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Non-destructive Quality Measurement of Horticultural Crops

David SlaughterBiological & Agricultural Engineering

UC Davis

Reference: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 sensessight, smell, sound, touch and taste

• Others are measures of harvest, storage, and handling characteristics that affect quality.

Bruise susceptibility• Non-destructive measurements allow 100%

samplingAllows sorting into uniform subunits, removal of substandard items, and identification of premium pieces.

Quality measurements• Size

Volume• Machine vision

Less accurate for irregularly shaped fruit

Mass• Electronic load cells

• Density (mass/volume)Bulk or individual fruit

• May indicate changes in porosity, soluble solids or water content.

• Index of quality or indicator of defectsFreeze damage, pithiness, hollow heart, puffiness or water core.

PowerVision1

2 3

4

4 views of the fruit in one image (one camera & mirrors)

Firmness measurements

Force Gage

Penetrometer

• Traditional Destructive MethodMagness-Taylor Penetrometer• Invented in 1925.

• Records the Maximum Force Required to Penetrate the Fruit.

• Manually Operated.

Fruit Firmness Measures• Destructive

Traditional MethodMaximum Force to Penetrate a Known Distance into Fruit.Uses a Device called a Penetrometer

• Non-DestructiveForce Required to “Squeeze” Fruit. Deformation

Forc

e

2

DurometerMeasures the amount of deformation resulting from a small force, 8 N (2 lbs)Max. deformation = 2.5 mm (1/10 inch)Use the ‘E’ tip for peaches & pears.Hand heldStand mounted$600 - $1100Will bruise soft fruit.

0 100

0 points(force =0)

0 100

100 points(Deformation = 2.5 mm)

(force = 8 N)

4040

0 100

40

40 points(Deformation = 1 mm)

(force = 3.2 N)

Durometer• Principle of operation

(Force & deformation values for ‘E’ tip)

Soft material Firm material

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 usingpenetrometer firmness > 10lbs:y=0.99(x) + 70.7, R2=0.50

Dur

omet

er S

core Spring

(compressed)

Spring (free length)

Electromagnet

Solenoid

Accelerometer

Direction of fruit travel

EmitterSensorOptical sensor

Range of constant impacting speed

UC Davis Impact Firmness Sensor

Source: Pictiaw Chen, UCD

0

0.5

1

1.5

2

2.5

0 2 4 6 8 10Time

FirmSoft

Impact Firmness Parameters

A

t

A

t

FirmnessC1 = A/tC2 = A/t2

Impact Firmness During Ripening of Mango

Source: Source: I. ShmulevichI. Shmulevich

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Nondestructive FirmnessLow Mass Impact Method

Sinclair iQTM

Nondestructive firmness tester.“Gently” taps the fruit and provides a Sinclair iQ firmness value.

OnlineModel

Bench Top model

Clingstone PeachesComparison of Penetrometer Firmness vs Sinclair Firmness

R2 = 0.58

Acoustic Firmness Parameters

Natural frequency and firmnessNatural frequency and firmnessFirmness Firmness = = f f 22 m m 2/32/3

wherewhere: : ff -- first resonant frequencyfirst resonant frequencymm -- fruitfruit’’s masss mass..

Acoustic Firmness MeasurementAweta/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

AFS Firmness sensor

Good

Bad

10000

32

2 mfS

⋅=

4

Firmness sensor

QuickTime™ and aYUV420 codec decompressor

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Impact vs. Acoustic FirmnessAcoustic Method

Global Measurement

Resonance of whole fruit is measured.

Some internal defects can be sensedWorks better on firm fruit

Impact MethodLocal spot measurement

Elastic properties ofexterior flesh is measured.

Cannot sense internal defects

Works better on soft fruit

Volatile Sensing

• Electronic nose32 co-polymer sensorsClassify volatiles using artifical neural network.

Detecting freeze damage in oranges

32 co-polymer sensors

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 biological materials in 3 ways:

Reflectance, Transmittance, and Absorption

Human Eye• Photoreceptors on retina• Cones

3 types, red, green, bluePhotopic (day) vision

• Not suited for night vision

• RodsAchromatic (black & white)Scotopic (night) vision

• 100 X more sensitive than cones.• Saturated during day.

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Quantifying Color• CIE (Commission

International de l’Eclairage)

• Developed a set of three “imaginary”primaries, x, y, z.

• To be used as a reliable way to describe the perceived color.

• Used to determine the tristimulus valuesX, Y, Z.

