CHEMICAL MODIFICATION AND COWPEA FORTIFICATION OF MAIZE

ABSTRACT

The high utilization and consumption levels of maize in developing countries call

for the investigation of new methods of processing to introduce variety as well as

improve the functionality and nutrient quality of maize-based foods.

This study was carried out to determine the effect of nixtamalization, fermentation

and cowpea fortification on maize and to identify the dominant microflora in

fermented nixtamalized maize. The effect of cooking and lime concentration was

determined using a 2x4 factorial experimental design, with cooking time (0, 30

mins) and lime concentration (0,0.33,0.5 and 1.0%). The cooking time and lime

concentration , significantly influenced the moisture absorption, pH and colour of

the samples. Water absorption capacity was dependent on the lime

concentration. These indices increased with increasing lime concentration used.

The lime did not significantly alter cooked paste viscosity, ash and protein content.

A 3 x 4 factorial experiment was used to study the effect of fermentation on the

characteristics of nixtamalized maize dough. Fermentation resulted in decreased

pH with a corresponding increase in titratable acidity. Fermentation decreased

the texture, water absorption capacity (25°C), cooked paste viscosity and colour

intensity of nixtamalized maize dough. Traditional maize dough facilitated

fermentation, by acting as a starter culture to produce lower pH and higher acidity

in the steeped:nixtamalized maize dough blends.

The central composite rotatable design for K = 3 was used to study the combined

effect of lime concentration (0- 1%), moisture content (55-65%) and cowpea level

(0-30%) on pH, titratable acidity, water absorption, texture, protein and viscosity

of nixtamlized maize dough (masa) during fermentation. The lime and cowpea

influenced the titratable acidity, water absorption capacity, protein content and the

cooked paste viscosity of the fermented cowpea fortified nixtamalized maize.

Increasing concentration of lime, during fermentation, generally decreased

titratable acidity, water absorption, work required to back extrude an amount of

cooked set slurry and cooked paste viscosity while the addition of cowpea

increased most of these indices.

The final pH and titratable acidity of the fermented nixtamalized maize were

comparable to that of the traditional maize dough. The microbial counts obtained

(aerobic mesophiles and lactic acid bacteria) for the nixtamalized maize and

traditional maize dough, were comparable after 24 hours of fermentation. Yeast

counts were slightly lower in the fermented nixtamalized maize dough. These

results showed that nixtamalized maize dough lends itself well to traditional

spontaneous fermentation with the resultant souring and development of the

characteristic flavours of traditionally fermented maize. The Lactic acid bacteria

identified in the fermented masa were L. plantarum, L. fermentum and L.

cellobiosus. Pediococcus spp. were also identified (found in fermented masa).