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This is to certify that the
thesis entitled

AN INVESTIGATION OF THE PHYSICOCHEMICAL PROPERTIES
OF CHLORINATED FLOUR

presented by

Sumei Wei

has been accepted towards fulfillment
of the requirements for

M. S. . Food Science and Human Nutrition
degree 1n

 

 

Major prvsor E

Date December 11, 1998

 

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AN INVESTIGATION OF THE PHYSICOCHEMICAL PROPERTIES OF
CHLORINATED FLOUR

By

Sumei Wei

A THESIS
Submitted to
Michigan State University
- in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Food Science and Human Nutrition

1998

ABSTRACT

AN INVESTIGATION OF THE PHYSICOCHEMICAL PROPERTIES OF
CHLORINATED FLOUR

By

Sumei Wei

This study was conducted to examine the effects of chlorination on the
physicochemical properties and cake baking performance of flour. Two levels of
chlorinated flour (pH 4.8 and pH 4.2) and one non-chlorinated control flour were used,
along with starch isolated from each of the treatments. Flour chlorinated at a high level
(pH 4.2) showed a significant increase in flour water-binding capacity, starch
hydrophobicity, and UV absorption of flour water extracts. Falling number tests indicated
that chlorination significantly affected the relative viscosity of both flour and starch
pastes. Rapid Visco-Analyzer measurements showed significant changes in flour or starch
pasting properties. At the chlorination levels used in this study, no changes in swelling
power or solubility of starch were observed. Surface tension of flour water extracts did
not show an appreciable difference between treatments. Among the three types of flour,
the one that was chlorinated to pH 4.8 produced cakes of the largest volume and best
overall quality. This study has confirmed that optimum levels of chlorination influences
the interactions between the starch fraction and other flour components significantly, thus

facilitating the formation of a firm flour gel structure and a stable cake batter.

DEDICATION

To my parents, brothers and sisters in China who are so dear to me.

iii

ACKNOWLEDGEMENTS

I wish to express my sincere thanks to my major advisor, Dr. R. Y. Ofoli, for his
guidance and support throughout the course of my study and preparation of this
manuscript. Thanks are also extended to Drs. P. K. W. Ng and G. M. Strasburg for
serving on my advisory committee and their suggestions.

Special thanks and appreciation are extended to Dr. Ng for generously providing
samples and laboratory facilities, and for the invaluable discussions. I am grateful to the
World Bank for offering me a scholarship during the first two years of my study, and to
Drs. Ofoli and Ng for providing me a research assistantship for the rest of this program.
Thanks are extended to Dr. Richard Schalek of the Composite Materials and Structures
Center for helping with the Environmental Scanning Electron Microscope. Many thanks
are also given to Ling, Vince, Monica, Alfred, Sara, and Pascale in Dr. Ng’s cereal
science group, and my “labmates” in colloid science group: Ari, Jamaica, Brian, Pan',
Connie, Avani, and Abhijit for their help in the various stages of this project and for their
precious friendship.

Finally, I would like to thank my husband, Da Ouyang, for his love, support and

constant encouragement.

iv

TABLE OF CONTENTS

TABLE OF FIGURES ....................................................................................................... vii
TABLE OF TABLES ....................................................................................................... viii
1. INTRODUCTION ....................................................................................................... l
1.1 General .................................................................................................................... 1
1.2 The Present Study .................................................................................................... 3

2. LITERATURE REVIEW ............................................................................................ 4
2.1 Physicochemical Properties of Chlorinated Flour and Starch Fraction ................... 4
2.1.1 Physicochemical Properties of Chlorinated Flour ........................................... 4
2.1.2 Physicochemical Properties of Starch Isolated from Chlorinated Flour ......... 6

2.2 Cake Baking Performance of Chlorinated Flour ................................................... 11
2.2.1 Cake Baking Mechanism ............................................................................... 11
2.2.2 Cake Batter Characteristics of Chlorinated Flour ......................................... 12
2.2.3 Cake Baking Performance of Chlorinated Flour ........................................... l3

3. MATERIALS AND EXPERIMENTAL METHODS ............................................... 15
3.1 Materials ................................................................................................................ 15
3.1.1 Wheat Flours ................................................................................................. 15
3.1.2 Chemicals ...................................................................................................... 15

3.2 Experimental Methods .......................................................................................... 15
3.2.1 Flour Fractionation ........................................................................................ 15
3.2.2 Analytical Tests ............................................................................................. 18
3.2.2.1 Moisture Content ....................................................................................... 18
3.2.2.2 Protein Content .......................................................................................... 18

3.2.2.3 Damaged Starch ........................................................................................ 19

3.2.3 Water Binding Capacity ......... 20
3.2.4 Concentration of Water Solubles .................................................................. 20
3.2.5 Ultraviolet Absorption of Water-solubles ..................................................... 21
3.2.6 Surface Tension of Aqueous Flour Extracts .................................................. 21
3.2.7 Falling Number Test on Flour and Starch ..................................................... 22
3.2.8 Pasting Properties of Flour and Starch .......................................................... 22
3.2.9 Swelling Power of Starch .............................................................................. 23
3.2.10 Determination of Starch Hydrophobicity ...................................................... 25
3.2.11 The Environmental Scanning Electron Microscopy Study ........................... 26
3.2.12 Baking of High-Ratio Cake ........................................................................... 26
3.2.12.1 Baking Procedure .................................................................................. 26
3.2.12.2 Batter Specific Gravity .......................................................................... 27
3.2.12.3 Cake Evaluation .................................................................................... 27

3.3 Statistical Analysis of Data ................................................................................... 27

4. RESULTS AND DISCUSSION ................................................................................ 29

4.1 Flour Fractionation ................................................................................................ 29
4.2 Physico-chemical Properties of Flour and Starch .................................................. 30
4.2.1 Moisture Content ........................................................................................... 30
4.2.2 Protein Content ....................................................................... 30
4.2.3 Damaged Starch ............................................................................................ 32
4.2.4 Water Binding Capacity ................................................................................ 33
4.2.5 Concentration of Water Solubles .................................................................. 34

4.3 UV Absorption of Water-solubles ......................................................................... 36
4.4 Surface Tension of Aqueous Flour Extract ........................................................... 38
4.5 Falling Number Test on Flour and Starch ............................................................. 38
4.6 Pasting Properties of Flour and Starch .................................................................. 42
4.7 Swelling Power of Starch ...................................................................................... 46
4.8 Study of Starch Hydrophobicity ............................................................................ 49
4.9 The Environmental Scanning Electron Microscopy Study ................................... 52
4.10 Baking of High-Ratio Cake ............................................................................... 53
4.10.1 Batter Specific Gravity .................................................................................. 53
4.10.2 Cake Evaluation ............................................................................................ 53

5. SUMMARY AND CONCLUSIONS ........................................................................ 56
5.1 Summary ............................................................................................................... 56
5.2 Conclusions ........................................................................................................... 59

6. RECOMMENDATIONS FOR FUTURE RESEARCH ........................................... 61
BIBLIOGRAPHY ............................................................................................................. 63
APPENDD( I. Explanation of the parameters measured by the Rapid Visco-Analyzer .. 70
APPENDD( II. Analysis of Variance (ANOVA) ............................................................. 72
APPENDIX III. Cake Internal Texture Grading ............................................................... 75

vi

TABLE OF FIGURES

Figure 1. Fractionation scheme for non-chlorinated and chlorinated flours ..................... 17

Figure 2. Changes in moisture contents for three starches (non-chlorinated,
chlorinated pH 4.8 and pH 4.2) held at 50% relative humidity and 25 °C ......... 35

Figure 3. UV absorption of water extracts from non-chlorinated control and
chlorinated flours ................................................................................................ 37

Figure 4. Surface tension of aqueous flour extracts as a function of concentration
(0.05-20 g flour on 14% moisture basis extracted per 100 ml water). ............... 39

Figure 5. Pasting curves of flours measured by the Rapid Visco-Analyzer using
a 23-min test profile ........................................................................................... 43

Figure 6. Pasting curves of starches measured by the Rapid Visco-Analyzer using
a 23-min test profile. .......................................................................................... 44

Figure 7. Swelling power (SP) and water solubility of starches, measured by
the water uptake method ..................................................................................... 48

Figure 8. Swelling factor (SF) of starch measured by the blue dextran exclusion
method ................................................................................................................ 50

Figure 9. Separation of initially uniform starch-oil-water mixtures into various layers. .51

Figure 10. Cross-view of cakes made from control and chlorinated flours ...................... 54

vii

TABLE OF TABLES

Table 1. Flour fractionation results showing percentage by weight of flour
fractions on a dry basis. ....................................................................................... 29

Table 2. Protein content, damaged starch, and water binding capacity of
flour and starch samples ...................................................................................... 31

Table 3. Falling number (FN) values measured for non-chlorinated and chlorinated
flours (pH 4.8 and pH 4.2), and for the starches isolated from the flours. .......... 40

Table 4. Pasting parameters of flour (non-chlorinated, pH 4.8 chlorinated, and
pH 4.2 chlorinated flours) measured by Rapid Visco-Analyzer 23-min test. ..... 45

Table 5. Pasting parameters of starch (isolated from non-chlorinated,
pH 4.8 chlorinated, and pH 4.2 chlorinated flours)

measured by Rapid Visco-Analyzer 23-min test. ................................................ 45
Table 6. Starch size determined by environmental scanning electron microscopy

(ESEM) ................................................................................................................ 52
Table 7. Baking results of control and chlorinated flours ................................................. 54
Table 11-1. AN OVA for flour and starch properties ........................................... 74
Table II-2. AN OVA for cake evaluation ......................................................... 75

Table III-1. Grading for internal texture of cakes based on the AACC standard
method 10-90 .............................................................................. 77

viii

1. INTRODUCTION

1.1 General

Chlorination is a process commonly used in the food industry to improve cake-
baking performance, and is achieved by infusing chlorine gas into flour. The process results
in changes in the physical and chemical properties of flour and flour components, which
enhance processing and end product performance. However, the mechanisms by which the
improvement is accomplished are not fully understood.

The quantity of chlorine gas added can be critical in enhancing cake quality.
Properly chlorinated flour produces high quality cakes, while non-chlorinated or over-
chlorinated flour produces cakes of inferior quality. When flour is chlorinated, its pH is
lowered. Thus, in general, the pH of the flour can be used as a good measure of the
chlorination level. An adequate treatment for most flours is at pH levels between 4.5 and
5.2 (Gough et al. 1978). A pH of 4.7-4.9 is commonly desired for most high-ratio cakes
(Hoseney 1994). It should be noticed that the pH drop caused by chlorination is not a reason
for the modification of flour components but a side effect of the chlorination process. A low
pH does not contribute to the specific modifications by chlorination (Worthington 1994).

