nondestructive quality measurement of horticultural...

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


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


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


A

t

Firmness Index

t

A

PeaktoTime

onAcceleratiPeakC


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


Under normal conditions the magnetic dipoles point in random directions.


The material is placed inside a powerful electro-magnet.

This causes the dipoles to align with the magnetic field.


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

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