Thermal  Hysteresis  of  Infrared Spectra  of  Corn  Starch-Water 
Systems

                             Masaru MIZOGUCHI (Japan)
             Faculty of Bioresources, Mie University, Mie 514


             Infrared  spectra of 0.10 mm thick corn  starch-water 
        systems  were  measured  with a  FTIR  spectrometer.  With 
        increasing temperature from 25 to 95 oC, the absorbance at 
        2700  cm-1 decreased abruptly around 80 oC due to  sol-gel 
        process.  The absorbance of the gel increased by  freezing 
        and returned to the unfrozen value after thawing.


1. introduction

     Infrared  spectroscopy method is useful for studies  on  the 
structure  of absorbed water.1) However, infrared is absorbed  so 
intensively  by  water that the method is normally used  for  the 
sample  containing less water. Mizoguchi et al. 2) have  measured 
infrared  spectra  of  NaCl frozen solution  and  determined  ice 
fraction in the NaCl solution by using the absorbance at 2700 cm-
1.  In this study the spectra of corn starch-water  systems  have 
been measured at the range of -60 to 95 oC and thermal hysteresis 
of the absorbance at 2700 cm-1 is revealed.

2. Experimental

2.1 Material
     The material used in the experiment was normal corn  starch, 
which was mixed with distilled water at 25 oC. The  concentration 
of the corn starch was 30.1 % by weight. 

2.2 Apparatus
     A  specially  designed  apparatus was  used2)  with  a  FTIR 
spectrometer.  The sample was kept in steps at a temperature from 
25 to 95 oC by heating, from 95 to 25 oC by cooling, and from -60 
to  25  oC  by heating after the sample was  frozen  with  liquid 
nitrogen.  The  measurement of infrared spectra was  made  for  a 
sample from 1800 to 4000 cm-1 at each equilibrated temperature. 

3. Results and Discussion
 
      Figure 1 shows thermal hysteresis of absorbance at 2700 cm-
1.  With increasing temperature from 25 to 95 oC, the  absorbance 
decreased abruptly around 80 oC.  This  is attributed to  sol-gel 
process  of  corn starch. 
     Comparing  the absorbances before and after heating, sol had 
higher absorbance than gel at 25 oC. Because the concentration of 
the  sample  remained  during   the  experiment,  the  amount  of 
infrared  absorption by corn starch and water should   be  equal.  
Corn  starch  is  dispersed  as  colloidal  particles  in    sol.  
Therefore, infrared was scattered rather than absorbed by the sol 
so that the apparent higher absorbance was  observed in the sol. 
     The absorbance of the gel increased by freezing and returned 
to  the previous value after thawing. This indicates that ice  in 
the  frozen  gel absorbs much infrared than liquid water  in  the 
unfrozen  gel  and  that the gel retains  the  arrangement  after 
freezing and thawing. 

4. Conclusion

     The  present method of using the absorbance at 2700 cm-1  is 
promising to investigate the interaction between water and starch 
including sol-gel process.

Acknowledgment

     This study was completed during a sabbatical leave at Purdue 
University. I  would  like to gratefully  acknowledge  the  advice 
given  by  Dr. P. F. Low at Purdue University.

Bibliography
1) G. Sposito and R. Prost, Chem. Rev., 82, 553(1982).
2) M. Mizoguchi and P. F. Low, Chem. Lett., 12, 2311(1992).
3) M. Mizoguchi and P. F. Low, Chem. Lett., 1, 77(1993).