The majority of chlorine added to flour is found in the water-soluble fraction in the
form of chloride ion. A large fraction of the chlorine is in flour lipids, especially in polar
lipids as found by Gilles et al. (1964), Huang et al. (1982a), and Wei et al. (1984). Their
studies indicated that chlorine preferentially interacts with the protein and lipid fractions of
flour. Although the amount of chlorine associated with starch appears to be limited in

comparison to other flour components, fractionation and reconstitution studies have

indicated that the starch fraction is the major component responsible for the improvement of
cake quality (Lamb and Bode 1963; and Sollars 1958; Johnson and Hoseney 1979).

Chlorine gas reacts with almost all flour constituents including starch, pentosans,
proteins and lipids. The chlorination process has profound effects on some of these
components. It has been reported that chlorine treatment depolymerizes starch (Huang et al.
1982a; Russell et al. 1987; Baldwin et al. 1997) and increases its hydrophobicity and
hydration capacity (Seguchi 1993a; Alexander 1933; Kulp et al. 1972). This has been
attributed to changes in starch surface proteins (Seguchi 1993b). Whistler and Pyler (1968)
observed depolymerization of pentosans due to chlorination. Chlorination destroys normal
gluten properties (Alexander 1933), increases hydrophobicity of gliadins (Sinha et al.
1997), and oxidizes cysteine, methionine and other amino acids (Ewart 1968; Tsen et al.
1971). Chlorine also combines chemically with lipids (Gough et al. 1978) and bleaches
flour pigments by addition across conjugated double bonds (Bath 1995).

In addition, chlorine treatment increases the water-soluble fraction of flour as well
as solubility of flour proteins (Kissell 1971; Tsen et al. 1971; Duviau et al. 1996), changes
the rheological properties of flour (N go et al. 1985; Conforti and Johnson 1992;
Worthington 1994), and alters the functional properties of flour lipids (Johnson et al.
1979; Donelson et al. 1984). The complexity of the flour system and the large number of
variables which can be manipulated in a given sample have led to conflicting
observations on these properties. Thus, to better understand the mechanisms involved,
further research is needed on the physicochemical changes in the flour and flour

components which are clearly attributable to the process of chlorination.

1.2 The Present Study

As a first approximation, a cake batter may be considered a colloidal dispersion.
Among the factors that contribute to the overall physicochemical nature of a colloidal
dispersion are the properties of the continuous phase, the dispersed phase and the
interfacial structure. This study is part of a larger research project on flour chlorination
designed to develop a molecular level of understanding of the mechanism of flour
chlorination from a colloidal perspective. The goal of this part of the project was to assess
the sensitivity of several techniques for detecting and characterizing the differences
between chlorinated and non-chlorinated flour samples. It is expected that this study will
make a significant contribution towards helping achieve the ultimate goal of promoting
better understanding of the mechanisms of flour chlorination.

The objectives of this study were to: (I) examine and evaluate the effects of
chlorination on the chemical and physical characteristics of cake flour and selected flour
components; and (2) elucidate the factors that may control flour performance during cake
baking.

This study is designed to give insight into the improvement of cake quality observed
for chlorinated flour in comparison to native flour. It should also provide useful
information to enable identification and exploration of alternatives to chlorination, since

there are some safety concerns about using chlorine gas in foods.

2. LITERATURE REVIEW
2.1 Physicochemical Properties of Chlorinated Flour and Starch Fraction
2.1.1 Physicochemical Properties of Chlorinated Flour

The physical and chemical properties of flour and flour components greatly
influence their performance in the final product. As an agent for improving cake baking,
chlorine gas has profound effects on the characteristics of soft wheat flour. It has been
reported that chlorine treatment increases flour water-binding capacity and solubility in
water, and solubilizes and modifies flour proteins (Kissell 1971; Tsen et al. 1971; Duviau
et al. 1996). In addition, the level of chlorination affects the degree of change in the
physicochemical properties of the flour.

Chlorine treatment destroys normal gluten properties. Alexander (1933) reported
that, after chlorination, the gluten was in a colloidal state and prevented dough formation.
A weakening of gluten proteins following chlorination was also reported in a sedimentation
test by Worthington (1994). Donelson and Wilson (1960b), by using fraction interchange
techniques, found that gluten had the greatest effect on cake volume and structure. They
noticed that gluten acts as a binder rather than as a structure element in the cake batter, and
that good-quality gluten is readily solubilized.

Sinha et al. (1997) analyzed wheat gliadins extracted from chlorinated and non-
chlorinated flour, using reversed-phase hi gh-performance liquid chromatography,
differential scanning calorimetry and fluorescence spectroscopy. They concluded that

chlorination increased the hydrophobicity of gliadins due to conformational changes.

Tsen et al. (1971) studied protein extractability in chlorinated flour, and found that
flour proteins were solubilized and modified by chlorine treatment. The chlorinated flours
showed an increase in water-soluble proteins up to a chlorination level of 4 oz. per cwt. (i.e.
hundredweight) flour (pH 3.63). However, the higher water extractability of flour proteins
was not found with highly treated flour (16 oz. per cwt., pH 2.06). It was suggested that
the chlorine cleaved the high-molecular—weight proteins into smaller, water-soluble
fragments at moderate chlorine treatment, while heavy chlorine treatment altered the
proteins to such an extent that they became insoluble.

Tsen et al. (1971) also detected changes in the UV spectra of the water and acetic
acid extracts induced by chlorine treatment after adjusting the extracts to the same
nitrogen content. They found that the absorption of the extracts at 280 nm increased with
chlorine treatment up to a level of 1 oz. per cwt. (pH 4.89). Further treatment led to a
decrease in absorption. They suggested that aromatic groups of amino acids such as
tyrosine, tryptophan, and phenylalanine had been modified by chlorine. An increase in
absorption was shown with chlorinated tyrosine but not with chlorinated tryptophan or
phenylalanine (Tsen et al. 1971). Similarly, Seguchi (1985) found an increase in UV
absorption with chlorinated bovine serum albumin (BSA).

Other reactions brought about by chlorination include saturation of lipids that are
unsaturated in their native state (Daniels et al. 1963), and oxidation of cysteine, methionine
and other amino acids in flour (Duviau et al. 1996; Ewart 1968; Tsen et al. 1971). Conforti
et al. (1993) reported a decrease in unsaturated fatty acids (i.e. linoleic and linolenic acids)
after chlorination, which was correlated significantly with the improvement of crumb

structure and increase in cake cell evenness.

There are discrepancies in reports on the effects of chlorination on the functional
role of flour lipids. Donelson et al. (1984) reported that lipids extracted from chlorinated
flour by hexane were the major factor controlling cake volume and crumb grain when they
were reconstituted into non-chlorinated flours. However, Johnson et al. (197 9) showed that
when lipids in chlorinated flour were replaced by lipids fractionated from untreated flour,
there was no effect on cake baking quality.

Rheological studies on dough texture could be used to help predict the behavior of
cake flour. Studies (Conforti and Johnson 1992; Worthington 1994) have shown that
chlorination of flours increased water absorption in dough and decreased dough stability
(tolerance to mixing) as measured by a farinograph. However, Tsen et al. (1971) reported an
increase in stability at lower levels of chlorine treatments followed by a rapid decrease at
higher chlorine levels. Alveograph results from the study of Worthington (1994) indicated a
loss of dough extensibility and elasticity.

Viscoamylograph measurements showed that chlorine treatment increased the
consistency of flour slurry (Seguchi 1977; Worthington 1994). In another study by Kulp et
al. (1972), however, they reported that a high level of chlorination caused reduction in the
paste consistency of flour. They attributed this to the depolymerization of starch by

chlorine treatment.

2.1.2 Physicochemical Properties of Starch Isolated from Chlorinated Flour

It has been reported that chlorination can oxidize and depolymerize starch granules,
and change the starch surface characteristics from hydrophilic to hydrophobic, as indicated

by an increase in oil-binding capacity (Seguchi 1984a). Kulp et al. (1972) found that starch

hydration capacity increased with increasing chlorine dosage. It was postulated that
hydrophobicity of chlorinated starch might enhance the interaction of starch granules with
other flour components such as proteins, resulting in greater transfer of water to starch
during swelling (Seguchi and Matsuki 1977; and Seguchi 1984a).

Huang et al. (1982a) reported that starches from chlorinated flours showed an
increase in B—amylolysis limits and a decrease in intrinsic viscosity as chlorination levels
increased. A higher B—amylolysis value indicated the occurrence of cleavage of OH ,4
bonds, since cleavage of (Jr-1,4 bonds would provide a new nonreducing end in the starch
and thus a new site for B—amylase attack. A decrease of intrinsic viscosity also indicated that

the starch was depolymerized by chlorination. They also reported the presence of a carbonyl
absorption band on infrared scans of starch from chlorinated flours, which suggested that
cleavages of C-2 and C-3 bonds occurred as a result of chlorination. Because no difference
in iodine affinities was observed between the non-chlorinated and chlorinated starch, they
suggested that the major effect of chlorine might be on the arnylopectin fraction.

X-ray photoelectron spectroscopy (XPS) showed that there is a higher proportion of
the hydrocarbon component on the surface of chlorinated starch than on the surface of non-
chlorinated starch (V arriano-Marston 1985). However, by using electron spectroscopy for
chemical applications (ESCA), or XPS, Russell et al. (1987) found that the portion of the
carbon signal ascribed to hydrocarbons was essentially unchanged in the chlorinated starch,
compared to non-chlorinated starch. They postulated that the enhanced hydrocarbon signal
observed by Varriano-Marston (1985) was probably due to a greater quantity of flour lipids
remaining bound on chlorinated starch. Instead they observed signals corresponding to

chlorine covalently bonded to carbon within lipoprotein complexes on the starch surface,

and sulphone signals indicating oxidized sulphur within the proteins as a result of chlorine
treatment.

Baldwin et al. (1997) used time-of-flight—secondary ion mass spectrometry (TOF-
SIMS) to study the surface chemistry of starch granules. They detected neither direct
addition of chlorine to starch polymers, nor oxidation of the C2 and C3 hydroxyls to
carbonyl groups. But they reported that chlorination modified the phosphocholine group of
starch surface phospholipids. They also postulated that chlorination depolymerized starch

(cleavage of (rt-1,4 and/or (rt-1,6 bonds of the glucan chains), based on the evidence that

some strong mass carbohydrate ions resulting from glucan chains (found with non-
chlorinated starches) were diminished in the spectra of chlorinated starch.

