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Journal of the Science of Food and Agriculture
J Sci Food Agric 80:657±664 (2000)
Physicochemical and rheological
characteristics of commercial nixtamalised
Mexican maize flours for tortillas
Rivelino Flores-Farı́as,1 Fernando Martı́nez-Bustos,1* Yolanda Salinas-Moreno,2
Yoon Kil Chang,3 Jésus González Hernández1 and Elvira Rı́os4
1
Laboratorio de Investigación en Materiales, Centro de Investigación y de Estudios Avanzados del IPN, Universidad Autónoma de
Querétaro, Facultad de Quı́mica, Centro Universitario, Cerro de las Campanas, CP 76010, Querétaro, Qro, Mexico
2
Laboratorio Nacional de Maı´z, INIFAP, Apto Postal 10, Chapingo, Edo de México, C P 56230, Mexico
3
Faculdade de Engenharı́a de Alimentos, Departamento de Tecnologı́a de Alimentos, Universidade Estadual de Campinas, CP 612113083 Campinas Sp, Brazil
4
Departamento de Biotecnologı´a y Bioingenierı´a CINVESTAV del IPN, Colonia San Pedro Zacatenco No 2508, México, DF, Mexico
Abstract: Three commercial nixtamalised Mexican maize ¯ours (CNMFs) designated HI-A, HI-B and
HI-C were evaluated in this work. For each brand, four samples corresponding to four consecutive
months of production were evaluated. Tortillas prepared by the traditional process of nixtamalisation
were used as the control. The maize ¯ours and their respective tortillas showed variations between
samples in their physical, chemical and rheological parameters. The three commercial maize ¯ours
incorporated additives and preservatives. The moisture content, colour, pH, subjective water
absorption capacity, water solubility index, water absorption index and swelling capacity of ¯ours
showed strong differences between the three CNMFs with respect to the chemical analysis. Important
differences in the protein, calcium and amylose contents were observed. Tortillas from CNMFs had a
blander maize ¯avour, less desirable texture and staled more rapidly than traditional tortillas. Some
modi®cations are required in the current Of®cial Mexican Quality Standard, principally in the
appropriate selection of additives and levels used in the preparation of CNMFs.
# 2000 Society of Chemical Industry
Keywords: maize; ¯ours; rheological characteristics; tortillas
INTRODUCTION
Since the invention of the nixtamalisation process until
the present day, the greatest achievement in the tortilla
industry has been the development of nixtamalised
¯ours (nixtamalisation process on a large scale). The
principal modi®cations made to the traditional process
include reductions in the times of alkaline cooking and
of steeping of the cooked grain. Also, in order to
improve the colour of tortillas, the cooked grain is
thoroughly washed, then hammer-milled, dehydrated,
fractionated and reformulated for speci®c applications. These modi®cations to the traditional process
affect the overall quality of tortillas. In order to
moderately compensate these adverse effects on the
quality of tortillas, some manufacturers use additives
and preservatives.
Nixtamalised ¯ours originated in 1949 and currently supply about 34% of the Mexican tortilla
market. The tortilla industry represents one-®fth of
the global food market in Mexico, with annual
production estimated at 11 million tons and sales of
4 billion dollars.1 Approximately 51 000 traditional
nixtamal mills and small tortilla factories (48% mills,
28% mills/tortilla factories and 24% tortilla factories)
exist in Mexico.2
In Mexico the daily per capita consumption of
tortillas is approximately 325 g. Tortillas also supply
70% of the calories and 50% of the protein consumed
daily. Maize tortillas supply 37% of the calcium
requirement for adults. In the traditional process of
nixtamalisation for preparing tortillas, the maize kernel
is cooked with water and alkali, steeped, usually overnight, and ground into masa. The masa can be pressed
into tortillas and baked, or the fresh masa can be
dehydrated, ground, sieved and blended to yield a
nixtamalised maize ¯our.
