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735
Nixtamalization, a Mesoamerican technology to process
maize at small-scale with great potential for improving
the nutritional quality of maize based foods
Wacher Carmen
Departamento de Alimentos y Biotecnología, Facultad de Química, UNAM, 04510 México, D. F. México.
Corresponding author: wacher@servidor.unam.mx
- Abstract -
“Nixtamalization” is the process of cooking maize grains in a lime solution, soaking
and washing them, to obtain “nixtamal”. Then it is stone-ground to obtain nixtamal
dough or masa. A variety of products are obtained from it and tortilla (flat pancakes
cooked in a griddle) is the most popular one. Although maize became a staple crop in
numerous African countries, this process has not been commonly adopted in Africa.
This paper reviews the technology of nixtamalization and highlights its benefits for
possible adoption in African countries.
This technology improves the quality of maize in different ways. From the
technological point of view, lime-cooking improves the rheological properties of the
dough (elasticity, resistance to tearing and cracking), conferring desired organoleptic
characteristics. It significantly increases its calcium content, releases bound niacin and
makes it available. Insoluble dietary fibre decreases from raw to nixtamalized maize;
however the relatively high levels that remain in the dough are of nutritional
significance. Total fat content decreases, but the lime cooking process does not cause
changes in fatty acid distributions. Protein quality, as shown by higher protein
efficiency ratios (PER) of nixtamal, compared to maize increases. In addition to these
nutritional benefits, lime-cooking has also been found to reduce significantly the
amount of mycotoxins that are present in maize. Fermentation of nixtamal further
enhances its nutritional properties. Being simple and inexpensive, conditions to
transfer this ancient technology to Africa could be assessed to contribute to improve
the nutritional quality of maize based foods.
Key words: Maize – Nixtamal.
_________________________
2ème Atelier international / 2nd International Workshop
Voies alimentaires d’amélioration des situations nutritionnelles
Food-based approaches for a healthy nutrition
Ouagadougou, 23-28 / 11 / 2003
Small scale industrial food production and fortification
736
- Résumé -
La nixtamalisation: un procédé mésoaméricain de
transformation du maïs à petite échelle présentant un
grand potentiel pour l’amélioration de la qualité
nutritionnelle d’aliments à base de maïs
La Méso-Amérique est fort probablement le berceau du maïs où il fut domestiqué et
devint un aliment de base. Au Mexique, le maïs représente la moitié des aliments
consommés et contribue à environ 50% des ingérés énergétiques, cette proportion
étant supérieure pour les populations à bas revenus.
La nixtamalisation est le procédé qui consiste à cuire les grains de maïs dans une
solution de chaux, à les tremper et à les laver pour obtenir le «nixtamal». Il est ensuite
broyé pour obtenir une pâte de «nixtamal» ou masa. De nombreux produits peuvent
en être dérivés dont la tortilla (fine galette cuite sur une plaque chauffée) qui est le
plus populaire. Bien que le maïs soit aussi devenu un aliment de base dans de
nombreux pays africains, ce procédé n’a pas été communément adopté en Afrique.
Cette technologie améliore la qualité du maïs de différentes façons. D’un point de vue
technologique, la cuisson à la chaux facilite l’élimination du péricarpe et l’hydrolyse
alcaline libère des gommes du péricarpe et saponifie les lipides du germe, ce qui
améliore les propriétés rhéologiques de la pâte (élasticité, résistance au déchirement
et au craquelage). La cuisson altère la structure cristalline de l’amidon, et la
réassociation des molécules constitutives de l’amidon durant le trempage est
importante pour développer les propriétés rhéologiques de la pâte de nixtamal.
L’intensité de la couleur, l’odeur et la flaveur sont affectées par la chaux, conférant
ainsi des propriétés organoleptiques désirées. La teneur en calcium est
significativement augmentée, ce qui est important car les apports de calcium par les
produits laitiers sont limités dans les pays en développement en raison de leurs coûts
et des problèmes liés à l’intolérance au lactose. Le traitement alcalin libère la niacine
et la rend disponible, c’est la raison pour laquelle les civilisations pré-colombiennes ne
souffraient pas de pellagre. La teneur en fibres insolubles diminue du maïs brut au
maïs nixtamalisé; toutefois les niveaux relativement élevés encore présents dans la
pâte sont encore d’intérêt nutritionnel. La teneur totale en lipides diminue, mais la
cuisson alcaline n’altère pas la distribution en acides gras. Les protéines du maïs sont
de mauvaise qualité à cause de leur concentration limitée en lysine et tryptophane. La
nixtamalisation améliore la qualité des protéines, comme l’indique la valeur plus
élevée du coefficient d’efficacité protéique (CEP) dans le nixtamal que dans le maïs.
