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Author: Merritt, Stephanie, G

Title: The Effect of Various Combinations of Whole Wheat Flour and

Modified Food Starch and Whole Wheat Flour and Wheat Flour on

Freeze-Thaw-Reheat Stability As Measured By Viscosity in Roux-

Gravy

Graduate Degree/ MS Food and Nutritional Sciences Major:

Research Advisor: Dr. Naveen Chikthammah, Ph.D.

Month/Year: Spring, 2012

Number of Pages: 48

Style Manual Used: American Psychological Association, 6th Edition

I understand that this research report must be officially approved by the Graduate School and that an electronic copy of the approved version will be made available through the University Library website

I attest that the research report is my original work (that any copyrightable materials have been used with the permission of the original authors), and as such, it is automatically protected by the laws, rules, and regulations of the U.S. Copyright Office.

My research adviser has approved the content and quality of this paper.

STUDENT:

NAME Stephanie Merritt DATE: May 16, 2012

ADVISER: (Committee Chair if MS Plan A or EdS Thesis or Field Project/Problem):

NAME Dr. Naveen Chikthammah, Ph.D. DATE: May 16, 2012

___________________________________________________________________________

This section to be completed by the Graduate School

This final research report has been approved by the Graduate School.

Director, Office of Graduate Studies: DATE:

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Merritt, Stephanie, G. The Effect of Various Combinations of Whole Wheat Flour and

Modified Food Starch and Whole Wheat Flour and Wheat Flour on Freeze-Thaw-Reheat

Stability As Measured By Viscosity in Roux-Gravy

Abstract

Developing a starch product with the combinations of a whole wheat native flour and

a modified food starch or a whole wheat native flour and a cross-linked wheat flour that can

withstand varying levels of freeze-thaw cycles followed by reheating and still maintain a

consistent viscosity as the fresh product could allow for many opportunities in the food

industry, in addition to other specialty industries. The objective of this study was to evaluate

the viscosities of various combinations (100:0, 75:25, 50:50, and 25:75) of whole wheat flour

(X) and modified food starch (Y) and whole wheat flour (X) and wheat flour (Z) in roux-

gravies at 0, 1, and 3freeze-thaw cycles followed by reheat. The sample treatment viscosities

of the whole wheat flour and modified food starch (X + Y) combinations and whole wheat

flour and wheat flour (X + Z) combinations were analyzed using a Brookfield Synchro-

Lectric Viscometer. For X + Y and X + Z treatment combinations (100:0, 75:25, 50:50, and

25:75) viscosity significantly increased with increasing number of freeze-thaw cycles

(p<0.05). In general, increasing levels of Y or Z increased viscosity of the roux-gravy.

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Acknowledgements

I would like to express my genuine appreciate and gratitude to the many people who

helped and assisted in completing my research and thesis. I would first like to express my

deepest thanks to Dr. Naveen Chikthammah, who has appreciably contributed to assisting of

the completion of my research design, experiment accomplishment, scientific and thesis

writing, and overall support as well. Additionally, I would like to thank Dr. Renee Surdick,

who supported the initial idea of this thesis idea and experimental design. Furthermore, I

would like to express gratitude to Connie Galep for allowing me to perform experiments in

the laboratories and supporting the completion of my research and thesis. Finally, I would

like to give great thanks to my family and friends for giving me full support as I completed

my research and thesis.

I would like to dedicate this thesis to my wonderful parents, who have shown me the

true meaning of hard work, dedication, and perseverance.

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Table of Contents

……………………………………………………………………………………………...Page

Abstract………………………………………………………………………………………...2

List of Figures………………………………………………………………………………….7

Chapter I: Introduction…………………………………………………………………………8

Statement of the Problem……………………………………………………………..12

Purpose of the Study………………………………………………………………….12

Research Objectives…………………………………………………………………..12

Assumptions of the Study…………………………………………………………….12

Definition of Terms…………………………………………………………………...13

Limitation of the Study………………...……………………………………………..14

Chapter II: Literature Review………………………………………………………………...16

Starch…………………………………………………………………………………16

Starch Granule………………………………………………………………………...17

Starch Composition…………………………………………………………………...17

Starch as a Thickening Agent………………………………………………………...20

Roux…………………………………………………………………………………..21

Industrial Uses………………………………………………………………………...23

Whole Wheat Flour…………………………………………………………………...23

Germ…………………………………………………………………………………..24

Endosperm……………………………………………………………………………24

Bran…………………………………………………………………………………...26

Wheat Flour Production………………………………………………………………27

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Modified Food Starch………………………………………………………………...28

Waxy Maize…………………………………………………………………………..29

Freeze-Thaw Stability………………………………………………………………...30

Retrogradation………………………………………………………………………...31

General Knowledge of Conventional Oven Cooking………………………………...32

Consistency/Viscosity………………………………………………………………...33

Chapter III: Methodology…………………………………………………………………….34

Materials & Description………………………………………………………………35

Table 1: Ingredient formulation used to prepare model roux – gravy (X +Y)………..36

Table 2: Ingredient formulation used to prepare model roux – gravy (X + Z)……….36

Viscosities of Roux-Gravy Data Collection…………………………………………..37

Data Analysis…………………………………………………………………………38

Limitations……………………………………………………………………………38

Chapter IV: Results……………...……………………………………………………………40

Chapter V: Conclusion………………………………………………………………………..42

Recommendations…………………………………………………………………….43

References………………………………………………………………………………….....45

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List of Figures

Figure 1: Structure of Amylose……………………………………………………………….20

Figure 2: Structure of Amylopectin…………………………………………………………..21

Figure 3: Structure of a Wheat Kernel………………………………………………………..28

Figure 4: A graph describing the mean viscosities of the sample treatments of X + Y at 0

freeze thaw cycles and 1 and 3 freeze-thaw cycles followed by reheating…………41

Figure 5: A graph describing the mean viscosities of the sample treatments of X + Z at 0

freeze thaw cycles and 1 and 3 freeze-thaw cycles followed by reheating………....42

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Chapter 1: Introduction

Starches have long been used for textural assistance. In the food industry, starch is the

most commonly used thickening and gelling agent due to the vast array of texture and

mouthful characteristics it provides. It is found as an ingredient in many foodstuffs such as

soups, sauces, gravies, and many processed foods (Arocas, Sanz, & Fiszman, 2009).

Starch granules have large, long-chain glucose polymers, which are insoluble in water

and do not form a true solution. These granules create a temporary suspension when stirred

into water, and if left undisturbed, they will settle out. In the uncooked stage, each starch

granule can swell slightly when absorbed in water, but as they are introduced to heat during

cooking, the granules swell or gelatinize irreversible causing the starch to leach out. This

feature of starch granules enables starch to be used as a thickener (Vaclavik & Christian,

2003).

Starch is made up of two molecules: amylose and amylopectin that are connected by

glycosidic bonds. Amylose is referred to as the straight-chain polymer, but the structure is

actually helical, allowing it to interact with other ingredients. Starches containing high levels

of amylose will show signs of gelling once gelatinized and cooled. Amylopectin is the chief

molecule in almost all starches. It is significantly larger than amylose and has a structure

made up of linked branches along the linear section of the polymer. Although amylose and

amylopectin are both comprised of the same units, they reveal very different properties and

functions, which add to functional performance and ingredient interactions in food structures

(Mitolo, 2006).

