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    TOXICOLOGICAL EVALUATION OF CERTAIN FOOD ADDITIVES



    WHO FOOD ADDITIVES SERIES 10





    The evaluations contained in this document were prepared by the
    Joint FAO/WHO Expert Committee on Food Additives*
    Rome, 21-29 April 1976



    Food and Agriculture Organization of the United Nations

    World Health Organization




    *Twentieth Report of the Joint FAO/WHO Expert Committee on Food
    Additives, Geneva, 1976, WHO Technical Report Series No. 599, FAO Food
    and Nutrition Series No. 1.

    Glycerol and glycerol di-acetate

    (Food Grade)

    Explanation

         Glycerol occurs naturally in varied combined forms as a simple,
    mixed or complex glyceride in association with fatty acids,
    carbohydrates, phosphate or amino acid. It rarely exists in
    significant amounts in the free form in natural fats or oils of
    animal, vegetable, marine or biological origin. Glycerol constitutes
    about 10% of the lipid molecule. Natural glycerol is isolated as a
    by-product from the hydrolysis of fats and oils during the manufacture
    of soaps, etc. Trace contaminants include fatty acids, their esters,
    and processing chemicals including background levels of heavy metals.

         Synthetic glycerol is produced by the hydrogenolysis of
    carbohydrate material (cane or corn syrup sugar), or from propylene
    and chlorine by a number of different processes including
    chlorination, chlorohydrination and hydrolysis. Natural and synthetic
    glycerine contain trace quantities of low-boiling components. Specific
    analysis of other components of one synthetic glycerine prepared from
    the hydrogenolysis of chlorhydrate material showed that it contained
    no more than 0.1%, 1,2,3-butanetriol and 0.1% of 1,2,4-butanetriol.
    The 1,2,3-butanetriol consists of erythro and threo isomers in the
    approximate proportion of 90% of the former to 10% of the latter
    (Atlas Chemical Ind., Inc., 1961).

         Glycerol prepared from propylene was shown to be free of aromatic
    compounds. The only specific contaminants identified were glycerine
    polymers and glyceraldehyde (Hine et al., 1953).

    Biological Data

    Biochemical Aspects

         Glycerol is readily metabolized and deposited as glycogen in
    the liver of young white rats (Catron & Lewis, 1929). Glycerol is
    metabolized by rats in a similar manner when administered
    intraperitoneally, intragastrically or intravenously. 14C-Glycerol
    administration results in a net synthesis of blood glucose and liver
    glycogen, as well as resulting in 14C incorporation into the lipids
    (neutral fat and phosphatides) of most tissues (Gidez & Karnovsky,
    1954). Administration of glycerol to 5 to 10 day-old rats resulted in
    a hepatic glycogenesis. This response was diminished in weaned and
    almost absent in animals less than 48 hrs old (Johnson et al., 1971).

         Phlorizinized dogs administered glycerol via stomach tube
    converted it almost completely to glucose which was excreted in the
    urine (Chambers & Deuel, 1925).

         Analogy with triacetin and other di and triglycerides of fatty
    acids shows that glycerol di-acetates will be rapidly hydrolysed by
    hydrolytic enzymes excreted into the gastrointestinal tract as well as
    by esterases present in all tissues. The resulting acetate and
    glycerol will be rapidly and completely metabolized.

    TOXICOLOGICAL STUDIES

    Special studies on reproduction

    Rat

         Groups of 9 males and 18 females were maintained on synthetic
    diets containing 30% glycerol. Rats receiving this diet were carried
    through seven successive generations. Young produced from females on
    the diet weighed on average 20% less than those from control females.
    Studies utilizing lower levels of glycerol were not successful because
    of nutritional inadequacies of the synthetic diet (Guerrant et al.,
    1947).

         In another study rats were maintained on diets containing 61%
    starch and no glycerol, or 20% starch plus 41% glycerol, or no starch
    plus 61% glycerol. Reproduction was not impaired by diets containing
    41% glycerol. However, no pregnancies occurred on diets containing 61%
    glycerol, presumably due to the inadequate nutritional quality of the
    diet (Johnson et al., 1933).

