Prediction of water content of baking powder using near-infrared
spectroscopy
T. Yano, J. Kohda, Y. Nakano
Department of Information Sciences, Hiroshima City University, Japan (tyano@hiroshima-cu.ac.jp)
Abstract
Water content is the most important factor for quality control of baking powder production.
Baking powder with high water content becomes a defective product because carbon dioxide
gas is released and inflates a polyethylene bag during storage and distribution. To measure the
water content of baking powder, it is difficult to apply dry weight method although the
method is generally accepted for measurement of water content of foods. Carbon dioxide is
released and the weight of baking powder gradually decreases while measuring water content
of baking powder by the dry weight method under high temperature.
In this study, the relationship between carbon dioxide generation rate and operating
temperature for the dry weight method was studied to apply the dry weight method to
measuring water content of baking powder. Furthermore, prediction of water content of
baking powder using near infrared (NIR) spectroscopy was studied to apply it to control of
water content of baking powder.
When the operation of the dry weight method was carried out at over 100°C, the higher
decomposition rate of baking powder was observed under higher operating temperature. At
50°C to 90°C operation, the weight of baking powder became almost constant. The optimum
operating temperature for the dry weight method was found to be 70°C.
In the prediction of water content of baking powder using NIR spectroscopy, baking powder
samples with various values of water content were prepared and NIR spectrum was measured
from 400 nm to 2500 nm at 2 nm intervals through a polyethylene sheet. Simple linear
regression analysis was used to obtain calibration equations relating NIR spectral data and the
water content obtained by the dry weight method using a calibration sample set (sample
number, n=60). The wavelengths at 964 nm, 1162 nm, 1416 nm and 1964 nm were selected to
make a calibration equation. When the calibration equation with 1162 nm was applied to the
prediction of water content for a prediction sample set (n=40), the prediction was successfully
carried out using NIR spectroscopy with correlation coefficient, r2=0.953 and standard error
of prediction, SEP=0.098 %. It may be possible to measure the water content of all packages
of baking powder using NIR spectroscopy.
Keywords: baking powder, water content, dry weight method, near infrared spectroscopy
Introduction
Baking powder is used to increase the volume and lighten the texture of baked goods such as
muffins, cakes, scones and steamed breads. Several hundreds different types of baking
powder are produced and purchased. Most kinds of baking powder are made up of an alkaline
component (typically baking soda, sodium bicarbonate), one or more acid salts and an inert
starch (cornstarch in most cases). Baking soda is the source of the carbon dioxide, which is
caused by an acid-activated decomposition of baking soda. The starch absorbs the moisture in
baking powder, and thus prolong shelf life by keeping the powder's alkaline and acidic
components from reacting prematurely.
heating
2NaHCO3 → Na2CO3 + H2O + CO2
NaHCO3 + HCl → NaCl + H2CO3
H2CO3 → H2O + CO2
There is no good method to measure the water content of baking powder, though water
content is the most important factor for quality control of baking powder production. It is
difficult to apply the dry weight method to baking powder although the method is generally
accepted for measurement of water content of foods. Carbon dioxide is released and the
weight of baking powder gradually decreases while measuring water content of baking
powder by the dry weight method under high temperature.
In this study, the relationship between carbon dioxide generation rate and operating
temperature for the dry weight method was studied to apply the dry weight method to
measuring water content of baking powder. Furthermore, prediction of water content of
baking powder using near infrared (NIR) spectroscopy was studied to apply it to control of
water content of baking powder.
NIR spectroscopy has been employed for the simultaneous prediction of the concentrations of
several substrates, products, and constituents in the samples from various fields such as food,
chemistry, polymers, cosmetics, textiles, pharmacy, agriculture, environment, life sciences etc.
NIR spectroscopy has several advantages; non-destructive and rapid analysis, multiple
component assay, no sample preparation, no solvents, and on-line measurement.
Materials and methods
The baking powder used in this study was consisted of 35% of sodium hydrogen carbonate,
45% of disodium dihydrogen pyrophosphate and 20% of cornstarch.
To observe the gas production from baking powder, mixture of 4 g of cornstarch and 9 g of
disodium dihydrogen pyrophosphate was mixed well after addition of water, and seven grams
of sodium hydrogen carbonate was mixed well with the mixture before packing into a bag and
heat-sealing. The volume of the bag was measured as increased volume of water when the
bag was soaked into the water in a measuring cylinder.
The conventional method to measure the water content is the dry weight method using an
infrared moisture meter (FD-620; Kett Electric Laboratory, Tokyo). It is regarded that the
water content becomes to be constant when the difference of weight is under 0.1%/2 min.
For the NIR method, the baking powder was packed in a sample cup (Foss NIRSystems Inc.)
and the cup covered with a polyethylene sheet was put into a spectrophotometer (NIRS
6500SPL, Foss NIRSystems Inc.) to measure the spectrum. The second derivative of
absorbance was obtained at a gap of 0 nm and segment of 20 nm. Simple linear regression
(SLR) analysis using the least-squares method was conducted on the second derivatives of the
NIR spectral data against the water content obtained by the dry weight method.
