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
GUAR GUM
Explanation
This substance was evaluated for acceptable daily intake for man
by the Joint FAO/WHO Expert Committee on Food Additives (see Annex 1,
Refs No. 20 and No. 33) in 1969 and 1973.
Since the previous evaluation, additional data have become
available and are summarized and discussed in the following monograph.
The previously published monographs have been expanded and are
reproduced in their 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-galactopyranose units attached by (1 -> 6) linkages to every
alternate mannose. The caloric value was determined in groups of
10 rats fed for one week a 5 g basal diet supplemented with either
1 g or 3 g corn starch or 1 g and 3 g guar gum. At 1 g level guar gum
was equivalent to corn starch but at the 3 g level there was a lower
equivalence. All animals had large intestines but normal faeces
(Anonymous, 1964). In a further bioavailable calorie assay groups of
10 male weanling rats (Sprague-Dawley) were given 5 g basal diet or
plus 0.5, 1, 2 g sucrose or 0.5, 1, 2 g guar gum for 10 days.
Comparison of the carcass weight gain showed that guar gum was not a
source of bioavailable calories (Robaislek, 1974). The rat can use
guar flour as a precursor for liver glycogen but at a much reduced
efficiency as shown by 15 controls receiving cocoa butter alone
(<0.1% glycogen), or cocoa butter + 30% wheat flour (2.6% glycogen)
and 18 test animals receiving cocoa butter + 30% guar flour (0.8%
glycogen) for two days (Krantz et al., 1948). The digestibility of
guar gum in rats fed 0.4 g/day was estimated to be 76% (Booth et al.,
1963). However another digestibility study in groups of five male and
five female rats (Purdue strain) on a mannose-free diet showed that
83-100% of mannose fed as 1% guar gum in the diet for 18 hours was
excreted in the faeces over a total of 30 hours. Some decrease in
chain length of galactomannans may have occurred probably through the
action of the microflora as mammals are not known to possess
mannosidase. Liberation of galactose 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 guar gum in vitro (Towle & Schranz,
1975).
Feeding chicks for four weeks on a diet containing 3%
cholesterol, 3% guar gum and 3% cholesterol + 3% guar gum reduced the
serum cholesterol level especially if both cholesterol and guar gum
were ingested. Liver cholesterol was only depressed if cholesterol and
guar gum were fed (Couch et al., 1966). Groups each of eight male
Holtzman rats were maintained on a purified synthetic diet, or the
diet plus 1% cholesterol, or the diet plus 1% cholesterol and 10% guar
gum for 28 days. The increased liver cholesterol and liver total lipid
induced by cholesterol feeding was largely counteracted by concurrent
feeding of guar gum (Ershoff & Wells, 1962). Ten per cent. but not 5%
guar gum added concurrently to a casein/sucrose diet with 1%
cholesterol and 10% corn oil significantly reduced serum and liver
cholesterol. Five per cent. guar gum reduced only the liver
cholesterol when only 5% corn oil was used with a commercial diet
(Riccardi & Fahrenbach, 1967).
TOXICOLOGICAL STUDIES
Special studies on teratogenicity
Teratological experiments with three species of animals (mice,
rats and hamsters) did not indicate that the test material was a
teratogen in mice at 170 mg/kg and 800 mg/kg although 6/29 dams died
at the highest level tested. Similar negative findings were seen in
rats up to 900 mg/kg and up to 600 mg/kg in hamsters (Anonymous,
1972).
Acute toxicity
Eighteen rats given guar gum in cocoa butter at 30% of their diet
for 48 hours showed no adverse effects (Krantz et al., 1948). Feeding
27% guar gum to rats for seven days caused 7/10 deaths due to probable
intestinal blockage (Anonymous, 1964).
Short-term studies
Rat
Five male rats were fed 0 and 6% guar gum for 91 days in their
diet. No differences were observed between the two groups in weight
gain and food efficiency (Booth et al., 1963). Fifteen rats were
fed a diet containing 0.5% guar gum and varying amounts of water for
21 days. Weight gain and protein efficiency increased with higher
water content (Keane et al., 1962).
Groups of 10 male and 10 female rats were fed in their diet
either 0, 1%, 2% or 5% guar flour for 90 days. At the end of the test
general behaviour, appearance, survival were not noticeably affected
by feeding guar gum. Growth was relatively low in males fed 2% and 5%
and food efficiency was slightly diminished in males of the 5% group.
Haematology, urinalysis, serum enzyme activities or blood sugar levels
showed no effects. Blood urea nitrogen values were slightly increased
in males at the 5% level. The relative weight of the caecum was
increased at the 2% and 5% levels in both sexes, that of the thyroid
only in males. Gross and histopathology revealed no changes
attributable to gum ingestion (Til et al., 1974).
Chicken
Groups of 20 chicks, one-day old, were maintained on diets
containing 2% guar gum for 21 days and showed depressed growth,
reduced nitrogen retention and fat absorption. Pancreatic weight was
significantly increased when diets contained guar gum in a high
protein (30%) diet (Kratzer et al., 1967).
