The Stability of Stevia
- Stability of high intensity sweeteners, such as stevia, is important for taste and safety
- Stevia is remarkably shelf stable as a dry powder, during manufacturing and processing, and in finished application over shelf life
- Stability of stevia has been proven under high heat and low pH conditions
Stevia is well known to the public as being 100% derived from nature, low-glycemic and tooth friendly. Stevia has other benefits that product developers should be aware of. It is pH stable, non-fermenting, water soluble, heat stable and has an excellent shelf life in typical food and beverage applications.
The Importance of Stability
Understanding the stability of high intensity sweeteners such as stevia is of vital importance. If a sweetener is not stable, then the sweet taste will deteriorate and the decomposition products could also give rise to off-flavors and potentially harmful by-products. In November 2011, the European Commission approved Regulation EU 1131/2011 approving of the use of steviol glycosides as a sweetener in foods and beverages (European Commission, 2011). This decision was based on extensive stability research reported on by the European Food Safety Authority (EFSA).
Stability testing of sweeteners should cover changes in physical, chemical, sensory and microbiological attributes over time. Stability should be evaluated to reflect three scenarios: 1) the sweetener itself when stored over time under various conditions 2) the sweetener during manufacturing and processing conditions for a variety of applications and 3) the sweetener in the final product stored over time under various conditions. With stevia, a typical measure for stability testing is the percent of total steviol glycosides remaining (%TSGs). The presence of various degradation products, such as steviol, can also be measured (Catharino, 2012).
Stability of Stevia Powder
Accelerated shelf life testing at 40°C and 75% relative humidity on a powdered stevia extract, revealed that over 95% TSG content was retained over the 122-week testing period (PureCircle, 2016). With that data, the predicted shelf life of stevia extract at ambient conditions is more than 5 years (ASTM, 2016). Research confirms the stability of single steviol glycosides as well. As a dry powder, rebaudioside M is stable for at least one year at ambient temperature under controlled humidity conditions (Prakash, 2014). Kroyer (2010), found that with 1 hour of heat treatment, stevioside powder was stable with treatment up to 140oC.
Stability of Stevia During Manufacturing and Processing
Stevia is generally heat stable so no sweetening power is lost during processing. For example, HTST (high temperature short time) and UHT (ultra high temperature processing) are commonly used for many beverage applications such as juices, iced tea and milk. Process testing performed by PureCircle® evaluated a sweetener comprised of multiple steviol glycosides at two conditions commonly seen in beverage processing: 1) pH of 3.2 at 88°C for 30 seconds (HTST) and 2) pH of 6.5 at 138°C for 10 seconds (UHT). No loss in TSG content was found for either treatment (see figure 1) (Pure Circle, 2016).
Published research confirms these findings. In coffee and tea applications made with stevioside, good stability was observed at elevated temperatures up to 120°C for one hour (Kroyer, 2010). Stevia is also stable in the presence of functional ingredients and other sweeteners. When incubated for up to four hours with individual water-soluble vitamins in aqueous solutions at 80°C, no significant changes were seen with stevioside and B-vitamins (Kroyer, 2010). Furthermore, a protective effect of stevioside on the degradation of ascorbic acid was observed, resulting in a significant delayed degradation rate. When formulated with other low-calorie sweeteners, no interaction was found at room temperature for the tested period of four months.
Stability of Stevia Over Product Shelf Life
It is important to evaluate stability over a range of pH. Most food and beverage applications are acidic in nature and necessitate ingredients such as stevia that are stable in acidic environments. Aqueous solutions of stevia buffered to a range of pH serve as model systems for applications such as soft drinks, coffee and tea. Stevioside, one of the steviol glycosides responsible for sweet taste, was found to be stable in aqueous solutions between pH values of 2 to 10 at 60°C and 80°C (Kroyer, 2010).
Stevia has proven stable over the shelf life of numerous products stored in various conditions. The first published research on the shelf life of stevia was published by Chang and Cook (1983). Results indicated that carbonated soft drinks formulated with rebaudioside A or stevioside had no significant chemical, microbiological or sensory changes when stored at room temperature for three and five months. Photodegradation of rebaudioside A was refuted in 2008 when the experiment was repeated by Clos et al (2008) with no resulting loss. A recent study has shown that the impact of ultraviolet light on the stability of rebaudioside A may be dependent on the buffer system used (Zhang, 2017).
Steviol glycosides have proven stable in a wide variety of food and beverages under normal shelf life conditions (Jooken, 2012). In a study of steviol glycoside blends in low fat milk, soy drink, fermented milk drink, ice cream, full-fat and non-fat yogurt, dry biscuits, and jam, no sign of decomposition of steviol glycosides was found in any of the samples over the course of shelf life testing. The authors concluded that the addition of steviol glycosides to a wide variety of foods and beverages do not alter the quality or the expected shelf life.
Stability is an important consideration when formulating foods and beverages with stevia. As an ingredient, stevia has proven to be stable as both a raw material and in a finished good. When incorporated into foods and beverages, stevia is stable under a variety of processing conditions including HTST and UHT. Furthermore, stevia remains stable throughout the shelf life of a wide range of products.
Figure 1 – TSG Content Before and After HTST and UHT Processing
- ASTM F1980-16, Standard Guide for Accelerated Aging of Sterile Barrier Systems for Medical Devices, ASTM International, West Conshohocken, PA, 2016, www.astm.org.
- Catharino, R. R. R. & Santos, L. L. S. On-line monitoring of stevioside sweetener hydrolysis to steviol in acidic aqueous solutions. Food Chem. 133, 1632–1635 (2012).
- Chang, S. S. S. & Cook, J. M. J. Stability studies of stevioside and rebaudioside A in carbonated beverages. J. Agric. Food Chem. 31, 409–412 (1983).
- Clos, J. J. F., DuBois, G. G. E. & Prakash, I. Photostability of Rebaudioside A and Stevioside in Beverages. J. Agric. Food Chem. 56, 8507–8513 (2008).
- European Commission, The. 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. 12, 205–206 (2011).
- Jooken, E. et al. Stability of Steviol Glycosides in Several Food Matrices. J. Agric. Food Chem. 60, 10606–10612 (2012).
- Kroyer, G. Stevioside and Stevia-sweetener in food: application, stability and interaction with food ingredients. J. für Verbraucherschutz und (2010). doi:10.1007/s00003-010-0557-3
- Prakash, I., Markosyan, A. & Bunders, C. Development of Next Generation Stevia Sweetener: Rebaudioside M. Foods 3, 162–175 (2014).
- PureCircle. Stevia and The PureCircle Advantage. (2016).
- Zhang, J. & Bell, L. N. Stability of the Stevia-Derived Sweetener Rebaudioside A in Solution as Affected by Ultraviolet Light Exposure. J. Food Sci. 82, 897–903 (2017).