During thermal scanning of dried pumpkin flour, a sharp melting point was noticed at 158°C. I am not sure whether this is contributed to by lipids or protein, do you have any suggestions?
Melting point is usually associated with the degree of compactness of the crystals. Considering the composition of pumpkin, most likely the carbohydrates are contributing toward the relatively high and sharp melting point. If you want to delve further, X-ray diffraction might reveal the nature of the crystals.
Dear Prof Ahmed
Currently work with pumpkin (extruded and dried). In our thermograms pumpkin flour (Cucurbita moschata) dont show melting points at the temperature that you said 158 C..Also in another work we demonstrate that influence of lipids and starch (Amylose - lipids complex increase thermal stability up 95 C). the event of protein denaturation ocurrs at lower temperature than 158 C. At this temperature I agree with prof Islam carbohydrates are contributing to the melting point instead proteins and lipids.
I believe in the same way and we have tested 3 types of freeze-dried pumpkin flour from 3 Asian countries and fortunately all three showed Tm at similar temperature range. I will further work after removal of fat and protein to make sure about the starch. The Tg for powders about 20-30C. Thanks both of you.
It is not very likely that the high melting point is related to lipids because most vegetable fats melt at far below this temperature. It is propable that at temperatures higher than 90°C most of the proteins contained in your sample are coagulated. Could you verify if coagulated proteins may have such a high melting point. Heating of food materials at such temperatures may cause very complex changes in the material which makes it difficukt to expalin by looking at one or two components of the food.
In our experience it would be the carbohydartes affecting the material. The proteins may have some contribution but probably very minor indeed. Suggest a chemical composition of the material especially investigating the starch and non-starch polysaccharides.
Did you measured the thermal properties by DCS (Differential Scanning calorimeter)?
what is the starch content of pumpkin flour ?
what is the range of temperature used to measure thermal properties?
Can I see the thermograph curve?
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