Fortification of Rice Technologies and Nutrients
Fortification of Rice Technologies and Nutrients
Fortification of Rice Technologies and Nutrients
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A N N A L S O F T H E N E W Y O R K A C A D E M Y O F SC I E N C E S
Issue: Technical Considerations for Rice Fortification in Public Health
This article provides a comprehensive review of the currently available technologies for vitamin and mineral rice
fortification. It covers currently used technologies, such as coating, dusting, and the various extrusion technologies,
with the main focus being on cold, warm, and hot extrusion technologies, including process flow, required facilities,
and sizes of operation. The advantages and disadvantages of the various processing methods are covered, including
a discussion on micronutrients with respect to their technical feasibility during processing, storage, washing, and
various cooking methods and their physiological importance. The microstructure of fortified rice kernels and their
properties, such as visual appearance, sensory perception, and the impact of different micronutrient formulations,
are discussed. Finally, the article covers recommendations for quality control and provides a summary of clinical
trials.
Keywords: rice fortification; technologies; nutrients; vitamins; minerals
Introduction: why rice fortification? addition, using rice to deliver micronutrients will
work only as long as fortified rice is economically
Rice is a rich source of macro and micronutrients
accessible to people at the bottom of the income
in its unmilled form. During rice milling the fat
pyramid. Unpolished rice is a rich source of vita-
and micronutrient-rich bran layers are removed to
mins B1, B6, E, and niacin.2 During polishing, the
produce the commonly consumed starch-rich white
majority (75–90%) of these vitamins are removed.
rice. White rice is the number one staple food in the
Only when parboiled does more than 50% of the
rice countries of southeast and northeast Asia, one
water-soluble vitamin levels of brown rice remain,
of the most densely populated regions in the world.
and this is due to their migration from the outer
Of the world’s rice production, 90% is grown and
layers to the endosperm.2
consumed in Asia. On average, 30% of calories come
from rice and this can increase to more than 70% Micronutrients: selection and suitability
in some low-income countries.1 In most languages
of these regions, the words for rice and food are It is important to stress that the selection of
synonymous. It should be noted that rice is also an micronutrients depends not only on their legal sta-
important staple food in several African countries tus, price, expected bioavailability, stability, and sen-
and the Americas. sory acceptability but also on the product forms
Rice is therefore a potentially excellent product fitting the applied fortification technology. In some
for delivering micronutrients to a very large num- applications, water-soluble forms might be suitable,
ber of people and has the potential to significantly and in others water insoluble or even oily forms
alleviate micronutrient deficiencies. However, this might be preferred.
will only achieve the desired result as long as the Minerals
sensory characteristics of the end product are not Zinc deficiency is often an important public health
discernibly changed and people do not object to issue. As in flour fortification, zinc oxide in rice for-
incorporating fortified rice into their daily diet. In tification is doubtless the product form of choice un-
less a highly water-soluble product form is needed.
[The copyright line for this article was changed on August Zinc oxide does not cause taste issues, has a good
1, 2014 after original online publication.] bioavailability, is cheap, and has no effect on color.
doi: 10.1111/nyas.12418
Ann. N.Y. Acad. Sci. 1324 (2014) 29–39
C 2014 New York Academy of Sciences. 29
Rice fortification in public health Steiger et al.
