inhibiting the formation of stronger covalent bonds in ugali containing
NS 5511 sorghum.
Increase in firmness of ugali after fortification did not appear to be
related to uji CPV reduction. This result is different from the findings
for uji (Section 3.1). The apparent inconsistency may be explained by
the differences in solids content hence, protein concentration, aswell
as the pH differences of these two types of porridges. Uji had 10%
solidswhile ugali had 33%solids.Aminimumprotein concentration is
required to form an extensive protein network (Acton, Hanna, &
Satterlee, 1981; Damodaran, 1996). The relatively higher solids
content of ugali and hence higher protein concentration may have
resulted infirmer ugali, with increasing protein content fromcowpea.
On the other hand, uji CPV was probably dependent mainly on
amount of retrograded starch, which was lower in fortified uji. A pH
level which permits an optimum balance of proteineprotein and
proteinesolvent interactions is required to form uniform strong
extensive networks (Damodaran,1996).The sorghumstorage protein,
kafirin, has an isoelectric point (pI) of 6,while cowpea’smajor storage
protein, globulin, has a pI of 5 (Csonka, Murphy, & Jones,1926). As uji
was acidic (pH 3.7), its proteins would assume a net positive charge
creating electrostatic repulsion thereby probably inhibiting formation
of extensive protein network.
Fortification with cowpea had no effect on the stickiness of Orbit
ugali, while NS 5511 showed no particular trend i.e. the panellists
did not detect the difference noted by the instrumental analysis,
suggesting that the effect was insubstantial for human perception
threshold. The fact that fortification resulted in decrease in stickiness
of NS 5511 sorghum ugali which was not detected by the
sensory panel was possibly because the tannins present cause
puckering of the skin and a feeling of dryness (Prinz & Lucas, 2000),
which probably masked the stickiness.
3.4. Other sensory properties of ugali
Analysis of variance (ANOVA) F-valueswere significant (p<0.05)
for all the 17 sensory attributes of ugali (Table 4), indicating that the
panellists were able to differentiate ugali prepared from the
different types of flour using the descriptive terms selected.
Principal component analysis (PCA) was used to understand the
relationships between the sensory attributes of ugali and the type
of flour used in their preparation, and to relate instrumental
textural properties of the sorghum foods to the human perception
of sensory qualities of ugali. With respect to the first objective,
Factor 1 (accounting for 47% of the variation in the sensory attributes),
separated ugali samples in terms of the sorghum cultivar
used in their preparation, whereas Factor 2 (representing 30% of the
variation) separated the samples based on presence or absence of
cowpea in the ugali (Fig. 2a). Concerning the second objective,
results from instrumental analysis of ugali texture (firmness and
stickiness) and the scores for these textural attributes by the
descriptive sensory panel were positively correlated as shown by
the PCA plot (Fig. 2b) and Table 5.
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