RA 00048.pdf - OAR@ICRISAT

Table 8.
Nutritional quality of the improved low-tannin sorghum variety, 2Kx17/B/1, as processed in
Tanzania. Rat balance tests according to Eggum et al. 1982.
Weight Feed Biological
gain consumed value Lysine
(g/day) (g/day) (%) (g/16g N)
1. Whole grain 1.26 9 7 55.9 2.0
2. Laboratory ugali whole grain 1.40 9.8 55.7 1.9
3. Hand decorticated in Tanzania 0 5 5 6 3 47.4 1.2
4. Ugali from (3) cooked in Tanzania 0 0 4 6.1 49.4 1.2
Table 9.
Effect of temperature on digestion of sorghum proteins by pepsin.
Whole kernel*
Dehulled kernel*
Variety Uncooked Cooked Uncooked Cooked
IS-11758 high-lysine
954063 normal
P-721 opaque
P-721 normal
88.6
88.9
93.0
92.9
45.3
50.6
56.7
46.4
78.2
81.7
85.7
81.1
41.4
37.1
43.0
40.7
* Percent solubilized by pepsin Average of duplicate values
(Ethiopia and Sudan). Results of pepsin digestibility
studies of some Sudanese sorghum breads are
now complete and show clearly that local processing
(fermentation to pH 3.8) significantly improves
in vitro protein digestibility of sorghum
proteins. Two fermented sheet-baked sorghum
products (kisra and abrey) from Sudan gave
pepsin digestibility values of 6 5 - 8 6 % (Table 10).
In contrast, unfermented cooked gruels made in
our laboratory from the same flours using the
Johns Hopkins cooking technique gave pepsin
values of only 4 4 - 5 6 % . Therefore, fermentation
improves pepsin digestibility of sorghum proteins.
Experiments on rats with similar diets (Eggum et
al. 1981) points in the same direction as the in
vitro studies although the differences are less in
vivo. Thus addition of acid to pH 3.8 while cooking
porridge from Feterita sorghum reduces the drop
in true digestibility of protein due to cooking from
13% to nil. Sorghum-based fermented infant
foods (nasha) are currently being prepared for
trials with children in Peru and Sudan, in cooperation
with Food Research Institute in Khartoum.
The biochemical basis of the reduced nutritional
value of some sorghum-based foods remains
unknown. One possibility being explored is related
to the protein solubility fractionation patterns
observed in sorghum versus other cereals. Nwasike
et al. (1979) showed that Landry-Moureaux
fraction III in sorghum comprises a much larger
proportion of the total prolamine proteins in
sorghum than in corn or pearl millet (Table 11).
Guiragossian et al. (1978) first demonstrated the
high proportion of cross-linked kafirins (fraction III)
in sorghum endosperms from both normal and
high-lysine grains (Table 12). The possibility exists
that the cross-linked kafirins in sorghum are
involved in the formation of complexes with
starch during cooking which then reduces availability
to digestive enzymes. It would be extremely
useful to have a sorghum mutant with reduced
fraction III kafirins to test this hypothesis, but
none are available at this time.
It is concluded from our present knowledge that
monotonous sorghum diets are especially detrimental
to growth and health and need supplementation
with adequate protein sources such
as legumes. Pushpamma et al. (1979) demons-
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