WATER ‘ HOLBING CAPACITY, UPED OXlDATION,‘
PEGEENT AM) CGLOR CHANGES 3N RADIATION
PASEURiZEB PREPAQKAGED FRESH BEEF
PRETRFATED WETH SGDEUM TRWOLYPHOSPHATE

Thesis for the [Degree of M. 8.
5110mm SEW BNWERSETY
PANFELG S. BELO, m.
1%8

1m

  
   

 

LIBRARY

Michigan State
University

M “.33

ABSTRACT

WATER—HOLDING CAPACITY, LIPID OXIDATION,
PIGMENT AND COLOR CHANGES IN RADIATION
PASTEURIZED PREPACKAGED FRESH BEEF
PRETREATED WITH SODIUM
TRIPOLYPHOSPHATE

By Panfilo S. Belo, Jr.

This work was undertaken as an attempt to retard drip
or exudate formation, lipid oxidation and oxidative dis-
coloration during irradiation and storage of radiation
pasteurized fresh beef through the combined use of sodium
tripolyphosphate and vacuum packaging. Beef slices were
dipped in sodium tripolyphosphate solution prior to vacuum
packaging, irradiation and storage at 38°F.

Drip loss measurements, thiobarbituric acid tests,
reflectance measurements, color and odor evaluations were
conducted throughout a 21 day storage at 38°F. The effect
of the subsequent exposure of vacuum packed beef samples to
the atmosphere was also evaluated relative to lipid oxida-
tion and oxidative discoloration. In general, phosphate
pretreatment and vacuum packaging proved to compliment
radiation pasteurization in the extension of the refriger-
ated shelf life of prepackaged fresh beef. While lipid
oxidation was inhibited during storage in vacuum, phosphate
pretreatment appeared to have effects on meats in addition
to drip control. Water—holding capacity and color retention
was improved during storage in vacuum and subsequent

exposure to the atmosphere.

WATER-HOLDING CAPACITY, LIPID OXIDATION,
PIGMENT AND COLOR CHANGES IN RADIATION
PASTEURIZED PREPACKAGED FRESH BEEF
PRETREATED WITH SODIUM

TRIPOLYPHOSPHATE

By

Panfilo S. Belo, Jr.

A THESIS

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

MASTER OF SCIENCE

Department of Food Science

1968

ACKNOWLEDGMENTS

The author expresses his sincere appreciation and
gratitude to Dr. Walter M. Urbain for his generous assist-
ance and constant guidance throughout the course of this
study and during the preparation of this manuscript.

Acknowledgment is extended to Dr. P. Markakis,
Professor of Food Science, and Dr. A. w. Farrall,
Professor of Agricultural Engineering, for their critical
reading of this manuscript.

Sincere thanks to Dr. B. S. Schweigert, Chairman,
Department of Food Science, for his encouragement during
the entire course of study.

To the United States Atomic Energy Commission, the
author is indebted for financing the irradiation project
under which this work was done (Contract No.: AT(ll-l)—

1689, Radiation Pasteurization of Fresh Meat and Poultry).

ii

TABLE OF CONTENTS

ACKNOWLEDGMENTS
LIST OF TABLES . . . . . . . . . . . .

LIST OF FIGURES . . . . . . . . . . .

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

Radiation Pasteurization . . .

Water—Holding Capacity and Drip Formation in
Fresh Beef

Lipid Oxidation and Pigment Changes in Gamma.
Irradiated Meat . . . . . . . . . .

MATERIALS AND METHODS

Meat . . .

Phosphate Pretreatment . . . . . .
Packaging Materials . . . . . . . . . .
Methods of Irradiation . . . . . . . . .
Drip Measurements . . . .
Phosphate Absorption Determination

pH Measurement

Water—Holding Capacity Determination . . .
Lipid Oxidation Determination . . . . . .
Measurement of Pigments . .
Organoleptic Evaluation (Color and Odor)

RESULTS . . . . . . .

Effect of Various Concentration of Sodium Tripoly-
phosphate Dipping Solution and Dipping Time on

Drip Loss and Phosphate Absorption in Fresh Beef.

Effect of Phosphate Pretreatment on Drip Formation,

pH and Water— —Holding Capacity of Radiation
Pasteurized Fresh Beef . . . . .

iii

Page

11

vi

\‘JUUUO

12
2O

2O
2O
2O
21
22
23
23
23
2H
26
28

30

3O

3O

Page

Effect of Phosphate Pretreatment, Vacuum
Packaging and Radiation on Lipid Oxidation
in Fresh Beef . . . . . . . . . . 39

Results in the Preparation of Standard Curve
For Pigment Determination . . . . . . . 43

Effect of Phosphate Pretreatment, Vacuum
Packaging, Radiation and Subsequent Exposure
to the Atmosphere on Color and Metmyoglobin

Formation in Fresh Beef . . . . . . 47
Organoleptic Evaluation (Color and Odor) . . 53
DISCUSSION . . . . . . . . . . . . . . 55
SUMMARY AND CONCLUSIONS . . . . . . . . . 62
BIBLIOGRAPHY . . . . . . . . . . . . . 64

iv

LIST OF TABLES

Table Page

1. Solution uptake and pH of fresh beef slices
after dipping in 10.0% solution of sodium
tripolyphosphate for 30 to 60 seconds and
draining for 10 to 15 minutes . . . . . . 37

2. Effect of phosphate pretreatment, vacuum
packaging, radiation and subsequent exposure
to the atmosphere lipid oxidation in fresh

beef during storage at 38°F . . . . . . 42
" 571 mu
3. Ratios of K/S at REE—mi for samples representing
100% myoglobin, 100% oxymyoglobin and 100%
metmyoglobin . . . . . . . . . . . 45

A. Effect of phosphate pretreatment, vacuum packag-
ing, radiation and subsequent exposure to the
atmosphere on color and metmyoglobin develop-
ment on fresh beef during storage at 38°F . . “9

5. Mean color and odor scores of phosphate treated
and untreated beef irradiated at various
pasteurizing doses of gamma radiation and
stored for 20 days in vacuum followed by one
day exposure to the atmosphere . . . . . 5“

LIST OF FIGURES

Figure Page

1. Dose levels of ionizing radiation required for
various biological effects (Proctor, 1959) . . A

2. Color cycle in fresh beef (Landrock and Wallace,
1955) I O O O O O O O O O O O O O 1“

3. Drip loss during storage at 38°F of fresh beef
slices dipped at various concentrations of
sodium tripolyphosphate for 30 seconds . . . 32

A. Phosphate uptake by fresh beef slices dipped
for various time intervals in 10. 0% sodium
tripolyphosphate after three weeks storage
at 38°F . . . . . . . . . . . 3A

5. Loss of drip in fresh beef slices that were
vacuum packed, irradiated at various pasteur—
izing doses of gamma radiation and then stored
for 21 days at 38°F. The drip in meat that was
treated with sodium tripolyphosphate solution
prior to irradiation is compared with the drip
in beef slices that were not treated . . . . 36

6. Percentage water retention of beef slices that
were vacuum packed, irradiated at various
pasteurizing doses of gamma radiation and
stored for 21 days at 38°F. The percentage
water retention of beef slices that were
treated with sodium tripolyphosphate solution
prior to irradiation is compared with the
water retention of beef slices that were not
treated . . . . . . . . . . . . . 38

7. Water retention during storage at 38°F of
‘irradiated fresh beef pretreated with sodium
tripolyphosphate . . . . . . . . . . A0

8. Progression of lipid oxidation changes in
irradiated fresh beef during storage in vacuum
for 21 days followed by exposure to the atmo-
sphere for three days at 38°F . . . . . . AA

vi

Figure

9. Assumed linear relation between ratios at
571 mu
525 mu

10. Effect of phosphate pretreatment on metmyo-
globin formation in irradiated and unir-
radiated fresh beef during storage for 21
days at 38°F followed by exposure to the
atmosphere for three days . . . . .

and the percentage metmyoglobin

vii

Page

A6

52

INTRODUCTION

There is at present a growing realization that there
is a need for centralized processing of retail cuts of
fresh meat in order to reduce cost in cutting operations
and in construction and equipment as well as to improve
cutting operations. Such centralization however, requires
much longer product life than what is now obtained. It
appears that in order to obtain such centralization, means
of preventing or retarding quality changes due to the
processes associated with meat spoilage must be sought.

It has been proposed that wholesaling fresh meat
based on radiation pasteurization would permit this cen—
tralization (Brownell gt_a1., l954)."Thi ‘method consists
of preparing packaged standard cuts of meat in retail-size
portions at a packing house rather than at the retail
market. The packaged meat would be pasteurized at the
packing house by means of a relatively low dose of
ionizing radiation prior to shipping to the retailer.

Although pasteurizing doses of ionizing radiation
(doses less than 1.0 Mrad) can prevent certain quality
changes in fresh meat from occurring by destroying a large
portion of microbial population, other changes not
associated with microbial growth occur during storage.
These changes include color changes, lipid oxidation,

1

formation or exudation of serum-like fluid commonly known
as drip, textural changes and changes in odor and flavor
(Coleby g£_al., 1960; Urbain, 1955, 1965). Such extended
refrigerator shelf life afforded by radiation pasteuriza-
tion can magnify this non-microbial degradation, thus
offsetting the beneficial effect of radiation pasteuriza-
tion.

