Fruit

About This Presentation

Title:

Fruit

Description:

Fruit & Vegetable Processing Postharvest Physiology I. INTRODUCTION Fruits and vegetables when harvested from vines or plants are living structures ... – PowerPoint PPT presentation

Number of Views:428

Avg rating:3.0/5.0

Slides: 78

Provided by: ome

Category:

more less

Transcript and Presenter's Notes

Title: Fruit

1
Fruit Vegetable ProcessingPostharvest
Physiology

I. INTRODUCTION
Fruits and vegetables when harvested from vines
or plants are living structures, continuing
metabolic reactions and sustaining physiological
processes for a considerable time during their
postharvest period.
Fruits and vegetables respire by taking up
oxygen, and giving off carbon dioxide and
generating heat
they also transpire, i.e., lose water in vapor
form.

The respiration and transpiration losses are made
up by replenishing water, photosynthates (sucrose
and amino acids), and minerals from the time-flow
of cell sap while fruits and vegetables are
attached to the plants or vines.
Subsequent to harvest, the source of water,
photosynthates and minerals are cut off, and they
enter into a deterioration or perishable phase.

Several changes take place in cell-wall
composition and structure that result in the
softening of the fruits and vegetables.
In general, visual color gradually changes as
chlorophyll is degraded and yellow pigment of the
skin and flesh increases in content.
In fruits and vegetables respiration involves the
enzymatic oxidation of sugars to carbon dioxide
(C02) and water, accompanied by release of
energy.
However, other substances such as organic acids
and proteins also enter the respiratory chain.

Consequently, the loss of these reserves in
fruits and vegetables results in the production
of energy and the accompanying need for oxygen
(0,) and removal of CO,.
Cellular water is lost because of respiration and
transpiration, resulting in fruits and vegetables
becoming soft, shriveled, and limp.
Anthocyanins that give the typical red, orange,
blue, and other pigments of some fruits and
vegetables may increase after harvest.

Apples, plums, pumpkins, and others enhance color
development in a packaging shed or in a
refrigerator.
The skins of some fruits and vegetables develop
bloom or waxes after harvest that gives them an
attractive appearance which may aid in reducing
transpirational losses.
Starchy fruits and vegetables undergo a decrease
in starch and increase in sugar and acids after
harvest.
However, there may be changes in the kinds of
acids present.

In certain cases as maturity advances,
astringency decreases caused by tannins or
polyphenols.
Volatiles and aroma components of many kinds of
fruits and vegetables are produced after harvest
if they are mature or ripe.
However, when they are harvested rather immature
or at the green stage for distant shipment,
they do not yield typical aroma.
For example, if Jordanian peaches are harvested
for shipment to Kuwait market they do not develop
as good aroma as when allowed to mature and ripen
on the tree.

Ethylene is one of the volatiles synthesized in
certain fruits and vegetables at certain stages
of maturity and development when it reaches a
high enough concentration, it triggers the
ripening process and more ethylene is produced
and the process of ripening is accelerated.
Growth, development. prematuration, maturation,
ripening, and senescence (Figure 1) are the most
important phases in fruit and vegetable ontology.
The growth of fruits and vegetables begins with
cell division and cell enlargement, which
accounts for the final size.

8
(No Transcript)
9

Growth and maturation is referred to as fruit
development.
Senescence is the period when anabolic and
biochemical processes give way to catabolic
processesleading to aging and final death of the
tissue.
Ripening generally begins during the later stages
of maturation and is considered the beginning of
senescence.
The relative changes in weight, sugars,
chlorophyll, and acidity are common to most
fruits and vegetables (Figure 2) but other
parameters such as respiration, flavor, aroma,
and carotenoids can vary from commodity to
commodity.

10
(No Transcript)
11

II. RESPIRATION
Respiration of fruits and vegetables is an index
of physiological activity and potent storage
life.
It is one of the basic processes of life and
directly related to maturation, handling,
transportation, and subsequently, storage life.
Respiration of fruits and vegetables involves the
enzymatic oxidation of sugars to carbon dioxide,
water, and release of energy (Figure 3).