The increased demand for Mexican foods in many
countries has encouraged signi®cant expansion in
nixtamalised maize ¯our production during the last
10 years. Commercial nixtamalised maize ¯ours
* Correspondence to: Fernando Martı́nez-Bustos, Laboratorio de Investigación en Materiales, Centro de Investigación y de Estudios
Avanzados del IPN, Universidad Autónoma de Querétaro, Facultad de Quı́mica, Centro Universitario, Cerro de las Campanas, CP 76010,
Querétaro, Qro, Mexico
E-mail: [email protected]
(Received 11 June 1999; revised version received 24 October 1999; accepted 19 November 1999)
# 2000 Society of Chemical Industry. J Sci Food Agric 0022±5142/2000/$17.50
657
R Flores-FarõÂas et al
(CNMFs) are produced with different characteristics
designed to yield a variety of products. The use of
CNMFs eliminates management techniques required
for securing, handling and properly processing maize
into tortillas. Moreover, CNMFs have consistent,
uniform properties and can be properly blended with
¯avours and other additives. CNMFs have a shelf-life
of several months or more when properly packaged,
whereas fresh masa spoils readily. Lack of ¯avour,
poor texture and increased costs of production are the
major disadvantages of products prepared from
CNMFs.
This study reports the results of physical, chemical
and rheological analyses of CNMFs and their tortillas.
The main objective of the ¯our characterisation was to
obtain a database which could be used to suggest some
modi®cations to the current Of®cial Mexican Quality
Standard.
EXPERIMENTAL
Raw materials
Three commercial nixtamalised maize ¯ours from
manufacturers in Mexico (1996) were collected for
testing. For each brand, four samples corresponding to
four consecutive months of production were evaluated. The four samples of each CNMF were blended
together in a domestic mixer (Kitchen Aid, K5SS) and
2.5 kg of each ¯our was stored at 4 °C in polyethylene
bags for further analysis.
Analytical methods
Moisture content, total protein (N 6.25), ash content and pH were determined using AACC methods
44-15A, 46-12, 08-03 and 02-52 respectively.3 Fibre
(method 7.054) and ether extracts (method 7.044)
were determined by AOAC procedures.4 Amylose
content was determined according to the method of
Juliano.5 Total starch was determined using the
enzymatic method (glucoamylase Diazyme L-200,
Miles Lab, Inc) and analysis of glucose (from the
hydrolysis of starch) with an automated colorimetric
procedure.6 Calcium, arsenic and phosphorus contents were determined using plasma emission spectroscopy (Analytical Instruments, model Spectro Flame
No 1665/88). The colour of samples was measured
with an Agtron Colorimeter. Particle size distributions
of ¯ours were determined by sifting 100 g samples with
a 75, 8XX, 10XX, 11XX and pan (200, 194, 148 and
126 mm respectively) mesh sieve, set for 20 min in a
Rotap testing sieve shaker (The WS Tyler Co, Cleveland, OH).
Analysis of additives and preservatives
Separation and analysis of the commercial gums were
carried out according to AOAC methods4 with some
modi®cations. Tri¯uoracetic acid (0.1 M) was used in
the hydrolysis of gums, and amberlite/ether was used
to extract sugars. Sugars were analysed by highperformance liquid chromatography (HPLC) using a
658
UV detector with diodes at 90 nm and a Hypersil 5
APS-2 column. The mobile phase was acetonitrile/
water (80:20 v/v). Analyses were carried out at a ¯ow
rate of 0.3 ml minÿ1 at 70 °C. All sugar standards were
from Sigma Co. Organic acids were identi®ed by
HPLC using a UV detector with diodes at 210 nm and
a Rezex organic acids column (250 mm 4.6 nm). The
mobile phase was sulphuric acid (0.005 M). Analyses
were performed at a ¯ow rate of 0.5 ml minÿ1. The
fatty acids composition was determined according to
AOAC method 28.060.4 A ¯ame ionisation detector
was used with an FFAP column (1.80 mm 22.4 nm).
The mobile phase was nitrogen gas. Analyses were
performed at a ¯ow rate of 28 ml minÿ1.
Relative viscosity
A Rapid Visco Analyser (RVA-3D, Newport Scienti®c
Pty, Australia) was used to measure the apparent
viscosity of samples. Samples of 4 g of CNMF and 3 g
of dehydrated tortilla were adjusted to 14 g kgÿ1
moisture. Distilled water was then added to keep the
total weight of water and sample constant at 28 g. The
rotating paddles were held at 50 °C for 2 min to
stabilise the temperature and ensure uniform dispersion, then heated to 92 °C at 5.6 °C minÿ1 and held
constant at that temperature for 5 min. The samples
were ®nally cooled to 50 °C at 5.6 °C minÿ1.
