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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

    See Also:
       Toxicological Abbreviations
       Tara gum (WHO Food Additives Series 21)
       Tara gum (JECFA Evaluation)

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