You may need to check for possible endothermic processes relevant for your system. 

Refer Carbohydrate Polymers 46, 2001, 179 - 184

Dear Colleague... DSC and Thermal analysis techniques in general were designed to follow or detect changes in samples during heating for temperature ranges far beyond room temperature. Your system is an organic mixture that can very efficiently followed with melting point apparatus, as simple as this. Place few mg of your sample  in a m.p. capillary and place it in the MP and follow the changes within such a low temperature range. You will notice the real change visually. Below 50 C DSC system will be stabilized and we may not rely on such changes unless the MP apparatus reveals a melting or a phase change... Good luck.... Mahmood 

Starch gel is -in my knowledge- a complex system (you should, of course, study the published literature for interpretation) and it is necessary to get high quality DSC diagrams for any interpretation. Having this in mind it should be mentioned, that the first peak could be an artifact (depending on room temperature and the thermostat temperature of the DSC). I recommend to start the measurement at least 20 degrees below the onset of the first peak to see whether it is an real event, or an effect of the apparatus. (Of course the thermostat of the DSC must be set to - 10 Degrees at least, to be sure, that controlled temperature equilibration takes place when the measurement starts. Furthermore I recommend to subtract the "zeroline"  of the DSC (that is the curve you get when you repeat the measurement with an empty crucible and same parameters) before you evaluate possible peaks produced by your sample. The baselines you have drawn are otherwise rather arbitrary and the result possibly faulty. I would not try to interpret your measurement without further information about the conditions of the measurement (thermostat temperature, room temperature,  mass of sample, DSC type etc.)

Good luck and regards Gunther Höhne

Thanks for everyone! First, I thought the first peak might be an artifact, however, i repeated another starch gel, still get the similar two peaks. I am wondering how to explain. and this peak is strong enough to be ignored, and can't be caused by sample preparation

If it is an artifact of the DSC, it will come again with every run whatever sample you have. Start the run at 20 degrees lower temperature an see what happens with the peak then.

Lower than 20 degree? why this condition have effect on the peak at 30 degree?

I am confused

• Don't be confused> to study or follow a change with DSC you need to start prior to the temperature range involved.   Thus , a change at 30o C must be studied starting from below 30. Not only the peak maximum is important, the whole peak must be investigated. Again I tell you "repeat the analysis by watching the behavior of the material inside the melting point apparatus. It will show you the exact case.. Good luck

Thanks so much, I will try the melting point apparatus