This natural condition of enclosing both amylose and amylopectin polymers is found

in the form of a starch granule (Mitolo, 2006). Amylose and amylopectin polymers are

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packaged into this granule. The granules are found in the form of a semi-crystalline

macromolecular structure that appear to be built up by deposits of successive layers

surrounding a central nucleus or hilum (deMan, 1999). The starch granule is held together by

semi-crystalline bundles which allow it to remain whole during heating without completely

disrupting it (Mitolo, 2006).

When starch cools, retrogradation occurs where the starch reverts to a more crystalline

structure. During this, amylose and amylopectin can participate in textural changes causing a

gritty mouth feel. This is caused by the realignment of the natural state of the starch

molecule. Freezing accelerates this process when the gel is exposed to a freeze-thaw cycle

where the water in the gel is frozen and thawed every time this cycle occurs. The ice crystals

that are melted during the thawing process are not able to reassociate with the starch, thus

shrinking the gel network from the loss water or syneresis (Vaclavik & Christian, 2003).

The quality of a finished starch product is based on several factors, such as the source

of starch, concentration of starch used in the formulation, the temperature of heating, and

other components like acid and sugar that interact with starch (Vaclavik & Christian, 2003).

There has been an increased interest in frozen products, which presents new challenges for

developers working with starch-based products. In the article, “Starch in frozen sauces”,

Denise Fallaw, technical manager for meat and convenience at Cargill Texturizing Solutions

in Wayzata, MN stated, “In frozen applications, it is important the starches have good

freeze/thaw stability to maintain these characteristics through multiple cycles of temperature

fluctuations” and Rachel Wicklund, food scientist at Tate and Lyle in Decatur, IL, explained

that temperature swings and freeze/thaw cycles are far more numerous than one person might

think, beginning in the manufacturing facility to the grocery display case. Combining the

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repeated freezing and thawing from the freezer door opening at the grocery store, with the

fluctuating temperatures before the product reaches the grocery store to the time that the

product sits in the grocery cart, it is understandable why freeze/thaw stability is so important

in the quality of the food product (Cited in Foster, 2009).

There are many different sources of starch on the market today. These products

originate from different types of cereal grains such as rye, oats, barley, rice, corn, and wheat

(Godon & Willm, 1994). Each grain contains different nutritional compositions that offer

various functional properties in a variety of food products (deMan, 1999). Examples of these

starches would be modified waxy maize, which is used primarily to convey viscosity (Light,

1989); wheat flour, used heavily in bread making, consists of 28% amylose and 72%

amylopectin and contains 0.3 grams per 100 grams of protein and 0.8 grams per 100 grams of

lipids. Waxy maize, which contains a mere 1.4-2.7% amylose and as much as 98.6%

amylopectin and also, has only 0.02-0.14 grams per 100 grams of lipids and does not

comprise of any protein (Eliasson & Gudmundsson, 2006).

Whole wheat flour is unlike that of wheat flour because it contains the germ,

endosperm, and bran that are found in the kernel. The way whole wheat flour performs in

food products is simultaneously related to its composition. Starch is a major component of

the wheat kernel. It is made up of over half of the dry weight. The amount of amylose,

approximately 23%, and amylopectin, roughly 77%, are found in wheat (Hegenbart, 1996).

This is significantly different than the mutant grain variety, waxy maize, which is almost

100% amylopectin. Waxy maize is the major source of starch produced in the United States

and is commonly deviated into a modified food starch. For the reason that modified food

starches impart functional properties that native starches are not able to provide, they have

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become a popular element in the food industry (Light, 1989).

Whole wheat flour is considered a native starch and because of this there are

limitations such as instability and the tendency to retrograde during freezing (Arocas, Sanz, &

Fiszman, 2009). Overall, modified food starches are able to assist with the granular integrity

and resist over processing, allowing the texture and appearance of the starch-based product to

be smooth and improve the consistency dramatically (Mitolo, 2006).

Roux is a mixture of flour and fat cooked together and used as a thickening agent for

soups and sauces. This term dates back more than 300 years in French cuisine where cooking

a flour and oil paste until the raw flavor of the flour cooks out and the roux has achieved the

desired color. A correctly cooked roux has a silky-smooth body and a nutty flavor while

thickening sauces and soups. A variety of fats can be used such as vegetable oil, olive oil,

butter, and in some instances, bacon grease and other rendered fats. A roux is distinctively

different from other thickeners because the starch source is cooked before use, removing the

raw flavor while preserving starch’s functional properties Thus, gravy is made from the roux

with the addition of a liquid, such as chicken stock or beef broth, that will assist in thickening

and flavoring (Allrecipes.com , n.d.).

There has been little research done on the consistency of a roux-gravy from the effect

of a freeze-thaw-conventional reheat cycle. Both heating and freezing can impact starch in

regards to the final texture, mouth feel, and consistency of a roux. A Brookfield Synchro-

Lectric Viscometer (Model RVT, Brookfield Engineering Labs. Inc., Stoughton, MA) was

used to measure the viscosity of the roux-gravy at both the initial processing and after freeze-

thawing followed by conventional reheating steps.

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Statement of the Problem

Starch is the staple ingredient in gravy-based products. Problems arise when a product

of such is put through a freeze-thaw-reheat cycle causing texture and mouth feel

inconsistencies from the initial processing to reheating steps. This research project is aimed at

creating a roux–gravy that enhances the textural and mouth feel features that maintains a

consistent viscosity through each processing step.

Purpose of the Study

The purpose of this investigation was to determine the effect of freeze-thaw-reheat

cycles on the viscosity of various combinations of whole wheat flour (X) and modified food

starch based roux-gravies (Y) and whole wheat flour (X) and wheat flour (Z) based roux-

gravies. The viscosities of the roux-gravies will be measured using a Brookfield Synchro-

Lectric Viscometer at the University of Wisconsin-Stout in Heritage Hall in the spring of

2012.

Research Objectives

This research project is aimed at determining the effect of freeze-thaw-reheat cycles

on the viscosities of various combinations of whole wheat flour (X) and modified food starch

(Y) based roux-gravies and whole wheat flour (X) and wheat flour (Z) based roux-gravies.

The following is a list of objectives for this study.

1. To determine the combination of whole wheat flour (X) and modified food starch

(Y) in a roux-gravy that will allow for a consistent viscosity from the cooking, cooling,

freezing, and thawing steps to conventionally reheating the roux gravy. This research was

done for the University of Wisconsin-Stout.

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2. To determine the combination of whole wheat flour (X) and wheat flour (Z) in a

roux-gravy that will allow for a consistent viscosity from the cooking, cooling, freezing, and

thawing steps to conventionally reheating the roux gravy. This research was done for an

organic farm in southwestern Wisconsin.

