WORLD HEALTH ORGANIZATION
Toxicological evaluation of some food colours, thickening
agents, and certain other substancse
WHO FOOD ADDITIVES SERIES NO. 8
The evaluations contained in this publication were prepared
by the Joint FAO/WHO Expert Committee on Food Additives which
met in Geneva, 14-23 April 19751
World Health Organization, Geneva 1975
1 Nineteenth Report of the Joint FAO/WHO Expert Committee on Food
Additives, Wld Hlth Org. techn. Rep. Ser., 1975, No. 576;
FAO Nutrition Meetings Report Series, 1975, No. 55.
The monographs contained in the present volume are
also issued by the Food and Agriculture Organization
of the United Nations, Rome, as
FAO Nutrition Meetings Report Series, No. 55A
ISBN 92 4 166008 2
(C) FAO and WHO 1975
TARA GUM
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 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 hydrolyzed tara
gum in vitro (Towle & Schranz, 1975) after conditioning to 1% tara
gum in the diet for three weeks.
TOXICOLOGICAL STUDIES
Acute toxicity
No information available.
Short-term tests
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 and
histopathology (Oshita et al., 1975).
Long-term tests
None available.
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. No information is
available on long-term effects in rodents. No studies on reproduction
and teratogenicity are available.
EVALUATION
Estimate of acceptable daily intake for man
Acceptable daily intake not specified.1*
1 The statement "ADI not specified" means that, on the basis of
the available data (toxicological, biochemical, and other), the total
daily intake of the substance, arising from its use or uses at the
levels necessary to achieve the desired effect and from its acceptable
background in food, does not, in the opinion of the Committee,
represent a hazard to health. For this reason, and for the reasons
stated in individual evaluations, the establishment of an acceptable
daily intake (ADI) in mg/kw bw is not deemed necessary.
* Temporary.
FURTHER WORK OR INFORMATION
Required by 1980.
(1) Adequate long-term studies in a rodent species.
(2) Reproduction and embryotoxicity (including teratogenicity)
studies.
REFERENCES
Oshita, G., Burtner, B. R., Kennedy, G. L., jr, Kinoshita, F. K. &
Keplinger, M. L. (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 Eidgenössische Technische
Hochschule Zürich submitted to the World Health Organization by
the Institut Européen des Industries de la Gomme de Caroube
Til, H. P., Spanjers, M. Th. & de Groot, 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 Inst.
Europ. des Industries de la Gomme de Caroube