2012_Leygonie et al_Impact of freezing and thawing on the quality of meat_Review

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Meat Science 91 (2012) 93–98
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Review
Impact of freezing and thawing on the quality of meat: Review
Coleen Leygonie a,b, Trevor J. Britz a, Louwrens C. Hoffman b,⁎
a Department of Food Science, University of Stellenbosch, Stellenbosch 7600, South Africa
b Department of Animal Sciences, University of Stellenbosch, Stellenbosch 7600, South Africa
⁎ Corresponding author. Tel.: +27 21 808 4747; fax:
E-mail address: lch@sun.ac.za (L.C. Hoffman).
0309-1740/$ – see front matter © 2012 Elsevier Ltd. All
doi:10.1016/j.meatsci.2012.01.013
a b s t r a c t
a r t i c l e i n f o
Article history:
Received 2 November 2011
Received in revised form 17 January 2012
Accepted 17 January 2012
Keywords:
Freeze
Thaw
Meat quality
Mitigation mechanisms
This comprehensive review describes the effects of freezing and thawing on the physical quality parameters
of meat. The formation of ice crystals during freezing damages the ultrastructure and concentrates the solutes
in the meat which, in turn, leads to alterations in the biochemical reactions that occur at the cellular level and
influence the physical quality parameters of the meat. The quality parameters that were evaluated are mois-
ture loss, protein denaturation, lipid and protein oxidation, colour, pH, shear force and microbial spoilage. Ad-
ditionally mechanisms employed to mitigate the effects of freezing and thawing were also reviewed. These
include the use of novel methods of freezing and thawing, ante and post mortem antifreeze protein inclusion
and vitamin E supplementation, brine injection and modified atmospheric packaging.
© 2012 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
2. Meat quality attributes affected by freezing and thawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
2.1. Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
2.2. Protein denaturation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
2.3. Oxidation of lipids and protein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
2.4. Colour (myoglobin proteins) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
2.5. pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
2.6. Tenderness (shear force) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
2.7. Microbial count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
3. Mitigation of the effects of freezing and thawing on meat quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
3.1. Novel freezing and thawing methods that increase the rate of phase transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
3.2. Anti-freeze proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
3.3. Ante and post mortem vitamin E supplementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3.4. Brine injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3.5. Modified atmosphere packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
1. Introduction
The practice of freezing meat to prolong its shelf-life has been
practised for thousands of years, although most improvements in
freezing technologies have occurred in the past century. The global
meat export industry is currently worth more than US$ 13 billion
+27 21 808 4750.
rights reserved.
and freezing plays an essential role in this industry in ensuring the
safety of the meat products being supplied to all regions of the
world. Nonetheless, the consequences of freezing and thawing on
the quality of meat remain a significant problem.
Freezing and thawing mainly influence the water fraction of meat.
Since the water is contained within and between the muscle fibres of
the meat, compartments are created in the tissue, which complicates
the process. As the water freezes, the concentration of the remaining
solutes (proteins, carbohydrates, lipids, vitamins and minerals) in-
creases, thereby disrupting the homeostasis of the complex meat sys-
tem (Lawrie, 1998). The changes in the immediate environment of
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94 C. Leygonie et al. / Meat Science 91 (2012) 93–98
the muscle fibres affect the cell membrane characteristics, which in
turn affect the quality of the meat (Fellows, 2000). An understanding
of the changes that freezing and thawing perpetuate in different meat
types and cuts is essential to the meat industry, as their main objec-
tive is to produce superior products with high resale values that are
both appealing and enjoyable to the consumer (Renerre, 1990).
The majority of the research conducted on freezing and thawing
of meat has focussed on the reduction of moisture loss. Añón and
Calvelo were the leaders in researching the effects of freezing on
meat quality from the 1970s to the 1990s. Their work was subse-
quently expanded on by Farouk and Swan (1998) from the 1990s
into the 2000s.
The shelf-life of meat is generally determined by appearance, tex-
ture, flavour, colour, microbial activity and nutritive value (McMillin,
2008). Of these characteristics, flavour is themost difficult tomeasure.
Flavour compoundsmay originate from lipid and peptide components
in the muscle or meat (Spanier, 1992). All of these parameters are
influenced by freezing, frozen storage and subsequent thawing.
This review aims to collate and assess the currently available liter-
ature on the effects of freezing and thawing on the quality of meat.
Specific emphasis is placed on the extent to which meat quality is
influenced by the rate at which freezing and thawing are performed.
In addition, potential means of mitigating the negative effects of
freezing and thawing on meat quality are discussed.
2. Meat quality attributes affected by freezing and thawing
2.1. Moisture
Freezing and thawing alter both the content and the distribu-
tion of moisture in meat tissue. Moisture as a quality characteristic
in meat can be evaluated in several ways, including drip loss; thaw
loss; cooking loss; water binding capacity and total moisture content.
Nonetheless, since the methods used to determine moisture loss and
changes in meat are not set by an international standard, it is often
difficult to directly compare and draw conclusions from studies in
the literature that have employed different methods for such
purposes.
Moisture loss in meat is inevitable post mortem due to the decrease
in pH (closer to the isoelectric pH of proteins), the loss of adenosine
triphosphate (ATP), and the steric effects due to shrinkage of the myo-
fibrils as a result of rigor mortis and conditioning (Huff-Lonergan &
Lonergan, 2005). These factors all act to release water that was previ-
ously immobilised and bound to proteins into the intrafibrillar spaces.The released water is then redistributed into the sarcoplasmic and
extracellular spaces. Freezing and thawing are known to affect the
amount of exudate (thaw loss and/or drip loss). Research conducted
to date has indicated that as the characteristic time to freeze increases
above 19.5 min, the amount of exudate that forms becomes markedly
higher than before freezing. The amount of exudate that forms, none-
theless, remains reasonably constant as the characteristic time of
freezing increases beyond 19.5 min (Añón & Cavelo, 1980). This phe-
nomenon has been associated with the size and distribution of the ice
crystals that form along the freezing gradient (Añón & Cavelo, 1980).
In terms of thawing, major differences in opinion exist regarding
the correlation between the rate of thawing and the extent of exudate
formation. Gonzalez-Sanguinetti, Añón, and Cavelo (1985) concluded
that a decrease in thawing time (time elapsed from −5 °C to −1 °C)
to below 50 min resulted in a decrease in exudate. This was attributed
to the melting of ice in the extracellular spaces causing an increase in
water activity, resulting in the net flow of water into the intracellular
spaces and its subsequent reabsorption by the dehydrated fibres.
These authors suggested that at increased rates of thawing, the rate
at which water becomes available exceeds the rate at which the fibres
can reabsorb water, with the excess water being excreted as exudate.
Haugland (2002) also proposed that an increased rate (or decrease
in time) of thawing caused less exudate to form. Ambrosiadis,
Theodorakakos, Georgakis, and Lekas (1994) reported that rapid
thawing of meat by submergence in water decreased the drip loss.
On the other hand, it was found in the latter study that microwave
thawing (35 min to reach 0 °C) increased the drip loss to within the
same range as ambient air thawing (5–7 h), but this drip loss was
still less marked than in the case of refrigerated thawing (28 h),
which resulted in the highest drip loss.
In general, there is consensus in the scientific literature on the
notion that freezing, frozen storage and thawing all contribute to a
decrease in the water-holding capacity of meat (Añón & Cavelo,
1980; Ngapo, Babare, Reynolds, & Mawson, 1999; Vieira, Diaz,
Martínez, & García-Cachán, 2009). It has been reported that the loss
in water-holding capacity is related to the disruption of the muscle
fibre structure, as well as the modification and/or denaturation of
the proteins. The composition of the drip has been found to consist
mostly of sarcoplasmic proteins (Savage, Warris, & Jolley, 1990).
Loss of moisture due to cooking has been reported not to differ
significantly between fresh and frozen meat samples, as well as for
samples frozen and thawed at different rates (Leygonie, Britz, &
Hoffman, 2012; Vieira et al., 2009). This is believed to be due to the
region in the muscle tissue from which cooking-loss water originates.
During cooking, the melting of the fat and the denaturation of the
proteins reportedly cause the release of chemically bound water
(Vieira et al., 2009).
2.2. Protein denaturation
It has been traditionally thought that protein denaturation could
result during freezing due to an increased intracellular ionic strength
following the migration of water to the extracellular spaces. Nonethe-
less, this mechanism has been refuted by several authors. Añón and
Cavelo (1980), Mietsch, Halász, and Farkas (1994) and Ngapo et al.
(1999) all suggested that protein denaturation does not contribute
significantly to quality loss, as they found no significant differences
in the amount and composition of proteins in the drip collected
from fresh samples and those samples that had been frozen and im-
mediately thawed. Some of these authors also used sodium dodecyl
sulphate polyacrylamide gel electrophoresis (SDS PAGE), capillary
gel electrophoresis (CGE) and differential scanning calorimetry
(DSC) to study the patterns of the protein exudate fraction and
found no significant differences between the aforementioned sam-
ples. It was, however, noted by these authors that the time and tem-
perature of the sample storage may have influenced the results
obtained and no new explanations were offered with regard to the
loss of meat quality during freezing. It would consequently be very
beneficial to evaluate the drip composition of such samples using
more modern techniques, such as proteomics.
After analysing meat samples for protein denaturation using DSC
thermograms, Wagner and Añón (1985) reported that myosin was
the protein most affected by freezing. The myofibrillar proteins
were reportedly denatured irrespective of the freezing rate, causing
unfolding of the protein and resulting in a lower enthalpy value. By
comparing the data from the DSC thermograms, enthalpy change
and ATPase activity, these researchers concluded that slow freezing
causes more pronounced protein denaturation than rapid freezing.
Benjakul, Visessanguan, Thongkaew, and Tanaka (2003) found that
freezing and frozen storage caused a marked decrease in Ca2+-
ATPase activity and an increase in Mg2+-EGTA-ATPase activity, which
translates into denaturation of myosin and the troponin–tropomyosin
complex. They also reported strong interactions between protein
oxidation (formation of carbonyls) and protein denaturation. The con-
tradictory results reported in the various studies suggest that more
research is required to establish the mechanisms involved in protein
denaturation during freezing and frozen storage.
95C. Leygonie et al. / Meat Science 91 (2012) 93–98
2.3. Oxidation of lipids and protein
The final temperature to which meat is frozen and stored deter-
mines the amount of unfrozen water that remains available for chem-
ical reactions to proceed. Petrović (1982) showed that biochemical
reactions could still take place in meat frozen and stored at tempera-
tures higher than −20 °C, since sufficient unfrozen water remained
available at these temperatures for such reactions to occur. The opti-
mum temperature for the frozen storage of meat has been reported
to be −40 °C, as only a very small percentage of water is unfrozen
at this point (Estévez, 2011). This fraction of water is believed to be
bound to other food constituents and thus is chemically inactive
(Nesvadba, 2008; Singh & Heldman, 2001). The freezing of the
water fraction also causes an increase in the solute concentration
both intracellularly and extracellularly, which is thought to be the
reason for the increased chemical reactivity during frozen storage
(Fennema, 1975). The ice crystals, depending on their size and loca-
tion, will disrupt the muscle cells, resulting in the release of mito-
chondrial and lysosomal enzymes into the sarcoplasm (Hamm, 1979).
The fraction of unfrozen water is also important in terms of oxida-
tion, since chemical reactions can occur during frozen storage that
initiate primary lipid oxidation (peroxidation) in the meat. This can
lead to radical secondary lipid oxidation upon thawing (Owen &
Lawrie, 1975) leading to adverse changes in colour, odour, flavour
and healthfulness. This phenomenon has been demonstrated by
Akamittath, Brekke, and Schanus (1990) and Hansen et al. (2004),
who reported accelerated lipid oxidation in frozen–thawed meat
that was subjected to a refrigerated shelf-life study.
The quality of the secondary products of lipid oxidation is gener-
ally measured using the thiobarbituric acid reactive substances
(TBARS) method. These secondary products cause rancid, fatty, pun-
gent and other off-flavours. The development of these flavours was
noted by Vieira et al. (2009), who stated that TBARS of fresh meat
were significantly lower than meat stored for 90 days at −20 °C.
Such observations indicate that frozen storage is not necessarily suffi-
cient to prevent oxidation from occurring. Although peroxidation
was not measured in the aforementioned study, it would be expected
that primary lipid oxidation would cease at such low temperatures
by 90 daysand secondary lipid oxidation would commence, which
should be detected by the TBARS method. Benjakul and Bauer
(2001) also found that freezing and thawing of muscle tissue resulted
in accelerated TBARS accumulation and attributed this finding to the
damage of cell membranes by ice crystals and the subsequent release
of pro-oxidants, especially the haem iron. There is also increasing
evidence to indicate that lipid oxidation takes place primarily at the
cellular membrane level and not in the triglyceride fraction. There-
fore, lipid oxidation has been reported in both lean and fatty meats
(Thanonkaew, Benjakul, Visessanguan, & Decker, 2006).
Protein oxidation can be linked to any of the pro-oxidative factors,
such as oxidised lipids, free radicals, haem pigments and oxidative
enzymes. Malonaldehyde is one of the substrates that react with pro-
tein derivatives to form carbonyls (ketones and aldehydes) (Xiong,
2000). Protein and lipid oxidation are, therefore, undoubtedly inter-
linked. Protein oxidation in meat may lead to decreased eating quality
due to reduced tenderness and juiciness, flavour deterioration and
discolouration (Rowe, Maddock, O'Lonergan, & Huff-Lonergan, 2004).
These changes are partially due to the formation of protein aggregates
through both non-covalent and covalent intermolecular bonds as reac-
tive oxygen species (ROS) attack the proteins. Other common changes
in oxidised proteins include amino acid destruction; protein unfolding;
increased surface hydrophobicity; fragmentation and protein cross-
linking. These all lead to the formation of protein carbonyls (Benjakul
et al., 2003; Liu, Xiong, & Butterfield, 2000; Xia, Kong, Liu, & Liu, 2009).
Freezing and thawing cause damage to the ultrastructure of the
muscle cells with the ensuing release of mitochondrial and lysosomal
enzymes, haem iron and other pro-oxidants. These increase the
degree and rate of protein oxidation (Xiong, 2000). The amino acid
residues that are mainly involved in these reactions are lysine, threo-
nine and arginine, the oxidation of which leads to the polymerisation
of proteins as well as peptide scission (Liu et al., 2000; Xia et al., 2009;
Xiong, 2000). These amino acids are mainly found in the myofibrillar
proteins, which account for 55–65% of total muscle protein and are
responsible for the majority of the physicochemical properties of
muscle foods (Xia et al., 2009). Protein oxidation destabilises the pro-
tein matrix leading to increased toughness, loss of water-binding
capacity and loss in protein solubility. The water-holding capacity
of meat that has undergone protein oxidation decreases due to the
shrinkage of the inter-filamental spaces, as the oxidation of the myo-
fibrillar proteins leads to the aggregation and coagulation of myosin
and actin. The shrinkage of the inter-filamental space results in an
increase in the extracellular space, thus decreasing the capillary
force that holds the water in the inter-filamental space. The other
oxidative changes to the proteins also decrease their ability to hold
water and hence the water leaches out of the meat as exudate (Lui,
Xiong, & Chen, 2010).
2.4. Colour (myoglobin proteins)
Myoglobin has been identified in exudate by gel-electrophoresis,
accounting in part for the change in the colour stability of meat
after freezing and thawing (Añón & Cavelo, 1980). It has also been
reported that denaturation of the globin moiety of the myoglobin
molecule takes place at some stage during freezing, frozen storage
and thawing (Calvelo, 1981). The denaturation leads to an increased
susceptibility of myoglobin to autoxidation and subsequent loss of
optimum colour presentation. This theory has been verified by
many authors by comparing the degree of bloom and the ability of
the meat to resist oxidation to metmyoglobin during refrigerated
storage post freeze/thaw (Abdallah, Marchello, & Ahmad, 1999;
Farouk & Swan, 1998; Lanari, Bevilacqua, & Zaritzky, 1990; Lanari &
Zaritzky, 1991; Leygonie, Britz, & Hoffman, 2011; Marriott, Garcia,
Kurland, & Lee, 1980; Otremba, Dikeman, & Boyle, 1999).
The existence of an enzyme system capable of reducingmetmyoglo-
bin back to myoglobin was proposed by Livingston and Brown (1981)
andwas termed themetmyoglobin reducing activity (MRA). The theory
is that in freshmuscle the enzyme is very active and themetmyoglobin
formed is quickly reduced to deoxymyoglobin and oxygenated back
to oxymyoglobin, thereby retaining the bloomed colour. However, as
the meat ages or is frozen, the activity of the MRA is decreased and
metmyoglobin begins to accumulate on the surface of the meat at a
rapid rate (Abdallah et al., 1999). Also, MRA and/or co-factors, such as
NADH, could be ‘lost’ from the post mortem sarcoplasmic environment
by leaching as exudate during thawing, and/or due to oxidation,
and/or be used by reactions unrelated to MRA, which will all contribute
to accelerated oxidation and loss of bloom (Abdallah et al., 1999). For
example, it is known that β-hydroxyacyl CoA-dehydrogenase (HADH)
is released from the mitochondrion cytoplasm during freezing and
thawing. This enzyme utilises NADH and would thus result in faster
inactivation of MRA (Abdallah et al., 1999; Lawrie, 1998).
