Effect of packaging materials on the quality of iron-fortified wholemeal flour during storage

Abstract

The effect of packaging materials on the physicochemical and rheological characteristics of iron-fortified wholemeal flour (WMF) during storage was determined. WMF was fortified with three fortificants, namely ferrous sulfate (30 ppm), ferrous sulfate + ethylenediamine tetraacetic acid (EDTA) (20 + 20 ppm) and elemental iron (60 ppm). Each flour was also fortified with 1.5 ppm folic acid. Moisture, flour acidity and peroxide value increased during storage, while protein and fat contents decreased. Highest conversion of Fe2+ into Fe(3+)was observed in flour fortified with ferrous sulfate (2.72%), followed by that fortified with ferrous sulfate + EDTA (1.49%) and elemental iron (1.06%). Water absorption and dough viscosity of iron-fortified flours increased during storage. The flour containing ferrous sulfate was most acceptable regarding sensory characteristics, followed by samples containing ferrous sulfate + EDTA. Fortified flours were more stable during storage than unfortified. Addition of EDTA increased the stability of flours and fortificants. The fortified flours stored in polypropylene bags proved more stable than those stored in the tin boxes.

Full text

EFFECT OF PACKAGING MATERIALS ON THE QUALITY OF
IRON-FORTIFIED WHOLEMEAL FLOUR DURING STORAGE
N. HUMA, S.U. REHMAN1, J.A. AWAN, M.A. MURTAZA and M.U. ARSHAD
Institute of Food Science and Technology
University of Agriculture
Faisalabad-38040, Pakistan
Accepted for Publication May 10, 2007
ABSTRACT
The effect of packaging materials on the physicochemical and rheologi-
cal characteristics of iron-fortified wholemeal flour (WMF) during storage
was determined. WMF was fortified with three fortificants, namely ferrous
sulfate (30 ppm), ferrous sulfate +ethylenediamine tetraacetic acid (EDTA)
(20 +20 ppm) and elemental iron (60 ppm). Each flour was also fortified with
1.5 ppm folic acid. Moisture, flour acidity and peroxide value increased during
storage, while protein and fat contents decreased. Highest conversion of Fe2+
into Fe3+was observed in flour fortified with ferrous sulfate (2.72%), followed
by that fortified with ferrous sulfate +EDTA (1.49%) and elemental iron
(1.06%). Water absorption and dough viscosity of iron-fortified flours
increased during storage. The flour containing ferrous sulfate was most
acceptable regarding sensory characteristics, followed by samples containing
ferrous sulfate +EDTA. Fortified flours were more stable during storage than
unfortified. Addition of EDTA increased the stability of flours and fortificants.
The fortified flours stored in polypropylene bags proved more stable than those
stored in the tin boxes.
PRACTICAL APPLICATIONS
The main role of packaging is to protect the product during handling,
distribution and storage against environmental and mechanical hazards. The
success of a fortification program depends on the stability of micronutrients
and food to which these are added. Chemical changes during storage badly
affect chapatti making and sensory properties. Exposure of the fortificant to
any factor including heat, moisture, air or light, and acid or alkaline environ-
1Corresponding author. TEL: +9241921105; FAX: +9241921105; EMAIL: drsalim_rehman@
yahoo.com
Journal of Food Processing and Preservation 31 (2007) 659–670. All Rights Reserved.
© 2007, The Author(s)
Journal compilation © 2007, Blackwell Publishing
659

