Toxicological evaluation of some food
additives including anticaking agents,
antimicrobials, antioxidants, emulsifiers
and thickening agents
WHO FOOD ADDITIVES SERIES NO. 5
The evaluations contained in this publication
were prepared by the Joint FAO/WHO Expert
Committee on Food Additives which met in Geneva,
25 June - 4 July 19731
World Health Organization
Geneva
1974
1 Seventeenth Report of the Joint FAO/WHO Expert Committee on
Food Additives, Wld Hlth Org. techn. Rep. Ser., 1974, No. 539;
FAO Nutrition Meetings Report Series, 1974, No. 53.
AMYLOSE AND AMYLOPECTIN
Explanation
Normal native starches consist of a mixture of 15-30% amylose and
70-85% amylopectin. Amylose structurally is a linear polymer of
anhydroglucose units, of molecular weight approximately between 40 000
and 340 000, the chains containing 250 to 2000 anhydroglucose units.
Amylopectin is considered to be composed of anhydroglucose chains with
many branch points; the molecular weight may reach as high as
80 000 000.
One hundred per cent. amylopectin or "waxy" starches are
commercially available having been extracted from special mutants of
the parent plant e.g. waxy corn or waxy rice. Starches with a very
high amylose content have also been produced, but on a limited scale
for special application. The granules of native starches are extracted
from the plant source by purely physical means, washed and dried. Even
in this way a certain small amount of modification takes place so that
the raw starch is strictly speaking not the same as it existed in the
plant. The changes which have taken place are, however, only of
academic interest. From the nutritional point of view it is important
to realize that the human gastrointestinal tract digests very
efficiently raw cereal and root starches such as wheat, maize, rice
and cassava but is not able to digest easily raw potato, arrowroot and
canna starches (Booher et al., 1951).
Digestibility of starches may be assessed by studying the action
of pancreatin or other sources of amylase (Leach & Schoch, 1961;
Sandstedt et al., 1962) or of taka-diastase (Kihara & Kawase, 1949)
in vitro on the raw granular starch, or by feeding the raw starch to
animals such as rats and chicks. But from the standpoint of use in the
human diet it is the gelatinized (cooked) form that requires
evaluation. From the work of Sanstedt et al. (1962) and Borchers
(1962) it is clear that both in vitro studies and animal feeding
establish the resistant character of some high amylose corn starches
to amylolytic attack.
Nevertheless it does not appear likely that in practice high
amylose corn starches in gelatinized form will present any problem of
digestibility to man, who has no difficulty with gelatinized potato
starch. The digestibility of raw granular potato starch in vitro was
15.98% under conditions where corn starch yielded a value of 65.64%
(Kihara & Kawase, 1949). In the studies by Sandstedt et al. (1962) the
susceptibility of potato starch in vitro to pancreatic digestion was
far lower than that of the most resistant high-amylose corn starch.
Although in vivo digestibility invariably exceeds the in vitro
value, it is unlikely that potato starch would prove more digestible
than high-amylose corn starch, either raw or gelatinized.
Comments:
These native starches should be regarded as food rather than food
additives.
EVALUATION
Estimate of acceptable daily intake for man
Not limited.*
REFERENCES
Booher, L. E., Behan, I. & McMeans, E. (1951) J. Nutr., 45, 75
Borchers, R. (1962) Cereal Chem., 39, 145
Kihara, Y. & Kawase, Z. (1949) Rept. Food Res. Inst. (Japan), 2, 25
Leach, H. W. & Schoch, T. J. (1961) Cereal Chem., 38, 34
Sandstedt, R. M. et al. (1962) Cereal Chem., 39, 123
* See relevant paragraph in the seventeenth report, pages 10-11.