L*, a*, b* color system• Cartesian coordinate

system• L* represents luminous

intensity• a* represents the red -

green content• b* represents the blue -

yellow content• Often used to describe

the color of biological materials

L*, a*, b* Example

a* = 500 XXn

⎛

⎝ ⎜

⎞

⎠ ⎟

13

−YYn

⎛

⎝ ⎜

⎞

⎠ ⎟

13

⎡

⎣

⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥

b* = 200 YYn

⎛

⎝ ⎜

⎞

⎠ ⎟

13

−ZZn

⎛

⎝ ⎜

⎞

⎠ ⎟

13

⎡

⎣

⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥

Lemon reflectance

Human eye

L* = 116 Y

Yn

⎛

⎝ ⎜

⎞

⎠ ⎟

13

−16

a* b* Chromaticity Diagram

Munsell Color System• Developed by painter Albert

Munsell in 1915• Hue = name of color

(e.g., purple, green, yellow)Dominant wavelength

• Value, lightness, or brightness

Similar to luminous intensityDivided into 11 equal steps

• (black=0, white = 10)Value ~ (ave. reflectance)0.5

• Chroma, purity, or saturation

Clingstone Peach Maturity

0

45

270

180

90

8080 degrees

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Mid IR Spectroscopy

• All organic and inorganic molecules, except homonuclear molecules (e.g., O2), absorb in the infrared region.

• The uniqueness of the infrared spectrum allows the analysis of mixtures of closely related organic compounds.

Mid IR Spectroscopy

• Typical Mid IR Spectrum

Absorbance Spectra• Below is a picture of a cup of water• What color would the water appear in the infrared?

Black

Typical Mid IR Pathlengths

• When measuring a material using Mid IR the following sample thicknesses are typical:

< 0.1

0.1-1

1-10

> 10

Pathlength (mm)Concentration (%)

0.05

0.10

0.20

> 0.5

Mid IR Reflectance

• Attenuated total reflectance (ATR)Based upon the concept of total internal reflection.

Light penetrates a fraction of a wavelength beyond the crystal and into the sample.The absorbance is summed over many internal reflections. SILICON or PbS DETECTOR

Pathlengths in the NIR

• WeakerAbsorbances in the NIR allow Longer Pathlengths.

• Many Biological Materials can be measured in their natural state in the NIR.

WHOLEGRAIN

SAMPLE

Transmission throughWheat Kernels.

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Absorbance Spectra NIR Applications to Biological Materials• Moisture

Grains, Forages, Fruits, Meat, Milk, Cheese, Seeds, Soil.

• ProteinGrains, Forages, Meat, Seeds.

• Soil Nitrogen• Ethanol

Beer, Wine.• Fat

Oil seeds, Milk, Meat, Cheese, Snack Foods, Human Triceps.

• CarbohydratesGrains, Breakfast Cereals, Fruits.

• StarchGrains, Seeds, Kiwifruit.

• FiberForages, Grains

• Amino AcidsGrains

• DefectsBruising, Contaminants.

Transmission Example

• Can you transmit light through a kiwifruit?

Yes

Sugar sensor

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4

6

8

10

12

14

16

18

4 6 8 10 12 14 16 18

NIR CALIBRATION RESULTS FOR SOLUBLE SOLIDS CONTENT OF INTACT PAPAYA

NIR

PR

EDIC

TED

SSC

(o BR

IX)

13 P

LS F

AC

TOR

S, 7

00-1

100N

M

SSC BY REFRACTOMETER (oBRIX)

r2=0.84, SEC=1.1oBRIX

NIR Applications• NIR calibrations are well suited for on-line

process control applications where the product type does not change.

• Global NIR calibrations that can be used across multiple products are difficult to develop due to the need to optimize wavelength selection for specific chemical interferences.

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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 (NMR)

• 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

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NMR - Data Analysis NMR - Online Quality Measurement

Prototype NMR Avocado Sorter NMR - Example Applications

• Seed/pit detection• Worm damage• Bruises• Water core• Freeze damage

Magnetic Resonant Imageof Partially Frozen Orange

Freeze Damaged Tissue

Healthy Tissue

Dielectric measurements• Behavior of non-metallic materials when

placed inside an alternating electric field.Moisture of dates and other “dry” fruits or nuts.

Metal Plate

Metal Plate

Dielectric Material+ +

-

++-

++

-

++

-+

+-

++

-

Before Energizing

+ Positive Charge +

- Negative Charge -

+ +-

+ +-

+ +-

+ +-

+ +-

+ +-

After Energizing

Dielectric Moisture Meter

Empty Walnut Drying Bin Bin Sides are a Capacitor with Walnuts as the Dielectric Material

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X-ray & Gamma-ray• Maturity of lettuce heads• Defect detection

Freeze damage in citrus -onlineSplit pits in peachHollow heart in potato -onlineBruises in apple

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Olive, showing fruit fly entrance hole

X-ray image showing tunnels. R. Haff