Other substrates such as organic acids, fats, and
proteins also play an important role during the
process of respirarion.
The energy produced by the oxidation of sugars is
convened into the energy of adenosine
triphosphate (ATP), as an energy carrier.
The oxidation of sugars takes place in several
steps under control of specific enzymes. A simple
formula for respiration may be as follows Sugar
602 gt 6C02 6H20 Energy

As indicated above this respiration of fruits and
vegetables involves the following aspects
1. Substrate the quantity of substrate
(predominantly sugars) in fruits and vegetables
available for respiration is a deciding factor
for their longevity at that temperate.
The weight loss due to increased temperature and
respiration usually is more than to five percent
depending upon the structure of the fruits and
vegetables.

2. Oxygen the supply of 02, for normal
respiration is generally adequate unless
intentionally restricted as in the case of CA
(Controlled Atmosphere) Storage.
3. Carbon Dioxide removal of respiratory CO2
requires more attention than supply of 02 because
CO2 may be in excess even when supply of 02 is
adequate.

A three to five percent reductions of 02
concentration would not have an adverse effect on
a product, but a comparable increase in CO2 could
suffocate and ruin certain fruits and vegetables.
4. Energy removal of heat from respiration is
vitally important otherwise the life of fruits
and vegetables will be reduced to an increased
temperature around the commodity.
Increase in rate of respiration causes
acceleration of substrate utilization.

5.Rate of Respiration The rate of respiration
determines the quantity of 02 that must he
available per unit of time.
The quantities of CO2 removed at he same time.
Increased rate of respiration will reduce the
storage life of product.
Rate of respiration is a function of temperature
and available concentration of 02 around the
fruits and vegetables.

In addition. some fruits such as potatoes will
have a lower rate of respiration than spinach or
lettuce due to inherent substrate available for
respiration and the anatomical variations of the
commodities.
The rate of respiration can he defined as the
weight of CO2 produced per unit fresh weight and
time (mg CO2/kg/h) (Table 1).
The rate of respiration may be expressed in ml
CO2/kg/h or the quantity of 02 taken up rather
than CO2 given out.

18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21

The classification of the rate of respiration is
presented in Table 2.
6. Initial Rate of Respiration the rate of
prevailing respiration or within a few hours
varies depending upon crop and temperature)
7. Average Rate of Respiration It is determined
by measuring rates at a definite time interval,
summing the rates thus determined, and dividing
by the number of intervals involved.

22
(No Transcript)
23

8. Effects of Temperature and Days in Storage on
Rate of Respiration the rate of respiration
generally increases as the temperature and the
storage duration of fruits and vegetables
increases.
However, at very high temperatures and at the
very long storage duration, the rate of
respiration decreases until the death of
products. However, one does not store fresh
commodities at such high temperatures (Figures 4
and 4A).
9. Effects of Commodity on Rate of Respiration
the rate of respiration varies depending upon
commodity and variety, also the commodity will
vary with other varieties of the same commodity.

24
(No Transcript)
25
(No Transcript)
26

10. Maturity of Fruits and Vegetables on
Respiration Rate fruits and vegetables harvested
at early maturity for distant market respire
faster than those harvested at the firm-ripe
maturity.
11. Vant Hoffs Law this law indicates that the
rate of chemical reaction is controlled by
temperature.
He coined the term Q10.This indicates at each
10C rise in temperature, the rate of reaction
doubles.
However, Q10 for respiration may not always be
doubled sometimes it may be more than doubled
depending upon the maturity and anatomical
structure of the fruits or vegetables.

Postharvest physiology is influenced by
preharvest factors on the farm or in the orchard.
Physiology of fruits and vegetables begins at the
time of blossoming or bud formation and is
affected by agricultural practicesfertilization,
variety, and irrigationand by environmental
factors such as sunlight duration and quality,
temperature, humidity, etc.
The genetics of fruits and vegetables determine
postharvest storage life. Those crops that are
most perishable such as lettuce, spinach,
strawberries and raspberries have a short growing
season life.

In contrast, Winesap apples which require 160 to
170 days to develop have a longer storage life.
Summer cultivars of apples generally have a
shorter storage life because they ripen earlier.
Likewise, early summer apples have a higher
respiration rate than fall apples they also have
a greater number of cells, more lenticels, and
give off more ethylene.

However, one should not conclude that the
differences in storage life of fruits and
vegetables can be explained simply by length of
growing season, respiration rate, or amount of
ethylene released.
It involves genetic factors which control growth,
development. postharvest behavior, and
physiological and morphological variations.

Ill. TEMPERATURE QUOTIENT OF RESPIRATION The
temperature quotient (Q10) is not the same for
all fruits and vegetables, nor will it be the
same for another variety of the same fruit.
The example is presented in Table 3.
As a general rule, it can be said that an apple
or pear will ripen as much in a day at 21 C as
it will in a week at 0 C.

