With respect to the reference in the paper (Link) I see that the melting point is quite low for the produced PHA as a result of the carbon source being used, I am using glycerol as the carbon source for the production of PHA and the melting of the PHA during the experiment starts at 75 degree celsius and goes until 140 degrees and then the degradation  of residual biomass takes place. There is a little variation in the melting point when I used different concentrations or % of glycerol for the production of PHA. I believe the variation on the carbon source accounts for the melting point and not the concentration ?? can someone explain me the background of it 

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0045214