Einfluß der Wasseraktivität auf enzymatische Veränderungen in gefriergetrocknetem Muskelfleisch

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Abstract
During storage of prerigor freeze-dried beef, glycogen is not broken down even at 97.5% r.h. (moisture content of the meat about 30%). However, the metabolites of glycogen -- glucose, fructose, and their phosphoric acid esters -- are changed during storage at r.h. greater than 25%, mainly by the effect of glycolytic enzymes. Also nonenzymic reactions of the Maillard type seem to occur. An accelerated breakdown of these carbohydrates with increasing water activity was found. Even though the sugar monophosphates are broken down, no increase in C3 metabolites was found. The reason for this could be that the energy-rich compounds glyceraldehyde phosphate and dihydroxyacetone phosphate form complexes with some proteins. It is suggested that also pyruvate reacts with free amino groups of proteins. The breakdown of carbohydrates increases in uncooked freeze-dried samples above 60% r.h. whereas nonenzymatic reactions of the Maillard type reach a maximum rate at nonenzymatic reactions of the Maillard type reach a maximum rate at 60% r.h. This also shows that the disappearance of carbohydrates during storage of freeze-dried prerigor beef is mainly due to enzymatic processes.