The starch surface is covered with proteins and lipids. Chlorination of wheat prime
starch granules changes the surface characteristics from hydrophilic to hydrophobic.
However, it is unknown whether the hydrophobic nature of starch granules from chlorinated
wheat flour is caused by a direct chlorination of prime starch or by interaction with other
flour components (Seguchi 1984b). Seguchi (1986) showed the presence of proteins on
wheat starch granule surfaces by using protein-specific dyes. Treatment with 7% HCl or
digestion by (Jr-amylase or pepsin caused the chlorinated wheat prime starch to lose its oil-
binding ability. This would appear to indicate that the oil-binding may be reduced when
proteins are released or dissolved from starch granule surfaces. Based on this result,
Seguchi (1986) attributed the oil—binding capacity of chlorinated prime starch to the
presence of proteins complexed with starch. Treatment of chlorinated starch with water-

saturated butanol (W SB) or chloroform-methanol, generally used as solvents for lipid

extraction, had little effect on decreasing oil-binding ability (Seguchi 1984a and 1984b).
This indicates that lipids did not affect the oil-binding ability of chlorinated starch.

In a model experiment, Seguchi (1985) found that a water-soluble protein, bovine
serum albumin (BSA), formed water-insoluble films after chlorination. Results from
sodium dodecyl sulfate (SDS) disc gel electrophoresis analysis indicated that the water
insolubility of BSA was not due to polymerization or decomposition. Since an increase in
absorption in the wavelength range of 260-400 nm was observed for chlorinated BSA,
Seguchi (1985) suggested that these spectroscopical changes were indicators of chemical
modifications, which may be responsible for the insolubility of BSA after chlorination. In
general, protein’s insolubility is evidence of an increase in hydrophobicity. He further
chlorinated amino acids, and found that chlorination increased the hydrophobicity of
tyrosine, lysine, and cystine, as determined by paper chromatography. It was suggested that
the hydrophobicity of chlorinated starch granules could be attributed to chlorinated amino
acids in the proteins on the starch granule surface.

Seguchi (1990) also studied the surface proteins on starch isolated from chlorinated
flour, using sodium dodecyl sulfate (SDS) slab gel electrophoresis and Sephadex G-150
column chromatography. He observed that some large molecular weight protein bands
(near M' = 45,000, and Mr = 24,000—45,000) increased gradually with chlorination, which
indicated the occurrence of polymerization of proteins during chlorination. It was also
reported that the amount of starch surface protein increased gradually with chlorination
levels (Seguchi 1990 and 1993b). In an earlier study, however, Seguchi (1987) observed no

increase or decrease of protein content by chlorination in the starch samples. It should be

noted that in these two studies, the same wet-fractionation method with acetic acid was used
to separate the starch from flour.

It was suggested that chlorine treatment increased the swelling capacity and
enhanced the gel-forming properties of starch (Alexander 1933; N go et al. 1985). Since
chlorine treatment depolymerizes starch granules, the starch granules may have a less rigid
molecular network and show a greater swelling after chlorination. However, the evidence
for an increase in starch swelling following chlorine treatment is conflicting (Gough et al.
197 8).

Gelatinization involves a progressive loss of order in starch granules when heated in
water, which leads to granule swelling and hydration, and solubilization of starch
molecules. The enthalpy of gelatinization can be determined quantitatively using
differential scanning calorimeter (DSC), which records heat flow as thermal events occur
during heating of starch. It was shown that the heat of gelatinization for starch-water slurry
produces an endothermic peak on the DSC therrnograrn (Stevens and Elton 1971).

Allen et al. ( 1982) studied the effect of chlorination on the gelatinization endotherm
of wheat flour as well as starch isolated from the flour using DSC. It was found that
chlorination did not significantly affect the transition temperatures, or enthalpies of either
the flour or the starch. But the enthalpy values observed for the chlorinated samples tended
to be a little lower, which indicated that less energy is needed for starch gelatinization after
chlorination. The transition temperatures indicate the onset and conclusion temperatures of
gelatinization while the enthalpy change measures the energy required for disrupting the

order structure of starch granules during gelatinization.

10

Kulp et al. (1972) examined the pasting behavior of starch isolated from flours of
different chlorination levels using Brabender Viscograph. They observed little changes in
paste viscosity, unless very high chlorine doses were used (above 4.0 oz. chlorine per cwt.
of flour). A decrease in paste viscosity was found with the starch isolated from highly

chlorinated flour. It was attributed to the degradation of starch by chlorination.

2.2 Cake Baking Performance of Chlorinated Flour
2.2.1 Cake Baking Mechanism

There are two types of cakes: those made with fat, called shortened or butter
cakes, and those made without fat, called sponge or foam cakes. Cakes made with fat
include plain yellow, white, chocolate, spice, and pound cakes. Sponge or foam cakes
include angel cakes, yellow sponge, and mock sponge cakes (Freeland-Graves and
Peckham 1987).

Cake batter is a multi-component and heterogeneous dispersed system. The
continuous phase is a liquid mixture of water, and soluble components of egg, sugar and
flour. The dispersed phase consists of gas bubbles, flour particles, oil and fat. During the
early stages of cake baking, the viscosity of the batter decreases as temperature increases,
and batter stability is reduced. This causes foam drainage and bubble coalescence. In the
middle stages (from about 65°C), the starch becomes gelatinized, causing the viscosity to
increase slightly. At the same time, the batter expands, due to the pressure within the air

cells. The final stages begin at about 85°C, when starch gelatinization is nearly complete

and protein coagulation is accelerating. At this point, batter expansion ceases, and gas is

11

released. Egg and flour proteins coagulate and continue to strengthen the structure until
the end of baking (Mizukoshi 1985).

To produce a good cake, the cake batter must have sufficient viscosity to prevent
the incorporated air bubbles from rising to the surface and being lost during the initial
heating. Cake setting must be timed to allow proper batter expansion by carbon dioxide
gas and water vapor. Sufficient gel strength is also needed for the cake to resist the
stresses exerted upon it as it cools, so complete baking can be achieved without collapse

(Kim and Walker 1992).

2.2.2 Cake Batter Characteristics of Chlorinated Flour

Guy and Pithawala (1981) conducted compression tests on cake batters using a
sponge cake formulation. They found that the batters of both chlorinated and heat treated
flour were significantly firmer between 80 and 90°C than that of untreated flour. Adding
egg albumen greatly increased the overall gel strength of the batters made from the treated
flours. However, untreated flour batters did not show any significant increase in firmness
following addition of egg albumen. Similar results were observed for the batters made
from starches isolated from treated and untreated flours. This indicated substantial
starch—protein interactions in the treated systems that were absent in the untreated flours.

Dynamic rheological studies by Ngo et a] (1985) showed that the batters prepared

with chlorinated flour had a higher storage modulus G’, a measure of elasticity, than the

batters prepared from untreated flours. However, pure flour-water systems prepared with

chlorinated and untreated flours did not show any difference in G’. This observation

12

appears to indicate that chlorination has a large influence on the interactions of flour

components with ingredients in cake mixes.

2.2.3 Cake Baking Performance of Chlorinated Flour

Cake shrinkage or collapse is one of the most undesirable results in cake making
(Mizukoshi 1985). It was reported that high baking powder ratio or high sugar to water
ratio causes dips in cakes (Kissell 1967; Kissell and Marshall 1962). Chlorination enables
the flour to carry higher levels of sugar and shortening so that high-ratio cakes can be
made without fear of collapse (Tsen et al. 1971; Kissell and Yarnazaki 1979; Gaines
1982). Cakes made from flour optimally chlorinated have higher volume, drier mouthfeel,
finer grain and whiter crumb color than those made from non-chlorinated flour.

Johnson and Hoseney (1979) studied the effect of certain ingredients in the cake
formula. At shortening levels above 24% of flour weight, the cakes made from non-
chlorinated flours showed a decrease in volume and had a poor grain. Over a range of
shortening contents (0-36%) used in their study, however, the volume and grain of cakes
made from chlorinated flours did not show any change. When wheat or corn starch was
used to replace part of the wheat flour, cakes baked from non-chlorinated flour did not
collapse. Although the starch improved the volume, it did not improve the grain of the
cakes. The quality of these cakes was still inferior to those made from chlorinated flour.
The replaced starch did not affect the baking quality of chlorinated flour. This may
indicate that chlorination brings about different interactions between starch and other

flour components.

13

By using a sponge cake formulation, Guy and Pithawala (1981) observed batter
behavior during baking. They found that cakes of both chlorinated and non-chlorinated
flours reached approximately the same height before the cakes made from non-
chlorinated flour collapsed in the’last 5 minutes of the baking period. The larger volumes
were obtained for the cakes made from chlorinated flour. Conforti and Johnson (1992)
found that angel food cakes prepared with non-chlorinated flour had a larger volume but
an inferior structural quality compared to those prepared with chlorinated flour. On the
contrary, the angel cakes made from chlorinated flour were low in volume but showed
less shrinkage, more even contour, and better crumb. Similar baking results were found
with Japanese-type sponge cakes, with lower volumes but better symmetry for those
baked with chlorinated flours (Worthington 1994).

Kissell and Yamazaki (1982) studied the effects of chlorination level on batter
expansion during baking and on final cake volume. They found that batter expansion was
always better for cakes made from chlorinated flours than those from untreated flours.

The white layer cakes had the highest expansion and volume at low levels of chlorination.

14

3. MATERIALS AND EXPERIMENTAL METHODS
3.1 Materials
3.1.1 Wheat Flours

Chlorinated and non—chlorinated commercial soft wheat flours were all obtained
from one source (King Milling Company, Lowell, MI). The flour was chlorinated by the
milling company to pH levels of 4.8 and 4.2. Non-chlorinated flour from the same source

was used as a control in this study.

3.1.2 Chemicals

Glacial acetic acid and sodium hydroxide were purchased from Fisher Scientific
(Pittsburgh, PA). Blue dextran was purchased from the Sigma Chemical Company (St.
Louis, MO). All chemicals used in this study were of reagent grade. Vegetable oil and

cake ingredients were obtained from commercial sources.

3.2 Experimental Methods
3.2.1 Flour Fractionation

In order to examine chlorination effects on the starch fraction, starch was
separated from flour, by using the acetic acid fractionation method according to Sollars
(1958), with some modifications as described in this section. The amount of flour
fractionated was reduced from 600 g to 500 g, and the quantities of reagents were also

reduced accordingly. The overall fractionation scheme is illustrated in Figure 1. All the

15

fractions obtained were freeze-dried for a week, instead of being air-dried as was done by
Sollars ( 1958).

1). Mer extraction: Five hundred grams (500 g) of flour was weighed and mixed
into 1500 ml of distilled de-ionized water, and stirred for 10 minutes with a Hobart mixer
(Hobart Corporation, Troy, OH) at the lowest speed, instead of the propeller-type
laboratory stirrer that was used in Sollars’ method. The suspension was centrifuged for 10
minutes at 2000 g. The supernatant was decanted and filtered through Whatrnan No.1
‘ paper, instead of through glass wool. The supernatant containing water-solubles was
freeze-dried instead of being concentrated and stored in the liquid state.

