Polishing millet grains makes them less nutritious

Millet grains which have their outer layers removed cook faster and last longer but are low in nutrients and fibre and higher in starch compared with dehusked ones, which potentially raises the glycemic load of Indian diets¹.

Researchers from the Madras Diabetes Research Foundation in Chennai and the ICAR-Indian Institute of Millet Research in Hyderabad analyzed the nutritional, microstructural and cooking properties of five small-seed millets.

The grains were dehusked to remove their inedible layer and ‘polished’ or debranned.

Using Fourier Transform Infrared (FTIR) spectra, X-ray diffraction (XRD) and scanning electron microscopy, the team found that debranning reduced dietary fibre, fat, mineral and phytate content in all the millets while enhancing available carbohydrates and amylose content. It also caused a drop in protein in all the grains except for the little and barnyard millets. Dehusked grains took longer to cook but retained their nutrients.

Debranned millets lost more solids and absorbed more water during cooking, probably due to the removal of the seed coats, which reduced their structural integrity. Electron microscopy revealed that debranning stripped the grains of seed coat and aleurone layers and caused partial loss of the primary cell layer. FTIR and XRD analyses indicated changes in chemical bonds and reduced crystallinity.

“Polished millets are fibre and nutrient depleted yet sold at a premium, misleading consumers into paying more for a product nutritionally akin to white rice,” says study co-author Shobana Shanmugam.

Millet grains are best consumed in their natural, minimally processed form, the researchers say.