Metabolic evaluation of rice protein

Rice protein occurs in milled rice as discrete particles called protein bodies, 1–4 μm in size. Very little variation in lysine content of rice protein has been observed at any protein level. Rat assays for protein quality by protein efficiency ratio, slope-ratio technique and nitrogen balance showed that the relative protein value of milled rices (6–15% protein) ranged from 42 to 82% of milk and egg protein. True digestibility of rice protein in rats ranged from 94 to 100% and biological value ranged from 68 to 75%. An increase in protein content results in an increase in the utilisable protein of the milled rice. Similar results were obtained with nitrogen-balance studies in Man. True digestibility is 79 to 85%, biological value ranging from 59 to 67% and NPU from 47 to 55%.Cooking reduces the digestibility but improves the biological value of milled rice protein in growing rats, resulting in similar net protein utilisation for raw and cooked rice. Lysine digestibility remains almost complete with cooking. A 15% fraction of cooked-rice protein is also indigestible in Man and is expelled as intact faecal protein particles.