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1,974

QUALITY CHARACTERISTICS OF
SOY SUBSTITUTED“ GROUND BEEF,

PORK AND TURK

Thesis for the Degree' of M. S:

"MICHIGAN STATE UNIVERSITY
CLAUDIA WHIPPLE

 

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ABSTRACT

QUALITY CHARACTERISTICS OF SOY SUBSTITUTED
GROUND BEEF, PORK AND TURKEY SYSTEMS

By

Claudia Whipple

The use of soy products in school lunch programs and other
institutional feeding services have rapidly increased their use
of soy products in ground meat systems. More recently, ground
beef—soy mixtures have appeared in the retail market. Further
research is needed to determine the effects of 30% soy substitutions
on various quality characteristics such as, sensory evaluations,
lipid and moisture retention, and its effect on the storage quality
of cooked meat systems.

An ll-member taste panel evaluated the 0% and 30% soy sub—
stituted meat systems for flavor, juiciness, mouthfeel and overall
acceptability. Cooking losses were determined for both the 0%
and 30% soy substituted systems. Both raw and cooked loaves were
analyzed for moisture and total lipid, which was extracted using
chloroform-methanol and separated into neutral and phospholipid
fractions using an activated silicic acid. The 2-thiobarbituric
acid test measured the rate of oxidative rancidity in these systems
when products were stored under refrigerated (5°C) and frozen (-llOC)
conditions for short periods of time.

The 30% soy substitution did not adversely affect the quality

characteristics of the ground beef and turkey systems. But the

CLAUDIA WHIPPLE

soy substitution did lower the flavor, juiciness and overall accept-
ability scores of the pork system. The use of 30% soy substitution
decreased the total and drip loss, whereas it did not affect the
volatile losses.

Thirty percent soy in these ground meat systems did not increase
moisture retention. While 30% soy did significantly decrease the
fat content of the raw beef, pork and turkey meat systems there was
no difference between the fat content of the cooked 0% and 30%
soy substituted meat systems. The lipids retained in both the 0%
and 30% soy substituted beef and pork systems apparently were the
same.

Although 30% soy substituted meat systems appeared to have a
slightly lower TBA values during refrigerated and frozen storage,

soy does not appear to prevent development of warmed-over flavor.

QUALITY CHARACTERISTICS OF SOY SUBSTITUTED

GROUND BEEF, PORK AND TURKEY SYSTEMS

By

Claudia Whipple

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

1974

M
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ACKNOWLEDGMENTS

I wish to express my sincere appreciation to Dr. Mary Ellen Zabik
for her patience and guidance throughout my entire course of

graduate study and the preparation of this thesis.

Special thanks are extended to Dr. L. R. Dugan, Jr. for his
encouragement and for the use of his laboratory equipment.
Appreciation is expressed to Dr. L. E. Dawson and Dr. E. LeGoff

for their critical review of this dissertation.

Finally, I would like to thank my family for their support and

encouragement which made it possible for me to obtain this degree.

ii

TABLE OF CONTENTS

INTRODUCTION......... ........................
REVIEW OF LITERATURE .......... . ..............

Soy Protein Products..... ............

Soy Protein Forms... ..... ....

Functional Properties........

Uses of Soy Proteins.........
Soy Protein in Meat Systems..

Quality Deterioration in Stored Meats ....... ..........

Mechanism of Lipid Autoxidation....... ...... ..
Lipids Responsible for Oxidation..............
Factors Influencing the Rate of Oxidation.....
Catalysts in Meat Systems.............
Antioxidants in Meat Systems..........
Measurement of Osidative Rancidity............

Development of the TBA Test.. ........ .
EXPERIMENTAL PROCEDURE ............. . ..........................
Preparation and Baking of Loaves ...... . .......... .....
Formula.............. ............ .. ... . . .

MethOd of Preparation........... ... ...... ..

BakingOOOOOOOOO0.0.0.000.........OOOOOIOOOOOOO
Division of Loaves for Analysis...............

Analyses....... ....... ... .......... ..

senSOWooo-oooooooooooo ......

Chemical........................ ..... .........
Moisture Analysis............. ...... ..
Total Lipid Extraction................
Separation of Neutral Lipid and
Phospholipids.......................
2-Thiobarbituric Acid Determination
‘ for Turkey and Beef.................
Modification for the TBA Method

for Ham .......... ..

Statistical ..... . ...... ......

iii

b

O\U‘IU|4-\

10
11
11
l4
17
18

23
23
23
23
25
26
26
26
27
27
27
28
29

31
32

Page

RESULTS AND DISCUSSION ......................................... 33
Cooking Losses.. ....................................... 33
Sensory Evaluation.... ................................. 36
Moisture.. ............................................. 41
Total Lipids... ............. . .................. ........ 45
Phospholipid and Neutral Lipid ..................... .... 49
TBA Determinations ............................... . ..... 53
SUMMARY AND CONCLUSIONS .................................... .... 63
PROPOSALS FOR FUTURE RESEARCH ............ . ......... . ...... ..... 66
BIBLIOGRAPHY ........... . ...... .................... ............. 67
APPENDICES.............. .............. ... ..... ................. 78

I. Analyses of Variance for Preliminary Evaluation
of Various Sensory Characteristics of 0%, 15%
and 30% Soy Substituted Meat Systems............. 78

II. Score Card for Ground Meat Systsms................. 79

iv

Table

10

11

LIST OF TABLES
Page

Amount of ingredients (grams) used in 0% and 30% soy
substituted ground meat systems.... ...... . ....... ..... 24

Means and standard deviations of total cooking loss
(Z), drip loss (Z) and volatile loss (Z) of soy
substituted meat systems.............................. 34

Analyses of variance of total cooking loss, drip
loss and volatile loss of soy substituted meat
systemSOOOOO...0.0....O0.0.0.0..........OOOOOCOOOO.... 35

Means and standard deviations of sensory evaluations
of soy substituted meat systems ........ ............... 38

Analyses of variance of sensory evaluation of soy
substituted meat systemSOCOOOOOOOOOO ..... ......OOOOOOO 39

Mean values and standard deviations of percentage
moisture of raw and cooked soy substituted meat
systemSOOOOOOO ..... O. ..... O. ..... ......OOOOOOOOOO ..... 41

Analyses of variance of percentage moisture of raw
and cooked soy substituted meat systems ..... .......... 42

Means and standard deviations of total lipid (Z),
phospholipid (Z) and neutral lipid (Z) of raw and
cooked soy substituted meat systems ..... .............. 46

Analyses of variance of total lipid, phospholipid
and neutral lipid of raw and cooked soy substituted
meat systems.......OOOOOOOOOOO.....OOOOOOOOOOOOOOOOIOO 47

Means and standard deviations of TBA numbers fgr soy
substituted meat systems stored at 5°C and -11 C...... 54

Analyses of variance for TBA numbers for storage
period and percentage soy in soy substituted meat
systemSOOOOOOOOOOOI............OOOOOIOOOOOOOCO00...... 55

LIST OF FIGURES

Figure Page

1 TBA Numbers for 0% and 30%osoy substituted ground
beef stored at 5°C and -11 C ..... ..................... 56

2 TBA Numbers for 8% and 30% soy substituted ground
pork stored at 5 C and -11°C.... ........ ......... ..... 57

3 TBA Numbers for OZOand 30% 38y substituted ground
turkey stored at 5 C and -11 C................. ...... . 58

vi

INTRODUCTION

The utilization of soy products has increased significantly
in recent years. On February 22, 1971, the United States Department
of Agriculture's Food and Nutrition Service issued Notice 219, which
permitted the use of up to 30% rehydrated textured vegetable products
to replace up to 302 of the meat or meat alternate portion in the Class
A school lunch menu. Approximately 23 million pounds of textured
vegetable protein (hydrated weight) were used in the school lunch
program during the 1971 - 1972 school year; this figure doubled the
following year (Butz, 1974). Since this approval of the use of tex-
tured vegetable products, there has also been a tremendous increase
in use in hospitals and other institutional food services and more
recently hamburger-soy mixtures have become available in the retail
market.

A major drawback to the use of soy in meat systems is the
consumer acceptance of the finished product. Soy companies advertise
that the use of soy in a meat system increases juiciness, flavor and
better shape retention (Rakosky, 1974). Soy products often have a
characteristic off-flavor described as "beany" or "cereal-like".

If the meat formulation is not prepared with enough seasonings to
mask the off-flavors, then consumers often find these foods objectionable.
Textured soy products are engineered to look, feel and taste like

ground meat; useage in beef systems is widely accepted, however, their

use in other systems such as with ground pork or ground turkey, should
be investigated more thoroughly.

Many hospitals use textured soy in their ground meat systems.

The use of 30% rehydrated soy in a ground beef product reduces by

almost 30% the amount of fat present in the raw product. Therefore,

one might expect a similar decrease in the amount of fat in the cooked
product, thus reducing both the amount of fat and the number of calories.
Since two major functional properties of soy proteins are their ability
to retain fat and moisture, it would be beneficial to investigate the
effects the incorporation of textured soy protein in ground meat systems
would have on the retention of lipids and moisture after cooking.

School lunch programs and hospitals often use rotating menus,
with the majority of schools being on a three week menu cycle. A
common practice in these institutional feeding programs is to store,
either by refrigeration or freezing, the cooked left-over meat until
it can be used again in the cycle. For example, left-over cooked
meatloaf might be frozen for two weeks, thawed, reground and added
to another product, such as spaghetti.

A major problem with cooked meat which has been stored at either
refrigeration or freezing temperatures is the development of off-
flavors and off-odors attributed to the autoxidation of the unsaturated
fatty acids present in the meats. Numerous studies have shown that
various meat systems, such as beef, pork and turkey, undergo lipid
oxidation at different rates when stored under the same conditions.

In a few studies the addition of soy to meat systems exhibits various

degrees of antioxidant ability. Further studies on the inhibition

of the development of a warmed-over flavor (WOF) in ground meat systems
are needed.

The objectives of this study are to investigate the use of a
textured soy product on the quality characteristics of ground beef,
pork and turkey. These characteristics include: sensory evaluations;
the effect of soy on cooking losses; the percentages of lipid and
moisture; a comparison of the neutral lipids and phospholipids; and
the rate of autoxidation which occurs in these soy substituted meat
systems when stored under refrigeration and freezing temperatures for

short periods of time.

REVIEW OF LITERATURE

Soy Protein Products
Soybean protein products are available in a wide variety of
forms for incorporation into numerous food products. Soy proteins
exhibit a number of important functional properties, and increase the
nutritional quality of the foods to which soy products have been
added. Their functional properties, however are the significant factors

in determining whether or not the product will be marketable.

Soy Protein Forms

Soy protein products are processed into several forms: flours,
grits, concentrates, isolates and textured soy proteins. Processing
methods have been reported extensively in the literature (WOlf, 1972;
Smith and Circle, 1972; Horan, 1974; Lockmiller, 1973).

Soy flours and grits contain approximately 50-55% protein. They
are prepared from flakes following hexane extraction to remove the 011.
These flours and grits can contain various levels of fat to yield the
following classifications: full fat, high fat, low fat and defatted,
the latter of which contains less than 1.0% fat. The amount of carbo-
hydrate present varies with the type of soybean and the method of
processing. An average soy flour contains approximately 33.52 carbo-
hydrate, of which 14.02 is soluble and 19.52 is insoluble (Koran, 1974).

