The New Nation
Professor Dr. M. Afzal Hossain
Stevia (Stevia rebaudiana) is an exotic plant in our country. It has both economical and medicinal importance. The main glycosidic compound accumulated in this plant is stevioside which is 250-300 times sweeter than sucrose. Stevia (also called sweetleaf or sugarleaf) is a genus of about 150 species of herbs and shrubs in the sunflower family (Asteraceae), native to subtropical and tropical South America and Central America. Stevioside is a glycoside of the diterpene derivative of steviol. Steviol glycosides are natural constituents of the plant Stevia rebaudiana Bertoni.
Man does not produce stevioside, or synthesize it in a laboratory or manufacture it. Man simply *extracts* it, just like nature produced it from the tiny leaf of a beautiful little South American plant. Thus stevioside is not "artificial" or "synthetic"; it is truly a natural product and also a "low-calorie" one.
Stevia is likely to become a major source of commertial sweetener for the growing natural food market in the future. The task at hand is to adapt stevia from a wild plant to a modern crop well suited to efficient mechanized production. In Canada, the necessary steps taken are: development of seed, seedling and crop production system including information on optimized crop inputs; weed and disease control; harvest and handling methods and a breeding program aimed at optimizing glycoside content and sensory characteristics. At present understanding the biology of the stevia plants and biochemistry of the sweet glycosides are prerequisites for conversion of stevia to a modern crop.
Stevia has garnered attention with the rise in demand for low-carbohydrate, low-sugar food alternatives. Stevia also has shown promise in medical research for treating such conditions as obesity and high blood pressure. Stevia has desirable effect on blood glucose, even enhancing glucose tolerance, and therefore it is attractive as a natural sweetener to diabetics and others on carbohydrate-controlled diets. Stevia is widely used as a sweetener in Japan, and it is now available in the US and Canada as well.
The plant leaves, their aqueous extract and purified steviosides are used as sweeteners. Stevia sweeteners have been produced commercially in Japan since 1977 and are widely used in food products, soft drinks (including Coca Cola), and for table use. Japan currently consumes more stevia than any other country; it accounts for 40% of the sweetener market.Today, stevia is cultivated and used in food elsewhere in east Asia, including China (since 1984), Korea, Taiwan, Thailand, and Malaysia. It is also found in part of South America (Brazil, Paraguay, and Uruguay) and in Israel. China is the world's largest exporter of stevioside.
Glycosides Present In Stevia
The leaves of stevia contain eight different steviol glycosides, the major constituent being stevioside. In terms of weight fraction, the four major steviol glycosides found in the stevia are:
2-4% rebaudioside A
1-2% rebaudioside C
Steviol is the basic building block of stevia's sweet glycosides. Stevioside and rebaudioside A are constructed by replacing the bottom hydrogen atom with glucose and the top hydrogen atom with two or three linked glucose groups, respectively.
Special features of stevioside:
250-300 times sweeter than sugar
Heat stable to 198-200 Celsius
Recommended for diabetics
Non-toxic readily soluble in water.
Stable to drying, preservation and storing
Extensively tested in animals
Extensively used by humans with no adverse effects
Stevioside Extract and Diabetes
Diabetics living in Asian countries have used stevia leaves with no side effects for many years.
Some studies have shown that stevia extract may help to reduce excessive blood sugar levels.During 1986 scientists from the Universities of Maringa and Sao Paolo studied the effect of stevia on blood sugar levels. The subjects that received the stevia were found to have significantly lower blood sugar levels. The outcome of this study gives a favourable indication that stevia can be beneficial to diabetics.
Even if stevia by itself may not lower blood sugar levels, its use allows diabetics to consume less sugar, which helps in achieving better blood sugar control. At this time stevia's mode of action in lowering the blood sugar is not fully understood. A trial in the Department of Endocrinology and Metabolism at Aarhus University Hospital, Denmark, showed that stevioside improves insulin secretion from mouse pancreas in the presence of glucose. The researchers stated, "Stevioside stimulates insulin secretion via a direct action on pancreatic beta cells." The results indicate that the compounds may have a potential role as an anti-hyperglycaemic agent in the treatment of type 2 diabetes mellitus".
Stevioside versus Artificial Sweetener
Artificial sweetener such as aspartame, saccharine, cyclamate etc. are used for diabetic subjects. But all of these artificial sweeteners have limitations e.g. aspartame a dipeptide of the amino acids aspartic acid and phenylalanine has been the subject of a vigorous public controversy regarding its safety and the circumstances around its approval because it has negative effects on headaches, brain tumors, brain lesions, and lymphoma ( Olney, 1996 and Roberts, 1991). Moreover there is also a positive correlation between saccharin consumption and increased frequency of cancer especially bladder cancer (Weihrauch M. R. and Diehl V, 2004). Since cyclamates appear to affect cells involved in the production of spermatozoa, the question has also been raised as to whether they may also be capable of damaging male reproductive DNA.
