Nutritional improvement of rice husks

The primary objective was to explore the chemical (NaOH treatment), physical (steam treatment, ground and whole rice husks), and biological (nitrogen supplements and solid-state fungi fermentation) methods of enriching the nutritional value of whole and ground rice husks. Rice husks were compared for their response to alkali and steam treatment and solid-state fermentation by Pleurotus sajor-caju. Treatment with 40 g/L NaOH for 21 days, followed by washing to pH 7, increased the in vitro digestibility (IVD) of ground husks from 0.16 to 0.49 and reduced neutral detergent fibre from 794 to 607 g/kg; and similar values were found for whole husks. Treatment with 40 g/L urea, steamed at 1 atm pressure for 60 min, or 20 g/L NaOH for 48-h followed by washing to pH 7, did not elicit these improvements. Fermenting husks for up to 25 days with or without organic nitrogen supplements (rice bran (RB) or palm kernel cake (PKC)) or fermenting ground husks after steam or 20 g/L NaOH for up to 21 days, promoted fungal growth and improved IVD and crude protein (CP) content without organic matter loss. However, supplementing with urea did not promote growth. Fermenting with supplements RB and PKC was better than without these supplements, and differences between ground and whole husks were small. The IVD after 20 g/L NaOH was larger than after steam treatment. The IVD of ground husks after 21 days pre-treatment were 83 and 23% larger than whole husks for the 20 g/L NaOH and steam treatments, respectively. Cost and environmental concerns preclude the use of NaOH. Although fermenting with supplements substantially enriches the quality of rice husks, its acceptance as a feed may require further cost-efficient improvements because the nutritional gains found were not sufficient to warrant using rice husks as an animal feed.