thermolabile
ther.mo.la.bile \-'la--.bi-l, -b*l\ \-la--'bil-*t-e-\ aj [ISV] : unstable 
   when heated; specif : subject to loss of characteristi c properties on 
   being heated to or above 55 C {many immune bodies, enzymes,and vitamins are 
   ~} - ther.mo.la.bil.i.ty n
 Webster's English Dictionary