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Nondestructive Quality Measurement of Horticultural Crops
David Slaughter
Biological & Agricultural Engineering
UC Davis
Additional information available at:
Technologies for Nondestructive Quality Evaluation of Fruits and Vegetables.
Abbott J.A. et al., Horticultural Reviews Vol. 20, 1997.
Quality measurements
Many quality measurement techniques have been developed to mimic the human senses sight, smell, sound, touch and taste
Others are measures of harvest, storage, and handling characteristics that affect quality. Bruise susceptibility
Non-destructive measurements allow 100% sampling Allows sorting into uniform subunits, removal of
substandard items, and identification of premium pieces.
Non-destructive measurements allow monitoring of quality over time.
Quality measurements
External Properties
Internal Properties
Size & Shape
Mass, Volume & Density
Appearance, Color &
Visible Blemishes
Composition, Flavor & Aroma
Texture, Firmness, Crispness, Mealiness
Internal Defects, Decay, Insect Damage
Machine Vision On-line vision systems
examine multiple views of each fruit as they travel on a conveyor. Provide measures of
size, shape and volume.
External blemishes can be detected with a high degree of reliability.
When combined with fruit weight, the density can be an indicator of internal quality.
Fruit rotates as it travels to expose all sides
4 imagesscanned at eachlocation
Traditionally a Destructive Method
Magness-Taylor Penetrometer
Invented in 1925.
Records the Maximum Force Required to Penetrate the Fruit.
Manually Operated.
Penetrometer
Fruit Firmness Methods
Destructive Maximum Force to
Penetrate a Known Distance into Fruit.
Measures tissue strength.
Non-Destructive Force Required to
“Squeeze” Fruit.
Measure of elastic tissue properties. Deformation
For
ce
FMAX
Rat
e o
f C
han
ge
Durometer Portable instrument used to
determine the ‘Shore A’hardness of rubber.
Handheld (or stand mounted).
Use ‘E’ tip for peaches or pears.
Uses a calibrated spring to measure the resistance to deformation.
$800 - $1200 Will bruise soft fruit.
A durometer consists of: A calibrated spring,
A tip displacement gage, and
A retractable tip
Principle of Operation
Pear
0 100
0 percent
40
Tip extends0.1 inches
CalibratedSpring
Principle of Operation
Pear
0 100
0 percent
40
0 100
100 percent
Pear
40
Tip extends0.1 inches
A very hard pear can press 100% of the tip into the probe
Principle of Operation
Pear
0 100
0 percent
40
Pear
0 100
40
40 percent
0 100
100 percent
Pear
40
A softer pear can only press the tip partially into the probe
Bartlett Pear
y = 0.5525x - 2.5
r2 = 0.77
20
25
30
35
40
45
50
55
40 50 60 70 80 90 100
'E' Durometer (%)
Imp
act
Fir
mn
ess
(Sin
clai
r) R2 = 0.77
Durometer measurement of Bartlett Pears
Durometer measurement of Bartlett Pears
logarithmic regression using all data:y = 14.174Ln(x) + 47.45, R2 = 0.9028
40
50
60
70
80
90
100
0 5 10 15 20 25
Penetrometer Firmness (lbs)
linear regression using penetrometer firmness > 10lbs:y=0.99(x) + 70.7, R2=0.50
Du
rom
eter
Sco
re
Spring (compressed)
Spring (free length)
Electromagnet
Solenoid
Accelerometer
Direction of fruit travel
EmitterSensorOptical sensor
Range of constant impacting speed
Low-mass impact methods are widely available for measuring firmness on-line. Spherical tip gently taps the fruit
Accelerometer on impacting arm senses tissue elasticity
Principle of Operation
A
t
Firmness Index
t
A
PeaktoTime
onAcceleratiPeakC
Principle of Operation
A
t
A
t
Firmness Index
t
A
PeaktoTime
onAcceleratiPeakC
Monitoring Impact FirmnessDuring Ripening of Mango
SourceSource : :II . .ShmulevichShmulevich
time
acce
lera
tion
CDay1=275
CDay7=65
UC Davis handheld nondestructive firmness sensor for orchard use.