Soy protein concentrates contain approximately 702 protein and can

be obtained by using an aqueous alcohol or dilute acid leach to remove

the soluble carbohydrate from the defatted flakes and flours. Soy
isolates are obtained by further processing soy flour to remove the
remaining water insoluble carbohydrate. This product contains up
to 90% protein,

Textured soy proteins are classified as being either extruded or
spun. A thermoplastic extrusion process, using heat and pressure, is
used to obtain an extruded product. The spun soy protein product is
obtained by preparing an alkalized spinning dope that is forced through
a spinneret and the fibers are then coagulated. The size, shape, color,
flavor and added nutrients can be altered to yield a wide variety of

products.

Functional Properties

Important functional properties, which vary with the type of soy
protein product, include: dispersibility, gelation, foaming, emulsion
stability, moisture and fat absorption (Smith and Circle, 1972;
Rakosky, 1974; Lockmiller, 1973; Wilding, 1974). Retention of functional
properties of soy protein products depends on the damage or denatura-
tion of protein during processing, the most critical step being removal
of the solvent during preparation of a defatted flake or flour (Koran,
1974). All of these functional properties must be considered before
a particular soy product is incorporated into a food product, because

of their overall affect on the textural properties of the end product.

Uses of Soy Proteins
Depending on the functional property desired, soy protein products
can be utilized in a number of products. Flours and grits are often

used in baked products. Since soy proteins cannot form a dough structure,

as can the gluten proteins of wheat, soy flour can be used only up

to a certain percentage before quality is decreased. Concentrates

and isolates are often used in processed meat products, baked goods,
dairy type products, frozen desserts and beverages. Legal limits have
been established to limit the amount of soy concentrate and isolate

in meat products.

Textured soy protein products are used to extend and supplement
ground meat systems. With the establishment of the FNS Notice 219
(USDA, 1971) allowing up to 30% rehydrated vegetable protein in a meat
product for Class A school lunch menus, there has been an increase

in the use of soy as ground meat extenders.

Soy Protein in Meat Systems

Nollman and Pratt (1972) substituted 2.22 textured vegetable
protein in meatloaves and evaluated them for cooking losses, texture,
juiciness and flavor and the cooked loaves were analyzed for moisture,
protein, ash and fat. They noted no differences in cooking losses,
protein or the amount of fat content when the soy-loaf was compared to
the control meatloaf. Judge g£_gl,, (1974) used 162 and 242
substitution with rehydrated soy protein concentrate in beef patties
and compared bacterial counts, light reflectance, cooking shrinkage and
paper release.

Carlin and Nielson (1974) used 30% soy substitution in beef loaves.
They investigated the retention of fat and moisture following reheating
after loaf frozen storage; differences in flavor; comparison of cooking
losses, and the quality of precooked loaves stored at -4°F for 0, 2,

4 and 6 months. Brant (1974) reported the use of textured soy products

at levels of 91, 182 and 27% in beef patties and their affects on
the protein, fat, moisture and ash content of the raw versus the
cooked state. However, due to "insufficient sample" the proximate
analyses of the 0% soy substituted cooked beef patties was not done,

so an accurate comparison could not be made.

Quality Deterioration in Stored Meats

When cooked meat is stored, even for relatively short periods of
time, the quality of reheated meat is usually less desirable than was
the freshly cooked meat. Various terms, such as "stale", "rancid"
and warmed-over" have been used to describe these undesirable flavor
and odor changes that develop in reheated cooked meat. Tims and Watts
(1858) reported that a rapid deterioration in flavor of cooked meat
occured after a few hours of storage at refrigeration temperatures.
When frozen pork sausage was stored for a relatively short period of
time, off-flavor developed which has been recognized in the meat industry
as "freezer-taste" (Turner 35 21,, 1954). Pre-cooked beef developed
off-odors and flavors more quickly after storage at refrigeration than
freezer temperatures (Chang £5 31,, 1961). Cash and Carlin (1968)
reported that the development of off-flavor was lower in the cooked
meat from raw frozen turkey roasts than from roasts pre-cooked before
storage at 00F.

Lipid autoxidation is responsible for undesirable changes in
odor, flavor and color (Tins and Watts, 1958; Greene, 1969). Raw and
frozen meat gradually deteriorate in quality due to lipid oxidation,

while lipids of cooked meat oxidize much more rapidly.

Mechanism of Lipid Autoxidation

The mechanism for lipid autoxidation has been reported extensively
in the literature (Dugan, 1961; Sherwin, 1972; Sato and Herring, 1973;
Schultz 25 £13, 1962). The free radical mechanism involved in oxida-
tion of lipids is believed to take place in three stages: initiation,
propagation and termination.

Initiation involves the formation of a free radical (R-) from
an unsaturated fatty acid (RH) as follows:

R11 4- 02— R' + OH
Initiators of autoxidation can be light, perticularly ultra-violet,
heat and heavy metals, such as copper and iron.

Propagation involves the formation of peroxide free radicals
(R00-) from the fatty acid free radicals (R-). These compounds are
then capable of abstracting another methylene hydrogen from another
fatty acid to form further free radicals (R5) and hydroperoxides
(ROOH). This reaction can be summarized as follows:

R° + 02 -——— ROO°
1100- + R’H — noon + R’-

This free radical chain mechanismiwill continue until termination
occurs when non-radical species are formed. A few of these species
are shown in the following reactions:

no + 1(- —- RR’
R- + 1(00- -— ROOR’
ROO- + 3300- ——- ROOR’ + 02
The R. may be a free radical inhibitor, such as an antioxidant,

which may react with the chain-continuing free radicals to form inert

end products (Dugan, 1961).

Unsaturated fatty acids are much more susceptible to autoxidation
due to the ease of removal of the ahydrogen to the double bond.
Methylenic hydrogens situated between two double bonds are much more
susceptible to free radical attack than those adjacent to one double
bond (Gunstone and Hilditch, 1945). The free radical formation,
addition of oxygen and eventual addition of another hydrogen, to form
hydroperoxides, can be depicted as follows:

-o-o- R’H ,
-(':-c-c- -—; -c- =c- —-» -<':-c=c- -—+ -?-c=c- + R-

H E E
a

Oxidation of various monenoic (such as oleic acid) and dienoic
(such as linoleic acid) fatty acids involves abstraction of the a
hydrogen and formation of various radical isomers, which, due to
shifts in the double bonds, yield numerous isomeric hydroperoxides.

For example from oleic acid (C 18:1) there is a possibility of four
isomeric hydroperoxides. From linoleic acid (C 18:2) there is a
theoretical possibility of three isomeric hydroperoxides: ll-
hydroperoxido -9,12-octadienoic acid, 13-hydroperoxido—9,ll-octadienoic
acid or 9-hydroperoxido-10,12-octadienoic acid. However, the latter
two occur more frequently.

The oxidation process becomes more complicated when the primary
products of autoxidation, the hydroperoxides, decompose, either by
thermal instability or by reacting with other compounds to produce
more free radicals, which then contribute to the chain reaction (Dugan,

1961). Hydroperoxides are colorless and odorless compounds and do

10

not account for the off-flavors and odors associated with lipid autoxi-
dation (Watts, 1954). HydrOperoxide degradation products are believed
to be responsible for off-odors and flavors characteristic of rancid
fats and oils (Kaunitz, 1962; Sherwin, 1972). Hydroperoxides undergo
scission to produce free radicals, which in turn react with more
compounds to form other compounds, such as aldehydes, ketones, alcohols,
acids, lactones and other unsaturated hydrocarbons which are chiefly
responsible for the off-odors and off-flavors (Lea, 1962). The follow-
ing reaction scheme illustrates scission and dismutation of hydroperoxide

compounds to carbonyl and hydroxy compounds:

1;! H
R—g-R’ ————-) R-g-R’ + on
n
R.
RH RO
R-c-o
R—é-R’ + R R-g-R fi- R-g—R’ + RH

...
ROB

Lipids Responsible for Oxidation

Lea (1957) reported that bound lipids contribute to the reactions
responsible for rancid odors and flavors in cooked meat. The reactivity
of the lipid is influenced by the degree of unsaturation that makes
up the particular lipid. Phospholipids from a particular tissue were
also found to be more unsaturated than triglycerides from the same
source. Hornstein g£_gl,, (1961) found that 19% of the fatty acids

in beef phospholipids had four double bonds, whereas only 0.12 of the

ll

triglycerides showed the same degree of unsaturation. The presence

of these highly unsaturated phospholipids renders the lipid more
susceptible to oxidation. Younathan and Watts (1960) showed that
proteolipids and phospholipid fractions contributed to the stale
flavors in cooked rancid pork, whereas the triglyceride fraction

did not. Campbell and Turkki (1967) found that neutral lipids were
lost more readily during cooking than phospholipids. Hornstein §£_§l,,
(1961) postulated that phospholipids were found in the bound form

and would not be as easily lost during cooking.

Factors Influencing the Rate of Oxidation

The extent to which lipid oxidation occurs during refrigerated
or frozen storage of meat and meat products is influenced by several
factors. These factors include fat characteristics, the temperature
at which it is stored, the packaging material, the storage period and
the presence of either antioxidants or pro-oxidants, whether naturally
present or added.

Catalysts in Meat Systems. Various types of compounds have been
implicated as having catalytic effects in lipid oxidation. Tappel
(1952,1953a) demonstrated that hematin compounds, such as hemoglobin,
hemin and cytochromes are powerful catalysts at 0°C.

The valence state of the heme protein is important, with the
ferric hemes being more active than the ferrous hemoproteins (Younathan
and Watts, 1959). Fox (1966) reported that during cooking pigments
are irreversibly converted to the denatured ferric chromogen, therefore
acting as pro-oxidants in uncured meats. No significant increase in

oxidative rancidity is noted in stored, cooked, cured meat as a result

12

of the pigment being present as the pink ferrous nitric oxide hemo-
chromogen form.

Non-heme iron has also been implicated as pro-oxidants (Lui,
1970; Sato and Hegarty, 1971). Lui and Watts (1970) removed the
Inetnwoglobin with hydrogen peroxide and significant lipid oxidation
was noted without the metmyoglobin being present. Sato and Hegarty
(1971) showed that non-heme iron accelerated the oxidation of lipids
that had been extracted from cooked meat. Ferrous iron has been shown
by Marcuse (1971) to have pro-oxidant ability. Sato and Hegarty (1971)
also reported that ferrous iron, in the presence of a small quantity
of ascorbic acid would act as potent lipid oxidation catalysts. Certain
metal salts, such as cuprous and ferric salts, which act as catalysts
at low levels, often exhibit inhibitory characteristics at higher
levels (Marcuse and Fredriksson, 1971).

Sodium chloride is often an added ingredient to meat products,
i.e. curing brines for hams. The oxidation accelerating effects of
salt have been reviewed extensively in the literature (watts, 1954;
Dugan, 1961; Zipser £5 21., 1964; Love and Pearson, 1971).