         Groups each of 20 rats (equally divided by sex) were dosed daily
    per os with either 1.0 ml distilled water or 1.0 ml of a 20% aqueous
    solution of glycerol/100 g body wt for eight weeks. Animals (P) from
    each group were then bred. The pregnant rats in each group were then
    divided into two groups of 5, one group continued to be dosed during
    pregnancy, and for 12 weeks subsequent to giving birth to the pups.
    The growth of the pups (F1) was monitored for 60 days. At 100 days
    some of the F1 generation were killed for histological examination of
    the reproductive organs. Ten males and ten females of the F1
    generation were mated on maturity. However, these animals were not
    administered glycerol. The F2 generation was monitored for growth and
    onset of estrus cycle. Administration of glycerol to the P rats had no
    effect on reproductive performance or growth of offsprings and onset
    of estrus cycle of F1 and F2 generations (Wegener, 1953).

        Acute toxicity

    (a)     Glycerol di-acetate
                                                                                               

                                                           LD50                Reference
    Substance           Species        Route          mg/kg body weight
                                                                                               

    Glycerol            Mouse          Oral           8.5 ml/kg BW             Spector, 1956

    Diacetate           Mouse          s.c.           2.5 ml/kg BW             "

                        Mouse          i.v.           2.3 ml/kg BW             "

                        Rat            s.c.           4.0 ml/kg BW             "

    (b)    Glycerol
                                                                                               

                                Oral LD50 mg/kg                   
    Animal                      Origin of glycerol                        Reference
                 Natural          Synthetic 1         Synthetic 2
                                                                                               

    Rat          27.5             -                   -                   Smyth et al., 1941

    Rat          27.2             27.2                -                   Hine et al.,
    (female)                                                              1953

    Rat          17.2 - 22.7      -                   19.4 - 26.6         Atlas Co.,
    (female)                                                              1961

    Rat          21.1 - 28.8      -                   19.8 - 26.4         Atlas Co.,
    (male)                                                                1961

    Mice         20.65  0.47a    20.81  0.58a       -                   Anderson et al., 1950

    Mice         23  1.3         23  1.9            -                   Hine et al.,
    (male)                                                                1953

    Guinea pig   7.75             -                   -                   Smyth et al., 1941

    Guinea pig   10  1.3         11.5  2.8          -                   Hine et al.,
    (male)                                                                1953

    Rabbit       14 - 18a         -                   -                   Deichmann et al,, 1941
                                                                                               
    a  cc/kg.
    Synthetic 1 - Prepared from propylene.
    Synthetic 2 - Prepared from carbohydrate material.
    
    Short-term Studies

    Rat

         Groups each of 5 female rats were given tap water to drink
    containing 0, or 5% by volume natural glycerin, or 5% by volume
    synthetic glycerin (prepared from propylene) for a period of 16 weeks.
    Ground rat rations were allowed ad lib. Hematologic studies
    (hemoglobin, erythrocytes, leucocytes and differentials) were made at
    monthly intervals. At the end of the test period the animals were
    sacrificed and submitted to necropsy. Gross and microscopic studies
    were made of the heart, lungs, spleen, stomach, intestines, kidneys,
    thymus, thyroid and adrenals. Weight gain was slightly increased in
    groups receiving glycerol. Hematologic parameters in test and control
    animals were similar. Histopathologic studies indicated that rats
    (3/5) in the groups receiving glycerol (both natural and synthetic)
    showed that several tubules near the junction of the cortex and
    medulla contained calcified masses. No other compound related effects
    were observed (Anderson et al., 1959).

         In another study groups each of 20 rats were administered daily
    per os either water, or 10 ml/kg body wt glycerol or at 20% aqueous
    solution. Dosing was for a period of 40 days. At the end of the test
    period the animals were autopsied, and histological examination made
    of the liver, kidneys, bladder and small intestine. The only compound
    related effect reported was calcium deposits in the urinary canals
    (Kopf et al., 1951).

         Groups each of 18 rats (Sprague Dawley strain), equally divided
    by sex, were maintained on diets containing 0, or 20%, 10% or 5%
    natural glycerol (99.8% glycerol, 0.02% low boilers) or 20%, 10% or 5%
    synthetic glycerol prepared by the hydrogenolysis of carbohydrate
    products (99.76% glycerol, 0.04% low boilers; and 1,2,3-Butanetriol
    0.11%, and 1,2,4-Butanetriol 0.09%) for 50 weeks. The protein in the
    test diets was balanced with that in the control diet by incorporation
    of casein. The calorie density of all diets was similar. There were no
    significant differences in the growth rate of the test and control
    animals. Gross pathological examination of tissues and organs showed
    that the only possible compound related effect was pituitary growths
    which accounted for the largest segment of all of the observed
    growths. However, there was no pattern or difference with respect to
    the source of glycerol for any of these growths. Microscopic
    examination of the tissues and organs showed no significant pathology
    that could be related to dose or type of glycerin. Frequent changes
    were associated with the kidney (tubular damage, protein counts,
    inflammation and glomerular fibrosis). In male rats there was no
    significant difference in the incidence between test and control. In
    the female, no pathological findings were reported in the control
    animals, but the incidence in the test groups was similar to that
    observed in the test males (Atlas Chemical Co., 1969).