Outre ces bénéfices nutritionnels, il a été aussi montré que la cuisson à la chaux
réduit significativement la quantité de mycotoxines présentes dans le maïs.
La fermentation du nixtamal améliore ses propriétés nutritionnelles. La fermentation
naturelle d’une pâte de nixtamal pour obtenir du pozol (une boisson préparée par
suspension de la pâte fermentée dans de l’eau) entraîne une amélioration de la
qualité des protéines. Dans la mesure où elle est simple et peu coûteuse, il semble
intéressant d’étudier les conditions du transfert de cette ancienne technologie en vue
d’améliorer la qualité nutritionnelle des aliments à base de maïs.
Mots-clés: Maïs – Nixtamal.
_________________________
Production et fortification dans les petites industries agroalimentaires
737
INTRODUCTION
Mesoamerica (a region from Northern Mexico to Honduras and Nicaragua) is very
likely the origin of maize1. It was cultivated throughout the American continent, but it
was only consumed as the main food by the Mesoamerican cultures and at the
Southeast of the United States2. Maize is capable of adapting to the most diverse
ecological conditions, but is not capable of self-reproduction, so it depends on man to
perpetuate. It is Mesoamerica where it was domesticated and consumed as a staple
food1. Maize was also consumed in South America; however its role was never as
important as in Mesoamerica2. In Mexico, half of the total volume of food that is
consumed is maize, which provides approximately 50 percent of the energy intake and
this proportion is even greater for lower income groups. A great culinary tradition
includes about 605 different foods made with maize3.
Maize has several nutritional limitations, especially the quantity and quality of its
essential amino acids and niacin4. It is thought2 that unless it is prepared by specific
techniques, its nutritional value is marginal and any human population that depends
on it as a major staple would suffer some degree of malnutrition. Alkali cooking was
the main technique used to improve its nutritional value.
Presently, alkaline cooking or “nixtamalization” is widely used in Mexico and Central
America to process maize. The traditional process, which is still widely used, consists
of cooking maize grains in a lime solution, soaking for 8 to 16 hours and washing them
by hand to remove the pericarp. This nixtamal is then stone-ground to obtain nixtamal
dough or masa. A variety of products (tortilla chips, tamales, tostadas, tacos,
enchiladas, panuchos, sopes, atoles, etc.) are obtained from it and tortilla (flat
pancakes cooked in a griddle) is the most popular one (figure 1). According to
Paredes-López and Saharópulos5, in rural areas tortillas provide 50% of the proteins
and 70% of de calories consumed daily.
Figure 1: Tortilla baking at San Cristóbal de las Casas, Chiapas, Mexico.
Small scale industrial food production and fortification
738
In the American continent, the societies that cultivate and consume large amounts of
maize, use the alkali treatment as a way of softening the outer kernel2. The alkali used
for cooking can include lime (Ca(OH)2), wood ashes (KOH) and lye (NaOH). Lime use
is restricted to Mesoamerica; North American producers use wood ashes and it is not
used in South America, except for one community in Venezuela2. Although maize
became a staple crop in numerous African countries, this process has not been
commonly adopted in Africa.