Assumptions of the Study

In this study, it is assumed that the whole wheat flour and the modified food starch

being used are similarly produced at the anonymous company of purchase as compared to

other milling companies. In addition, it is thought that the oven used in this research is

comparable to the ovens used by research and development departments that work with

starch-based products.

Definition of Terms

The following terms have been defined for the purpose of this research paper to help the

reader fully understand the information.

AACC International: a non-profit organization of members who are specialists in the

use of cereal grains in foods (Widjaja, 2006).

Aesthetics: the logic of exquisiteness learned through mind and sentiment studies.

Amyloplast: accountable for the production and well-being of starch granules.

β-glucans: D-glucose monomers polysaccharides connected by β-glycosidic bonds.

Crystal Structure: distinctive collection of molecules in a crystalline liquid.

Hydrogen Bonding: a form of bonded intermolecular strength that subsists between

two partial electric charges of differing polarity.

Hydroxyl Groups: an oxygen atom joined by a lone bond to a hydrogen atom in

functional assemblies.

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Gelatinization: to form into a jelly structure or texture.

Glucose: a sugar with the structure of: C6H12O6.

Gluten: the nitrogenous material that remains after a grain has been washed to remove

the starch.

Glycosidic Bond: joining of a carbohydrate molecule to another group through a

covalent bond.

Gristing: grinding a certain amount of grain.

Hemicellulose: a group of polysaccharides with more intricacy than sugar, but less

intricate than cellulose.

Molecule: the tiniest particle made up of two or more atoms that are adhered by

chemical forces while maintaining its physical and chemical properties of the material.

Mouth Feel: a perceptible feeling that a food offers to the mouth.

Nucleation: the start of chemical or physical alterations at distinct areas in a matrix.

Pentosan: a class of polysaccharides.

Plastid: the location of construction and maintenance of significant chemical

compounds used by the cell.

Polymer: a small and plain molecule made up of repeated connected units that can be

either of natural or synthetic compounds and typically, a high molecular weight exists.

Polymerization: the development of forming a polymer or copolymer.

Reducing Group: any sugar that has an aldehyde or a ketone group in solution.

Syneresis: the reduction of a gel assisted by the expulsion of liquid.

Tempering: an application done by heating or cooling to bring a material to an

appreciable texture, hardness, or consistency.

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Whole Grains Council (WGC): The Whole Grains Council helps consumers find

whole grain foods and understand their health benefits, helps manufacturers produce

appetizing whole grain products, and helps the media write precise, gripping stories about

whole grains (Widjaja, 2006).

Limitation of the Study

There is one limitation to this study. The quality and age of the Brookfield Synchro-

Lectric Viscometer may impact the precision and accuracy of the measurements for viscosity.

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Chapter II: Literature Review

Introduction

Five different sections are included within this chapter. The first section includes

information about starch. This knowledge will define the basic familiarity of starch, the

starch granule, the composition of starch, how it is used as a thickening agent, and its

purposes and uses in the food industry. The next section discusses whole wheat flour and the

background information that includes composition and the flour milling process. The third

section discusses modified food starch and information regarding composition, purposes in

the food industry, and as a derivative of waxy maize. The fourth section discusses freeze-

thaw stability as an effect on starch-based products, the impact of retrogradation, and the

general knowledge of conventional oven heating. The final section includes a discussion

about the consistency and viscosity of a roux–gravy.

Starch

Carbohydrates are the second most plentiful and widely allocated food components in

the world (Hizukuri, Abe, & Hanashiro). The main use of starch is to supply the chief source

of carbohydrates in the diet. Starch can be defined as a highly functional, reactive

carbohydrate, which can be modified chemically, physically, or enzymatically for specific

needs. In the food industry, starches have been traditionally used as an ingredient at

reasonably low levels for nutritional purposes and its functional properties in food systems.

Additionally, starches play a vital role when it comes to manipulating texture, moisture,

consistency, aesthetics, and shelf stability in processed foods (Pomeranz, 1991).

Starch exists mainly in most green-leafed plants, such as the root and tuber in tapioca

and potato plants, in the stem-pith in sago, and in the seed of cereal plants, which includes

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wheat and waxy maize. The purpose of starch in cereal grains is to store it as energy during

dormancy or germination, until sugar is photosynthesized in the green leaves (Lineback &

Inglett, 1982).

Starch Granule

Starch is found in the form of granules. In cereal plants, such as wheat and waxy

maize, the granules are made by amyloplasts, which are found in the plastids. Because wheat

and waxy maize are considered simple starch granules, plastids only consist of one granule.

Wheat has two types of starch granules: the large lenticular and small spherical. The large

lenticular granule is initially formed by the plastid and soon after the plastids produce

evaginations, where the small spherical granules are formed. Constriction causes the

amyloplasts to be separated from the original plastid (Hoseney, 1994).

A highly organized nature of an unharmed granule can be observed under a polarized

light microscope. This exhibits a well-defined birefringence or maltese cross pattern that

resembles a dark cross. It has been determined that amylopectin is accountable for

crystallinity and amylose being responsible for birefringence (Lineback & Inglett, 1982).

During heating, the granule’s structure is changed significantly by granular disruption

(Friedman, 1995). When enough water is present, gelatinization occurs, causing the medium

to become more viscous. (Lineback & Inglett, 1982).

Starch Composition

Starch is created mostly of glucose and other minor The intramolecular hydrogen

bonds become disturbed, thus causing the amorphous regions to hydrate first. As the

viscosity of the medium increases, the granule continues to swell. However, once the granule

has swelled to a point that the internal bonding has lost its integrity, the granule bursts and

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viscosity decreases constituents at very low levels (Eliasson & Gudmundsson, 2006). Within

cereal starches, low levels of polar lipids, nitrogen, and phosphorus in the form of

phospholipids exist. Starch is essentially polymers of D-glucose and two distinguishable

types of polymers: amylose and amylopectin (Hoseney, 1994).

Amylose (Figure 1) is considered the linear polymer of D-glucose linked

glycosidic bondsormally, amylose is presumed as linear, but this is only for part of

the molecule, where the remnants appear to be lightly branched. The molecular weight is

typically less than 500,000, but varies significantly among species of plants, within species,

and the stage of plant maturity (Mitolo, 2006). When starch is heated above the gelatinization

temperature, amylose leaches from the starch and is essentially linear, but as the temperature

is raised, amylose becomes of greater molecular weight and more branched. These extra

branches are known as long–chain branching, with side chains of hundreds of glucose that

remain at bonds. Due to the linear nature of Amylose, it is able to provide unique

properties, such as being able to be precipitated from a solution of starch, its tendency to

associate with itself, and its ability to readily retrograde (Hoseney, 1994).

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Figure 1. Structure of Amylose. Mitolo, J.J. (2006). Starch Selection and Interaction in

Foods. In A.G. Gaonkar & A. McPherson, Ingredient Interactions: Effects on Food Quality

(pp.141). Boca Raton, FL: CRC Press.