31
(No Transcript)
32

Thus it is apparent that refrigeration is an
effective means of extending the commercial life
of fresh produce.
Fruit growers and shippers have learned by
practical experience that the growing season has
a powerful influence on the storage age of
fruits.
For example, it has been recognized that t is
hazardous to store or to ship Bartlett pears
grown in cool coastal areas to distant places,
because they often develop core breakdowna
physiological disorder that makes pears too soft
and mushy.

Some cultivars of apples grown in cool climates
cannot tolerate storage temperature of 0 C and
must be stored at higher temperatures such as
(2.24.4 C) In order to avoid low temperature
breakdown.
Sweet as well as sour cherries develop scald when
weather in is unusually warm and dry during the
several weeks before harvest
Chemical reactions of respiration are controlled
by temperature and ideally, one could expect a
Q10 of about 2.5 for respiration.

This means that for a 10C rise in temperature,
the respiration would double.
Rapidly growing young tissue respires faster than
that which develops slowly.
The rate of respiration of asparagus is one of
the highest rates of all fruits and vegetables
because of the rapidly growing shoots of the
plant.

Fruits and vegetables vary in respiration rates
and there are differences between cultivars and
their maturitiesso it is not to be expected that
the respiration rate will be a fixed value at any
given temperature.
It tends to be more constant at temperatures of
(0 to 4.4C) than at higher temperatures of (21.1
to 26.7C).
At the temperature range (0 4.4C), where fruits
and vegetables are held the longest-time, their
heat of respiration is a factor to be included in
calculating the refrigeration requirements for
refrigeration storage and transportation.

In the case of fruits and vegetables, after
harvest, fast cooling is generally desirable
especially for perishable soft fruits such as
berries and leafy vegetables.
This not only reduces metabolic activity of
fruits and vegetables, but also controls fruit
decay.
Fungi and other microorganisms increase rates of
respiration as do bruises and mechanical
injuries
the most serious consequences of holding fruits
and vegetables at high temperature is the
hastening of ripening, and shortening of storage
and marketing life.

37
Climacteric and nonclimacteric fruits and
vegetables

A large number of fruits and vegetables show a
sudden and sharp rise in respiratory activity
called the climacteric rise during the life
cycle
whereas others which do not show climacteric rise
are called nonclimacteric fruits and vegetables.

The time of harvest for climacteric fruits and
vegetables is critical for their maximum storage
life and quality.
Non-clirnacteric fruits and vegetables are
allowed to ripen on plants or vines and the
resulting maturity is regulated by storage.
Maturity tests such as color, brix, acidity, and
others are employed to determine whether they can
meet standard grades and can be legally sold.

39
The classification of edible fruits and
vegetables according to their respiration pattern
40

Respiratory patterns vary from growth and
development and also from fruit to fruit and
vegetable to vegetable
most leafy vegetables are of non-climacteric
nature (Figure 5).
Respiration is not merely a catabolic process,
but it provides energy to synthesize enzymes,
cell membrane constituents, and other material
necessary for life of the cell.
It takes place within the cell at the site of the
various enzymes that participate in the process
of respiration.

41
(No Transcript)
42

Respiration and ripening can be retarded by
reducing the amount of O2.
Ethylene, if O2 is present, will increase the
respiration rates and other metabolic processes
as well.
The ethylene may come from the fruit or the
vegetable itself or be added to the atmosphere.
In a fruit or a vegetable that has climacteric
rise in respiration, ethylene treatment initiates
the rise earlier, but the rates reach no higher
levels.
The climacteric in respiration of certain fruits
generally occur at the onset of processes
involved in ripening.
The peak of respiration does not always coincide
with peak of ripening.

43
IV. ETHYLENE PRODUCTION AND EFFECTS

The Chinese knew in ancient times that pears
could be ripened by exposing them to the smoke of
incense burned in closed rooms.
Many years ago in Florida and California, oranges
were colored or more correctly degreened by
exposure to fumes from kerosene stoves or exhaust
from a gasoline engine in a special coloring
room.
Ethylene is the active degreening agent in stove
gas and a concentration of 4 ppm would degreen
lemons in 6 to 8 d.