Nixtamalization improves the quality of maize in different ways:
CHANGES IN THE MICROSTRUCTURE OF MAIZE DURING NIXTAMALIZATION
From the technological point of view, lime-cooking alters the microstructure of the
outermost layers of maize pericarp, which shows a corrugated-like structure5. Surface
materials dissolve partially and this facilitates pericarp removal during washing. The
aleurone layer remains attached to the endosperm; it behaves as a semi-permeable
envelope and might contribute to reduce protein losses. Most of the germ is retained
during nixtamal and tortilla making process and contributes to the overall nutritional
properties of the product. Boiling in lime causes removal of starch granules, so that
the soft (inner) endosperm is greatly altered: starch arrangement becomes irregular
and some fibrils connect the dispersed starch granules5. Important structural
alterations, caused by heat denaturation of proteins, cross-linkages produced by
unusual aminoacids and disruption of the tertiary structure of proteins occur. The
endosperm proteins remain attached to the starch granules; lime cooking changes the
physical appearance of protein bodies6. Improved digestibility of nixtamal proteins may
be due to a better accessibility to them caused by starch gelatinization and changes in
the protein matrix5.
LIME COOKING ALTERATIONS THAT RESULT IN TECHNOLOGICAL IMPROVE-
MENTS
Alkaline cooking and the steeping step cause water and calcium to be taken up by
the grain7. The role of lime is important, as it allows faster water absorption and
distribution throughout the grain components and it modifies the outer layers, so that
the pericarp fraction becomes gummy and sticky7. The alkaline treatment degrades
and solubilizes cell wall components and this facilitates pericarp removal. Alkaline
hydrolysis releases gums from the pericarp and saponified lipids from the germ that
improve the rheological properties of the dough (elasticity, resistance to tearing and
cracking). Alkali-soluble non-cellulosic wall polysaccharides (mainly arabinoxylan)
show interesting functional properties as adhesives, thickeners, stabilizers, emulsifiers
and film formers7. According to these authors, the presence of germ, which is not lost
during nixtamalization, gives more machinability to the masa, with a higher tolerance
to mixing and less susceptibility to breakdown. So, the traditional process results in
masa with desirable properties of cohesiveness and adhesiveness. This is attributed
to swelling of starch granules, to the presence of fibre gums from the nixtamalized
pericarp and of saponified lipids from the germ.
During steeping, the grains absorb water and are softened due to the distribution of
water7. Cooking alters starch crystallinity and reassociation of starch molecules during
steeping is important to develop the rheological properties of nixtamal dough.
Grinding disrupts the grain structure, dispersing cellular components and starch
polymers. Masa can be considered to be a network of solubilized starch polymers with
dispersed, uncooked and swollen starch granules, cell fragments and lipids8.
Production et fortification dans les petites industries agroalimentaires
739
According to Gómez et al.9, swollen and partially gelatinized starch granules in a
network of dispersed starch polymers, allows tortilla shaping during kneading and gas
retention (puffing) during baking. Protein bodies swell, lose their shape and in some
cases are physically destroyed during baking or drying6. After baking, starch granules
and endosperm pieces are glued together by amylose, protein, lipids and cell wall
components. During the 45-60 sec of baking time, water evaporates from the tortilla
surface. Granules on the surface are partially gelatinized and more dehydrated; those
in the middle are more gelatinized9. This results in stretchable and elastic tortillas that
are resistant to tearing and cracking.
Organoleptic changes brought about by nixtamalization are probably the most
important for consumers. Colour intensity, smell and flavour are affected by lime,
conferring desired organoleptic characteristics. Lime affects tortilla colour and its
intensity is related to carotenoid pigments, flavonoids and pH. The development of
colour during nixtamalization is more complex, as calcium hydroxide reacts with
different pigments10. Tortilla flavour is enhanced by Maillard browning reactions
occurring between reducing sugars and peptides and unsaturated fatty acids.
LIME-COOKING ALTERATIONS THAT RESULT IN NUTRITIONAL IMPROVEMENTS
Dry matter losses occur during lime cooking and steeping and this is a drawback of
nixtamalization. Total dry matter losses in commercially processed corn have been
reported to be 2.8 to 10.7% between cooking and steeping and 1.6-2.0% during
washing. The average composition of the suspended solids in “nejayote” (the cooking,
steeping and washing water, which is discarded) was: 64% non-starch
polysaccharides (mainly pericarp fiber), 20% starch and 1.4% solids washing11.
However, the alkaline process induces some significant favourable compositional
changes in maize:
Changes in protein content and quality
According to Bressani et al.12, the protein content of raw maize varies from 9.4 to
10.2%, of cooked maize from 10.0 to 10.6% and of tortillas from 9.5 to 11.0%.
