S. N. HELAMBE AND S. G. BADHE
P.G. and Research center,
Dept. of Electronics, Deogiri College, Aurangabad, India.
Abstract:
A food preservative that includes permitted acids and chemicals is used
to prolong the shelf life of food. Preservatives stop the enzymatic actions that occur
during the spoilage. These preservatives also affect the food quality. A low frequency
Time Domain Reflectometry (TDR) was developed and used to study different types of
preservatives. In the present work impedance of Sodium Benzoate and Urea is
calculated. Different molar concentrations of both the preservative were prepared with
freshly collected distilled water. All the aqueous solutions are kept in temperature
controller unit, which was controlled and monitored by computer. It was observed that
the impedance of Sodium Benzoate decreases with increase in concentration (0.005- 0.1)
and temperature (25oC, 35oC, 45oC & 55oC) where as urea solution does not show any
measurable changes in impedance for various concentrations and at various
temperatures.
KEYWARDS :
Impedance, spectroscopy, frequency, Reflectometry, molar, aqueous.
INTRODUCTION :
Chemicals perform an important role in preserving the food. When the food is spoiling there are
many molecular changes in the foodstuffs and the chemical preservatives used to preserve the foodstuff
stop those changes occurred. Taking into consideration capability of impedance spectroscopy provides an
important approach to estimate microbial population in foodstuffs (2, 3). Electrical Impedance
spectroscopy is used to calculate impedance, conductivity and dielectric constant (4). Impedance
measurement has been used for quality control in food industries (5) for identification (6, 7), enumeration
(8, 9, 10) of indicator microorganisms and of estimation of antimicrobial activity (1, 11).
We are lead to the concept of determination of certain chemicals that are used as preservatives in distilled
water. Our aim to study the impedance variation of the aqueous solution of preservatives of different
concentrations by using the developed low frequency TDR working in the range of 200MHz.
Experimental details:
We have developed an instrument for measurement of impedance based on time domain
technique. A low frequency TDR of the range 200MHz and 5ns rise time was developed. The co-axial
transmission line with characteristic impedance of 50 ohm was used for study of the preservatives. Various
rod and strip types of probes were designed and studied to check the impedance and conductivity. Out of
those a strip type probe of 5.5cm length is used for the further study. For study of the properties of liquid
under consideration we immerse the probe in the liquid.
Temperature controller system was developed to control the temperature during the experiment. This
unit consists of water bath with an electric heater and a test tube holder, PT100 to sense the temperature,
computer to monitor and control temperature.
Experimental procedure:
Food grade sodium benzoate and chemical grade urea is used to prepare the required solutions. Ten
different molar concentrations (0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, and 0.1molar) are
prepared with freshly collected distilled water. These different molar concentrations are kept in water bath
at different temperatures, 25oC, 35oC, 45oC and 55oC. A probe connected with pulse generator through
coaxial cable is immersed in the aqueous solution of sodium benzoate and urea. Afast rising pulse is applied
through the coaxial transmission line. The rising pulse gets reflected back from the solution under
consideration. The nature of the pulse is depends on the properties of the liquid. This pulse is observed and
stored in the Digital Storage Oscilloscope i.e. DSO. This data was then collected in an external storage and
further calculations were done. Each time the probe was thoroughly cleaned with acetone and dried.
Results and discussion:
A graph of Sodium benzoate conductivity against molar concentration is as shown in fig.1. The
graph shows that conductivity of sodium benzoate is increasing as increase in temperature as well as molar
concentration of the aqueous solution.
Fig.1 Sodium benzoate conductivity of different molar concentration at different temperature.
Fig. 2 shows the urea conductivity graph, in which we can't observe any noticeable change in urea
conductivity for lower concentration from 0.005molar to 0.05molar solutions but there is a very small
increase for the higher concentration from 0.06 molar to 0.1 molar solutions.
Fig.2 Urea conductivity of different molar concentration at different temperature.
Conclusion:
Sodium benzoate solution shows decrease in the impedance as the molar concentration increases. The
same type of behavior has been observed for increase in temperature for the sodium benzoate solution.
Urea solution of different molar concentration at different temperature doesn't show any noticeable
changes for lower concentration, as there is increase in temperature but there is a small increase for higher
concentration.
References:
1. C. Gerolimatou, A. Batrinou, J. Tsaknis, V. Spiliotis, “Comparison of the Impedance Splitting Method to
the Agar Dilution Method for the estimation of the antimicrobial activity of Food Preservatives”, Journal of
Rapid Methods and Automation in Microbiology. 12 (2004) 259-267
2. Estimation of Microbial Populations in Frozen Concentrated Orange Juice using Automated Impedance
Measurements, J. L. Weihe, S. L. Seibt, W. S. Hatcher, Journal of Food Science, Volume 49 Issue 1, Pages
243 – 245.
3. Nardo Ramírez, Angel Regueiro, Olimpia Arias, Rolando Contreras, “Electrochemical impedance
spectroscopy: An effective tool for a fast microbiological diagnosis”, Biotecnología Aplicada, 2009; 26:
72-78.
4. Ms. Rajenimbalkar V. S. “Dielectric Relaxation study of ternary mixture of organic at microwave
frequency using time domain reflectometry (TDR) technique”. Thesis submitted Dr. Babasaheb Ambedkar
Marathwada University, Aurangabad.
5. R. Bossuyt, G. Waes, “Impedance measurements to detect post pasteurization of pasteurized milk”, J.
Food – Prot, 4 (1983) 622-624.
6. J.D. Philipps, M.W. Griffiths, “An electrical method for detecting Listeria spp.”, Letters in Applied
Microbiology, 9 (1989), 129-132.
7. K.O. Colquhoun, S. Timms, C.R. Fricker, “Detection of Escherichia coli in potable water using direct
impedance technology”, Journal of Applied Bacteriology, 79 (1995), 635-639.
8. T. Deak, L.R. Beuchat, “Evaluation of indirect conductance method for the detection of yeasts in
laboratory media and apple juice”, Food microbiology. 10 (1993) 255-262.
9. L. Curda, M. Plockova, E. Svirakova, “Growth of Lactococcus lactis in the presence of nisin evaluated
by impedance method”, Institute of Chemical Technology, Prague, (1995).
Golden Research Thoughts • Volume 2 Issue 7 • Jan 2013 3
USE OF ELECTRICAL IMPEDANCE SPECTROSCOPY FOR........
0.02
0.03
0.04
0.05
0.06
0.07
0 0.02 0.04 0.06 0.08 0.1
c
o
n
d
u
c
t
vi
i
t
y
molar concentration
Urea conductivity
25
35
45
5510. K., Futschik, A. Pfuetzner, A. Doblander, H. Asperger, “Automatical registration of microorganism
growth by a new impedance method", Abstr. Int. Meet. Chem. Eng. & Biotechnology, Achema. 88 (1988)
3.
11. G. Kroyer, K. Futschik, “The Impedance Splitting method for microbiological analysis of food
Preservatives”, Reprint-Biotech Lab International. 2 (1997) 3-4.
No comments:
Post a Comment