2). Acid extraction: The dough was transferred from the centrifuge bottles to a
Waring Blender cup, with half of the dough transferred at a time. Five hundred milliliters
(500 ml) of an acetic acid solution of sufficient strength (4 ml glacial acetic acid and 496
ml distilled de-ionized water) was added to obtain a pH of 3.5. The suspension was
agitated for 2 minutes, then centrifuged for 10 minutes at 2000 g. The acid extract was
decanted into a beaker. The same procedure as above was applied to the other half of the
dough. The residues were combined and extracted for 1 minute with an acetic acid
solution of sufficient strength (1 ml glacial acetic acid and 500 ml distilled de-ionized
water) to maintain the pH at 3.5. Then the suspension was centrifuged and the
supernatant was decanted.

3). Recovery of gluten: The pH of the combined acid extracts was adjusted with
5N sodium hydroxide to 6.4. The extracts were centrifuged at 2000 g for 30 minutes. The
supernatant was decanted, and the gluten was removed, and cut into thin strips, and

freeze-dried.

16

 

 

I Flour I

 

Extract with water
Centrifuge

 

 

 

 

Water-soluble: I 111801013168

 

1

Extract with acetic acid (pH 3.5) _

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Centrifuge
Solubles I Insolubles I
pH 6.4 pH 5.0
Centrifuge Centrifuge
Gluten
Upper layer Lower layer
I Tailings I Primestarch I

 

 

 

Figure l. Fractionation scheme for non-chlorinated and chlorinated flours.

17

4). Recovery of tailings and prime starch: Five hundred milliliters (500 ml)
distilled de-ionized water was added into the residue from step 2, and the pH was
adjusted from 3.6 to 5.0 by adding 0.5N NaOH while stirring. The suspension was
centrifuged for 10 minutes at 2000g. The supernatant was decanted. The upper layer of
the residue (tailings) in the centrifuge bottles was removed with a spatula, then suspended
in distilled de-ionized water and freeze-dried. The lower and white prime starch layer was
suspended in water, and the liquid was removed by filtration in a Buchner funnel. The

moist starch cake was re-suspended in distilled de-ionized water, and freeze-dried.

3.2.2 Analytical Tests
3.2.2.1 Moisture Content

The moisture contents of the flours and starches were determined in duplicate,
using the air-oven method (AACC 1990, method 44-15A). Two grams (2 g) of flour
samples or 1 g of starch samples was used, since starches were limited in quantity. The
samples were weighed in a pre-weighed aluminum weighing dish, and dried at 130 °C for
an hour in an Isotemp Oven (Fisher Scientific, Pittsburgh, PA), cooled in a desiccator and
then re-weighed. The percent moisture was calculated as the weight loss per 100 g of wet

sample.

3.2.2.2 Protein Content

The protein contents of the whole flours and starches were determined in

duplicate, using a standard micro-Kjeldahl procedure (AACC 1990, method 46-13).

18

Sample size varied with sample type. A 0.25 g sample size was used for whole flour. For
starches, a 0.4 g sample size was used due to their low protein contents. Each sample was
digested with sulfuric acid in the presence of catalysts, and the total organic nitrogen was
converted to ammonium sulfate. The digest was neutralized with 50ml alkali and distilled
into 10 ml of boric acid solution, then titrated with a standard acid. Methylene blue was
used as an indicator in the sample titrations. The percentage of nitrogen was calculated
according to the titration result. A conversion factor of 5.7 was used to convert the

percent nitrogen (N) to percent protein (AACC 1990, method 46-13).

3.2.2.3 Damaged Starch

Damaged starch contents of flours and starches were measured in duplicate,
according to AACC standard method 76-30A (AACC 1990). The determination is based
on the fact that damaged starch is susceptible to fungal or-amylase, while undamaged
starch is not. One gram (1g) of sample (14% moisture content) was digested by 0.05 g
fungal a—amylase in 45 ml acetate buffer (pH 4.6-4.8) for 15 rrrinutes (incubated in a 30
°C water bath). Then 3 ml sulfuric acid (112804) and 20 ml sodium tungstate solution
were added to terminate the reaction. The mixture was filtered, and 5.0 ml of filtrate
transferred into test tube, then 10 ml alkaline ferricyanide solution was added. The 0t-

amylase converted the damaged starch to maltose and reduced ferricyanide to
ferrocyanide. Extra ferricynide reacted with starch-potassium iodide (KI) and produced

iodine, which was titrated with sodium thiosulfate. The titration result was converted to

19

maltose content according to Table 22-18 in AACC standard method 22-18 (AACC

1990). The percent damaged starch was evaluated according to the content of maltose.

3.2.3 Water Binding Capacity

The water binding capacity of flour and starch was determined according to
Shelke et al (1992). The flour (2.5 g, as is) was weighed in duplicate into centrifuge
tubes, dispersed with 25 ml of distilled water, held for 30 minutes at room temperature,
then centrifuged at 1500 g for 10 minutes. The centrifuge tubes were then drained for 10
minutes at an angle of 30° to remove supematants, and the residues in the centrifuge
tubes were re-weighed. For starches, a 2.0 g sample size was used, and accordingly
dispersed with 20 ml of distilled water. The water binding capacity was calculated as the
amount of distilled water retained by the flour or starch as a percentage of the original

sample weight, on a 14% moisture basis.

3.2.4 Concentration of Water Solubles

Flours (100 g on a 14% moisture basis) were weighed into the mixing bowl of a
Hobart mixer. Half of the total water to be added was poured into the bowl, and mixed
for 1 minute at a slow speed. Flour sticking to the wall of the mixing how] was scraped
down, and the other half of the water was added. The mixture was stirred for 1.5 minutes
at a medium speed. The flour on the wall of the rrrixing bowl was scraped down again,
and mixed for 1.5 minutes at a slow speed, then 6 minutes at a medium speed. The

batters were transferred to centrifuge bottles, and centrifuged at 1100 g for 15 minutes.

20

 

One milliliter (1 ml) of solution was taken in duplicate to weighing dishes, and heated at
120°C for an hour in the oven to determine the soluble content.

The total water added was 135 ml, consistent with the water level used during
baking. The above procedure is the standard one used in batter mixing for cake baking

(AACC 1990, method 10-90).

3.2.5 Ultraviolet Absorption of Water-solubles

Aqueous flour extracts (1 to 5% weight/volume) were obtained by stirring 1.00 to
5.00g flour on 14% moisture basis into 100 ml distilled de-ionized water for 4 minutes
and centrifuging at 3000 rpm for 10 rrrinutes. The absorption of the supernatant was
determined over the UV range of 200-350 nm using a Diode Array Spectrophotometer
Hewlett Packard 8452A. The absorbance at UV 280 nm was recorded as an indication of

the concentration of proteins in the extracts.

3.2.6 Surface Tension of Aqueous Flour Extracts

Aqueous flour extracts (0.05 to 20% flour on 14% moisture basis) were prepared
according to Evers et al. (1990). Flour of 0.05 to 20 g was stirred gently into 100 ml
distilled de-ionized water. The suspension was left for 20 minutes in an ice-bath to
minimize enzymatic activity, then centrifuged at 1100 g for 15 minutes. The supernatant
was decanted to the sample vessel of a Kruss K12 Interfacial Tensiometer (Kruss USA,
Charlotte, NC). Bubbles and dust particles were removed with a glass pipette (Evers et al.

1990). After equilibrating at 30°C for 30 rrrinutes, the surface tension was measured, by

21

 

using the Wilhelmy plate method according to the procedures described in the operational
manual of the tensiometer. The mean of 10 values at 30-second intervals was recorded as

the surface tension at that concentration.

3.2.7 Falling Number Test on Flour and Starch

The falling number was determined for flours and starches in duplicate, according
to AACC method 56-81B (AACC 1990). Seven grams (7 g) of sample (14% moisture
basis) were added to 25 ml of distilled de-ionized water in a test tube, which was then
vigorously shaken and immersed in a boiling water bath. The suspension was stirred by
moving the stirrer up and down for 60 seconds. The stirrer was then allowed to drop by
its own weight from its uppermost position. The total time, in seconds, for the stirrer to
reach the bottom was recorded as the “falling number.” The rate of the stirrer’s fall is

related to the viscosity of the slurry.

3.2.8 Pasting Properties of Flour and Starch

The pasting properties of flour and starch were determined in triplicate and
duplicate, respectively, according to a 23-minute test procedure described in the Rapid
Visco-Analyzer (RVA) operational manual (Newport Scientific Pty. Ltd. 1995,
Australia). A weighed sample (3.5 g of flour or 3.0 g of starch at 14% moisture basis) was
added to 25.0 ml of distilled water in a disposable aluminum sample cup. A disposable
plastic paddle was placed in the sample cup to mix the contents during heating. After

seven seconds of vigorous stirring (900 rpm) to disperse the sample and help induce rapid

22

 

equilibration of temperature, a stirring speed of 160 rpm was used for the remainder of

the test. While stirring, the mixture was equilibrated at 50°C for 1 rrrinute, then put on a
heating cycle of 95°C in 7.5 minutes, held at 95°C for 5 minutes, cooled down to 50°C in
7.5 minutes, and then held at 50°C for 2 minutes. A pasting curve was obtained and

evaluated for the following parameters: pasting temperature, peak viscosity, time to peak,
breakdown, minimum viscosity (trough), setback, and final viscosity (see Appendix I for

description).

3.2.9 Swelling Power of Starch

The influence of chlorination on starch swelling power was examined by both the
traditional water uptake method (Leach et al.1959) and the blue dextran dye exclusion
method (Tester and Morrison 1990).

1). Water uptake method: 0.2 g starch was suspended in 20.0 g distilled water in a
centrifuge tube, incubated and shaken in a water bath for 30 minutes at a constant

temperature between 40° and 95°C, then centrifuged at 4000 rpm for 20 minutes. The
supernatant was carefully drawn off. An aliquot of the supernatant was dried in an oven
at 120°C for 3 hours. The percentage of solubles extracted from starch was calculated on
a dry basis. The tube and the remaining starch paste were re-weighed. The swelling power
was calculated as the weight of sedimented paste per gram of dry starch. This value was

corrected for solubles to measure the swell of the undissolved portion of the starch.

23

 

Since the calculation of swelling power with this method is based on the weight of
the sedimentation paste, it includes the water within the swollen granules and the water in
the interstices between swollen granules.

2). Blue dextran dye exclusion m_ethod: This method is based on the observation
that blue dextran (Mr = 2x106) does not penetrate swollen granules, hence it remains in
the free water outside the swollen granules. Since only intragranular water is counted in
calculation of the swelling factor, this method measures true granule swelling. Fifty
milligrams (50 mg) starch (corrected to 0.1 mg) was suspended into 5 ml distilled de-
ionized water in a centrifuge tube. The tube was incubated horizontally with constant
shaking in a water bath for 30 minutes at a constant temperature between 40° and 80°C.
The tube was cooled down rapidly, and 0.5 ml of blue dextran (5 mg/ml) was added and
mixed. After the mixture was centrifuged at 1500 g for 6 minutes, the absorption of the
supernatant (As) was measured. The absorption of a blank reference (AR) without starch
was also measured. Samples were measured in duplicate.