There is also no effect at the levels used on vitamin A creases the RBV by 60%. In absolute terms the avail-
stability. Zinc sulphate works as well, but it is more ability is only at 3%. Emulsified nanoparticles are
expensive and there might be a negative effect on expensive and the high cost from this formulated
vitamin A stability when used together.3 product might be an obstacle.6 In some countries,
Iron is considered one of the most limiting mi- such as the United States, ferric orthophosphate
cronutrients, especially in diets based mainly on is used in rice fortification, but this nearly white
polished rice. Unpolished rice contains about 2.6 powder has an even lower bioavailability than ferric
mg iron/100 grams. The native molar ratio of phy- pyrophosphate.7,8
tate to iron (>10) might inhibit absorption. In pol- Ferrous sulphate should only be used in special
ished rice the iron level can be as low as 0.4–0.6 mg/ cases due to its interaction with the rice matrix. Only
100 grams.2 Considering the already low bioavail- dried ferrous sulphate is useful and the product is
ability of iron in unpolished rice due to the amount limited to use in only a few technologies. It might
of phytate,4 the physiological effect of the reduction be used in dusting and in some coating techniques;
of intrinsic iron from milling is expected to be low. however, it can turn brown over time when convert-
Iron fortification and polishing of rice improves the ing to ferric sulphate. In addition, the water solu-
phytate:iron ratio. Food processing, food prepara- bility of ferrous sulphate is an issue. Washing and
tion, and side dishes consumed together with for- cooking rice leads to high losses of this iron form,
tified rice might influence bioavailability in posi- especially if excess water is drained after cooking.
tive and negative ways. Thus, bioavailability studies Ferrous sulphate has a metallic taste, and its taste
based on the active substance alone have to be con- and color effects depend on the quality of the fer-
sidered with care. Fortification of rice with iron is rous sulphate used, even when specifications might
only indicated if other suitable vehicles for iron for- be identical.
tification are not available in the food basket. Iron ethylenediaminetetraacetic acid sodium salt
Ferric pyrophosphate is often used in rice for- (NaFeEDTA) became an important ingredient in ce-
tification. It is nearly white or off-white, and due real fortification, mainly in wheat and maize flours.
to its low solubility at the pH of rice, interaction Due to the high iron bioavailability in the presence of
with other rice components and other nutrients absorption inhibitors, such as phytate, NaFeEDTA
is low. Thus, the effect on color during storage would be a product form of choice in rice fortifi-
of rice kernels is minimal. Also important is the cation. However, in fortification that uses nutrient-
minimal effect on the promotion of rancid fat or loaded rice (coating) or fortified extruded kernels
degradation of vitamin A. Regular ferric pyrophos- with inclusion rates of about 1:50 to 1:200, there
phate has a mean particle size of about 20 m and are still color issues to be solved because of the high
shows a relatively low interaction with the food concentration in the fortified kernels. In addition,
matrix; however, the bioavailability of this grade is the effect of NaFeEDTA on vitamin A stability has
the lowest among the ferric pyrophosphates. Milled to be considered.
ferric pyrophosphate has a mean particle size of Ferrous fumarate is widely used in cereal forti-
about 2–3 m; it has a higher bioavailability than fication; however, in rice fortification it is not rec-
regular ferric pyrophosphate, and it shows more ommended because of its effects on color and taste.
interaction with the rice matrix.3,5 Nanoparticles Elemental iron, though cheap, is also not recom-
of ferric pyrophosphate in an emulsifying matrix mended. It does not work in dusting and in ex-
(Sunactive R
) are not water soluble, but are re- truded kernels as it leads to gray discoloration and
ported to have a bioavailability comparable to fer- its bioavailability is low. Other iron forms are dis-
rous sulphate due to the very small particle size. cussed in the literature, and their suitability for rice
However, this depends heavily on the food matrix, fortification remains open.
