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Plant Foods for Human Nutrition 59: 5154, 2004.C 2004 Springer Science+Business Media, Inc.

51

Sensory Properties Changes of Fortified Nixtamalized Corn Flour

With Lysine and Tryptophan During Storage

KRZYSZTOF N. WALISZEWSKI,1, YOKIUSHIRDHILGILMARA ESTRADA1 & VIOLETA PARDIO1,21 Instituto Tecnol ogico de Veracruz, Unidad de Investigacion y Desarrollo en Alimentos, A.P. 1380 Veracruz, Veracruz, 91700 Mexico; 2 Facultad de

Medicina Veterinaria y Zootecnia, Universidad Veracruzana, Veracruz, Veracruz Mexico (author for correspondence; e-mail: kw@itver.edu.mx)

Abstract. This study was conductedto determinesensorychanges of for-

tified nixtamalizedcornflour with lysineand tryptophan up to 83,100, and

150%of suggested FAO patternafter 2 months storageat roomtemperature

(30 C). Totally,16 trained panelistsparticipated in sensory study of tortilla

made of enriched and normal corn flours where six attributes and a total

of 19 descriptors were taken into consideration. A reflectance colorimeter

was also used in determination of changes in tortilla color parameters. No

significant differences were found in the analysis of 19 descriptors of tor-

tilla made of enriched and normal nixtamalized corn flour after 2 months

storage. Also, no color parameterchanges werefound between normal andenriched tortillas.

Key words: Amino acids, Enrichment, Storage, Tortilla

Introduction

The traditional method of producing masa for tortillas is to

cook corn in a water solution of calcium hydroxide, allow

it to steep to cause softening, hydration, and gelatiniza-

tion of mainly starch and proteins, and finally to wash with

water to remove residual lime, pericarp, and some solu-

ble small molecular nutrients. The masa is then drum dried

and grinded to obtain corn nixtamalized flour. In the 1990s,

Latin American countries have shown important progress in

the industrial production of nixtamalized corn flour primar-

ily used for tortillas, chips, tamales, and other typical staple

foods. More than 2.7 million tons/year of dry nixtamalized

corn flour are industrially produced in Mexico [1].

For Mexicans, and other Latin Americans the tortilla is

the most important protein source. However, due to low

protein levels and the deficiencies of lysine and tryptophan,

many studies for nixtamalized corn flour and tortilla for-

tification have been conducted. In these studies, chemical

score of tortilla protein was increased by supplementation

with plant origin proteins (mainly soybean) and also animalorigin proteins [25]. Results of these studies have been

used very little in practice due to tortilla negative change

of sensory properties like flavor, color, and texture. On the

other hand, in Mexico, results for nixtamalized corn flour

enrichment with vitamins B1, B2, B6, folic acid, and ele-

ments Fe and Zn was introduced in practice [6].

Among different studies of cereal fortification, one can

consider that direct free amino acid supplementation seems

to be the easiest way. Initial studies of Bressani group on

tortilla enrichment with lysine and tryptophan indicated that

positive nitrogen balance was achieved when children were

fed enriched tortilla of 1.5 g protein/kg/day [2, 7]. In these

studies, no results were published on the effect of amino

acid supplementation on sensory properties of enriched tor-

tilla, For the past 6 years, Fermex in Mexico (Kyowa sub-

sidiary, Kyowa, Japan) has been offering a low priced and

highly purified lysine and tryptophan for human consump-

tion. In our previous study, sensory panelists results as wellas color parameter changes of enriched tortilla, have shown

that nixtamalized corn flour would be supplied up to 83%

of lysine and tryptophan level [8]. In this study, lysine and

tryptophan were added directly to the masa in water solu-

tion used to prepare tortilla and some doubts appeared if

these free amino acids added in powder form to nixtamal-

ized corn flour could affect sensory properties of the flour

during storage and finally tortilla sensory quality.

The present study was conducted to determine sensory

changes of fortified nixtamalized corn flour with lysine and

tryptophan up to 83, 100, and 150% of the FAO recommen-

dation level after 2 months storage at room temperature

(30 C).

