analysis, effectively demonstrating the chemical properties of the Stevia leaves in as close to a natural state as is possible (Jackson et al. 2009; Massoud 2001). Other studies used liquefied samples of Stevia leaves or even extracts of these leaves for mass spectrometer analysis, or utilized combinations of liquefied, dried, and natural sample substances (Gardana et al. 2010; Rajasekaran et al. 2008).
The level and number of the differences in sample preparation utilized in the incorporated studies is matched by the differences in the actual mass spectrometer analysis techniques utilized. Electrospray ionization mass spectrometry was used as the sole means of analysis in one study (Jackson et al. 2009), while this technique was utilized as a comparison in another study that explored new liquid-based mass spectrometry techniques (Gardana et al. 2010). Other studies also utilized these high performance liquid chromatography techniques, sometimes in combination with dry mass spectrometer techniques, in order to determine the precise chemical makeup of the Stevia leaves and the prevalence of diterpene glycosides in the plant at various stages (Rajasekaran et al. 2008; Massoud 2001).

Discussion

These differences in the preparation of the Stevia leaf samples and the specific tools of mass spectrometry analysis that were utilized in these different studies were significant in many respects, including in the further validation of each other's findings given the disparity of the different techniques used to establish these findings. At the same time, the results of these varying analyses are largely similar in their assessment of the diterpene glycosides and their prevalence within the leaves of the Stevia plant; this is the essential fact behind the mutual reinforcing of the different findings in these varied research studies and their published findings. Examining each of the results of these studies independently, however, yields a…