This study was initiated as an attempt to retard
the non-microbial degradations occurring during storage
of radiation pasteurized fresh beef through the combined
use of phosphate pretreatment and vacuum packaging. The
entire process involves: (1) sodium tripolyphosphate
pretreatment of beef slices to control drip formation and
to improve waterAholding'capacity; (2) vacuum packaging
to prevent lipid oxidation and retard the rapid oxidation
of the heme pigments oxymyoglobin and myoglobin to brown
ferric metmyoglobin; (3) low dose irradiation and refrigera-
tion to control microbial spoilage and (A) exposure of
the beef slices to the atmOSphere to regenerate the red
pigments prior to display. The effectiveness of the entire
process was evaluated relative to drip formation, water—
holding capacity, color changes and lipid oxidation after
21 days storage at 38°F. As the study progressed, however,
the possibility of defining more fully the significance of
phosphate treatment on the color of the product became

apparent and was investigated.

REVIEW OF LITERATURE

Radiation Pasteurization

 

Since the early times, man has always sought means
of preserving his food for future consumption. As
technology advances, he has tried and applied new tech-
niques of protecting his food from spoilage. In relatively
recent years, a new approach to the problem of preventing
microbial spoilage in foods has been developed. This
involves treatment of the foodstuffs with ionizing radia-
tion from electron or X-ray generators or from a radionu—
clide (Proctor g£_a1., 1942; Brasch and Huber, 1947).
Among the many types of ionizing radiations, only the
high energy cathode rays, soft X-rays, and gamma rays find
application in food preservation (Hannan, 1955).

The various biological applications of ionizing
radiation have been conveniently grouped into various dose
ranges depending upon the particular objective. A summary
of the effects of different doses on various forms of life
as described by Proctor (1959) is shown in Figure 1.

In food preservation, the application of radiation
has been grouped into two broad categories: low—dose
irradiation involving doses up to 1.0 Mrad and high dose
irradiation involving doses above 1.0 Mrad (Brownell gt_§l.,
1954, 1955; Brownell, 1961; Heiligman, 1961). The former

3

 

Effective against enzymes in situ

[1

Effective against viruses

 

 

 

 

 

 

Effective against sporulating bacteria

Effective against non—sporulating bacteria and molds

 

 

 

 

 

Pasteurization Sterilization

Effective against insects

 

 

 

 

Effects on mammals

 

 

 

 

L..—
l J J 1 1 4 J 8
IO2 103 IOLl 105 10° 107 10
(rep)

Fig. l.é-Dose levels of ionizing radiation required
for various biological effects (Proctor, 1959).

is known as radiation pasteurization and the latter,
radiation sterilization. Radiation doses from 1.0 to 5.0
Mrad have been applied to ham, bacon, chicken, beef and
other meat and poultry products to accomplish "commercial"
sterilization. “A “in thermal sterilization, it has the
purpose of destroying all the microorganisms that might
lead to spoilage of the product under normal storage con-
ditions. 0n the other hand, pasteurizing doses of ionizing
radiation (doses less than 1.0 Mrad) have been applied to
luncheon meat, fresh meat and poultry, seafoods, fruits

and vegetables. In this case, most but not all of the

 

microorganisms in the product are destroyed and their number
is reduced to such an extent that the shelf life after
treatment is substantially extended. The time taken for

the surviving microorganisms to re-establish themselves

in numbers which normally cause spoilage is greatly
lengthened and hence, storage life can be extended.

According to Federal Food, Drug and Cosmetic Act of
the United States Government, radiation is a food additive.
Its use is regulated by the Food and Drug Administration
and other government agencies. The regulation specifies
a minimum and a maximum dose of the particular kinds of
ionizing radiation used and the conditions carried out
during the irradiation process. Presently, the use of
radiation as a means of food preservation has been approved
for two foods; They are: (1) potatoes, for sprout
inhibition, and (2) wheat and wheat products, for insect
disinfestation.

In the U.S.S.R., The Ministry of Health has approved
still other products in addition to potatoes and grains.
Official clearance has been given to the following products:
fresh fruits and vegetables, raw meats, eviscerated chilled
chicken, and culinary prepared meat products for reduction
of microorganisms for shelf life extension; and onions for
the purpose of sprout inhibition (Metlitskii gt_al., 1967).
In Canada, clearance for the use of gamma radiation from

cobalt-60 to inhibit sprouting in potatoes and onions has

been approved by the Food and Drug Directorate (MacQueen,
1966). The use of gamma radiation to inhibit sprouting in

potatoes has also been approved in France and Israel.

Effects on Fresh Meat

The use of radiation pasteurization as a new food
preservation process has been extensively examined. Its
effect on microbial spoilage in meat has been carefully
investigated (McLean and Sulzbacher, 1953; Wolin gt_al.,
1957; Evans and Batzer, 1960; Rhodes, 196A; Hersom and
Hulland, 196A).

The various chemical changes taking place in meat
under the influence of pasteurizing doses of ionizing
radiation have been reported by Wilson (1959), Obara and
Ogasawara (1960) and Pal'min (1962).

The earlier works with radiation pasteurization of
fresh meat suggested that the degree and character of
various organoleptic changes depend on the dose, methods
of treating the meat during irradiation and storage
(Brownell gt_al., 1955; Schultz g£+al., 1956; Groninger
g§_al., 1956; Doty gt_al., 1956).

In 1960, Lea gt_a1. suggested that when beef is
radiation pasteurized and stored in air, the maximum dose
which does not cause significant loss of quality is likely
to be below rather than above 100 Krad and that the
deteriorative changes in fat may be the limiting factor.

Heiligman (1961) on the other hand, reported that the

refrigerated (36° to 40°F) shelf life of vacuum packed
raw beef steak can be extended to at least 16 weeks by
treatment with low dose radiation (500 Krad).

Sokolov (1965) observed that it is difficult to
detect changes in smell and taste in meat which has been
exposed to 50 Krad. Changes in smell, taste and color are
insignificant at doses 50 to 100 Krad, noticeable at 500
Krad and very pronounced at doses 1.0 to 2.0 Mrad.

The maximum dose of gamma radiation that can be
applied to beef or lamb at 32°F in the absence of air,
without causing changes in organoleptic qualities detect-
able by the trained panel, was reported by Rhodes and
Shepherd (1966) to be 0.4 Mrad. They also reported that
beef packed in vacuum and given 0.3 and 0.4 Mrad dose had
normal meat odor after ten weeks at 32°F and showed no
changes during the four days exposure to the air. Similar
results were reported by Rhodes gt_al. '(1967) in their
studies on beef from barley fed animals.

Recently Urbain §£_al. (1968) reported that irradia-
tion at 50 to 150 Krad in combination with phosphate
treatment and vacuum packaging can extend the shelf life
of prepackaged fresh beef to about 21 days at 38°F.

WateréHolding Capacity and Drip
Formation in Fresh Meat

 

Water—holding or water-binding capacity is defined

as the ability Of the meat to hold fast to its own or

added water during application of any force such as pressing,
heating, grinding and centrifugation (Hamm, 1960). This
important property of meat has been shown to influence
color, flavor, tenderness, Juiciness and other meat quali-
ties during all processing operations after slaughter
(Arnold g£_al., 1956; Hamm, 1960; Lawrie, 1966).

In fresh meat the diminution of water holding capacity
is manifested by the exudation or formation of serum like
fluid commonly known as drip. This physical phenomenon is

common in retail and prepackaged fresh meat cuts. Aside

 

from being directly related to water-holding capacity,
drip formation has been shown to be influenced by the area
of the cut surface, the type of cuts, time of storage and
temperature at which the fresh cut is kept (Hamm, 1960;

Lawrie, 1966).

Use of Polyphosphates

It has been shown that incorporation of poly- or
condensed phosphates into meats improve their water-holding
capacity (Bendall, 1954; Mohler and Kiermeier, 1955;
Swift and Ellis, 1956, 1957; Kamstra and Saffle, 1959;
Sherman, 1961; Mahon, 1961). Investigations over the past
decade indicate that phosphates merit a place in meat pro-
cessing techniques. Different fields of application to
meat and meat products have been recognized and these
include: (1) cooked whole meat such as ham, picnics and

bacon; (2) cooked comminuted meats such as sausages;

(3) poultry. The use of sodium tripolyphosphate in pre-
venting drip formation in radiation pasteurized fish and
shellfish has been reported by Spinelli gg_al. (1967).

Several postulates have been advanced to explain
the nature of the action of polyphOSphates in improving
the water—holding capacity of meats. For instance,
polyphosphates, due to their anionic nature, are believed
to increase water—holding capacity through lowering of the
isoelectric pH of muscle proteins (Hamm, 1960). Grau e£_a1.
(1953) and Hamm (1956, 1958b) advanced the theory that
sequestering action of polyphosphate on calcium, magnesium
and zinc increases the water—holding capacity of raw meats.
Wierbicki g£_a1. (1957a) demonstrated that calcium
chloride and magnesium chloride increase fluid retention
of beef heated at 70°C. Popp and Muhlbrecht (1958) however,
take the view that polyphosphates do not increase the water
absorption capacity of the meat. 0n the contrary, they
merely restore the water absorption ability possessed
before slaughter of the animal.

In general, however, it is agreed that the tissue
contractile proteins actin and myosin in particular, are
largely responsible for the water-binding capacity of
muscle meat. The increase of water binding is the result
of the interaction between these and other fibrillar
proteins. Yasui et_al. (1964) Showed that there are two

types of phosphate bindings of polyphosphate to myosin.

 

10

The first of these is a direct binding of highly poly-
merized polyphosphate such as hexametaphosphate and the
other type is the preferential cation binding followed by
di— or tripolyphosphate binding. The second type of
reaction is greatly enhanced by the presence of univalent
ions, whereas the first is inhibited under this condition.
Improvement of water retention by ion binding is the

result of the changes in the charge of protein induced by

the ions. Under conditions in which ions are not bound,

f;.-..v'h"‘1"!" 9

polyphosphates increase the ionic strength and solubilized

 

the proteins. B

Effect of Ionizing Radiation.