The calculation of the swelling factor (SF) was based on starch weight (corrected
to 12% moisture) and a density of 1.4 g/ml. The swelling factor was calculated as the
volume of the swollen starch granules divided by the initial volume of the starch of
weight W (in milligrams). The equations used were as follows:

The volume of free water (ml) in the system is given by

FW = 5.5[fiR—I— 0.5
A

S

The volume of water absorbed in the intra-granular space can then be calculated as

V,=5.o-FW

24

 

The initial volume of starch of weight W in mg is

V0=_W_
1400

Now, the volume of the swollen granules can be determined from the sum of the two
volumes above:
V2 = VI + V2

Finally, the swelling factor can be calculated:

3.2. 10 Determination of Starch Hydrophobicity

This experiment was designed to observe the behavior of starches in water-oil
mixtures and the effect of chlorination on starch hydrophobicity. Non-chlorinated,
chlorinated pH 4.8, or pH 4.2 starch (0.2 g) was each weighed into seven small glass
tubes. Then water and vegetable oil were added to the seven tubes at a ratio of 1:11, 1:9;
1:6; 1:5; 1:2; 1:1; and 2:1. The total volume of water and vegetable oil was 6 ml. The
tubes were stopped by a rubber stopper, shaken for one minute with a Fisher Vortex
Genie2 (Bohemia, NY), and then set on stand. Each tube was then observed over a
period of time to determine if the starches had a preference for the water or the oil phase,

or whether a stable mixture would result.

25

 

3.2.11 The Environmental Scanning Electron Microscopy Study

The starch samples were dispersed in distilled de-ionized water (starch: water = 1:
2). Two drops of the suspension were loaded into the sample holder on the hot stage of a
microscope. The sample was covered with a ceramic plate and heated up to 100°C at a
rate of 5°C/min. When the temperature reached 100°C, the ceramic cover was removed.
Holding at 100°C, the sample was imaged with a 20KV accelerating voltage at a sample
chamber pressure of ~6 torr.

The samples were then cooled down from 100°C to 30°C at a rate of 5°C/min.
Images were taken at 100°C, 90°C, 80°C, 70°C, 60°C, 50°C, 40°C, and 30°C on the same
focused spots for comparison.

Two points at each side of the particle were selected, and the particle diameter
was calculated by a computer. Seventy-two (72) readings were recorded for each sample

from the images taken at 100°C. Thirty-six (36) readings were recorded from the images

taken as samples cooled down from 100°C to 30°C.

3.2.12 Baking of High-Ratio Cake
3.2.12.1 Baking Procedure

The high-ratio white layer cakes were baked in duplicate according to the AACC
method (AACC 1990, method 10-90). The formula used was: 100 g flour, 140 g sugar, 50
g shortening, 12 g non—fat dry milk, 9 g dried egg whites, and 3 g salt. The quantity of
baking powder was determined from the table given in this procedure, based on the

laboratory elevation and the barometric pressure on the day of baking. A water-to-flour

26

 

ratio of 135:100 was used for chlorinated and non—chlorinated flours. The batter was
mixed in a Hobart mixer (model N-50, Hobart Canada, North York, Ontario, Canada).

The cakes were baked at 190°C for 25 rrrinutes in a Rotary Hearth Test Baking Oven

(National Mfg. Co., Lincoln, NE).

3.2.12.2 Batter Specific Gravity

Batter specific gravity was determined in duplicate using a container of known
volume. The ratio of batter weight to the weight of an equivalent volume of water was

reported as the batter specific gravity.

3.2.12.3 Cake Evaluation

Cake volumes were measured by the rapeseed displacement method. The internal
texture was subjectively graded according to AACC method 10-90 (AACC 1990).
Indices for cake volume, uniformity and symmetry were determined, based on objective

measurements from a cake template provided for AACC method 10-91 (AACC 1990).

3.3 Statistical Analysis or Data

Using the data analysis tools of Microsoft Excel 7.0, one-way analysis of variance
(AN OVA) was performed to determine if any significant differences existed among the
treatments (non-chlorinated, chlorinated pH 4.8 and pH 4.2 flours or starches isolated
from the flours). A significance level of 0.05 was used. When a significant difference was

found among the treatments, protected least significant difference (LSD) was used to

27

 

compare and rank them. When there was no significant difference among the treatments,
Turkey’s test was used to compare the means with the critical value - honestly significant

difference (HSD) (see Appendix II).

 

28

4. RESULTS AND DISCUSSION
4.1 Flour Fractionation

The flours were separated into four fractions: water-solubles, gluten, tailings, and
prime starch, using the acetic acid method described above. The total recovery and the
relative amounts of each fraction obtained are shown in Table 1. The total recoveries of

the three types of flour were in a narrow range of 94.9-96.0%. Chlorinated pH 4.2 flour

 

yielded slightly more water-solubles than the other two flours.

Table 1. Flour fractionation results showing percentage by weight of flour fractions on a

dry basis.

 

 

 

 

Flour Water-solubles Gluten Prime Starch Tailings Total
(%) (%) (%) (%) Recovery (%)

Unchl. 6.3 6.4 53.1 29.1 94.9

Chl.-pH 4.8 6.2 5.8 60.0 24.0 96.0

Chl.-pH 4.2 6.6 5.7 54.6 28.5 95.4

 

 

 

 

 

 

 

 

Compared to the non-chlorinated flour, the chlorinated flours produced slightly
less gluten when extracted by acetic acid. This result indicates that gluten was probably
destroyed during the chlorination process. This is in agreement with the study of Tsen et
al. (1971), in which it was reported that the amount of acetic acid extractable protein

decreased with increasing levels of chlorination.

29

The pH 4.8 flour produced more prime starch and less tailings in comparison to
both the pH4.2 and the non-chlorinated flours. This suggests a strong interaction between
the starch and tailings in pH 4.8 flour which affects the separation of tailings from the
starch. Seguchi (1984) found similar results for the recovery of starch and tailings from
flours at different levels of chlorination. He reported that prime starch could not readily
be recovered from flour chlorinated at a level of 4.26 g/kg of flour (pH 2.96) or greater.

The flour fractionation results with chlorinated pH 4.8 flour are in agreement with
the findings of Sollars (1958), who reported that flours chlorinated to a pH of 4.82
yielded smaller amounts of tailings and gluten and a larger amounts of prime starch

compared to non-chlorinated flour.

4.2 Physico-chemical Properties of Flour and Starch
4.2.1 Moisture Content

The moisture contents of the flours were 9.38, 10.82, and 10.73% for non-
chlorinated, pH 4.8, and pH 4.2, respectively. The higher moisture contents of the
chlorinated flours were probably due to moisture pick-up by the flours during handling
and/or storage. The moisture contents of starches isolated from the flours were in the

range of 0.29—0.43% after freeze—drying.

4.2.2 Protein Content

The protein contents of flours and starches (14% moisture basis) are shown in

Table 3. The protein contents of the flours were in the range of 7.5-8.5%, which are

30

 

 

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31

typical protein levels in cake flour for high-ratio cakes. The non-chlorinated flour had a
higher protein content than the chlorinated flours. This result was unexpected, given that
the chlorinated and non-chlorinated flours were supposed to have come from the same
source. A difference in flour sources may cause a difference in protein contents. In
addition, it is possible that chlorination may offer another explanation for this difference,
since chlorine treatment alters flour proteins and may affect the recovery of nitrogen in
the flour.

The starches isolated from non-chlorinated flour had a higher protein content than
the starch from chlorinated flours. This would indicate that chlorination did not increase
the surface protein of the starch granules. The results agree with findings of Seguchi
(1987), who reported no increase in the surface proteins on the starches isolated from

chlorinated flours by the acetic acid procedure.

4.2.3 Damaged Starch

The damaged starch contents for non-chlorinated, pH 4.8 and pH 4.2 flour were
6.97, 6.48, and 6.77%, respectively, showing no significant difference among the
treatments. It should also be noted that the levels of damaged starch in these flours are
acceptable for cake baking purposes. For the starches isolated from the control, pH 4.8
and pH 4.2 flour, the damaged starch contents were 2.17, 2.30, and 1.95%, respectively

(Table 3), again with no significant differences among treatments (p>0.05).

32

 

4.2.4 Water Binding Capacity

The water binding capacity of each flour or starch was determined as the amount of water
retained by the hydrated flour or starch. As shown in Table 3, water-binding capacity of
pH 4.2 flour and starch were significantly higher (p<0.05) than for the other treatments.
There was no significant difference between the non-chlorinated and pH 4.8 samples.
Having a higher water-binding capacity implies that chlorinated pH 4.2 flour may have a

higher batter viscosity, and thus a higher ability of its batter to hold gas bubbles in.

Shelke et a1 (1992) studied the water binding capacity for chlorinated and aged
flours. They found that chlorinated flours had higher water binding capacity than the
untreated control flour. Aged flour showed higher water binding capacity than freshly
milled flour, and chlorination increased the rate of age-related change in water binding
capacity. They also found that flour water binding capacity was highly correlated with

batter viscosity, cake volume, and cake symmetry index.

The above measurements gave the water-binding capacity of flour or starch in
excess water. In this study, it was also observed that the chlorination affected the
absorption of moisture by dry starch. After dry starches with similar initial moisture
contents (0.29 - 0.43%) were held in an atmosphere of 50% relative humidity at room
temperature for 2 hours, the moisture contents of the starches isolated from non-
chlorinated, pH 4.8 and pH 4.2 flours were measured as 4.02, 4.08 and 4.91%,
respectively. The starch from chlorinated pH 4.2 flour absorbed significantly more water
than that from non-chlorinated and chlorinated pH 4.8 flours during the 2 hours. When

the starches were held overnight under the same conditions, the moisture contents

33

 

 

increased to 10.25, 9.92, and 9.65% for non-chlorinated, and chlorinated pH 4.8 and pH
4.2, respectively. There was no significant difference in the final moisture content among
the treatments. The final moisture contents tended to decrease with chlorination levels
(Figure 2). These observations may indicate a difference in the mechanism for water
absorption between the starch isolated from chlorinated flour and that from non-

chlorinated flour.

Huang et al (1982b) measured the water activity of flours held over water in a
desiccator (a relative humidity of 100%) for 15 hours at room temperature. They found
that non—chlorinated flour and starch fractions adsorbed more water. The final moisture
contents were 17.74, 15.55, and 15.43% for non-chlorinated, pH 4.95 (1-02 chlorine per

cwt. flour), and pH 4.35 (2-oz chlorine per cwt. flour) chlorinated flours, respectively.