Materials and Methods

Nixtamalized Corn Flour

Fresh nixtamalizedcorn flour wasobtainedfrom theMaseca

company (Veracruz, Mexico). This flour was enriched with

highly powdered and human consumption grade L-lysine

and L-tryptophan supplied fromFermex, Orizaba, Veracruz,

Mexico in the following amount: treatment 1 (1.3 g kg1

and 0.1 g kg1), treatment 2 (2.1 g kg1 and 0.25 g kg1),

and treatment 3 (4.4 g kg1

and 0.68 g kg1

), respectively.These supplementations correspond to 83, 100, and 150%

of the FAO recommendation level due to lysine and trypto-

phan content. Each set of flour was initially mixed during

5 min in a proportion of 1:20 (w/w amino acids-corn flour)

and mixed in a model M-5 laboratory mixer (Littelford

Day, Florence, KY, USA). The volume was then increased

in the same proportion to finally reach 5 kg of enriched

corn flour. Normal and enriched corn flours were stored in

closed glass jars in controlled temperature incubator (Cole

Parmer, Vernon Hills, IL, USA) at constant temperature

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30 C during 2 months of storage. National producers rec-

ommend storage time of nixtamalized corn flour in tropical

climate for up to 2 months due to possible rancid oxidation

process. Tortillas were prepared by mixing 1000 g of nix-

tamalized enriched corn flour with 1400 ml of tap water to

obtain the masa (dough). Portions of 28 g of masa were me-

chanically pressed with a lab-scale special tortilla press to

form 15-cm diameter raw tortillas and were baked on a steel

plate in a gas-fired oven for 6070 sec. Tortillas were kept

in thermoisolated plastic containers. Within 5 min of prepa-

ration, warm tortillas (5055 C) were offered to panelists

in individual booths, under sensory controlled laboratory

conditions.

Sensory Analysis

Thirty-seven candidates for panelists were selected from

students of the Instituto Tecnologico de Veracruz, Veracruz,Mexico who enjoyed eating tortillas. This study used se-

quential analysis with normal tortilla and tortilla supplied

with 0.1 g kg1 of salt. Each day, candidates participated

in 30-min training sessions, receiving a separate set of

samples within each sensory attribute: aroma, flavor, af-

ter taste appearance, manual and oral texture. For aroma

analysis, tortillas were placed in plastic containers packed

with perforated aluminum foil and were smelled twice. For

flavor analysis, tortillas cut in triangles were offered on

plastic plates. Samples were not swallowed and purified

water was offered for oral rinsing and a cuspidor for ex-

pectoration. Samples of tortilla were consumed for after-

taste analysis and the result was recorded after 2 min of

consumption. All judgments were conducted in individual,

divided booths maintained at 21 C, under low, red illumi-

nation. The tortillas appearance was judged under 200-W

incandescent white bulbs in each booth. At the same time

each day three sensory sessions were conducted. Candi-

dates were carefully screened for their taste acuity, ability

to recognize and describe common flavors and textures, and

their ability to evaluate the intensity of their perceptions us-

ing a rating scale. Candidates were subjected to sequential

testing during 3 months of training on randomly selected

days.

During sessions, candidates described a list of attributesmentioned in Table 1. Analysis of the data delineated or

irrelevant descriptors allowed for the selection offinal pan-

elists. For this evaluation the parameters of statistical se-

quential analysis were po = 0.45 and p1 = 0.85 with and

of 0.05 and permitted the selection of only 16 final pan-

elists [9]. For sensory analysis, samples of three treatments

and control were compared in terms of degree of deviation

from the control using a nonnumerical 8-cm graphic scale

where 0 = less than control, 4 = same as control, and 8 =

more than control.

Table1. A listof references generatedby descriptors

of the panel

Attribute Descriptor

Aroma Corny

Flavor Corny

CornyRancid

Bitter

Burnt lime

Aftertaste Dry

Sticky

Bitter

Rancid

Appearance Yellowness

Uniformity of cooking

Manual texture Softness

Rollability

Fragility

Dryness

Graininess

Oral texture DrynessSoftness

Doughness

Color Measurements

Enriched tortillas were subjected to surface color analy-

sis by five measurements in duplicate with the Minolta re-

flectance colorimeter Chroma Meter Cr-200 (Minolta Corp.