Early studies cited an increase in lipid oxidation in raw
refrigerated and frozen cured pork (Watts and Peng, 1947a; Watts and
Pend, 1948). Chang and Watts (1950) reported that the amount of free
moisture in the food system determined whether salt would increase
or decrease lipid oxidation. They observed that 102 salt solutions
inhibited lipid oxidation slightly, however, above 151 they noted
an increase in oxidation. When equivalent concentrations of sodium
chloride were brought into contact with fat over a wide surface area,

much higher peroxide values were obtained with samples prepared by

12

of the pigment being present as the pink ferrous nitric oxide hemo-
chromogen form.

Non-heme iron has also been implicated as pro-oxidants (Lui,
1970; Sato and Hegarty, 1971). Lui and watts (1970) removed the
Inetnwoglobin with hydrogen peroxide and significant lipid oxidation
~ was noted without the metmyoglobin being present. Sato and Hegarty
(1971) showed that non-heme iron accelerated the oxidation of lipids
that had been extracted from cooked meat. Ferrous iron has been shown
by Marcuse (1971) to have pro-oxidant ability. Sato and Hegarty (1971)
also reported that ferrous iron, in the presence of a small quantity
of ascorbic acid would act as potent lipid oxidation catalysts. Certain
metal salts, such as cuprous and ferric salts, which act as catalysts
at low levels, often exhibit inhibitory characteristics at higher
levels (Marcuse and Fredriksson, 1971).

Sodium chloride is often an added ingredient to meat products,
i.e. curing brines for hams. The oxidation accelerating effects of
salt have been reviewed extensively in the literature (Watts, 1954;
Dugan, 1961; Zipser §£“££., 1964; Love and Pearson, 1971).

Early studies cited an increase in lipid oxidation in raw
refrigerated and frozen cured pork (Watts and Peng, 1947a; Watts and
Pend, 1948). Chang and Watts (1950) reported that the amount of free
moisture in the food system determined whether salt would increase
or decrease lipid oxidation. They observed that 102 salt solutions
inhibited lipid oxidation slightly, however, above 152 they noted
an increase in oxidation. When equivalent concentrations of sodium
chloride were brought into contact with fat over a wide surface area,

much higher peroxide values were obtained with samples prepared by

12

of the pigment being present as the pink ferrous nitric oxide hemo-
chromogen form.

Non-heme iron has also been implicated as pro-oxidants (Lui,
1970; Sato and Hegarty, 1971). Lui and Watts (1970) removed the
Inetnwoglobin with hydrogen peroxide and significant lipid oxidation
- was noted without the metmyoglobin being present. Sato and Hegarty
(1971) showed that non-heme iron accelerated the oxidation of lipids
that had been extracted from cooked meat. Ferrous iron has been shown
by Marcuse (1971) to have pro-oxidant ability. Sato and Hegarty (1971)
also reported that ferrous iron, in the presence of a small quantity
of ascorbic acid would act as potent lipid oxidation catalysts. Certain
metal salts, such as cuprous and ferric salts, which act as catalysts
at low levels, often exhibit inhibitory characteristics at higher
levels (Marcuse and Fredriksson, 1971).

Sodium.chloride is often an added ingredient to meat products,
i.e. curing brines for hams. The oxidation accelerating effects of
salt have been reviewed extensively in the literature (watts, 1954;
Dugan, 1961; Zipser gt_gl,, 1964; Love and Pearson, 1971).

Early studies cited an increase in lipid oxidation in raw
refrigerated and frozen cured pork (Watts and Peng, 1947a; Watts and
Pend, 1948). Chang and Watts (1950) reported that the amount of free
moisture in the food system determined whether salt would increase
or decrease lipid oxidation. They observed that 102 salt solutions
inhibited lipid oxidation slightly, however, above 152 they noted
an increase in oxidation. When equivalent concentrations of sodium
chloride were brought into contact with fat over a wide surface area,

much higher peroxide values were obtained with samples prepared by

13

drying rather than in solution. Therefore, in food systems where salt
and low free moisture are present, as in partially dried or frozen
systems, an increase in lipid oxidation would be expected.

The mechanism by which salt increases the rate of lipid oxidation
is not fully understood and the studies in the literature are often
contradictory. Banks (1937) and Lea (1939) proposed a theory that
salt was not a pro-oxidant but that it only promoted the activity of
lipidoxidases. However, later studies by Banks (1944) and Tappel
(1952,1953a) demonstrated that no lipidoxidase was present in the meat
but rather the increase in autoxidation was due to the heme pigments,
which are powerful catalysts of lipid oxidation. Hills and Conochie
(1946) attributed the direct oxidative affect of the sodium chloride
to the reactivity of the chloride ion. However, watts and Peng (1947a)
and Ellis £5 21., (1968) showed that various chlorides and halogens
did not have the same affect as sodium chloride, thereby casting
doubt on Hill's theory.

Younathan and Watts (1959) observed that oxidative reactions
occured less readily in cured meats which retained their pink color.
Sodium nitrite converts the pigments to the catalytically inactive
ferrous nitric oxide. This results in a higher stability towards
lipid oxidation under refrigeration conditions than with uncured
cooked meat in which the pigment is present as ferric hemochromogen.

As the cured meat pigment is slowly oxidized to the ferric form, a
resulting increase in lipid oxidation would be expected. Salt has been
shown to increase hematin oxidation to the ferric form, with or without

fat present. Thus, the role of salt may be to oxidize the hematin to

14

the ferric state, thereby initiating oxidation of nearby unsaturated
lipids (Dugan, 1961).

Zipser g£_§l,, (1964) demonstrated that heme catalysis was
stopped by the addition of nitrite, but that it was the sodium Chloride
that increased lipid oxidation of ham in the freezer. Heme catalysis
and sodium chloride catalysis increased when nitrite was absent.
Ellis g£_§l,, (1968) compared the effects of 0.03% sodium nitrite,
2.0% sodium chloride and a combination of the sodium chloride and
sodium nitrite on the rate of lipid oxidation. They noted that trace
amounts of sodium nitrite promoted lipid oxidation at a somewhat higher
rate than that of the sodium chloride. The combination of sodium
chloride and sodium nitrite promoted a faster rate of oxidation than
the sodium chloride alone. There appeared to be an independent, yet
additive effect of these two compounds on lipid oxidation. Ellis and
co-workers proposed that these two compounds activated different

catalytical systems, the mechanism of which remains unknown.

Antioxidants in Meat Systems. Antioxidants are substances that
slow down the rate of lipid oxidation. The choice of the antioxidant
is determined by the requirements of the systems and the characteristics
of the antioxidant being used. The antioxidant should be effective
at low concentrations, have no undesirable characteristics, be safe
to handle and use and be low in cost. These compounds are generally
aromatic compounds which are amine or phenolic in nature (Dugan, 1957).
Antioxidants terminate the free radical chain mechanism by any
of the following ways: by donating an electron to the peroxy radical;

by donating a hydrogen to the peroxy radical before or after being

15

partially oxidized. An example of how a ring substituted phenol acts

as a chain terminator can be illustrated as follows:

R1 _H R1
(3) A .
112.11 , R2 0 ———-) R2
R
R3 3

 

 

 

 

I II III
(b) 2 II ; dimer
(c) III + 02 A #> R2 R1
3:0
oOO
R
3

R2 R1
(d) III + R00 ————$ K30
R00
R3

Termination will result if either (a), (b) or (d) occurs. However,
if (c) occurs the phenol will react as a transfer agent without decreasing
the overall rate of autoxidation. Most antioxidants have optimum
levels at which they function but they can exert pro-oxidant effects
by acting as transfer agents, as in (c) (Dugan, 1957).

Antioxidants that are often added to meat systems include
n—propylene gallate (PG), butylated hydroxyanisol (BHA), and synergists,
such as polyphosphates, citric acid and sodium ascorbate.

Lineweaver £5 31., (1952) and Klose g£_gl,, (1952) investigated
the use of various antioxidants in frozen creamed turkey and frozen
turkey, respectively. Neille and Page (1956) used various levels of

monosodium glutamate, BHA and full fat soy flour in frozen ground pork.

16

Little difference was noted between the soy treated raw and cooked
samples. There was no significant differences between the different
levels of antioxidants used.

Naturally occuring antioxidants include the plant flavanoids
and compounds produced during prolonged heating at high temperatures
(Watts, 1962). Hot water extracts from various vegetable sources
were reported to retard lipid oxidation in cooked meats (Ramsey and
Watts, 1963). Researchers have attributed the antioxidant activity
of various vegetable extracts to flavanoids and their ability to
accept free radicals and break the chain reaction (Ramsey and watts,
1963; Pratt and Watts, 1964). Pratt (1972) investigated the use of
various soybean products. He noted potent antioxidant activity in
lipid-aqueous systems and postulated that this ability was due to
flavanoid components that occur naturally in soybeans.

Zipser and Watts (1961) reported that under prolonged heating,
antioxidant substances were produced in uncured canned meats. Sato
£5 51,, (1973) noted that browning reaction produced which occured
during the interaction of sugars and amino acids, inhibited the
development of warmed-over flavor (WOF) in cooked ground beef.
Reductic acid which is formed during browning reactions (Hodge, 1963)
was found to be a very effective inhibitor. It was thought that this
was due to its ascorbic acid type reaction. Maltol, produced from a
Maillard type reaction, was also found to be an effective inhibitor,
probably acting as a free radical inhibitor, however the exact mechanism
in unknown. This study also investigated the use of various vegetable
protein products (cottonseed, textured soy flour and textured vegetable

protein) in ground beef. There was a noted decrease in the development

17

of WOF during refrigeration, when these products were used. Sato

and co—workers (1973) suggested that the inhibition of the development
of WOF in these products was due to the production of antioxidant
substances by the interaction of amino acids and carbohydrate upon
heating. Vegetable soy protein products contain appreciable amounts
of protein and carbohydrate (Rakosky, 1971), which would contribute

to these browning reaction.

Measurement of Oxidative Rancidity

Watts (1954) and Dugan (1955) have reviewed the objective methods
commonly used to determine the degree of oxidative rancidity that has
occurred in foods, fats and oils. The most commonly used tests for
determining the degree of rancidity are: The active oxygen method,
determination of carbonyl compounds, peroxide values, which measures
the degree of unsaturation and the 2-thiobarbituric acid test (TBA),
which measures the amount of malonaldehyde.

The majority of the tests for oxidative rancidity involve the
extraction of the fat (mainly triglycerides) from.meat tissues. How-
ever, the primary lipids involved with autoxidation and the development
of rancidity are phospholipids and proteolipids (Younathan and Watts,
1960) which are not extracted by normal hydrocarbon solvents, but require
more polar solvents such as methanol and ethanol (Lea, 1957). The
TBA test has the advantage that the fat does not need to be separated
from the other meat tissues. It would therefore be expected to measure
the malonaldehyde produced from the autoxidation that has occurred
in all of the lipid fractions. The TBA test also measures an end

product of lipid autoxidation, malonaldehyde, while the peroxides are

18

intermediate compounds of autoxidation which do not accumulate due to
their rapid decomposition (Watts, 1954).

Malonaldehyde itself does not contribute to off-odors and flavors
(Tarladgis g£_§l,, 1960). However these researchers did show a highly
significant correlation between the TBA test and sensory evaluation
of this rancid odor. Zipser g£_§l,, (1964) observed correlation of
rancid odors and TBA values with cured and uncured pork. Kwon and
Watts (1963) noted that the production of malonaldehyde was a useful
indicator of flavor deterioration. The TBA test has been used to
determine the degree of rancidity in a wide range of products which
include dairy products, meats, fish, baked and cereal goods and fats

and oils (Corliss, 1963).

