Presented: by Surachai Sungzikaw
สุรชัย สังข์ศรีแก ้ว
Workshop on Metrology in Food Safety, Agricultural
Products and Product Safety, Hangzhou, PR China,
June 2-6, 2008

1.
2.
3.
4.
About Cassava
The Determination of Starch Content in
Cassavas for Trade in Thailand
A Comparison of Starch Content Values
Measured by Reimann Balance and Electronic
Balance
A Comparison of Different Methods for
Estimating Starch Content of Cassava Tubers between:
- Underwater Method and
- Determination of Dry Matter by Oven Method


Cassavas are cultivated in most equatorial regions.


Cassava tubers are long and tapered


Cassava tubers are very rich in starch.

Indonesia
Ubi kettella
Kaspe
South America
Africa
India
Thailand
Manioca
Yucca
Mandioca
Aipim
Manioc
Cassava
Tapioca
Cassava
Source: International Starch Institute, Science Park Aarhus, Denmark

Source: The world cassava economy , FAO


Officially for trade, determined by
Reimann Balances verified by Weights and Measures Bureau

Also determined by the electronic scale in combination with computer-based calculations
(under pattern testing)

1. Determination of Starch Content by Reimann Balance
.
Weigh 5000 g clean tubers into upper basket in air

1. Determination of Starch Content by Reimann Balance
.
Weigh 5000 g clean tubers in the upper basket in air
Move the tubers into the lower basket under water

1. Determination of Starch Content by Reimann Balance
.
Weigh 5000 g clean tubers into upper basket in air
Move the tubers into the lower basket under water
Weigh the tubers again in water
Determine of
Starch Content

2. Determination of Starch Content by the electronic scale in combination with computer-based calculations
Source: Genius Design & Engineering Co.,Ltd.

The Construction of the scale
4.
5.
1.
2.
3.
Indicating Device
Load Cell
Basket (load-receiving element)
Water Bucket
Hydraulic Lift
Source: Genius Design & Engineering Co.,Ltd.

Measuring Procedure for Determination of Starch Content
With clean water, lift the bucket to the empty basket until the basket is completely immersed in water.
Weigh the empty basket immersed in water and record the weight of basket by the indicating device.
Move the bucket back to the lower position.

Measuring Procedure for Determination of Starch Content
Weigh 3-6 kg clean cassava tubers into the basket in air.
Lift the bucket to the basket containing cassava tubers until the basket is completely immersed in water and weigh again.
Starch content of the sampling is calculated by a microprocessor in the indicating device.

Comparison of Starch Content Values Measured by
Reimann Balance and the Electronic Balance
1
Measuring by Reimann Balance

Comparison of Starch Content Values Measured by
Reimann Balance and Electronic Balance
2
Measuring by the electronic balance

Sample
No.
1
2
5
6
3
4
7
8
9
Varieties
KU50
Kan Deang
KU50
Kan Deang
Rayong 90
KU50
KU50
Rayong 90
Rayong 90
Places
North-East
North-East
North-East
North-East
North-East
East
East
East
East

1.
2.
Calibrated the Reimann Balance and electronic balance with class M mass
1 standard
Programmed in the Computer of The
Electronic Balance to calculate starch content by the following equation:
Starch Content

(SG

1.00906)
0.004845
%

W o
W u
= weight of the cassava sample in air
= weight of the sample under water
SG = specific gravity
BC = basket compensated weight
( BC = weight in air – weight under water)


First determined starch content of 5 kg, 3 kg, and
1 kg wet clean tubers by Reimann Balance

Second determined starch content of the same samples by the Electronic Balance

Sample
No .
1
2
Sample
Sizes
5 kg
3 kg
1 kg
5 kg
3 kg
1 kg
Starch Content Values
Reimann Electronic
21.2
21.1
21.1
26.7
26.3
26.3
21.11
21.04
21.12
26.59
26.54
26.06


Basket’s weight compensation for the Electronic
Balance is significance for measurement of specific gravity by Under Water Weight method

Specification of the basket comprised with the
Electronic Balance have to be considered


With the determination of cassava tubers by the
Electronic Balance, there is no significant difference on the starch content values of by decreasing each sampling weight to 1000 g. from
5000 g.

A Comparison of Different Methods for Estimating
Starch Content in Cassava Tubers


To revise the correlation equation between specific gravity and starch content of cassava tubers

To obtain the information for developing the
Electronic Balances

Methods of Determination of Starch
Content
1.
2.
Under Water Weight Method
Determination of Dry Matter by Oven at
130  C


The experiments were carried out to determine starch contents in the same samples by Under Water
Weight method and by Oven method at 130  C


For Under Water Weight method
• Analytical balance weighing to the nearest 0.01 g
• Vessel with clean water
• Stainless steel wire for hanging the sample weighed in water


For the Determination of Dry Matter by Oven Method
• Analytical balance weighing to the nearest 0.1 mg
• Dishes of aluminum with tight-fitting lids
• Electrically heated oven
• Desiccator containing an effective desiccant

1.
2.
Determined of specific gravity of cassava tubers by Under Water
Weight method
Calculated starch content values with the following equation:
Starch Content = (SG – 1.00906)/0.004845 %

3.
4.
Determined of dry matter of cassava tubers by Oven at 130  C
Calculated starch content values with the empirical equation published by
FAO as follow:
Percent Starch Content = Percent Total Dry Matter – 7.3 %
Source: 1. ISI
01-1 e Determination of Dry Matter in Starch by Oven Drying at
130 o C
,
International Starch Institute, Science Park Aarhus, Denmark
2. Cassava processing, FAO

Under Water Weight
SG
%
Starch
1.092
17.1
1.097
1.103
1.106
1.111
1.118
1.125
1.128
1.136
1.145
1.152
1.152
22.5
23.9
24.6
26.3
18.2
19.3
20.1
21.1
28.0
29.5
29.5
Oven at 130 C
Dry Matter
%
Starch
30.7
23.4
35.7
36.8
38.1
39.0
34.1
35.5
35.5
37.6
40.5
43.2
43.2
28.4
29.5
30.8
31.7
26.8
28.2
28.2
30.3
33.2
35.9
35.9
D
%
Starch
6.3
5.9
5.6
6.2
5.4
8.6
8.9
8.1
9.2
5.2
6.4
6.4


The starch content values estimated by UWW method are significant different from by Oven method

To confirm this, other reliable methods are required to make more comparison such as
Krochmal and Kilbride or Near Infrared
Reflectance (NIR)

The correlation equation between specific gravity and starch content of cassava tubers should be revised

A cassava field in Chonburi, Thailand