Introduction

Stevia (Stevia rebaudianaBertoni) is an herbaceous perennial plant of the Asteraceae family. It is native of Paraguay, where it grows wild in sandy soils. They were used by indigenous peoples in Paraguay and Brazil since before recorded history.1Stevia rebaudianaleaves contain non-cariogenic and non-caloric sweeteners, whose consumption could exert beneficial effects on human health. It became more widely known outside central South America following the 1887 ‘discovery’ of stevia by botanist, Antonio Bertoni.2 Due to its sweetness, stevia has been given many names including sweet leaf, sweet herb of Paraguay, honey leaf and candyleaf.2,3The plant is new to Malaysia even though it is commercially cultivated in Brazil, Paraguay, United States of America and some Asian countries such as China, Japan, Korea and even Thailand.

The plant, especially the leaves, produces diterpene glycosides, primarily steviosideand rebaudioside, which have a sweetening effect reportedly 40–250 times sweeter than sucrose. For this reason, interest in this plant has picked up in recent years because of its potential as a non-calorific natural sweetener – a boon to the health food industry, particularly targeted to individuals with an obesity problem as well as diabetics. Interest in this plant has also arisen in Malaysia as a result of the sugar shortage not too long ago. Except in the extreme northern part of the Peninsula, the generally wet climate of Malaysia does not favour sugarcane cultivation, and the country has been largely dependent on sugar imports to satisfy local demand. Malaysians are known for their ‘sweet tooth’, consuming a lot of sugar not only in their drinks and beverages but also in their snacks, such as traditional cakes. This unhealthy habit may be partially responsible for the alarming rise in diabetic cases – from 0.65% of the population in 1960 to 16–18% in 1998.

Description

Stevia is an erect growing plant in Malaysia which can grow up to 20-30cm tall before it starts flowering. The leaves are sessile, green and developed in pairs measuring about 2.5-3.5cm wide and 3-6cm long. The flowers are white measuring about 8-15mm in diameter and formed at the tip of the growing shoots. The mature seeds are black and very small (0.5-1.0g/1000 seeds).1The stem is weak-pubescent at bottom and woody. The rhizome has slightly branching roots.

Stevia is highly adaptable and can be planted on various soil types. It is however more suited on loam and sandy loam soil with high organic matter content. The plant requires long days for maximum growth before it starts flowering. The critical sunshine hour is about 13 for maximum growth, biomass yield and thus the steviosides content. Under growing conditions with 13-16 daily sunshine hours, the crop can grow to 0.9-1.0m tall before it starts flowering.

Uses

Stevia leaf extracts are used in Japan, Korea and certain countries of South America to sweeten soft drinks, soju, soy souce, yogurt and other foods, whereas in the United States it is used as dietary supplements. The leaf extract of Stevia rebaudiana has been used traditionally in the treatment of diabetes6. The main sweet component in the leaves of Stevia rebaudianais stevioside, which are thought to possess antioxidant, antimicrobial and antifungal activity.

Stevioside and rebaudioside A are the main sweetening compounds of interest, which are 110-270 and 180-400 times sweeter respectively as compared to cane sugar. They are thermostable even at temperatures of up to 200 °C, making them suitable for use in cooked foods. S. rebaudiana has a great potential as a new agricultural crop since consumer demand for herbal foods is increasing and proximate analysis has shown that Stevia also contains folic acid, vitamin C and all of the indispensable amino acids with the exception of tryptophan. Thus, Stevia cultivation and production is an alternative to sugar for the diabetic patients and those on diet because of the very low calorie and no carbohydrates, fats or proteins.6 Since the leaves of Stevia plants have functional and sensory properties superior to those of many other high-potency sweeteners, Stevia is likely to become a major source of high-potency sweetener for the growing natural food market in the future.

Stevia sweetener extractives have been suggested to exert beneficial effects on human health, including antihypertensive, antihyperglycemic non-cariogenic, antihuman rota virus activities, glucose metabolism and renal function. Aqueous extract of Stevia rebaudiana dried leaves induce systemic and renal vasodilation, causing hypotension, dieresis and natriuresis in rats.