Amylopectin (Figure 2) is also composed of D-glucose that is mainly linked by

glycosidic bondsbut branched to a greater degree with 4–5% being bonds

(Mitolo, 2006). Due to this level of branching, the unit chain is only 20–25 glucose units long

on average. It is considered a giant molecule, being one of the most enormous found in nature

due to its molecular weight of 10,000,000 Daltons, having 595,238 glucose residues, and

29,762 chains with an average degree of polymerization of 20. The molecule is made up of

three types of chains: A-chains, comprised of glucose linked B-chains consisting of

glucose linked andand C-chains that have glucose with

andlinkages in addition to a reducing group. Therefore, A-chains don’t have

branches, whereas B-chains do and C-chains are branched and have the only reducing group

within amylopectin (Hoseney, 1994).

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Figure 2: Structure of Amylopectin. From Mitolo, J.J. (2006). Starch Selection and

Interaction in Foods. In A.G. Gaonkar & A. McPherson, Ingredient Interactions: Effects on

Food Quality (pp.142). Boca Raton, FL: CRC Press.

Starch as a Thickening Agent

Starch is used in food production as a thickener sequentially to improve textural

functionalities, water retention, and to supply to the lesser energy intake in dietary products

(Korus, Juszczak, Witczak, & Achremowicz, 2004). The thickening of food products is

accomplished by the swelling of the starch granule. The starch granule is insoluble in cold

water. If exposed to cold water, it will begin to swell slightly, but eventually it will shrink

back to its original size (Pomeranz, 1991). Once a starch granule is introduced to progressive

heat in a water suspension, it begins to swell and at the same time loss of birefringence

occurs. This is called gelatinization and depending on the species of starch, swelling can

begin occurring between 56-78°C. The loss of birefringence happens when To is reached and

causes the birefringence to vanish. This loss signifies that the order in the starch granules is

lost. However, this does not mean that the order at the crystalline level is gone. The loss of

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birefringence occurs over a more vast temperature range when less water is used. The most

frequent way to conclude the gelatinization temperature range is to follow the loss of

birefringence in surplus water (Eliasson & Gudmundsson, 2006).

The mechanism that allows this phenomenon to occur is by the weakening of the

hydrogen bonds breaking in the amorphous area. After the initial gelatinization, the starch

granule will continue to swell with hydration. Ultimately, these swollen granules grow so

large that they take in all of the free water that still remains and begin to swarm each other,

causing a thick body consistency and short texture of a cooked starch paste. Overall, the

starch granules are hydrated and swelled to a greater extent than their original size, the loss of

the dark maltese cross or birefringence occurs, there is an increase in lucidity, a rapid increase

in viscosity and the linear molecules are diffused from the burst granules. However, this

starch paste is not a solution. The gelatinized granules do not completely dissolve, thus acting

as elastic gel particles (Pomeranz, 1991).

Roux

Roux is used in soups, sauces, and stews as a thickener and as a flavor additive.

Typically, it is a combination of wheat flour and a clarified fat, such as butter. Due to its

ability to be used as both a thickener and a flavoring agent for many dishes, it is very

important to understand how cooking roux affects the physical characteristics of the final

product (Krasnow, Hirson, & Shoemaker, 2011).

When producing a roux, the flour and fat are combined together and heated for a short

time over a low to medium heat depending on the final product’s use. The roux is heated to

the point where the raw flavor is cooked off, but not to the stage where the flour is toasted

(Krasnow, Hirson, & Shoemaker, 2011). This is due to the peroxidase enzymes in the flour

21

to be inactivated and allowing the starch constituents to become modified (Hardacre,

Campanella, Budiman, & Hemar, 2004). As the temperature of the roux rises during cooking,

the thickening ability of the roux weakens. The thickening power of the roux depends on the

starch granule’s size and shape, the polysaccharide matrix, and the collaboration of these

characteristics (Krasnow, Hirson, & Shoemaker, 2011).

The behavior of the starch gel is significantly influenced by the addition of a lipid.

With the addition of lipids, the gelatinization and swelling power are reduced and averts the

leaching of lower molecular weight portions, such as amylose when starch is heated.

Typically, when the fragments, such as the amylose are leached, it is correlated with the

swelling power of the starch granule. The type of lipid constituent that interrelates with the

starch is also important. Triglycerides, monoglycerides, free fatty acids, or steroids will each

impart different properties as it reacts with the starch granule during swelling (Friedman,

1995).

The blend of flour and a lipid in a roux is essential when presenting a smooth, rich

texture in roux-based foods. The viscosity of roux produced from flour and butter is

influenced by ingredient features. Because it is a suspension of starch granules in a lipid,

60% of the volume fraction is occupied. It has been determined that the viscosity of a roux is

proportional to the volume fraction of the starch granules in the suspension. To impart a

consistent viscosity in a roux, the ratio of starch to water must be constant and the oil

absorption by the flour must be optimized with the cooking time and temperature the roux is

being cooked at (Hardacre, Campanella, Budiman, & Hemar, 2004)

The main function of the fat in the roux is to impart distinctive flavors and aromas. As

the temperature during cooking is raised in the roux, many changes occur with the ketones,

22

furancs, pyrazines, and carboxylic acids. The distinct flavor and aroma compounds produced

during cooking are due to the fat source (Krasnow, Hirson, & Shoemaker, 2011).

Industrial Uses

Starch has been used in the food industry for the following six functions:

1. Colloidal stabilizers in foods such as salad dressings

2. Moisture withholding in food such as cake mixes

3. Gelation agent in foods such as confections

4. Binding agent in foods such as ice cream cones and wafers

5. Coating and glazing management in foods such as candies and nut meats

6. Thickening agent in foods such as sauces, pie fillings, and gravies

In most instances, starch is used as a thickening agent and typically consumed in a

cooked paste form. In the United States, starch is used for its aesthetic appeal, how it crafts

foods to be presentable to the eye, assists in desirable texture and mouth feel, to avoid

separation of ingredients, and to offer a transporter for delicate flavors, rather than using it

solely as a nutritional purpose. As a thickening agent, it represents a major portion of total

starch sales in the food industry (Pomeranz, 1991).

Whole Wheat Flour

Wheat is a member of the grass family (Gramineae), which is made up of cereal grains

that produce dry, one-seeded fruits. These fruits are caryopsis or commonly named a kernel

or grain. On average, wheat kernels are about eight millimeters in length and weigh

approximately 35 milligrams. The kernel contains a pericarp or fruit coat that tightly encases

the seed and clings to a seed coat. An embryo or germ, an endosperm surrounded by a

nucellar epidermis, and a seed coat are found in the seed (Hoseney, 1994). Wheat is

23

recognized as red or white by the color that exists on the kernel surface, as soft or hard, and as

spring or winter. It is considered as the most versatile grain because it can be used in many

applications. It can be used as flour to structure the source of many food products, such as

pastas, noodles, cereals, flours for baking, and starch production (Medved, 1986).

Whole wheat flour is categorized as a whole grain. According to the Whole Grains

Council (WGC, 2004) and AACC International (2000), foods can be considered a whole grain

if the foods consist of almost the same relative proportions of bran, germ, and endosperm as

the original grain kernel (Cited in Widjaja, 2006).