ments during processing, packaging, distribution, or storage affects its stabil-
ity. Flour containing elemental iron and ferrous sulfate with EDTA remained
stable up to 42 days. The unfortified flour and flour containing ferrous sulfate
remained stable for 21 days in tin boxes and 28 days in the polypropylene
bags. Wheat flour milling industry would be benefited from this research if
government is keen to launch iron fortification program in the country to curb
iron deficiency anemia among population.
INTRODUCTION
The success of a fortification program depends on the stability of micro-
nutrients and food to which these are added. Exposure of the fortificant to any
of the physical and chemical factors including heat, moisture, air or light, and
acid or alkaline environments during processing, packaging, distribution or
storage affects its stability (Lotfi et al. 1996). Mineral elements are more stable
during the manufacturing processes than vitamins. Mineral elements such as
copper, iron and zinc are adversely affected by moisture, and may react with
food components such as proteins and carbohydrates (SUSTAIN 2000).
Chemical changes during storage of flour badly affect its chapatti-making
properties (Sur et al. 1993). Changes in physicochemical and baking proper-
ties of stored flours are observed in tropical countries. Stored flours either
release or absorb moisture until atmospheric equilibrium is reached (FAO
1965). Protein, crude fat, free amino acids, proteolytic activity, diastatic activ-
ity and damaged starch decrease with an increase in the length of storage (Sur
et al. 1993). Lipid rancidity of stored flour depends on type of flour, level of
iron, temperature, fat content and its moisture level (Lotfi et al. 1996). Fat
acidity is an indicator of low baking quality of flour and decrease in crude fat
content. This phenomenon is common in samples having high moisture
content that relates to activity of lipases and lipoxidases (Leelavathi et al.
1984; Matz 1996; Rehman et al. 2006). Lipid hydrolysis affects the sensory
characteristics decreasing product acceptance. Moreover, catalytic effect of
iron on fat oxidation during storage is another major problem when cereal
foods are used as vehicle for iron fortification (Hurrell 1997).
The major hazards of stored flour are molds, bacterial attack and insect
infestation (Jay 1990; Kent and Evers 1994). Moisture, storage time and
temperature control the rate of fungal growth that occurs in stored flour at
about 14% or slightly higher moisture content (Matz 1996). As the microor-
ganisms grow, they produce both moisture and heat, as a result of their
metabolism, which then leads to damage to the stored flour. Insects consume
flour, increase fat acidity and also contaminate the product causing a major
sanitation problem (Pedersen 1992). Various packaging materials are applied
660 N. HUMA ET AL.

to protect the wheat flour from such deteriorating agents during storage at
commercial scale, but information regarding storage stability of iron-fortified
flour at household-simulating conditions is scanty. The objective of this study
was to determine the effect of packaging materials on the physicochemical and
rheological characteristics of iron-fortified wholemeal flour (WMF) during
storage.
MATERIALS AND METHODS
Wheat Flour and Fortificants
WMF was produced on a China chakki (grinder) equipped with 1-mm
mesh size sieve from commercial wheat variety, Inqlab 91. Three iron
fortificant premixes, namely FeSO4+folic acid (FS) (30 +1.5 ppm),
FeSO4+ethylenediamine tetraacetic acid (EDTA) +folic acid (FSE)
(20 +20 +1.5 ppm) and elemental iron +folic acid (EI) (60 +1.5 ppm) sup-
plied by Micronutrient Initiative (MI), Canada were used for fortification of
flour.
Fortification and Packaging
A locally designed automatic microfeeder was installed on the China
chakki for mixing fortificants. Polypropylene bags (30 SWG) and tin boxes
(22 gauge) of 20 kg capacity were used for packing of flour. Bags and boxes
containing different fortified flours were stored on a laboratory shelf at
ambient temperature (30–35C) and relative humidity (45–80%) for 42 days.
Stability Studies
Proximate Composition. Flour samples were analyzed after 14 days of
storage interval for moisture (AACC 44-31), crude protein (AACC 46-11A),
crude fat (AACC 30-25), crude fiber (AACC 32-10) and ash (AACC 08-16).
Nitrogen-free extract (NFE) was determined by difference (AACC 2000).
Iron Content. Total iron in flour samples was determined after 14 days
of storage interval by dry ash method using a spectrophotometer (model Cecil
CE 7200, Aquarius, England) at 510 nm according to method no. 40–41A
(AACC 2000).
Phytic Acid. Phytates were determined following the procedure of Haug
and Lantzsch (1983).
661EFFECT OF PACKAGING MATERIALS ON QUALITY OF WMF

Conversion of Ferrous into Ferric State
Conversion of Fe2+into Fe3+in fortified flours was determined by using
method no. 36 (AOAC 1990) with some modifications. For the determination
of ferrous, a 10-g sample was diluted to 100 mL with deionized water. After
shaking well for 15 min, the contents were filtered. To 10 mL of the filtrate,
1-mL hydroxylamine HCl was added and allowed to stand for 5 min. Then,
5-mL acetate buffer (pH 4.6) and 1-mL orthophenanthroline were added.
Absorbance of solution was determined at 523 nm with a UV-visible recording
spectrophotometer (model Cecil CE 7200, Aquarius) after 30 min. Standard
curve was prepared by dissolving 0.07 g standard Fe(NH4)2SO4·6H
2Oin
100-mL distilled water (stock solution). Standards of ferrous iron 1–8 ppm
were prepared by taking 1–8 mL of stock solution in a 100-mL volumetric
flask and by making volume to the mark with distilled water. The ferrous
contents were calculated by using the following formula:
YX=0 074.
XY=0 074.
Ferrous iron ppm
()
=×X100 10
where Y=absorbance and X=concentration of Fe2+(ppm).
Ferric iron (ppm) total iron ferrous iron=−
Peroxide Value (POV) and Total Acidity
POV was measured using the method described by Krik and Sawyer
(1991), and total acidity by titrating flour solution against NaOH (method no.
02-31, AACC 2000) after 14 days of storage interval.
Mold Count
The viable mold count was determined by counting mold colonies in flour
every 14 days during storage period with a pour-plate method on Sabouraud
agar medium (Beneke 1962).
Rheological Characteristics
Measurement of water absorption (WA), dough stability (DS), dough
development time (DDT), tolerance index (TI) and softening of dough (SD)
662 N. HUMA ET AL.