In addition to that, it has been demonstrated that the ethanolic extract of Stevia rebaudiana leaves contained high level of total phenolic compounds and were capable of inhibiting, quenching free radicals to terminate the radical chain reaction, and acting as reducing agents. Furthermore, the ethanolic extract of Stevia rebaudianaleaves showed strong antioxidant activity by inhibiting DPPH, hydroxyl radical, nitric oxide, superoxide anion scavenging and hydrogen peroxide scavenging activities when compared with standard ascorbic acid. Thus, it can be concluded that ethanolic leaf extract of Stevia rebaudianacan be used as an accessible source of natural antioxidants with consequent health benefits.

Regulatory Control in Malaysia

Commercial interest in steviol glycoside sweeteners has been high for a long time. Technical problems reducing a bitter or licorice aftertaste, coupled with regulatory barriers caused by inadequate specifications and unresolved safety questions, had prevented steviol glycoside sweeteners from becoming more widely marketed2. Questions on specifications, safety and special population effects have prevented steviol glycosides from obtaining a legal status permitting their use as sweetener in most countries.

In Malaysia, Stevia rebaudiana is allowed in the pharmaceutical products as sweetener. The safety of Stevia is still in the debate as there are many conflicting findings on the literature. Some regulatory bodies such as United States Food and Drug Administration (USFDA) has not permitted the use of whole-leaf or crude Stevia extracts as there are concerns on its safety such as blood sugar control, effects on the reproductive, cardiovascular and renal systems. However, more clinical research is needed before the safety of Stevia can be confirmed.

References

1. Globinmed. Global Information Hub on Integrated Medicine [homepage on the internet]. No date [cited 13/4/2014]. Available fromhttp://www.globinmed.com/index.php?option=com_content&view=article&id=79351:stevia
2. Carakostas M.C., Curry L.L., Boileau A.C. et.al. Overview: The history, technical function and safety of rebaudioside A, a naturally occurring steviol glycoside, for use in food and beverages. Food and Chemical Toxicology. 2008; 46: S1-S10.
3. Madan S., Ahmad S., Singh G.N. et.al. Stevia rebaudiana (Bert.) Bertoni- A Review. Indian Journal of Natural Products and Resources. September 2010; 1(3): p.267-286.
4. Tan S.L., Wan Zaki W.M., MuhamadGhawas, M.Mansor, P. and Zawawi M. 2010 Stevia (Stevia rebaudianaBertoni). In TeknologiPenanamandanPemprosesan Primer TumbuhanUbatan (Musa Y., Mansur P., Yahaya H., Wan Zaki, W.M. and Aini, Z. editor).
5. Preliminary Evaluation and Selection of Stevia under Malaysian Conditions. J. Trop. Agric. and Fd. Sc. 36 (2)(2008): 000-000.
6. Shukla S., Mehta A., Bajpai V.K. et.al.In vitro antioxidant activity and total phenolic content of ethanolic leaf extract of Stevia rebaudiana Bert.Food and Chemical Toxicology. 2009; 47: p.2338-2343.
7. Roberto L.M., Antonio V.G., Liliana Z.B. and Kong A.H. Stevia rebaudianaBertoni, source of a high-potency natural sweetener: A comprehensive review on the biochemical, nutritional and functional aspects. Food Chemistry. June 2012; 132(3): p. 1121-1132.
8. Goyal S.K., Samsher, Goyal R.K. Stevia (Stevia rebaudiana) a bio-sweetener: a review. Int J Food SciNutr. 2010; 61(1):p. 1-10.
9. Australian Government. Department of Health, Therapeutic Goods Administration. ACCM extracted ratified minutes, Meeting 2 [homepage on the internet]. C2010 [updated 2010 June 4; cited 2014 April 19]. Available from http://www.tga.gov.au/about/accm-recommendations-2010-02.htm
10. United States Food and Drug Administration.www.fda.gov (Data retrieved on 4 July 2014)