Germ

The wheat germ (Figure 3) encompasses 2.5–3.5% of the kernel and is comprised of

two major parts: the embryonic axis or rudimentary root and shoot and the scutellum or a

small shield-like structure. The two parts function as a storage organ. The embryonic axis is

made up of 16% oil and the scutellum is 32% oil. The germ also consists of relatively high

amounts of protein (25%), sugar (mainly sucrose and raffinose, 18%), and ash (5%). The

germ does not contain starch, has many enzymes, and is high in B vitamins and vitamin E,

with values as high as 500 ppm of total tocopherol (Hoseney, 1994).

Endosperm

The endosperm (Figure 3) is made up of three types of cells: peripheral, prismatic, and

central. These cells differ in size, shape, and their location within the kernel. The cell walls

of the endosperm are comprised of pentosans, β-glucans, and hemicelluloses. Depending on

the location of the cell wall in the kernel, thickness varies due to the location of the cultivars

and the types of hard and soft wheat. Wheat flour is made up of the contents and cell walls of

the endosperm. The peripheral, prismatic, and central cells are packed with starch granules

24

that are inserted in a protein matrix, which is mostly all gluten, the storage proteins of wheat.

The starch granules are large in size and shaped as a lens that can occur up to 40 µm, but can

be spherical in shape and as small as 2- 8 µm in diameter (Hoseney, 1994). They constitute

54–72% of the dry weight in the wheat kernel, while the two molecules comprised in the

starch granule, amylose and amylopectin, ranged from 17–29% and 71–83% (Pomeranz,

1991).

As part of the wheat grain the endosperm texture plays an important role because it

establishes both the hard and soft wheat’s final use in food products (Turnbull, Marion,

Gaborit, Appels, & Rahman, 2002). There are distinct differences between soft and hard

wheat endospems. A trait of hard wheat is that the protein and starch create a tight adherence

as the protein coats the starch surface allowing for high water retention. The hemicellulose in

the wheat absorbs great amounts of water causing the cell wall to thicken. In contrast, soft

wheat flour is not able to absorb high amounts of water and as a result, the cell walls are much

thinner. Additionally, the bond between starch and protein is much stronger when hard wheat

breaks through the cell wall and starch granules. The bond becomes significantly weaker

when the hard wheat ruptures through the cell contents and at the starch–protein interface.

The durability of the starch–protein bond is reason to explain the hardness of the wheat kernel

(Pomeranz, 1991).

The appearance of the endosperm is also an important feature. Depending on the

wheat variety, the endosperm can appear hornlike, translucent, opaque, or floury. Typically,

hard wheat and high protein content have been associated with translucency, while soft wheat

and low protein content have been found to be opaque. This is explained by the amount of air

spaces in the wheat kernel that diffract and diffuse light to create a translucent or opaque

25

appearance (Hoseney, 1994).

Bran

The third major component of a grain is the bran or outer hull (Figure 3), which is

approximately 16% of the wheat kernel. This component is layered and has an outer coat of

the wheat kernel. It contains an outside pericarp layer, which provides protection to the seed

and an inside layer that consists of the seed coat. The bran is roughly comprised of 19% of

the protein, 3–5% lipid, minerals such as iron, and is approximately 14.5% of the seed. A

distinct feature of bran is that it offers cellulose and hemicellulose, which adds a rich source

of fiber to the diet (Vaclavik & Christian, 2003).

26

Figure 3: Structure of a Wheat Kernel. Saunders, R.M. (1980). Wheat bran as a dietary fiber.

In G.E. Inglett & G. Munck, Cereals for food and beverages: Recent progress in cereal

chemistry (pp. 139). New York, NY: Academic Press.

Wheat Flour Production

The production of whole wheat flour is done in a mill. There are different milling

methods that can be done, depending on the type of grain and/or flour being produced

(Wingfield, 1980). The basic process of producing flour is done by separating the endosperm

from the bran and germ. Due to the differences in the endosperm, bran, and germ’s physical

properties, these tightly bound structures can be mechanically separated. Several hours prior

to milling, the bran and endosperm are stressed by conditioning or tempering. This is done by

adding water to the wheat to harden the bran and weaken the endosperm for easier separation

due to the differences in friability. Next, gristing occurs, where different batches of wheat are

gristed together to make a mix able to produce the required flour quality. During the milling

27

process a steady pulverization occurs followed by maturing. Maturing involves oxidative

changes that occur in storage, thus improving rheological properties (Pomeranz, 1991).

Modified Food Starch

Modified food starches have become an essential component in the food industry since

their invention in the 1940s. Almost all areas in the industry employ starch’s functional

properties to aid in the appeal of the final product. Modified food starch, also called starch

derivatives, is prepared by physically, enzymatically, or chemically treating native starch, thus

altering the properties of the starch (Light, 1989).

There are three major reasons why starches are modified, the first being that modified

food starches offer functional properties that native starches cannot give in food functions.

For example, in a roux–gravy, the starch imparts a thickening ability, a smooth short

consistency, and the handiness in an instant gravy. In addition, modified food starches can

assist with absorbing or hindering moisture, binding, disintegrating, producing different

textures, developing various coatings, and steadying an emulsion. Secondly, starch is

plentiful and readily accessible, and thirdly, it can supply a financial advantage in many food

applications due to the inexpensive processing and abundant supply as compared to gums,

which are much higher priced ingredients (Light, 1989).

As mentioned previously, starch contains linear and branched polymers of glucose:

amylose and amylopectin. These glucose units can have up to three reactive hydroxyl groups

that are the foundation of all of starch’s unique derivatizations. This includes: granular

swelling, loss of birefringence, native crystallite melting, solubilization, and retrogradation.

The modification of starch typically affects these occurrences by hybridization, chemical, and

physical modification of the native starch. Examples of chemical modification include

28

derivatization and conversion, where physical modification incorporates pregelatinization,

particle size alteration, and moisture regulation (Light, 1989).

A principal type of modified food starches is cross-linking. Cross-linking is a

treatment that involves small amounts of compounds to be added to starch polymers to react

with hydroxyl groups. The purpose of cross-linking is to enhance the resistance to

overcooking, acidic environments, high shear, or extreme temperatures. This will create a

short texture or less swelling and thickening to cooked dispersions of starch and allows for the

starch to become more durable against breakdown (Vaclavik & Christian, 2003).

Waxy Maize

Modified food starches are commonly derived from waxy maize. This is because

waxy maize contains almost 100% amylopectin, which imparts advantageous viscosity

characteristics. In the United States, waxy maize is by far the most important starch source in

the food industry (Lineback & Inglett, 1982). It was developed in 1909 by plant breeders and

became a very popular food ingredient during World War II. The starch granule size of waxy

maize can range in size from 5–25 µm and its granules are multisided or polygonal (Hood,

1980).

Waxy starches have much more diverse compositions compared to normal starches.