Water absorption index, swelling capacity and water
solubility index
The water absorption index (WAI) and water solubility index (WSI) were determined following the
methods of Anderson et al. 7 The methods measure the
quantity of water incorporated in the ¯our and also the
soluble solids dissolved in water at 30 °C. The swelling
capacity (SC) was determined following the method of
Leach et al. 8 Samples were weighed (2.5 g) into 50 ml
plastic tubes, mixed with water (40 ml) at 60, 70 and
80 °C respectively for each experiment, then incubated
horizontally on a reciprocating shaker for 30 min and
held at constant temperature in a bath. Slurries were
centrifuged for 30 min at 3000 g and the supernatant
was decanted into previously weighed aluminium tins.
Tins were dried for 24 h at 105 °C and weighed. The
gel left inside the tubes after decanting the supernatant
was weighed. The ratio between gel-forming solids
and soluble solids was measured as grams of water per
gram of ¯our. The method measures the capacity of
the CNMF to absorb water at different temperatures.
X-ray diffraction analysis
X-ray powder diffraction was performed on dried
samples according to the method described by
RodrõÂguez et al. 9 The samples were ground to a ®ne
powder to pass through a screen with a mesh of
150 mm. The powder samples were densely packed in
an aluminium frame. X-ray diffraction patterns of the
samples were recorded on a Siemens D500 diffractometer operating at 35 kV, 15 mA and with Cu Ka
Ê . Data were collected
radiation of wavelength 1.5406 A
J Sci Food Agric 80:657±664 (2000)
Characteristics of commercial nixtamalised Mexican maize ¯ours
from 4 to 30 ° on a 2y scale with a step size of 0.05 °.
Data were reported as interplanar d-spacing values
Ê . The crystallinity (%) was calculated
expressed in A
by normalising the integrated diffracted intensity over
the measured 2y range to the integrated non-coherent
intensity. The non-coherent intensity was obtained by
subtracting the sharp diffraction peaks from the total
diffraction pattern using Siemens Socabim V3.2 software
Preparation of tortillas by traditional nixtamalisation
process
Five kilograms of commercial white maize (ToluquenÄo, grown at Edo de MeÂxico, 1996) hard endosperm
(normal) was cooked with water (15 l) and lime
(2 g kgÿ1 w/w) at a temperature of 85 °C for 55 min.
The cooked kernels (nixtamal) were steeped for 12 h in
the cooking liquor (nejayote). The cooked grain was
then washed and milled on a stone mill to obtain the
fresh masa. The consistency was deemed to be suitable
when the masa pressed between two metallic plates
covered with plastic ®lm did not stick to them. The
consistency of the masa varies according to the
quantity of water added. Excessive water results in a
soft and sticky masa, while too little water results in a
hard masa with inferior handling properties. The masa
was rounded and shaped in the form of ¯at discs using
a manual form (Casa GonzaÂlez, MeÂxico, DF). The
masa discs were baked on a hot griddle at 290 10 °C
for 27 s on one side, followed by 30 s on the opposite
side, and were then turned onto the ®rst baked side
until puf®ng during the ®nal time on the griddle. The
tortilla dimensions were 1.19 0.1 mm thickness,
12.8 0.2 cm diameter and 18.25 0.5 g weight.
Tortillas from each treatment (n = 20) were evaluated
after cooling for 30 min at room temperature (25 °C).
Also, tortillas from each treatment were stored in
polyethylene bags at 4 °C for 24 or 48 h and reheated
(3 min) in a cloth napkin using a microwave oven.
Tortillas from each treatment were dehydrated at
room temperature, milled and stored at 4 °C in
polyethylene bags for further analysis.
Preparation of maize tortillas from CNMFs
Tortillas were prepared by mixing 5 kg of each instant
¯our in a domestic mixer (Kitchen Aid, K5SS) with
suf®cient water until an adequate consistency of the
masa for the elaboration of tortillas was achieved, then
following the same method as described for the
traditional process.
