Title: Alternative Sweeteners

Stevioside 175
these were not considered specific because of the lack of clear dose responses
(22). In a 2 year chronic oral toxicity study performed in male and female Wistar
rats fed a diet containing 85% pure stevioside (0, 0.2, 0.6, and 1.2%), it was
concluded that the maximum no-effect level of stevioside was equivalent to 1.2%
of the diet. The rats did not show any treatment-related changes in growth, general
appearance, and clinical biochemical values relative to controls. It was projected
from this study that an acceptable intake of stevioside in humans would be 7.938
mg/kg/day (23). In a carcinogenicity study, stevioside of high purity (95.6%)
was added to the diet of male and female F344 rats at concentrations of 0, 2.5,
and 5% for 2 years. Histopathological examination showed that there was no
significantly altered development of neoplastic or non-neoplastic lesions attributable
to any organ or tissue, except for a decreased incidence of mammary adenomas
in females and a reduced incidence of chronic nephropathy in males. Although
there was a significant decrease in the final survival rate of males treated
at the 5% dietary incorporation level, it was concluded that stevioside is not
carcinogenic in rats under the experimental conditions used (24).
The acute toxicity of stevioside and of steviol, the aglycone obtained from
this sweetener on enzymatic hydrolysis, has been investigated in the mouse and
hamster, as well as the rat (both males and females). Stevioside was not lethal
to any of the test animals at doses up to 15 g/kg body weight (25). The LD 50
values for steviol in hamsters (which were more susceptible to this compound
than either mice or rats) was 5.20 and 6.10 g/kg body weight for males and
females, respectively. Death was attributed to acute renal failure, and severe degeneration
of the proximal tubular cells was observed histopathologically. The
LD 50 value for steviol in mice and rats was 15 g/kg body weight in both cases
(25).
B. Genetic Toxicity Studies
Partially purified extracts and pure sweet constituents (stevioside, rebaudiosides
A-C, dulcoside A, steviolbioside) of S. rebaudiana have been tested extensively
for their mutagenic activity. None of these substances has been reported to be
mutagenic when evaluated with Salmonella typhimurium strains TA98, TA100,
TA1538, and TM67 or Escherichia coli strain WP2, either in the presence or
absence of metabolic-activating systems (1, 2).
However, it was shown in the mid-1980s that steviol (Fig. 2), the aglycone
of all of the S. rebaudiana sweet constituents including stevioside, is mutagenic
in a forward mutation assay using S. typhimurium TM677 in the presence of a
metabolic-activating system derived from a 9000 g supernatant fraction from
the livers of Aroclor-1254–pretreated rats. Unmetabolized steviol was inactive
in this system (2). These observations were confirmed independently by two other
groups (26, 27). Moreover, metabolically activated steviol gave positive re-