Effect of parboiling on thiamine content of rice.

Parboiling destroys a part of the total thiamine content of paddy while protecting the
remaining vitamin from milling loss. Soaking per se does not lead to loss, but much thiamine
is leached out if paddy splits during soaking; soaking at high pH also may reduce it.
Steaming destroys the thiamine partly. The thiamine is protected against milling loss
by mere high temperature soaking of paddy (70° C. or above) or by soaking and steaming,
but not by soaking alone at lower temperatures. This protection thus appears to be
caused by embedding of the inner bran and scutellum layers in the endosperm, consequent
on gelatinization, rather than by inward diffusion of the vitamin. Presence of more
bran pigments in milled parboiled rice than in raw rice and their greater adhesion to
the endosperm support this hypothesis.