The sugar or sucrose is the most popular sweetener in the world. However, for adverse health effects of sucrose and known artificial sweeteners, interest in and search for no calorie natural sweeteners has been intensified in recent years.Very fortunately, stevioside was found which can satisfy the urge for sweet comsumption of diabetic subjects.
Research on Stevia at Biochemistry Laboratory of BAU
(A Prospect to Diabetic Subjects in Bangladesh)
Stevia research is in progress in the food biochemistry laboratory of Biochemistry Department, Bangladesh Agricultural University under the leadership of Prof. Dr. M. Afzal Hossain in collaboration with Bangladesh Sugar Research Institute (BSRI), Iswardi from the very beginig of the introduction of this plant in Bangladesh from Bankok.
However, no work has been carried out so far to utilize stevia extracts in the formulated food for diabetic subjects. Based on its potentiality as a food sweetner Prof. Dr. M. Afzal Hossain with his group has a vision to use stevioside extracts initially in milk products, biscuits, bread, chocolates, ice-creams, and soft drinks in order to meet the demand of sweet for diabetic subjects.
At the moment in his laboratory a group of post-graduate students are involved in a research project entitled " Formulation of cereal & legume based theraputic food containing semipurified antidiabetic and cholesterol lowering active principles from stevia plant"
Recently, a team of post-graduate students from the same Department visited NABISCO biscuit factory to demonstrate the use of stevia extract (extract produced in the BAU-Food Biochemistry lab) as an alternative to table sugar as an ingredient of biscuit. It is very encouraging to note that the sugar free buiscuits produced were sweet and generally acceptable. Research work is in progress to impove the colour, texture and delicacy of the biscuits. For the consumers' acceptance it is imperative that in addition to dietary quality, the product(s) is also attcactive.
Political Controversy About Stevia
Some countries like USA, Singapore and Hong Kong have restricted the use of stevoside by on "toxicological information on stevia is inadequate to demonstrate its safety". In 1991, based on an anonymous complaint, the United States Food and Drug Administration (FDA) labeled stevia as an "unsafe food additive" and restricted its import.The reason was limited toxicological information on it. This ruling was controversial, as stevia proponents pointed out that this designation violated the FDA's own guidelines under which any natural substance used prior to 1958 with no reported adverse effects should be generally recognized as safe . Similarly, the FDA requires proof of safety before recognizing a food additive as safe and a similar burden of proof is required for the FDA to ban a substance or label it unsafe. Now the question arises that why some countries restricted the use of stevia? It is believed that they acted in response to lobby by sugar industry and the FDA action against stevia "a restraint of trade to benefit the artificial sweetener industry.
On the contrary, millions of Japanese people have been consuming stevia for over thirty years with no reported or known harmful effects. In 2006, the World Health Organization (WHO) performed a thorough evaluation of recent experimental studies of stevioside and steviols conducted on animals and humans, and concluded that "stevioside and rebaudioside A are not genotoxic in vitro or in vivo .The US FDA itself states: "the stevioside, has reportedly been approved for use in foods in Brazil and Japan. The product is used in these countries as a table-top sweetener in virtually all food commodities and as a flavor enhancer in such products as teas."
Stevioside exhibits a menthol-like bitter aftertaste which diminishes with increasing purity of the product.
Available information indicates that stevioside is an excellent sweetner for diabetics. It has numerous benefits as a sweetener. It can be used by diabetics, obese persons and patients suffering from phenylketonuria, an illness which requires a strict diet without artificial sweeteners such as aspartame. Stevioside tastes about 300 times sweeter than table sugar, which means only a small amount is needed for sweetening purposes. It can be used as a table top sweetener, in soft drinks, baked goods, pickles, fruit juices, tobacco products, confectionery uses, jams and jellies, candies, yogurts, pastries, chewing gum, sherberts, etc.
Stevia represents a new opportunity for researchers, farmers and food industries alike. Since markets exist for stevia now, production and optimization must occur in parallel. The production of remarkably high levels of one class of secondary metabolite (stevioside) is of significant interest for chemists, biochemists and geneticists and may prove to be a foundation for the production of new metabolites in the future.As stevia is introduced in Bangladesh, research efforts are needed in developing appropriate techniques for commercial cultivation and utilization of this magic plant as a safe alternative of sucrose.
(The writer is a Scientist of international repute and Professor, Department of Biochemistry, Bangladesh Agricultural University, Mymensingh)