Production Practices and Quality Assessment of Food Crops. Vol. 1

2 R. M. Madakadze and J. Kwaramba
for classification of fresh vegetables for market consumption or specifications for
vegetables for the processing companies (Martens and Baardseth, 1987).
The establishment of specifications for a product of good quality is a complicated
matter that requires the cooperation of producers, dealers, authorities and consumers.
A consumer survey conducted to gain information about consumer satisfaction
with food products showed that they were strongly critical of taste and appearance
(Handy and Harger, 1977). Although vegetables are important from a nutritional
point of view (Goddard and Mathews, 1979), the food has no nutritional value
until it is eaten. Sensory quality properties are therefore of primary importance to
the consumer in the decision to buy (and eat) vegetables (Stevens, 1974).
Quality can be further divided into external and internal quality (Martens and
Baardseth, 1987). External quality includes attributes concerning appearance (e.g.
colour, size and shape). Internal quality includes attributes concerning flavour and
texture. Flavour is influenced by chemical properties and perceived mainly by the
senses of taste and smell. The chemical substances may include carbohydrates,
fat, protein, oils, organic acids and water. Texture is caused by a combination of
physical properties and perceived by the senses of kinaesthesis, touch (including
mouthfeel), sight and hearing. The physical properties may include number, nature
and conformation of constituent structural elements (e.g. proteins, starch and cellulose).
Instrumental, physical and chemical methods used for quality evaluation
ought to be calibrated with respect to sensory response. A chemically measured
change of a product may not be perceived as a change by the human sense. Most
of the postharvest quality changes reported in the literature are measured by instruments
or by chemical analyses with no reference to sensory criteria, or with
incomplete description of how the sensory analysis is performed (Martens and
Baardseth, 1987).
Several constraints are encountered in the production of quality vegetables in
the tropics. These include land availability, pests, diseases and marketing. Pest
control is hampered by lack of knowledge and high costs of inputs especially
chemicals. Most producers have little choice in selecting land for cropping since
there are no alternatives. Some of these factors also affect crop growth, development
and quality of the harvested produce. Other factors that affect growth and
development of the vegetables include the climatic conditions and the environment
as a whole. During site selection factors such as rainfall, temperature,
topography, soil, and day length must be considered, as they directly affect the quality
of vegetables. These factors including water availability, water quality and general
farm practice all integrate to give the required quality.
The environment is composed of elements such as land, climate and other plants.
Some plants may adapt to the climate but fail to adapt to the soil conditions, this
then affects the quality of the harvested produce. Vegetables can either be grown
in protected environments or in the open field. Regardless of this fact, they still
require specific temperature, water, light, soil and all the other conditions in order
to grow and yield quality produce. This chapter aims to highlight the growing
environmental conditions for vegetables and how they affect the quality of specific
vegetables namely tomatoes, cabbages, sweet potatoes and squash.