Regarding lysine and tryptophan, which are the two most limiting aminoacids in maize,
the same authors reported that lysine content does not change significantly due to
processing (158-166 mg/g N in raw maize to 152-165 mg/g N in cooked maize, to 145-
175 mg/ g N in tortilla), but lime cooking and tortilla baking decrease tryptophan
content in maize from an average value of 38 mg/g of nitrogen in raw maize to 26
mg/g of N in tortillas. Another report2, indicates that there are considerable losses of
total nitrogen during the cooking process, but the relative amount of lysine in nixtamal
is increased 2.8 times, tryptophan is increased slightly and the isoleucine/leucine ratio
increases 1.8 times.
Regarding protein quality, Bressani et al.12 showed that rats fed a casein diet showed
weight gain, food intake and protein efficiency ratio (PER) significantly greater than
those for rats fed diets on raw and processed maize, confirming other reports on the
low quality of maize protein. However, the beneficial effect of lime cooking was
demonstrated, as animals consuming diets made from maize dough and tortillas
showed a weight gain and PER significantly (p < 0.01) greater than animals fed raw
maize diets.
Nixtamalization alters the solubility patterns of maize proteins. Lime cooking and
tortilla baking decrease the solubility of albumins and globulins (salt-water-soluble)
and prolamins (alcohol-soluble). This alters the molecular weight distribution of the
different protein fractions13. Bressani and Scrimshaw14 showed that cooking with lime
Small scale industrial food production and fortification
740
selectively enhances the nutritional quality of corn and that this probably results from a
relative decrease in the solubility of the zein portion (deficient in lysine and tryptophan)
of the corn proteins. This procedure selectively enhances the quality of the corn
protein that is available for enzymatic digestion.
Minerals
One of the most important contributions of nixtamalization is the increase in the
calcium content of tortillas. Serna-Saldívar et al.13 reported it increases 750%, which is
over 85% available15. This is relevant, as calcium intake from dairy products in
developing countries is limited by their high cost and problems associated with lactose
intolerance. Low calcium intake also causes osteoporosis, which affects mainly post-
and premenopausic women and elderly men. Nixtamalization also improves the
calcium/phosphorous ratio16. Martínez-Flores et al.17 studied the effect of calcium
absorption on physical properties and composition of rat femurs, comparing rats fed
with raw whole corn (RC), tortillas made from extruded masa with 0.25% lime content
(TEWL) and without lime (TE), and nixtamal tortillas (NT). The femurs of rats fed with
TEWL and NT were heavier, thicker, and longer, showed greater crystallinity and were
more resistant to fracture than the femurs of rats fed with RC and TE.
Phytic acid (myo-inositol hexaphospohoric acid), which reduces the bioavailability of
minerals, is found in relatively high concentrations in the germ (which is not eliminated
during nixtamalization). This is reduced from 8% (when low calcium concentration,
0.4%, is used to nixtamalize maize) to 30-45% (when high, 1.2% calcium
concentration is used). This reduction can be attributed to its lability to heat16. The
same authors reported that the amount of calcium in nixtamal is considerably greater
than the amount of phytic acid in the grain, so that this could be easily saturated by
calcium. This would prevent iron from binding to it and be available for absorption.
They showed that higher calcium concentrations used for nixtamalization led to higher
increments in ionizable iron. Soaking time did not affect these parameters.
Bressani et al.18 evaluated the composition of tortillas made by 5 different families and
the maize used to prepare them. Besides the increase in calcium content (from 48.3 ±
12.3 in maize to 216.6 ± 41.5 in tortilla), Ca:P balance improved and Fe (4.8 ± 1.9 in
maize to 7.0 ± 4.8 in tortilla), Cu (1.3 ± 0.2 in maize to 2.0 ± 0.5 in tortilla) and
Zn (4.6 ± 1.2 in maize to 5.4 ± 0.4 in tortilla) concentrations increased. They proposed
these minerals come from the lime or from the containers used to nixtamalize maize.