 

Changes in water—holding capacity of meat due to
ionizing radiation have been observed by various workers.
Groninger gt_al: (1956) showed that there was a slight
increase in expressed drip in meat due to irradiation
from 0.6 to 15 Mrad. 'Noticeable loss in water—holding
capacity in meat proteins was reported by Cain gt_al.
(1958). Kuprianoff (1957) also noted that irradiation
often results in loss of juice and he theorized that this
effect is due to structural changes in muscle proteins.

Loss of fluid as drip was among the changes observed
by Rhodes and Shepherd (1966) during the extended storage
of radiation pasteurized lamb sides and beef Joints. The
amount ranged from 0 to 5% of the weight of the meat. As

a consequence of the exudation, part of the soluble pigment

11

in the drip was transferred to the surface layers of the
fat and gave a faint pinkish tinge. It is, however,

uncertain whether this fluid was exuded as an inevitable
consequence of the post-mortem changes or was induced by
the application of pasteurizing doses of ionizing radia-

tion.

Methods of Determination

Most of the methods used in the determination of
water-holding capacity of meat are based on the measurement
of water liberated by application of pressure on the muscle
tissue. These include sedimentation method (Mohler and
Kiermier, 1953a), centrifugation (Janicki and Walczack,
1954a; Kormendy and Gantner, 1954; Hamm, 1958b; Wiebicki,
gt_a1., 1957a; Sherman, 1961), pressing method (Grau and
Hamm, 1953; Wismer—Pedersen, 1958; Wierbicki, 1958) and
ultracentrifugation (Lloyd and Morgan, 1933). The exact
amount of loosely bound water in meat cannot be deter-
mined by any of these methods. Meat contains various
protein components and the water of hydration of each is
not known and besides the amount of physically absorbed
water is changed by the various laboratory methods. The
relative changes in water holding capacity, however, can
'be determined by considering the various muscle proteins
as a single component and by using the same method under
the same experimental conditions (Wierbicki and Deatherage,

1958).

 

l2

Lipid Oxidation and Pigment Changes
in Gamma Irradiated Meat

 

Meat undergoes oxidative deterioration during
exposure to the atmosphere and radiation. The two types
of oxidative changes which occur in meat are the oxidation
of fats and of heme pigments. Oxidation of fats is
manifested by the formation of rancid odor and flavor
whereas oxidation of heme pigments causes discoloration.
These two processes have been shown to be‘inter-related
and in fact they can accelerate one another (Watts, 1954).

Together they constitute a large part in the spoilage of

 

fresh meat especially in prepackaged or retail cuts.

Lipid Oxidation

The formation of peroxides in lipid during irradia-
tion had been demonstrated (Mead, 1952; Hannan and
Shepherd, 1954;‘Poling’gt_al,,'1955; Chipault et_ag,,
1958). The radiation-induced oxidation in meat has been
reported to be affected by total dose, dose rate, presence
or absence of oxygen during irradiation and post-
irradiation storage, presence of free radial acceptors
and antioxidants, and temperature during irradiation and
storage (Chipault, 1962).

In 1960, Lea gt_al. reported that a dose of 100 Krad
greatly accelerated lipid oxidation in beef'at chilled
storage, while at 50 Krad, the effect was variable but

always appreciable.' Samples irradiated at 25 Krad

13

however, showed signs of oxidation only after a very long
storage.

The reduction of preformed lipid peroxides by
radiation in inert atmosphere and anaerobic packaging has
been reported (Goldblith and Proctor, 1955; Groninger
33431., 1956; Lea 32:31., 1960; Greene and Watts, in press).

Methods of evaluating oxidative changes.-—The degree
to which fats in meat and meat products have undergone
oxidation has been evaluated by means of several chemical
and physical methods. These include peroxide value
determination (Lea, 1939), Kreis test (Patton gt_al., 1951),
manometric measurements of oxygen uptake (Tappel gt_§1.,
1961), and thiobarbituric acid test (Sinnhuber g§_al.,
1958; Tarladg s gg_a1., 1960; Evans, 1961). Organoleptic
evaluation of rancidity in meat has also been carried out
by several investigators (Timms and Watts, 1958; Tarladgis

et a1., 1962; Greene and Watts, in press).

Oxidative'Discoloration

Meat has a purplish color immediately after Slaughter.
Upon exposure to the atmosphere, it quickly assumes a
bright red color and longer exposure turns it to brown.
These color changes have been shown to be caused principally
by the reaction of myoglobin with atmospheric oxygen (Hill,
1933; George and Stratman, 1952; Watts, 1954; Landrock and

Wallace, 1955; Fox, 1966).

14

The color cycle which occurs in fresh meat have been
fully elucidated. The cycle is shown in Figure 2. The

cycle starts with myoglobin which is a purplish compound

Oxidation at low
0 concentration

 

 

 

 

2
-02
Oxymyoglobin > Myoglobin > Metmyoglobin F
(scarlet red)< +0 (purple) <E- (brown) '
2 reducing

agent

.mfl [-

Fig. 2.-—Color cycle in fresh beef (Landrock and
Wallace, 1955).

 

t‘t . I

and in which the iron in the phorphyrin ring of the heme
protein is in the ferrous state. This type of color is
normally predominant in uncut meats; 'Upo 'exposure to air,
oxygen attaches to heme protein forming'a scarlet red
compound, oxymyoglobin. This reaction is an oxygenation
and is reversible depending upon the concentration of
oxygen. If the oxygen supply is cut off as in vacuum
packaging, the oxymyoglobin is transformed to myoglobin.
Myoglobin in turn can be oxidized to a brown compound,
metmyoglobin in which the iron in the phorphyrin ring of
the heme protein is in the ferric state; This reaction
takes place if the oxygen concentration is low. The
metmyoglobin can be transformed to myoglobin by means of
reducing agents and by enzymatic reduction: Enzymatic

reduction of metmyoglobin in anaerobically packed meat has

15

been observed by Walters and Taylor (1963) and Cutaia and
Ordal (1964).

Several factors have been reported to influence
metmyoglobin discoloration. Niell and Hasting (1925) were
the first to observe that the rate of oxidation of the
heme pigments was accelerated at low partial pressure of
oxygen. Later, Brooks (1935) and George and Stratman
(1952) reported that at 1 to 20 mm Hg partial pressure of
oxygen, there was a maximum rate of oxidation of heme
pigments. The rate at these pressures, however, was
dependent on the concentration of the pigment, pH and
temperature. Landrock and Wallace (1955) reported that
oxygen permeability of packaging films affects the rate of
*oxidative discoloration of prepackaged fresh meat. They
further showed that with oxygen—impermeable film, the
metabolic process involved in pigment change would
eventually stop for lack of oxygen. At this condition
the heme pigments are in fully reduced myoglobin state.
Upon re—exposure to the atmosphere, the reduced myoglobin
would oxygenate and the meat would "bloom.”

The role of pH in the metmyoglobin formation has
been reported by Cutaia and Ordal (1964) and Stewart
§£_§l. (1965). Their results agreed in that as the pH
of the meat decreases (from 5.95 to 5.45) the rate of
metmyoglobin conversion to myoglobin decreases. This
effect was attributed to the effect of pH upon the enzyme

systems causing the generation of reducing power.

16

Stewart gt_al. (1965) are of the opinion that met-
myoglobin formed during storage is a result of two
opposing factors. These factors are autoxidation of the
ferrous pigment to metmyoglobin on one hand and enzymatic
reduction on the other hand. The net result of these two
reactions is determined by the various factors as pH,
temperature and other environmental factors. I“

Meats irradiated with ionizing radiations often
undergo pronounced color changes.‘ These color changes have
been noted and reported by many investigators (Ginger et_§1,
1955; Groninger et a1., 1956; Schweigert et a1., 1955;
Tappel, 1956). It is generally observed that meat
irradiated in excess oxygen undergoes brown discoloration
with formation of metmyoglobin either immediately after
irradiation or upon subsequent storage; 'With high irradia—
tion doses, the hematin compounds may be destroyed
oxidatively tO‘a large extent. In the practical range of
irradiation (0.046 to 2.8 Mrad) according to Tappel (1956),
these oxidative changes can be avoided by irradiation in
inert atmosphere or high vacuum.

Lea g£4a1; (1960) and Rhodes and Shepherd (1966)
reported that pasteurizing doses of ionizing radiation
greatly accelerated oxidation of heme pigments under
aerobic conditions. Similar results were reported by
Rhodes g£_a1.'(1967) in their studies on irradiated beef

from barley fed animals.

17

Methods for investigation of color changes in meat.--
Measurement of the amounts of the various forms of myo-
globin present at the surface of the meat have been
carried out in several ways. Broumand EE_§£' (1958)
applied absorption spectrophotometry to extracts of meat
taken from the surface of beef cuts. Winkler (1939a)
and Winkler g£_§1. (1940) described an objective method
for following color changes on meat surface using a
photoelectric comparator. A rapid nonedestructive technique
for measuring the relative concentration of oxymyoglobin,
myoglobin and metmyoglobin at the surface of the meat
based on reflectance spectrophotometry has been proposed
by Dean and Ball (1960). Stewart gt_a1. (1965), Snyder
(1965), and Snyder and Armstrong (1967).

