Lecture 2: Biological Aspect of Postharvest Handling of Crops
BIOLOGICAL ASPECT OF
At the end of the lesson, the learners are expected to:
1. Classify fruits and vegetable based on their morpho-
anatomical structures and length of postharvest life;
2. Relate the morpho-anatomical structures of fruits and
vegetables on the length of their postharvest life;
3. Determine the chemical bases for handling common fruits
4. Explain important physiological processes that affect the
postharvest life of fruits and vegetables; and
5. Determine the factors affecting the physiological processes
of fruits and vegetables after harvest.
1 Classification of Crop Produce
2 Structure of Fruits and Vegetables
3 Chemical Basis for Handling Fruits and
4 Post harvest Physiology
5. Factors affecting Physiological
Processes in Fruits and Vegetables
CLASSIFICATION OF CROP PRODUCE
• FRUITS: Botanically, are mature ovaries and
seed bearing parts of plants
grains, legumes, nuts, cucumbers, coffee ,
mangoes, peppers, tomatoes, citrus, bananas,
grapes, strawberry, pineapple, lanzones, rambutan,
dragon fruit, kaong, etc.
The succulent, high
moisture and generally
sweet fruits and
consumed raw as
dessert rather than
Vegetables are all other parts of
plant which are edible.
Include: roots, stems, tubers , leaves
These are generally consumed,
processed in one form or the other and
part of main meal.
Harvested fruits and vegetables
have the following characteristics:
high moisture content
MORPHO- ANATOMICAL BASIS FOR
PERISHABILITY OF FRUITS AND
The response of a commodity to its
surroundings and to the method of handling
depends on what organ it is.
1. Plant part or organ utilized
Leaves and flowers wilt easily, flower
buds open, fruits ripen, bulbs, tubers
and storage roots sprout and shoot
Fruits and fruit vegetables
vary in the nature of their fruit
The fruit wall consists of both
the peel and the edible portion
excluding the seed.
2. Nature of the fruit wall
Some terminologies in relation to
Rind – the tough and leathery peel of
citrus and watermelon.
Pulp – the edible portion of citrus.
Aril – the edible portion of rambutan,
mangosteen, durian and
The nature of the fruit wall greatly
influences the effect of the
environment on the organ and its
susceptibility to mechanical
The thin outer part of the
fruitwall and succulent pulp of
some fruits like tomatoes make
them susceptible to damage.
Fruits with leathery peel are less
susceptible to bruises as in starfruit and
Fruits with thick and hard fruit wall like cucumbers,
melons and squash are better able to withstand damage
than those with soft fruit walls like tomatoes and
It determines the reactive area for
penetration of chemicals and
3. Surface area to volume ratio
The greater the surface area to
volume ratio, the faster the diffusion
of gases involved in respiration, exit
of water through transpiration and
entry of microorganisms and
These result to shorter
The cuticle is the non-cellular waxy layer above
the epidermal cells of the commodity.
The epidermal cells comprise the first layer of the
cells exposed to the environment.
4. Nature of the cuticle
The thicker and more complex the cuticle, the
greater is its protective capacity for:
penetration of microorganism and chemicals
escape of flavor components
Immature fruits deteriorate at a faster rate than
mature ones. Mature fruits have thick, complex and
waxy cuticles whereas immature ones have thin,
irregular and less waxy cuticle.
In winged beans, the wing portion has thinner
cuticle hence it wilts at a faster rate than the other
parts of the pod.
Lanzones is not waxy. Hence, Lanzones
losses water fast which shows up as
browning. Banana deteriorates at a much
Pomelo has thicker rind hence losses
water slower compared to dalandan.
The stomata are the main passageways
for the loss of water and entry of air for
The more stomata , the faster will be the
deterioration of the commodities.
5. Number of Stomata
As the cuticle develops
during full development and
maturation some of the stomata
Pechay has 13,000 stomates per
in the lower surface of one leaf
and possibly twice as much for both
Immature fruits have more stomata
than mature ones which partially
explains why immature fruits deteriorate
Hairs or spines are elongations
of the epidermal cells.
Visible hairs or spines are known
as emergences, while tiny hairs
which may not be visible to the
naked eye are called trichomes.