was carried out with a Brabender Farinograph (model 380, Duisburg,
Germany). Measurement of amylase activity was carried out with a Brabender
Amylograph (model-3126, VS 6-5). These characteristics of dough of iron-
fortified wheat flours were determined at 0, 21 and 42 days of storage interval
(AACC 2000).
Statistical Analysis
Data were statistically analyzed by applying analysis of variance and
t-test to determine the effect of fortificants, packaging materials and storage
periods on stability of flours. Duncan’s multiple range test was applied to
determine the level of significance (Steel et al. 1997). Statistical significance
was set at Pⱕ0.05 probability level. The experiment was repeated thrice.
RESULTS AND DISCUSSION
Proximate Composition
The proximate compositions of iron-fortified flours after storage intervals
are presented in Table 1. During storage, moisture increased while protein and
fat contents of the flours decreased significantly. The packaging materials were
found to have significant effects on moisture and NFE (Table 2).
In an earlier study, nonsignificant changes occurred in the chemical
characteristics of iron-fortified WMF packed in cotton bags. Moisture content
was somewhat lower as compared to unfortified flour. This depends on
changes in relative humidity and storage temperature (Rehman et al. 2006). It
may be attributed to the hygroscopic nature of the fortificants (Rehman et al.
2003).
In the present study, flour samples stored in bags lost more moisture than
samples stored in tin boxes. It has been observed that initial moisture content
TABLE 1.
EFFECT OF STORAGE ON PROXIMATE COMPOSITION OF FORTIFIED FLOURS
Storage days Moisture (%) Protein (%) Fat (%) Fiber (%) Ash (%) NFE (%)
0 7.6b 11.9 1.99a 2.3 1.6 74.6
14 7.6b 11.9 1.97ab 2.3 1.6 74.6
28 7.7ab 11.9 1.95bc 2.3 1.6 74.6
42 7.8a 11.9 1.92c 2.3 1.6 74.5
Means with different letters in a column differ significantly (P<0.05).
NFE, nitrogen-free extract.
663EFFECT OF PACKAGING MATERIALS ON QUALITY OF WMF

of flour packed in polyethylene bags (75 gauge) increases initially and
decreases subsequent storage (Marathe et al. 2002).
The decrease in fat content during storage might be because of the
breakdown of fat into free fatty acids and glycerol by lipase in the presence of
moisture and pro-oxidants including light and heat. Leelavathi et al. (1984)
have demonstrated that fat deterioration occurs at faster rate in flour containing
12% moisture than that containing 7.5% moisture. The moisture content in the
present study ranged between 7.0 and 8.0%, which caused less deterioration in
fat in the samples containing FSE. Fortificants had no significant effects on
proximate composition except the ash content (Table 3). The ash in unfortified
flour was lower than that in the fortified flour samples because the fortified flour
contained iron compounds, which resulted in increased ash content.
Iron and Phytic Acid Content
The initial mean iron content was 75.1 ppm which was not affected
significantly as a result of subsequent storage (Table 4). The results revealed
highly significant differences in total iron content of unfortified and fortified
flour samples (Table 5). However, packaging materials had no effect on the
total iron content of the fortified samples (Table 6).
TABLE 2.
EFFECT OF PACKAGING MATERIALS ON PROXIMATE COMPOSITION
OF FORTIFIED FLOURS
Packaging materials Moisture (%) Protein (%) Fat (%) Fiber (%) Ash (%) NFE (%)
Tin boxes 7.9a 11.9 1.9 2.3 1.6 74.4b
Polypropylene bags 7.5b 11.9 1.9 2.3 1.6 74.8a
Means with different letters in a column differ significantly (P<0.05).
NFE, nitrogen-free extract.
TABLE 3.
EFFECT OF DIFFERENT FORTIFICANTS ON PROXIMATE COMPOSITION
OF FORTIFIED FLOURS
Flour Moisture (%) Protein (%) Fat (%) Fiber (%) Ash (%) NFE (%)
Control 7.7 11.9 1.9 2.3 1.6b 74.6
FS 7.7 11.9 1.9 2.3 1.6b 74.6
FSE 7.7 11.9 1.9 2.3 1.7a 74.6
EI 7.7 11.9 1.9 2.3 1.7a 74.6
Means with different letters in a column differ significantly (P<0.05).
FS, FeSO4+folic acid; FSE, FeSO4+ethylenediamine tetraacetic acid +folic acid; EI, elemental
iron +folic acid; NFE, nitrogen-free extract.
664 N. HUMA ET AL.