Gur-Arieh et al. (1967) reported that the high-starch fraction of hard wheat flour
bound the first 7% of water (mass/mass on a dry basis) according to a Brunauer, Emmet,
and Teller (BET) monolayer. Further absorption of water up to 26% built up hydration
layers on the surface. Starch from chlorinated flour picked up more moisture first,
compared to non-chlorinated starch. Measurements of isotherms during water vapor

sorption on starch surfaces would help to elucidate these differences.

4.2.5 Concentration of Water Solubles

In the liquid phase of the flour-water mixture, the water-soluble contents were

5.54, 5.68, and 6.53% for non-chlorinated, pH 4.8 and pH 4.2 flour, respectively. The

34

 

 

 

 

 

 

 

D Moisture added
overnight (%)

I Moisture added in
2 hr. (%)

I Initial moisture (%)

 

 

 

 

 

 

Moisture content (%)

 

 

 

 

 

 

Figure 2. Changes in moisture contents for three starches (non-chlorinated, chlorinated
pH 4.8 and pH 4.2) held at 50% relative humidity and 25 °C.

35

water-soluble content was significantly higher (p<0.05) in the mixture of pH 4.2 flour.

There was no significant difference in water-soluble contents between pH 4.8 flour and

non-chlorinated flour. Flour water-solubles was reported to have an influence on cake
volume. An increase in water-solubles beyond the normal level tended to decrease

cake volume (Donelson and Wilson 1960a).

4.3 UV Absorption of Water-soluwa

The absorption peak of the aqueous flour extracts was in a wavelength range of
250-310 nm. Since proteins show strong absorption at 280 nm primarily due to
tryptophon and tyrosine residues in the proteins. The absorbance at UV 280 nm was read
as an indication of protein content. As shown in Figure 3, the water extract of pH 4.2
flour gave a higher absorption at 280 nm. However, there was little difference between
the absorption of non-chlorinated and chlorinated pH 4.8 flour.

The differences in the absorbance at UV 280 nm are possibly due to differences in
protein extractability. Kissell (1971) analyzed the water-soluble fractions of cake flour for
soluble protein using the Kjeldahl method, and reported that flour chlorination increased
the amount of water-extractable proteins.

Modification of aromatic amino acids in proteins by chlorination may be another
reason for the increase in the absorption values. Tsen et al. (1971) found an increase in
absorbance at UV 280 nm by chlorinated tyrosine. By adjusting all the extracts to the
same nitrogen content, Tsen et al (1971) detected changes in the UV spectra of water and
acetic acid extracts after chlorine treatment. The absorption at 280 nm increased with

chlorine treatment up to a level of 1 oz. per cwt. (pH 4.89). Further treatment (pH 4.51

36

 

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37

and below) led to a decrease in UV absorption, which means that high level of
chlorination did not cause an increase in UV absorption. If this finding is true, then the
large increase in absorbance at 280 nm for pH 4.2 chlorinated flour observed in this study

could be due mainly to solubilization of flour proteins by chlorination.

4.4 Surface Tension of Aqueous Flour Extract

During batter processing, more liquid-air interfaces are produced. The surface-
active components at the interface determine the gas retention capacity and baking
quality. Surface-active components in flour such as proteins, lipids and pentosans are all
involved in reducing the surface tension of water and stabilizing the liquid-air interface.

Figure 4 shows that there was no significant difference in the surface tension
values measured on the water extracts of chlorinated and non-chlorinated flours. In
addition, there was no significant change in surface tension over the concentrations of the
flour extracts used in this study. It is possible that the surfactants may have saturated the
air-water interface at the lower concentration, thus further increases in soluble

concentration did not reduce the surface tension any further.

4.5 Falling Number Test on Flour and Starch

The falling number test is commonly used to determine a—amylase activity in
cereal grain. It relies on the ability of or-amylase to liquefy gelatinized starch. The starch
polymer is cleaved by (Jr-amylase into smaller polysaccharide units. Thus the viscosity of

the flour-water slurry is reduced. A high or—amylase activity is related to a low sample

38

 

3

 

 

 

 

 

 

 

 

 

A m -
E
2 50 A
g 0. A A A
c 40. 9 a U Q Q Q
.2
in
E3 304 o Non-chi.
o x Chl.-pH4.8
o
g 20" A GIL-pH4.2
:
U) 10.

o I I I I

0 5 10 15 20 25

Flour extract (°/o, WN)

Figure 4. Surface tension of aqueous flour extracts as a function of concentration
(0.05-20 g flour on 14% moisture basis extracted per 100 ml water).

39

viscosity and a low falling number value. Differences in both amylase activity and starch
susceptibility to enzyme attack contribute to the falling number values. Any factor
affecting the relative viscosity of the flour or starch paste may affect the falling number

values.

The values of the falling numbers of chlorinated flour and starch were
significantly higher (p<0.05) than for non-chlorinated flour and starch. However, there
was no significant difference in the falling numbers for pH 4.8 and pH 4.2 flours or

starches (Table 3). For the flours, chlorination may inactivate a-amylase in the flour,
thus giving the chlorinated flour a higher falling number value due to its lower (Jr-amylase
activity. The low pH of the chlorinated pH 4.2 flour is not favorable for or-amylase

activity, and may provide an explanation for the higher falling number value for

chlorinated flour at pH 4.2.

Table 3. Falling number (FN) values measured for non-chlorinated and chlorinated flours
(pH 4.8 and pH 4.2), and for the starches isolated from the flours. A higher FN value
indicates a higher relative viscosity.

 

 

 

 

 

Chlorination level FN of flour FN of starch
Non-ch]. 283 b 592 b
Chl.-pH 4.8 384 a 718 a
Chl.-pH 4.2 447 a 722 a

 

 

 

 

Note: Each. value is the mean of replicates. Means followed by the same letter in the
same column are not significantly different (P<0.05).

40

It was reported that lower levels of chlorination increased a-amylase activity,
while higher levels of chlorination decreased tit-amylase activity (Huang et al. 1982b).
Flours with a high or-amylase activity should give a low falling number. In this study, the

pH 4.8 flour did not show a lower falling number value than non-chlorinated flour. It
suggests that a—amylase activity may not be the only factor affecting the falling number of
the flours.

The falling number tests on flour indicated that chlorinated flour pastes were
firmer (higher falling number) than those of non-chlorinated flour. The firmer structure of
chlorinated flour pastes may prevent cakes from collapsing during baking. This is in
agreement with Guy and Pithawala’s (1981) compression tests on cake batters. They
found that the firmness of the chlorinated flour batter was much higher than that of
untreated flour batter.

The falling numbers of chlorinated starch were significantly higher (p<0.05) than
non-chlorinated starch. It is unlikely that a-amylase activity contributed to this since or-
amylase activity is generally negligible in starches isolated from flours by the acetic acid
procedure. In the three treatments (see section 4.7, Swelling Power of Starch), there was
no difference in the water solubilities of starch during heating. Thus, the water solubilities
did not contribute to the higher falling numbers for starches isolated from chlorinated

flours.

41

 

4.6 Pasting Properties of Flour and Starch

The pasting behavior of flour or starch during heating and cooling in water was measured
with a Rapid Visco-Analyzer. The viscosity curves for flours and starches are shown in
Figure 5 and Figure 6, respectively. The viscosities are reported in rapid visco units
(RVUs, 1 RVU = 12 CF). The pasting parameters for flours and starches are reported in
Table 4 and Table 5, respectively. There were significant differences in the pasting
characteristics of the flours, including peak, trough (hot paste), breakdown, setback and

final viscosity (see Appendix I for definition of the parameters).

The peak viscosity for the pH 4.2 flour is significantly higher than non-chlorinated
and pH 4.8 flours, while non-chlorinated and pH 4.8 chlorinated flours had about the
same peak viscosity. Inhibition of or-amylase activity by chlorination or low flour pH may
cause an increase in peak viscosity observed for pH 4.2 chlorinated flour. Trough
viscosity, final viscosity, and setback increased with chlorination level (i.e. pH 4.2 > pH
4.8 > non-chlorinated control). The chlorinated pH 4.8 flour showed less breakdown
value, which is defined as the peak viscosity minus trough viscosity. The higher final
viscosity values for chlorinated flours indicate that chlorination increased flour gel
strength, which could help prevent post-baking collapse of the cakes. The pH 4.2 flour
had the highest breakdown value followed by non-chlorinated control flour, with pH 4.8
flour showing the least breakdown. The breakdown value indicates the resistance of the

flour to mechanical disintegration.

42

 

 

Viscosity RVU

 

 

 

 

 

 

 

350 100
Temperature
300 . Profile
— 90
250 -
— 80 8
200 - E
___ O
150 . 7" g
0
. I-
100 - """""""""" — so
— Unchl.
so 1 Chl.-pH4.8
h- 50 —- Chl.-pH4.2
— Term (0)
o ---- r I r t
0 5 10 15 20 25

Time (min)

Figure 5. Pasting curves of flours measured by the Rapid Visco—Analyzer using a
23-min test profile. The viscosities shown are the average of three trials for non-

chlorinated, pH 4.8 chlorinated, and pH 4.2 chlorinated flours, along with the
temperature profile.

43

 

 

 

 

 

350 1th
Temperature
Profile
3m ‘ - 90
23) -
a " 8°
or 211) -
\'-.
ii? \'~.._ - 7°
é1m- \\;>
— 60
1:13 -
50 _ - 50
0 L l I I ‘0
0 5 10 15 25
Time (min)

 

 

Q

2

3

E

O

O.

E

O

I'-
— Undrl.
------ Chl.—pH4.8
—— Chl.-pH4.2
— Temp (C)

 

 

 

Figure 6. Pasting curves of starches measured by the Rapid Visco-Analyzer using a 23-
min test profile. The viscosities shown are the average of two trials for the starches
isolated from non-chlorinated, pH 4.8 chlorinated, and pH 4.2 chlorinated flours, along

with the temperature profile.

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45

The difference in the pasting properties between starches was not as large as that
between flours. However, what appear to be minor differences should not be neglected.
The highest peak viscosity was obtained from starch fractionated from pH 4.8 flour,
followed by starch from non-chlorinated control flour, with the lowest peak viscosity and
an earlier peak time for starch from pH 4.2 flour. Starch from pH 4.8 flour was more
resistant to breakdown than that from non-chlorinated flour, and showed the least setback.

The earlier peak time for starch from pH 4.2 flour indicated an earlier swelling.
This is in agreement with the DSC study of Allen et al. (1982), who found that the
enthalpy values observed for chlorinated samples tended to be a little lower. Since starch
swelling, thermal and mechanical disintegration, and solubles leached from the granules are
all involved in pasting, it is difficult to give one simple explanation for the complicated
pasting behavior.