and in rice this has proved not to be the case. It Neither unpolished nor polished rice are rich
has been shown that in hot-extruded rice the rela- sources of calcium. Calcium carbonate (CaCO3 )
tive bioavailability (RBV) of ferrous sulphate from is a suitable calcium source and has a whitening
micronized dispersible ferric pyrophosphate is only effect, which might be useful in hot extrusion if
24%. If added to rice without extrusion, the RBV more opaque kernels are needed (levels up to 30%
is only 15%. Thus, the hot-extrusion process in- CaCO3 occur in fortified kernels). Hot extrusion
at high mechanical energy input leads to glossy, As brown (unpolished) rice is an excellent source
semi-transparent kernels that resemble parboiled of thiamine and white rice is not, it was logical
kernels. Other calcium sources are calcium chlo- to consider the addition of this nutrient to white
ride or calcium lactate gluconate, but these are used rice. Thiamine mononitrate is the form most of-
for only special purposes. Calcium chloride has lim- ten used. It is less soluble and less hygroscopic than
itations due to the effect on taste. There are rice for- thiamine hydrochloride. The use of hydrochloride
tification techniques reported in the literature that makes sense only in techniques where high water
require highly soluble forms and, in these cases, cal- solubility is needed. Depending on the fortification
cium lactate gluconate is recommended. However, level, thiamine modulates taste; it is sensitive to heat
to achieve any real fortification with calcium, large above 70 °C and, accordingly, has processing losses
quantities of CaCO3 in the portion are required. and long-term storage losses of 30–40%.
Considering inclusion rates of only 0.5–1% of for- Riboflavin and riboflavin 5-phosphate are both
tified kernels (extruded or coated), the kernels will colorants and water-soluble vitamins. Fortification
hardly have sufficient carrier capacity to supply nu- with this riboflavin is possible but leads to intensely
tritional, meaningful calcium quantities. A negative colored kernels in cases where coating or extrusion
effect on iron absorption at these quantities of cal- technologies are used. Because processing losses are
cium is not likely. close to 50%, in most cases fortification with this
Other nutrients used, for example, include sele- vitamin is not done.
nium in the form of sodium selenite, which is used The following four B vitamins are highly stable
in Costa Rica.7 during processing and storage. The first is vitamin
B3, also known as vitamin PP, nicotinic acid, or
Vitamins and other nutrients niacinamide. The latter is the form of choice for
Vitamin A palmitate, stabilized with antioxidants fortification. Nicotinic acid is less suitable as it is
such as butylated hydroxytoluene (BHT) and/or a strong irritant and the handling is critical. Sec-
butylated hydroxyanisole, is the most frequently ond, vitamin B6 is a colorless, tasteless water-soluble
used form of vitamin A in grain fortification. Vi- vitamin; the suitable application form is pyridox-
tamin A acetate performs less well as the storage ine hydrochloride. Third, folic acid (vitamin B9) is
stability is not good; usually, spray-dried forms are a yellow/orange–colored vitamin, which is used in
used. In special cases, oily vitamin A forms are used, small quantities so as to minimize effect on color;
depending on the technology. Among the most fre- and there is no effect on taste. For physiological
quently used micronutrients in rice fortification, vi- reasons, it is highly recommended to apply folic
tamin A is the most sensitive. It is sensitive to light, acid in combination with the fourth vitamin B, vi-
elevated temperature, trace elements, and oxygen, tamin B12, which is a pink-colored substance that
as well as to low pH. The presence or absence of has nearly no effect on color because of the low level
iron has a large effect on stability of vitamin A. Pro- in final food products, and is neutral with respect to
cessing, washing, and cooking losses of vitamin A taste. Only spray-dried forms, such as vitamin B12
are moderate, though storage losses, especially at el- 1% or 0.1%, should be used, but not triturations,
evated temperatures, can be substantial (4–10% per which have a low content uniformity.
month at least depending on temperature, product Vitamin C, as either ascorbic acid or sodium
form, and fortification technology9 ). High-quality ascorbate, is suitable for rice fortification but re-
vitamin A has a light yellow color and has no color quires special formulation techniques. Both of the
effect on the fortified kernels. above forms may lead to a color change of the forti-
Vitamin E acetate can be used either as a dry fied kernels (to orange/light brown) but they work
preparation or a pure oily form, again depending well in combination with -carotene (provitamin
on the technology. In contrast to vitamin A, vitamin A). The combination of -carotene and vitamin C
E is very stable in its acetate form. The product is yields attractive orange kernels. The processing and
white or colorless. storage losses of vitamin C are in the range of 30–
Vitamins D and K are not currently used in rice 50%.
fortification. However, extrapolating from the other -Carotene is, at the same time, a provita-
oil-soluble vitamins, their suitability is likely. min and a colorant. It is a very stable form of a
vitamin A when protected with an antioxidant (e.g., to cook in excessive water. In developing countries
ascorbate); however, the conversion of -carotene to where intensive rice washing is practiced, dusting is
retinol depends on the vitamin A status, the amount not recommended.
of fat in the diet, and genetic disposition.
