On Food and Cooking

remove water and concentrate it, the high
temperatures break the already enzyme-
damaged molecules into smaller pieces that
are less efficient thickeners, and the paste
requires that much greater reduction to obtain
the desired thickness. If instead the raw puree
is cooked quickly close to the boil, the result
is a thicker sauce that requires less subsequent
reduction. The pectin and cellulose enzymes
are denatured and become inactive, while at
the same time the cell walls are disrupted by
the heat. The cell-wall pectins that escape into
the fluid phase during the concentration
heating are longer molecules and more
efficient thickeners.

The Thickening  Components  of

Tomatoes

Total   Solids,

%   by  weight

Pectin  and Hemicellulose

Content,    %   by  weight

Raw tomatoes5–100.5–1.0