Development of the TBA Test. Animal tissues, incubated aerobically,
were found to produce a red color when reacted with 2-thiobarbituric
acid (Kohn and Liversedge, 1944). They suggested an unidentified
carbonyl compound was responsible for the color development. In 1947
Bernheim and co-workers postulated that the color was due to a pro-
duct of oxidation from unsaturated fatty acids. Wilbur 25 El}: (1949)
observed the ability of various aldehydes and sugars to develop color
and concluded that it was the result of a three carbon compound.

The compounds responsible for the Kreis color reaction test for
rancid fats were thought to be the result of epihydrin aldehyde or its
acetals (Powick, 1923). Patton and co-workers (1951) questioned this
reasoning and found evidence that malonic dialdehyde was responsible
for Kreis color reaction. Patton and Kurtz (1951) also demonstrated
that malonic dialdehyde produced a red color when heated in the presence

of 2-thiobarbituric acid.

l9

Sinnhuber g£_§l,, (1958) proposed that the red pigment was a
condensation product of two molecules of 2-thiobarbituric acid and
one molecule of malonaldehyde with the elimination of two molecules

of water, which can be illustrated as follows:

HS r) 0H s-{K SH
0 o
\\ ’x 4
+ C-CHz-C + H 0
N 3’ \a \ =CH-CH-CH \ 2
on on

Upon acid hydrolysis 1,1;13-tetraethoxpropane (TEP) yields malon-

 

aldehyde. It was then possible to specify a "TBA Number" as mg of
malonaldehyde per 1,000 3 sample (Sinnhuber and Yu, 1958).

Dahle st 21., (1962) proposed a mechanism of malonaldehyde
formation from conjugated fatty acids with three or more double bonds.
They theorized that with the 8 ° Y unsaturated peroxide radicals, a
5 membered peroxide ring would be formed as shown in the following

reactions:
ICH2\

CH-CH
R- cu-CH’ ‘CH CH- cn-R'

1 °2
ICH'CH\ ICE».

R-CH-CH (‘11 CH=CH-R’
g B Y

on. 1 CH CH
R-CH-CH’ CH‘CH’ 2\TH/ \R'

—0

20

The formation of malonaldehyde can then take place as follows:

ICH'C‘RCHICH» IGKR.

R-CH=CH ffl

O

' CH-CH- ~cn
R-CH=CH/ + fl/w‘lc' + ‘R’
o o

Lillard and Day (1964) reported the formation of malonaldehyde from
the oxidation of various dienals, produced as result of oxidation of
unsaturated fatty acids. There is then the possibility that malonalde-
hyde can be produced from autoxidation of polyunsaturated fatty acids
and from the oxidation of secondary products of autoxidation.

There have been reported in the literature a number of different
ways to perform TBA tests (Sidwell g£_§l,, 1954; Turner ggugl,, 1954;
Sinnhuber and Yu, 1958; Sunnhuber 3531:, 1958; Tarladgis, _e_t__§_1_.,
1960; Tarladgis g£_al,, 1964; Marcuse and Johansson, 1973).

Sidwell g£.§l,, (1954) described a steam distillation method for
dried milk, a fraction was then reacted with TBA and the color read
directly. Turner and co—workers (1954) reacted pork with TBA in come
bination with trichloroacetic and phosphoric acid, the color was then
extracted with an iso-amyl alcohol-pyridine mixture. Fishery products
were heated with TBA in the presence of hydrochloric and trichloro-
acetic acids and pyridine, the color was then extracted with petroleum
ether (Sinnhuber and Ye, 1958). Tarladgis g£_gl,, (1960) proposed a
technique which used a distillation step which heated the sample
directly rather than passing steam through it as had Sidwell's

earlier method (Sidwell g£_§l,, 1954).

21

Tarladgis and co-workers later observed that the structure of TBA
was altered upon acid-heat treatment (Tarladgis g£_§l,, 1964). They
proposed a new technique which did not involve an acid-heat treatment
but rather allowed the TBA and a sample of filtrate to stand for 15
hrs in the dark at room temperature. However, they noted that they
were still not sure whether acid and heat were needed to release malon-
aldehyde from precursors in the oxidized product.

Kwon and Watts (1963) postulated that pre-formed malonaldehyde
had reacted with other food components and would not be distillable.
They proposed the term "distillable malonaldehyde" when using the
TBA Number. Kwon and Watts (1964) observed malonaldehyde in aqueous
solution and drew several conclusions. Malonaldehyde is capable of
undergoing enolization from its diketo form (I) to its enolate anion (II)

which is nonvolatile. It is also possible to form a volatile chelated

form (III).
0 ’i‘
”\{x 5‘1} a BIA?
2 A N
I ‘ II III

Approximately'962 of malonaldehyde is in the enolic form (II)
in aqueous solution. These various tautomeric forms are very pH
dependent, the enolic form (II) occurs at a pH>7, while the chelated
form.(III) occurs at a pH<3. Maximum volatilization of free-preformed
malonaldehyde would therefore occur at a pH<3. Addition of acid
is then necessary to free malonaldehyde from secondary combinations
with other food constituents. The malonaldehyde in the enolate anion

form.might be stable against further irreversible reactions by formation

22

of metal chelates from which the malonaldehyde can be recovered by
acid and heat.

Other authors have reported the reaction of malonaldehyde with
various other compounds, found in food systems. Brown (1962) showed
a loss of malonaldehyde through its reaction with quanidine to form
2-aminopyrimidine, Kwon and Olcott (1965) observed interactions between
proteins and malonaldehyde. Buttkus (1966) reported reaction between
the amino acids of myosin and malonaldehyde. Crawford 22 El: (1966)
and Chic and Tappel (1969a) reacted malonaldehyde with glycine to form

an enamine.

EXPERIMENTAL PROCEDURE

Three ground meat systems, using 0% and 30% soy substitutions
were investigated to observe differences in sensory evaluations,
cooking losses, moisture, total lipid, phospholipid and neutral lipid
content and development of oxidative rancidity during short term

storage at refrigeration and freezing temperatures.
Preparation and Baking of Loaves

Formula

The basic formula used in this study was adapted from various
recipes which were investigated during preliminary research. Table 1
lists the formulas used for the three ground meat systems.

All of the ingredients were purchased in common lots. The soy
product was an unflavored spun vegetable protein.1 Turkey was ground
from thighs containing a natural proportion of skin, and purchased
from a Michigan poultry processor. Pullman hams, ground pork and
ground beef (20% fat) were obtained from the Michigan State University

Food Stores.

Method of Preparation
Enough meatloaf mixture of each variable was prepared for five

replications. The ham and turkey thighs were ground separately through

 

1Temptein, Miles Laboratories, Elkhart, Indiana.

23

24

a Hobart Food Cutter, Model 84181D, using a 3/16 in plate. The tex-
tured soy protein was rehydrated in cold water for 5 min. The ground
meat and rehydrated textured soy was then mixed for approximately

1 min in a Hobart Mixer, Model K-200, in order to thoroughly mix the
two ingredients. The remaining incredients were divided into thirds,
each portion was then added separately and mixed into the meat for
approximately 30 sec. Finally both the 0% and 30% soy substituted
meatloaf mixtures were then reground through the Hobart Food Cutter

to insure uniformity.

Table 1. Amount of ingredients (grams) used in the preparation of
02 and 302 soy substituted ground meat systems.

 

Meat system

 

 

Ingredient

Beef Turkey Porka
Ground meatb 1703 1703 1703
Bread Crumbs 207 207 207
Dried Onions 38 38 38
Salt 10 10 10
Poultry Seasoning 10
Bar-B-Q Sauce 75
Catsup 187

 

aA 50:50 mixture of ham.and pork was used.

bFor the 302 soy substituted loaves 1192 g of ground meat was used

in addition to 170 g of textured soy protein and 340 g of cold water.

25

Approximately 1500 g of meatloaf mixture was placed in a
10 x 4 x 35-in Ham Loaf Press and held under pressure for 5 min in
order to obtain loaves of the same degree of compactness. Each loaf
was then wrapped first in Reynolon Food Service Film, rewrapped in
aluminum foil and stored at -11°C for periods up to 5 weeks. The
loaves were removed from the freezer and thawed at 5°C for 14 hrs
prior to baking.

Since ham is susceptible to increased rancidity upon freezing,
the pork loaves were prepared on the day of baking from ground pork
purchased in a common lot and frozen at -11°C and ham which was held
at 5°C. The procedure was the same as the beef and turkey, except

that a Kitchen Aid Mixer, Model K—SA was used to mix the ingredients.

Baking

The 02 and 302 soy substituted loaves were randomly assigned
as two preparations for any one "baking" day. The loaves, which were
supported on racks in 9 x 12-in baking pans lined with aluminum foil,
were baked in a General Electric, 30-in compact oven Model CN 16,
with the damper half closed and the grid set at medium. The oven
temperature was maintained at 177jl°C by a Versatronik controller.
Loaves were baked to an internal temperature of 77°C, which was
determined by an iron constantan thermocouple lead inserted in the
center of the loaf. Upon removal from the ovens the loaves were allowed
to stand for 5 min before total, volatile and drip losses were de-

termined according to the method outlined by Funk.g£_a1,, (1966).

26

Division of Loaves for Analyses

The middle third of each loaf was used for sensory evaluation.
The end slices were removed and discarded. Three consecutive k—in
slices were taken from each end portion for the 2-thiobarbituric acid
tests. These slices were then wrapped in aluminum foil and samples
were stored at either 5°C for 0, 2 and 4 days or -ll°C for l, 2 and 3
weeks. Assignment of slices was rotated so that each slice was used
the same number of times for the TBA determinations at any one tempera-
ture and storage time. The remaining loaf was ground, mixed thoroughly

and used for moisture and lipid analyses.
Analyses

Sensory

Samples were assigned random numbers and served warm to an
ll-member trained taste panel. Taste panel members were trained so
that they could correctly identify samples containing soy protein in
paired comparison. Beef and turkey were used to familarize the panel
members with the score card. Preliminary research, which compared OZ,
152 and 302 soy substituted ground beef, showed that there were no
significant differences between quality characteristics of exterior
color, interior appearance, and interior color. (See appendix).
Since significant differences occurred for flavor, juiciness, mouth—
feel and over—all acceptability scores, these four quality characteris-
tics were evaluated in the present study using a descriptive score

card, with scores of 7 being optimum. (See appendix).

27

Chemical

Duplicate determinations were made for each analysis. Raw and
cooked ground meatloaf mixtures werenused for all analyses except
for the TBA determinations, which were carried out on cooked samples
only. Methanol and chloroform were glass distilled. The acetic acid
for the TBA determinations was refluxed with 2 g TBA/100 md acetic

acid for three hrs and then distilled.