Coating
Rice is a good source of amino acids except for
lysine, another essential nutrient of interest. By sup- One of the oldest ways to prevent micronutrient
plying additional lysine with a rice-based diet, the losses through washing is to add high concentra-
biological value of rice protein can be increased sub- tions of micronutrients to a fraction of the rice and
stantially. One option is fortifying rice with lysine to subsequently coat the rice kernels with water-
hydrochloride; although highly water soluble, the resistant edible coatings, and then mix the coated
majority of coextruded lysine will survive washing kernels with normal rice in ratios ranging from 1:50
and cooking of rice.9 to 1:200. Most methods have in common the addi-
tion of a solution or suspension of micronutrients.
Technologies
Several coating layers, usually alternated with layers
Successful vitamin and mineral fortification of rice of coating material alone, are added by spraying the
continues to be a technological challenge, in con- suspension through nozzles into a rotating drum
trast to the fortification of wheat flour or maize containing the rice kernels to be fortified. The same
meal, which does not cause serious issues except drum is generally used during drying of the kernels
for the potential stability issues of low-quality vita- by means of a hot air current. Many different coat-
min A forms. The size difference between rice ker- ings have been tried, including waxes, acids, gums
nels and micronutrients is much greater than that (e.g., agar), starches, and cellulosic polymers (e.g.,
between flour and micronutrients. Simply mixing hydroxypropyl methylcellulose, ethyl cellulose, and
rice kernels with a micronutrient blend will lead methylcellulose10–12 ). Except for ethyl cellulose or
to micronutrient separation, inhomogeneity, and pectin-coated kernels, washing losses are between
losses during production, transport, and further rice 20% and 60%. When cooking with an excess of
preparation, especially rice washing. water, the majority of water-soluble nutrients will
One form of intrinsic micronutrient improve- be lost (60–90%).12 The major problems encoun-
ment in rice, rather than fortification, was the in- tered with coating technologies are related to color,
troduction of parboiling. Before removing the bran, taste, and a loss of micronutrients during washing,
rice kernels are soaked, steamed, and dried again. as well as during cooking. High variability is re-
During these steps, the content of vitamins B1, ported among technologies,7 and in many of them,
B6, and niacin in the endosperm increases three consumers are easily able to distinguish the fortified
fold due to their migration from the bran into the kernels, which will most likely be discarded during
endosperm.2 In the case of high rice consumption, rice cleaning. As opposed to extrusion technologies,
the total daily need of these vitamins might be cov- where micronutrients are dispersed throughout the
ered. However, other micronutrients, such as iron extruded kernel body, in coating the micronutrients
and zinc, are not elevated in white rice after par- are concentrated on the surface. The coating layer
boiling; this is why other means of micronutrient of the kernel makes them highly visible, particularly
fortification are advisable. if the micronutrient forms are colored. In addition,
the taste effects of the superficially present product
Dusting
will be high, and the resistance against mechani-
During dusting, micronutrients in the form of fine cal separation and removal during washing low. If
particles are blended with the bulk rice. This method the coating is not resistant to cooking, it is likely
makes use of the electrostatic forces between the rice that the micronutrient layer will come off leaving
surface and the micronutrients. Nevertheless, there the vitamins more exposed to heat and moisture.
is a segregation risk.7 In addition, washing and/or Some commercially available coated rice fortifica-
cooking in excess water that is then drained leads tion premixes claim to be stable during washing and
to significant losses. These losses are such that, in cooking. It is advisable to stress-test these materials
the United States, a warning has to be printed on before incorporation into national fortification pro-
the label not to rinse the rice before cooking or not grams. Coating technologies generally imply a lower
Figure 3. Schematic drawing of kernel microstructure of native and recomposed rice (not drawn to scale).