Ramsey, NJ, USA). The result of each measurement was a

mean of three instrument repetitions. During measurement

the instrument was moved on the surface of each tortilla ona straight line from side to side. The instrument was cali-

bratedagainst a standard yellowreferenceplate(L = 84.46,

a = 4.86,and b = 58.23).The L , a,and b color space was

selected based on its documented adequacy for theoretically

quantifying color parameter changes. In terms of its three

coordinates L, a, and b, these data were converted to differ-

ent functions of color as hue value, chroma, and total color

difference. Three derived functions were computed from

the L, a, and b readings as follows

Hue angle tan1(b/a)

Chroma (a2

+ b2

)1/2

Total color difference (DE) = [(L Lo)2

+ (a ao)2 + (b bo)

2]1/2

Statistical Analysis

All sensory analysis data were evaluated by analysis of vari-

ance with Tukeys paired comparison test ( = 0.05) using

the Minitab 13 (Minitab Inc., College Park, PA, USA) sta-

tistical package.

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Table 2. Means and standard deviations for sensory attributes of corn tortillas enriched with lysine and tryptophan

at different levels and stored during 2 months

Attribute Descriptor Control Treatment 1 Treatment 2 Treatment 3

Aroma Corny 4.00 0.58 4.08 0.50 4.16 0.36 4.08 0.54

Flavor Corny 3.95 0.40 3.90 0.30 4.15 0.385 4.10 0.59

Rancid 3.97 0.14 4.07 0.21 4.02 0.28 4.09 0.47Bitter 4.00 0.07 4.05 0.18 3.99 0.26 4.03 0.31

Burnt lime 4.01 0.13 4.06 0.28 4.01 0.39 4.04 0.38

After taste Dry 3.98 0.29 3.84 0.45 4.02 0.42 4.07 0.45

Sticky 4.03 0.11 3.98 0.25 3.94 0.31 4.06 0.23

Bitter 3.99 0.17 4.02 0.14 4.01 0.23 4.07 0.15

Rancid 3.99 0.10 4.05 0.25 4.01 0.17 4.04 0.28

Appearance Yellowness 4.02 0.13 4.10 0.29 4.07 0.27 4.04 0.33

Uniformity of cooking 4.00 0.22 4.01 0.45 4.01 0.41 4.02 0.52

Manual texture Softness 4.06 0.25 4.18 0.25 4.02 0.46 4.13 0.50

Rollability 3.93 0.30 4.18 0.24 4.12 0.40 4.04 0.50

Dryness 4.01 0.19 3.88 0.34 4.00 0.33 3.92 0.55

Fragility 4.01 0.32 3.89 0.34 4.00 0.39 4.15 0.34

Oral texture Grainess 4.03 0.33 4.08 0.48 3.95 0.63 3.98 0.52

Dryness 4.05 0.32 3.98 0.38 4.04 0.44 4.04 0.31

Softness 3.99 0.37 3.98 0.38 4.03 0.54 4.04 0.41Doughyness 4.17 0.26 4.19 0.27 4.04 0.32 4.08 0.42

Results and Discussion

Study carried out about 20 years ago by Paredes-Lopez and

Mora-Escobedo [10] showed that nixtamalized corn flour

stored under conditions of high temperature and for rel-

ative high humidity developed negative changes in some

sensory attributes observed by a higher fat acidity. Also in-

soluble protein increased and available lysine and protein

digestibility decreased. In Mexico, during last 10 years sen-

sory quality of nixtamalized corn flour has improved. Over

98% of excellent quality flour is commercialized in sealed

paper bag of 20-kg each destined to small baking units for

tortilla production, and due to high daily tortilla production,

fresh flour is supplied every week. Less than 2% is com-

mercialized in 1-kg well-packed but not sealed paper bag

and recommended storage time is maximum 2 months. In

our study normal and enriched corn flours ofaw below 0.4

were stored in closed glass jars in controlled temperature of

30 C during 2 months. Also nixtamalized flour was stored

in sealed jars which permitted us to avoid flour humidifi-

cation and possible formation of nonenzymatic browning

products and rancid reaction as occurred in the mentionedbefore study [10].