Moisture analysis. Moisture in the raw and cooked meatloaf

 

mixtures was determined by drying 2 g samples, weighed to the nearest
0.001 g, for 6 hrs at 90°C and under a vacuum of 27-in of Hg and
reweighed following cooling. Percentage moisture in each sample

was calculated according to the following formula,

Z moisture =_w§_of moisture lost (3), x 100
wt of original sample (g)

 

Total Lipid Extraction. The total lipid extraction was carried
out using modifications of the procedure described by Bligh and Dyer
(1959). To maintain solvent relationships, 34 and 50 ml of distilled
water were added to 66 g samples of raw and cooked meatloaf mixtures,
respectively. Meatloaf samples were weighed to the nearest 0.001 g,
combined with appropriate water and blended with 100 ml of chloroform
and 200 ml of methanol in a Waring blender, attached to a powerstat to
reduce line voltage to 55 volts. An additional 100 ml of chloroform
and 100 m1 of distilled water were then added separately and the samples
blended 3 min after each of these additions.

The extract was filtered through a Coors No. 3 Buchner funnel,

lined with Whatman No. 1 filter paper, by the use of slight vacuum.

28

The blender, residue and funnel were rinsed with 5 - 10 ml aliquots
of chloroform and methanol, these washings were then added to the
filtered extract. The filtered extract was then placed in a 500 ml
separatory funnel; the side arm flask was rinsed with 5-10 ml ali-
quots of chloroform and methanol and added to the separatory funnel.
The lipid-containing chloroform layer was then transferred to a 250 m1
volumetric flask, and brought to volume with additional chloroform.
Ten milliliter aliquots of fat extract were pipetted into dried pre-
weighed 50 ml erlenmeyre flasks and the chloroform evaporated under
nitrogen. The percentage lipid, on a wet weight basis was calculated
based on the weight of the lipid content of the aliquot, according to
the following formula.

2 lipid - wt of lipid (g)/1O ml x 25 x 100
wt of sample (g)

In order to compare raw and cooked percentage lipid values, the
lipid percentages on a wet weight basis were converted to percentages
of lipid on a dry weight basis by the following formula.
2 lipid (dry wt) - Z lipid (wet wt) x 100
Z solids

Separation of Neutral Lipid and Phospholipid. The total lipid
fraction was separated into neutral lipid and phospholipid fractions
using modifications of the procedure described by Choudhury ggngl.,
(1960). This involved a separation on activated silicic acid, in
which the neutral lipids were removed by washing with chloroform,
followed by removal of phospholipid with methanol.

Silicic acid was activated by drying silicic acid in a 100°C

oven for 16 hrs. A slurry was prepared by the addition of chloroform

29

to a 5 g activated silicic acid and a 10 ml aliquot of lipid extract
in a 250 m1 beaker. This slurry was allowed to stand for 30 min at
room temperature. The slurry was then transferred to a 150 ml 60-M
Buchner funnel fitted with a fritted disk and then washed with 300-
400 ml of chloroform using slight vacuum. The remaining phospholipid
containing silicic acid was then washed with 200-300 ml methanol.
Each solvent was then decanted into a 500 m1 round bottom flask with
5-10 ml aliquots of the apprOpriate solvent which was used to wash
the side arm flask. A Rotovapor was used to reduce the volume of
solvent to 5-10 ml which was then decanted into a dried, preweighed
50 ml erlenmeyer flask. The remaining solvent was then evaporated

to dryness using nitrogen. Final traces of solvent were removed by
placing the flasks in a 100°C oven for 5 min. Percentages of neutral
lipids and phospholipids in the total lipid sample were calculated
according to the following formulas.

Z neutral lipid - wt of neutral lipid (g)/10 ml x 100
wt of total lipid (g)/1om1

 

 

Z phOSpholipid - wt ofphogpholipidp(g)110 ml x 100
wt of total lipid (g)/10 ml
2-Thiobarbituric Acid Determination for Turkey and Beef. The

TBA.method employed was similar to the distillation method as outlined
by Tarladgis g£_§l,,(1960). TBA determinations were done on cooked
samples which had been stored for 0, 2 and 4 days at 5°C and l, 2
and 3 weeks at -ll°C. The frozen slices were thawed for 14 hrs at
5°C before being analyzed. Each slice was ground before duplicate
samples were taken. A 10 g sample was blended for 2 min with 50 m1

of distilled water in a Waring blender at low speed. The mixture was

30

then quantitatively transferred to a 500 ml round bottom flask with
47.5 ml distilled water. The pH was lowered to 1.5 by adding 2.5 ml
of HCl (2:1). A small amount of Dow antifoam was sprayed into the
flask to prevent foaming. The distillation apparatus consisted of the
flask connected to a 300 mm Vigreaux distillation column, which was
attached to a Leibig condensor. Heating mantles were used to distill
the mixture as rapidly as possible. After 50 m1 of the distillate were
collected in a 100 ml graduated cylinder, it was stoppered and the
mixture inverted several times. Five milliliters of the distillate
were then pipetted into a 50 ml glass-stappered test tube and 5 ml
of 0.02 M TBA in 90% acetic acid were added. The contents were gently
mixed before boiling and placed in a boiling water bath for 35 min,
then tubes were placed in a cold water bath for 10 min. A sample from
the tube was read on a DB Spectrophotometer against a blank at a wave-
length of 532 nm. The Z T was converted to absorbance by Iscotables
(Iscotables, 1972).

In order to determine the distillation constant to obtain the
"TBA Number", a standard curve and percentage recoveries were obtained.

8M, 1 x 10‘8M, 9 x 10'9u, and 7 x 10'924) of

Dilutions (3 x 10-
1,1,3,3—tetraethoxypr0pane (TEP), which yield malonaldehyde on acid
hydrolysis, were used to obtain a standard curve. The TEP dilutions
were used to replace the 5 m1 of distillate and the procedure was
continued as previously outlined. The percentage recovery in all
systems was obtained by adding 5 ml of 3 x 10-8M TEP to the sample

before distillation and determining the amount recovered. Recovery

was calculated to be 70%.

31

Two different ways have been presented in the literature to
calculate the distillation constant (k). Tarladgis g£_§l,, (1960)
used the following formula.

k - cone in moles/5 ml distillate x M.W. of malonaldehyde
0.D. (absorbance)

x 107 x 100

wt of sample Z recovery

 

 

 

Witte 2; 21., (1970) however included the consideration of sample

equivalent and their formula is as follows:

k = §_ x MW x 106 x 100

P

;>

S = conc in moles/5 ml distillate (l x 10-8)

A = absorbance (0.146)
MW a molecular weight of malonaldehyde

E = sample equivalent (10 g/100 ml x 5 ml = 0.5)

P - Z recovery

"TBA Numbers" were calculated according to the distillation constant
as determined by Witte's method and reported as mg of malonaldehyde

per 1000 g of sample.

Modification of the TBA Method for Ham. According to Zipser

 

and Watts (1962) small amounts of nitrite are capable of significantly
reducing TBA numbers of rancid meat. This interference occurs in the
distillation step of the TBA procedure and it believed to be due to
nitrosation of malonaldehyde. Sulfanilamide is used to bind the

nitrite to form a diazonium salt. Since the pork mixture contained

SOZ ham, a determination of the amount of nitrite present was made.

Ten grams of meatloaf mixture were ground with 50 ml of double distilled

water for l min. This mixture was centrifuged for 5 min at 15000 rpm.

32

Ten milliliters of supernatant were pipetted into an evaporating dish
containing 10 ml of a 1:1 mixture of 12 sulfanilic acid in 30Z acetic
acid and 0.1Z napthylamine in 30Z acetic acid. The red color that

developed was compared to standards of NaNO ranging from 50 ppm

2
to 200 ppm. The 10 g sample of ham loaf contained less than 100 ppm'
nitrate, which according to Zipser and Watts (1962) was a "mild"
test. The only modification necessary to make was to use 1 ml of
0.5Z sulfanilamide and 49 m1 of distilled water, which was ground

with the 10 g sample of meat and the procedure was then continued as

previously described for turkey and beef.

Statistical

Analyses of variance between OZ and 30Z soy substitutions were
calculated by a Wang 600 computer for the following factors: sensory
evaluations of flavor, juiciness, mouthfeel and overall acceptability;
and total, drip and volatile losses. Analyses of variance between
OZ and 30% soy substitutions and raw and cooked states were calculated
by a Digital Computer, Model PDP-ll/40RSTS for the following factors:
total lipid; moisture; phospholipid and neutral lipid; and TBA values
for the two storage periods of 5°C and -11°C. Duncan's Multiple Range
Test (1957) was used to sort out significant differences revealed

by analysis of variance.

RESULTS AND DISCUSSION

Ground beef, pork and turkey meat systems, using OZ and 30Z
soy substitutions were prepared. Sensory evaluations, cooking losses
and determination of the rates of oxidative rancidity, during short
term storage at 50C and -ll°C, were determined on the cooked loaves.
The percentage moisture, total lipid, phospholipid and neutral lipid

content were determined for both the raw and cooked loaves.

Cooking losses

Total cooking losses were determined by measuring weight changes
between raw and cooked meats. Drip losses were designated as the
material that accumulated in the pan during cooking and volatile
losses were calculated as the difference between the total cooking
losses and drip losses. Total, drip and volatile cooking losses are
presented in Table 2, whereas summaries of analyses of variance for
cooking losses are presented in Table 2, whereas summaries of analyses
of variance for cooking losses are presented in Table 3.

The OZ soy substituted beef loaves had a 13.3Z total cooking
loss, whereas the 30Z soy substituted beef had a significant (p<0.05)
lower cooking loss of only 9.8Z. Analyses of variance established
a very high significant difference in the amount of drip loss between
the OZ and 30Z soy substituted beef. There were however, no significant

differences between the volatile losses of the two systems.

33

34

Table 2. Means and standard deviations of total cooking loss (Z),
drip loss (Z) and volatile loss (Z) of soy substituted
meat systems.

 

Cooking Losses

 

 

Meat System Z Soy __‘
Total Drip Volatile
o 13314.43 2.9:ro.3 10.4:1.2
Beef
30 9.8:1.8 0.4:0.l 9.4fl.7
0 15.8:l.4 5.9fl.4 10.0i0.2
Pork
30 12.2f2.3 0.4:0.1 11.812.l
0 16.6:0.7 0.5:0.l 16.010.7
Turkey
30 ‘ 15.6fl.5 0.1:0.1 15.5f1.5

 

3Based on 5 replications

35

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.Aufiafipmnoua mo Ho>oa «H we» as unmosmaawam««
.auHHHnmnoua mo Ho>oa um «so an uauofimaawam«

 

 

 

qu.o mmo.o mwo.o w canoes

mam.o «amm.o Rom.a H tnom hexane
a dance

Hmm.m wwq.H Neo.m a swan“:

Hmm.m *«aqwm.mm keooq.~m H mom xuom
a Hmuoa

omH.~ woo.o mmo.~ m afinufiz

som.~ «wwoam.mfl «as~.a~ H aom have
m Hooch

mawumao> aqua Hmuoa

mo oouoom soumhm umoz

mouoovm one:

 

.maoumhm puma wouauaumnam hon mo
mmoa oaaumao> vow mmoa mane .mmoa wowxooo Hmuou mo ooomwuo> mo mommaoa< .m manna

36

Analysis of variance showed that total cooking losses of 15.8Z
for the OZ soy substituted pork was significantly higher (p‘0.01)
than that of 12.2Z for the 30Z soy substituted pork. Drip losses of.
5.92 and 0.4Z were calculated for OZ and 3OZ soy substituted pork,
respectively; these differences were very highly significant (p<0.001).
The volatile losses were not significantly different.

