Toxicology Letters, 17 (1983) 159-166

Elsevier

159

THE EFFECTS OF DIETARY GUM KARAYA (STERCULZA) IN MAN

(Toxicology; metabolism; gum karaya; Sterculia gum)

M.A. EASTWOOD, W.G. BRYDON and D.M.W. ANDERSON

Wolfson Gastrointestinal Laboratory, Western General Hospital, Edinburgh EH4 2XU; and Chemistry Department, The University, Edinburgh EH9 3JJ (U.K.)

(Received December 17th, 1982)

(Accepted January 7th, 1983)

SUMMARY

Following a 7-day control period, 5 male volunteers consumed 10.5 g gum karaya (GK) daily for 21

days. Measurements before and at the end of the test period showed that the ingestion of GK had no

significant effect on the following: intestinal transit time, faecal wet or dry weight, concentrations of

faecal fat, total and individual volatile fatty acids, bile acids, and neutral sterols; breath hydrogen and

methane concentrations; glucose tolerance; serum cholesterol, HDL cholesterol, triglycerides and

phospholipids; plasma biochemistry; haematological indices; urinalysis parameters. The daily test intake,

which was large in relation to the very minor amounts of GK used in foodstuffs, did not cause any toxic

effects in terms of the wide range of measurements made; moreover the GK had no metabolic action of

any consequence.

INTRODUCTION

GK, the dried exudate from Sterculia urens Roxb. and other Sterculia spp. (fam. Sterculiaceae) is a complex, partially acetylated, polysaccharide of very high A4, [I]. From the structural studies available [2-51 it appears that the macromolecules are cylindrical in shape and highly branched, with interior galacturono-rhamnan chains to which are attached galactose and rhamnose end-groups. Glucuronic acid is also present [3]. Detailed analyses [6, 71 of specimens obtained from the main gum- producing Indian and African Sterculia spp. have shown that they are very similar in chemical composition and physicochemical properties.

Abbreviations: AST, aspartate amino transferase; GK, gum karaya; INGAR, International Natural

Gums Association for Research Ltd.

0378-4274/83/$ 03.00 0 1983 Elsevier Science Publishers B.V.

160

Because of its unusual stability towards acidic hydrolysis and enzymatic degrada- tion, GK has a long history of use at the 0.002-0.8% level in foodstuffs as an emulsifier, stabiliser and thickener; pharmaceutically, it is also used in laxative preparations, dental fixatives, and as an adhesive in colostomy appliances.

GK does not act as a teratogen [8] nor as a mutagen [9]. To meet the requirements of Directive 74/329/EEC, amended by Directives 78/612/EEC and 80/597/EEC, studies in rats have shown [lo] that the no-untoward-effect level is 5% (w/w) of the diet and that 95% of the GK ingested appeared in the faeces [ll]. To provide evidence derived from tests in man, as requested [12] by international regulatory committees, a study was sponsored by INGAR. This report presents the results.

MATERIALS AND METHODS

The GK, kindly supplied by Norgine Ltd., London, from a consignment used for routine manufacturing purposes, conformed to the current B.P. and Food Chemical Codexes and to the specifications of identity and purity published by the Joint FAG/WHO Expert Committee on Food Additives [13]. In addition, detailed analyses gave the following data: loss on drying, 17.6%; ash, 8.0%; nitrogen, 0.17%; intrinsic viscosity [n], 550 cm3/g; &&, 4.7. 106; specific rotation, [aID, +49”; the sugar composition after hydrolysis was 24% galacturonic acid, 10% glucuronic acid, 34% arabinose, 32% rhamnose. These analytical parameters are similar to those for the GK used in a recent subacute toxicity study [lo] and to those established for GK from authentic Stem&a spp. [6, 71.

To simulate, as closely as possible, the mode of ingestion of GK present as an ad- ditive in foodstuffs, each volunteer consumed three portions of GK, each of 3.5 g, daily. Individual portions were prepared in 200-ml polypots, fitted with lids, by ad- ding 3.5 g of GK (40-60 mesh) carefully with stirring to cold water (175 ml). The GK was allowed to hydrate completely for 24 h to give a fluid gel prior to consumption.