In our previous study of enrichment of fresh nixtamal-

ized corn flour with lysine and tryptophan at three forti-

fication levels the following attributes: aroma (descriptor

corny), flavor (descriptors: corny, rancid, bitter, and burnt

lime), aftertaste (descriptors: dry, sticky, bitter, and rancid)

and appearance (descriptors: yellowness and uniformity of

cooking), manual texture attribute: including softness, dry-

ness, and fragility have shown no statistical difference be-

tween treatments and control [8]. But in the case of analy-

sis of manual texture attributes (rollability) and oral texture

attributes (graininess and softness), statistical differences

were found between control and treatment 1 compared to

treatments 2 and 3. Even though statistically different in

three attributes, tortillas of treatment 2 and 3 were still of

high acceptability for human consumption.

In this study, as shown in Table 2, no difference wasfound

between all 19 descriptors when control treatment wascom-

pared to results of three levels of enrichment of tortilla. It

is surprising that no difference was found but it may be that

during 2 months storage of nixtamalized corn flour some

sensory attributes changes masked three texture attributes

changes as rollability, graininess, and softness which were

found in our previous study for treatment 2 and 3. The pro-

cess of washing of nixtamalized corn to remove mainly

calcium hydroxide helps to remove many small molecu-

lar weight nutrients like saccharides, amino acids, and free

fatty acids which could be produced off flavors directly

or indirectly by reactions with lysine and tryptophan. Low

humidity and water activity helped to control possible re-

action of added amino acids with other compounds mainly

residues of sugars. In our recently published study, cornflour enriched with lysine and tryptophan did not lose im-

portant amounts of these amino acids after storage for up to

2 months at 30 C [11].

Results of the effect of lysine and tryptophan enrich-

ment on color parameter changes (L, hue, and chroma) in

tortilla are shown in Table 3. Statistical analysis of mean

results by Dunnett (p 0.05) did not show any difference

between control and treatments. It means that nonenzymatic

browning products have not occurred during 2 months

storage.

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Table3. Results of L,hue, andchromaof enriched nixtamalizedcorn flour

after 2 months storage

Color parameters

L Chroma Hue

Control 78.230

1.641 58.056

0.622 90.347

0.489Treatment 1 78.465 1.114 57.882 0.751 90.572 0.651

Treatment 2 79.177 1.542 57.672 0.568 90.326 0.583

Treatment 3 78.885 1.092 57.928 0.739 90.793 0.720

These results have shown that direct enrichment of nix-

tamalized corn flour does not change any of 19 attributes

of corn tortilla, but for practice, we recommend fortifica-

tion of lysine and tryptophan up to only 83% of amino acid

composition of FAO ideal protein [12]. The reason is that

threonine is the third limiting amino acid of the protein of

nixtamalizedcorn flour at 83% of FAO protein composition.

In 1999 in Mexico, Maseca company introduced into

practice a fortified nixtamalized corn flour with 0.5% pre-

mix supplied with vitamins B1, B2, B6, folic acid, and ele-

ments Fe and Zn. This flour is mainly targeted to marginal

and low economic groups by some state governments to de-

crease malnutrition and we hopethat enrichment with lysine

and tryptophan will be introduced soon. It is recommended

that the government agencies of the countries where tortilla

is the basic staple food and principal protein source will

take this into consideration and establish the level of en-

richment to correct protein deficiency. To ensure that lysine

and tryptophan will be incorporated in an adequate way in

the whole of tortilla, we recommend that tortilla produc-

ers should add these amino acids into water before masapreparation. Amino acids could be supplied separately in

the amount which corresponds with enrichment of a 20-

kg bag of nixtamalized corn flour. If for some reason it is

impossible, enriched corn flour with lysine and tryptophan

could be produced and stored up to 2 months at room tem-

perature without any undesirable sensory changes.

References

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