Rice is the most important cereal crop for human consumption. It is the staple food for over 3 billion people (most of them economically challenged) constituting over half of the world’s population.
The nutritional composition of one cup of cooked rice
|Brown rice||White rice|
|Polyunsaturated fatty acids (g)||0.6||0.1|
*Daily requirement of thiamin is 1.2 mg for an adult man
**Enriched or parboiled rice
which provided an adequate food supply for large populations. These have included corn in the Americas, wheat in the Near East and southern Europe (Greece and Rome), and rice in China and India. The use of rice spread rapidly from China, India, and Africa, and at the present time it is used as a principal food throughout the world. After the discovery of the Americas, the use of rice took hold in both continents. The national dish of Belize in Central America, for example, is composed of rice and beans. There are now hundreds of rice recipes, with each ethnic cuisine having developed individual recipes. Almost all cookbooks have rice recipes, including recipes for risottos and pilafs. Vegetarians, in particular, cherish rice because it is such an excellent food and can be prepared in so many different and appetizing ways. Rice, delicious in itself, readily takes on any flavor that is added. Long-grain rice, when cooked, becomes separate and fluffy, while medium-grain rice is somewhat chewier. Short-grain rice tends to clump together and remains sticky with its starchy sauce. Arborio is an example of a short-grained rice. Wehani rice has a nutty flavor. Basmati rice (aromatic) is very popular, as isjasmine rice.
Rice is the only subsistence crop grown in soil that is poorly drained. It also requires no nitrogen fertilizer because soil microbes in the rice roots fix nitrogen and promote rice growth. Rice adapts itself to both wetlands and dry soil conditions.
Rice is a high-carbohydrate food with 85% of the energy from carbohydrate, 7% from fat, and 8% from protein. However, rice also has a considerable amount of protein, with an excellent spectrum of amino acids. The protein quality of rice (66%) is higher than that of whole wheat (53%) orcorn(49%).Ofthe small amount of fat in brown rice, much is polyunsaturated. White rice is extremely low in fat content.
A cup of cooked rice has approximately 5 grams of protein, which is sufficient for growth and maintenance, provided that a person receives adequate calories to maintain body weight or to increase it, if full growth has not yet occurred. Asiatic children for whom rice is the chief food source have not developed protein deficiency disorders such as kwashiorkor, as have infants that are fed corn or cassava as a chief staple after weaning. Growth and development are normal on a rice diet. Due to its easy digestibility, rice is a good transition food after the cessation of breast or formula feeding.
Rice and Thiamine Deficiency
In Asiatic populations, rice has been, and still is, a main source of nutrition. Thiamine, or vitamin B1, is contained in the outer husk and coating of the rice kernel. When the technology for polishing rice became available, people took to eating white rice in preference to brown rice, but that process removed thiamine, causing beriberi, or thiaminedeficiency, in many people, as well as heart and nerve diseases.
Dutch physicians in Java and Japanese physicians particularly noted the occurrence of beriberi with edema, heart failure, neuropathy, and many deaths. Thi-amine, of course, was an unknown substance at that time. The history of rice is of interest in illustrating how the technology to make a food more appetizing (i.e., white rice versus brown rice) led to an epidemic of a new disease for those populations whose food intake was largely based upon rice. Studies by physicians in Japan and in Indonesia led to a cure for beriberi that included a more varied diet, plus the use of rice husks and the outer coatings of rice, which contained thiamine.
Today, much of the rice consumed is either enriched with thiamine or parboiled, which leads to retention of thiamine in the matrix of the white rice kernel. Beriberi, as a disease from the consumption of white rice, is now rare if the rice is parboiled or enriched. However, some varieties of polished (white) rice may not be enriched with thiamine. Thus, when thiamine intake from other food sources is limited, thiamine deficiency could still occur. In the United States, thiamine deficiency typically occurs in chronic alcoholics.
Rice for Medical Therapy and Prevention
Rice has been the mainstay of treatment for a number of conditions, particularly hypertension at a time when few effective drug therapies were available. In the 1940s, Walter Kempner developed a treatment for mild, and even malignant, hypertension at Duke University. His hypothesis was that a low-protein diet, free of salt, would be an effective treatment. He devised the “rice diet,” which consisted of rice, fruits, and vegetables. This treatment had good results: the blood pressure of his patients fell, and even malignant hypertension was partially reversed. In addition, blood cholesterol levels also fell. Since this was a cholesterol-free and low-fat diet, it was one of the first to document a cholesterol-lowering effect from diet.
The other therapeutic role of rice is in the treatment of allergies. Rice seems to be nonallergenic, and rice milk has been fed to infants allergic to cow’s milk. Rice proteins have also been incorporated into standard infant formulas.
Genetic Engineering of Rice
“Golden rice” was genetically engineered to contain beta-carotene, not present in standard rice, to combat the widespread vitamin A deficiency and ensuing blindness in the children of the developing world. Beta-carotene is a vitamin A precursor that is converted to the vitamin by enzymes of the intestinal mucosa. Vitamin A, or retinol, is then absorbed and transported to the tissues, including the structures of the eye. Golden rice would thus seem to be an advance in the fight against vitamin A deficiency in rice-eating populations. However, there are some concerns about golden rice and other genetically engineered foods. Genetically engineered products have not necessarily been proven safe, and environmental or social risks may outweigh potential benefits that they may bring about.
Clinical trials of golden rice are needed before it is accepted universally. Only when it is clearly determined that itcan prevent vitamin A deficiency in experimental animals, and that it presents no hazards, will this genetically engineered food be considered safe for use in human nutrition. Further, society itself must also decide if genetically created foods are acceptable, a point currently in dispute.
Sequencing the Rice Genome
Since the 1960s, the “green revolution” has improved the yield of rice, and now the “green genome revolution” may bring about further improvements.
The rice genome has now been sequenced, an achievement of great importance. The sequence of the rice genome will provide the template for the sequencing of other grasses (maize, barley, wheat, etc.). The genome sequences are now known for the japonica rice favored in Japan and other countries with a temperate climate, and for the indica subspecies of rice grown in China and most other parts of Asia. This knowledge will permit a future harnessing of genes for disease prevention, drought resistance, nutritional improvement, and many other possible modifiable features of rice. As a recent issue of Science suggested, a “green gene revolution” is needed to meet the challenge of “population growth, loss of arable land and climate changes.”