Total and volatile losses were not significantly different for
the turkey meat systems. Significant (pK0.05) differences were noted
between the drip losses of 0.6Z and 0.1Z for the OZ and 30Z soy
sbustituted turkey, respectively.

Drip losses consists of fat that has melted out during the
cooking process whereas volatile losses are a result of the evapor-
ation of water and other volatile compounds (Paul and Palmer, 1972).
Since two of the important functional properties of soy proteins are
its ability to bind fat and its ability to retain moisture (Walf, 1970),
it would be expected that the incorporation of texturized soy protein
would result in a decrease in total cooking losses, a subsequent de-
crease in cooking drip and a possible decrease in volatile losses.
Soy substitutions decreased cooking losses in both beef and pork
systems whereas it decreased drip loss in all three systems. There
were no significant differences in the volatile losses between the

levels of soy in any of the soy substituted meat systems.

Sensory Evaluation
An ll-member, trained taste panel evaluated the OZ and 3OZ
soy substituted meat systems for the quality characteristics of

flavor, juiciness, mouthfeel and overall acceptability, using a 1-7

37

descriptive score card, with 7 being optimum. The sensory taste
panel results are presented in Table 4, and the analyses of variance
to determine significant differences are presented in Table 5.

Although the non-soy substituted meat loaves scored slightly
higher, all of the flavor scores for beef and turkey systems were
from 5.3 to 6.0 and were not significantly different. The OZ and
3OZ soy substituted pork loaves did differ significantly (p<0.01)
with respect to flavor, with scores of 6.4 and 4.6, respectively.

The significant difference for the pork system may be due to the for-
mulation, since pork systems did not contain any additional flavorings,
such as tomato in the beef system or poultry seasoning in the turkey
system, to mask the "off"-flavor that is reported to be associated with
soy. Descriptive terms used by the panelists indicated 3OZ of the

soy substituted pork loaves had off-flavors whereas only 3Z of the

OZ soy substituted pork flavor scores indicated a presence of an "off"-
flavor.

The OZ soy substituted beef and turkey systems scored slightly
higher for juiciness than the 30Z soy substituted loaves, although
these differences were not significant. There were highly significant
differences (p<0.01) in juiciness between the OZ and 3OZ soy substituted
pork systems. The taste panelists scored on both loaves as being
slightly dry with over 56Z of the responses indicating that the non-
sov substituted loaves were dry, whereas 83Z thought the 302 soy
substituted pork was dry.

Juiciness is a very complex sensation and several factors must
be considered. Not only is the amount of moisture important but also

the amount of fat present and the availability of the fat to be sensed

38

.moouuoowaaou n so vommmo

.95“? $53 a no? .TH mo 33mm

 

 

 

flows; may; Towns found on
I I zoxuoa

m.o+m.m Nata Nat: «65.0 o

ogre 336 may?» firm: on
I I I I fluom

Box; «656 .336 «.923 o

hours... ....ofld N535 Towns on
I I I I Mwmm

m.o+o.m 336 Oct...“ afield o

HHouo>o Hoownuooz mmmdwuwah uo>on

mom N acumen umuz

coaumoam>m huomaom

 

o.mamum%m nous
oouauwumnsm mom mo mooaumoao>o mnemoom mo m:oauofi>ov pudendum mom memo: .q manna

39

.muHHHpaHoua Ho Ho>mH NH on» us HamoHHHameaw

 

 

 

 

oo~.o mNH.o woo.o mom.o w ofisufiz
Hom.o «Ho.o omo.o mmo.H H sow smxuae
a HmuOH
Noq.o nnq.o omm.o Hwo.o m casuaz
«HHNH.G Hmo.H .«osa.~ ««HHH.H H aom spam
m Hooch
oom.o on.o Hmo.o mmm.o m oHnuHS
qu.o mNo.o omN.o om~.o H sow «mum
a dance
Hamuo>o Hoomnuooz mmmowofiaw uo>oam
ouwoom can: we oouoom aoumhm use:
.maoummm umoa oououwumoom how no moowumoHo>o huomaom mo ooooaum> mo momaaoo< .n manna

40

in the mouth when evaluating the product for juiciness. For the
cooked OZ and 3OZ soy substituted pork there were no significant
differences between the amount of fat present (Table 8) nor the
amount of moisture present (Table 6) in either of the cooked pork
systems, therefore it is speculated that the soy binds the fat in
such a way that it does not promote a sense of juiciness, which would
explain the lower'scores in all of the 30Z soy substituted systems.
Mouthfeel is a very difficult sensation to evaluate. The term
"pebbly" was used to describe the optimum mouthfeel of a ground meat
system. No significant differences were found between mouthfeel of
the OZ and 3OZ levels of soy in any of the meat systems. unless there
are extremes to evaluate, such as very mushy as compared to very gritty,
it is hard to distinguish the varying degrees in between the two
extremes.
Evaluation for overall acceptability indicated that there were
no significant differences between the OZ and 30Z levels of soy in the
beef and turkey systems. This can be explained by the fact that the
textures soy protein products have been engineered to be substituted
into ground meat systems, in particular ground beef, so as not to
change the textural appearance, mouthfeel, juiciness or flavor of these
systems (Rakosky, 1974). The textured soy protein, Temptein "Meat-
Like Nuggets" used in this study were unflavored and colored dark
brown, so when rehydrated they blended in quite well with the ground
beef and ground turkey thighs, without significantly changing the
overall appearance. There was however, a highly significant difference
(p<0.01) in the overall acceptability of the soy substituted pork

systems, with the OZ soy substituted loaf receiving a score of 5.8

41

and the 30Z soy substituted loaf receiving 4.1. A major contributing
factor for the lower scores for the 30Z soy substituted pork loaves
might have been the difference in color of the loaves, with the OZ
soy substituted loaf being pinker in color, which is more character-

istic of a "ham" loaf.

Moisture
The percentage moistures for the three meat systems are presented
in Table 6, and analyses of variance to determine significant dif-
ferences are presented in Table 7. Significant differences among
levels of soy and state of meat (raw or cooked) were pinpointed using
Duncan's Multiple Range Test (1957).

Table 6. Mean values and standard deviations of percentage moisture
of raw and cooked soy substituted meat system.

 

 

 

State
Meat System Z Soy
Raw Cooked

o 58.431.0" 54.41-1.6
Beef

30 58.7:0.6 53.1f1.5

O 54.9tl.4 53.6tl.8
Pork

30 57.3tl.O 52.lfl.5

O 62.9:O.9 57.4:O.8
Turkey

30 61.8:O.6 55.7:O.4

 

vaBased on 5 replications.

42

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.AHHHHHmHous Ho HmpmH NH ms» nu namUHmHame««

 

 

qoq.o ~o~.m omn.H 0H oHnqu
:OHuoo
nem.o oom.m mmo.m H nuouaH
axanq¢.moH «somH.om «aamaH.mHH H oumum
«««Nmm.m mon.m om~.H H xom
mH Houoa
emxuse xuom «can

we mouoom

 

mumsvm com:

 

.msmumxm umoa
wououHumoom mom ooxooo wow so» no ououmHoa owouaoouoa mo moooHum> mo mothma< .m oHoma

43

Cooked beef loaves had significantly less (p<0.001) moisture
than did the raw loaves but no significant differences were noted
between the raw OZ and 30Z soy substituted beef loaves nor between
the cooked OZ and 30Z soy substituted beef systems. Non-soy sub-
stituted beef loaves retained more moisture (93.1Z) than did the
soy substituted beef (90.5Z).

Analysis of variance showed significant differences (p<0.01)
between the raw and cooked state of the OZ and 3OZ soy substituted
pork systems. Using Duncan's Multiple Range Test no significant
difference was noted between raw and cooked OZ soy substituted pork,
however a very highly significant difference was noted between the
raw and cooked 30Z soy sbustituted pork. The percentage moisture
retained by the OZ soy substituted pork was 97.6Z, while the 3OZ
soy substituted loaf retained only 90.0Z moisture.

Very highly significant differences were noted among the levels
of soy and the raw and cooked state of the turkey loaves. Duncan's
Multiple Range Test showed very highly significant differences between
the raw and cooked states of both the OZ and 30Z soy substituted
turkey systems. Significant differences (p<0.05) were also noted
between the raw OZ and 30Z soy substituted turkey. Moisture retention
in both the raw and cooked turkey systems were quite similar, i.e.
91.3Z and 90.1Z for OZ and 30Z soy substituted systems, respectively.

A decrease in the moisture content from the raw to the cooked
state would be expected due to the denaturation and coagulation of
the proteins which would lessen the water holding capacity of the
tissue. The free water would be squeezed out as the structure shrinks
and when heated in a dry atmosphere, most of the water would evaporate,

forming the major portion of volatile losses. Volatile losses are

44

related to the amount of moisture lost during cooking, therefore,

it would be expected that since there was no significant difference

in moisture between the cooked OZ and 3OZ soy substituted beef and

pork systems, no significant difference would be noted between volatile
losses. There was however, a significant difference (p<0.001) between
percentage moisture in the OZ and 3OZ soy substituted cooked turkey
systems; however, no significant difference between the volatile

losses of the OZ and 30Z soy substituted turkey systems.

Soy proteins are hydrophilic and would therefore be expected
to absorb and retain water (Wolf, 1970). During the preparation of
the soy for incorporation into the meat systems, the soy absorbed
two times its weight in water. However, the results from this study
indicate that the 3OZ soy substituted meat systems did not retain
as much water as the OZ soy substituted systems, however the only
significant difference occurred in the ground turkey system.

Two studies were found in the literature which compared moisture
contents of non-soy and soy substituted meat systems. Carlin and
Nielson (1974) reported the use of 3OZ textured soy protein in ground
beef loaves. Both the OZ and 30Z soy substituted beef loaves were
analyzed for moisture in the raw systems and in subsequently reheated
loaves. They noted the raw percentage moisture for OZ and 3OZ soy
substituted beef to be 62.2Z and 63.8Z, respectively. However, the
percentage moisture for the OZ soy substituted beef increased to 64.2Z
upon reheating and the 30Z soy substituted beef decreased to 61.6Z.
Brant (1972) analyzed OZ and 27Z substituted beef patties (raw and

cooked) for moisture. In the raw state the OZ soy substituted beef

45

contained 57.4Z moisture while the raw 27Z soy substituted beef con-
tained 55.5Z moisture. Upon cooking the 27Z soy substituted beef
decreased to 54.9Z or retained 93.7Z moisture. However, due to
"insufficient sample" the OZ soy substituted cooked beef were not
analyzed. No substantial evidence was found to support or contradict

the findings of these studies.

Total Lipids

A chloroform methanol extraction was used to determine the
percentage of total lipid in the three meat systems. Lipids were
calculated on a dry weight basis in order to compare raw and cooked
lipids. The values for total, phospholipid and neutral lipid are
presented in Table 8, and analyses of variance to determine sig-
nificant differences among these lipid values are given in Table 9.