Reflectance spectrOphotometry as applied to meat is
based on the fact that the reflectivity of the three major
pigments (myoglobin, oxymyoglobin and metmyoglobin) is
the same at a single point at 525 mp. This point which is
known as the isosbestic point of the three pigments, can
be used as a reference for total pigment content (Snyder,
1965; Stewart gt_a1., 1965). Myoglobin and oxymyoglobin
are isobestic at 571 mu while 474 mu is the isosbestic
point for oxymyoglobin and metmyoglobin; Using the ratio
of the isosbestic point at any two pigments to the isos—
bestic point of the three pigments, the relative concen-

tration of any pigment can be obtained; ‘For instance, the

18

ratio of the reflectivity at 571 mu to that at 525 mu will
give the relative amount of metmyoglobin while the ratio
at 474 mu to that at 525 mu will measure the relative
amount of myoglobin in the total pigment present at the
meat surface.

Coupled Oxidation of Heme Pigments
and Lipids in Meat

 

 

HaurowitZ'§£_al.'(l94l) showed that free radical
intermediates from lipid oxidation can decompose hemes
causing loss of color. On the other hand, evidence was
shown by Younathan and Watts (1960) and'Brown'gE_a1.

(1963) that during oxidation of oxymyoglobin and myoglobin
ferric heme pigments can catalyze the oxidation of the
tissue lipids in meat.

It appears that vacuum packaging is the most feasible
method to use in conjunction with radiation pasteurization.
One disadvantage of vacuum packaging, however, is that
reduced myoglobin which is purple predominates on the meat
surface. This is not the typical color the consumer
associates with fresh meat.

The use of phosphate seems to offer a solution to
the existing problem of drip formation in prepackaged fresh
meat. Phosphate may also have a beneficial effect on the
color of the meat.

By using phosphate, vacuum packaging, irradiation

and subsequent exposure of the meat to the atmosphere, a

19

solution to the existing problem of prepackaged fresh meat

salable life extension is anticipated.

MATERIALS AND METHODS

Mae:
Rounds from U.S.D.A. "Commercial" grade round were
used throughout these experiments. The beef was freshly
cut from the intact rounds of unknown history received
at the meat department of Michigan State University Food
Stores. Further cutting and preparations of the meat

samples were done at the Food Science Laboratory.

Phosphate Pretreatment
PhOSphate pretreatment was carried out by dipping
meat samples into phosphate solutions. 'Sodium tripoly-
phosphate was obtained from Calgon Corporation, Pittsburg,
Pennsylvania; Preparations of dipping solutions are

based on percentage weight aqueous solution.

Packaging Materials

Packaging materials used include:

1. Laminate ("L" pouches) consisting of polyester
(Mylar) base with a thin coat of polyvinylidine chloride
(saran) applied to the outer surface and a heavier
extrusion coat of polyethylene on the inner surface which
acts as a sealant. These highly gaSéimpermeable pouches

were supplied by the International Kenfield Distributing

2O

21

Company under the trade name "IKD Super All-Vak #13."
The size of the pouches used was 7" x 8".

2. Plasticized polyvinyl chloride fresh meat wrap
film "Resinite RMF—61" manufactured by the Borden Chemical
Company. This is a highly oxygen-impermeable film.

Package sealing is accomplished by the Kenfield
package sealer (Model C-14) which has a vacuum and gas

flush attachments.

Methods of Irradiation

Irradiation was conducted using the pool-type
Co—60 gamma source housed in the Food Science Building,
Michigan State University, East Lansing, Michigan. The
strength of the source was measured to be 51,000 curies
in May, 1967. The dose rate at 50 cm from the source
center was measured to be about 200 Krad per hour.

The source is comprised of 24 BNL MK-l doubly
encapsulated source strips arranged in a cylindrical
pattern and when the source is in the fully up-position,
are enclosed in a stainless safety shield having an out—
side diameter of 34.5 cm. The time required to raise the
source from the bottom of the pool to the fully—up
position was 19—21 seconds. The pool depth is 15 feet.

Packaged meat samples which were mounted on cardboard
supports were placed at measured distances from the source

center and exposed to gamma radiation for a predetermined

22

length of time. The time and distances were based on

doses previously measured by Fricke chemical dosimeter.

Drip Measurements

 

In the determination of the optimum phosphate con-
centration and optimum dipping time that will effectively
retard drip formation, the method of Howard (1956) for r
drip measurement was used. Beef slices having a dimension 3
of 5 x 5'x 1 cm (shortest dimension being in the direction

of the muscle fiber) were dipped in phosphate solution,

 

drained and placed in taped aluminum dishes approximately
8 cm in diameter and 5 cm deep. In each aluminum dish

were placed glass grids which served to keep the samples
out of contact with the exuded fluid. 'Sample and container
were weighed immediately and sealed with cellophane tape

to prevent moisture loss through vaporization. Samples
were then stored in the refrigerator maintained at 38°F.
Periodic determinations of drip loss throughout the storage
period were made by measuring the loss in weight of samples.
This was done by transferring the sample to a tared
container and weighing. The loss in weight was calculated
as percentage drip loss.

For retail size samples used in the study on the
effect of various pasteurizing doseS'of ionizing radia-
tion on drip formation, an alternative method was used.
Samples were packed in moisture-impermeable film, vacuum

sealed, irradiated and stored in the refrigerator. Loss

23

of weight was determined at the end of storage by draining

the samples on a wire screen. The drip loss was calculated

as loss of weight.

Phosphate Absorption Determination

The amount of sodium tripolyphosphate solution that
was absorbed by the meat was determined by weighing the
samples before and after dipping and draining.

Analyses for total phosphorus content of both
treated and untreated samples were made to determine the
amount of sodium tripolyphosphate that was absorbed by
the meat. In the analyses, meat samples were ground and
phosphorus was determined on aliquots by colorimetric

method of the Association of Official Agricultural

Chemists (1960).

pH Measurements

 

The pH of the meat was measured before and after
phosphate pretreatment, immediately'after irradiation,
during storage and at the end of 21 days. A 1:10
mixture of the meat sample and distilled water was
blended in a Waring Blendor. The pH of the blended
mixture was determined with a Beckman Model 76 Expando-

metric pH meter.

Water-holdinggCapacity Determination
The centrifugation method by Sherman (1961) for the

determination of percentage water retention was used.

24

Meat samples were ground by passing three times through

a laboratory-size mincer fitted with 3-mm plate. Ten
grams of meat were weighed into a tared centrifuge

tube (50 m1 capacity) and 10.0 ml of distilled water was
introduced from a burette. After thorough mixing with

a glass rod, the tubes were stoppered and the mixture was
allowed to stand overnight for 18 to 24 hours at 38°F.
The stopper was removed and the tube was centrifuged at
3000 rpm for 20 minutes in a Lourdes Model AX centrifuge.
Afterwards, the supernatant fluid was decanted through a
presoaked and drained filter paper resting in‘a glass
funnel into a 10 ml graduated cylinder that could be read
to within 0.05 ml. The mixture was drained into the
filter paper for 10 minutes. The watereholding capacity
of the sample expressed as percentage water retention per
gram of meat was calculated by the equation given as

follows:

0

Vol. (m1) fluid added - vol. (m1) fluid not absorbed

Weight (gm) of meat X 100

Lipid Oxidation Measurements

 

Lipid oxidation was measured by thiobarbituric acid
(TBA) test (Tarladgis §t_a1,, 1960). A ten gram meat
sample was blended with 50 m1 of distilled water in a
Waring Blendor for two minutes. The mixture was trans-

ferred quantitatively into a Kjeldahl flask by washing

25

with an additional 47.5 ml distilled water. The pH of

the mixture was adjusted to about 1.5 by adding 2.5 m1
concentrated HCl. A small amount of Dow Silicone defoamer
was placed into the lower neck of the flask and the mixture
was heated on the Kjeldahl distillation apparatus. Using
the highest heat obtainable on the distillation apparatus,
30 m1 distillate were collected within 10 minutes from the
time boiling begins.

A 5-m1 aliquot of the distillate was pipetted into a
glass stoppered tube and 5 m1 of 0.02 M‘2ethiobarbituric
acid in 90% glacial acetic acid solution were added.

After mixing the contents, the tube was immersed in a
boiling water bath for 35 minutes. A distilled water-
TBA reagent blank was prepared and treated the same way
as the samples.

After heating, the samples were cooled in tap water
for 10 minutes. 'A portion of the solution was transferred
to a colorimeter test tube and the optical density was
read against the blank at wavelength of 538 mu. A Bausch
and Lomb Spectronic 20 Spectrophotometer was used.

Results are expressed as TBA number based on
malonaldehyde standard curve. The standard curve was
prepared by making appropriate dilutions of 1 x 10-3M 1,
l, 3, 3-tetra—ethoxy—propane standard solutions to give

8

amounts ranging from 5 x 10- to 2 x10-7 moles

malonaldehyde in 5 m1. Determination were run directly

26

on 5 ml by the method described above for testing the
distillate.

The TBA number, expressed as milligrams malonaldehyde
per 1000 grams of meat, was calculated based on the 68%

distillation recovery as reported by Tarladgis et a1. (1961).

‘Measurement of Pigments

Visual observations of meat samples were made during
storage in vacuum and during exposure to the atmosphere.
Subsequently, samples were prepared for reflectance
measurements. The method used to determine the relative
amount of pigments at the surface of the meat was reflect-
ance spectrophotometry as described by Snyder (1965) and
Stewart §t_a1. (1965). A Beckman D.U. Spectrophotometer
with reflectance attachment was used. Samples were con-
tained in plastic ice cube holders of dimension great
enough to cover the light port of the reflectance attach-
ment. A freshly scraped block of Mg) was used as a
reference standard.

Reflectance readings were obtained on the absorbancy
scale at 571 mp, 525 mu and 474 mu. The readings were
next converted to reflectance values for infinitely thick
samples or reflectivity value (Rm) using standard tables
which relate absorbance to percentage transmittance.
Reflectivity valueS'(Rm) were in turn converted to K/S
values using Table D in the appendix of Judd and Wyzecki

(1964). K is the absorption coefficient and S is the

27

scattering coefficient. These values account for the
fact that a fraction of light is scattered by the opaque
meat surface, and that the proportion of the light
absorbed by the pigment to the scatterd light from the
sample decreases with increasing reflectivity.

The ratio of K/S at 474 mu and K/S at 571 mu to

K/S at 571 mu
K/S at 525 mu

was used to determine the relative amount of metmyoglobin

 

that at 525 mu were obtained. The ratio

by referring to a standard curve.

To develop a standard curve, reflectance measure—
ments were taken with meat samples in 100% myoglobin,
100% oxymyoglobin and 100% metmyoglobin. 'Preparations
of these samples were done as follows:

Samples of 1 3/4 x 1 1/2 x 3/4 inch dimensions were
prepared from the ribeye (semitendinosus) muscle of
"Commercial" grade beef bottom round and placed in plastic
ice cube holders. The samples were immediately vacuum
packed in oxygen-impermeable pouches (allowing them to
bloom as little as possible) and left at room temperature
for four hours. This time period was enough to obtain
samples having a predominantly myoglobin pigment as
indicated by the constant reflectance spectra. The samples
were then measured as representing 100% myoglobin.

The samples were then unwrapped, left for two hours
at 38°F, packaged in oxygen permeable film (Resinite RMF—

61) and stored overnight at 38°F. The reflectance of the

28

samples was measured and was considered to represent that
of 100% myoglobin.
The same samples were unWrapped and the surface was

painted with 1.0% K Fe(CN)6 at one hour intervals. The

3
samples were then overwrapped with Resinite RMF-61 film
and stored overnight at 38°F. The reflectance of the
samples was measured the following day and was considered
to represent that of 100% metmyoglobin.
Reflectance readings were obtained at 571 mp,
525 mu and 474 mu against a reference standard MgO.
Readings were obtained on the absorbancy scale and then
converted to reflectivity value (Rm). Reflectivity values
were in turh'converted to K/S values. The ratio of K/S
at 474 mu and K/S at 571 mu to that at 525 mu was obtained.
An assumed linear curve between K/S ratio at 571 mu/
525 mu for 0 and 100% metmyoglobin was constructed. This
curve served as standard curve in the determination of the

relative proportion of metmyoglobin at the surface of the

samples.

"Organoleptic Evaluation (Color and Odor)

Meat samples which have been stored for 20 days in
vacuum were rewrapped with oxygen-permeable film and
eXposed to the atmosphere for one day at 38°F. Samples
were then presented to a panel consisting of 10 to 12
Judges. The panel was asked to rate the color and odor

0f the meat on the following scale: 'poor, very bad, bad,

29

fairly bad, marginal, fairly good, good, very good and
excellent. Numerical values of 1 to 9 (from poor to

excellent) were assigned and the average sensory scores

were calculated.

RESULTS

Effect of Various Concentrations of Sodium
"Tripolyphosphate Dipping Solution and
Dipping Time on Drip Loss and Phosphate
‘ Absorption in Fresh Beef

The first part of this study was designed to
determine the optimum concentration of sodium tripoly-
phosphate dipping solution and the optimum dipping time
that will effectively retard drip formation in beef slices
during storage at 38°F for 21 days.' The amount of sodium
tripolyphosphate that was absorbed by the meat was also
determined. Beef Slices were prepared from ribeye muscles
of "Commercial" grade round. The meat was trimmed of
adipose tissue and sliced into samples with a dimension
of 5 x 5 x 1 cm. Samples were cut in such a way that the
shortest dimension is in the direction of the muscle
fiber.

The ribeye muscle from a "Commercial" grade round
was selected since it is convenient to prepare uniform
size samples and there is some indication that cuts from
the ribeye muscle are more sensitive to drip than cuts
from other parts of the carcass. The pattern of cutting
the samples is based on the findings that the amount of
drip from small samples is greater when the shortest

Ciimension (i.e., its thickness) is along the fibers of

30

31

the muscle than when it is across them (Howard,
1956).

In the determination of the optimum concentration
of dipping solution that will effectively retard drip
formation, samples were dipped in 2.5, 5.0, 7.5 and 10.0%
(per cent by weight) aqueous solution of sodium tripoly-
phosphate for 30 seconds and drained on a wire screen
for about 10 to 15 minutes. The temperature of the
dipping solution was about 72°F. Samples that were not
dipped were run along as control. The samples were then
placed in aluminum dishes and stored at 38°F.‘ Periodic
determination of the amount of drip formed during the
entire storage period was conducted using the method pre—
viously described;‘ Three identical'eXperiments were con-
ducted at different times with different pieces of meat
and the average of nine measurements per treatment is
shown in Figure 3. ‘It is shown that drip formation was
effectively prevented to a greater degree when the samples
were dipped in 7:5% and 10.0% aqueous solution of sodium
tripolyphosphate than when they were dipped in 2.5% and
5.0% solutions. Samples which did not have any pretreat-
ment showed considerable amount of drip loss during the
21 days storage.

To determine the optimum dipping time that will
effectively retard drip formation, samples were dipped in

10.0% aqueous solution of sodium tripolyphosphate for

DRIP LOSS

32

 

 

 

6.0-
H control
5.03_ H 205% .
o—«35.0%
H7 5% °
“.044 . u
A H10.0%
S
(5 3.0% -
F3
3 0
>4 2.0» 0
m /
R
v 1 0‘. ./
O A
0 0 — j, g/I:
0 7 14 21

STORAGE TIME (DAYS)

Figure 3.-—Drip loss during storage at 38°F of
fresh beef slices dipped at various concentrations of
sodium tripolyphosphate for 30 seconds.

33

0, 10, 20, 30, 60 and 120 seconds. The samples were
drained and stored at 38°F for 21 days. Periodic deter-
mination of drip was conducted throughout the storage
period.

The amount of sodium tripolyphosphate absorbed by
the meat at various dipping time was determined by total
phosphorus analysis before and after dipping and draining.
Figure 4 shows the results. Dipping from 30 to 120
seconds resulted in a significant retardation of drip
formation throughout the entire 21 day storage at 38°F.
The amount of sodium tripolyphosphate absorbed by the meat
shows a rapid increase from 10 to 60 seconds dipping time.
This, however, tends to level Off from 60 to 120 seconds.

It is apparent that dipping times from 30 to 120
seconds in 10.0%’sodium tripolyphSOphate can effectively
retard drip formation up to 21 days at 38°F. Phosphate
uptake determinations at various dipping times showed a
mean sodium tripolyphosphate uptake of 0.43% at 30
seconds, 0.53%'at‘60 seconds and 0.57% at 120 seconds.

Effect of PhOSphate Pretreatment on Drip
‘Formation, pH and WatereHolding Capacity
_—Iof‘Radiation'Pasteurized'Fresh‘Beef

The following experiments tested the effectiveness of
phosphate pretreatment in retarding drip formation in
radiation pasteurized beef slices stored in vacuum at
38°F for 21 days; Beef ribeye muscles from "Commercial"

grade round were trimmed of adipose tissue and sliced

34

 

 

 

 

E] O. .0

m

m

o

m

g 0. .0

LL]

BA

<38 0.

mt:

Dec: ,0

mta

c>m

L133 0,

0..

:33 \ o——O’sodium tripolyphos-

O \ phate absorbed 2'0

Efifi 0.20; \

tr: O—Odrip loss

B b\ ‘L1 0

E 0.10" x\\ '

H \\

D \O_ _________

8 0.00 , T. , ----- <O.O
0 30 60 90 100

DIPPING TIME (SECONDS)

Figure 4.--Phosphate uptake by fresh beef slices
dipped for various time intervals in 10.0% sodium tri—
polyphosphate and drip loss after three weeks storage
at 38°F.

35

into 1 to 2 cm thick samples. The weight of the samples
ranged from 100 to 250 grams. After weighing, the samples
were dipped in 10.0% aqueous solution of sodium tripoly-
phosphate for 30 to 60 seconds. The temperature and pH
of the dipping solution were about 72°F and 9.5
respectively; ~The'samples were next drained on a wire
screen for 10—15 minutes, weighed and vacuum packed in
oxygen-impermeable pouches (IKD-Super A110Vak #13). They
were mounted on cardboard supports and irradiated at 0,
50, 100, 150, 250 and 500 Krad. Samples which did not
have phosphate treatment were irradiated at the same
dosages." After irradiation they were dismounted from the
supports and stored at 38°F for 21 days.

The amount of sodium tripolyphosphate solution that
was absorbed by the meat and pH changes during the dipping
process were determined. Table 1 gives these results.

The amount of solution uptake is shown to vary between
meat samples used in different runs;’ The amount of
solution uptake by various meat samples ranged from 0.91
to 2.00 per cent by weight. In all cases, the treatment
process caused an increase in the pH of the meat. The
increase in the pH ranged from 0.37 to 0.45 pH unit.

Data in Figure 5 show that in Spite of the increase
in weight due to the dipping process, much less per—
centage drip loss was observed on the treated samples than
on the control. There appeared to be no noticeable change

in the amount of drip formed as caused by the various

36

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37

TABLE 1.--Solution uptake and pH of fresh beef slices after
dipping in 10.0% solution of sodium tripolyphOSphate for 30
to 60 seconds and draining for 10 to 15 minutes.

 

 

* pH Before pH After % Solution
Experiment Dipping Dipping Uptake**

l 5.50 5-95 1.00—1.62

2 5.60 6.03 0.91-1.62

3 5.75 6.12 1.14-2.00

 

*
Identical experiments performed at different times
and on different pieces of meat.

