Stevia rebaudiana Bertoni – a perennial semi-shrub plant species belonging to the genus Stevia, classified in Asteraceae family, has its origin from South America. The plant is well-known for its leaves to be rich in natural sweet compounds steviol glycosides, which are 300 times sweeter than table sugar. Thousand years ago, Paraguay natives and Brazilians extensively used the leaves of this small herbaceous plant to sweeten their bitter drinks, tea and medicines. Gurani Indians of South America had also widely used this plant for more than fifteen centuries. This plant was first described in detail by a Swiss botanist Dr. Moisis Santigo Bertoni in 1899. In 1905, it was named scientifically as Stevia rebaudiana after a Paraguayan chemist Dr. Rebaudi. It has many names in different countries of the world but more commonly known as sweet leaf, candy leaf, honey leaf, sweet herb, honey yerba, sugar leaf or sweet herb of Paraguay.
It has been introduced as a crop and commercially grown in many countries like, Brazil, Mexico, Korea, Columbia, Venezuela, USA, China, Thailand, Indonesia, Tanzania and Canada. At present, China is the main center of its cultivation as it is the largest exporter of steviosides – sweetening compounds in stevia. Japan is the largest consumer where stevia dominates 40% of its sweetener market.
Stevia plant could be found growing in semi-arid habitats ranging from grassland to scrub forest to mountain terrain. It can grow in marshy and salt-affected soil preferring sandy soils with warm sunny position. Suitable natural climate is semi-humid, sub-tropical with temperature extremes from 21oC to 43oC and average 24oC. It is a short day plant that grows up to 0.6m in the wild and flowers from January to March in the southern hemisphere.
When cultivated in fertile soil, stevia plant can grow up to 1 meter. It bears many branches with serrated opposite leaf arrangement. The size of the leaf may be up to 3-4cm. Pretty flowers are tiny, white in color with pale purple throat. For producing sweet leaves, these flowers must be pinched off or leaves must be harvested before flowering because flowers can steal sweetness from the leaves and also because chemicals responsible for leaf sweetness are at their peak before the onset of flowers. Cultivation of stevia is made through seed.
More than 100 phytochemicals have been isolated from stevia rebaudiana, of which the best known are steviol gylcosides – the chemical compounds responsible for stevia plants sweetness. These glycosides were discovered in 1931 by two French chemists. The leaves are the useable part which contain natural complex mixture of eight sweet diterpene glycosides viz. stevioside, steviolbioside, rebaudioside (A, B, C, D, E) and dulcoside A. Among these eight diterpene glycosides, stevioside is major constituent (3-18 per cent in dry leaves) and the sweetest glycoside that is 300-350 times sweeter than sugar followed by rebaudioside A (4-13 per cent in dry leaves). These two compounds have superior solubility in water and a positive taste profile that are safely metabolized by the body without any effect.
Besides these sweet glycosides, stevia is also a nutrient rich herb containing substantial amount of other nutrients, like 80 to 85 per cent water, protein, fibre, amino acids, free sugars, iminosugar steviamine, lipids, essential oils, ascorbic acid, beta carotene, riboflavin, thiamine, austroinulin, nilacin, rebaudi oxides, gibberellic acid, indole-3-acetonitrile, apigenin, quercetin, isoquercitrin, luteolin, miocene, kaempferol, stigmasterol, xanthophyllus, umbeliferone, chlorogenic acid, caffeic acid, dicaffeoylquinic acid, chromium, cobalt, magnesium, iron, potassium, phosphorus and trace elements.
Stevia has so many diverse beneficial attributes that the importance of this miracle plant cannot be neglected. Stevioside finds its uses as natural sweetener and flavor enhancer in pickles, soya sauce, ice creams, soft drinks, chew gum, cookies and tea. It is 100 per cent natural, non-fermentable low caloric product. It remains heat stable up to 198-200oC, an obviously superior character over artificial sweeteners.
In Pakistan, excessive sugar intakes and use of artificial sweeteners such as saccharin, aspartame, asulfam-K in beverages and food products have become a major health concern. Majority of our society is at risk for a high number of precarious health conditions that can lead to various diseases such as diabetes, obesity, blood pressure, heart diseases and cancer. According to a WHOs statement, Pakistan ranks seventh in diabetes population with 12.9 million diabetic patients. There is a fundamental need for an alternative sweetener in place of sugar, or other chemical sweeteners which have been proved as carcinogenics.
Pakistan has a diverse weather conditions with temperature range from 0oC in winter to above 48oC in summer season. These environmental conditions make Pakistan a suitable place for the cultivation of stevia. It can be cultivated in Punjab and Quetta in Balochistan. Promoting the cultivation of stevia can reduce burden on other sugar crops e.g. sugarcane and sugarbeet. It has the potential to replace some or all of the sugar in recipes without the physical characteristics of the food products. It has certainly earned the right to be considered a safe, natural sugar substitute and alternative sweetener used as a functional food ingredient to sweeten a diverse variety of consumer products. Less cost than sugar and relative potent sweetness intensities have proposed it cost effective sucrose substitute.
In conclusion, sweet herb Stevia rebaudiana Bertoni possesses a valuable future. Its metabolites have commercial value in many countries and have multiple uses as sugar alternatives in beverage, foods and medicine. Health promoting effects of this magic herb introduces it as a well-known therapeutic agent and an efficient herbal medication for the treatment of various diseases. Realizing the importance and potential of this plant, a road map must be formulated for its cultivation in Pakistan. Various research institutes in the field of plant sciences and agriculture need to conduct adaptation trials and to devise technology for its production in the country.
The author is M.Phil Research Scholar in Molecular Biology, National Center of Excellence in Molecular Biology, Punjab University, Lahore. He can be reached at <firstname.lastname@example.org> while the co-author is M. Sc (Hons.) Plant Breeding and Genetics, Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad.