Explanation:

Parboiling causes a gelatinization of the starch during the boiling and during cooling the amylase molecules re-associate with each other and form a tightly packed structure. The kernels are harder and appear glassier after the parboiling process. The parboiling process moves micronutrients contained in the bran, which is usually removed in the whitening process in the rice mill, to the endosperm. Parboiled rice is therefore more nutritious than white rice.
Parboiling also mends little cracks that might have developed in the endosperm during postharvest processing and therefore head rice recoveries of parboiled rice are higher.