**
Range obtained from 18 samples (per cent by weight).

pasteurizing doses of ionizing radiation. There was,
however, a slight increase in drip loss due to vacuum in
both phosphate treated and the untreated samples.

Figure 6 shows the percentage water retention of
irradiated meat samples after 21 days of storage at 38°F.
It is shown that phosphate pretreatment greatly increased
the water holding—capacity of the beef samples. The
increase in the percentage water retention due to phosphate
pretreatment ranged from 6.40 to 9.00%. The percentage
water retention or water holding capacity is shown to
differ among samples used in different runs. No large
changes in percentage water retention due to pasteurizing

doses of gamma radiation were observed.

38

 

 

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when Hm pow oonopm coco ocm coapmHUMD magmw mo momoo wcflmflszoummo msofism> pm umpmflomnnfl
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o I Apahxv omen

a m N « I*mv:oEHthKa
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NOIJNM mm s

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koém
devotes n D

@333. 33.32% I I

39

In Figure 7, the percentage water retention during
storage of beef slices treated with sodium tripolyphosphate
solution prior to irradiation at 100 Krad is compared with
the percentage water retention of beef that was not treated.
The gercentage water retention of unirradiated beef samples
with and without phosphate treatment is also compared. It
is shown that phosphate treated samples have relatively
high percentage water retention compared with the untreated
ones. No significant changes in water retention due to
irradiation at 100 Krad was observed. There was, however,

a slight increase in water retention in all cases during e3
storage for 21 days at 38°F.
Effect of Phosphate Pretreatment, Vacuum

Packaging and Radiation on Lipid
Oxidation in Fresh Beef

 

The object of this part of the study was to determine
the degree of lipid oxidation that has occurred on beef
samples after 21 days at 38°F and the effect of phosphate
treatment, vacuum packaging and irradiation on lipid
oxidation. Also of interest was the effect of exposing
the meat to the atmosphere after 21 days in vacuum on
lipid oxidation.

Beef slices (1 to 2 cm thick) from ribeye muscle of
"Commercial" grade rounds were dipped in 10.0% aqueous
solution of sodium tripolyphosphate and vacuum packed in
oxygen impermeable film (IKD Super All-Vak #13). The

samples were irradiated at 0, 50, 100, 150, 250 and 500

40

 

“mm menial
“
9”
O
F

  

 

14.0 2” H- phosphate treated - O Krad
- . O---. - phosphate treated -100 Krad

A""~A- untreated - 0 Krad
O—--O - untreated - 100 Krad

 

10.0 h— _I— n A
0 17.0 11m 21.0

TDEIOFEWGMfiE UMIS)

Figure 7.——Water retention during storage at 38°F of
irradiated fresh beef pretreated with sodium tripolyphosphate.

41

Krad and stored at 38°F. Samples which did not receive
phosphate pretreatment were exposed to the same dosages.
At the end of 21 days, the vacuum of each pouch was broken.
Representative samples were taken from the individual
slices immediately upon opening and analyzed for TBA number.
The remaining portion of the slice was rewrapped with
oxygen permeable film and exposed to the atmosphere at
38°F. Daily measurements of lipid oxidation (TBA number)
were conducted during this time. Results of these
experiments are shown in Table 2.

It can be observed (Table 2) that vacuum packaging
retarded lipid oxidation up to 21 days of storage at 38°F.
This is evidenced by the relatively low TBA numbers
obtained at the end of 21 days. Upon exposure to the
atmosphere, however, TBA numbers began to increase with
storage time up to three days. Differences in TBA numbers
among the phosphate treated samples and untreated ones
were less pronounced. No large differences in TBA numbers
were observed between irradiated and unirradiated samples.
In general, there appeared to be more variability in TBA
numbers among meat samples used in various experiments.

In a separate set of experiments, the progression
of lipid oxidation changes was followed during storage
under vacuum and during the subsequent exposure to the
atmosphere. Phosphate treated and untreated beef slices

were vacuum packed and irradiated at 0 and 100 Krad. After

42

TABLE 2.-—Effect of phosphate pretreatment, vacuum packag-
ing, radiation and subsequent exposure to the atmosphere
on lipid oxidation in fresh beef during storage at 38°F.

 

TBA Numbera
After 21 Days Exposed to the

 

Experi— Dose Phosphate
ment* (Krad) Treatment**

 

 

 

Days in ' Atmosphereb
Vacuum
l 2 3
0 O 0.08 0.36 0.60 1.04
P 0.09 0.49 0.68 1.10
50 0 0.13 0.51 0.72 1.13
P 0.13 0.36 0.57 1.08
100 O 0.14 0.41 0.61 1.12
1 P 0.13 0.53 0.69 1.07
150 O 0.17 0.46 0.58 1.15
P 0.22 0.34 0.52 1.07
250 O 0.27 0.36 0.54 0.79
P 0.17 0.42 0.49 0.84
500 O 0.31 0.43 0.51 0.87
P 0.14 0.33 0.50 0.90
0 O 0.33 0.52 0.91 1.71
P 0.36 0.58 0.78 1.75
50 0 0.36 0.54 0.78 1.73
0.31 0.67 0.82 1.86
100 O 0.34 0.56 0.79 1.55
2 P 0.28 0.50 0.92 1.61
150 0 0.26 0.43 0.78 1.53
P 0.24 0.47 0.85 1.56
250 O 0.26 0.39 0.79 1.56
P 0.26 0.41 0.77 1.55
500 O 0.28 0.39 0.80 1.48
P 0.28 0.38 . 0.75 1.48

 

¥__
Identical experiments performed at different days with
different pieces of meat.

**
O--untreated; P—-phosphate treated.
3Average of two replicates

bNumber of days exposed to the atmoSphere.

43

irradiation they were stored at 38°F. At the end of 0, 7,
14 and 21 days, the samples were analyzed for TBA number.
0n the twenty-first day the samples were rewrapped with
oxygen permeable film and stored for three more days at
38°F. Daily TBA number determinations were made during this
time. Figure 8 gives the results. It can be observed that
in all cases there was a slight increase in TBA numbers
during the first seven days under vacuum. This however
decreased from the seventh to the twenty—first day. No
large difference in the degree of lipid oxidation between
phosphate treated and untreated samples, and between
irradiated and unirradiated samples was observed. Upon
exposure to the atmosphere, however, there was a slight
increase in TBA numbers in all cases on the first day
and continued to increase up to the third day.
‘ResultS'in the Preparation of‘Standard
Curve for Pigment Determination

In the setting up of the assumed linear curve between
the limiting K/S ratios at 571 mU/525 mu for 0 and 100%
metmyoglobin, samples were obtained from the various ribeye
muscles used in color and pigment changes studies. The
preparation of the samples to obtain 100% myoglobin, 100%
oxymyoglobin and 100% metmyoglobin was performed on the
same day the various storage studies were set up. A total
of sixteen determinations was accumulated and the results

were summarized in Table 3. From the data, the standard

44

2.5

io——O -no]stmnte-Olhud
2-0 o---O - phosphste treated - 0 Krad

D--—D - no phosphate - 100 Krad
lymmdb - phosphate treated - 100 Krad

 

 

 

 

TEME(E'SNEMGE(IMIS)

Figure 8.-—Progression of lipid oxidation changes in
irradiated fresh beef during storage in vacuum for 21 days
followed by exposure to the atmosphere for three days at 38°F.

45

571 mu
TABLE 3. Ratios of K/S at 556—53

100% myoglobin, 100% oxymyoglobin and 100% metmyoglobin.

for samples representing

 

K/S at 571 mu
K/S at 525 mu

 

 

 

Pigment No. of Samples

Range Average
Myoglobin 16 1.22-1.44 1.32
Oxymyoglobin l6 1.15—1.39 1.33
Metmyoglobin 16 0.52-0.66 0.59

 

curve for determination of the relative proportion of
metmyoglobin was constructed. It is shown in Figure 9.

Table 3 summarizes K/S ratio at 571 mu/525 mu
calculated from the reflectance readings of 16 samples.
The average K/S ratio at 571 mu/525 mu are 1.32 for
myoglobin and 0.59 for metmyoglobin. Stewart et a1. (1965)
reported K/S ratio at ggé—gfi-of 1.4 for myoglobin and 0.56
for metmyoglobin. The slight discrepancy in the values
may be attributed to the fact that they used ground
samples while in the present studies solid cut samples
were used.

In using the K/S ratios at %%%—%%, a linear relation

is assumed between the ratios and the percentage metmyoglobin

in the meat samples (Figure 9).

46

 

1,40

1.20

. '8

is

 

K/S at 571 mu
K/S at 525 mu

 

0.70

0.50
100 90 80 7o $netawoglob1n 30 20 10 o

o 10 20 75 myoglobin + % moglobin 80 90 100

Figure 9.--Assumed linear relation between ratios

Of K/S at 3;3-%% and the percentage metmyoglobin.

47

Effect of Phosphate Pretreatment, Vacuum
Packaging, Radiation and Subsequent
Exposure to the Atmosphere on
Color and Metmyoglobin
Formation in Fresh Beef

 

 

 

The purpose of this part of the work was to determine
the combined effect of phosphate pretreatment, vacuum
packaging and irradiation on the color of the fresh beef
slices after 21 days storage at 38°F. Also of interest
was the response with respect to the regeneration of red
color at the surface of the meat during exposure to the
atmosphere after storage in vacuum.

