Prediction of Water Content
& C7 Sugars using NIR
Spectroscopy
R.J. Blakey, S.Z. Tesfay,
K.M. Blakey, J.P. Bower, I. Bertling
University of KwaZuluKwaZulu-Natal,
School of Agricultural Sciences and
Agribusiness,
Horticultural Science
Introduction
• Maturity measured using water
content/dry matter
• C7 sugars major non-structural
carbohydrates in avos
• NIRS able to non-destructively predict
organic compounds
• Water, proteins, carbohydrates, lipids
1
Need for Prediction
• Highly variable fruit
• Variable ripening is a major
problem
• “In any box of avocados the
fruits will vary in the time they
take to ripen. This is because
the fruits on the tree 'set' over a
long period.”
period.” www.avocado.co.za
• Poor quality fruit exported
• Need to prolong storage
potential
Objectives
•
Develop equations to quickly and accurately
predict:
1.
2.
3.
4.
5.
6.
7.
Water content
Sugars
Lipids
Protein
Physiological disorders
Storage potential
Days to ripen
2
Ultimate Aim
• Development of postharvest model for
avocados
• Every avocado can be quantified
• Storage potential
• Physiological disorders
• Days to ripen
• Eating quality
• Export fruit are of consistent high quality
Materials & Method
• Fruit from Tzaneen, Howick
• Water Content
• Freeze dry
• Sugars
• HPLC
• NIRS
• FOSS “NIRS6500”
NIRS6500”
• Reflectance mode
• Vision© software
3
Southern Africa
Tzaneen
Howick
Visuals: Google EarthTM
Howick: Everdon Estate
Visuals: Google EarthTM
4
Tzaneen: Westfalia Estate
Visuals: Google EarthTM
What is NIR?
Waveband
700-2500nm
Figure: Portion of electromagnetic spectrum (100nm - 1mm)
5
What is NIRS?
• Organic compounds absorb NIR radiation
at specific wavebands for specific bond
types
• N-H, O-H & C-H bonds
• Samples high in moisture: higher absorptions
in regions associated with hydroxyl (O-H)
bonds
• Able to discern & quantify individual
compounds in a sample
An Avo in NIRS
1.4
Water
C-H
1.2
Absorbance
1.0
Red
Water
NH2
C-H
Blue
0.8
0.6
Green
0.4
C-H
0.2
0.0
400
-0.2
Water
600
800 1000 1200 1400 1600 1800 2000 2200 2400
Wavelength (nm)
Figure: Typical NIR spectrum of a whole avocado with compounds
6
Results
&
Discussion
Equation Development
Full Sample Set
Math Pretreatments &
Sample Selection
Calibration Set
Regression
Equation
Pass & Accept
Fail & Try Again!
Validation Set
Outlier Set
7
1. Water Content
Calibration Set
R2
= 0.91
Validation Set
SEP = 2.75
SEC = 2.67
n = 86
n = 597
2. Mannoheptulose
Calibration Set
Validation Set
R2 = 0.84
SEP = 3.71
SEC = 3.71
n = 70
n = 211
8
3. Perseitol
Calibration Set
R2 = 0.78
Validation Set
SEP = 2.22
SEC = 2.77
n = 52
n = 201
4. Total C7
Calibration Set
R2 = 0.78
Validation Set
SEP = 4.81
SEC = 4.59
n = 50
n = 201
9
5. Days to Ripen
• R2 = 0.69
• SEC = 1.35
• SEP = 1.76
• 83% of fruit will
ripen within ±2 days
of predicted date
• 50% of the fruit will
ripen with ±1 day of
predicted date
Practically…
• In a sorted Count 16 box:
• At least 13 of the fruit will ripen within
±2 days of a set day
• At least 8 of the fruit will ripen with ±1
day of the set day
10
Frequency
3
2
1
0
7
8
9
10
11
12
13
Days to Ripen
Figure: Frequency distribution of a ‘count 16’
16’ box sorted
to ripen 10 days after harvest
Application
Actual WC
Harvest
(%)
Date
12/7/2007
71.5
Predicted
WC (%)
71.1
7/8/2007
70.1
70.0
31/8/2007
63.3
68.1
11
Explanation
Calibration Set
Inadequate number
of samples
Discussion
• ‘Hass’ is a difficult cultivar
• Thick, rough skin
• Reduced penetration of NIR radiation
• Results still acceptable
• Very large data set needed
• ‘Days to ripen’ depends on many
endogenous factors
12
Commercially
Potentially:
Sinclair
iQTM
20 fruit/min/lane
Firmness
Tester
120-600 fruit/min/lane
Commercial
NIRS in
New
Zealand for kiwis
4 measurements/fruit
Other Parameters
Whole Fruit
•
•
Proteins
Lipids
• Fatty acids
• Saturation
• Anti-oxidants
Avocado Oil
•
•
•
•
•
Moisture
Purity
Oxidative stability
Authenticity
Fatty acid composition
13
Conclusion
• Water & C7 sugars in avocados can be
predicted using NIRS
• Improvements and adjustments needed
for commercial viability, but results are
promising
• NIRS has fantastic potential in avocado
industry
Many Thanks To:
• Hans Merensky Holdings
• Westfalia Agribusiness
• South African Avocado Growers
Association
• Staff & colleagues at UKZN
14