After this discovery, ethylene became generally
used for degreening citrus fruits, bananas, honey
dew melons and tomatoes.
Ripe bananas give off ethylene that ripens green
bananas during shipping.
Similarly emanations of ripe pears or apples
ripen other fruits because of ripe pears and
apples giving off ethylene which accelerates the
ripening of other unripened fruits.
Production of ethylene depends upon fruits and
vegetables (Table 4).

45
(No Transcript)
46

A classification of fruits and vegetables
according to their ethylene production rates is
presented in Table 5.
However, there is no consistent relationship
between ethylene production capacity of the
produce and its perishability.
Ethylene gas inhibited the sprouting of potatoes.
Small quantities of ethylene is produced by
practically all plant parts and tissues, fruits,
vegetables, flowers, leaves, roots, tubers,
seeds, and fungi.

47
(No Transcript)
48

Very low concentrations of ethylene are required
to produce biochemical and physiological
responses in climacteric fruits and vegetables,
such as acceleration of the ripening process, and
in contrast,
applied ethylene increases the respiration of
non-climacteric fruits and vegetables,
the magnitude of the increase being dependent on
the concentration of ethylene (Figure 6).

49
(No Transcript)
50

There is a relationship between the physiological
age and the response of cantaloupes and tomatoes
to continuous treatment with ethylene.
Because of ethylenes marked accelerative
effects on ripening of both climacteric and
non-climacteric fruits, it is considered to be a
plant growth hormone.
The effect of ethylene as a ripening stimulant
can be inhibited by CO2 concentrations in or
around the fruits and decreased O2.

These conditions prevail in controlled atmosphere
storage.
Effects of ethylene on fruits and vegetables held
at 0 to 4.4C is not possible to detect
nor is it detectable at higher temperatures of
about 35C.
Wholesalers and retailers should know that fleshy
fruits and vegetables give off large quantities
of ethylene at increased storage temperature.
fleshy fruits and vegetables should not be store
and shipped with susceptible commodities such as
green and leafy vegetables, carrots, and lettuce.

Also, fruits and vegetables should be stored at
low temperatures to increase their shelf life
otherwise their quality and storage life reduces.
Apples, pears, carrots, etc. should not be stored
in the same room or in a transportation
container.
Ethylene is synthesized within the cell
enzymetically from methionine.
The sites of reaction within the cell are
mitochondria.
The avocado will not ripen on the tree but will
ripen and show a climacteric rise in respiration
after picking.

It is believed that an inhibitor of ripening is
present in the leaves of the trees.
Pears are another fruit that must be picked
before they are tree ripe in order to develop a
good eating quality.
Some cultivars of pears must be exposed to colds
storage temperatures before they ripen normally.
Recent research has shown that low temperatures
bring about synthesis of ethylene in pears.

It is now believed that accumulation of ethylene
in fruits and vegetables precedes the rise in
respiration, triggering the climacteric rise of
unripe fruits earlier.
Climacteric rise in respiration is an indication
of the onset of senescence, indicating that the
fruits should be harvested before it starts this
rise in respiration.
Picking fruit at the peak of respiration offers
the best storage quality.

The effects of various growth regulators on
fruits and vegetables ripening are attributed to
inducing ethylene production.
e.g., the stimulation of the ripening of figs by
the application of 2,4,5-T.
Chemicals that are used to bring about abscission
of fruits and vegetables important in fruit
thinning and mechanical harvesting, have been
shown to cause ethylene production.
Ethylene-releasing chemicals are in commercial
use in agriculture to bring about desired changes
in plants or plant products.

The chemical 2-chloroethyl phosphoric acid
(Etheral, CEPA, Ethephon) is one of these.
This chemical breaks down, releasing ethylene
within the plant tissue and modifying plant
flowering, vegetative growth, dormancy,
abscission, fruit maturation and ripening,
disease, and freeze resistance.
Although ethylene is a useful chemical in the
control of growth and ripening responses, it has
some harmful effects.
It can cause premature ripening in fruits,
defoliation in plants, lethal damage to nursery
stock, petal fall, failure in bud opening in
flowers, russeting lettuce, and bitterness in
carrots.

57
VI. TRANSPIRATIONAL LOSS

Water is lost from fruits and vegetables as they
grow on a tree or a vine
they may decrease in volume during the warm and
dry part of the day, but regain their moisture at
night.
With an increase in the relative humidity of the
storage atmosphere, there is a decrease in
transpiration.
After harvesting, the process of transpiration
continues but there is no way to replenish it.

