RA 00048.pdf - OAR@ICRISAT

Table 7.
Comparison of results from nitrogen balance studies in sorghum with similarly obtained
corresponding data from other staple foods.
Apparent N balance
Stool weight
Absorption Retention Wet Dry Stool energy
% % (g/day) (g/day) (Kcal/day)
Sorghum 46 14 224 39.0 183
Wheat 81 20 95 13.3 60
Rice 66 26 67 11.6 58
Potato 66 34 165 20.3 78
Maize 73 27 133 2 6 8 117
Casein 81 38 95 15.5 63
involving children in Peru using all staple food
diets based on gruels made of sorghum, maize,
wheat, rice and potatoes. Their results indicate
that whole grain sorghum is "markedly inferior" to
wheat, rice, potato and maize as a source of
dietary protein and energy in diets unsupplemented
with proteins and amino acids fed to
children. MacLean et al. (in press) thus conclude,
"whole grain sorghum is a bulky and poorly
digestible source of dietary energy for children."
Table 7 summarizes the results of 26 dietary
sorghum periods in comparison with corresponding
data from other staple foods. The poor
absorption (46 ± 17%) and retention (14 ± 10%)
of nitrogen and the high content of energy in the
stools from sorghum made it, in this experiment,
a very poor source of dietary protein. Maize was
intermediate between sorghum and the other
staple foods in energy digestibility as measured
by the stool energy. Sorghum was associated
with a dramatic slowing of the rate of weight gain
in these experiments, which presumably resulted
from excessive fecal energy losses and as a
response to inadequate quantity and quality of
dietary protein. The return to the control diet was
associated with a prompt resumption of weight
gain and a rebound in apparent nitrogen retention,
the latter being further indicative of protein
inadequacy during the sorghum period.
All sorghum diets based on sun dried powders
of traditional Tanzanian food products fed to rats
(Table 8. Eggum et al. 1982) also display extremely
low weight gains and low biological value (BV)
of protein as measured in balance trials. Lysine is
extremely low (2.0%) in the raw material and
decreases markedly in the hand decorticated
product (1.2%) while ugali porridge cooked on the
whole grain seems to be more nutritious (weight
gain 1.40 g/day) than the porridge from the
decorticated grain virtually producing zero growth.
It is seen in Table 8 that the rats could not cope
with the food intake in the most lysine deficient
diets indicating an increased strain on the animals.
However, the protein and energy digestibility in
these trials were quite high (about 90%). Eggum
et al. (1982) concluded that the performance of
the rats on sorghum diets in this trial fundamentally
was due to the low level of lysine. Although it is
difficult to compare feeding experiments from
different organisms such as rat and man, two
major factors could be hypothesized to explain
these results.
First, dietary factors such as starch/protein
availability could affect the sorghum digestion
especially in the experiment with children fed the
diet as a gruel. Second, the low lysine content of
these diets would call for supplementation with
properly balanced protein, e.g., milk. A search was
made at Purdue for an in vitro system sensitive to
the digestibility differences between sorghum
and other cereals. Axtell et al. (1981) found that
porcine pepsin in vitro shows these digestibility
differences. The results in Table 9 show that
uncooked sorghum proteins have a high pepsin
digestibility (78-100%), which drops to a range of
4 5 - 5 5 % after cooking. It is therefore essential
that more research be conducted to determine
the nutritional consequences of local methods of
preparation of sorghum foods in countries in
Africa, Asia and Latin America. It is assumed that
the most sophisticated methods of food preparation
would have evolved in areas of the world
where sorghum has been used for the longest
period of time, i.e., the center of origin of the crop
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