Typically, standard starches contain roughly 20–30% amylose and 70–80% amylopectin,

whereas waxy starches consist of about 99% amylopectin and only minute portions of

amylose. Therefore, waxy starches have very different rheological properties as contrasted by

dispersions of normal starches. As stated in the article, “Shear-thickening properties of waxy

maize starch dispersions”,

29

It is well known that for the pastes of a normal starch, a gel structure will

develop on cooling at room temperature. Generally, the short-term

development of the gel structure and the crystallinity in starch gels was found

to be dominated by irreversible gelation and crystallisation within the amylose

matrix, while the long-term retrogradation of the starch gels which was

reversible could be attributed to amylopectin. The pastes of waxy starches

could not develop a gel structure, due to the fact that unlike amylose, which is

linear or slightly branched, amylopectin in the pastes is highly branched and

could not form gels under normal conditions. (Wang, Wang, Li, Zhou, &

Ozkan, 2011, pp.1).

Due to this fact, it is very appropriate to modify waxy maize to impart the functional

properties to create a desirable food product.

Freeze–Thaw Stability

Storage stability of starch-based foods is one of the main concerns in food

applications, especially if the product has to be frozen. In extreme instances of a thickened

starch product, poor storage conditions can result in syneresis from the food product. This

potentially makes the consumer believe that the food has been spoiled through

microbiological activity when actually it was just a means of poor stability. Therefore,

controlling retrogradation during freezing is a challenge (Pomeranz, 1991).

This effect is accompanied by the freeze–thaw cycle, which basically is when starch

thickened products are frozen and thawed and/or exposed to thermal temperature fluctuations

that can ultimately occur at any stage of processing, storage, or distribution. These courses

then can change quality attributes such as syneresis, organoleptic and/or textural differences

30

associated with these types of foods (Eliasson & Kim, 1992).

Starch’s ability to endure the objectionable physical changes that occur during

freezing and thawing have been coined the term, freeze–thaw stability. These transformations

have been credited to the phase separation due to retrogradation and starch crystallization.

Freeze – thaw stability varies noticeably with the source of starch, but it is known that starch

modification improves this effect considerably. In addition, factors such as starch

concentration, pH, cooking conditions, freezing rate, and other components present can affect

overall freeze–thaw stability (Eliasson & Kim, 1992).

Retrogradation

Retrogradation is a slow, progressive characteristic of starch molecules that associate

during cooking. Once a food product is thawed for consumption, the moisture is separated

from the matrix, thus causing texture softening, drip loss, and worsening of quality (Gill,

Kaur, Sogi, & Chandi, 2009). Retrogradation is basically described as recrystallization during

freezing after gelatinization has occurred. This causes the crystalline structure to change to an

ordered double helical structure from amorphous glucans. This is brought on by low

temperatures, starches that contain high amylose content, and the presence of polar

substances, such as salts (Sobolewska-Zielinska, & Fortuna, 2010).

Consequently, intermolecular distances between starch molecules weaken, causing

water to be removed from the gel and dehydration of the product. During cold temperature

freezing, insoluble starch, mainly amylose, leaches from the starch granules. During each

freeze–thaw cycle, the amylose molecules and the non–branched portions of amylopectin link

together by hydrogen bonding. This occurs in the first stage of retrogradation and

simultaneously, starch gel rigidity is induced by amylopectin crystallization. Once a product

31

has been introduced to freezing, retrogradation of the starch molecule speeds up and during

each freeze – thaw cycle it is accelerated drastically (Sobolewska-Zielinska, & Fortuna,

2010).

Comparatively, it has been found that cereal starches, such as whole wheat flour are

more susceptible to retrogradation. However, this phenomena can be controlled by a starch’s

molecular weight, concentration, temperature during heating, and the presence of non–starch

constituents, which can include lipids, acids, hydrocolloids, surfactants, saccharides, and salts.

Retrogradation can also be hindered by starch modification (Sobolewska-Zielinska, &

Fortuna, 2010).

General Knowledge of Conventional Oven Cooking

Conventional ovens are the most common type of household ovens. According to

custom, most households in the United States are equipped with one and every day they are

used by people to cook foods from casseroles to breads to desserts and the list goes on. These

ovens are able to use gas or electricity depending on the homeowner’s preference and/or the

available connection in the home.

Conventional ovens are not to be confused with convection ovens, which use a fan to

force heated air inside the oven to circulate around the food. It allows the food item to cook

much faster compared to a standard conventional oven. On the contrary, conventional ovens

use heat as well to cook the food, but do not force heated air throughout the oven during cook

time; consequently cook time takes longer than convection type ovens. This heat is produced

by two resistance elements. The top unit is used in broiling, whereas the bottom unit is used

for the baking period. Overall, the temperature that a food product is cooked and the time that

it is spent in the oven can affect the final product (Dragon, 2011).

32

Viscosity

The desired texture of food has significant economic deliberations, thus making is a

critical feature of roux-gravy texture (Bourne, 2002). The consistency of a roux–gravy

product is essential from the fresh to freezing to thawing stages. It is important that it remains

consistent throughout the entire process to allow for a desirable product. Consistency is

defined as a degree of viscosity that has unfaltering observance to the same principles, course,

and/or form. Consistency is measured by viscosity, which is the property of a fluid that

resists the ability for fluid to flow and the degree of measurement to which a fluid acquires

this property (Bourne, 2002). As mentioned before, viscosity in starch-based products is

influenced by the swelling of the starch granule during heating in the presence of water.

Viscosity is increased concurrently with the weakening of the hydrogen bonds, causing an

increase in granular size. This is done by the intramolecular hydrogen bonds becoming

disturbed, thus causing the amorphous regions to hydrate first. As the viscosity of the

medium increases, the granule continues to swell. However, once the granule has swelled to a

point that the internal bonding has lost its integrity, the granule bursts and viscosity decreases

(Lineback & Inglett, 1982).

Therefore, the viscosity in a roux–gravy is a significant issue that affects the final

product’s quality. A major influence on the product’s viscosity is heat transfer, effectiveness

of processing, type, and content of the starch. Furthermore, the chemical structure of the

starch being used can impact the overall flow of the roux–gravy due to amylose:amylopectin

ratio. If the starch contains more branching or amylopectin, the higher the viscosity will be,

whereas if more amylose is present, the greater the gel strength will be (Zeng, Zhang, & Lee,

1996).

33

Viscosity plays an important role in this study. As previously mentioned the

features described that impart viscosity characteristics will be studied to determine the ideal

amount of whole wheat flour (X) and modified food starch (Y) in combination that will allow

for a consistent roux–gravy from the cooking, cooling, freezing, and thawing steps to

reheating the product and/or the amount of whole wheat flour (X) and wheat flour (Z) in

combination that will allow for a consistent roux–gravy from the cooking, cooling, freezing,

and thawing steps to conventional reheating the product. This will be done in two successive

studies.

34

Chapter III: Methodology

The purpose of this study was to determine the influence of starch combinations on the

freeze-thaw-reheat stability of a roux-gravy model system assessed by viscosity

measurements (stability was indicated by a lack or a minimal change in viscosity).

Combinations of two starches types indicated below (X + Y or X + Z) at varying levels were

tested for viscosity following freeze-thaw-reheat in the roux-gravy model system.