The moisture content of most fruits and
vegetables is high and weight loss during
transportation and storage can be a serious
economic factor, especially if fruits are sold by
weight.
In most fruits and vegetables with 5 to 10 loss
in moisture content, the product are visibly
shriveled as a result of cellular plasmolysis.
The pedicels of cherries and calyx of
strawberries turn brown and dry and the berries
become dull and loose luster.
Hence, quick cooling is necessary to preserve
fresh appearance.

The weight loss of fruits and vegetables in
storage depends upon size, maturity, composition
and structure, air surrounding them, storage
temperature, relative humidity, velocity of air
in the storage, thickness of cuticles, size and
number of stomata and lenticels, and other
factors.
A practical way to minimize this effect is to
cool the fruit quickly using hydrocooling
containing antifungal chemicals which will both
cool the fruits and control the adhering fungal
growth.

Similarly, lettuce and other leafy vegetables are
cooled by sprinkling cold water on them followed
by vacuum treatment.
Preventive loss of water from fruits and
vegetables can be attempted both by reducing
respiration as well as transpiration.
Fruits and vegetables should be precooled before
storage at lower temperatures.
Sometimes, it is essential to package the produce
in semi-permeable polyethylene or mylar bags.
When dry fruits and vegetables, such as nuts or
dried fruits, are stored in polyethylene
containers, the problem is to maintain desirable
low RH (about 60) and to avoid fungal growth.

61
(No Transcript)
62
A. MINIMIZING TRANSPIRATIONAL LOSS

There is only one way to reduce shriveling and
drying of fruits and vegetables in storage rooms
and that is by increasing RH.
Vegetables as well as fruits can be protected
from a lower RH by using various types of
permeable polyethylene bags or films or by
providing moisture in the form of ice or
hydrocooling.
Hydrocooling fluid should contain a fungicide to
prevent microbial growth.

63
B. RELATIVE HUMIDITY AND TEMPERATURE

Water loss is rapid at low relative humidity (RH)
and slower at higher RH because the air in the
room contains less water vapor than it can hold
at the temperature of the room
thus water vapor is readily transferred from the
humid interior of the leafy vegetables of fruits
to the relatively dry air.
In contrast, if the RH in the room is 100 (water
saturated atmosphere), the air in the room and
fruits or vegetables are balanced in respect to
moisture content, the gradient between the two is
low, and moisture loss is nil.

The amount of moisture the air can hold before it
becomes saturated rises with temperature
increase.
More water is required to saturate air at 15.6C
than at 4.4C.
Accordingly, at 15.6C and 90 RHI, the air is
drier than in a room at 4.4C and 90 RH
resulting in rapid dehydration of the produce.

Further, water has a greater tendency to
evaporate as its temperature rises. Hence, RH is
always expressed with temperature.
As the temperature increases, the quality of the
produce decreases (Figure 7)
likewise the quality also decreases as fruits and
vegetables experience a postharvest field delay
as seen in Figure.

66
(No Transcript)
67
(No Transcript)
68
C. AIR MOVEMENT

High velocity air causes rapid evaporation by
continuously removing water that is saturated.
Air movement should be sufficient enough to
effectively remove respiratory heat from the
produce after it has cooled to the temperature of
the room, trailer, or rail car.

69
D. ATMOSPHERIC PRESSURE

Water evaporates more rapidly in lower
atmospheric pressure than in higher. For every
10 decrease in pressure water loss will increase
10.
Thus the rate of water loss in an airplane will
be about 20 more than a sea level due to the
difference in pressure alone. Should the lower
air pressure be coupled with lower RH and
relatively higher temperature, a significant
amount of water can be lost from produce during
air transit.
Therefore, during air transportation of fresh
fruits and vegetables, appropriate pressurization
should be maintained especially over 5,000 ft
altitude.

70
VII. CHILLING INJURIES

Chilling injury is a disorder induced by low
nonfreezing temperatures which occurs in certain
susceptible plants or produce (Table 6).
Usually this damage can occur in tropical fruits
and vegetables when stored al low refrigerated
temperatures (Table 7).

71
(No Transcript)
72
(No Transcript)
73

Chilling injury affects sweet potatoes, bananas,
and most tropical and subtropical fruits.
Chilling injury induces decay and can be avoided
by storing at higher temperatures.
Vegetables such as potatoes and sweet potatoes
should
Susceptibility of various vegetables to chilling
injury are presented in Table 8