However, complex interrelationships between ma- lows the addition of up to 10% of recomposed rice
terial, machine, and process parameters make it dif- kernels to natural rice kernels without a perceivable
ficult to exactly predict end-product properties. This change in product properties.24 Figure 4 shows nat-
is why it is still common to apply the trial-and-error ural rice kernels compared with cold-, warm-, and
principle in extrusion experiments and why process hot-extruded recomposed rice kernels.
functionalities are often shown as a function of the
SME input only.32 Comparison of various technologies
Reconstituted rice kernels by cold extrusion ap- Process stability
pear opaque, while warm-extruded kernels pro- The first challenge for micronutrients in rice for-
duced on an enhanced pasta press appear translu- tification is the process itself to produce fortified
cent and more closely resemble natural rice kernels. The applied heat, the humidity during heat-
kernels.7,24 Wang et al.33 showed that twin screw– ing, the drying steps, and the presence or absence of
extruded products exhibited superior integrity, fla- air influence stability. In general, the process losses
vor, and texture after cooking and less change are between 0% and 20% in coating or extrusion
after overcooking compared with cold-extruded technologies, depending on process, nutrient, and
reference products prepared on a conventional matrix. In dusting, the process loss itself is con-
pasta press. Hot-extruded kernel appearance can be sidered to be the smallest of all losses, as no se-
adapted well to different types of rice by modifying rious stress is applied; however, segregation is an
the choice of raw material (amylose/amylopectin ra- issue.7
tio and granulation) and/or process parameter set-
tings (moisture content, screw configuration/SME Storage stability
input). Opaque and translucent rice with smooth Storage stability depends on many factors, of which
and rough surfaces can be obtained (Fig. 4). Cook- the most critical is vitamin A, as compared with
ing time, firmness, and water uptake ratio of both other nutrients it is sensitive to oxidation, especially
warm- and hot-extruded kernels is similar to natural in the presence of humidity and at elevated temper-
rice, while cold extrusion leads to a softer texture.7 atures. The concomitant presence of iron ions en-
Warm and hot extrusion allows mimicking of the hances storage losses, even if non-water-soluble iron
texture of natural rice kernels to an extent that al- phosphates or pyrophosphates are applied. Rice has
Figure 4. Visual appearance of natural rice, recomposed rice kernels produced with cold extrusion, warm-extruded kernels
produced on two different types of pasta extruders, and kernels produced with one type of hot extrusion but using different screw
configurations, resulting in different specific mechanical energy (SME) input.
with which dryer), as well as depreciation and to a coefficient variance of about 10% due to the few
interest costs. kernels in the sample, on the basis of the formula
Final costs are dominated by the raw material cost, CV% = √ 100
N
. Thus, in noncooked rice the whole
especially of the carrier used, the rice. If the technol- sample of 200 g has to be milled and mixed, and
ogy allows the use of cheap broken rice as starting then an aliquot can be used for analysis. In cooked
material, it is a cost advantage. This is one of the key rice, it is necessary to homogenize the cooked soft
advantages of extruded fortified kernels. Rice flour kernels, mix the paste, and then take the aliquot.
