1. DETERIORATION
OF
FRESH PRODUCE

2. The Nature of Harvested Produce
 Deterioration is a term applied to any change
that leads to a loss of quality such as plant
physiological changes, mechanical damage,
water loss and any other form of injury to the
product.
 Although now removed from the mother
plant, the harvested products continues to
undergo all of the living processes it did prior
to being harvested.

3.  Fresh products start to die as soon as they
harvested, yet they only maintain their
marketability whilst alive.
 Postharvest horticulture is concerned with
slowing down the rate of deterioration in
harvested produce and maximizing shelf-life.
 With the correct application of the appropriate
postharvest techniques, this “dying” process
can be slowed down.

4. Factors Enhancing Deterioration
A harvested product is exposed to six stresses that
enhance its rate of deterioration and subsequently,
reduce its shelf-life. These are :
 The removal of its supply of water
 The absence (in most instances) of photosynthetically
active light levels
 The imposition of atypical temperature regimes
 The mechanical injury caused by harvesting
 The increased susceptibility to microbial infection through
harvest and handling wounds.

5. Photosynthesis
 This is the process in green plants that
converts the sun’s energy in the presence of
carbon dioxide and water into carbohydrates
(food), oxygen and water.
CO2 + 2H2O  (CH2O) + O2 + H2O
 Photosynthesis can only occur if there is light.
 The light must be of a high intensity to be
photosynthetically active.

6.  Hence, from a postharvest perspective,
photosynthesis and therefore, carbohydrate
(food) production for the stops at the point of
harvest.
 This means any living processes that occur
after harvest are fuelled by a limited reserve
of stored carbohydrates, which will be
depleted overtime. As fresh produce is eaten
to provide a source of carbohydrates, the
depletion of this reserve must be minimized.

7. Respiration
 Respiration is used as an indicator of
metabolic activity in plant tissue.
 This physiological process breaks down the
carbohydrates produced during
photosynthesis, in the presence of oxygen to
give carbon dioxide, water and heat energy. It
does not require light proceed and occurs
day and night.
C6H12O6 + 6O2 6CO2 + 6H2O + Heat

8.  Respiration is a reversible reaction that can
move in either direction depending on the
environmental conditions present at the time.
 High oxygen concentrations promote the
forward direction whereas, high carbon
dioxide concentrations promote the backward
direction of the reaction.

9.  Hence, the process is easily manipulated by
altering the environmental conditions around
the product.
 This is basis of the postharvest technologies
known as controlled atmosphere (C.A.) and
modified atmosphere (M.A.)
 The aim of these postharvest techniques is to
slow down the rate of forward movement of
the respiration process.

10.  Respiration after harvest must considered as
follows :
 Stored carbohydrates are used as photosynthesis
does not usually occur after harvest.
 Oxygen is necessary for the respiration process.
A supply of oxygen must be maintained to the
cells in the product if it is to remain in a living
state.

11.  Carbon dioxide produced. This must be removed,
usually through ventilation.
 Water is produced. This can have an influence on
the composition and texture of the product.
 Respiration produces heat. In fact, there are 673
joules of heat energy produced for each gram
molecular weight of glucose respired. It is
character that causes all sorts of problems in the
distribution of harvested horticultural produce.

12.  Temperature is by far the most important
single factor in postharvest quality control.
The rate of respiration and hence, the rate of
heat production, depends on temperature-the
higher the temperature, the higher the rate.

14.  Immature plant tissue has a generally higher
rate of respiration than a more mature form of
tissue. Hence products such as broccoli,
sweet corn, asparagus, spinach, peas and
cut flowers have high rates of respirations.
 The rate of each respiration of each of these
products will in turn be determined by the
product temperature.

16. Classification of fruit and vegetables according to
their respiration rates
Very High
Rate
High Rate Moderate
Rate
Low Rate Very Low
Rate
Asparagus
Broccoli
Mushroom
Spinach
Sweet corn
Avocado
Blueberry
Cut flowers
Green bean
Strawberry
Apricot
Banana
Cabbage
Carrot
Cherry
Peach
Pear
Tomato
Apples
Garlic
Grape
onion
Sweet
potato
Nuts

17. There are two common patterns of respiration
found during the ripening phase of fruit.
1. Climacteric
The characteristic of this respiratory pattern
is the significant increase is the rate of
respiration at the onset of the ripening
phase. This is a measurable increase which
continuous to rise to climacteric peak before
easing off when the fruit attains ripeness.

18.  Fruits which show this climacteric pattern of
respiration include :
 Apples
 Avocado
 Banana
 Kiwifruit
 Mango
 tomato

20. 2. Non-climacteric
This pattern of respiration can have either an
upward or downward trend, depending on the
particular product. However, there is no
significant increase in the rate of respiration
at the onset of ripening. Products that show a
non-climacteric pattern of respiration include :
strawberry, cherry, cucumber, grape, orange,
lemon, pineapple.

22. Senescence
 The development of fruits and vegetables can
be divided into three major physiological
stages after germination.
 These three stages are termed growth,
maturation and senescence.
 Growth involves an increase in size and dry
matter ; maturation overlaps growth and
involves a variety of activities ; and
senescence involves a breakdown in dry
matter.