The DSC thermograms of gelatin and collagen found to exhibit two endotherms at 70-80 oC and 215-225 oC respectively. First endotherm is said to be the denaturation enthalpy of protein during which helix to coil transition is taking place. Whether the same endotherm (70-80 oC) signify the release of bound water molecules??? What is the endotherm corresponds to 215-225 oC?
maybe at high temperature of endotherm (215-225) is due to the crystal of triple helics in collagen, since collagen has Hierarchical structure. A good orientation of helical macromolecules forms crystals. You can try XRD test for you collagen samples.
Hi the first endotherm is your water and the second is your melt. What you can do to verify this is to check the enthalpy. For the gelatin helix-coil transition with Type A Gelatin Bloom No 280 the melt enthalpy should be ~ 11.5 J/g for the as-received powder and the Tmp = 225 dC when measured in an open pan. If you look at the enthalpy of the first peak it is probably a consequence of ~ 10 % water with a peak onset of ~ 80 dC in the powder so re-calculate both enthalpies based on their weight percent and compare these to the expected enthalp of water and gelatin. As the water content increases the onset temperature of the helix-coil transition will decrease. As the Bloom No decreases the helix-coil enthalpy decrease. Effectively the helix-coil transition is being measured in a dry sample using an open pan
If you use a hermetically sealed pan with water contents of < 10 wt-% you will see the Tmpeak reduce to < 100 dC because now you are not removing the water from the system (Gordon-Taylor Equation) but you may see spurious 'peaks' in your thermogram as a consequence of the buckling (usually seen at ~ 80 dC) if the water content is > 10 % in this case you need to use stainless steel pans
Hope this helps
this Proved that gelatin melted at this temperature(215 to 225). Also, Curve of DSC shows an endothermic peak at 70 to 80 oC that the water molecules within the cavity of that are removed At this temperature. However,
The peak at 70-80 is denaturation of collagen.
For eliminate the influence of water peak can be used sealed pans.
Collagen is a material with a well defined supramolecular structure that can be dismantled at temperatures well above 100 °C if the sample moisture does not exceed 10-15% (w/w). Minced collagen in the presence of excess water shows a dramatic downward shift of the endothermic signal (even below 50°C). These results come from sealed pan DSC investigation. Gelatin is a fully denaturated material that usually contains large amounts of moisture and should exhibit a partially reversible gel/sol transition.
I suggest investigations with TG-DSC equipment to split the effects related to the release of water from those related to the "denaturation" of collagen.
I largely agree with Crowley's comments.
Yes TGA will help you to assess water content (weight loss between RT and ~ 150 dC) gelatin degradation onset ~ > 280 dC and you can then use this to evaluate the enthalpy of you lower endotherm. Enthalpy of vapourisation of water = 2.260 kJ/g so if you sample weight is 10 mg and it contains 10 % water then the expected enthalpy of the water peak would be 2.260 J/g - I suspect that you have run your samples in vented pans - you need to check the weight of your sealed pan before and after the run as any weight loss will affect your DSC results. As I said earlier because Al pans have a relatively low ability to withstand pressure if you have > 10 % water contents and you want to examine the Tm of 'wet' samples then you will need to use hermetically-sealed steel pans (these are expensive)
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