Title: Alternative Sweeteners

214 Kinghorn and Compadre
form. Phyllodulcin was then selectively extracted in high purity at pH 10 with
a nonpolar solvent (2). The relative sweetness of phyllodulcin has been variously
reported as 400 and 600–800 times sweeter than sucrose, although the compound
exhibits a delay in sweetness onset and a licorice-like aftertaste (2). There have
been extensive attempts to modify the phyllodulcin structure to produce compounds
with improved sensory characteristics. As a result of such investigations,
it has been established that the 3-hydroxy-4-methoxyphenyl (isovanillyl) unit of
phyllodulcin must be present for the exhibition of a sweet taste, but the phenolic
hydroxyl group and the lactone function can be removed without losing sweetness
(2, 16, 21). To date, the phyllodulcin derivatives that have been produced synthetically
seem to have limitations in terms of their water solubility, stability, and/
or sensory characteristics (2). Phyllodulcin remains an attractive target for total
synthesis, with a number of additional procedures reported recently (22–24).
The fermented leaves of H. macrophylla var. thunbergii (Japanese name
amacha) are used in Japan to produce a sweet tea that is consumed at Hamatsuri,
a Buddhist religious festival (2). This preparation is listed in volume XIII of the
Japanese Pharmacopeia and is used also in confectionery and other foods for
its cooling and sweetening attributes (20). A 1987 estimate indicated that demand
for extracts of Hydrangea species containing phyllodulcin was 1 metric ton, with
a value of 15 million yen (2). Pure phyllodulcin has been found to be nonmutagenic
in a forward mutation assay and also not acutely toxic to mice when administered
by oral intubation at up to 2 g/kg body weight (2). The low solubility in
water and the sensory shortcomings of phyllodulcin that have been mentioned
would seem to limit the prospects of this natural product from becoming more
widely used as a sweetener in the future.
D. Sweet Proteins
1. Thaumatin
Thaumatins I and II are the major sweet proteins obtained from the arils of the
fruits of the West African plant Thaumatococcus daniellii (Bennett) Benth. (Marantaceae),
with altogether five different thaumatin molecules now known (thaumatins
I, II, III, and a and b) (2, 25). Thaumatin I, composed of 207 amino acid
residues, of molecular weight 22,209 daltons, has a relative sweetness of between
1600 and 3000 when compared with sucrose on a weight basis (2, 25). Thaumatin
protein (which is known by the trade-name of Talin ® protein) was comprehensively
reviewed by J.D. Higginbotham in the First Edition of Alternative Sweeteners
in terms of botany, production, biochemistry, physical characteristics, sensory
parameters, sweetness synergy with other substances, applications (including
flavor potentiation and aroma enhancement effects), safety assessment, cariogenic
evaluation, and regulatory status (2) and has been featured in other reviews
on sweet proteins (25–27). Accordingly, this sweet protein is not considered in