Texture of masa and tortillas
The texture of the masa (®rmness and adhesiveness)
and tortillas (tensile strength and cutting force) was
determined using a TA.XT2 Texture Analyser
(Texture Technologies Corp, Fairview Road, Scarsdale, NY, USA and Stable Micro System, Godalming,
Surrey, UK). Firmness and adhesiveness of the masa
(50 g sample in the form of a disc of 5.4 0.1 cm
diameter and 1.3 0.1 thickness) were determined by
J Sci Food Agric 80:657±664 (2000)
penetrating a TA-18 Stainless steel probe of 1.27 cm
diameter at a speed of 2 mm sÿ1 to a depth of 4 mm,
and the results were recorded in kgf. The tensile
strength of the tortillas was determined using a sample
of tortilla 4 cm wide placed in TA-96 retention pincers.
The test was carried out at 2 mm sÿ1 and the pincers
were moved apart until the tortilla sample was broken.
Tortillas from each treatment (n = 20) were evaluated
after cooling for 30 min at room temperature (25 °C).
Also, tortillas from each treatment were stored in
polyethylene bags at 4 °C for 24 or 48 h and reheated
(3 min) in a cloth napkin using a microwave oven. The
pieces of tortilla that were not used for tensile strength
tests were used to determine the cutting force using the
TA-90 attachment. The texturometer head moved the
probe downwards at a rate of 2 mm sÿ1 to a penetration
depth of 15 mm until the tortilla was cut. The tensile
strength and cutting force were expressed as the peak
force (kgf) required to break and cut the tortilla strip.
Rollability and puffing of tortillas
Tortilla rollability was determined according to the
method described by Bedolla.10 Tortillas from each
treatment (n = 20) were evaluated after cooling for
30 min at room temperature (25 °C). The tortillas were
rolled around a glass rod of 4 cm diameter and the
degree of breakage was determined using a subjective
scale from 1 to 5, where 1, 2, 3, 4 and 5 corresponded
to 0, 25, 50, 75 and 100% degree of breakage of the
tortilla length respectively. The tortilla puf®ng was
estimated subjectively during the ®nal time on the
griddle, by observing the percentage of the total
surface of tortilla that puffed, on a scale from 1 to 3,
where 1 corresponded to complete puf®ng (70±
100%), 2 to medium puf®ng (30±70%) and 3 to no
puf®ng (0±30%).
Statistical analysis
The data were analysed using the Statistical Analysis
System.11 Tukey analysis (p < 0.05) was applied for
means with signi®cant differences.
RESULTS AND DISCUSSION
Chemical and physical characteristics
The samples differed signi®cantly in moisture content
(10.0±10.8 g kgÿ1) and pH (6.2±6.9). Their densities
varied from 0.40 to 0.44 g cmÿ3. Also, some signi®cant
differences were observed in amylose, ash, calcium
and protein contents (Table 1). Similar contents of
starch, amylose, ash, calcium, ®bre and protein in
CNMFs for various uses from the USA have been
previously reported.12±14 Various differences in chemical composition of the maize and conditions of
processing used during CNMF production may be
responsible for the differences in chemical composition.
The phosphorus content was highest in HI-C
(12.02 mg kgÿ1), followed by HI-B (11.78 mg kgÿ1)
and ®nally HI-A (10.03 mg kgÿ1). Arsenic was not
659
R Flores-FarõÂas et al
Component (g kgÿ1)
CNMF
Table 1. Chemical properties of commercial
nixtamalised maize flours (n = 3)
HI-A
HI-B
HI-C
Starch
Amylose
Ash
Calcium
Fibre
Protein (N 6.25)
68.020a
66.770a
67.820a
30.550a
29.840b
29.630b
1.380a
1.280b
1.440a
0.117b
0.123b
0.182a
1.510a
1.450a
1.440a
9.690b
10.270a
9.200c
Means with the same letter in the same column are not signi®cantly different for Duncan (a = 0.05).
found in the CNMFs. The intensity of re¯ectance
varied signi®cantly among ¯ours, HI-A showing the
highest value (73.5%), followed by HI-B (69.5%) and
®nally HI-C (59.0%). Various factors are likely to
affect the colour of CNMFs: (1) composition of the
maize (pigments and/or phenolic compounds); and (2)
differences in processing conditions used among
manufacturers (concentration of lime, extent of washing of nixtamal, degree of starch gelatinisation, etc).