The total lipid values for the OZ soy substituted beef decreased
from 25.2Z to 17.5Z upon cooking, retaining 69.4Z of the fat; whereas
the 3OZ soy substituted beef retained 88.2Z fat, decreasing only
from 17.8Z to 15.7Z as a result of cooking. Analysis of variance
showed very highly significant differences between both the levels
of soy and the raw and cooked state, with a highly significant
p<0.01) interaction occuring. Duncan's Multiple Range Test demonstrated
that there was a significant (p<0.001) difference between raw OZ
and 30Z soy substituted loaves as would be expected since up to 3OZ
of the total fat was replaced by 3OZ rehydrated soy, which contained
less than lZ fat. No significant differences were noted between the
cooked OZ and 3OZ soy substituted beef. A very highly significant

difference was noted between the raw and cooked OZ soy substituted

.moOHumoHHaou n no oomomo

.oHnHH Hmuou mo owouooouoe no manage

.mHmmo uanoB hue o no oouoHooHoom

 

46

 

 

 

 

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oHQHH UHQHH
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mom N mom N ououm amumhm non:
.maoumhm umoa oouauHumnoo >om ooxooo one son mo Auv oHaHH
Hmuusoo com nan oHaHHosamone . NANV oHeHH Hmuou mo moOHuMH>mo ohmooMumnonm mono: .w oHQmH

47

Table 9. Analyses of variance of total lipid, phospholipid and neutral
lipid of soy substituted meat systems.

 

Mean Squares

 

Meat System Source df

 

Total Phospho- Neutral
lipid
Total 19
Soy 1 107.185*** 0.612 1.859
Beef State 1 123.SO4*** 11.401 8.312
Inter-
action 1 37.812** 6.613 2.516
Within 16 2.782 1.505 2.808
Total 19
Soy 1 139.921*** 2.644 49.609*
Fork State 1 165.312*** l9.0l3*** 0.047
Inter-
action 1 51.520** 1.860 8.594
Within 16 3.411 0.875 10.817
Total 19
Soy 1 181.202*** 24.860*** 740.545**
Turkey State 1 10.951 25.765*** 912.520**
Inter-
action 1 4.232 2.115 1062.080**
Within 16 3.240 1.583 66.380

 

*Significant at the SZ level of probability.
**Significant at the lZ level of probability.
***Significant at the 0.1Z level of probability.

48

beef, however no signifciant decrease in raw and cooked lipids was
found in the 30Z soy substituted beef.

Raw OZ soy substituted pork decreased from 30.7Z total lipid
to 21.8Z upon cooking, retaining 71Z total lipid. The 3OZ soy sub-
stituted pork decreased from 22.2Z to 19.7Z total lipid upon cooking,
retaining 88.7Z total lipid. Very highly significant differences
(p<0.001) between levels of soy and the raw and cooked states were
determined by analysis of variance and the differences evaluated
according to Duncan's Multiple Range Test. Significant differences
(p<0.001) in total lipids were found between raw OZ and 3OZ substituted
pork loaves. No significant differences, however, were observed
between the cooked OZ and 3OZ soy substituted pork or the 3OZ soy
substituted raw and cooked pork systems. Nevertheless, raw non-soy
substituted loaves contained significantly (p<0.001) more lipid than
the cooked non-soy substituted loaves.

The percentage fat retained for the OZ and 3OZ soy substituted
turkey were 88.2Z and 97.7Z, respectively. Soy substituted systems
had significantly less (p<0.001) fat than did the non-soy substituted
loaf. There was a very highly significant difference between the
raw OZ and 3OZ soy substituted turkey. No significant differences
however, occurred as a result of cooking. .

An important functional prOperty of soy protein is its ability
to bind fat (Wofl, 1970). It would therefore be expected that products
containing soy would retain more fat than a OZ soy substituted meat
system, as shown by the results in this study. As a result of the
large amount of fat retained, cooking drip exhibited the expected

decrease with the increased level of soy (Table 3).

49

The total lipids for the OZ soy substituted soy beef loaves were
higher than those reported by Campbell and Turkki (1967) for raw and
cooked ground beef muscle. This may be explained by the fact that
ground beef has adipose tissue included, whereas the beef muscles did
not. The values reported in this study for raw and cooked percentage
total lipids for the OZ soy substituted pork loaves are similar to
the values reported by Campbell and Turkki (1967) for ground pork.

The trend for increased fat retention in soy substituted meat
systems is substantiated by reports in the literature. Carlin and
Nielsen (1974) reported a 94Z retention of fat upon reheating with
the use of 3OZ soy substituted beef as compared to only 65Z fat retention
upon reheating of the OZ soy substituted beef patties. Brant (1974)
reported a 79Z fat retention with the use of 27Z textured soy protein
beef patties, again however, due to "insufficient sample" the cooked
OZ soy substituted beef patties were not analyzed. Although the
addition of soy diluted the fat in the raw state, soy retained the
fat better, therefore the levels of fat in the cooked loaves was
essentially the same, so that soy substitution in the meat loaves

would not result in a decrease in calories.

Phospholipid and Neutral Lipid
Percentages of phospholipid and neutral lipids were determined
by using a separation on silicic acid by washing with chloroform and
methanol. Percentages for these values were determined on the total
weight of the lipid (Table 8).
As a result of cooking the relative concentration of phospho-
lipid in the OZ and 3OZ soy substituted beef increased from 4.0Z to

6.6Z and from 5.5Z to 5.8Z, respectively. Analysis of variance

50

(Table 9) revealed that there was a significant difference (p<0.05)
between the raw and cooked state. Duncan't Multiple Range Test
pinpointed this difference to be a significant (p<0.05) increase in
the OZ soy substituted beef phospholipid as a result of cooking. No
significant differences between OZ and 30Z soy substituted raw and
cooked beef phospholipid or between 30Z soy substituted raw and cooked
beef phospholipid were noted. There were no significant differences
between the neutral lipids in either the level of soy or the raw
and cooked state of the beef loaves.

The percentage phospholipids increased with cooking from 3.9Z
to 6.5Z for the OZ soy substituted pork systems and from 5.3Z to 6.6Z
for the 3OZ soy substituted pork systems. Significant differences
(p<0.05) between the raw and cooked states of the 3OZ soy substituted
pork systems, and very highly significant differences between raw
and cooked OZ soy substituted pork were indicated by Duncan's Multiple
Range Test. Significant differences (p<0.05) were noted between raw
OZ and 3OZ soy substituted pork, while no significant differences
were found between the cooked OZ and 30Z soy substituted pork loaves.
A significant difference did occur between the OZ and 3OZ soy sub-
stituted pork neutral lipids in the raw state, however no significant
change was found as a result of cooking for either the OZ or 30Z
soy substituted pork systems.

The percentage phospholipids decreased during cooking from
8.1Z to 6.5Z for the OZ soy substituted turkey systems and a similar
decrease occurred with the 30Z soy substituted turkey, decreasing from
11.0Z to 8.1Z. Highly significant differences were found between the

raw OZ and 3OZ soy substituted turkey system, with no significant

51

differences occuring between the cooked OZ and 3OZ soy substituted
turkey loaves. A significant decrease (p<0.0l) in phospholipid content
occurred as a result of cooking with the 30Z soy substituted turkey‘
system, while cooking did not cause a significant decrease in the
percentage of phospholipid in the Z soy substituted turkey system.

A very highly significant decrease was observed in the neutral lipid
content of the raw and cooked OZ soy substituted turkey as a result of
cooking, decreasing from 92.7Z to 65.9Z. No significant difference

was found between the raw and cooked 3OZ soy substituted turkey. No
significant difference was observed between the raw OZ and 3OZ soy
substituted turkey systems, however very highly significant differences
did occur between the cooked OZ and 3OZ soy substituted turkey loaves.

Relative increase in the phospholipid content occurred in both
the OZ and 30Z soy substituted beef and pork systems as a result of
cooking. These results are consistent with those reported by Campbell
and Turkki (1967) for ground beef and pork. This increase has been
attributed to the fact that phospholipids are an integral part of
the muscle cell and are closely associated with the protein (Campbell
and Turkki, 1967; Lea, 1957). The neutral lipids however, are inter-
cellular and are more readily rendered from by the tissue during
cooking than are the phospholipids.

The decrease, rather than the increase, in phospholipid content
in the cooked turkey systems is rather difficult to explain. Lee
(1972) reported a decrease in the phospholipid content of chicken
as a result of frying in corn oil, however no explanation was given.

Decreased proportion of phospholipid in the cooked turkey system

52

may be related to the fact that poultry meat contains more unsaturated
fatty acids (Hilditch ggflal., 1934; Chang and Watts, 1952) than either
beef or pork, and the fact that phospholipids contained a much higher
percentage of unsaturated fatty acids than neutral lipids (Hornstein
§£_§i,, 1961) which might allow a melting out of phospholipids
accounting for the decrease or the phospholipid may break down during
cooking so they are not measured by the analysis procedure used.

No clear explanation can be given for the very highly signifi-
cant decrease in the neutral lipid content of the raw and cooked
OZ soy substituted turkey systems. Even though the neutral lipid
values for the other OZ and 3OZ soy substituted meat systems were not
the same, they did show the same trends, however this was not the
case with the turkey system. There are several possible explanations
for these results. First, insufficient solvent may have been used to
elute the neutral lipid from the silicic acid, however there should
have been a substantial increase in the phospholipid content since
the solvent used in this step was more polar, but this was not the
case. Another possibility is that not enough solvent was used to
elute all of the phospholipid from the silicic acid, which would
indicate that the phospholipid content is low. The other possible
explanation is that the neutral lipid oxidized much more rapidly
when the solvent was being evaporated off the the loss occurred in
that step.

No studies were found in the literature which compared the types
of lipids present in raw and/or cooked soy substituted meat systems.
It is interesting to note that in each case the percentage phospholipid

appeared to be slightly higher for the 3OZ soy substituted meat systems

53

than for the OZ soy substituted meat systems, however analysis of
variance showed that the difference was not significant. This slight
increase may be attributed to the fact that of the lZ residual fat
which remains after processing or textured soy protein products, up

to 3OZ of this lipid may be phospholipids (Williams, 1974; Blair, 1974).

TBA Determinations

In order to evaluate the addition of 30Z soy on the quality
of cooked stored meat systems, 2-thiobarbituric acid tests were
used to determine the rate of oxidative rancidity under refrigerated
(5°C) and frozen (-ll°C) conditions. The TBA values are reported
in Table 10, and the analyses of variance to determine significant
differences for the level of soy and storage periods (refrigerated
and frozen) are presented in Table 11.

The slow increase in oxidation of ground beef under both re-
frigerated and frozen storage can be seen in Fig. l. The only sig-
nificant difference that occurred between the TBA values of OZ and 302
soy substituted beef was for day 2. There was no significant increase
in the rate of oxidation for either the OZ or 3OZ soy substituted
beef stored under refrigerated or frozen storage.

The increase in rancidity for the OZ and 30Z soy substituted
pork systems can be seen in Fig. 2. There appeared to be a substantial
increase, then a leveling off of TBA values for the refrigerated pork
loaves. This increase in rancidity was very highly significant
(p<0.01), however soy substitution did not significantly affect
TBA values.

The frozen pork systems became much more rancid (Fig. 2) than

did the beef systems frozen for the same period of time. There was,

54

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59

however, no significant increase in rancidity found in the three
week frozen storage of the pork systems stored for 3 weeks.

