On Food and Cooking

granules but leaves cellulose fibers intact;
most animals can digest starch, but not
cellulose. Cellulose is a structural support
that’s laid down in cell walls in the form of
tiny fibers analogous to steel reinforcing bars,
and it’s made to be durable. Few animals can
digest cellulose, and hay-eating cattle and
wood-eating termites can do so only because
their guts are populated by cellulose-digesting
bacteria. To other animals, including
ourselves, cellulose is indigestible fiber
(which has its own value; see p. 258).
Hemicelluloses and Pectic Substances These
polysaccharides (made from a variety of
sugars, including galactose, xylose, arabinose)
are found together with cellulose in the plant
cell walls. If the cellulose fibrils are the
reinforcing bars in the cell walls, the
amorphous hemicelluloses and pectic
substances are a sort of jelly-like cement in
which the bars are embedded. Their
significance for the cook is that, unlike