Analysis of additives and preservatives
Water-soluble gums are added to improve the waterbinding capacity, which helps the retention of
¯exibility of tortillas during storage. The highest
concentration of guar gum was determined in ¯our
HI-A (0.38 g kgÿ1), followed by HI-B (0.32 g kgÿ1)
and ®nally HI-C (0.20 g kgÿ1). Also, xanthan gum was
present in HI-C (0.18 g kgÿ1). When industrial producers introduced modi®cations to the traditional
process of tortilla production, the masa and ®nal
product had lower quality attributes. For this reason,
some industrial producers of CNMFs use gums and/or
emulsi®ers to improve and maintain the functional
properties of tortillas, helping to counteract the effects
of natural variations due to the lack of nixtamalised
pericarp and germ fractions released during alkaline
cooking and removed by thorough washing of the
cooked grain during production of CNMFs.15 Probably these modi®cations made to the traditional
process and the addition of additives and preservatives
result in a faster staling of tortillas prepared with
CNMFs. Mould inhibitors such as potassium sorbate
were determined in HI-A (0.40 g kgÿ1). The ef®ciency
of preservatives is optimised by addition of acidifying
agents to reduce the pH; however, the high pH
achieved by increasing the lime concentration can also
be used for preservation purposes without additional
preservatives. The CNMFs included propionic acid,
0.17 g kgÿ1 in HI-A, 0.20 g kgÿ1 in HI-B and
0.35 g kgÿ1 in HI-C. Some emulsi®ers such as soya
oil were detected in HI-C (10 g kgÿ1), the monoglyceride amidan in HI-B (7.3 g kgÿ1) and stearoyl
lactylate in HI-A (0.53 g kgÿ1).
The removal of most nixtamalised germ, generally
carried out by thorough washing of the grain during
production of CNMFs, adversely affects the functional and nutritional characteristics of masa and
tortillas. Various authors have reported that the
addition of monoglycerides to ¯our or starch slurries
increases peak viscosity16±18 and improves masa
660
machinability. Whistler19 reported that 6 g kgÿ1 of
maize oil in water is well stabilised by maize ®bre gum,
showing it has good qualities as an adhesive.
Particle size distribution
Signi®cant differences in particle size distribution
among CNMFs were found (Fig 1). Flours are
fractionated and reformulated for speci®c applications.14 The ®rst and second largest amounts of
particles from CNMFs were retained over pan and
sieve number 75 (200 mm) respectively.
Gomez et al 12 reported that nixtamalised maize
¯ours for table tortillas exhibited a more homogeneous
distribution of particle sizes than did those for fried
products. The ®ne fractions are responsible for most of
the water uptake and viscosity development during
mixing. Tortillas required ®ne particles to develop
cohesiveness in the masa for acceptable rollability in
the ®nished product.20 Coarse particles reduced
puf®ng during frying.12
WAI and SC at 60, 70 and 80 °C and WSI at 30, 60, 70
and 80°C
High water absorption capacity is required for
production of tortillas with acceptable ¯exibility and
reheating ability and for development of steam inside
the tortilla during baking.14 Signi®cant differences
were found in WAI and SC at 60, 70 and 80 °C and
WSI at 30, 60, 70 and 80 °C among CNMFs (Figs
2±4).
The WAI showed signi®cant differences (p < 0.05)
among the three samples evaluated (Fig 2). Sample
HI-B showed the maximum value and sample HI-C
the minimum value.
Figure 1. Particle size distribution of commercial nixtamalised maize
flours.
J Sci Food Agric 80:657±664 (2000)
Characteristics of commercial nixtamalised Mexican maize ¯ours
Figure 2. Water absorption index of commercial nixtamalised maize flours.
Figure 4. Water solubility index at 30, 60, 70 and 80°C of commercial
nixtamalised maize flours.
