Thesis Abstract

The first objective was to determine if particle size distribution (PSD) of differently milled samples had an influence on hydration properties of the meals. The second objective was to select samples with particle size distribution most similar to the control and prepare akara from them. Functional properties of paste and akara quality were also determined. Sieve shaking and laser diffraction were used to determine PSD. Plate mill setting with the largest clearance yielded samples with 1558 microns mean diameter; this sample also produced akara that was most similar in proximate composition and textural quality to the control-WTM (wet milled). HM-2.54 (Hammer mill with 2.54 mm screen) was found to be the ideal sample as it had low amount of fat (~21%) and received high sensory ratings.

Thesis Overview

INTRODUCTION

            1.1 Background of the study

Cowpea is a drought-resistant crop, a characteristic that makes it ideal for growth in East and West Africa. It is a high protein food and forms a major part of the African diet. Paste prepared from cowpea is usually consumed in the form of akara (fried cowpea paste), moin-moin (steamed cowpea paste), and koki (whipped and steamed paste with spices and palm oil). To make akara, whole cowpea seeds are soaked, decorticated by rubbing, and ground using a mortar and pestle (wet milling). Salt, onions, and, fresh peppers are added according to taste, and the paste is then whipped before frying. Whipping incorporates air into the paste thus giving the final product its much-desired spongy texture.

Traditionally, cowpea is processed by wet milling. This process takes a long time and is very tedious and laborious. An alternative processing technique is dry milling. The cowpea can be milled into flour and then hydrated to the desired consistency and used for akara production. This reduces soaking time and the process of preparing akara is shortened. Dry milling has its limitations, however, and research indicates that the dry milled cowpea makes poor quality akara, which is dense and hard in texture. The poor quality of akara is attributed to the fine particle size of the flour. Fine milling breaks down the cell wall materials, thus destroying the fiber structure (Kethireddipalli et al., 2002a). This leads to poor water absorption by the flour, which subsequently affects the water holding (WHC) and swelling capacity (SWC) of the flour. Poor WHC and SWC lead to a product with tough texture and poor quality.

The method of dry milling used in processing cowpea also determines the paste properties and the end product quality. Dry milling can be done by using various mills, screen sizes, and clearances. This in turn leads to flours of varying particle size and hence, the end product made from these flours differs in quality too. The real challenge here is to produce flour that makes a similar or better product than the wet-milled one. This can be done by evaluating the effect of milling techniques on respective particle size distributions and then manipulate various factors to produce a particle size distribution similar to that of wet-milled paste.

Investigations revealed that a large initial particle size plus a blending step during paste preparation considerably improves the functional characteristics of paste and quality of final product. In this study an attempt has been made to enhance and reproduce the quality of dry milled product by manipulating its particle size and blending times. Particle size distribution significantly influences paste functional properties and end quality of akara.

1.2 Problem statement

Traditionally, cowpea is processed by wet milling. This process takes a long time and is very tedious and laborious. An alternative processing technique is dry milling. The cowpea can be milled into flour and then hydrated to the desired consistency and used for akara production. This reduces soaking time and the process of preparing akara is shortened. Dry milling has its limitations, however, and research indicates that the dry milled cowpea makes poor quality akara, which is dense and hard in texture. The poor quality of akara is attributed to the fine particle size of the flour. Fine milling breaks down the cell wall materials, thus destroying the fiber structure (Kethireddipalli et al., 2002a). This leads to poor water absorption by the flour, which subsequently affects the water holding (WHC) and swelling capacity (SWC) of the flour. Poor WHC and SWC lead to a product with tough texture and poor quality.

1.3 Objective of the study

The main aim of the study is to examine the effects of processing on the storage stability and functional properties of cowpea flour in the production of flour and moi moi.

The study was guided by the following minor objectives;

To determine the particle size distribution for dry milled products

To determine the particle size distribution for wet milled products

To assess similarities between the functional properties of dry and wet milled products.

1.4 Research Questions

What is the particle size distribution of dry milled products?

What is the particle size distribution of wet milled products?

What are the similarities between dry and wet milled products?

1.5 Research hypothesis

H1: Dry milled product with a particle size distribution similar to that of traditional wet-milled paste will translate into similar paste properties and end product.

1.6 Scope and limitation of the study

This study which is titled the effects of processing on the storage capacity and functional properties of cowpea flour in the production of moi moi and akara was aimed at accessing the effects of particle size distribution and milling method on the storage capacity and functional properties of cowpea paste in the production of moi moi and akara. The study was limited to assessing the effects of variables on the case study, no study was made on methods of improving the performance of cowpea paste in the production of moi moi and akara.

1.7 Definition of terms

Storage: This can be defined as the action or method of storing something for future use.

Stability: This can be seen as the state of being stable.

Cowpea: This refers to a plant of the pea family native to the Old World tropics, cultivated for its edible pods and seeds

Flour: The word flour refers to a powder obtained by grinding grain, typically wheat, and used to make bread, cakes, and pastry.

Moi moi: Moimoi or Moin-Moin is a Nigerian steamed bean pudding made from a mixture of washed and peeled black-eyed peas, onions and fresh ground peppers.