The special name for the hair of
rambutan is spintern.
6. Amount of Hairs and/or Spines
The more trichomes, the faster is
the deterioration since they increase
the surface area to volume ratio of the
A single rambutan fruit has
200 to 400 spinterns with several
trichomes per spintern.
Lanzones has trichomes
aside from having no wax on
the cuticle. Chinese cabbage
has more trichomes
than mustard while
pechay has none.
Lenticels are circular groups of
protruding air-filled cells with a
central opening which often takes
the place of stomates in fruits,
stems and roots.
7. Presence of lenticels
Laticifers are sap or latex producing
ducts surrounding the vascular bundles.
When the laticifers are cut open
(when harvested or injured) latex is
released. Hence the flows of latex on the
stem must be avoided or washed off
before it hardens.
8. Presence of laticifers
CLASSIFICATION OF FOOD CROPS BASED
ON THEIR POSTHARVEST LIFE
Perishables are food crops whose
food value is maintained over a short
period of time after harvest.
Durables are food crops which can
be maintained as food over a long
period of time.
The Chemical Bases of Handling the
1. Carbohydrate Content
Fruits and vegetables are complex carbohydrates which
supply nutrients, such as vitamins and minerals.
Storage organs contain more carbohydrates hence
usually last longer.
When sugars are being converted to starch, there is a
loss of sweetness in commodities such as in corn.
The conversion of starch to sugars in potatoes (when
stored at a temperature below 10ºC) becomes
undesirable for processing. Sugar causes browning
2. Presence of protopectins
Pectic substances are mainly deposited in
the cell wall and middle lamella, acting as
cementing materials. They occur in the form of:
Total pectic substances increase in amount
during the development of fruits.
As the fruit ripens, the contents of soluble
pectates increase while the total pectic
Protopectin is one of the
substances which form insoluble
salts with calcium or magnesium
and is found as a cementing
substances between cells.
Pectin is a carbohydrate in the
cell wall of plants. It is a breakdown
product from hemicelluloses
(protopectins) which is generated
during ripening of the fruit.
Pectin itself is later broken
down to pectinic acid and finally
pectic acid. During this chemical
breakdown process, the fruit gets
softer as the cell walls degenerate
Guava, pineapples and
oranges contain high pectin, while
soft fruits like cherries and
strawberries contain few.
Under acidic conditions, pectin
forms a gel. This effect is used for
making jams and jellies.
The change of color during ripening is due
to changes in the pigments.
Color Main Pigment
Green, blue green,
yellow green in most
Red in tomatoes
Orange of carrots
Red in strawberry
Yellow in papaya
Purple in eggplant
Main Pigments Responsible for specific color of some
Pigment Color Found in
anthocyanins blue/purple/red berries, grapes, red peppers, beets,
beta-carotene orange/yellow carrots, pumpkin, sweet potatoes,
citrus, papaya, melon, squash
curcumin yellow turmeric
lutein yellow/orange kale, broccoli, spinach
lycopene red tomatoes, watermelon, red
zeaxanthin yellow corn
You need not worry about the fat content of
avocado, as this fat is not harmful nor does it increase
your cholesterol levels.
Saturated fats, are those types of fat that are
harmful and increase cholesterol levels. However,
monounsaturated fats(avocado fat is of this type) and
polyunsaturated fats, are not harmful and do not
increase cholesterol levels. On the contrary
monounsaturated fat and avocado fat help lower
At maturation, reducing sugar
increases while the acidity
decreases, hence the matured/ripe
commodities taste sweeter.
Different practices in PHM
Physiological Processes that Occur
in Harvested Commodities
All fruits and
vegetables are living
They use oxygen and produce
carbon dioxide during respiration,
the process by which
carbohydrate and other
substrates, such as organic
acids, proteins and fats, are
Different practices in PHM
1. Respiration is an oxidation process by
which organic materials or products of
photosynthesis are broken down to simpler
forms accompanied by the release of energy
C6H12O6 + O2 CO2 + H2O + energy
Different practices in PHM
thereby provides the
for cells to maintain
structure and for
such as color and
Different practices in PHM
The substrates cannot be
replenished once the fruit or vegetable
has been removed from the plant.
