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large protein molecules. An adsorption resin is then used to remove organic
substances, principally mogrosides, and allows unwanted compounds, such as
reducing sugars and mineral salts, to pass through. The resin is eluted with
aqueous ethanol, the eluent being partially concentrated under reduced pressure
then decolourised. The liquor is then further concentrated to approximately 40%
soluble solids to yield the fi nal product, which may also be spray-dried at 120°C
to obtain a powder (Heimbach 2009).
The sweet components are cucurbitan (triterpene) glycosides, the mogrosides,
comprising 1% or more of the dried fruit and of which mogroside V (Fig. 3.6)
is more than half. Commercial extracts can range from 30-90% total mogrosides
(II, III, IV, V and VI), of which IV, V and VI are potently sweet. The sweetness
of commercial LHG is dictated by the content of mogroside V. Manufacturers
are striving to raise this level and one major supplier guarantees not less than
40% mogroside V, while products with more than 50% are likely to become more
common. Virtually pure mogroside V is also available. Much of the non-mogroside
material in extracts comprises protein and carbohydrates (including fl avonoids
and melanoidins) in variable amounts.
Physico-chemical properties
Dried extracts are light tan, fi ne powders with a mildly fruity odour. There seem
to be no published quantitative data, but solubility in water is said to be good -
unsurprisingly, since the product is obtained by aqueous extraction. Stability is
also claimed to be good but, again, there are no comprehensive data to support
this. One manufacturer indicates that LHG is stable to UHT and retort processing
and stable in the pH range 3-7. It seems likely that the inherent robust stability of
Fig. 3.6
Structure of mogroside V.
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