made from broken rice is the starting material. The
outcome is kernels similar to intact, nonbroken rice
kernels. If the market price difference between bro- Studies with fortified rice
ken kernels and intact kernels offsets the production Various efficacy trials have recently been conducted
cost of extruded kernels, then extrusion will be even for hot-extruded kernels in India37,38 and for cold-
cheaper than dusting. Coating technologies require extruded rice grains in Latin America39 and Asia.40
intact and thus more expensive rice kernels, if the Significant improvement could be demonstrated for
coated kernels should have the form of intact rice zinc41 and the added vitamins, for example B1,42
kernels. In some cases broken rice is coated; how- B12,38 or A.3 Most of the studies investigating the
ever, broken rice is less appealing. effect of iron fortification used high amounts of iron
A further cost driver is energy cost. During ex- (above 10 mg/100 g), but even intervention levels of
trusion, irrespective of whether it is cold, warm, or 3 mg/100 g were able to decrease the anemia fre-
hot extrusion, water and/or steam are added, part of quency, for example, in the Philippines.43 In a study
which has to be removed at the end of the process. performed in Thailand, the negative effect of vari-
The drying step is far more costly than the precon- ous rice phytate levels on iron absorption could be
ditioning step (in warm and hot extrusion) and the demonstrated, but also demonstrated was the iron
extrusion process itself. Drying is usually done ei- absorption–enhancing effect of ascorbic acid–rich
ther by using a fluid bed or pasta dryers and is energy vegetables when added to the rice meal.44 Various
intensive. Thus, the additional costs of fortification review articles and summaries give an overview of
for rice millers might vary substantially in the range published data.3,7,36
of 3–6% of the bulk rice costs.
Quality control aspects Conclusion and outlook
When analyzing fortified rice, it is helpful to know With respect to product properties, such as wash
which technology was applied in order to get reli- stability, shelf stability, cooking behavior, visual ap-
able results. Dusted rice is the easiest to analyze; the pearance, and cooked rice texture, both warm and
added nutrients are on the surface of the rice kernels hot extrusion can be recommended. Dusting is not
and easy to remove. a suitable technology where wash-stable fortified
In rice fortified with either coated or extruded rice rice is required; and coating technologies require
kernels there are additional challenges. First of all the wash-stable coatings. Hot extrusion allows a broad
micronutrients are bound on or in the carrier. This adaptation of kernel properties and most closely
is of special importance in extruded rice, especially resembles natural rice after cooking, while visual
hot-extruded rice. The partly- or fully-gelatinized appearance of warm-extruded kernels is ideal be-
starch and the denaturized protein bind effectively fore cooking.24 Both processes lead to perfectly ac-
with the micronutrients. Enzymatic degradation of ceptable product properties in a 1:200 to 1:50 di-
the fortified kernels is needed before extraction.3 In lution with natural rice. From the processing side,
addition, in already fortified rice only about 0.5–2% the decision could thus be made on the basis of the
of kernels carry the added nutrients. The sample type of other products manufactured in the same
size has to take this into account. When an inclusion factory (i.e., pasta-type equipment is favorable for
rate of 1% is used the minimum sample size that is a pasta producer and extrusion equipment for a
needed for one analysis is 200 g, which corresponds breakfast cereal or snack producer). To compare the
to about 10,000–12,000 rice kernels. But only 100– bioavailability of added nutrients in the rice ma-
120 kernels carry added micronutrients. This leads trix, an in-depth study of warm- and hot-extruded
23. Seiler, W. Verfahren zur Herstellung von Teigwaren, danach 35. Chung, H.-J. et al. 2002. Comparison in glass transition
erhältliche Teigwaren und Anlage zur Durchführung des and enthalpy relaxation between native and gelatinised rice
Verfahrens. Patent WO/2005/079597. January 9, 2005. starch. Carbohyd. Polym. 48: 287–298.
24. Mueller-Fischer, N. 2009. Structuring of starch matrices. In- 36. PATH. 2013. Ultra Rice Technology Research Summary
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25. Harper, J.M. 1981. Extrusion of Food. Boca Raton: CRC Press. files/MCHN_u_r_res_sum_tbl.pdf.
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the quality of rice pasta. J. Sci. Food Agr. 82: 203–216. cronized ground ferric pyrophosphate reduces iron de-
27. Huang, J.C. et al. 2001. Model prediction for sensory at- ficiency in Indian schoolchildren: a double-blind ran-
tributes of non-gluten pasta. J. Food Quality 24: 495–511. domized controlled trial. Am. J. Clin. Nutr. 84: 822–
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