The SC at 60, 70 and 80 °C (Fig 3) increased with
increasing temperature owing to the disruption of the
crystalline structure of starch and also to the higher
water absorption capacity of gums. At 60 °C the three
samples showed the same behaviour as observed for
the WAI. At 70 °C the highest values of SC were for
HI-A and HI-B, while HI-A and HI-C showed the
highest values at 80 °C. Water absorption is important
economically to commercial masa producers and
functionally to CNMFs. This property is related to
particle size, extent of starch gelatinisation, starch
damage percentage and the presence of natural gums
from hydrolysis of the pericarp or additives.1 The WSI
increased as the WAI decreased. HI-A showed the
highest values of WSI at 30, 60, 70 and 80 °C (Fig 4).
The lowest values at 30 and 70 °C were for HI-B, while
the WSI of HI-C at 80 °C did not show any signi®cant
difference from that of HI-A. The WSI is a property
that re¯ects the quantity of soluble solids in water,
indicating the degree of cooking that presents the
¯our. Bedolla and Rooney13 and Almeida-Dominguez
et al 14 reported similar values of WAI and WSI for
CNMFs from the USA.
HI-A (7.1%), while ¯our HI-B (5.6%) was most
affected with respect to its crystalline structure.
Probably the addition of gums to the CNMFs affected
the crystallinity of starch. HI-C and HI-A were the
¯ours that showed the highest contents of gums. For
native starch, strong peaks were observed at 2y values
of 15.1, 16.4, 17.5 and 22.6 °, corresponding to dÊ respectively.
spacings of 5.95, 5.39, 5.2, 4.7 and 3.9 A
This pattern closely matches reported values for Atype cereal starches.21,22 The modi®cation of the
physical structure of starch granules observed by
X-ray diffraction showed that the CNMF process
reduced starch crystallinity. Gomez et al 20 reported
that the crystallinity of maize starch decreased during
tortilla processing and determined the formation of a
peak characteristic of the V-type amylose±lipid complex pattern during the production of fried tortilla
chips. MartõÂnez-Bustos et al 1 suggested that the
combined action of calcium hydroxide and extrusion
conditions completely modi®ed the organised structure of starch to form a starch±calcium complex
(crystalline region).
Pasting properties
X-ray diffraction
Fig 5 illustrates the diffractograms of the analysed
samples. The crystallinity of raw maize was lower
(9.11) than that of ¯our HI-C (9.38%). The latter
showed the highest values for crystallinity, followed by
Figure 3. Water absorption capacity at 60, 70 and 80°C of commercial
nixtamalised maize flours.
J Sci Food Agric 80:657±664 (2000)
Signi®cant differences in Rapid Visco Analyser pasting
properties between CNMF and nixtamal samples were
found. Flour HI-C developed a high peak viscosity
Figure 5. X-ray diffraction pattern of commercial nixtamalised maize flours
and nixtamal.
661
R Flores-FarõÂas et al
Table 2. Characteristics of texture of fresha masas prepared
with commercial nixtamalised maize flours (n = 3)
CNMF
Cohesiveness (kg) Adhesiveness (kg)
HI-A
HI-B
HI-C
Nixtamal
0.254b
0.286a
0.209c
0.308a
0.033a
0.036a
0.030b
0.036a
a
After cooling for 30 min at room temperature.
Means with the same letter in the same column are not
signi®cantly different for Duncan (a = 0.05).
viscosity of ¯ours, such as alkaline cooking, drying step
and concentration of lime.
Figure 6. RVA pasting characteristics of commercial nixtamalised maize
flours.
Texture of masa
similar to that of nixtamal (control), followed by HI-A
and ®nally HI-B (Fig 6). However, the minimum
viscosity during the cycle at 92 °C was lower for
nixtamal than for CNMFs. The addition of gums,
emulsi®ers, additives and preservatives affects the
pasting properties of CNMFs.15 These differences in
viscosity characteristics are attributed to the presence
of gums released during traditional alkaline cooking
and saponi®ed germ that remains after traditional
washing of nixtamal, improving its viscosity characteristics as compared to CNMFs where the cooked
grain was thoroughly washed to substantially remove
pericarp and germ fractions in order to improve the
colour of the ¯our. The results on viscosity characteristics are lower than those reported for CNMFs for
various uses from the USA.14 These differences can be
attributed to the diversity of processing conditions.