Clingstone Peaches
Comparison of Penetrometer Firmness vs Impact Firmness
R2 = 0.6
OnlineModel
Bench Top model
Sinclair Nondestructive firmness tester. “Gently” taps the fruit and provides a Sinclair iQ firmness
value.
Acoustic Firmness Measurement Aweta/Autoline on-line acoustic firmness sensor
“Gently” taps fruit and “listens” with a microphone.
Uses Fourier analysis to determine the natural frequency of the fruit.
Firmness = f2 * m2/3
On-line model
Bench top model
Acoustic Firmness Principle
Natural frequency and firmness Acoustic Firmness =f2 m2/3
where :f - first resonant frequency
m - fruit’s mass.
Acoustic Firmness sensor
Good
Bad
10000
3
22 mf
S
NondestructiveOn-line Firmness sensor
AWETA online firmness sensor Acoustic & Impact
sensors
Impact vs. Acoustic Firmness
Acoustic Method Global
Measurement Resonance of
whole fruit is measured.
Some internal defects can be sensed
Works better on firm fruit
Impact Method Local spot
measurement Elastic properties of
exterior flesh is measured.
Cannot sense internal defects
Works better on soft fruit
Volatile Sensing
Electronic nose 32 co-polymer sensors
Classify volatiles using artificial neural network.
Detecting freeze damage in oranges
32 co-polymer sensors
Headspace Ethanol measurement for Freeze Damage Oranges are placed in one quart plastic bags.
Ethanol predicts freeze damage with 80% to 90% accuracy in 7 fruit batches.
Slightly damaged (<15%) fruit are not detected.
• Volatiles accumulate for 1/2 hr at room temp. (Not suited for on-line use.)
• $800 Etoh
Sensor.
Electromagnetic Spectrum
X-RAY
ULTRA-VIOLET
INFRAREDRADIOWAVE
MICROWAVE
108 109 1010 1011 1012 1013 1014 1015 1016 1017
1010 109 108 107 106 105 104 103 102 10 1
FREQUENCY (Hz)
WAVELENGTH (nm)
NIR
VISIBLE
Material/Light Interactions
Light interacts with produce in 3 ways: Reflectance, Transmittance, and Absorption
L*, a*, b* color system Color can be used in
many crops as an index of maturity or ripeness.
Instruments to measure the peel color of fruits and vegetables are available from several manufacturers.
L* represents luminous intensity
a* represents the red - green content
b* represents the blue - yellow content
a* b* Chromaticity Diagram
a*= red to green axis
b*= yellow to blue axis
Hue = name of color (e.g., yellow, green)
Measured in degrees
Clingstone Peach Maturity
0
45
270
180
90
80
Gardner ‘a’ value or CIE hue angle have been demonstrated to be good indices of clingstone peach maturity.
Peaches with a flesh hue angle below 80 degrees are mature
CIE hue angle
Infrared Spectroscopy
All organic and inorganic molecules, except homonuclear molecules (e.g., O2), absorb light in the infrared region.
The light absorptions in the infrared typically cause vibrations in a molecule.
C = LOG10[1 / T]L
• Beer-Lambert Law
SymmeticStretch
In-planeScissoring
• Allows optical measurements of chemical constituents in the sample.
Absorbance Spectra Below is a picture of a cup of water
What color would the water appear in the infrared?
Black
Absorbance Spectra
NIR Applications in Food
Moisture Grains, Forages, Fruits,
Meat, Milk, Cheese, Seeds, Soil.
Protein Grains, Forages, Meat,
Seeds.
Soil Nitrogen Ethanol Beer, Wine.
Fat Oil seeds, Milk, Meat,
Cheese, Snack Foods, Human Triceps.
Carbohydrates Grains, Breakfast
Cereals, Seeds.
Starch Grains, Seeds, Kiwifruit.
Fiber Grains, Forages.
Amino Acids Grains
Defects Bruising, Contaminants.
On-line Near Infrared (NIR) Measurements
High light source power (150 - 300 Watts) allows transmission measurement of intact citrus in the NIR.
