Introduction

Rice (Oryza sativa) is the staple food for half of the world’s population.

Due to its starch content, it is an excellent source of calories. Its proteins have a higher yield than those of other cereals and it is a hypoallergenic food, easily digestible, with versatile functional properties.

Seed structure:

There are over two hundred varieties. Among Spanish varieties, *bomba* rice stands out for being thick and round, and it absorbs flavours very well.

Commercial Types of Rice

• Whole, brown, or unpolished rice, simply husked.
• White rice (processed or standard), a polished product without the double layer beneath the husk and without the germ. This is achieved using emery-coated rollers. The by-product obtained is rice bran, rich in protein and fibre.
• Parboiled rice, rice subjected to pre-cooking. It improves digestibility and contains more nutrients, especially B vitamins, minerals, and slightly more protein and fat.

Chemical Composition

The composition of rice varies greatly depending not only on the variety and the different parts of the grain, as shown in the table, but also on the degree of processing.

The husk contains a high proportion of cellulose and ash, rich in silica.

Bran and germ are rich in proteins, fats and water-soluble vitamins, although these three components are largely lost during the polishing process. Rice bran is not used directly in human food due to its instability. It is easily altered due to its content of enzymes, lipase, peroxidase, and a high fat content. It becomes acidic and rancid quickly.

The endosperm is rich in carbohydrates, especially starch. Within the endosperm, composition varies: from the outer to the inner layers, starch content increases while protein, lipid and vitamin content decreases. Protein is far more abundant on the surface of the grain — approximately 20% — compared to 5% in the centre. Lipids and vitamins are also more concentrated on the surface, but are nearly absent in the core.

Rice Fortification

Rice can be enriched through impregnation with supplements. The nutritional value also increases significantly through the parboiling process, as the hydrothermal treatment of the husked rice followed by drying and milling transfers the water-soluble nutrients from the bran into the endosperm, thereby enriching it and increasing the biological value of the proteins.

Use of Rice By-products

• Bran is usually marketed together with the germ; stabilisation is necessary by thermally inactivating lipases.
• Rice bran oil can also be extracted, with a profile very similar to olive oil.
• Residual flour (from defatted bran)

Rice Storage

In general, the quality of rice improves with storage. Newly harvested rice is of lower quality and more difficult to digest, although aged rice loses vitamin content.

Very little change in composition, except for vitamins.

During storage, proteins may undergo some insolubilisation, but total nitrogen content remains mostly unchanged.

Total lipid content hardly varies, but free acidity may increase.

There may be an increase in reducing sugars at the expense of non-reducing sugars.

It should be stored in cool, dry places and is not recommended to be kept in the fridge.

Nutritional Value of Rice

The biological value of rice proteins (60%) is lower than that of wheat (75%). Even so, its biological value is relatively high, partly because rice protein is rich in glutelins (80%) and low in prolamins. Prolamins are low in lysine, and since they are a minority in rice, the lysine deficiency—typically the limiting amino acid in cereals—is not as pronounced compared to other cereals. In rice, lysine is the first limiting amino acid, followed by threonine. Rice is deficient in B vitamins.

Dietary Value

Rice is especially recommended in diets for kidney, liver, and stomach conditions. It is easily digestible. If white, it is advised in cases of diarrhoea or gastroenteritis.

It is essential to start changing habits regarding rice consumption. We must encourage the consumption of brown rice as it is underutilised and is nutritionally much more interesting due to its fibre, vitamin, and mineral content. It is true that it is more difficult to cook because it requires longer cooking times, but it is well worth it for all its benefits.