2. Maturity indices
Principles dictating at which stage of maturity a fruit or
vegetable should be harvested are crucial to its
subsequent storage
Three stages
◦ Maturity
Indicative fruit being ready for harvest.
At this point edible part of fruit or vegetable is fully developed in
size, although may not be ready for consumption
◦ Ripening
Rendering the product to be edible
◦ Senescence
Last stage characterized by natural degradation of the fruit or
vegetable
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3. Practical Uses of Maturity
Indices
To prepare regulations which often include a
guide for minimum and maximum maturity that is
acceptable for a given commodity
Marketing strategies to obtain premium prices for
commodities “Supply and demand” delaying or
expediting harvesting and shipping of a particular
crop at the beginning or end of the season
requires a measure of maturity if quality is to be
maintained
Efficient use of labor – A measure of maturity is
important for organizing start and end dates for
harvesting to ensure labor and equipment
availability and reduce harvesting costs
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4. Methods to judge maturity
Skin color
Optical methods
Shape
Size
Aroma
Fruit opening
Leaf changes
Abscission
firmness
Juice content
Oil content and dry matter
percentage
Moisture content
Sugars
Acidity
Specific Gravity
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5. Judging maturity
Age-related
Number of days from
planting to maturity
Days from full bloom to
harvest
◦ Subject to environmental
influences season to
season variation
◦ Can be modified by
incorporating heat units
with the chronological
index to take account of
the weather pattern
during the growing
season.
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6. Judging maturity….
Physical properties
◦ External and internal color;
useful for many horticultural products
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Color charts produced for many commodities
Measuring fruit surface
color using a colorimeter
7. Judging maturity…
Physical Properties…
◦ Size:
May not be a good indicator of maturity as can
be influenced by many factors but useful for
peas, beans, potatoes, celery
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8. Judging maturity…
Physical Properties
◦ Shape:
Some crops are harvested when reaching a certain
shape. For example banana (3/4 full, full ¾ and round
full), cucumber
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9. Judging maturity…
Physical properties – cont
◦ Solidity
head lettuce and cabbage are harvested on the basis of
the solidity of the head
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10. Judging maturity…
Texture
◦ Firmness - (apples,
pears, peaches) used
to determine harvest
date and to evaluate
quality
◦ Tenderness -
measured with
tenderometer - peas
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11. Judging maturity…
Morphological changes
◦ Development of an abscission layer –
muskmelons
◦ Development of a waxy layer on the epidermis –
plums, grapes, honey dew melons
◦ Development of netting on the surface –
muskmelons
◦ Internal structure - formation of gel-like material
surrounding the seeds of tomatoes
◦ Prior to tip opening - asparagus
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19. Examples – fruit maturity
index
Index Example
Elapsed days from full bloom
to harvest
Apples, pears
Mean heat units Pears, apples, sweet corn
Abscission layer Melons, apples
Surface morphology &
Structure
Cuticle formation on grapes and
tomatoes, netting on some melons,
gloss of some fruits (development of
wax)
Size All fruits and many vegetables
Specific gravity Cherries, water melons, potatoes
Shape Angularity of banana fingers, full cheeks
of mangoes, compactness of broccoli
and cauliflower
Solidity Lettuce, cabbage, brussels sprouts
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20. Maturity indices….
Textural properties
Firmness Apple, pears, stone fruits
Tenderness Peas
Color (external) All fruits and most of vegetables
Internal color and structure Formation of jelly like material in tomato
fruits, flesh color of some fruits
Compositional Factors
Starch content Apple, pears
Sugar content Apple, pears, stone fruits, grapes
Acid content; sugar-acid ratio Pomegranate, citrus, papaya, melons, kiwi
fruits
Juice content Citrus fruits
Oil content Avocado
Astringency (tannin content) Persimmons, dates
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21. Maturity indices of some
vegetables
Vegetable Index
Radish and carrot Large enough and crispy
Potato, onion, garlic Tops beginning to fry and topple out
Ginger Large enough (over mature- tough and fibrous)
Green onion Leaves at its broadest and longest
Cowpea, yard long bean,
winged bean
Well filled pods that snap readily
Lima bean and pigeon pea Well filled pods that are beginning to lose their greenness
Okra Desirable size reached and tips of which can be snapped
readily
Snake gourd Desirable size and thumbnail can still penetrate flesh
easily
Egg plant, bitter gourd, slicing
cucumber
Desirable size reached but still tender
Sweet corn Exudes milky sap when thumb nail perpetrates kernel
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22. Maturity indices of some
vegetables
Vegetable Index
Tomato Seeds slipping when fruit is cut, change in color – green
to pink- red
Sweet pepper Deep green color turning dull or red
Musk melon Easily separated from the vine with a slight twist leaving a
clean cavity
Honey dew melon Change in fruit color from slight greenish white to cream,
aroma noticeable
Watermelon Color of the lower part turning creamy yellow, dull hollow
sound when thumped
Cauliflower Curd compactness (over-mature- loose)
Broccoli Bud cluster compactness (over-mature- loose)
Lettuce Big enough before flowering
Cabbage Head compactness (over-mature- head crack)
Celery Big enough before it becomes pity
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23. Non-destructive maturity analysis
Electronic Nose
◦ Used to detect aroma volatiles in a range of food
types.
