I have a problem with DSC bread measurement. I used the conditions from the publication: Fresh breads were cut in four pieces, and a sample (approximately 10 mg) was taken from each one and tightly packed to an aluminium pan. The pan was closed with a lid and weighed. Calorimetric measurements were performed with Mettler DSC 1 within a temperature of 10C (2min), 10C-160C (10C/min). The reference sample was a pierced twice Al empty pan. Why I have different curve shape than in publication? What kind of sample preparation should I make?
1. First of all, the DSC profile depends on the previous storage conditions of the crumb. The lack of signal might be due to the fact that retrogradation has not yet proceeded to a significant extent in your samples. You mentioned that the sample was fresh bread, which is not expected to give a response in DSC.
2. When heating up to 160 C you have to ensure that your pans can withstand elevated pressure. In our lab, at T > 100 C in Perkin-Elmer equipment we used stainless steel pans which were hermetically sealed with a special device. You can do a check on water loss during the DSC scan by measuring sample weight before and after your run.
3. You have to ensure that there is good contact between sample and pan. If crumb samples give an erratic response you can try to perform a scan of bread in water (for example at a starch:water ratio of 1:4, taking into account the water content in the crumb). If you want to assess the melting process at the real moisture content in the bread, you could use an inert heat-resistant silicon oil.
I have attached a paper by Yu and Christie on some experimental aspects of DSC on starch. If you cannot open the file, the reference is: L. Yu, G. Christie, Carbohydr. Polym. 46 (2001) 179-184.
Thank you for your answers. The problem was the contact between the sample and the pan. Moreover, I have observed that the heating rate helps a lot.
everyone, i have also a problem with retrogradation.
Starch gels prepared at a concentration of 10% was placed in the refringerator for almost 8 days, and no retrogradation was found with the help of SAXS. that is to say, no 9nm lamellar repeat distance appeared.
I don't know why
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