A separate set of experiments was conducted in this
particular study. In order to reduce the variability of
pigment constituents between muscles, samples were obtained
solely from ribeye muscle of "Commercial" grade beef. The
meat was trimmed of adipose tissue and cut into 1 to 2 cm
thick slices. ‘The slices were then dipped in sodium
tripolyphosphate solution, drained and vacuum packed in
oxygen—impermeable pouches. They were then irradiated at
0, 100, 200, 300, 400 and 500 Krad. Samples not treated
with sodium tripolyphosphate were exposed to the same
dosages. After irradiation the samples were stored at
38°F.

At the end of 21 days, the vacuum of each pouch was
broken and the samples were prepared for reflectance
measurements. Samples were cut into pieces having

1 3/4 x 1 1/2 inches dimensions, placed in plastic ice

48

cube holders and wrapped with oxygen permeable-film
(Resinite RMF-6l). The preparation of the samples and
reflectance measurements were done quickly making
exposure to the atmosphere as short as possible. Visual
observations'on the color of the samples were also made.
The samples with oxygen-permeable film wrap were further
stored at 38°F. After 24 hours, reflectance measurements
were again made.

Experimental data presented in Table 4 indicate that
there is a considerable difference in color between
phosphate treated samples and untreated samples. The
visual observation showed that in general, phosphate
treated samples appeared purple in color while the
untreated ones were brown after 21 days in vacuum.
Reflectance measurements showed that reduced myoglobin
predominates*in phosphate treated samples while consider—
able amounts of brown pigment metmyoglobin are present
in the untreated samples. Pasteurizing doses from 50
to 300 Krad did not show any detectable effect on metmyo—
globin formation. At 400 to 500 Krad, there was a slight
discoloration, with the phosphate treated samples appearing
purplish brown while the untreated ones appeared brown.

Exposure of the meat to the atmosphere for a day at
38°F, shifted the color of phosphate treated samples from
purple to red. Samples without phOSphate pretreatment on

the other hand remained brown. In all cases, there was an

49

TABLE 4.—-Effect of phosphate pretreatment, vacuum packaging,

radiation and subsequent exposure to the atmosphere on color

and metmyoglobin development on fresh beef during storage at
38°F.

 

Storage time (days)

 

 

 

 

 

Phosphate 21* 22xx
Dose Treatment
(Krad) ***‘ 'Color % Color %
(Visual Metmyo- (Visual Metmyoa
observa- globin “ observa- globin
tion) tion)
0 0 Brown 11.5 Brown 28.2
P Purple 0.0 Red 2.0
50 0 Brown 9.0 Brown 24.7
P Purple 0.0 Red 3.2
100 0 Brown 5.0 Brown 18.0
P Purple 0. Red 7.0
200 0 Brown 11.5 Brown 28.0
P Purple .0 Red 3.0
300 0 Brown 10.3 Brown 27.5
P Purple 0.0 Red 9.5
“00 0 Brown 21.2 Brown 43.0
P Purplish Reddish
brown 9.0 brown 11.5
500 0 Brown 47.0 Brown 66.0
P Purplish Reddish
brown 10.0 brown 20.2
x

No. of days in vacuum.

xx
21 days in vacuum plus one day exposure to the
atmosphere.

xxx
0—-untreated; P--phosphate treated.

aaverage of two determinations.

50

increase of metmyoglobin during exposure to the atmosphere.
Reflectance measurements after exposure showed that both
unirradiated samples and those irradiated at 50, 100, 200
and 300 Krad with phosphate pretreatment have lower per-
centages of metmyoglobin than samples that received similar
dosages but were not treated with phosphate. The pigments
in the phosphate treated samples appeared to be in
oxygenated form as evidenced by the predominant red colora—
tion. Phosphate treated samples that were irradiated at
400 and 500 Krad appeared reddish brown. The amount of
metmyoglobin, however, is less than those samples that were “*i
exposed to 400 and 500 Krad but did not receive phosphate
treatment.

Studies on the progression of pigment changes during
storage were performed at different times using a different
set of meat samples. Samples from ribeye muscle with
1 3/4 x 1 1/2 x 3/4 inches dimensions were prepared. After
dipping in 10.0% solution of sodium tripolyphosphate, the
samples were placed in plastic ice cube holders, vacuum
packed in oxygen-impermeable pouches and irradiated at 0
and 100 Krad. 'Samples without phosphate treatment were
exposed to the same dosages. After irradiation, the samples
were stored at 38°F. At the end of 0, 7, 14 and 21 days,
reflectance measurements were conducted directly on the
samples while still in the package." At the end of 21 days,

the vacuum of each pouch was broken. ‘The'samples were

51

rewrapped with oxygen-permeable film and stored at 38°F
for three more days. Daily reflectance measurements were
conducted during this time.

The progression of metmyoglobin formation during
storage in vacuum and during the subsequent exposure to the
atmosphere of phosphate treated and untreated beef slices
irradiated at'0 and 100 Krad is shown in Figure 10. It I
is apparent that the percentage metmyoglobin is lower in
phosphate treated samples than in untreated ones throughout
the storage period in vacuum and during exposure to the
atmosphere. There was a rapid increase in metmyoglobin
formation beginning between the seventh and fourteenth
days up to the twentyefirst day of storage in vacuum in
the case of beef slices without phosphate 'pretreatment.

In phosphate treated samples, a slight increase in methO-
globin was observed beginning between the fourteenth and the
twenty-first days. At the end of 21 days in vacuum, all
samples that did not have phosphate treatment appeared
brown while the phosphate treated ones retained their

deep purple color. Upon subsequent exposure to the
atmosphere, the predominant purple color of the phosphate
treated samples reverted to red color. No such reversion
was observed with the 'untreated ones. There was, however,
in all cases an increase in metmyoglobin at the surface of
the meat sampleS'after three days exposure to the atmo-

sphere. It is also apparent from Figure 10 that irradiation

52

60A)!» 0

./
50.04- ?
I

.-——-O - no phosphate - 0 Krad . '

A—«o - no phosphate - 100 Krad \‘I-C
40.0 L O”---O - phosphate treated - 0 Krad 0
D—oo—D - phosphate treated - 100 Krad I
A»

' f"

 

10.0

 

 

 

4
O 4 8 12 16 20 24
STORAGE TIME (DAIS)

Figure 10.——Effect of phosphate pretreatment on metmyo—
globin formation in irradiated and unirradiated fresh beef
during storage for 21 days at 38°F followed by exposure to the
atmosphere for three days.

53

at 100 Krad did not affect metmyoglobin formation in

phosphate treated and untreated samples.

Organoleptic Evaluation (Color and Odor)

The combined effect of phosphate treatment, vacuum
packaging, radiation and the subsequent exposure to the
atmosphere on color and odor of the meat was tested.

Beef slices from the ribeye muscles of commercial grade
round were phosphate treated, drained, vacuum packed and
irradiated at 0, 50, 100, 250 and 500 Krad. They were
stored at 38°F. ‘At the end of 20 days the vacuum of each
pouch was broken.' The samples were then rewrapped with
oxygen-permeable film and exposed to the atmosphere for

one more day at 38°F. Similar treatments were given to
beef samples which did not receive phosphate pretreatment.
Panel acceptability tests on color and odor were made after
exposure to the atmosphere. Results are shown in Table 5.

The data of Table 5 show that the color of phosphate
treated samples is superior to that of the untreated ones.
Panel members distinctly preferred phosphate treated
samples (colorwise) to the untreated ones. The mean
color scores of phosphate treated samples ranged from
fairly good to good (6.0 to 7.0), while those of the
untreated ones ranged from fairly bad to marginal (4.0 to
5.0). There was no large difference in odor scores between

phosphate treated and untreated samples. ‘Unirradiated

54

samples and those that were irradiated at 500 Krad received

lower ratings than those irradiated at 50, 100 and 200 Krad.

TABLE 5.--Mean color and odor scores of phosphate treated
and untreated beef irradiated at various pasteurizing doses
of gamma radiation and stored at 38°F for 20 days in vacuum

followed by one day exposure to the atmosphere.

 

Phosphate

 

 

 

 

Experi- No. of Dose Treated Untreated
x
ment Judges (Krad) Mean Mean Mean Mean
Color Odor Color Odor
Score** Score** Score** Score**
0 6.9 5. 4.0 5.4
50 6.5 7.4 4.5 7.0
1 10 100 7.0 7.3 4.1 6 9
250 6.8 6.8 4.1 6.2
500 5.9 5.8 3 7 5.5
0 7.1 5 6 5.4 5 5
2 12
100 7.2 7 0 5.3 7 2

 

x
Identical experiments

with different pieces of meat.

xx
Scoring code:

Acceptable Range

 

9 - excellent

8 — very good

7 - good

6 - fairly good

performed at different times

'Unacceptable Range
4 - fairly bad

 

3 — bad
2 - very bad
1 — poor

5 - marginal

DISCUSSION

In vacuum packed beef Slices which were radiation
pasteurized and stored for 21 days at 38°F, a large amount
of drip or exudate was observed in the packages. This
drip formation in the package is undesirable from the
standpoint of consumer acceptability. When the beef
Slices were dipped in sodium tripolyphosphate solution
prior to vacuum packaging and irradiation, the amount of
drip formed was reduced considerably. 'Also the water-
holding capacity and appearance of the product were
improved. This difference between the phosphate treated
and the untreated beef samples clearly shows that phosphate
pretreatment can compliment vacuum packaging and radiation
pasteurization in the extension of the refrigerated shelf
life (38°F) of fresh beef.