The study lasted for 28 days. After a control period of 7 days, 5 healthy male volunteers, aged 30-56 years and free from gastrointestinal disease and symptoms, consumed three 3.5 g portions of pre-hydrated GK daily for a further 21 days. Following an overnight fast, the control period started with a 4-h glucose tolerance test. Blood for glucose and insulin estimations was taken before consumption of a glucose solution (50 g anhydrous glucose in 200 ml water), and at 30-min intervals thereafter. At the outset blood was also taken for fasting serum lipid estimations (cholesterol, HDL cholesterol, phospholipids and triglycerides), haematology (haemoglobin, white cell and platelet count, and full blood picture) and biochemical analyses (plasma urea, electrolytes, bilirubin, AST, alkaline phosphatase, calcium, phosphate, creatinine, uric acid, protein, albumin). During the glucose tolerance test, end-alveolar air samples were taken at 30-min intervals for hydrogen and methane determinations by gas chromatography [14]_ At the start of the next day,

161

40 radio-opaque markers were swallowed to allow measurements of intestinal transit time and give confirmation of complete faecal collection [15]. During the next 5 days all faecal output was collected in plastic slings and stored at -2O’C until analysis. A diet diary detailing amounts and type of food eaten was kept by each participant; the dietitian who analysed the information also obtained a 24-h recall diet history. On one day a 24 h urine collection was made.

Compliance was monitored by daily contact with the subjects. During the third week the above sequence of procedures was repeated with the exception of the glucose tolerance, haematological, and biochemical tests, which were made on the last day of the third week of diet supplementation.

The individual faecal collections were weighed, thawed, mixed in a known volume of water, homogenised, and an aliquot was freeze-dried. The intestinal transit time, determined by radiology of the individual stools, was the time taken for 80% of the pellets to appear in the faeces. The freeze-dried material was analysed for faecal bile acids [16], neutral sterols [17], fat [18] and volatile fatty acids [19].

Plasma glucose concentrations were determined (automated glucose oxidase method) and blood glucose concentration was estimated from this value using the haematocrit. Plasma insulin concentrations were determined by a radioim- munoassay technique.

A full blood analysis was made (automated Coulter S counter and manual methods) and heparinised plasma samples were analysed (Technicon Auto Analyzer). Total serum lipids were analysed (Technicon Auto Analyzer) for cholesterol and for HDL cholesterol [20], serum triglycerides [21], and phospholipids [22].

The data obtained were evaluated where appropriate by the Student t-test and by the Wilcoxon Rank Sum Test.

RESULTS

The results of the diet enquiry for the first and fourth weeks showed no statistical- ly significant differences in the individual intakes of protein, fat, carbohydrate, sugar, alcohol or fibre.

Table I summarises the results for faecal and serum measurements before and after GK supplementation. The completeness of faecal collection was confirmed by the recovery of more than 90% of the markers in all collections. The intestinal tran- sit time did not change in any of the subjects. GK had no significant effect on daily faecal wet or dry weight nor on the concentrations of faecal fat, total or individual volatile fatty acids, bile acids, and neutral sterols. Similarly GK had no significant effect on serum cholesterol, HDL cholesterol, triglycerides and phospholipids (Table II), haematological indices (Table III) and plasma biochemistry (Table IV). In measurements made on day 1 and 28 of the experiment, the breath hydrogen con- centration remained unchanged, at less than 20 ppm for all subjects, over a period

162

TABLE I

THE EFFECT OF GUM KARAYA INGESTION ON FAECAL MEASUREMENTS

Control period After 3 weeks

Mean (range)

wet weight, g/24 h

dry weight, g/24 h

fat, mmo1/24 h

volatile fatty acids, mmol/24 h

acetate, mmol/24 h

propionate, mmo1/24 h

butyrate, mmo1/24 h

total volatile fatty acids, mmol/g dry weight faeces

bile acids, mmoV24 h

bile acids, mmol/g dry weight faeces

neutral sterols, mmol/24 h

transit time. h

135

(84 - 160)

