Rice proteins

Protein quantity and quality of rice

Rice kernels, more simply called grain, contain approximately seven percent protein; despite being a modest quantity, rice proteins are qualitatively superior to those of any other cereal.

However, like all vegetable protein sources (soy, beans, cereals and vegetables), rice proteins are deficient in some essential amino acids, specifically lysine and tryptophan as regards the proteins of polished rice, and only lysine for those of brown rice. This last amino acid makes up 4% of rice proteins, a percentage twice higher than that contained in wheat or corn flour. The percentages of threonine and methionine, two other essential amino acids, are also very high compared to those of the others. cereals.

To fill the qualitative and quantitative deficiencies of rice proteins, it is sufficient to supplement the diet with legumes, or animal proteins (fish, meat, eggs and dairy products).

The biological value of rice protein is higher than that of any other cereal, including wheat, which compensates for the slightly lower protein content. According to FAO data, the biological value of rice proteins is 69 (compared to 49 for wheat and 44 for corn).

Tab. 1 Essential amino acid content in some foods and relative biological value of proteins

Food Isoleucine Leucine Lysine Methionine Phenialalanine Threonine Tryptophan Valina Biological value Egg 393 551 436 210 358 320 93 428 100 Bean 262 476 450 66 326 248 63 287 44 Grain 204 417 179 94 282 183 68 276 62 Naus 230 783 167 120 305 225 44 303 49 Potatoes 236 377 299 81 251 235 103 292 34 Rice 238 514 237 145 322 244 78 344 69 Soy 284 486 399 79 309 241 80 300 67

Values ​​are expressed as mg of amino acids per gram of protein nitrogen. The hen's egg is considered to have an ideal protein value and other foods are compared to it in order to express the protein value (from Chrispeels & Sadava - Applied plant biology, Piccin, 1996).

The quantity and quality of rice proteins obviously vary according to the variety and the industrial process undergone by the kernels; for example, they are superior in the wholemeal and parboiled product compared to the polished one.

The absence of gliadinic and glutenin fractions typical of wheat - which allow the formation of gluten but which in many cases cause serious food intolerances (for example celiac disease) - makes rice proteins a food suitable for everyone, even for those who suffer of celiac disease.