Freshly prepared iron-fortified flour samples contained 1.2% phytate
which decreased significantly to 1.0% at the end of storage period. The studies
revealed significant effect of storage, while nonsignificant effect of packaging
materials and fortified flour samples on phytate content. Reduction in phytic
TABLE 4.
EFFECT OF STORAGE ON CHEMICAL COMPOSITION OF FORTIFIED FLOURS
Storage
days
Total iron
content
(ppm)
Phytate
content
(%)
Conversion of
Fe2+into Fe3+
(%)
POV
(meq/kg)
Acidity
(%)
Mold
count (¥102)
0 75.1 1.2a 1.4d 0.8d 0.2c 2d
14 74.6 1.1b 1.6c 1.2c 0.3b 4c
28 75.1 1.0c 1.9b 1.5b 0.4a 7b
42 74.1 0.9d 2.1a 1.6a 0.4a 14a
Means with different letters in a column differ significantly (P<0.05).
POV, peroxide value.
TABLE 5.
EFFECT OF FORTIFICANTS ON CHEMICAL COMPOSITION OF FORTIFIED FLOURS
Flour Total iron
content
(ppm)
Phytate
content
(%)
Conversion of
Fe2+into Fe3+
(%)
POV
(meq/kg)
Acidity
(%)
Mold count
(¥102)
Control 48.0d 1.1 – 1.2b 0.32a 8.5a
FS 75.9b 1.1 2.7a 1.4a 0.28b 7.5a
FSE 67.8c 1.1 1.5b 1.1c 0.29b 5.0b
EI 107.3a 1.1 1.1c 1.4a 0.29b 5.4b
Means with different letters in a column differ significantly (P<0.05).
FS, FeSO4+folic acid; FSE, FeSO4+ethylenediamine tetraacetic acid +folic acid; EI, elemental
iron +folic acid; POV, peroxide value.
TABLE 6.
EFFECT OF PACKAGING MATERIALS ON CHEMICAL COMPOSITION
OF FORTIFIED FLOURS
Packaging materials Total iron
content
(ppm)
Phytate
content
(%)
Conversion
of Fe2+into
Fe3+(%)
POV
(meq/kg)
Acidity
(%)
Mold
count
(¥102)
Tin boxes 74.9 1.1 1.8a 1.3 0.3 7a
Polypropylene bags 74.6 1.1 1.7b 1.3 0.3 6b
Means with different letters differ significantly (P<0.05).
POV, peroxide value.
665EFFECT OF PACKAGING MATERIALS ON QUALITY OF WMF