The starches used in the study were:

Whole wheat flour (Whole Grain Milling Company, Welcome, MN) (indicated as X)

Modified food starch (Penford Food Ingredients, Centennial, OH) (indicated as Y)

Wheat flour (a cross-linked proprietary blend obtained from a provider requesting

anonymity) (indicated as Z)

This chapter includes a description of the materials, sample preparation and

methodology, statistical/data analysis, and the limitations of the study.

Materials and Description

Starches X, Y, and Z were obtained from suppliers indicated above. The starches

were stored at room temperature. Other roux-gravy ingredients used included unsalted butter

(Organic Valley Cooperative, LaFarge, WI) and chicken stock (Emeril’s Organic All-Natural

Chicken Flavored Stock), purchased at a local grocery store in Menomonie, WI (Lammer’s

Food Fest and Marketplace Foods). The unsalted butter and chicken stock were stored at

40°F.

Table 1 shows the ingredients formulations (in grams; percentages in parentheses)

used to prepare the batches of the model roux–gravy.

35

Table 1

Ingredient formulation used to prepare model roux – gravy (X + Y).

Ingredient

Treatment 1 X=100% Y=0%

Treatment 2 X=75% Y=25%

Treatment 3 X=50% Y=50%

Treatment 4 X=25% Y=75%

Butter 22.5 (4.50%) 22.5 (4.50%) 22.5 (4.50%) 22.5 (4.50%)

X 37.0 (6.92%) 27.8 (5.19%) 18.5 (3.46%) 9.3 (1.73%)

Y 0.00 (0.00%) 9.3 (1.73%) 18.5 (3.46%) 27.8 (5.19%)

Chicken Stock 440.5 (88.10%) 440.5 (88.10%) 440.5 (88.10%) 440.5 (88.10%)

Total 100.00% 100.00% 100.00% 100.00% Table 2

Ingredient formulation used to prepare model roux – gravy (X + Z).

Ingredient

Treatment 1 X=100%

Y=0%

Treatment 2 X=75% Y=25%

Treatment 3 X=50% Y=50%

Treatment 4 X=25% Y=75%

Butter 22.5 (4.50%) 22.5 (4.50%) 22.5 (4.50%) 22.5 (4.50%)

X 37.0 (6.92%) 27.8 (5.19%) 18.5 (3.46%) 9.3 (1.73%)

Z 0.00 (0.00%) 9.3 (1.73%) 18.5 (3.46%) 27.8 (5.19%)

Chicken Stock 440.5 (88.10%) 440.5 (88.10%) 440.5 (88.10%) 440.5 (88.10%)

Total 100.00% 100.00% 100.00% 100.00% A Tappan stove top coil burner was preheated to a heating level 4 (on a 7 scale).

Unsalted butter was placed into a medium sized stainless steel sauce pan and melted for two

minutes. Starch combinations X + Y or X + Z (formulation levels and treatments indicated in

Tables 1 or 2) were added to the melted butter and mixed constantly for one minute to bring

the mixture to the consistency of a standard roux. The roux was heated for two minutes to

reach a temperature of 150° F followed by simmering. During the simmering step, the

chicken stock was added and continuously stirred for two minutes until visible thickening of

the roux-gravy occurred (thickening may indicate gelatinization of the starch particles in the

roux-gravy). The mixture was simmered for approximately 30 minutes with constant stirring

36

(10 seconds every two minutes to avoid scorching of the bottom) during which time the

temperature of the roux–gravy reached 175°F. The mixture was then removed from heat and

allowed to cool to room temperature for approximately one hour. Upon cooling, the sample

treatments (roux-gravy) were dispensed into a 500 gram disposable baking dish (Sonoco,

Hartsville, SC) and covered with aluminum foil. The viscosity of the cooled sample

treatments were measured using a Brookfield Synchro-Lectric Viscometer.

Prepared roux-gravy treatments made using starch combination X and Y or X and Z

were allowed to undergo freeze-thaw cycling (1 or 3 cycles). Each cycle of freeze-thaw was

performed by placing the sample treatments in a freezer at a temperature of 5°F (Maytag,

Benton Harbor, MI) for 12 hours followed by thawing at room temperature for 12 hours.

Samples that underwent freeze-thaw (1 or 3 cycles) were then reheated in a Tappan

Conventional Double Oven for 30 minutes at 400°F. The treatments were cooled to room

temperature after the reheating step. The viscosity of the reheated/cooled samples were

measured and calculated for viscosity using the Brookfield Synchro-Lectric Viscometer to

determine the effect of freeze-thaw- reheat on treatment(s) viscosity.

Viscosity Measurement of the Roux-Gravy

The Brookfield Synchro-Lectric Viscometer was used to measure viscosity of the

roux–gravy treatments (0 freeze-thaw cycles and 1 or 3 cycles of freeze-thaw cycles followed

by reheat). Five hundred grams of each treatment sample were dispensed into a 12 ounce cup

(Solo Cup, Lake Forest, IL) and allowed to sit for one minute before measurements were

taken. Viscosity measurements were conducted by fixing and leveling the viscometer head.

Spindle sizes were selected based on treatments. For treatments with 100% whole wheat flour

(X), spindle size five was used. For all other treatments, spindle size six was used. The

37

spindle was inserted into the sample until it reached the immersion groove cut into the

spindle. A rotation speed of 10 RPM was selected and the spindle was allowed to rotate for

30 seconds after which the dial reading was recorded and viscosity calculated using the below

formula:

viscosity (cps) = dial reading x Brookfield Synchro-Lectric Viscometer

conversion factor

Data Analysis

Measurements were carried out in triplicate. Analysis of Variance (ANOVA) was

conducted on the viscosity measurements of the treatments. One way ANOVA to determine

treatment effects (effects of starch combinations on roux-gravy viscosity) was conducted

using the Microsoft Excel program available on MS Office (Microsoft Office, Redmond,

WA) and the post-hoc Tukey’s test was conducted to determine differences among viscosities

dependent upon treatments and freeze-thaw cycles followed by reheat using the SPSS

software (IBM, Armonk, NY).

Limitations

The limitations of this research conducted as part of this study are the following:

1. The study used blends of flours/starches. While whole wheat flour was obtained

from retail; one of the starch blends was provided by a manufacturer who

requested anonymity. The inability to divulge the source of the wheat flour

interferes with the free dissemination of research information.

2. Viscosity is a measure of the resistance of flow in materials. The objective of this

study was to determine the textural changes in a roux-gravy that was frozen and

reheated. While viscosity is one measure of texture, viscosity profiles do not

38

wholly provide information about texture. Including other texture measurements

(sensory, spectroscopy, texture analysis, consistometer) may have enhanced the

strength of thus research work.

3. A viscometer is used to determine viscosity by measuring the torque required to

rotate a spindle in a fluid. The viscosity or resistance to flow is proportional to the

speed of the viscometer and the spindle size and shape. While there are many

models of viscometers used today and some being more advantageous than others,

the Brookfield Synchro-Lectric Viscometer Model RVT (Brookfield Engineering

Labs. Inc., Stoughton, MA) was the only viscometer available for use. Other

viscometer models that would allow for digital readings of torque, shear, and

viscosity may have enhanced the accuracy of this research work’s results.