36

(23 - 49)

15

(8 - 24)

9.5

(7.1 - 14.4)

5.7

(4.2 - 9.9)

1.73

(1.1 - 2.7)

1.6

(1.2 - 2.3)

0.37

(0.19 - 0.40)

0.93

(0.60 - 1.54)

26

(14 - 67)

1.81

(1.3 - 2.0)

63

(40 - 69)

139

(104 - 173)

38

(29 - 46)

14

(10 - 27)

11.4

(6.0 - 15.0)

7.3

(3.7 - 10.2)

1.8

(1.0 - 2.1)

1.5

(0.7 - 2.1)

0.31

(0.20 - 0.33)

0.68

(0.61 - 1.15)

21

(15 - 35)

1.4

(1.1 - 3.0)

68

(41 - 92)

TABLE II

THE EFFECT OF GUM KARAYA INGESTION ON HUMAN SERUM LIPIDS

Control period After 3 weeks

Mean + S.D.

Cholesterol, mmol/l 5.6 t 0.5 5.4 + 0.77

HDL cholesterol, mmol/l 0.99 ? 0.25 0.78 + 0.14

Triglycerides, mmol/l 1.2 t 0.4 1.4 + 0.5

Phosoholioids, m&l00 m1 221 f 20 224 * 14

of 150 min after the ingestion of 50 g of anhydrous glucose. Ingestion of GK for

21 days had no effect on the breath methane concentration of all subjects, regardless

of whether they were natural methane producers or non-methane producers. Reduc-

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ing sugars were not detected in urine specimens, and there were no statistically significant differences in the mean glucose and insulin concentrations (Figs. 1 and 2), after the ingestion of GK for 21 days.

DISCUSSION

The intake of 3 x 3.5 g GK daily for 21 days was well tolerated. The ingestion of GK had no significant effect on glucose tolerance, serum cholesterol, HDL cholesterol, triglycerides, and phospholipids; plasma biochemistry; haematological indices; urinalysis parameters. There was also no significant effect on wet or dry stool weight, faecal constituents, or transit time. It is unlikely that the GK influenc- ed any of the factors believed to affect stool weight, water-holding capacity [23], production of volatile fatty acids [24], or proliferation of bacteria 1251. There were no changes in breath hydrogen and methane concentrations nor in faecal volatile

165

fatty acid concentrations. This suggests that there was no increase in bacterial metabolic activity or mass as a result of GK entering the caecum and that the GK macromolecules were not degraded significantly during passage through the colon. Although these are indirect inferences, they are in agreement with the report [ll] that GK was not metabolised by rats and appeared virtually quantitatively in the faeces.

Thus GK appears to produce no toxic effects and to have little metabolic effect on the host. This is in contrast to the effects established for some other plant gums and polysaccharides. Gum arabic [26] and whole raw carrot [27] cause the normal concentrations of breath hydrogen and methane to increase; guar galactomannan alters glucose tolerance significantly in both normal and diabetic subjects [28].

The amount of GK used in U.K. foodstuffs production is estimated by INGAR to be slightly less than 100 tonnes per annum. For a population of 55 million this suggests an average intake per person per annum of only 2 g, i.e. approx. 5 mg/day. The results of a subacute toxicity study in rats [IO] indicate, allowing for the customary lOO-fold safety factor, an Acceptable Daily Intake (ADI) of 40 mg/kg/day in man. Such an intake (2-3 g daily) is also adequately covered by the amount of GK (10.5 g) ingested daily in this study.

ACKNOWLEDGEMENTS

We thank INGAR for financial support; the Haematology and Clinical Chemistry Departments and the Metabolic Unit, Western General Hospital, Edinburgh, for specialised analytical services; and Miss S. Douglas, Dietitian, Western General Hospital, Edinburgh, for dietary intake estimations.

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