[Influence of water activity on the enzymatic changes in freeze-dehydrated muscle. II. Reactions of carbohydrates (author's transl)]

[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.

[Influence of water activity on the enzymatic changes in freeze-dehydrated muscle. IV. Change in the activity of glycolytic enzymes during storage (author's transl)]

The influence of water activity (25-65% r.h.) on the changes in activity of glycolytic enzymes during storage (up to 120 days) of freeze-dehydrated bovine muscle was investigated. For this purpose, at different times of storage the decrease of glycogen and the increase in lactate in the rehydrated samples were determined. At 25% r.h. no loss in activity was observed. However, during storage at 40% r.h. and higher the glycolytic activity decreased; this effect increased with rising water activity. The denaturation of the enzyme proteins might be due to Maillard reactions, particularly to the reaction of proteins with the highly reactive glycolytic metabolites glyceraldehyde phosphate and dihydroxyacetone phosphate.