[Influence of water activity on the enzymatic changes in freeze-dehydrated muscle III. The breakdown of muscle lipids (author's transl)].

During storage of freeze-dehydrated bovine muscle triglycerides and cholesterolesters are slowly hydrolyzed even at 25% relative humidity (r.h.). The extent of lipid hydrolysis in the tissue increases with rising water activity, the final degree of hydrolysis being dependent on water activity. It has been demonstrated that these changes are due to the effect of muscle enzymes. Phospholipids are not hydrolyzed even at 65% r.h. This might be due to an association of the phospholipids with membranes or to a lack of phospholipase activity in the freeze-dehydrated tissue. The fact that lipids in muscle tissue are hydrolyzed at water activities at which water soluble substrates are not split by hydrolyses agrees well with general ideas about the influence of water activity on the enzymatic breakdown of lipids. Freeze-dehydrated beef should not contain more than 3% moisture in order to prevent undesirable flavour changes caused by lipid changes during storage.