◦ Has been used for determining fruit maturity based on
the production of aroma volatiles. Statistical analysis
must be performed to interpret data.
◦ Most research literature is based upon method
verification and comparing data with more established
methods of evaluating maturity.
Acoustic firmness sensor
◦ Method taps the fruit and then “listens” for vibrations
(resonance attenuated vibration).
◦ Fruit of different maturities produce different vibration
profiles. Measures whole product not just a restricted
area. (http://www.aweta.nl)
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24. Non-destructive maturity analysis
Spectroscopic analysis
◦ Various different methods based upon the
interaction of atoms or molecules with the
electromagnetic spectrum.
◦ Visible spectral imaging (380 – 770 nm).
Measuring surface color based on absorption of light
energy by reactive groups in chlorophylls, carotenoids
and anthocyanins.
Used in packing lines to detect color of apples and
peaches.
◦ Fluorescence imaging
Achieved by measuring electromagnetic radiation in the
visible range following excitation with short wavelength
radiation. Greatest use of application is in the
measurement of chlorophyll fluorescence.
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25. Non-destructive
maturity analysis
Near infrared spectrophotometry
(NIRS) (750 nm – 2500 nm)
◦ uses the near-infrared region of the
electromagnetic spectrum (from about 800
nm to 2500 nm).
◦ Suitable for measuring compounds
containing OH- (Hydroxyl group - ethanol,
methanol, CH- (methyl- group) and NH-
groups (amino acids.- amine group).
◦ Extensively used in the food industry. Can
be used to measure firmness, acidity, brix
and color of fruits.
◦ Can be used but equipment is
sophisticated and expensive and speed is
too slow for commercial applications.
◦ (Ref: Abbott 1999 Postharvest Biology and
technology 15: 207-225)
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NMR and MRI imaging
26. Postharvest Biology
Biological factors affecting deterioration
◦ Respiration
◦ Ethylene production and response
◦ Compositional changes
◦ Growth and development
◦ Transpiration and water loss
Environmental factors affecting deterioration
◦ Temperature
◦ Relative humidity (RH)
◦ Ethylene
◦ Atmospheric gases
◦ Light
◦ Nutrition
◦ Mechanical damage
Pathological disorders and insect infestation
◦ Pathological disorders
◦ Insect infestation
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27. Respiration
Aerobic respiration is the process by which stored organic
materials (carbohydrates, proteins, fats) are broken down into
simple end products with the release of energy.
Oxygen (O 2 ) is used in this process, and carbon dioxide
(CO 2 ) is produced
The loss of stored food reserves in the commodity during
respiration hastens senescence as the reserves
This results in
◦ loss of flavor quality
◦ loss of salable dry weight
The energy released as heat, known as vital heat, affects
postharvest technology considerations such as estimations of
refrigeration and ventilation requirement
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28. Phases of the respiratory climacteric in a
ripening climacteric fruit
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29. A schematic of compositional changes
associated with fruit ripening
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30. Respiration
Aerobic respiration involves a series of three complex reactions
◦ add an energy containing phosphate group to the substrate molecule
◦ rearrange the molecule
◦ breakdown the molecule to a simpler one
The three interconnected metabolic pathways are
◦ Glycolysis,
◦ Tricarboxylic acid (TCA) cycle,
◦ Electron transport system
Glycolysis, i.e., the breakdown or lyse of glucose, occurs in the
cytoplasm of the cell.
Tricarboxylic acid (TCA) cycle, which occurs in the mitochondrial
matrix, involves the breakdown of pyruvate into CO2
Electron transport system, which occurs on membranes in the
mitochondria, involves the production of ATP from the high energy
intermediates FADH2 (flavin adenine dinucleotide) and NADH
(Nicotinamide adenine dinucleotide)
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