The behaviour of the viscosity developed during the
cooking cycle (from 50 to 92 °C) re¯ects the capacity
of particles to absorb water and the capacity of starch
and gums to swell as the slurry is heated. During the
cycle of constant temperature (92 °C) the viscosity
developed results from the resistance to mixing of the
particles. The ®nal cycle of cooling (from 92 to 50 °C)
shows the setback of the starch granules; the viscosity
is increased owing to the alignment of the chains of
amylose. The presence of additives (gums) and/or
natural gums affects to a great extent the viscosity
behaviour.15 Also, other factors affect the pasting
Masas prepared with HI-B had the highest cohesiveness (equal to control), followed by HI-A and ®nally
HI-C (Table 2). The adhesiveness of HI-A and HI-B
did not show signi®cant differences from those values
determined for masa from nixtamal (control). Similar
results for adhesiveness and cohesiveness of masas
prepared by the traditional process were reported by
MartõÂnez-Flores et al. 23 The viscosity and consistency
of masa can be affected by additives such as gums and
emulsi®ers.12 Higher values of adhesivity are associated with sticky masas and poor machinability
characteristics. The desirable properties of cohesiveness and adhesiveness of masa prepared by the
traditional process can be attributed to appropriate
swelling of the starch granules, hydrolysis of the
pericarp to release gums from the nixtamalised
pericarp (hemicelluloses), and the presence of saponi®ed lipids from the germ.15
Analysis of tortillas
Fresh tortillas prepared from CNMFs showed good
puf®ng and rollability when they were made and after
1 or 2 days of storage. The rollability of tortillas from
CNMFs decreased after 2 days of storage. However,
they did not show signi®cant differences from the
control (Table 3). The tortillas prepared by the
conventional process (nixtamalisation) showed excellent sensory characteristics (¯avour) and maintained
their rheological properties during 2 days of storage.
Table 3. Puffing and rollability of tortillas prepared with commercial nixtamalised maize flours (n = 3)
Characteristic
CNMF
HI-A
HI-B
HI-C
Nixtamal
Tortilla puf®ng
1.25a
1.50a
1.50a
1.00a
a
b
Rollability of fresh tortilla
Rollability after 1 day of storage c
Rollability after 2 days of storage c
1.00a
1.00a
1.00a
1.00a
1.00a
1.00a
1.12a
1.00a
1.75a
2.12a
1.75a
1.50a
a
Estimated subjectively during the ®nal time on the griddle, by observing the percentage of the total surface of tortilla that puffed, on a scale from 1 to 3, where 1
corresponded to complete puf®ng (70±100%), 2 to medium puf®ng (30±70%) and 3 to no puf®ng (0±30%).
b
After cooling for 30 min at room temperature.
c
Stored at room temperature (25 °C), then reheated (3 min) in a microwave oven.
Means with the same letter in the same column are not signi®cantly different for Duncan (a = 0.05).
662
J Sci Food Agric 80:657±664 (2000)
Characteristics of commercial nixtamalised Mexican maize ¯ours
Characteristic (kg)
CNMF
HI-A
HI-B
HI-C
Nixtamal
FTTS a
TTSA1DS b
TTSA2DS c
FTCF d
TCFA1DS e
TCFA2DS f
0.248ab
0.199b
0.243a
0.278a
0.414a
0.440a
0.433a
0.477a
0.561b
0.560b
0.579b
0.730a
2.190a
1.930a
2.140a
2.220a
3.520a
3.090a
4.000a
3.550a
5.360a
4.570a
5.190a
5.910a
a
Fresh tortilla tensile strength, measured after cooling for 30 min at room temperature.
Tortilla tensile strength after 1 day of storage at room temperature.
c
Tortilla tensile strength after 2 days of storage at room temperature.
d
Fresh tortilla cutting force, measured after cooling for 30 min at room temperature.
e
Tortilla cutting force after 1 day of storage at room temperature.
f
Tortilla cutting force after 2 days of storage at room temperature.
