The influence of seed coat and cotyledon structure on cooking characteristics of cowpeas

Abstract

Cowpea (Vigna unguiculata L. Walp) is an important legume mainly used for human consumption worldwide, particularly in developing countries. Cowpea legume is rich in protein (25%), carbohydrates (70%), dietary fibre, minerals and vitamins. Cowpea comprises a range of varieties that breeders release based primarily on agronomic characteristics, such as yield, early maturity and drought tolerance. However, consumers do not always adopt all the released cowpea varieties. Cooking characteristics such as cooking time and sensory properties (i.e. appearance, texture, flavour) of cooked cowpeas are believed to be quality characteristics for legume acceptability by consumers. Physicochemical characteristics are known to influence cooking characteristics of cowpeas. These characteristics may be influenced by seed coat and cotyledon structure. The present study focuses on the effect of seed coat and cotyledon structure on cooking and sensory characteristics of cowpeas and how this in turn influences consumer acceptability of cowpeas. The influence of seed coat thickness and cotyledon compactness on cooking characteristics of four cowpea types (thick seed coat/compact cotyledon (Bechuana White), thick seed coat/porous cotyledon (IT82E 18), thin seed coat/compact cotyledon (Black Eye) and thin seed coat/porous cotyledon (California Black) was studied. Seed coat thickness was found to influence water absorption during soaking. Cowpeas with thin seed coats had higher rates of water absorption during soaking due to its amorphous cell layer that rendered the seed coat more permeable compared to the palisade cell layer found in cowpeas with thick seed coats. Cotyledon compactness influenced cooking time of cowpeas. Cowpeas with porous cotyledons cooked faster compared to cowpeas with compact cotyledon probably because of the structural arrangement of porous cotyledon cells that provide more intercellular spaces for rapid water entry, cell expansion and separation favouring a faster cooking process compared to compact cotyledon. Seed coat and cotyledon structures directly influenced very few of the cooking and sensory characteristics. Sensory attributes such as cooked cowpea flavour, degree of sweetness, degree of sweet aftertaste, and degree of mushiness positively contributed to consumers’ liking of cowpeas. Raw cowpea flavour, bitter taste, degree of bitter aftertaste and degree of firmness contributed to consumers’ disliking of cowpeas. Chemical composition of cowpeas probably influences sensory characteristics of cowpeas more than seed coat and cotyledon structures. It is recommended that breeders work together with food scientists in order to release cowpeas types that are preferred by consumers (i.e. cowpeas with good appearance (low percentage of splitting), good flavour and soft texture upon cooking. Please cite as follows: Penicela, L 2010, The influence of seed coat and cotyledon structure on cooking characteristics of cowpeas, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-06292011-154445/ > E11/438/gm