TARA GUM
EXPLANATION
This substance was evaluated for acceptable daily intake for man
at the eighteenth, nineteenth, twenty-fourth, twenty-fifth, and
twenty-eighth meetings of the Joint FAO/WHO Expert Committee on Food
Additives (Annex 1, references 35, 38, 53, 56, and 66). Toxicological
monographs were issued after the nineteenth and twenty-fifth meetings
(Annex 1, references 39 and 57). A temporary ADI of 0-12.5 mg/kg b.w.
was allocated at the twenty-fifth meeting, which was extended at the
twenty-eighth meeting. 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 unit on average. In a bioavailability calorie assay,
groups of 10 male weanling Sprague-Dawley rats were given 5 g tara
gum for 10 days. Weight-gain comparisons showed that tara gum was
not a source of bioavailable calories (Robaislek, 1974).
A digestibility study in groups of 5 male and 5 female Purdue
strain rats on a mannose-free diet showed that 88-100% of the mannose
fed as 1% tara gum in the diet for 18 hours was 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
microflora, as mammals are not known to possess mannosidase.
Liberation of galactose units was not determined (Tsai & Whistler,
1975).
Incubation of solutions or suspensions of tara gum with human
gastric juice, duodenal juice + bile, pancreatic juice, or succus
entericus (with or without added rabbit small intestine membrane
enzymes) produced no evidence of hydrolysis (Semenza, 1975).
Rat large intestine microflora partially hydrolysed tara gum
in vitro after conditioning to 1% tara gum in the diet for 3 weeks
(Towle & Schranz, 1975).
Toxicological studies
Special studies on carcinogenicity
Mice
Diets containing 0, 2.5, or 5% tara gum were fed to groups of 50
male and 50 female B6C3F1 mice for 103 weeks. There were no
significant differences in survival between mice fed tara gum and the
control group. Depressions in body-weight gain greater than 10% were
observed in both sexes fed diets containing 5% tara gum. There were no
histopathological effects associated with the administration of tara
gum. Under the conditions of the experiment, tara gum was not
carcinogenic for B6C3F1 mice (Melnick et al., 1983).
Rats
Groups of 50 male and 50 female F344 rats were fed diets
containing 0, 2.5, or 5% tara gum for 103 weeks. All animals were
observed twice daily for morbidity and mortality. Body weights,
clinical signs, and feed consumption were recorded monthly. At the end
of the study the animals were killed, autopsied, and examined for
grossly-visible lesions. All organs were examined microscopically.
There were no histopathological effects associated with the
administration of the test material. Under the conditions of the
experiment tara gum was not carcinogenic for F344 rats of either sex
(Melnick et al., 1983).
Special study on embryotoxicity
Rats
Four groups of 25 Wistar female rats were fed diets containing 0,
1.25, 2.5, or 5.0% tara gum from day 6 to day 16 of pregnancy. On day
21 all females were sacrificed and the fetuses removed. There was no
evidence of embryonic and/or teratogenic effects caused by the tara
gum in any of the dose groups. No maternal toxicity was observed
(Becker, 1986).
Special study on reproduction
Rats
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 generations were mated to produce 2 litters. Females of
the F1 generation produced 3 litters. Ten males and 20 females were
retained at weaning from the second litter of each dietary group for
use 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; 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 weights of the tara gum F2 parental males
and the F0 and F1 parental females than of the controls. There was
a statistically-significant reduction in the number of pups viable at
lactation days 12 and 21 in the tara gum group and pup weights were
significantly lower than those of the controls in the tara gum groups
at days 4, 12, and 21 of the F1 generation and days 1, 4, 12, and 21
of the F3 generation. There were no other significant differences in
reproductive performance. No significant differences were noted in
parental premating food consumption, mortality, or gross microscopic
pathology. The following statistically-significant differences in
organ weights and organ-weight ratios were observed for the tara gum
group as opposed to the control group: lower absolute liver and brain
weights and higher kidney, testes, heart, and brain-to-body-weight
ratios. These differences were ascribed to the lower body weights of
the tara gum F2 weanlings, from whom the values were obtained
(Domanski et al., 1980).
Acute toxicity
No information available.
Short-term studies
Mice
Groups of 10 male and female mice were fed diets containing 0,
0.31, 0.63, 1.2, 2.5, or 5.0% tara gum for 13 weeks. At the end of the
study all animals were killed and subjected to complete gross
microscopy. Histopathological examination was carried out on tissues
from all animals in the control and highest-dose groups. None of the
mice died and no compound-related effects were detected (NTP, 1982).
Rats
Groups of 10 rats of each sex were fed diets containing 0, 0.31,
0.63, 1.2, 2.5, or 5% tara gum for 13 weeks. No deaths occurred during
the study. All animals were subjected to complete gross necroscopy.
Mistopathologic examination was carried out on tissues from all
animals in the control and highest-dose groups. During
histopathological examination, fewer mature spermatozoa were found in
the testes of 4/10 male rats receiving 5.0% tara gum than in the
controls. No other compound-related effects were observed (NTP, 1982).
