On Food and Cooking

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.