Faster respiration rates will result
in loss of food nutritional value, loss of
saleable weight, poorer flavor, and thus
reduced product quality.
This process is a very good indicator of
the potential postharvest life of a
Faster respiration means faster release
of heat which increases the temperature of
the surroundings of the commodity
especially if packed tightly.
The energy source is depleted and the
built up of compounds necessary for
maintaining the organization of the tissues
and cells stops.
The commodities with high respiration
rates cannot be expected to last long.
Commodities with low respiration
rates are storage organs.
Ex. Onions, potato, gabi, sweet potato,
yams and ginger. Respiration date as
about 1.52 mg CO2/kg/ha
Commodities with intermediate rates
are exemplified by many fruits at
The respiration rate of lanzones is 70 mg
Commodities with high rates are organs at
Ex: asparagus, snap beans, cauliflower, okra,
young corn, bean sprouts. the respiration rate is
570.6 mg CO2/kg/ha at 26 degrees centigrade.
The main organs of a plant are root, stem, leaf,
flower and fruit.
To keep these organs alive, their organization must
Once there is a breakdown in this organization
even at the cellular level, there is a corresponding
change in the metabolism of the commodity which
eventually shows in the state of deterioration.
To maintain the organization and sustain
metabolism, energy is made available through
respiration using carbohydrates accumulated before
Post Harvest Changes
A view of spoilage of fresh fruits by microbes and biochemical changes
Product quality at
Poor quality of products due
improper handling after harvest
Lengthening of postharvest life,
therefore, calls for good production
practices in order to have greater energy
source at harvest, and respiration should
be slowed down after harvest to enable the
source of energy to last for a long period
2. Transpiration is the loss of
water from the plants.
Most fruits and vegetables are
composed of cells loosely bound
together with considerable
intercellular spaces which
interconnect and lead to lenticels
Water from cells vaporizes
into the intercellular spaces and
maintains an essentially
Water vapor may then move
to the atmosphere through the
stomates or lenticels, stem
scars or through injured areas
or directly through breaks in the
Horticultural products can be
regarded as “water inside pleasing
packages” or “water with a mechanical
Therefore, water loss or
transpiration is a major factor affecting
quality of fruits and vegetables.
Consequences of water loss
loss in weight of all commodities
softening of fruits and vegetables
wilting of leaves and flowers
shrivelling of fruits and root crops
stem end rind breakdown of oranges
discoloration of rambutan and lanzones
Fresh fruits and vegetables consist
mainly of water.
It could be as high as 98% by weight in
fully turgid leaves.
Loss of water can dry up a commodity.
A 10% loss in weight may result in
100% commercial loss.
The high amount of water in
commodities makes them succulent
and therefore susceptible to mechanical
Implication: The faster
water is lost from the
commodity, the faster it
losses its freshness.
should be slowed down
to keep the commodity
3. Ethylene Production
Ethylene (C2H4) is a hormone in gas
form which causes the following in
promotes sprouting of root, tuber
and bulb crops
induces abscission of leaves, petals
Implication: If you want to avoid the
ethylene effects, eliminate ethylene
from the atmosphere surrounding the
commodity. On the other hand, if you
want to hasten the ripening process
add ethylene or induce it to increase.
Conditions which will slowdown the
rate of respiration and transpiration
1. Low Temperature
The higher the temperature above
the optimum temperature, the faster is the
rate of respiration and transpiration and
consequently shorter postharvest life.
Keeping a commodity at a low
temperature is thus the most effective
way of extending postharvest life.
2. Low oxygen in the immediate
A high concentration of oxygen (21%)
will result to faster respiration rate and shorter
Oxygen levels below 21% but usually
not less than 5% will slow down respiration.
Very low oxygen concentration will however
result in fermentation which is an abnormal
form of respiration resulting in alcoholic odor
or undesirable flavor and tissue collapse
3. High relative humidity
The lower the relative humidity of the
air, the faster is the transpiration.
Since commodities are considered to
have relative humidity close to 100%, it is
therefore important to keep them under
moist conditions, that is, at high relative
humidity even at low temperature.