Dog
Four groups of five male and five female beagles were fed 0,
1%, 5% or 10% of a precooked mixture of guar and carob bean gum
(proportions not stated) for 30 weeks. Only at the 10% level were
gut hypermotility and soft bulky faeces observed, probably of no
toxicological significance. Also at the 10% level digestibility was
reduced. No adverse haematological, urinary, gross and
histopathological and ophthalmological findings were noted (Cox et
al., 1974).
Monkey
Two monkeys received 1 g of guar flour in their diet daily.
Wellbeing, growth and haematology (RBC, WBC, Hb, urea) remained
normal. One monkey died after 16 months, the other was sacrificed at
24 months. No abnormalities were noted on gross and histopathology
(Krantz, 1948).
Long-term studies
Rat
Out of two groups of 15 male and 15 female rats receiving either
0 or 5% guar flour in their diet seven males and eight females
survived in each group and were followed up for 24 months. One test
animal died after 12, 18, 19 and 22 months, the last surviving test
animal was sacrificed after 24 months. Three control rats survived to
24 months. All animals appeared in good health, had similar body
weights. Histology of liver, kidney, spleen, gut and bone marrow
showed no abnormality (Krantz et al., 1948).
OBSERVATIONS IN MAN
Five volunteers ingested 1 g of guar flour in capsule per day for
10 days without any apparent effects (Krantz, 1947).
Comments:
Guar gum is consumed in some parts of the world as a component of
guar flour. One study using guar gum at less than 15% of the diet
pointed to guar gum being calorically equivalent to corn starch. More
recent studies, however, on digestibility and caloric availability
in vivo in rats at dietary levels of 1-2% and in vitro studies
with human enzyme preparations showed no evidence of hydrolysis by
mammalian intestinal enzymes. Rat gut flora in vitro partially
hydrolizes guar gum. A recent adequate short-term study in rats
revealed no adverse effects apart from caecal enlargement and thyroid
enlargement in one sex only. The significance of these findings for
human safety evaluation is doubtful. The long-term study, though not
adequate by present standards, revealed no adverse effects at the 5%
level.
EVALUATION
Acceptable daily intake not specified.*
REFERENCES
Anonymous (1964) Evaluation of Jaguar A-20 and Karaya gum. Assay
report No. 3110860 and 3110861. Unpublished report from the
Wisconsin Alumni Research Foundation submitted to the World
Health Organization
Anonymous (1972) Teratologic evaluation of FDA 71-16 (guar gum) in
mice, rats, hamsters and rabbits. Unpublished report from the
Food and Drug Research Labs, Inc. submitted to the World Health
Organization by the Food and Drug Administration, United States
of America
* 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/kg bw is not deemed necessary.
Booth, A. N., Hendrickson, A. P. and De Eds, F. (1963) Physiologic
effects of three microbial polysaccharides on rats, Toxicol.
appl. Pharmacol., 5, 478-484
Couch, J. R., Bakshi, Y. K., Fergusson, T. M., Smith, E. B. & Creger,
C. R. (1967) The effect of processing on the nutritional value of
guar meal for broiler chicks, Brit. Poultry Sci., 8, 243-250
Cox, G. E., Baily, D. E. & Morgareidge, K. (1974) Subacute feeding in
dogs with a pre-cooked gum blend. Unpublished report from the
Food and Drug Labs, Inc. submitted to the World Health
Organization by Hercules BV
Ershoff, B. H. & Wells, A. F. (1962) Effects of gum guar, locust bean
gum and carrageenan on liver cholesterol of cholesterol-fed rats,
Proc. soc. exp. biol. med., 110, (3), 580-582
Keane, K. W., Smutko, C. J., Krieger, C. H. & Denton, A. E. (1962) The
addition of water to purified diets and its effect upon growth
and protein efficiency ratio in the rat, J. Nutr., 77, 18-22
Krantz, J. C. (1947) Unpublished report from General Mills, Inc.
submitted to the World Health Organization
Krantz, J. C., jr (1948) The feeding of guar gum to rats (lifespan)
and to monkeys. Unpublished report from the University of
Maryland, School of Medicine submitted to the World Health
Organization by General Mills Chemicals, Inc.
Krantz, J. C., jr, Carr, C. J. and de Farson, C. B. (1948) Guar
polysaccharide as a precursor of glycogen, J. Amer. Diet. Ass.,
24, 212
Krutzer, F. H., Rajaguru, R. W. A. S. B. & Vohra, P. (1967) The effect
of polysaccharides on energy utilization, nitrogen retention and
fat absorption in chickens, Poultry Sci., 48, 1489-1493
Riccardi, B. A. & Fahrenback, H. J. (1967) Effect of guar gum and
pectin N.F. on serum and liver lipids of cholesterol fed rats,
Proc. Soc. Exp. Biol. Med., 124, (3), 749-752
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 locust bean gum in rats. Unpublished report
from Centraal Instituut voor Voedingsonderzoek TNO submitted to
the World Health Organization by Hercules BV 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