Cereals are the major source of food for direct human consumption. Wheat, maize and rice represent the most important cereal crops, accounting for 94% of the total cereal consumption worldwide (4). Because of its wide local consumption, acceptability, reach and quantum of consumption, rice (Oryza sativa) far exceeds the requirements of a staple food vehicle that can be considered for fortification purposes at a population-level intervention.
According to the Codex Alimentarius, rice is defined as “whole and broken kernels obtained from the species Oryza sativa L” (5). There are approximately 22 species of the genus Oryza, of which 20 are wild. Two species of rice are important for human consumption: Oryza sativa, cultivated in Asia, North and South America, the European Union, the Middle East and Africa, and Oryza glaberrima, confined to Africa, where it is fast being replaced by Oryza sativa (6).
Paddy rice is the end-product of the harvesting and threshing of rice grains. The paddy rice is made up of an outer husk layer, germ and bran layers, and the endosperm. Various levels of milling can remove the outermost husk layer to yield brown rice kernels, or further remove the bran and germ layers to yield white rice kernels. On average, paddy rice produces 25% husk, 10% bran and germ, and 65% white rice (7, 8).
In an average diet, 30% of calories come from rice and this can increase to more than 70% in some low-income countries, which makes rice a potentially good vehicle for delivering micronutrients to a very large number of people. From the 740 955 973 tonnes of rice produced in 2014, 90% were produced and consumed in Asia (9).
Rice is a rich source of macro- and micronutrients in its unmilled form. During rice milling, the fat as well as the micronutrient-rich bran layers are removed to produce the commonly consumed starch-rich white rice, removing 75–90% of the B-group vitamins thiamine, niacin and vitamin B6,1 and vitamin E (10).
In many cases, procedures for fortification of rice and flours (wheat and maize) have been viewed and managed similarly, and many of the conclusions on the impact of fortification programmes are based on experiences with wheat flour, or on programmes simultaneously fortifying wheat and maize flour (11). It is now recognized that there is much more variability in processing fortified rice, and that the principles that apply to fortification of wheat flour may not necessarily apply to fortification of rice (12).
The technologies currently available for fortification of rice with vitamins and minerals are listed next.
Hot extrusion: dough made of rice flour, vitamin/mineral mix, and water is passed through a single- or twin-screw extruder that cuts it into grain-like structures that resemble rice grains. Hot extrusion involves relatively high temperatures (70–110 °C), obtained by preconditioning and/or heat transfer through steam-heated barrel jackets. It results in fully or partially precooked simulated rice-like grains that have a similar appearance (sheen and transparency) to unfortified rice kernels (13).
Cold extrusion: the only thermal energy used comes from the heat generated during the process itself; thus, this is primarily a low-temperature (below 70 °C) forming process, resulting in grains that are uncooked, opaque and easier to differentiate from unfortified rice kernels. The rice premix thus developed is blended with natural polished rice at a ratio of about 1:200, to produce fortified rice (13).
Coating: high concentrations of micronutrients are added to a fraction of the rice and subsequently coat the rice kernels with water-resistant edible coatings; the coated kernels are then mixed with unfortified rice in a ratio ranging from 1:50 to 1:200. The major problems encountered with coating technologies are related to colour, taste and a loss of micronutrients during washing, as well as during cooking. High variability is reported among technologies for coating and in many of them, consumers are easily able to distinguish the fortified kernels, which will most likely be discarded during rice cleaning (13, 14).
Dusting: the polished rice grains are blended with the powder form of the vitamin/mineral premix. The vitamin/mineral mix sticks to the grain surface because of electrostatic forces. Nutrients are removed through washing and therefore a remark about not washing before cooking should be included in package (10, 15).
The temperatures used during the extrusion process have been recently refined to include other categories and temperature ranges that are slightly different from the above-mentioned definitions: hot extrusion (80–110 °C); warm extrusion (60–80 °C) and cold extrusion (30–50 °C) (16). In general, the extruded or coated fortified rice kernels are then blended with unfortified rice in a ratio ranging from 1:50 to 1:200 (16).
There are other technological processes that can increase the nutritional content of rice.
Parboiling refers to soaking, steaming and drying the rice kernels before removing the bran, thus increasing the content of thiamine, niacin and vitamin B6 in the endosperm by three-fold, owing to their migration from the bran into the endosperm, without changes in iron or zinc contents (17).
Germination: the steps involved in preparing germinated brown rice include soaking high-quality brown rice for 20 h in water at temperatures of 30–40 °C, then washing and cooking. The product is packaged either dry (at a moisture level of 15%) or wet (at a moisture level of 30%). The soaking process improves the rice texture and also increases the availability of nutrients, such as vitamins B6, B12 and E, lysine, magnesium, fibre, inositol, potassium, zinc and magnesium. This process also heightens bioavailable forms of protein and fibre (18).
Six countries have mandatory fortification of rice with at least iron and folic acid (Costa Rica, Nicaragua, Panama, Papua New Guinea, Philippines and United States of America [USA]). In 2016, the status of fortification was: Costa Rica 100% implementation, Papua New Guinea 80%, USA 70%, Philippines 1%, while in Panama and Nicaragua the implementation rate varied. Another six countries have non-mandatory, market-based fortification programmes (Brazil, Peru, Colombia, Indonesia, Mali and Myanmar) (19).
Decisions about which nutrients to add, and the appropriate amounts to add to rice, should be based on the nutritional needs and gaps in dietary intake of the target populations; the usual level of consumption of fortifiable rice; the sensory and physical effects of the fortificant on the rice kernels; the fortification process used in the production of the fortified kernels; the availability and coverage of fortification of other staple food vehicles; the population consumption of vitamin and mineral supplements; the costs; the feasibility of implementation; and the acceptability to consumers (20–23).
The supply chain for rice in a given country is an intricate network of public and private entities that links farmers, rice millers, rice collectors and traders, wholesale traders, retailers, and food processors to the final consumers. Other stakeholders include transporters; companies that supply seeds, agrochemicals and agricultural equipment; irrigation companies; inspection agencies; government departments of commerce, tax and agriculture; and other state agencies that control the prices of paddy, according to their individual governmental policies (24).
Countries can integrate food fortification as part of their national efforts to address malnutrition in all its forms, specifically micronutrient deficiencies and insufficiencies. The choice and concentration of nutrients for rice fortification should be considered in the context of the strategy, including consideration of the vitamin and mineral nutritional needs and the estimated dietary intake gaps of the target populations; the usual level of consumption of rice; the sensory and physical effects of the fortificant on the rice kernel and on the blended rice; the fortification of other food vehicles; population consumption of vitamin and mineral supplements; the costs; the feasibility of implementation; and the acceptability of the fortified rice to the consumers (21).
Fortification programmes should include appropriate quality-assurance and quality-control programmes at mills, as well as regulatory and public health monitoring of the nutrient content of fortified foods and assessment of the nutritional and health impacts of the fortification strategies. There are also specific country or community settings to evaluate and decisions to make. For example, from a quality-control point of view, it is desirable that milling is centralized in few mills, although people who mainly consume locally produced, unprocessed rice are less likely to benefit from an industrial, large-scale, rice-fortification programme.
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The B-complex vitamins include B1, thiamine; B2, riboflavin; B3, niacin; B6, pyridoxine; B9, folate; and B12, cyanocobalamin. Thiamine, riboflavin, niacin and folic acid are commonly referred to by name, and their names are used throughout this document; the others are referred to by vitamin number.