A 90-day feeding study was carried out on groups of 10 male and
10 female rats at dietary levels of 0, 1, 2, or 5% tara gum. No
abnormalities were observed in general appearance, behaviour, or
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 body-weight decrease was found in males in the 2%
group; no effects on food intake or efficiency were observed.
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 were observed in
males only. No lesions were found on gross or histopathological
examination that could be attributable to the ingestion of tara gum
(Til et al., 1974).
Dogs
Three groups of 3 male and 3 female beagle dogs received 0, 1, or
5% tara gum in their diet for 90 days. No abnormalities were noted
with regard to behaviour, mortality, haematology, urinalysis, clinical
chemistry, organ weights or gross histopathology examination
(Oshita et al., 1975).
Long-term study
Rats
Groups of 50 male and 50 female Charles River 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 by both males
and females in the tara gum group at a number of weeks. This may have
been due to the physical characteristics of the control diet, of which
there may have been 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 statistically-significant differences in haematocrit
values at 12 months in male rats, in total erythrocyte and leukocyte
counts in male rats at 99 weeks, in monocyte counts in female rats at
12 months, in reticulocyte counts in female rats at 18 months, and in
haemoglobin concentration at 99 weeks. 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, BUN at 12 months in females, and
SGOT activity in females at 3 months. A significant decrease was noted
in total cholesterol levels at 6 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 final sacrifice the following statistically-significant
changes were noted in animals given tara gum: higher adrenal gland to
body-weight ratio in males and lower absolute brain weight in females.
No significant differences were reported between the tara gum and
control groups with respect to gross or microscopic pathology (Carlson
& Domanski, 1980).
Comments
Studies in rats on the in vivo digestibility and caloric
bioavailability of tara gum show that it is not digested by mammalian
intestinal enzymes, but it is partially hydrolysed by rat intestinal
flora. Human intestinal enzymes do not hydrolyse tara gum in vitro.
Short-term studies in rats and dogs showed no evidence of adverse
effects at the 5% level. A long-term study in rats demonstrated no
significant toxicity. Carcinogenicity studies in mice and rats fed
diets containing up to 5% tara gum were negative. A reproduction study
reviewed by an earlier Committee indicated a possible effect of 5%
tara gum on lactation, since pup body weights and viability tended to
be lower in the tara gum groups than in the controls given cellulose.
A new study indicated no evidence of embryonic and/or teratogenic
effects.
EVALUATION
Estimate of acceptable daily intake for man
ADI "not specified".
REFERENCES
Becker, B., Schafroth, P., Terrier, C., & Sachsse, K. (1986).
Embryo-toxicity (including teratogenicity) study with tara gum in
the rat. Unpublished report No. 53335 from Research & Consulting
Company AG, Itingen, Switzerland. Submitted to WHO by
Unipektin AG, Zurich, Switzerland.
Carlson, W.A. & Domanski, J. (1980). Two-year chronic oral toxicity
study with tara gum in albino rats. Unpublished report from
Industrial Bio-Test Laboratories, Inc., Northbrook, IL, USA.
Domanski, J., Carlson, W., & Frawley, J. (1980). Three generation
reproduction study with tara gum in albino rats. Unpublished
report from Industrial Bio-Test Laboratories, Inc.,
Northbrook, IL, USA.
Melnick, R.L., Hutt, J., Haseman, J.K., Deter, M.P., Grieshaber, C.K.,
Wyand, D.S., Russfield, A.B., Murthy, A.S.K., Fleischman, R.W., &
Lilja, H.S. (1983). Chronic effects of agar, guar gum, gum
arabic, locust-bean gum, or tara gum in F344 rats and B6C3F1
mice. Fd. Chem. Toxicol., 21, 305-11.
NTP (1982). Carcinogenesis bioassay of tara gum in F344 rats and
B6C3F1 mice (feed study). National Toxicology Program Technical
Report Series No. 224. Available from National Technical
Information Service (Publication No. PB82-195546),
Springfield, VA, USA.
Oshita, G. et al. (1975). 90-Day subacute oral toxicity study with
tara gum in beagle dogs. Unpublished report from Industrial
Bio-Test Laboratories, Inc., Northbrook, IL, USA. Submitted to
WHO by Hercules Incorporated.
Robaislek, E. (1974). Bioavailable calorie assay of guar gum.
Unpublished report from WARF Institute, Inc. Submitted to WHO 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 Swiss Federal Institute of
Technology, Zurich. Submitted to WHO by Institut Européen des
Industries de la Gomme de Caroube.
Til, H.P., Spanjers, M.T., & De Groot, A.P. (1974). Sub-chronic
toxicity study with tara gum in rats. Unpublished report from
Centraal Instituut voor Voedingsonderzoek, TNO. Submitted to WHO
by Hercules Incorporated 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 WHO by Hercules
Incorporated.
Tsai, L.B. & Whistler, R.L. (1975). Digestibility of galactomannans.
Unpublished report submitted to WHO by Institut Européen des
Industries de la Gomme de Caroube.
See Also:
Toxicological Abbreviations
Tara gum (WHO Food Additives Series 16)
TARA GUM (JECFA Evaluation)