I suppose it is the thermo-plastification of starch - basically a partial amylopectin degradation that disrupts the starch grains. It would be expected somewhere between 60-120 °C depending on the type of starch (grain size, amylopectin content) and processing parameters. Water acts as a plasticizing agent and makes the process more pronounced.

Your DSC endotherm is more or less at the right temperature but it is very broad and the enthalpy is improbably high. What you observe is most likely the evaporation of water (ca 2200 J/g). This points to DSC pans that are not properly sealed. Your DSC profile suggests that your upper temperature was largely in excess of 120 Celsius, which may have caused pan leakage. Follow the instructions of the supplier for the maximum T to be allowed if water is present. For this type of experiments starch concentration has to be below 40 % and a starch weight of a few milligrams is recommended. Look into the literature for details.

Thank you both , i would further like to know what is the ratio of water to starch you use ?

We don't use water, it's quite volatile and slowly evaporates from the plasticized starch. We use other plasticizing agents, usually glycerol. It depends on the application, of course. You may get a true water-born solution with up to a few % of starch. Above that, you usually get a colloidal solution, gel, soft waxy solid, or flexible thermoplastic starch (TPS). The actual limit and solubility differ regarding the type of starch you have. Use chemically modified starch for better solubility. When we mix it with glycerol (or another plasticizer), we usually leave it overnight for the plasticization to take place. There is plenty of literature on starch/glycerol and starch/water blends, so just a few examples for many:

Article The Effects of Citric Acid on the Properties of Thermoplasti...

Article Thermodynamics of starch-water systems: An analysis from sol...

Looping into the

According to the literature, starch:water ratios 1:5 to 1:3 are common. Up to 40 % starch the DSC profile does not depend on starch concentration. At higher starch concentrations DSC profiles become more complex and start to depend on the relative amount of water. See J.W. Donovan, Biopolymers 1979.

The correct citation is: J.W. Donovan, Biopolymers 18 (1979) 263-275.

I agree with the sugg.estion from Professor Peter A. M. Steeneken . The pan had not been tightly sealed, since the heat flow was too high, possibly according to water evaporation. I recommend to repeat the test, using 1:3 ratio and a smaller amount of starch, containing in a pan (40μL volume), empty pan as control.

Peng Guo Peter A. M. Steeneken Petr Lepcio Thanks alot for the indepth answers,I would further like to know that if I add 6ul water in 2mg starch, what should be the total weight I write in DSC.

Also how do I set my baseline ?

The heat of gelatinization is calculated per gram dry starch. In your example you work with 0.002 x dm gram dry starch, where dm = the fraction of dry matter in your starch. If you assume that 6 ul added water weighs exactly 0.006 gram, starch concentration in the DSC = 0.002 x dm x 100 /0.008 %. Please note that it is customary in DSC to express all additions by weight, using a precision balance. Volumes are not accurate enough. By weighing the pans before and after the experiment you can check for pan leakage.

Base lines are generally determined from runs with empty pans.

I am still confused with the amount to be taken as 2mg starch do not cover the base of the pan !

Just try it. You have to add 6 mg of water as well. Seal the cup and mix by gently moving the pan over a horizontal surface a couple of times. Then you run the tests and compare your results with literature data for corn starch with regard to the transition temperatures T0, Tp and Tfinal and the gelatinization enthalpy Delta H. The latter is expected to be about 10-15 J/g starch. I am out of office until end of August so I cannot provide you with references at the moment. Of course you also have to check the reproducibility.

Just try it. You have to add 6 mg of water as well. Seal the cup and mix by gently moving the pan over a horizontal surface a couple of times. Then you run the tests and compare your results with literature data for corn starch with regard to the transition temperatures T0, Tp and Tfinal and the gelatinization enthalpy Delta H. The latter is expected to be about 10-15 J/g starch. I am out of office until end of August so I cannot provide you with references at the moment. Of course you also have to check the reproducibility.

Just try it. You have to add 6 mg of water as well. Seal the cup and mix by gently moving the pan over a horizontal surface a couple of times. Then you run the tests and compare your results with literature data for corn starch with regard to the transition temperatures T0, Tp and Tfinal and the gelatinization enthalpy Delta H. The latter is expected to be about 10-15 J/g starch. I am out of office until end of August so I cannot provide you with references at the moment. Of course you also have to check the reproducibility.

Excuse me for the multiple messages. I have to do this on my phone which is rather awkward because of the error messages I got.

I did 6 times same experiment as you said and i dont see any reproducilibilty , infacy in none of my other samples too where i also run the triplicates.

It seems that your procedure is not working properly. Try some tests like the melting of indium and of ice. Ensure that your maximum T when working with water is not higher than 110 Celsius and check for pan leakage by weighing before and after. In case of failure contact your supplier or supervisor.

See also the concise method description in J. Jane et al. Cereal Chemistry 76 (1999) 629-637. Pdf available in Google Scholar.

I propose to continue eventual discussion by e-mail.

Prof. Steeneken mentioned all the issues and I'm going to give you a hint that could solve the problem. As noted by others, the peak shows water evaporation rather than starch gelatinization. This reflects that your starch didn't reach to an equilibrium state before the experiments. Moreover, the starch content within the pan had been too high. The points here are to 1- use ratios containing more water (try at least 1:3 st:wa) 2- give the mixture at least 12 h to equilibrate: you can prepare a bulk mixture of starch and water (e.g. 10g st in 30g water) and put it on a roller-mixer for 12 h and then after a strong vortex mixing transfer 10 microliters of the mixture to the pan and run the test after sealing the pan.

Seid Reza Falsafi Peter A. M. Steeneken Peng Guo the only thing left with me for test and trial is the DSC running conditions now. I usually do it as Hold at 20 C for 1 minute, Scanning from 15 to 150 C, And then cooling to 20 C.

what is the standard one which i should follow for the starch gelatinization.

I highly appreciate your timely responses and efforts.

TIA

150 C is not useful and is much too high when using alumina pans. To prevent pan leakage the maximum is 110 C. At higher T you need stainless steel pans. Scan rate 10 C/min is standard.

According to experience, the ratio of starch to water is required to be 1:3, and it is not required to put the lid during preparation.