recently I did experiment in culture cell treated with Curcumin. I made a stock of Curcumin with concentration 10 mM from 36 mg of Curcumin powder in 10 ml of DMSO. i treated my cell with concentration of Curcumin 50 mikroMolar from fresh stock of Curcumin 10 mM that I just made, and I got a clear medium in my cell. After that I keep my Curcumin stock at -20 C. today, i'm repeat my experiment and using same doses and curcumin stock that i used before, but in my medium i see black dot ?!(like if your curcumin not dissolve properly). Any suggestion what might be the problem? thank you