Plants that changed the world: rice

Scout Davies tells us everything we’ve ever needed to know about rice, a staple food source in many countries

Around 20 per cent of human energy intake worldwide comes from rice. Rice is often eaten boiled, but can also be used to make rice flour, sweets, rice wine or vinegar, and products such as cosmetics and medicines, as well as being used in crafts and for religious purposes.

There are currently over 40,000 types of rice in the world. It is thought to have originated in the Yangtze Valley in China, as far back as 6000–9000 BCE, but there is some debate about this.

Rice (Oryza sativa) is a type of grass which typically grows in wet paddy fields. It has inflorescence panicle flowers, which are flowers that grow in clusters arranged on stems attached to the main branch. It can grow taller than 1 m, or even 5 m when in deep water.

Nutrition

White rice is high in carbohydrate and low in fat, and has moderate amounts of protein. It has lower fibre and vitamin and mineral content than brown rice.

These differences are down to processing. A grain of white rice is a grain of brown rice minus the rice germ, the surrounding rice bran and the hull.

White rice is created by milling and processing the grain until all that’s left is the endosperm. This process removes the nutritional benefits of the whole grain: the rice bran and germ provide fibre, protein, vitamins and minerals. But it makes the rice quicker to cook and easier to digest, so the energy from the grain can be used faster.

Rice has an additional benefit of being free of glutens, the proteins found in wheat. These proteins can affect the immune system of some people, particularly those with autoimmune diseases and allergies such as coeliac disease.

Fortification

Because rice is such a popular food, particularly in low- and middle-income countries, it is often fortified with minerals such as iron, zinc, folate, iodine and calcium, and vitamins such as A, B12 and D, to address malnutrition.

Early varieties of fortified rice were created by adding micronutrient powder that sticks to the grains. Unfortunately, even though instructions to not wash the grains appeared on packaging, typical preparation and cooking methods often rinsed away the enrichment.

Three more sophisticated techniques are now used, which take into account cultural and societal standards:

  • coating involves spraying the surface of the grain with several layers of a vitamin and mineral wax or gum coat, which adheres to the grain better
  • hot extrusion involves passing a dough of rice flour, vitamins, minerals and water through an extruder at temperatures of 70–110°C, which leaves partially pre-cooked grain-like pieces that resemble rice grains
  • cold extrusion is similar to hot extrusion but uses a simple pasta press and works at lower temperatures

In both types of extrusion, a ‘fake’ rice is created which is blended with natural polished rice at a ratio of around 1:200 grains. It remains a technical challenge to create fortified rice that not only looks like actual rice but stands up well during cooking and preparation.

Research and development

Rice has the smallest genome of all cereals, with only 12 chromosomes. This makes it a prime candidate for genetic modification. In the 1960s, a GM rice was created which was more resilient and yielded up to three times greater produce. However, these GM crops require more artificial pesticides and fertilisers in order to flourish.

In China, new types of GM crops similar to rice and wheat, known as crop wild relatives, are being produced to thrive in extreme conditions, such as those that may result from climate change. Producing just 1 kg of rice takes up to 3,000 litres of water, so the rice on your plate has an impact on the environment. Researching this impact and finding solutions is vital for the planet’s future.

Other research is looking at changing the structure of rice to reduce its calorific value, which could help to reduce obesity.

For instance, scientists in Sri Lanka are adding coconut oil to white rice while it boils and cooling it for 12 hours before oven-drying and then reheating it. This process lowers the GI (glycaemic index) of the rice so its sugars are absorbed more slowly by the body. Some of the starches in the rice are removed or converted into forms that are harder to digest, which results in less excess glucose in the body that would get stored as fat.

Lead image:

Matheiu Shoutteten/Flickr CC BY NC ND

References

Questions for discussion

  • Would you eat modified rice for greater vitamin and mineral content or to reduce your calorie intake?
  • Do the benefits of creating higher-yielding crops outweigh concerns such as the greater need for artificial pesticides and fertilisers that these crops have?

About this resource

This resource was first published in ‘Plants’ in May 2016.

Topics:
Ecology and environment, Immunology, Biotechnology and engineering
Issue:
Plants
Education levels:
14–16, 16–19, Continuing professional development