biological catalysts: that is, they increase the rate of specific chemical reactions that otherwise would occur only very slowly, if at all Enzymes thus cause chemical change Some enzymes build molecules up, or modify them; some break molecules down Human digestive enzymes, for example, break proteins into individual amino acids, and starch into individual glucose units A singe enzyme molecule can catalyze as many as a million reactions per second Enzymes matter to the cook because foods contain enzymes that once did important work for the plant or animal when it was alive, but that can now harm the food by changing its color, texture, taste, or nutritiousness Enzymes help turn green chlorophyll in vegetables dull olive, cause cut fruits to turn brown and oxidize their vitamin C, and turn fish flesh mushy And bacterial spoilage is largely a matter of bacterial enzymes breaking the food down for the bacteria’s own use With a few exceptions — the tenderizing of meat by its own internal enzymes, the firming of some vegetables before further cooking, and fermentations in general — the cook wants to prevent enzymatic activity in food Storing foods at low temperatures delays spoilage in part because it slows the growth of spoilage microbes, but also because it slows the activity of the food’s own enzymes Cooking Accelerates Enzyme Action Before Stopping It Because the activity of an enzyme depends on its structure, any change in that structure will destroy its effectiveness So cooking foods sufficiently will denature and inactivate any enzymes they may contain One vivid example of this principle is the behavior of raw and cooked pineapple in gelatin Pineapples and certain other fruits contain an enzyme that breaks proteins down into small fragments If raw pineapple is combined with gelatin to make a jelly, the ... and inactivate any enzymes they may contain One vivid example of this principle is the behavior of raw and cooked pineapple in gelatin Pineapples and certain other fruits contain an enzyme that breaks...With a few exceptions — the tenderizing of meat by its own internal enzymes, the firming of some vegetables before further cooking, and fermentations in general — the cook wants to prevent enzymatic activity in food. .. wants to prevent enzymatic activity in food Storing foods at low temperatures delays spoilage in part because it slows the growth of spoilage microbes, but also because it slows the activity of the food? ??s own enzymes