Agriculture Reference
In-Depth Information
1
Introduction
Debbie Rees
PERISHABLE PLANT PRODUCTS
The storage and transport of food are central to the way in
which human civilisation has developed. Fifteen million
years ago our human ancestors moved from living in
tropical rain forests to savannah. One of the reasons that this
migration was possible was that at the same time the human
diet changed to include seeds and nuts, and our human
ancestors learnt how to store these between seasons (Kays
1991). Seeds (grains) and nuts are often referred to as
dura-
bles
as they are less perishable than other food products and
can be relatively easily stored. They are generally plant
parts that have a physiological role that requires them to
keep over extended periods of time; thus seeds may remain
dormant over a considerable time before they sprout to form
a new plant. Durables are distinguished from the
perishable
plant products by characteristics such as high dry matter
content and hard texture, and they tend to be small and
homogeneous in shape. Perishable plant products, on the
other hand, have high moisture content and tend to be softer
so that they are more susceptible to physical damage.
Perishable plant products include fleshy fruits (apples,
tomatoes bananas, mangoes), root crops (potatoes, cassava,
sweet potato, yam, onion), leafy vegetables (cabbage, spin-
ach, lettuce), and vegetables arising from stems (celery).
There is a wide range in storability among the perisha-
bles once they have been harvested. Root crops (storage
roots and tubers) tend to be the least perishable. This is
consistent with their physiological purpose to survive
between growing seasons in order to produce a new plant.
Fruits and flowers, on the other hand, are very perishable,
often with a potential storage life of only a few days. As
far as the plant is concerned, their physiological role is
transient; once it is complete the tissues die, usually
through the process of
senescence
, an active, programmed
cell death. Leafy vegetables are very prone to water loss
once they have been separated from the plant roots, which
normally act as their source of water.
When considering the main constraints to storage for
durable and perishable plant products, pests and diseases
are very important for durables, whereas maintenance of
quality in perishable products is very dependant on the
physiological health of the plant tissues.
FRUITS
Given their key importance in world economy, a large part
of this topic is devoted to fleshy fruits. Over the decades,
as our understanding of their development and its control
has increased, fruits have been classified into two types
depending on the biological control of ripening, specifi-
cally the role of the plant hormone ethylene, and the
respiratory characteristics (Rees & Hammond 2002).
The classification of fruit into climacteric
and non-climacteric
Biologically fruits are classified as
climacteric
or
non-
climacteric
according to their respiratory behaviour and
ethylene production rates during ripening. The volatile
plant hormone, ethylene, stimulates a wide range of plant
responses including fruit ripening (Oetiker & Yang 1995;
Rees & Hammond 2002).