The increase in oxidation for the frozen and refrigerated turkey
systems is illustrated in Fig. 3. The 02 soy soubstituted turkey
shows a steady increase in TBA values during the refrigerated storage,
whereas the 302 soy substituted turkey shows a much slower rate of
increase. This steady increase for the 0% soy substituted turkey
was found to be very highly significant (Table 11). There was a
significant (p<0.05) difference in TBA values between the 02 and 30%
soy substituted turkey for day 4, with the 302 soy substituted turkey
being much less rancid. There was no significant increase in rancidity
either in the 0% or 302 soy substituted frozen turkey, nor was there
a significant difference between the 0% and 302 soy substituted turkey
loaves for any given week.

The Z-thiobarbituric acid test measures the amount of malon-
aldehyde that has been produced as a result of autoxidation. The
oxidation of cooked meat is believed to be catalyzed by ferric heme
derivatives formed during thermal heating (Younathan and Watts, 1959,
1960). Fox (1966) reported that as a result of cooking the pigments
in uncured meats are irreversible converted to the denatured ferric
chromogen. Therefore uncured meats would be expected to increase
lipid oxidation, which is responsible for the stale, off-odors asso-
ciated with reheated cooked meats (Toms and Watts, 1958).

Cooked beef stored in the refrigerator would be expected to
increase more rapidly than if stored in the freezer (Chang g£_§l,,
1961). The results from this study indicate that rancidity did not

increase significantly in either the 02 or 302 soy substituted beef

60

after 4 days at 5°C. The beef systems oxidized much slower at -11°C
than at 5°C as was expected. The soy did not have a significant

effect on the level of rancidity in the -11°C stored beef, and the only
significant difference was noted for day 2 for the beef systems stored
at 5°C.

Cured meats can be held longer at refrigerated temperatures than
at a freezer temperature (Younathan, 1959). The stability of the
refrigerated cured meats towards lipid oxidation is also high compared
to the stability of uncured meats held under the same condition
(Zipser gt al., 1964). The reason cured meats are more stable toward
lipid oxidation at refrigerated conditions is that the sodium nitrite
used in curing converts the pigments to the catalytically inactive
ferrous nitric oxide (Younathan and Watts, 1959). Pigment losses
have been shown to parallel lipid oxidation in refrigerated hams,
with the cured meat pigment being oxidized to the ferric form or
the prophyrin ring is destroyed (Younathan and Watts, 1959). The
pork system in this study consisted of a 50:50 mixture of cured ham
and uncured ground pork. The pork system would therefore not be
expected to be as stable towards lipid oxidation as if only cured
ham had been used. There was a greater increase in rancidity in the
pork systems under 5°C than with the beef systems stored under the same
condition. Pork lipids are more highly unsaturated than beef lipids
and would be more easily oxidized (Watts, 1954).

Lipid oxidation that occurs in frozen cured pork is salt cata-
lyzed rather than heme catalyzed as in the other two systems. The
proposed mechanism for this was reported earlier. There was a much

more rapid increase in lipid oxidation with the pork systems stored

61

at -11°C than with either the beef or turkey systems stored under

the same conditions. There were no significant differences between

the 02 and 30% soy substituted pork loaves stored under refrigerated
conditions. There was also no significant increase in rancidity

for either of the two frozen pork systems as would have been expected.
This lack of rancidity deve10pment might be due to the fact that the
individual replications of the pork system more than those of the other
meat systems varied so (Table 10) which caused higher standard devia-
tions than were found for the other systems.

Poultry lipids are much more highly unsaturated than beef pork
lipids (Hilditch gt al., 1934; Chang and Watts, 1952) and would be
expected to show a marked increase in lipid oxidation under refriger-
ated storage, as was shown by the results in this study (Fig. 3).
Jacobson and Koehler (1970) reported a decrease in flavor evaluation
for refrigerated dark turkey meat during a 4—day storage; with
corresponding increase in TBA values. They recommended freezing
cooked turkey immediately after cooking in order to delay the develop-
ment of off-odors and flavors associated with lipid oxidation. Marion
and Forsythe (1971) attributed the increased lipid oxidation in dark
poultry meat to the fact that heme catalysis is more active in red
muscle, which contains a larger amount of myoglobin than does white
muscle from poultry. The increase in rancidity for the turkey systems
stored at -ll°C was much slower as was expected. Soy substitution
did not significantly affect the TBA values in the turkey systems
stored at -ll°C.

The 30% soy substitution significantly (p<0.001) reduced the

rate of lipid oxidation in turkey systems stored at 5°C. Soy

62

substitution had also reduced the rate of lipid oxidation in the
beef systems at 5°C (p<0.05) but this reduction occurred only for
the values for day 2 of storage.

Carlin and Nielsen (1974) reported that after 6 months storage
at -4°F randicity was not as detectable in a 30% soy substituted
beef loaf as it was in the 02 soy substituted beef. They attributed
this to either an antioxidant property of the soy or that the strong
flavor masked the off-flavor associated with lipid oxidation.

The antioxidant affect of soy has been reported in the liter-
ature as being related to the naturally occurring flavanoid compounds
(Pratt, 1970), or to substances produced as a result of interactions
between amino acids or proteins and carbohydrates upon heating (Sato
g£_§l,, 1973). The flavanoid compounds are water soluble and unless
bound in some way, would be lost during the processing of a textured
soy protein. However, there are no reliable quantitative methods for
determining the flavone compounds in the textured or spun fiber pro-
ducts (Blair, 1974).

Sato g£_§l,, (1973) reported a lower TBA increase with a 22
soy substituted ground meatloaf stored at 4°C for 2 and 5 days than
with the 0% soy substituted ground meat systems, stored under the
same conditions. They attributed this stability towards the develop-
ment of rancidity to the production of reducing-type compounds as
inhibitors of WOF. Vegetable protein products contain appreciable
amounts of carbohydrate and protein (Rakosky, 1971). The Temptein used
in this study contained 64.0% protein and 18.42 carbohydrate. These
reducing-type substances would occur as a result at interaction
between amino acids and proteins of meat and soy and the carbohydrates

of soy and meat, upon heating.

SUMMARY AND CONCLUSIONS

This research project investigated the affects of a 30% soy
substitution on ground beef, pork and turkey systems. Cooking
losses, sensory characteristics of flavor, juiciness, mouthfeel
and overall acceptability and TBA values, which determines the rate
of oxidative rancidity, were evaluated for cooked loaves prepared
with 0% and 30% soy substitutions. Both the raw and cooked 0% and
30% soy substituted meat systems were also analyzed for moisture,
total lipid, phospholipid and neutral lipids.

The taste panelists scored the 30% soy substituted beef and
turkey systems slightly lower than the non-soy substituted system,
but all scores were above 4.6 on a 7 point scale and none of the
differences were significant. However, taste panelists scored the
302 soy substituted pork system significantly lower than the 0%
soy substituted pork system for all quality characteristics except
mouthfeel. Since the textured soy protein used in this study was
engineered to blend with beef, it was expected to blend well with
the turkey system, however color differences were obvious between the
02 and 30% soy substituted ham loaf which would contribute to the lower
scores.

The 302 soy substitution decreased total cooking losses in both
the beef and pork systems. Soy substitution decreased drip loss in

all three systems; nevertheless, no differences were found in volatile

63

64

losses between the 0% and 30% soy substitutions in any of the three
systems.

Cooking resulted in very highly significant decrease in percentage
moisture for the 02 soy substituted beef and turkey systems, for all
three 30% soy substituted systems.

Due to dilution with a low fat product the raw 30% soy sub-
stituted beef, turkey and pork systems had significantly less fat
than did corresponding 0% soy substituted meat systems. The 302
soy substituted systems, however, retained more total lipid than did
the 02 soy substituted systems, therefore there was no significant
difference between the total lipid content of the cooked 0% and 30%
soy substituted beef and pork systems. Thus, consuming 30% soy sub-
stituted meat would not be a beneficial way to decrease the total
number of calories or the amount of fat in one's diet.

The amount of phospholipid in both the 0% and 30% soy substituted
beef and pork systems increased as expected. The decrease in phos-
pholipid content of the 0% and 302 soy substituted turkey systems
might be explained by the fact that poultry is much more highly
unsaturated and contains a larger percentage of phospholipid than
the other two systems. There appeared to be no significant difference
in neutral lipid content as a result of cooking for either the 0%
or 302 soy substituted beef or pork systems, while the only signi—
ficant difference was found between the 0% and 30% soy substituted
turkey systems, with the 0% soy substituted system containing less
neutral lipid.

The TBA values indicated that the 30% soy substituted systems

were initially slightly more rancid, but at some point during either

65

refrigerated or freezer storage, the rate of oxidation for the 0%
soy substituted pork and turkey increased more rapidly so that their
TBA values were higher than those of the 30% soy substituted meat
systems after storage. The only significant difference in TBA values
of 02 and 302 soy substituted meat, however occurred in the refri—
gerated turkey system. The ground beef underwent oxidative rancidity
at a much slower rate during storage at both refrigerated and freezing
temperatures, than did the other two types of meat systems, and the
302 soy substituted beef system had higher TBA values throughout the
storage periods.
The data from this study seem to indicate that:
1. Use of 30% soy substitution did not adversly affect the
quality characteristics of ground beef and turkey systems.
2. Ham loaves substituted with 30% soy were judged to be less
flavorful, have less desirable color and lower overall
acceptability.
3. No differences were found in the total lipid content of
the OZ and 30% soy substituted meat systems.
4. Fat contents were similar in the beef and pork soy substi-
tuted meat systems.
5. Although 30% soy substituted meat systems appeared to have
a slightly lower TBA value during refrigerated and frozen
storage, soy does not appear to prevent the development

of WOF in cooked meats.

PROPOSALS FOR FUTURE RESEARCH

A number of interesting observations were made during this
study which warrant further investigation. The following areas
of research are proposed:

1. The trend of a slower rate of oxidation with the
30% soy substituted meat systems should be investigated
more thoroughly. Model systems using unsaturated fatty
acids and soy protein extracts would indicate more speci-
fically whether or not the soy protein exhibited antioxidant
properties.

2. Further study is needed to determine whether or not
soy protein products interfere wish the TBA determinations
by forming complexes with the malonaldehyde, which in turn
would give lower values.

3. The turkey phospholipid and in particular the neutral
lipid results of this study and the lack of published results
indicates that additional studies should be conducted to de—
termine what changes occur in poultry lipids as a result of

cooking.

66

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APPENDICES

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APPENDIX II

SCORECARD FOR GROUND MEAT SYSTEMS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sample Name
Date
Directions:
1. Put name and date on score card.
2. Read the scorecard over carefully.
3. Each sample has a number. Record its data by making an K
through the box on the corresponding numbered scorecard.
4. If there is an "off" flavor please describe.
Score Flavor Juiciness Mouthfeel Overall
1 very bland very dry mushy
2
3 mod. bland mod. dry mod. mushy
4
5 31. bland 31. dry 31. mushy
6
7 meaty and juicy pebbly excellent
pleasantly
spiced
6
5 31. off 31. wet sl. gritty good
4
3 mod. off mod. wet mod. gritty poor
2
1 off very wet gritty unaccept-
able
Comments:

79

 

"ImmmmES