NIR On-lineSugar sensor
Miller & Zude-Sasse (2004)
NIR on-line testred grapefruit (20 oC)
On-line NIR Evaluation Study
Miller & Zude−Sasse (2004) Evaluated on-line NIR SSC sorter (Mitsui Qscope) 5.5 fruit/second belt speed Red & white grapefruit were studied
Results: Fruit temperature during sorting must match
temperature during calibration. Measurements on smaller fruit were more accurate
than on larger fruit.
Brix Sorting Test Results (2 categories)
Classification accuracy: 79% (76% - 100%)
NIR Applications
Recently some commercial, handheld NIR instruments have become available.
Limited independent evaluations of these instruments have been conducted.
Factors to consider: Temperature
Sunlight Handheld NIR Sensor
Fluorescence
(vibration or heat)
Some molecules can re-release absorbed optical energy as a lower energy photon.
http://probes.invitrogen.com
Example: Using citrus peel oil fluorescence to determine fruit quality
Tangeretin a nonvolatile, neutral flavone.
fluoresces an orange color under long wave UV (Swift, 1967).
High levels in peel oil of orange, grapefruit and some tangerines, low levels in lemon (Manthey & Grohmann, 2001).
Events that cause peel oil release can be detected using UV fluorescence.
Peel Oil under Blacklight
grapefruitlemon
lime
orange
tangerine
Viewed under blacklight
grapefruitlemon
lime
orange
tangerine
Low level offreeze damage
Moderate to severe freeze
damage
Freeze Damaged Oranges Fluoresce
Relationship to flesh damage Varies with both freezing &
thawing conditions.
• Agreement between the USDA and UV methods ranged from 35% to 85% in lab. and field studies in 2006 & 2007
Thrip Damage
Fluorescence due to extensive thrip damage Blasco et al. (2007)
Thripdamage is also visible under blacklight
Note that the infected lemon does not fluoresce
Appearance of decay lesions under UV light
Smilanick, 2008
0 2 31
75
50
25
0
Initial
After 3 weeks
%
Fluorescence classNONE VERY HIGH
Quality (% choice or higher) of navel oranges Initially and After 3 weeks storage at 60F
GoodFruit
Smilanick2008
Grove Inspection using UV flashlights
Hydrogen
Nuclear Magnetic Resonance (NMR)
Hydrogen atoms in a biological material act like magnetic dipoles due to the rotation of the electron around the proton. S
N
Electron
Proton
MagneticDipole
Nuclear Magnetic Resonance (NMR)
Under normal conditions the magnetic dipoles point in random directions.
Nuclear Magnetic Resonance (NMR)
The material is placed inside a powerful electro-magnet.
This causes the dipoles to align with the magnetic field.
Nuclear Magnetic Resonance (NMR)
A radio frequency (RF) pulse is then used to “knock”the atoms out of alignment.
Nuclear Magnetic Resonance
When the RF pulse stops, the atoms spiral back into alignment with the magnetic field.
The time it takes for realignment is called the relaxation time (usually within milliseconds).
The realignment process creates its own radio frequency signal that is detected by the system.
NMR measurement of Avocado Quality
NMR - Data Analysis
NMR - Example Applications
Seed/pit detection
Worm damage
Bruises
Water core
Freeze damage
Magnetic Resonant Image of Partially
Frozen Orange
Freeze Damaged Tissue
Healthy Tissue
Portable MR System
Magnet
Electronics
Permanent magnet NMR sensor(Quantum Magnetics Corporation, San Diego,CA)
Fruit
Dielectric measurements
Before Energizing
�Metal Plate
Metal Plate�
Dielectric Material
++
-
+
+-
++
-
++
-+
+-
++
-
�+ Positive Charge +
�- Negative Charge -
+ +
-
+ +
-
+ +
-
+ +
-
+ +
-
+ +
-
After Energizing
Behavior of non-metallic materials when placed inside an alternating electric field. Moisture of dates and other “dry” fruits or nuts.
Dielectric Moisture Meter
Empty Walnut Drying Bin Bin Sides are a Capacitor with Walnuts as the Dielectric Material
X-ray & Gamma-ray
Maturity of lettuce heads
Defect detection Freeze damage in citrus -
online
Split pits in peach
Hollow heart in potato -online
Bruises in apple
Olive, showing fruit fly entrance hole
X-ray image showing tunnels.
R. Haff