15.2.3.1   Enzymatic action
	Many foodstuffs, such as fruit, vegetables, meat and fish, contain enzymes, which have a catalytic action and break down nutrients. Like microorganisms, enzymes are also dependent to a considerable extent on the temperature and water content of the goods.   The optimum temperature for enzymatic activity is 45°C. Lower temperatures slow down activity; however, activity is possible at far lower minus temperatures than is the case with microorganisms. Most enzymes are not inactivated until a temperature as low as -20 to -30°C is reached. Frozen goods therefore have only a limited storage life: if stored for many months, enzymatic processes may cause undesired changes and finally lead to spoilage.   Enzymatic activity is also associated with water: enzymes only become active when they are in the form of swollen proteins. Table 5 shows the activity of enzymes and microorganisms as a function of temperature.   °C Enzymes which affect flavor and structure Microorganisms which cause mold growth Microorganisms which cause food poisoning 20 high level of activity rapid development rapid development 15 10 5 0 slow development - 5 slow development inactive - 10 inactive - 15 - 20 low level of activity - 25 - 30 - 35   Table 5: Activity of enzymes and microorganisms as a function of temperature; taken from Alders [2]

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