The significant differences in the pasting characteristics of the flours are
indications of the effect of chlorination. The pasting behavior of the starches was
different from the flours from which they originated. This suggests that other flour
components have a significant effect on the pasting characteristics of the starch, following

chlorination.

4.7 Swelling Power of Starch

The starch fraction of chlorinated flour is considered the major factor in
improving cake-baking quality. Starch swells during the heating of cake batter. The

influence of chlorination on starch swelling power was examined by both the traditional

46

water uptake method (Leach et a], 1959) and the blue dextran dye exclusion method
(Tester and Morrison, 1990). The water uptake method does not distinguish water within
the swollen starch granules (intragranular water) from water in the interstices between the

swollen granules.

1) Water uptake method: The changes in the swelling power and water solubility

”mg

of the starches during heating are shown in Figure 7. There was no significant difference
in swelling power between chlorinated and non-chlorinated starches. Moreover, L"
chlorination did not increase the solubility of starches in this experiment.

A two-stage swelling power was observed. The starches gradually swelled from

50° to 70°C. There was a period of slow swelling between 70° to 85°C. The swelling
increased again rapidly above 85°C. The two-stage swelling pattern indicates different

bonding forces involved in the different stages of starch swelling process. The pattern of
starch solubility is different from that of swelling power. In this study, the solubility of

starch showed an exponential increase over the temperature range of 40° - 95 °C.

2) Blue dextran dye exclusion method: This method is very sensitive to many
factors, and has not been used widely. The standard deviation of a two-replicate

measurement was up to 2.11 swelling factor (SF) units. The difference in swelling factor

 

shown in Figure 8 can not be considered as the difference in swelling factor between the

three starches since the variations were greater than the differences between treatments.

47

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48

4.8 Study of Starch Hydrophobicity

At lower oil-to-water ratios (1:11 and 1:9), the oil-bound starch flocs settled at the
bottom of the tubes for each of the three starches. The flocs of starch isolated from
chlorinated flour looked fluffy and constituted a larger volume, compared to the starch
isolated from non-chlorinated flour.

At higher oil-to-water ratios (above 1:6), the mixture containing starch isolated
from non-chlorinated flour was separated rapidly into a bottom water layer with starch
sediment and an upper starch floc bound with oil. However, the mixture containing
chlorinated starch separated very slowly into a clear bottom water layer and an upper
starch floc bound with oil (Figure 9). After one hour, there was a thin layer of oil on top
of the mixture in the tube containing non-chlorinated starch. The separation time of the
mixture increased with chlorination level. When the oil-to-water ratio was increased to
2:1, the mixtures separated into three layers, i.e. an upper oil layer, a middle starch floc,
and a bottom water layer.

This study provides evidence that the starch isolated from chlorinated flour is
more hydrophobic and is more successful in binding oil. In all cases, the starch isolated
from pH 4.8 flour had an intermediate behavior between non-chlorinated flour and pH 4.2
flour. The hydrophobic nature of chlorinated starch may improve incorporation of air
during batter mixing, and increase cake volume. It may also help to disperse fat or oil

evenly in the cake batter and stabilize it.

49

 

 

 

 

 

 

 

 

 

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4
2
o. . . . , T . . . .
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Term-3(0)

Figure 8. Swelling factor (SF) of starch measured by the blue dextran exclusion method
according to Tester and Morrison (1990). Each datum is the average of two replicates,
with a standard deviation of up to 2.11 units.

50

 

 

Oil
/ —‘

 

 

 

 

 

 

 

 

 

 

Starch floc ]
/ f, /, AJ. Starch floc

 

Water // // .

A
0"" I ‘
a" I, "l
’0’ ’l / 'l
'l ’/ '4 I o
I I
U ll '// I,
V / ’ Water
—

/ Starch ,' /

Non-chlorinated starch mixture Chlorinated starch mixture (pH 4.2)

 

 

 

 

 

\
\

\
\

\

 

 

 

 

 

 

 

 

Figure 9. Separation of initially uniform starch-oil-water mixtures into various layers.

51

4.9 The Environmental Scanning Electron Microscopy Study

The results of ESEM experiments (Table 6) showed that the starch from
chlorinated flour did not swell any more than that from non-chlorinated flour when heated
up to 100°C in water with a starch to water ratio of 1:2. This observation is in agreement
with the results from the swelling power measurements in this study. The initially swollen
starch of chlorinated flour shrank less than that of the control flour when cooled down

from 100°C to 30°C.

Table 6. Starch size determined by environmental scanning electron microscopy (ESEM).

 

 

 

 

 

Starch Mean Diameter at 100°C Shrinkage Index
(um)
Non-ch]. 17.82 0.08
Chl.-pH 4.8 16.88 0.06
Chl.-pH 4.2 16.76 0.02

 

 

 

Note: Shrinkage index is calculated as:
(mean diameter at 100°C - mean diameter at 30°C) I mean diameter at 100°C.

An equatorial groove was observed on the starch isolated from pH 4.2 flour when
heated to 100°C. However, it was not observed for starches isolated from non-
chlorinated and chlorinated pH 4.8 flours. This morphological change in the starch may
indicate a structural change due to flour chlorination. This study was conducted on starch
heated in limited water to mimic baking procedure, in which limited water is actually

used. The chlorination effect may be amplified by heating the starch in excess water.

52

 

4.10 Baking of High-Ratio Cake
4.10.1 Batter Specific Gravity

Batter specific gravity is an important factor in the evaluation of the cake-baking
quality of flour. The specific gravity values measured for batters of non-chlorinated, pH
4.8 and pH 4.2 flour were 0.92, 0.87 and 0.85, respectively. Although there was no
significant difference in batter specific gravity between these flours (p>0.05), there was a
slightly declining trend for chlorinated flour. The increase in starch hydrophobicity may
increase the amount of air incorporated into the cake batter, hence giving the batter a

lower specific gravity.

4.10.2 Cake Evaluation

The high-ratio white layer formulation (AACC 1990, method 10-90) was used to test the
cake-baking potential of the flours. The cross-sectional views of cakes made from non-
chlorinated and chlorinated flour are shown in Figure 10. The subjective scores and
objective measurements are summarized in Table 7. The volumes of cakes baked from
non-chlorinated, pH 4.8 and pH 4.2 flour were 863, 900 and 791 ml, respectively. There
were significant differences in cake volume (p<0.05) with the biggest volume obtained
from pH 4.8 flour, followed by non-chlorinated, and the pH 4.2 flour, respectively. Cakes

made from pH 4.8 flour had less shrinkage than those made from pH 4.2 flour.

53

 

Unchl.

Chl.-pH4.8

Chl.-pH4.2

 

Figure 10. Cross-view of cakes made from control and chlorinated flours.

Table 7. Baking results of control and chlorinated flours.

 

 

 

 

 

 

 

 

 

 

Flour Volume Volume Shrinkage Symmetry Uniformity Internal
(ml) Index Value (cm) Index (cm) texture
(cm) (cm)
Unchl. 863 b 10.9 b 1.75 ab 1.85 a -0.15 a 68
Chl.-pH 4.8 900 a 11.5 a 1.50 b 1.85 a 0.05 a 96
Chl.-pH 4.2 791 c 9.9 c 1.85 a -0.10 b 0.10 a 68

 

 

 

Note: Each value is the mean of two replicates. Means followed by the same letter in the
same column are not significantly different (P<0.05).

54

The cakes made from both non-chlorinated and chlorinated pH 4.8 flours gave
positive symmetry indices, which indicated peaked cakes. A negative symmetry index
value was obtained for cakes made from pH 4.2 flour. A negative symmetry index
indicates a collapsed cake and is undesirable.

Cakes with a uniformity index close to zero are good in uniformity. A positive or
negative value indicates that one side of the cake is higher than the other side. The cakes
baked from chlorinated pH 4.8 flour were better in uniformity than those from non—
chlorinated and chlorinated pH 4.2 flours. From the statistical analysis, however, there
were no significant differences in uniformity index among the three flours.

Based on the objective measurements, the pH 4.8 and non-chlorinated flours had
very similar overall baking performance in terms of shrinkage, symmetry, and uniformity.
The internal texture of cakes made from pH 4.8 flour scored higher than those from non-
chlorinated flour. The parameters used to evaluate the internal texture are shown in

Appendix III.

55

5. SUMMARY AND CONCLUSIONS

5.1 Summary

This study investigated the effects of chlorination on the physicochemical
characteristics of cake flour and selected flour components. Two levels of chlorinated
flours (pH 4.8 and pH 4.2) along with an non-chlorinated flour were used. Starch was
isolated from the flours by the acetic acid wet-fractionation procedure and freeze—dried.
Property changes as a result of chlorination were examined by physicochemical means on
flour, flour water extract, and the starch component.

Analytical tests were conducted on all samples. Surface properties and UV
absorption were measured on flour water extracts. The effects of chlorination on the flour
and starch components were evaluated by falling number tests, pasting characteristics
with a Rapid Visco-Analyzer, and water-binding capacity. The swelling power, solubility
and hydrophobicity of the starches were also measured. The behavior of starches during a
heating and cooling cycle was examined visually by an Environmental Scanning Electron
Microscope. The effects of chlorination on the flour and starch properties were correlated
with cake-baking properties.

In fractionating the flours, water-solubles were first obtained by extracting flour
with water, then extracting gluten with a dilute acetic acid. The final two-layer residue
was separated into tailings and prime starch. All these fractions were freeze-dried. The
water-solubles content was higher in pH 4.2 flour, but there was no significant difference
in water solubility between pH 4.8 and non-chlorinated flours. Compared to the non-

chlorinated control, chlorinated flour yielded less gluten, which would indicate that gluten

56

was destroyed during chlorination. The prime starch recovery increased when the flour
was chlorinated to pH 4.8, but decreased when the flour was chlorinated further to pH
4.2. The pH 4.8 flour produced more prime starch and less tailings than the other two
treatments, which indicates that the interaction of pH 4.8 starch with other flour
components is different from those in the other two flours.

Physicochemical analysis was conducted on the samples to determine the
moisture content, protein content, damaged starch content, water-binding capacity and
water extractability. The moisture content, protein content and damaged starch for the
flours were all acceptable for soft wheat flours used for cake-baking. There was no
increase in protein content in the starches isolated from chlorinated flours. The
chlorinated pH 4.2 flour showed a higher water-binding capacity and water solubility than
the non-chlorinated flour and the chlorinated pH 4.8 flour. The starch isolated from pH
4.2 flour also showed a higher water-binding capacity than the other starches.

UV absorption of flour extracts at 280nm showed that the water extract of pH 4.2
flour gave a higher absorption, while there was little difference between the non-
chlorinated control and pH 4.8 flours. This result indicated that a high chlorination level
increases the amount of water-extractable proteins. In addition, the increase of ultraviolet
absorption may be due to the modification of aromatic groups of amino acids by chlorine.
However, the changes in water-solubles as a result of flour chlorination were not evident
in the surface behavior as measured by surface tension.

