STEVIA: AN EMERGING NATURAL SWEETENER FOR FOOD INDUSTRY

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Phytoconstituents of Stevia
Steviol Glycosides

The Joint Expert Committee on Food Additives (JECFA) committee in its fifty-first meeting (1999) stated that “Before the substance is reviewed again specifications should be developed to ensure that the material tested is representative of the material of commerce. Further information was required on the nature of the substance that was tested, on the metabolism of the Stevioside in humans and on the activity of Steviol in suitable studies of Genotoxicity in- vivo.”

JECFA in its 63rdmeeting (2004) at Geneva has noted that “Steviol glycosides are natural constituents of the plant Stevia rebaudiana bertoni which contain at least ten different glycosides, the major constituents being Stevioside and Rebaudioside A”. The material evaluated at that meeting contains not less than 95% glycosylated derivatives of Steviol, primarily Stevioside, Rebaudioside A and C and Dulcoside A, with minor amounts of Rubausoside, Steviolbioside and Rebuioside B, D, E and F. In the same meeting the JECFA has brought out a detailed tentative specifications of the Steviol glycosides which includes
1. Stevioside
2. Rebaudioside A
3. Rebaudioside C
4. Dulcoside A

JECFA has allotted a temporary ADI of 0 to 2 mg/kg BW for Steviol glycoside (expressed as Steviol) on the basis of the NOEL for Stevioside (970 mg/kg bw/day or 383 mg/kg bw/day, expressed as Steviol in the two years) after a study on rats and using a safety factor of 200. This safety factor incorporates a factor of 100 for inter and intra species differences and an additional factor of 2 because of the need for further information.

The committee noted that this temporary ADI only applies to products complying with the specifications. New tentative specifications were prepared, accompanied by a chemical and technical assessment. JECFA also recommended for the collection of following information for commercially available products15.

·         Analytical data on distribution and concentration of all components Steviol glycosides, including those that were not identified in the tentative specifications.

·         Method of analysis for the determination of all components Steviol glycosides, including those that were not identified in the tentative specifications.

·         The nature and concentration of the fractions that do not contain Steviol glycosides.

·         The quantities of residual solvents from isolation & purification steps of the manufacturing process.

·         The hydrolytic stability of the Steviol glycoside in acidic foods and beverages.

Chemical Name:
The following are the chemical names for the principal and secondary Steviol glycosides:
Stevioside: 13-[(2-O-β-D-glucopyranosyl-β-D-glucopyranosyl) oxy] kaur-16-PM-18-oic acid β-Dglucopyranosyl ester.

Rebaudioside A: 13-[(2-O-β-D-glucopyranosyl-3-β-Dglucopyranosyl-β-D-glucopyranosyl] oxy.kaur-16-PM-18-oic acid β-Dglucopyranosyl ester.

Rebaudioside C: 13-[(2-O-α-L-rhamnopyranosyl-3-O--β-Dglucopyranosyl- β-D-glucopyranosyl -β- D-glucopyranosyl-β-D-glucopyranosyl] oxy. kaur-16-PM-18-oic acid β-D- glucopyranosyl ester.

Dulcoside A: 13-[2-O-α-L-rhamnopyranosyl-β-Dglucopyranosyl] oxy kaur-16-PM-18-oicacid β-D- glucopyranosyl ester.

Chemical formula: 
The following are the chemical formulas for the principal and secondary Steviol glycosides:
Stevioside: C38H60O18

Rebaudioside A: C44H70O23

Rebaudioside C: C44H70O22

Dulcoside A: C38H60O17

Chemical structures of Steviol Glycosides:

Compounds  Name

R1

R2

Stevioside                           

β-Glc

β-Glc-β-Glc (2→1)

Rebaudioside A                    

β-Glc

β-Glc-β-Glc (2→1)                   

          ↓                 

          β-Glc (3→1)

Rebaudioside C

β-Glc

β-Glc-α-Rha (2→1)

          ↓

          β-Glc (3→1)

Dulcoside A 

 

β-Glc-α-Rha (2→1)

Steviol (R1=R2=H) is the aglycone of the Steviol glycosides. Glc and Rha represent, respectively, glucose and Rhamnose sugar moieties.

Pharmacological studies:
Antihyperglycemic Effect of Stevioside

Department of Endocrinology and Metabolism C, Denmark studied Antihyperglycemic effect of Stevioside in type 2 diabetic subjects. The acute effects of Stevioside in type 2 diabetic patients were studied. 12 type 2 diabetic patients were included in an acute, paired crossover study. A standard test meal was supplemented with either 1g of Stevioside or 1g of maize starch (control). Blood samples were drawn at 30 minutes before and for 240 minutes after ingestion of the test meal. The authors concluded that as compared to control, Stevioside reduce the incremental area under the glucose response curve by 18% (P= 0.013). The insulinogenic index (AUC (i insulin)/ AUC (i, glucose) was increased by ~ 40% by Stevioside compared to control (P<0.001) 16. Therefore “Stevioside reduces postprandial blood glucose levels in type 2 diabetic patients indicating beneficial effects on the glucose metabolism. Stevioside may be advantageous in the treatment of type 2 diabetes.

Antihypertensive effect of Stevioside
A double-blind placebo-controlled study of the effectiveness and tolerability of oral Stevioside in human hypertension was studied and no significant adverse effect was observed and quality of life assessment showed no deterioration.  Although the hypotensive effect of Stevioside was not better than other antihypertensive drugs, it appears comparable and almost all the active drugs. Almost all the active treatment group patients showed significant lowering of blood pressure. The antihypertensive effect of crude Stevioside obtained from the leaves of S.rebaudiana (Bertoni) Bertoni (Compositae) on previously untreated mild hypertensive patients was examined.

All adverse events were prospectively recorded but no major adverse clinical effects were observed ruing the trial. Systolic and diastolic blood pressure decreased (p<0.05) during the treatment with crude Stevioside, but a similar effect was observed in the placebo group. Therefore, cured Stevioside up to 15.0 mg/kg/day did not show an antihypertensive effect. Moreover, the results suggest that oral crude Stevioside is safe and supports the well-established tolerability during long-term use an as sweetener in Brazil17-19. Inhibitory effect of Stevioside on calcium influx to produce antihypertension was investigated.

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