Irradiation at pasteurizing levels (50 to 500 Krad)
did not have any effect on the formation of drip. There
was, however, noticeable increase in drip formed due to
the pressure exerted by the vacuum on meat samples. The
amount of drip in untreated samples was markedly greater
than in phosphate treated samples. 'Immediately after
dipping in sodium tripolyphosphate solution, water-holding
capacity of the beef samples increased.' Phosphate pre-
treatment also increased the pH of the meat. Irradiation

55

56

at 50 to 500 Krad did not produce any effect on the water-
holding capacity. During storage, however, a slight
increase in water-holding capacity was observed in both
irradiated and unirradiated samples.' This increase can be
attributed to the phase of aging undergoing in meat during
storage which tends to increase water holding capacity
(Hamm, 1960). In all cases, phosphate treated samples
'maintained their high pH values (5.8-6.1) up to 21 days
at 38°F. 0n the other hand, untreated samples showed lower
pH values (5.2—5.4). The pH of the untreated samples
after 21 days at 38°F is within the vicinity of the iso-
electric pH (5.0-5.5) of the meat where there is a minimumi
water-holding capacity.

Drip control is obtained through the use of phosphate
in an amount approximately 0.5% by weight.' This amount
is in accordance with the present U.S.D.A. regulations for
those meats to Which the addition of phosphate is permitted.
At present these meats do not include fresh beef. Dipping
does, however, result in marked but not serious increase
in the slipperiness of the meat slices.' The degree of
slipperiness of the meat tends to dissipate during storage
but still is perceptible after 21 days.

Vacuum packaging can effectively retard rancidity
in radiation pasteurized meat. The low TBA numbers found
during storage in vacuum suggests that exclusion of air

during irradiation and storage can retard lipid oxidation.

57

The slight increase in TBA number during the first week of
storage is presumed to be caused by the residual oxygen
trapped in the muscle tissues. As the supply of oxygen
began to decrease, however, the production of malonalde-
hyde as measured by the TBA test immediately dropped.

The availability of oxygen is an important factor in the
storage studies conducted with radiation pasteurized beef.
Upon exposure to the atmosphere of the samples stored in
vacuum, the degree of lipid oxidation increased.

Sodium tripolyphosphate has been shown to be an
effective antioxidant in cooked meat and fish (Timms and
Watts, 1958; Ramsey and Watts, 1963).‘ Green and Watts (in
press) reported that in raw meat, sodium tripolyphosphate
did not show any antioxidant property. ‘It is presumed
that the phosphate groups are being hydrolyzed by the
phosphatases in the muscle. The results presented in
Table 2 and Figure 8 further illustrate the ineffectiveness
of sodium tripolyphosphate as an antioxidant in fresh beef.

Irradiation in vacuum at 50 to 500 Krad did not cause
any inhibition in lipid oxidation. The results are similar
to those obtained by Greene and Watts (in press) in their
studies on lipid oxidation on ground raw beef. All of
the irradiated meats evaluated for odor in this study did
not Show any perceptible Sign of rancidity after 20 days

in vacuum and one day exposure to the atmosphere at 38°F.

 

58

Visual observations showed that in general, all
meats pretreated with sodium tripolyphosphate had a superior
color than the untreated ones. When meat slices were vacuum
packed their color immediately changed to purple with the
phosphate treated samples appearing darker than the
untreated ones.' It is presumed that the difference in the
ultimate pH and water holding capacity caused such
variability in the degree of darkness of the beef slices.
A high pH has been shown to correspond to dark color
(Hall et_ai., 1944; Bate-Smith, 1948; Janicki g£_ai., 1967).
The effect of pH may be based on the well known relation
of pH on water holding capacity (Grau, 1953; Janicki and
Walczak, 1954). In general, the darkening of meat color
by added salts may be due to the increase of meat hydra-
tion. This may explain the influence of polyphosphate on
meat color (Wismer-Pedersen, 1959d). Furthermore, since
the darkness of meat color is related to the total energy
reflected from the surface, any change in the physical
and chemical properties of the meat would affect it
(Janicki g£_ai., 1967). As would be expected, darkness
of meat color increases with the increase of water holding
capacity and pH with the pigment remaining constant.

In general, radiation from 50 to 500 Krad did not
Show any immediate effect on the color of the vacuum
packaged fresh beef. In some cases, however, brown

coloration at the surface of the meat changed to a purplish

59

color during irradiation. This change is presumably due
to the fact that irradiating in vacuum tends to generate
reducing conditions in meat. Similar observation was also
reported by Urbain gt_ai. (1968). During storage,
however, samples which have been exposed to 400 to 500
Krad showed some discoloration. Presumably, these dose
levels (400 and 500 Krad) enhanced denaturation of the
globin moiety of the heme proteins during storage.

Both in phosphate treated and in untreated samples
which were irradiated in vacuum, the reduced form of myo—
globin was the predominant pigment'during the initial
storage period. During storage, however, the amount of
metmyoglobin increased. The brown metmyoglobin discolora-
tion in phosphate treated samples was produced more slowly
as shown by reflectance measurement which was employed to
measure the relative proportion of metmyoglobin at the
surface of the meat. 'On the other hand, a rapid rate of
brown discoloration was observed in samples which did not
receive sodium tripolyphosphate pretreatment. This dif—
ference in the rate of metmyoglobin discoloration can
well be explained in that where oxygen is absent as in
vacuum packaging the surviving activity of the cytochrome
enzymes (in particular succinic dehydrogenase) can reduce
metmyoglobin already formed (Lawrie, 1966). This reducing
activity, however, is influenced by pH of the meat. It

has been shown that as the pH decreases, the rate of

60

metmyoglobin reduction decreases (Cutaia and Ordal, 1964).
Evidence has also been shown that autoxidation of mammalian
myoglobin increases as the pH decreases (Matsuura et_ai.,
1962). The effect of sodium tripolyphosphate treatment on
pH of the meat would be the logical explanation of the
observed changes in metmyoglobin discoloration during
storage in vacuum of phosphate treated samples. Although
the pH increase ‘due to phosphate treatment in this
experiment only ranged from 0.4 to 0.5 pH unit, this could
have a marked effect on enzymatic reductions of metmyo-
globin.

It is apparent that lipid oxidation and pigment dis-
coloration can be retarded in radiation pasteurized fresh
beef by the combined use of vacuum packaging and phosphate
treatment. The purple color that predominates in vacuum
packaged fresh beef, however, is not the typical color the
consumers associate with fresh meat.' Red color has been
associated by the consumers with good quality meat. In
order to regenerate the red color at the surface of the
meat samples, they were exposed to the atmosphere after
storage in vacuum. All of the irradiated meats which did
not have phosphate pretreatment showed no regeneration of
red color upon exposure. On the other hand, phosphate
treated samples appeared red indicating that exposure to
the atmosphere resulted in the oxygenation of the reduced

myoglobin (which is predominant at the surface) to

61

oxymyoglobin. Longer exposure, however, resulted in
increase of brown discoloration.

In general, there was no large difference in odor
scores between phosphate treated and untreated samples.
It is evident, however, that unirradiated samples and
those that were irradiated at 500 Krad received lower
odor scores than those at 50, 100, and 250 Krad. At
times, panel members appeared rather inconsistent as
individuals in reporting their opinion on the same samples

from one observation to another. But they unanimously

 

agreed that unpleasant changes were occurring in the é~—m
unirradiated samples and those that were exposed to 500

Krad. Spoiled odor due to an apparent microbial

spoilage seemed to predominate in unirradiated samples

while slight irradiation odor was perceptible in samples

irradiated at 500 Krad. Panel members did not observe a

distinct rancid odor in all cases.

SUMMARY AND CONCLUSIONS

The use of sodium tripolyphosphate in conjunction
with radiation pasteurization of prepackaged fresh beef
was studied.‘ Dipping beef slices in sodium tripoly-
phosphate solution of appropriate concentration prior to
irradiation is compatible with radiation pasteurization
of vacuum packed fresh beef slices.‘ The pretreatment can
compliment radiation pasteurization in that during storage,
drip or exudate formation is minimized and the water
holding capacity of beef is improved. ‘Dri ~control is
obtained through the use of sodium tripolyphosphate in an
amount approximately 0.5% by weight.

The combined effect of phosphate pretreatment,
vacuum packaging and radiation on lipid oxidation was also
studied. From the TBA test data and odor evaluation, it
was concluded that exclusion of air during irradiation and
storage retarded lipid oxidation or rancid odor formation
up to 21 days at 38°F. Phosphate treatment and radiation
(50 to 500 Krad) did not show any effect on lipid oxida—
tion in meat packed in vacuum.

Reflectance measurements and visual observations
indicated that phosphate pretreatment in combination with
vacuum packaging inhibited brown pigment discoloration at

the surface of radiation pasteurized fresh beef. The

62

63

amount of metmyoglobin in phosphate treated samples was
lower than in those samples that did not receive phosphate
treatment. Phosphate treated samples retained their
purple color up to 21 days in vacuum at 38°F while the
untreated samples appeared brown.

Exposure to the atmosphere after storage in vacuum
resulted in the regeneration of red color at the surface
of the beef samples which have been pretreated with
sodium tripolyphosphate.’ There was, however, indication
of increased lipid oxidation and metmyoglobin discolora-
tion in both phosphate treated and untreated samples
during storage in air.

The odor evaluation showed that in general, all meats
which were not radiation pasteurized had an odor which
indicates microbial spoilage. At high pasteurization
levels of radiation (500 Krad) there was a distinct
irradiation odor noted by the panel judges. Those that
were irradiated at 50 to 250 Krad showed no signs of
such odors. "Panel judges preferred the color of phosphate
treated sampleS‘to that of the untreated ones after the
samples have been exposed to the atmosphere for one day
following 20 days in vacuum at 38°F.

Based on the experimental findings reported, it can
be concluded that the three agents, radiation, phosphate
treatment and vacuum packaging used in combination can

extend the refrigerated life of fresh beef up to 21 days.

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64

 

many: - -. _. p l

 

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