In falling number tests, chlorinated flours gave a higher falling number than the

non-chlorinated control, which indicated that chlorination increased the gel strength of

57

the flour. Similar results were observed for starches isolated from those flours. The firmer
structure of chlorinated flour gel may prevent cakes from collapsing during baking.

Pasting properties were measured on flours and starches by the Rapid Visco-
Analyzer method. The highest peak viscosity was observed for chlorinated pH 4.2 flour.
There was practically no difference between the peak viscosities of the non—chlorinated
control and pH 4.8 flours. However, pH 4.2 flour had the highest breakdown value, with
pH 4.8 flour showing the least breakdown. Trough viscosity, final viscosity, and setback
all increased with increasing chlorination levels. A different pasting behavior was
observed for the starches isolated from the flours. The highest peak viscosity was
obtained for the starch fractionated from pH 4.8 flour, with the lowest peak viscosity and
an earlier peak time for starch from pH 4.2 flour. Starch from pH 4.8 flour was more
resistant to breakdown than that of the non-chlorinated control, and showed the least
setback. The fact that the pasting properties of the starches were different from the flours
from which they originated suggests that other flour components may have a significant
effect on the pasting characteristics of the starch. It can also be postulated that
chlorination of flour modified the starch, and hence changed the way in which the starch
interacts with other components. I

Swelling power and solubility studies on starches did not show appreciable
differences between chlorinated and non-chlorinated flours. Therefore, the higher
viscosity observed for chlorinated flour could not be attributed to starch granule swelling
or solubles leaching from the swollen granules. Hydrophobicity studies on the starches
indicated that chlorination increased the hydrophobicity of the starch granules in the

flour. Starch hydrophobicity increased as the chlorination level increased.

58

The results of ESEM tests confirmed that starch isolated from chlorinated flour

did not swell any more than that from non-chlorinated flour when heated up to 100°C.

However, the swollen starch from chlorinated flour shrank less than that from the non-

chlorinated control flour when cooled down from 100°C to 30°C. An equatorial groove

was observed on the starch from pH 4.2 flour when heated in limited water.

The high-ratio white layer formula was used to evaluate cake-baking performance
of the flours. The specific gravity of cake batter made from chlorinated flour tended to be
lower. This result suggests that chlorinated flour enhanced the incorporation of air into
the cake batter. Objective evaluation of the cakes included measurements of the cake
volume, volume index, shrinkage value, symmetry index, and uniformity. Cakes made
from chlorinated pH 4.8 flour gave the highest volume. Based on the objective
measurements, the chlorinated pH 4.8 and non-chlorinated flours had very similar overall
baking performances in terms of shrinkage, symmetry and uniformity. In the subjective
evaluations which were based on the internal texture, however, the cakes made from non-

chlorinated flour scored lower than those from pH 4.8 flour.

5.2 Conclusions

The flour that was chlorinated to pH 4.8 produced cakes of the best volume and
overall quality. Flours chlorinated to pH 4.2 flour were over-chlorinated and produced
smaller cakes of inferior quality. The chlorination of flour produced changes in the
overall characteristics of both the flour and the starch components. These changes include

an increase in flour solubility, water-binding capacity, flour pasting viscosity, and

59

solubilization of flour proteins. Evidently, chlorination increased starch hydrophobicity
and hydration capacity. At the chlorination levels used in this study, no changes in
swelling power and solubility of starch were observed.

Chlorination had a significant effect on the flour pasting profiles. The highest
peak viscosity was observed for chlorinated pH 4.2 flour. Although there was no
difference in peak viscosity between the non-chlorinated control and the chlorinated pH
4.8 flour, the pH 4.8 flour showed the least breakdown. Trough viscosity, final viscosity,
and setback all increased as chlorination levels increased. Since no such effects were
observed with starches isolated from the chlorinated flours, this suggests that the
interaction between the starch isolated from chlorinated flour and other flour components
play a significant role. The interaction facilitated formation of a firm flour gel structure

and a stable cake batter.

l.

6. RECOMMENDATIONS FOR FUTURE RESEARCH

Chlorine treatment modifies the surface of the starch granules, thus the interactions
between starch and other flour components. An approach based on surface and colloid
science is needed to examine the starch granule surface modification by flour
chlorination and the interaction between the starch granule and other flour components

or cake ingredients.

Because of the large range of starch granule sizes (1-30 um), which is in the upper

range of colloidal particles (10‘ — 1049 m), some common surface and colloidal
techniques may not be readily applicable. Modeling of the surface characteristics of
chlorinated starch may provide a way to study the interactions.

A well-designed microscopic approach can be used to physically examine the starch
surface morphology and dynamic changes in starch and batter behavior during heating.
This visual examination will help interpret results from macroscopic observations.
Development of alternatives to the chlorination process can be tried by imitating the
physicochemical characteristics of chlorinated flour through formulation or physical

Wilt.

61

BIBLIOGRAPHY

62

BIBLIOGRAPHY

AACC (American Association of Cereal Chemists). 1990. Approved methods of the
AACC. The Association, St. Paul, MN.

Alexander, CL. 1933. The results of bleaching Michigan soft winter wheat cake flour by
the Brabender electric bleaching apparatus. Cereal Chem. 10:623.

Allen, J.E., J.W. Sherbon, B.A. Lewis, and LP. Hood, 1982. Effect of chlorine treatment
on wheat flour and starch: measurement of thermal properties by differential
scanning calorimetry. J. Food Sci. 47: 1508.

Baldwin, P.M., C.D. Melia, and MC. Davies, 1997. The surface chemistry of starch
granules studied by time-of flight secondary ion mass spectrometry. J. Cereal Sci.
26:329.

Bath, DE. 1995. Selected factors affecting cake flour gualig (hydration capacig,
chlorine effect). Ph.D. dissertation. Kansas State University.

Carlsson, T.L-G. 1981. Law and order in wheat flour dough: Colloid asmts of the wheat
flour dough and its lipid and protein constituents in QUCOUS media. Ph.D. thesis. Lund

University.

Coke, M., R]. Wilde, E.J.Russell and DC. Clark. 1990. The influence of surface
composition and molecular diffusion on the stability of foams formed from
protein/surfactant mixtures. Journal of Colloid and Interface Science 138:489.

Conforti, PD. and J.M. Johnson, 1992. Use of the farinograph in predicting baking quality
of unchlorinated and chlorinated flours. J. Food Quality 15:333.

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67

APPENDICES

68

APPENDDC I

69

APPENDIX I

Explanation of the parameters measured by the Rapid Visco-Analyzer

1. Peak viscosity:

Maximum viscosity developed during or soon after the heating portion of the test, in
RVU (Rapid Visco Unit).

2. Peak time:
Time at which the peak visocity occurred, in minutes.

3. Pasting temperature:
Temperature where viscosity first increases by at least 2 RVU over a one minute
period using profile STD2, in °C.

4. Peak temperature:
Temperature at which the peak viscosity occurred, in °C.

5. Holding strength:
Minimum viscosity after the peak, normally occurring around the commencement of
sample cooling, in RVU.

6. Breakdown:
Peak viscosity minus trough viscosity, in RVU.

7. Final viscosity:
Viscosity at the end of the test, in RVU.

8. Setback (from Trough):
Final viscosity minus trough viscosity, in RVU.

9. Setback from Peak:
Final viscosity minus peak viscosity, in RVU.

7O

APPENDD( II

71

APPENDIX II

Analysis of Variance (AN OVA)

Table II-l. ANOVA for flour and starch properties

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Attribute Source of SS df MS F P-value F crit
Variation
Flour protein Treatment 0.3152 2 0.1576 525.4 0.0002 9.5521
content Error 0.0009 3 0.0003
Total 0.3161 5
Starch protein Treatment 0.0033 2 0.0016 140* 0.0301 9.5521
content Error 0.0003 3 0.0001
Total 0.0036 5
Flour water Treatment 0.0086 2 0.0043 12.1 0.0078 5.1432
binding Error 0.0021 6 0.0004
“Pauly Total 0.0108 8
Starch water Treatment 0.0140 2 0.0070 69.8 0.0001 5.1432
binding Error 0.0006 6 0.0001
“WW Total 0.0146 8
Flour falling Treatment 27226.3 2 13613.2 29.4 0.0107 9.5521
number Error 1390.5 3 463.5
Total 28616.8 5
Starch falling Treatment 44587.5 2 22293.8 14.3 0.0023 4.4590
number Error 12438.7 8 1554.8
Total 57026.2 10
Flour Treatment 1.1557 2 0.5778 59.7 0.0038 9.5521
solubility Error 0.0290 3 0.0097
Total 1.1847 5
Damaged Treatment 0.2422 2 0.1211 3.8 0.1526 9.5521
starch in flour Error 0.0968 3 0.0323
Total 0.3391 5
Damaged Treatment 0.1249 2 0.0625 3.7 0.1569 9.5521
starch in Error 0.0513 3 0.0171
Starch Total 0.1762 5

 

 

 

 

 

 

 

 

 

72

 

 

Table II-2. AN OVA for cake evaluation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Attribute Source of SS df MS F P-value F crit
Variation
Volume Treatment 12289.3 2 6144.7 1 18.2 0.0014 9.5521
Error 156.0 3 52.0
Total 12445.3 5
Volume index Treatment 2.79 2 1.395 167.4 0.0008 9.5521
Error 0.02 3 0.008
Total 2.81 5
Shrinkage Treatment 0.13 2 0.065 6.5 0.0812 9.5521
value Error 0.03 3 0.010
Total 0.16 5
Symmetry Treatment 4.08 2 2.042 87.5 0.0022 9.5521
index Error 0.07 3 0.023
Total 4.15 5
Uniformity Treatment 0.07 2 0.035 3.5 0.1643 9.5521
index Error 0.03 3 0.010
Total 0.1 5

 

 

 

 

 

 

 

 

 

 

73

 

APPENDIX III

74

APPENDIX HI

Cake Internal Texture Grading
Table III-1. Grading for internal texture of cakes based on the AACC standard method

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10-90
Internal Factors Score (Points)
Unchl. Chl.-pH 4.8 Chl.-pH 4.2

Uniformity (10pts.) 2 10 6
Cells (30pts.) Size (10pts.) 6 8 6

Thickness of walls (10pts.) 2 10 6

Moisture (10pts.) 10 10 8
Texture (34ptS-) Tenderness (14pts.) 12 14 10

Softness (10pts.) 8 10 4
Grain (16pts.) 10 16 10
Crumb color (10pts.) 8 8 8
Flavor (10pts.) 10 10 10
Total 68 96 68

 

 

 

 

75

 

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