Means with the same letter in the same column are not signi®cantly different for Duncan (a = 0.05).
b
Table 4. Quality of tortillas prepared with
commercial nixtamalised maize flours (n = 3)
Traditionally prepared tortillas were more stretchable,
elastic and resistant to tearing and cracking. Also, the
work required to produce deformation in the test strips
was much greater for traditional tortillas than for
CNMFs tortillas. This fact is very important in the
®nal tortilla quality attributed to the components
released, such as gums from the pericarp and the
presence of saponi®ed lipids of the germ, affecting the
appropriate rheological characteristics of masa and
tortillas.15 Fresh tortillas prepared from CNMFs HI-A
and HI-B showed good characteristics of tensile
strength when they were made and after 1 day of
storage. However, after 2 days of storage the tensile
strength decreased. The cutting force of tortillas from
CNMFs did not show signi®cant differences from the
control when they were made and after 1 and 2 days of
storage (Table 4). The increased costs, lack of ¯avour,
poor texture and staling in products prepared from dry
masa ¯our are the major disadvantages of CNMFs.12
Probably the adverse factors of the texture of masas
from CNMFs and the faster staling of their tortillas are
associated with the lack of natural gums present in the
nixtamalised pericarp and saponi®ed fatty acids of the
germ.15
Correlation coefficients between characteristics of
CNMFs and quality of tortillas
WAI was correlated with pH (r = ÿ0.884), protein
content (r = 0.831, p < 0.05), calcium content (r =
ÿ0.709, p < 0.05), SC at 60 °C (r = 0.935, p < 0.05),
particle size pan (r = ÿ0.788, p < 0.05), ¯our colour
(r = 0.722, p < 0.05), maximum viscosity in ¯our
(r = 0.895, p < 0.05), maximum viscosity in tortilla
(r = ÿ0.854, p < 0.05) and ®nal viscosity in tortilla
(r = ÿ0.857, p < 0.05). Also, ¯our colour was correlated with calcium content (r = ÿ0.827, p < 0.05);
SWAC with protein content (r = 0.832, p < 0.05) and
maximum viscosity in ¯our (r = ÿ0.841, p < 0.05); and
pH with WAI (r = ÿ0.884, p < 0.05), SC at 60 °C
(r = ÿ0.802, p < 0.05) and maximum viscosity in ¯our
(r = 0.868, p < 0.05).
According to the results, the factors that best predict
masa and tortilla quality are WAI and SC at 60 °C and
viscosity characteristics of ¯ours and tortillas. Bedolla
J Sci Food Agric 80:657±664 (2000)
and Rooney13 concluded that the objective tests which
best predict the tortilla-making quality of dry masa
¯ours are particle size distribution, water uptake, pH,
colour and amylograph peak viscosity.
CONCLUSIONS
The protein, ash and calcium contents showed
variations between samples. The particle size distribution, SWAC, WAI, SC at 60 °C and WSI were
different in the three samples analysed. Guar and
xanthan gums in different concentrations were found
in CNMFs. Mould inhibitors such as potassium
sorbate and propionic acid were determined in
CNMFs. Also, the samples contained some emulsi®ers such as soya oil, amidan and stearoyl lactylate.
The crystallinity of CNMFs was reduced with respect
to raw maize. The behaviour of CNMFs during
viscosity analysis was similar to that of nixtamal. The
tortillas prepared by the conventional process (nixtamalisation) showed excellent characteristics of ¯avour,
maintaining their rheological properties during 24 h of
storage. Undoubtedly, the addition of additives and
preservatives helps to improve some properties of masa
and tortillas. However, the nature of these additives
and preservatives differs from that of the natural
components of nixtamalised maize, resulting in
modi®cations of ¯avour and staling of tortillas. Some
modi®cations are required in the current Of®cial
Mexican Quality Standard, principally in speci®cations referring to type of grain or grains used (cereals or
others); grain with genetic manipulation (higher
content of protein, amino acids, ®bre or other
components); colour, particle size, pH, shelf-life and
appropriate selection and levels of additives and
preservatives; forti®cation (vitamins, proteins,
minerals, ®bre and amino acids) and levels used in
the preparation of CNMFs; and yield of masa and
tortillas.
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J Sci Food Agric 80:657±664 (2000)
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