08.09.2008: Stevioside and rebaudiana A (Rebiana) from Stevia rebaudiana Bertoni
Stevia is grown by small farmers in Paraguay and Brazil. Its culture is very difficult and does not suit global agriculture practices. That is why great agricorporations did not started extensive stevia plantations.
The dried leaves of Stevia rebaudiana Bertoni, contain the sweet-tasting stevioside 3-8%, rebaudioside A approximately 1%, D, and E, and dulcosides A about 0.27%. Rebaudioside D and E, together with dulcoside B are minor components counting for 0.03 to 0.04 % of the dried leaves.
Stevioside is a glycoside with a glucosyl and sophorosyl residue attached to the aglycon steviol.The structure of rebaudioside A is the same as that of stevioside except that the sophorosyl residue is replaced by a glucosyl-(1-3)-sophorosyl residue. Stevioside and rebaudioside A are therefore in focus of safety and stability studies.
Sweetening power: The sweetening powers of stevioside is 100, rebaudioside A 130, and the dulcosides 30 times that of sucrose.
The food industry is eager to introduce stevioside and rebaudioside A in its products because it is a natural, and overall a low priced sweetener.
Safety concerns about rebiana [1]
Kobylewskil and Eckhert 2008, in a study prepared for the CSPI, concluded that the FDA should ensure that the genetic toxicity studies that produced either positive or conflicting results be repeated. The authors added that studies that look at potential DNA adducts related to the potential reactive metabolites (C-13 carbonium ion or the epoxide) of steviol would be a strong addition to the genotoxicity data. Finally, the FDA should require carcinogenicity and toxicology studies in rats and in mice before accepting rebaudioside A as a GRAS substance or approving it as a food additive. The authors call for more genotoxicity tests, because of the evidence that derivatives of stevia that are closely related to rebiana damage DNA and chromosomes.
Coca-Cola and Pepsi are planning to introduce new drinks made with rebiana, an extract of stevia leaves that is 200 times sweeter than sugar. But according to the study of Kobylewskil and Eckhert, several, though not all, laboratory tests show that the sweetener causes mutations and DNA damage, which raises the prospect that it causes cancer. The CSPI asks the FDA for additional tests before accepting rebiana as Generally Regarded as Safe, or GRAS.
Stevia is legal in foods in Japan and several other countries, but the United States, Canada, and the European Union bar stevia in foods because of older tests that suggested it might interfere with reproduction. New tests sponsored by Cargill did not find such problems. [2]
Acute renal failure induced by steviol, breakdown product of stevioside [3]
Toskulkao and colleagues 1997 investigated the acute toxicity of stevioside and steviol (a product of enzymatic hydrolysis of stevioside). Stevioside and steviol at a dose as high as 15 g/kg BW was not lethal to mice and rats.
Hamsters did not die with Stevioside doses as high as 15 g/kg BW, however, their LD50 values of steviol were 5.20 and 6.10 g/kg BW for males and females, respectively. Severe degeneration of the proximal tubular cells of hamster kidneys, with acute renal failure induced by steviol were noted by the authors.
Stevioside and steviol are not mutagenic but toxic at high concentration [4]
Klongpanichpak and colleague 1997 found that stevioside and steviol showed no mutagenic effect on both tester Salmonella typhimurium TA 98 and TA 100 strains either in the presence or absence of metabolic activating system. The authors stress, however, that high concentration of stevioside and steviol showed some toxic which decreased in the presence of the metabolic activating system.
No genetic risc from stevioside and steviol [5]
According to Brusik 2008 the mutagenic activity of steviol and some of its derivatives, exhibited in strain TM677, related by some authors, was not reproduced in the same bacteria having normal DNA repair processes.-induced clastogenic effects at extremely high dose levels in vivo were found. The author concludes that neither stevioside nor steviol do not pose a risk of genetic damage following human consumption.