Results and discussion
16
140℃
○　50℃
□　60
◇　70
△　80
▽　90
14
12
Reduced weight (%)
Optimum operating temperature of dry
weight method
The effects of the temperature at the dry
weight method on the weight of baking
powder are shown in Fig. 1. When the
operation of the dry weight method was
carried out at over 100°C, the weight of
baking powder decreased linearly and the
higher decomposition rate of baking powder
was observed under higher operating
temperature. At 50°C to 90°C operation, the
weight of baking powder became almost
constant. The slopes of lines in Fig. 1 were
plotted in Fig. 2. The optimum operating
temperature for the dry weight method was
may be 70°C.
130℃
10
120℃
8
6
110℃
4
100℃
2
0
0
5
10
15
20
Time (min)
Figure 1 Time courses of reduced weight of baking powder
during measurement of water content.
1.4
Weight reducing rate (%/min)
1.2
1
0.8
0.6
0.4
0.2
0
50
70
90
110
130
150
Temperature (℃）
Figure 2 Effect of temperature on weight reducing rate of
baking powder.
70
Volume of bag (mL)
60
50
40
30
20
0
1
2
3
4
5
Water content (%)
Figure 3 Effect of water content of baking powder on gas
production.
Sodium Hydrogen Carbonate
Disodium Dihydrogen Pyrophosphate
Cornstarch
2
d log(1/R)
Effect of water content of baking powder on
gas production
The effect of water content of baking powder
on the gas production was shown in Fig. 3.
No gas production was observed under 3% of
water content. However gas production
increased as water content increased over 3%.
The water content of baking powder should
be kept under 3% to avoid gas production
during storage and distribution of baking
powder.
NIR spectra
NIR second derivative spectra of baking
powder and raw materials of baking powder
are shown in Fig. 4. Absorption of NIR
caused by water was observed at 760 nm, 970
nm, 1450 nm and 1940 nm (Osborne et al.).
The negative peaks around at 1000 nm, 1400
nm and 1900 nm may be caused by water.
Very low water content is observed on the
spectra of sodium hydrogen carbonate and
disodium dihydrogen pyrophosphate. While
the water content of cornstarch was relatively
high. Water in the baking powder was
derived mainly from water in cornstarch. It is
better for baking powder production that
cornstarch dried well is obtained.
Prediction of water content using NIR
spectroscopy
In the prediction of water content of baking
powder using NIR spectroscopy, baking
powder samples with various values of water
content were prepared and NIR spectrum was
measured from 400 nm to 2500 nm at 2 nm
intervals through a polyethylene sheet. SLR
analysis was used to obtain calibration
equations relating the NIR spectral data and
the water content obtained by the dry weight
method using a calibration sample set
(sample number, n=60). The wavelengths at
964 nm, 1162 nm, 1416 nm and 1964 nm
were selected to make calibration equation.
Calibration and validation results for water
content in the baking powder are summarized
in Table 1. Good results of calibration and
validation were obtained using 1162 nm,
1416 nm and 1964 nm. While relatively bad
results were observed at 964 nm. When the
calibration equation with 1162 nm was
applied to the prediction of water content for
a prediction sample set (n=40), the prediction
was successfully carried out using NIR
spectroscopy with correlation coefficient,
r2=0.953 and standard error of prediction,
SEP=0.098 % as shown in Table 1 and Fig. 5.
Baking Powder
500
1000
1500
2000
2500
Wavelength (nm)
Figure 4 Second derivative spectra of baking powder
and raw materials.
It may be possible to measure the water
content of all packages of baking powder
using NIR spectroscopy.
2.5
Conclusions
(%)
2
C
pre
1.5
The optimum operating temperature for the
dry weight method to measure the water
content of baking powder was studied and
1
found to be 70°C.
Prediction of water content of baking powder
packed with a polyethylene sheet using NIR
0.5
spectroscopy was studied. Simple linear
0.5
1
1.5
2
2.5
C (%)
regression analysis was used to obtain
act
calibration equations relating NIR spectral Figure 5 Correlation between water content in baking powder,
C , and that predicted by NIR, Cpre, with the calibration
data and the water content obtained by the act
2
dry weight method using a calibration sample equation produced using d log(1/R) at 1162 nm,
2
set (n=60). When the calibration equation Cpre = 2.242 - 714.14 d log(1/R) .
with 1162 nm was applied to the prediction
of water content for a prediction sample set (n=40), the prediction was successfully carried
out using NIR spectroscopy with correlation coefficient, r2=0.953 and standard error of
prediction, SEP=0.098 %. It may be possible to measure the water content of all packages of
baking powder using NIR spectroscopy.
Table 1 Calibration and validation results for water content in the baking powder.
Calibration (n=60)
Validation (n=40)
Wavelength
2
2
(nm)
SEC (%)
r
SEP (%)
Bias
r
964
0.822
0.209
0.899
0.143
0.039
1162
0.904
0.154
0.953
0.098
-0.020
1416
0.920
0.140
0.945
0.108
0.032
1964
0.904
0.154
0.846
0.179
-0.033
r: correlation coefficient, SEC: standard error of calibration, SEP: standard error of prediction.
References
Osborne, B.G., Fearn, T., Hindle, P.H. (1993). Practical NIR spectroscopy with applications in food and beverage
analysis (pp. 13-35), Longman Scientific & Technical, UK.