TARA GUM
Explanation
This substance was evaluated for acceptable daily intake for man
(ADI) by the Joint FAO/WHO Expert Committee on Food Additives in 1975
(see Annex, Ref. 37). A toxicological monograph was issued in 1975
(see Annex, Ref. 38).
Since the previous evaluation, additional data have become
available and are summarized and discussed in the following monograph.
The previously published monograph has been expanded and is reproduced
in its entirety below.
BIOLOGICAL DATA
BIOCHEMICAL ASPECTS
The principal component of this gum is a galactomannan with a
linear chain of (1--->4) linked ß-D-mannopyranose units with
alpha-D-glactopyranose units attached by (1--->6) linkages to every
third mannose unite on average. In a bioavailable calorie assay,
groups of 10 male weanling rats (Sprague-Dawley) were given 5 g basal
diet alone or with 0.5, 1, 2 g sucrose or 0.5, 1, 2 g tara gum for
10 days. Comparison of the carcass weight gain showed that tara
gum was not a source of bioavailable calories (Robaislek, 1974). A
digestibility study in groups of five male and five female rats
(Purdue strain) on a mannose-free diet showed that 88-100% of mannose
fed as 1% tara gum in the diet for 18 hours were excreted in the
faeces over a total of 30 hours. Some decrease in chain length of
galactomannan may have occurred probably through the action of the
microflora as mammals are not known to possess mannosidase. Liberation
of galactose units was not determined (Tsai & Whistler, 1975).
Incubation of solutions or suspensions with human gastric juice,
duodenal juice + bile, pancreatic juice and succus entericus with or
without added rabbit small gut membrane enzymes produced no evidence
of hydrolysis (Semenza, 1975). Rat large gut microflora partially
hydrolysed tara gum in vitro (Towle & Schranz, 1975) after
conditioning to 1% tara gum in the diet for three weeks.
TOXICOLOGICAL STUDIES
Special studies on reproduction
Rat
A three generation reproduction study was carried out in CD
strain Charles River albino rats. Groups of 10 male and 20 female
animals were fed a diet containing 5% alpha cellulose (control) or 5%
tara gum. The same dose and animal numbers were employed for
successive generations throughout the study. In each generation the
parental animals received the test diets for 11 weeks prior to mating
and then through mating, gestation and weaning. The females of the F0
and F2 generation were mated to produce two litters. Females of the
F1 generation produced three litters. Ten males and 20 females were
retained at weaning from the second litter of each dietary group as
parental animals for the next generation. Ten weanlings per sex per
dietary group from the F3b litters were selected for histopathologic
examination of 12 tissues and organs, and organ weight values were
also obtained. All other animals were subjected to gross necropsy.
At several weeks during the study, there were instances of
statistically lower body weight in the tara gum F2 parental males and
the F0 and F1 parental females.
There was a statistically significant reduction in the number of
pups viable at lactation days 12 and 21 in the tara gum group. There
were significant lower pup weights in the tara gum groups at days 4,
12, and 21 in the F1 generation and days 1, 4, 12 and 21 of the F3
generation. There were no other significant between group differences
in reproductive performance.
No significant between group differences were noted in parental
premating food consumption, mortality and gross or microscopic
pathology.
The following statistically significant differences in organ
weights and organ weight ratios were observed for tara gum group as
opposed to the control group: lower absolute liver and brain weights
and greater kidney, testes, heart, and brain to body weight ratios.
These differences were ascribed to the lower body weight of the tara
gum F2 weanlings from whom the values were obtained (Domanski et al.,
1980).
Acute toxicity
No data available.
Short-term studies
Rat
A 90-day feeding study was carried out in groups of 10 male and
10 female rats at dietary levels of 0, 1, 2 or 5% of the diet. No
abnormalities were observed in general appearance, behaviour, and
survival in any of the groups. Growth, food intake and food efficiency
were slightly decreased at the 5% dietary level in both sexes. A
relative lowering of the body weight was found in the males in the 2%
group, but no effect on food intake and efficiency. Haematology and
urinalysis showed no treatment-related differences. A significant
increase in blood urea nitrogen was observed in males at the 5%
dietary level. At the 2% and 5% levels, an increase was found in the
relative weight of the caecum. An increase in the relative weight of
the thyroids at the 2% and 5% levels and a slight increase in the
relative weight of the kidneys at the 5% level was observed in males
only. No lesions were found on gross and histopathological examination
attributable to the ingestion of the gum (Til et al., 1974).
Dog
Three groups of three male and three female beagles received
either 0, 1, or 5% tara gum in their diet for 90 days. No
abnormalities were noted as regards behaviour, mortality, haematology,
urinalysis, clinical chemistry, organ weights, gross histopathology
(Oshita et al., 1975).
Long-term studies
Rat
Groups of 50 male and 50 female Charles River Strain albino rats
were fed diets containing 5% alpha cellulose (control) or 5% tara gum
for up to two years. An interim sacrifice of 10 animals/sex/group was
carried out after 12 months.