acid of WMF during storage has been reported previously by researchers
(Poonam and Salil 1993; Anshu and Neelam 1995; Wahab et al. 2004). Hinnai
et al. (2000) reported reduction in both phytic acid and ferrous iron in iron-
fortified flour during storage. Other treatments play a part in the reduction of
phytate content in flour. During flour processing, soaking of flour activates the
phytase and thus increases phytic acid hydrolysis, thereby reducing phytate in
the final products (Fretzdorff and Brummer 1992).
Conversion of Fe2+into Fe3+
Initially, conversion of Fe2+into Fe3+was recorded as 1.4%, which sig-
nificantly increased to 2.1% at the end of the storage period (Table 4). Con-
version of Fe2+into Fe3+in flour samples stored in tin boxes was higher (1.8%)
than those stored in polypropylene bags (1.7%) (Table 6). Maximum conver-
sion of Fe2+into Fe3+was observed in flour containing FS (2.7%), followed by
samples fortified with FSE (1.5%) and EI (1.1%). This might be caused by the
presence of EDTA, which controls the conversion of Fe2+into Fe3+during
storage. The results agree with previous findings (Rehman et al. 2006).
POV and Total Acidity
Among the chemical changes associated with wheat deterioration, the
extent to which fat has been least hydrolyzed by lipases can be used as a
criterion of soundness; this is usually determined by measuring POV (Matz
1996). The POV increased significantly from 0.8 to 1.6 meq/kg during storage
of flour for 42 days (Table 4). The POVs of flour samples containing FS and
EI were higher than those containing FSE, and unfortified flours (Table 5).
Rancidity develops in WMFs during storage, but it is comparatively less than
WMF, which adds bitter taste and musty odor (Leelavathi et al. 1984). Hinnai
et al. (2000) reported that rancidity in flour increases from 1.4 to 2.9% after 6
weeks of storage. The reaction involved in oxidative rancidity is catalyzed by
metals such as Fe and Cu (Kent and Evers 1994).
Total acidity of flour at the beginning was 0.2%, which significantly
increased to 0.4% at the end of the study period (Table 4). The increase in flour
acidity may be attributed to the accumulation of linoleic acid during storage
which is subsequently oxidized (Kent and Evers 1994). The increase in acidity
may also be caused by the lipase action on the triacylglycerols and other
acylated lipids, and production of free fatty acids (Sanches-Marinez et al.
1997). Unfortified flour exhibited significantly highest acidity when other
factors were pooled (Table 5).
Mold Count
Flour samples containing FSE and stored in polypropylene bags showed
minimum colony-forming units (5 ¥102/g). An increasing trend in the colony-
666 N. HUMA ET AL.

forming units was found in all flour samples during 42 days of storage
(Table 4). Flour stored in tin boxes contained higher colony-forming units of
molds as compared to that stored in polypropylene bags (Table 6). Maximum
mold count was found in the unfortified flour. Mold growth is one of the causes
of deterioration of flour during storage under sultry conditions because flour is
hygroscopic in nature and absorbs moisture from its surroundings (Jay 1990).
The colony-forming units of molds per gram of sample varied from 1.2 ¥104
to 99 ¥107of highly deteriorated Norwegian cereal grains (Stenwig and Liven
1988). Higher initial moisture content contributes more toward the spoilage of
grain and flour (Sinha et al. 1988). The molds present in flour increase rapidly
in number if its moisture content is 16% or higher. The pH of flour also has
substantial effect on the development of molds in flour during storage (Barton-
Wright 1938).
The samples of unfortified flour were spoiled by the end of the study. The
color of flour turned dark brown because of the presence of maggots of weevils
that started appearing after 15 days. However, minimal changes in color were
observed in flour stored in the polypropylene bags compared to tin boxes. The
results are quite consistent with the findings of Potus and Suchet (1989).
Rheological Characteristics
Rheological characterization of wheat flour gives valuable information
concerning the quality of raw material, the textural characteristics of the
finished products and properties needed for the design and development of
new equipment (Castell-Perez and Steffe 1992).
Rheological characteristics were significantly affected by storage period,
different fortificants and packaging materials except DS on which storage
period and different fortificants had no effect (Tables 7–9). There was an
increasing trend in WA, DDT, TI, SD and amylase units during storage.
Addition of fortificants decreased the WA, TI and SD. During stability study of
WMF containing FeSO4, EDTA and folic acid, the WA capacity, DDT, DS and
SD increased during 3 months of storage (Rehman et al. 2003).
TABLE 7.
EFFECT OF STORAGE ON RHEOLOGICAL CHARACTERISTICS OF FORTIFIED FLOURS
Storage days WA (%) DS (min) DDT (min) TI (BU) SD (BU) AM (AU)
0 66.0b 11.0 6.2c 49.2 90.8b 1,431c
21 66.7a 11.3 7.3a 47.9 103.8a 2,488b
42 66.8a 10.7 7.0b 49.8 106.0a 2,860a
Means with different letters in a column differ significantly (P<0.05).
WA, water absorption; DS, dough stability; DDT, dough development time; TI, tolerance index; SD,
softening of dough; BU, Brabender unit; AM, amylograph; AU, amylographic unit.
667EFFECT OF PACKAGING MATERIALS ON QUALITY OF WMF

CONCLUSIONS
Stability of fortified WMF depends on the nature of the fortificant. Flour
containing elemental iron and ferrous sulfate with EDTA remained stable up to
42 days. The unfortified flour and flour containing ferrous sulfate remained
stable for 21 days in tin boxes, and 28 days in the polypropylene bags. The
flour stored in polypropylene bags proved more stable than that stored in the
boxes. Addition of iron to WMF catalyzes fat oxidation, and development of
rancidity increases.
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