39

Chapter IV: Results

Mean viscosities (cps) of the model roux-gravy samples that underwent 0 freeze-thaw

cycles or 1 and 3 freeze-thaw cycling followed by reheat are presented in Figure 4 and Figure

5 (X + Y combinations and X + Z combinations, respectively). For all X + Y (whole wheat

flour + modified food starch) treatment combinations (100:0; 75:25; 50:50; and 25:75) the

viscosity values significantly increased with increasing number of freeze-thaw cycles

(p<0.05). Increasing levels of Y (whole wheat flour) increased viscosity of the roux-gravy

(Figure 4).

Figure 4: graph describing the mean viscosities of the sample treatments of X + Y (whole

wheat flour + modified food starch) at 0 freeze thaw cycles and 1 and 3 freeze-thaw cycles

followed by reheating. Error bars represent standard error of the mean. Bars indicated with

different alphabets indicate significant difference (p<0.05) in mean viscosity values among

the treatments.

A

C

E F

B

D

E

H

B

G G

H

-5000.00

5000.00

15000.00

25000.00

35000.00

45000.00

55000.00

65000.00

75000.00

85000.00

100-0 75-25 50-50 25-75

Vis

cosi

ty (

cps)

Treatment Samples of X (whole wheat flour) and Y (modified food starch)

0 Freeze-Thaw Cycles

1 Freeze-Thaw Cycle

3 Freeze-Thaw Cycles

40

For X + Z (whole wheat flour + wheat flour) treatment combinations (100:0; 75:25;

50:50; and 25:75) viscosity significantly increased with increasing number of freeze-thaw

cycles (p<0.05). In general, increasing levels of Z increased viscosity of the roux-gravy

(Figure 5).

Figure 5: graph describing the mean viscosities of the sample treatments of X + Z (whole

wheat flour + wheat flour) at 0 freeze thaw cycles and 1 and 3 freeze-thaw cycles followed by

reheating. Error bars represent standard error of the mean. Bars indicated with different

alphabets indicate significant difference (p<0.05) in mean viscosity values among the

treatments.

A

D

G

H

B E

G

I

C

F

G

J

0.00

10000.00

20000.00

30000.00

40000.00

50000.00

60000.00

100-0 75-25 50-50 25-75

Vis

cosi

ty (

cps)

Treatment Samples of X (whole wheat flour) and Z (wheat flour)

0 Freeze-ThawCycles1 Freeze-Thaw Cycle

3 Freeze-ThawCycles

41

Chapter V: Conclusion

A major observation in this study was the increase in the viscosity of the roux-gravy

with increasing numbers of freeze-thaw cycles. This observation has been previously

observed by Eliasson & Kim (1991) and Gill et al. (2009).

The observation can be attributed to the phenomenon of starch granule swelling,

which occurs during the weakening of the hydrogen bonds that are breaking in the amorphous

area (matrix) of the starch granule (Pomeranz, 1991). Once a starch granule is introduced to

progressive heat in a water suspension, it begins to swell and at the same time loss of

birefringence occurs (Eliasson & Gudmundsson, 2006). The starch granules are hydrated and

swelled to a greater extent than their original size and a rapid increase in viscosity occurs

(Pomeranz, 1991). The starch granules are being consecutively damaged as the number of

freeze-thaw cycles are increased (Szymonska et al., 2002). With freezing and succeeding

thaw cycles, the starch granules become more disarrayed, allowing the water in the matrix to

become more available (White, Abbas, & Johnson, 1989). This allows the water from the

exterior and amorphous areas of the starch granules to form new pathways, allowing the water

to break through into the opened interior areas of the starch granule (Oates, 1991).

Additionally, the subsequent freeze- thaw cycles may cause ice crystals to develop,

thus providing a location for nucleation of the water to occur (Gill et al., 2009). This allows

ice crystals to form into larger ice crystals, causing the starch granule structure to be

destroyed (Eliasson & Kim, 1991). Overall, the density of the starch granules is more

resistant due to the freezing of external water in the matrix (Fannon et al., 2004).

Furthermore, the reheating after the final thawing stage may have allowed for

continued thickening caused by the leaching of the soluble polysaccharides (Friedman, 1995).

42

With an increase in the number of freeze-thaw cycles, starch granules will become more

disorganized, thus leaching amylose (Gill et al., 2009).

The second significant observation was that as proportions of Y or Z increased, the

viscosity of the roux-gravy increased. This observation can be attributed to the replacement

of native starches with modified starches that may deteriorate the starch granule structure due

to the steric methods causing the hydroxyl groups to become obstructed, thus reducing

hydrogen bonding activity in the starch granule matrix (Wootton & Bamunuarachchi, 1979).

It may also be attributed to the modification process of the native starch, during which

gelatinization may occur, damaging the native starch (even supposing the design is managed

under controlled conditions) (Wootton & Bamunuarachchi, 1979). Modification methods

disturb the structure of starch granules, allowing the granules to be more vulnerable to

hydration and total breakdown at freezing conditions (White, Abbas, & Johnson, 1989).

Native starches do not impart the functional properties that modified starches offer.

Little research has been conducted on the effect of starch blends exposed to different levels of

freeze-thaw cycles followed by reheating. A roux-gravy containing the optimal combination

of a native starch and a modified starch that could withstand freeze-thaw cycling followed by

reheating and mitigate viscosity would be an ideal starch product addition to the food industry

in the United States.

Recommendations

The following recommendations were made for the future research in order to

maintain a similar viscosity from initial processing through freeze-thaw cycles and reheating.

1. In this study, waxy maize corn starch was used as the modified food starch native

source. For future product development at the University of Wisconsin-Stout it is

43

recommended that a modified food starch with a lower content of amylopectin be used

to minimize viscosity values.

2. Whole wheat flour was used as the native starch source. It is recommended that a

native starch source with more similar properties to the modified food starch, such as

waxy maize be used for the purpose of a symbiotic relationship between the two starch

sources to mitigate the viscosity of the starch blend after freeze-thaw cycles followed

by reheat.

3. There were three different freeze-thaw cycles (0, 1, and 3) that the sample treatments

(roux-gravy) were exposed to for a length of 12 hours of freezing and 12 hours of

thawing. It is recommended that less harsh parameters of the freeze-thaw cycles be

analyzed.

4. It is recommended that the X and Z starch blend of 50% whole wheat flour and 50%

wheat flour be presented to the organic farm in southwestern Wisconsin. Due to the

results, the starch blend can maintain a consistent viscosity through the harsh freeze-

thaw cycles and reheating conditions based on the viscosity values. However, it is

recommended that a different method to better predict texture characteristics, such as

sensory analysis is used.

44

References

All about roux. (n.d.). Retrieved October 1, 2011, from

http://allrecipes.com/HowTo/all-about-roux/detail.aspx

Arocas, A., Sanz, T., Fiszman, S.M. (2009, April). Clean label starches as thickeners in

white sauces. Shearing, heating and freeze/thaw stability. Food Hydrocolloids, 23,

2031–2037.

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