Statistically significant lower body weight and body weight
changes were noted at a number of weeks in both male and female
animals in the tara gum group. There were also statistically
significant reductions in food consumption in the tara gum groups both
males and females - at a number of weeks. This may have been due to
the physical characteristics of the control diet (alpha cellulose
added) which may have accounted for greater spillage and therefore
greater apparent food consumption in the control animals.
Some changes in haematological measurements were noted in rats in
the tara gum groups. These included a statistically significant
decrease in haematocrit values at 12 months in male rats, in total
erythrocyte count and leukocyte count in male rats at 99 weeks, in
monocyte count in female rats at 12 months and in reticulocyte counts
in females at 18 months. Statistically significant increases were
reported in the haemoglobin concentration at 99 weeks, in the
monocytes at 12 months and reticulocyte count in female rats given
tara gum.
With respect to clinical chemistry, statistically significant
increases in animals given tara gum were noted for the following
measurements: SGPT activity in males at 12 months; fasting serum
glucose, and BUN at 12 months in females and SGOT activity in females
at three months. A significant decrease was noted in total cholesterol
levels at six and 12 months in females given tara gum.
At the 12-month interim sacrifice the following statistically
significant changes were noted in males fed 5% tara gum: significantly
greater brain to body weight, testes to body weight and heart to body
weight ratios and significantly lower liver to brain weight ratio. At
the final sacrifice the following statistically significant changes
were noted in animals given tara gum; lower adrenal gland to body
weight ratios in males and lower absolute brain weight in females.
No significant differences were reported in between the tara gum
and control groups with respect to gross or microscopic pathology
(Carlson & Domanski, 1980).
Comments
The studies in rats on the in vivo digestibility and calorie
bioavailability show that this gum is not digested by mammalian
intestinal enzymes but is partially attacked by rat gut flora. Human
gut enzymes do not hydrolyse this gum in vitro. Short-term studies
in rats and dogs showed no evidence of adverse effects at the 5%
level. The observed effects on caecal weight were discussed in a
previous report and were not considered significant for man. The
effect on thyroid weight without concomitant histopathological changes
was also considered to be of doubtful significance. The previous
report indicated the need for adequate long-term studies on rodent
species, as well as reproduction and embryotoxicity (including
teratogenicity) studies. A long-term study in rats demonstrated no
significant toxicity. The reproduction study indicated a possible
effect of 5% tara gum on lactation since pup body weights and
viability tended to be lower in the pups in the tara gum groups as
compared to the controls given cellulose. No studies on teratogenicity
are available.
EVALUATION
Level causing no toxicological effects
Rat: 5% in the diet equivalent to 2500 mg/kg bw.
Estimate of temporary daily intake for man
0-12.5 mg/kg bw.
FURTHER WORK OR INFORMATION
Required by 1984
Multigeneration reproduction study in rats at several dose
levels.
Teratogenic study.
REFERENCES
Carlson, W. A. & Domanski, J. (1980) Two-year chronic oral toxicity
study with tara gum in albino rats. Unpublished data. Industrial
Bio-Test, Northbrook, Illinois, United States of America
Domanski, J., Carlson, W. & Frawley, J. (1980) Three generation
reproduction study with tara gum in albino rats. Unpublished
data. Industrial Bio-Test, Northbrook, Illinois, United States of
America
Oshita, G. et al. (1975) 90-day subacute oral toxicity study with tara
gum in beagle dogs. Unpublished report from Industrial Bio-Test
Labs, Inc. submitted to the World Health Organization by Hercules
Incorporated
Robaislek, E. (1974) Bioavailable calorie assay of guar gum.
Unpublished report from WARF Institute, Inc. submitted to the
World Health Organization by Institut Européen des Industries de
la Gomme de Caroube
Semenza, G. (1975) Report on the possible digestion of locust bean gum
in the stomach and/or in the small intestine in an in vitro
study. Unpublished report from the Eidgenossische Technische
Hochschule Zurich submitted to the World Health Organization by
the Institut Européen des Industries de la Gomme de Caroube
Til, H. P., Spanjers, M. Th. & De Greet, A. P. (1974) Sub-chronic
toxicity study with tara gum in rats. Unpublished report from
Centraal Instituut voor Voedingsonderzoek TNO submitted to the
World Health Organization by Hercules B.V. and Institut Européen
des Industries de la Gomme de Caroube
Towle, G. A. & Schranz, R. E. (1975) The action of rat microflora on
carob bean gum solutions in vitro. Unpublished report from
Hercules Research Center submitted to the World Health
Organization by Hercules Incorporated
Tsai, L. B. & Whistler, R. L. (1975) Digestibility of galactomannans.
Unpublished report submitted to the World Health Organization by
Professor H. Neukom, Chairman of the Technical Committee of
Institut Européen des Industries de la Gomme de Caroube