Extraction of stevia

COMMERCIAL EXTRACTION OF STEVIOL GLYCOSIDES

The Stevia rebaudiana Bertoni comprises a complex mixture of compounds including eight glycosides: stevioside, steviobioside, dulcoside, and rebaudiosides A, B, C, D, and E. The most abundant substances are stevioside and rebaudioside A.

There are many patents for the commercial extraction of steviol glycosides and these patents can be classified as those based on solvent,  solvent plus a decolorizing agent,  adsorption chromatography , ion exchange, and selective precipitation of individual glycosides. The most favoured extraction processes involve four steps: aqueous or solvent extraction, ion exchange, precipitation or coagulation with filtration, then crystallization and drying.

All the conventional extraction processes follow a similar methodology ie the stevia leaves are extracted with hot water or alcohols. In some cases, the leaves are pretreated with nonpolar solvents such as chloroform or hexane to remove the essential oils, lipids, chlorophyll, and other nonpolar substances.

A Japanese patent for the production of stevia glycosides uses supercritical fluid extraction (SCFE) with CO₂ and a cosolvent. Methanol, ethanol, and acetone were used as cosolvents. The purification step is accomplished by adsorption.

The extract is clarified by precipitation with salt or alkaline solutions. The extract is concentrated and redissolved in methanol for crystallization of the glycosides. The crystals formed are almost pure stevioside.

Extracting Stevia at Home:

There are many home made instructions on how to extract Stevia from home grown Stevia plants. Here is one:

Instructions

Things You'll Need:

• Stevia
• Grain alcohol
• Vodka
• Covered container
• Cheesecloth
• Coffee filter

1.     Harvest your stevia in the morning when the essential oils peak. You must use stevia grown without pesticides, as the extract-making process concentrates undesirable chemicals. Wash the leaves and stems and remove any brown plant parts.

2.     Chop the leaves and stems coarsely. You must prepare enough fresh stevia to fill two lightly packed measuring cups.

3.     Combine the stevia with one cup of clear grain alcohol or vodka. You can use flavor-infused vodkas for variety, such as pear or citrus.

4.     Leave the stevia mixture steeping overnight in a covered container, but not more than 48 hours. Excessive steeping increases bitterness. Stir or gently shake the mixture several times while it steeps.

5.     Strain the alcohol and stevia mixture through cheesecloth or coffee filter to remove the plant matter. The mixture should appear greenish.

6.     Bring the stevia extract to a simmer over medium-low heat for 30 minutes. This evaporates the alcohol and concentrates the extract.

7.     Store the extract in the refrigerator up to three months. You must dilute the extract to taste before using with water.

 by justin lim