    Long-term Studies

    Rat

         Groups each of 48 rats (Sprague Dawley strain) equally divided by
    sex were maintained on diets containing 0, 20%, 10% or 5% natural
    glycerol (99.8% glycerol, 0.02% low boilers), or 20%, 10% or 5%
    synthetic glycerol prepared by the hydrogenolysis of carbohydrate
    products (99.76% glycerol, 0.04% low boilers, and 1,2,3-Butanetriol
    and 1,2,4-Butanetriol, 0.09%) for two years. The protein in the test
    diets was balanced with that in the control by incorporation of
    casein. The caloric density of the test and control diets was similar.
    The following parameters were measured during the study: mortality,
    growth, efficiency of caloric utilization, water consumption, volume
    of urine excreted, urinalysis (including specific gravity, sediment,
    acetone, albumin, sugar and oxalate), hematologic studies (including
    white blood cells and differential count, red blood cells, hematocrit
    and hemoglobin) and biochemical studies (including blood glucose, urea
    nitrogen, plasma cholesterol, serum alkaline phosphatase and
    transaminases), and bromsulfalein retention. At the termination of the
    study the animals were killed, and subjected to a complete autopsy,
    including determination of organ/body weight ratios, as well as gross
    and microscopic examination of the tissues and organs. Rats fed diets
    containing glycerol gained weight more rapidly than control rats.
    Urine analysis, hematologic and biochemical determinations were
    similar for test and control animals. Male rats fed diets containing
    synthetic glycerol showed a slight dose related trend of increased
    water consumption. Organ/body weight ratios of male and female rats
    showed a significant increase in kidney ratio of rats maintained on
    diets containing 20% glycerol, and of the heart of rats maintained on
    diets containing 10% glycerol. Histopathological examination of organs
    and tissues did not reveal compound or dose related effects (Atlas
    Chemical Ind., 1969).

         Groups each of 22 (Long-Evans strain) rats, equally divided by
    sex were maintained on diets containing 5, 10 or 20% natural glycine
    or synthetic glycerol (prepared from propylene). The control group
    consisted of 26 rats (equally divided by sex). The 20% groups were
    maintained for one year on the test diets, all other groups for two
    years. Urinalysis of hematologic studies were made at 3 monthly
    intervals during the first year of the study, then at 6 month
    intervals. Urinalysis and hematologic parameters were similar for test
    and control animals. Liver glycogen and fat content of the livers of
    rats in the 20% group were similar for the natural and synthetic
    glycerin groups. Organ/body ratios showed females receiving 20%
    synthetic glycerin had liver/body ratios significantly higher than
    controls and females receiving 5% synthetic glycerin had heart/body
    ratios significantly greater than those on the 5% natural glycerin.
    Microscopic examination of the liver, spleen, adrenals, kidney, small
    intestine, bladder and reproductive organs showed no compound or dose
    related effects (Hine et al., 1953).

    Observations in Man

         Fourteen (10 male, 4 female) graduate students ingested 110 g of
    95% glycerol in 3 divided doses with their food daily for a period of
    50 days. Preceding and following this period were 10 day control
    periods. Uric acid excretion and basal metabolism were not
    significantly affected, nor were there changes in red and white blood
    cell counts or hemoglobin level during the test period. No adverse
    effects were reported (Johnson, 1933).

    Comments

         Glycerol occurs naturally in fats and other substances which are
    in part made up of lipid complexes. Glycerol may be derived from
    natural sources, primarily triglycerides, or be synthesized by the
    hydrogenolysis of carbohydrate materials or from products such as
    propylene. Evidence is available to show that glycerol is metabolized
    in the body to form glycogen or provide a direct energy source. In
    addition, long-term studies are available to show that synthetically
    derived glycerols are biologically similar to naturally derived
    glycerol.

         Because certain butanetriols can be contaminants of glycerol
    produced by hydrogenolysis of carbohydrates, there is need to specify
    maximum levels of such contaminants.

    EVALUATION

         ADI for man not specified.


    See Also:
       Toxicological Abbreviations