Inside the Stevia Leaf
The leaves of Stevia rebaudiana Bertoni contain several steviol glycosides, the compounds that give stevia intense and concentrated sweetness. All steviol glycosides share a common steviol backbone. The differences between the various steviol glycosides are due to the number and arrangement of sugar molecules attached to the steviol core. There are many steviol glycosides naturally present in the stevia leaf, but 11 steviol glycosides are typically focused on by product developers due to their relative abundance in the leaf and corresponding approved use.1 Generally rebaudioside A and stevioside are the major glycosides found in stevia leaves based on dry weight, with steviosides like rebaudioside D in much lower concentrations in the plant. A combination of any the individual approved steviol glycosides can contribute to the 95% or more steviol glycoside content required to meet the JECFA specification. In fact, for the purposes of food science and great taste, steviol glycosides are increasingly used in combinations in packaged foods and beverages to achieve the ideal sweetness profile given the food matrix or beverage composition.
Stevia Leaf Extracts
Stevia leaf extracts must adhere to the established specifications of identification and purity to be used in food by various national and global food safety authorities.2 The process of purifying stevia into high purity stevia leaf extract is similar to how other plant-based ingredients, such as cane sugar or natural vanilla extract, are made through a series of steps beginning with the harvested, raw plant material through to the end product. The process begins by drying the leaves and then steeping them in water. Next, the liquid extract is filtered and separated from the leaves and stems. The plant extract is further purified with water or food grade alcohol. If food grade alcohol is used, it is later removed. Other process may be used in some cases. Once this is complete, stevia extract compounds are the exact same compounds as found in the leaves, that is, they are molecularly identical. The extraction and purification process gives purified stevia leaf extract a cleaner, more sugar-like taste than crude stevia extracts, which may contain plant components and add additional flavors other than a purely sweet taste. And to reiterate, crude stevia extracts are not approved for use in foods and beverages around the globe. Only high purity stevia leaf extracts have been approved for use in foods and beverages. The end product is a highly purified stevia glycoside sweetener or flavor suitable for use in a range of foods and beverages. Depending on the sweetener glycoside mixture, the sweetness level can be 200 to 350 times sweeter than traditional table sugar. For example, it only takes an average of three stevia leaves to reduce 25% of the calories in a can of soda (12 oz; 355ml).
Working with stevia
Steviol glycosides are stable during preparation and storage conditions for a variety of foods and beverages, and are not sensitive to light exposure. However, because high-purity stevia leaf extracts are an intense sweetener, they do not provide bulk or other functional benefits that nutritive sweeteners like sugar provide in foods and beverages. This can present a challenge when changing a recipe to reduce nutritive sweeteners with stevia such that a direct replacement or substitution is usually not feasible. For example, sugar controls the formation of ice crystals in frozen desserts and enhances the smoothness and flavor of ice cream, prevents spoilage in jellies and preserves, speeds the growth of yeast in breads (which contributes to fluffiness), and promotes browning during baking and cooking. Therefore, replacing sugar with stevia in some recipes may require additional modification to the recipes, and in many foods and beverages stevia is blended with a nutritive sweetener like sugar to simultaneously reduce calories while maintaining the functional and taste benefits.
This was demonstrated in a study done in India where Kulfi (a popular Indian dessert) was produced with 50, 60 and 70% of the sugar replaced by 0.05, 0.06 and 0.07% refined stevia extract powder respectively.3 At higher levels of sugar replacement there was a significant decrease in specific gravity, melting rate, carbohydrate percentage and total calorie content and a significant increase in freezing point, hardness and fat, protein, ash and moisture percentage. Through experimentation, it was discovered that Kulfi prepared by replacing half the sugar content with stevia was found to be on par with the full sugar control. Reductions greater than 50% sugar replacement resulted in bitterness, lack of brownish appearance and presence of icy texture. Sometimes to help offset the functional results of removing up to half of the sugar, product developers will choose to include various bulking agents which can vary from polyols to complex carbohydrates that provide fiber. This suggests there is an ideal range of sugar reduction from a sensory and food science perspective and that stevia-sugar blends are often ideal in formulation strategies for sweetened foods and beverages. Food scientists continue to explore ways to use stevia sweeteners. Proposed uses for stevia include soft drinks, teas, jellies and jams, ice cream, yogurts and other dairy products, cakes and desserts, confections, and alcoholic beverages.
- European Commission Regulation (EU) No 1131/2011 of 11 November 2011 amending Annex II to Regulation (EC) No 1333/2008 of the European Parliament and of the Council with regard to steviol glycosides. Official Journal of the European Union. December 11, 2011. Retrieved June 13, 2013: http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2011:295:0205:0211:EN:PDF
- International Stevia Council. Steviol Glycosides. http://www.internationalsteviacouncil.org/index.php?id=196. Accessed on October 15, 2014.
- Giri A, Rao HG, V R. Effect of partial replacement of sugar with stevia on the quality of kulfi. J Food Scie Technol. 2014; 51(8): 1612-1616.