Stability of stevioside and rebaudioside A in carbonated acidic beverages [6]
Chang and Cook 1983, observing the stability of pure stevioside and rebaudioside A in carbonated phosphoric and citric acidified beverages during long-term storage, reported some degradation of both sweeteners after 2 months of storage at 37 °C, but no significant changes at room temperature or below following 5 months of storage of stevioside, or 3 months of storage of rebaudioside A. Exposure to 1 week of sunlight did not affect stevioside but resulted in approximately 20% loss of rebaudioside A. Heating at 60 "C for 6 days resulted in 0-6% loss of the sweeteners.
Degradation of stevioside and rebaudioside A is acid-promoted, not by sunlight [7]
Clos, DuBois and Prakash 2008, working for Coca-Cola Company and Cargill, performed stability tests with Rebiana, traded as Truvia , the common name of rebaudioside A. They reported no significant photodegradation in acidic beverages exposed to light, containing rebaudioside A or steviosid. Degradation of the sweeteners were acid-promoted.
The authors challenge the Chang and Cook 1983 article which had suggested that rebaudioside A is unstable to sunlight exposure, while the structurally homologous stevioside is stable, however found rebaudioside and stevioside light stable, and degradation of the sweeteners were acid-promoted.
The position of the European Union [8]
The European Commission in an opinion on Stevia Rebaudiana Bertoni plants and leaves from 1999, responding to a request for authorisation to market as a novel food for the plants and dried leaves of Stevia rebaudiana Bertoni concluded that there are no satisfactory data to support the safe use of these products as ingredients of food or as sucrose substitute for diabetics and obese individuals. No appropriate data were presented to enable the safety of the commercial plant product to be evaluated. Stevia was therefore banned in the EU.
[1] Kobylewski1, Sarah; Eckhert, Curtis D.: Toxicology of Rebaudioside A: A Review . University of California, Los Angeles.
http://cspinet.org/new/pdf/stevia-report_final-8-14-08.pdf
[2] CSPI: Lab Tests Point to Problems with Trendy New Stevia Sweetener. CSPI Urges More Testing Before Stevia Extract is Used in Food, Drinks
http://www.cspinet.org/new/200808281.html
[3] Toskulkao, C.; Chaturat, L.; Temcharoen, P.; Glinsukon, T.: Acute toxicity of stevioside, a natural sweetener, and its metabolite, steviol, in several animal species. Drug and chemical toxicology 1997, vol. 20, nr 1-2, pp. 31-44
http://cat.inist.fr/?aModele=afficheN&cpsidt=2715813
[4] Klongpanichpak S, Temcharoen P, Toskulkao C, Apibal S, Glinsukon T.: Lack of mutagenicity of stevioside and steviol in Salmonella typhimurium TA 98 and TA 100.
J Med Assoc Thai. 1997 Sep;80 Suppl 1:S121-8.
http://www.ncbi.nlm.nih.gov/pubmed/9347659
[5] Brusick D.J.: A critical review of the genetic toxicity of steviol and steviol glycosides.
Food Chem Toxicol. 2008 Jul;46 Suppl 7:S83-91. Epub 2008 May 16.
http://www.ncbi.nlm.nih.gov/pubmed/18556105
[6] Chang, Shin S.; Cook, Joanne M.: Stability studies of stevioside and rebaudioside A in carbonated beverages. Journal of Agricultural and Food Chemistry. 1983; 31(2) Pages 409 - 412; Doi: 10.1021/jf00116a056
http://pubs.acs.org/cgi-bin/abstract.cgi/jafcau/1983/31/i02/f-pdf/f_jf00116a056.pdf
[7] Clos, J.F.; DuBois,G.E.; Prakash, I.: Photostability of Rebaudioside A and Stevioside in BeveragesJournal of Agricultural and Food Chemistry Published online ahead of print, ASAP Article, doi: 10.1021/jf801343e
[8] European Commission: Scientific Committee on Food CS/NF/STEV/3 Final 17 June 1999: Opinion on Stevia Rebaudiana Bertoni plants and leaves .
http://www.food.gov.uk/multimedia/pdfs/stevioside.pdf