Vitamins
Maize is deficient in niacin, so a population whose diet consists mainly on maize
would be likely to develop pellagra if other dietary constituents were not present2. The
alkaline treatment releases bound niacin and makes it available19; this is the reason
why pre-Columbian civilizations did not suffer pellagra. On the other hand, Cravioto et
al.20 reported small losses of thiamin, riboflavin and niacin and a 40% loss in yellow
corn tortillas carotene during nixtamalization.
Dietary fiber and fat
The nixtamalization process helps to eliminate the pericarp, so insoluble dietary fiber
decreases from raw to nixtamalized maize; however the relatively high levels that
remain in the dough are of nutritional significance. According to Bressani et al.12, who
studied chemical changes during rural tortilla production in Guatemala, dietary fiber of
nixtamal dough (9.3 - 9.6%) is lower than that of raw maize (12.2 - 12.8%); however
total dietary fiber content of tortillas is higher (10.3 - 11.7%), possibly due to the
development of insoluble compounds when the maize dough is placed in the hot plate
Production et fortification dans les petites industries agroalimentaires
741
to bake tortilla. The same authors reported that total fat content decreases from 4.7%
(w/w) in raw maize to 2.8 (w/w) in tortillas, but the lime cooking process does not
cause changes in fatty acid distributions.
Mycotoxins
The maize grain is frequently invaded by moulds of the genera Aspergillus, Fusarium
and Penicillium. In addition to the nutritional benefits mentioned earlier, lime-cooking
has also been found to reduce significantly the amount of mycotoxins that are present
in maize21,22. Fusarium verticillioides and Fusarium proliferatum are capable of
producing fumonisins and frequently found in corn. Apart from causing animal
diseases, human esophageal squamous cell carcinoma has been linked with
consumption of fumonisin-contaminated corn. Dombrink-Kurtzman et al.21 reported
that tortillas made with naturally contaminated maize contained 18.5% of the initial
concentration.
The traditional nixtamalization process has been reported to reduce levels of aflatoxin
B1 by 94% and aflatoxin M1 by 90%22.
INDUSTRIALIZATION OF TORTILLAS
Tortilla elaboration has gone beyond the home-made procedure to become an
artisanal process, with small "nixtamal mills" and "tortillerías". About 100,000
establishments are dedicated to tortilla elaboration1. These are small family-type
shops, where most of the population goes everyday to get fresh tortillas. These places
are very important, because of the high preference for ready-made tortillas. Important
agroindustries have also developed to obtain dry nixtamal flour. In 1996, Torres
Salcido23 reported about 34% of tortillas was made in Mexico from nixtamal flour.
Although the use of maize in Mexican cooking has received international recognition,
its daily consumption for an important part of the population is a monotonous diet of
tortillas and beans, which does not provide enough nutrients for a good physical and
mental development. Fortification of foods that are generally consumed, as tortillas,
can benefit most of the undernourished population. In 1997 Mexico established the
addition of 7 micronutrients in nixtamal flour: vitamins A and C, riboflavin, niacin, folic
acid, iron and zinc, to counteract deficiencies in the diet of the rural population
especially. For this reason, fortified nixtamal flour is distributed by the government at
subsidized prices24.
NIXTAMAL FERMENTATION
Fermentation of nixtamal further enhances its nutritional properties. According to
Cravioto et al.25, after natural fermentation of nixtamal dough to obtain pozol (a
beverage prepared by suspending in water this acidified dough), riboflavin, niacin and
protein concentrations increase. Tryptophan and lysine concentrations increased from
0.46 g/100 g protein in maize to 0.71 g/100g in pozol and 3.05 g/100 g in maize to
3.96 g/100 g in pozol, respectively. The calculated biological value of pozol proteins
was 66.75%, compared to that of maize (55.60). In accordance with this, protein
efficiency ratio values for pozol and maize were 1.52 and 1.05 weight increase of
rats/g consumed protein, respectively.
Small scale industrial food production and fortification
742
CONCLUSION
The quality of maize is greatly improved by the ancient technology of nixtamalization.
It induces favourable modifications in its organoleptic attributes, rheological properties
and nutritional value. Being simple and inexpensive, conditions to promote the use of
this ancient technology to Africa could be assessed to contribute to improve the
nutritional quality of maize based foods. Furthermore, it would be interesting to
investigate if such a technology could apply for some other cereals (e.g. sorghum)
widely consumed in Africa.
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