All forms of oxidation are considered to be associated with one
another. Thus, when lipid oxidation is initiated it results in the forma-
tion of pro-oxidants capable of reacting with oxymyoglobin, which
in turn leads to metmyoglobin formation. The same logic applies to
protein oxidation (Farouk & Swan, 1998). Oxidation can consequently
be compared to a chain reaction within meat, initiated by the lipid
fraction and carried over to the myoglobin fraction. Hence, if lipid
oxidation were accelerated by frozen storage, this would increase
the quantity of free radicals present, leading to an increased rate
of myoglobin oxidation. If the MRA has become less effective in com-
bating oxidation, this would explain why a more rapid decrease in
colour stability is observed post-freezing in meat subjected to chilled
retail display (Xiong, 2000).
96 C. Leygonie et al. / Meat Science 91 (2012) 93–98
2.5. pH
The pH of meat that has been frozen and thawed tends to be lower
than prior to freezing (Leygonie et al., 2011). As pH is a measure of
the amount of free hydrogen ions (H+) in a solution, it is possible
that freezing with subsequent exudate production could cause dena-
turation of buffer proteins, the release of hydrogen ions and a subse-
quent decrease in pH. Alternatively, the loss of fluid from the meat
tissue may cause an increase in the concentration of the solutes,
which results in a decrease in the pH. A further explanation for this
finding may involve the deamination of proteins by microbial or
enzymatic action, with the ensuing release of hydrogen atoms
(Leygonie et al., 2011).
2.6. Tenderness (shear force)
There is general agreement in the literature that the tenderness
of meat increases with freezing and thawing when measured with
peak force (Farouke, Wieliczko, & Merts, 2003; Lagerstedt, Enfalt,
Johansson, & Lundstrom, 2008; Shanks, Wulf, & Maddock, 2002;
Wheeler, Miller, Savell, & Cross, 1990). It has also been found that
the increase in tenderness is correlated to the length of frozen storage
and the degree to which the meat was aged prior to freezing. The
tenderising effect of freezing seems to be negated when the meat
was sufficiently aged prior to freezing (Vieira et al., 2009).
The mechanism involved in the tenderisation is thought to be
a combination of the breakdown of the muscle fibres by enzymatic
action during proteolysis, ageing, and the loss of structural integrity
caused by ice crystal formation. The formation of large, extracellular
ice crystals disrupts the physical structure, largely breakingmyofibrils
apart and resulting in tenderisation. However, the formation of small
intracellular ice crystals increases the rate of ageing probably by
the release of protease enzymes (Vieira et al., 2009), although many
alternative postulations existin the literature.
Contradictory results have been obtained from sensory evaluation
of tenderness (Lagersted et al., 2008), where a lower peak force was
reported in freeze/thaw samples compared to chilled meat. In this
case the trained sensory panel rated the freeze/thawed meat signifi-
cantly less tender than the chilled meat. This sensory result was
attributed to the loss of fluid during thawing that resulted in less
water available to hydrate the muscle fibres; thus, a greater quantity
of fibres per surface area seemed to increase the toughness as per-
ceived by the sensory panel. The decrease in the shear force was
attributed to the loss in membrane strength due to the ice crystal
formation thereby reducing the force needed to shear the meat (Lui
et al., 2010).
2.7. Microbial count
Neither freezing nor thawing appears to decrease the number of
viable microbes present in meat. During freezing, however, microbial
spoilage is effectively terminated as the microbes become dormant.
Unfortunately, they regain their activity during thawing (Löndahl &
Nilaaon, 1993). As thawing is a much slower process than freezing
and is less uniform, certain areas of the meat will be exposed to
more favourable temperature conditions for microbial growth. This
is of particular concern when air thawing is employed. In addition
to the risk of high temperature exposure, there is an increase in mois-
ture and nutrients available to microbes post freeze/thaw due to exu-
date formation. The moisture lost during thawing is rich in proteins,
vitamins and minerals derived from the structural disarray caused
by the freezing process, which consequently provides an excellent
medium for microbial growth. For this reason, good hygiene and
handling practices are even more important for meat that is to be
frozen and thawed compared to that which is to be sold fresh
(Pham, 2004).
Vieira et al. (2009) found in their study that beef frozen for up to
90 days, previously aged for 3 and 10 days, did not spoil due to micro-
bial growth. They did, however, report an increase in the levels of
psychrotrophic bacteria during the 90-day frozen storage, which
were probably favoured above the other bacteria by the thawing
process (48 h at 4 °C in a cooler). Greer and Murray (1991) found
that the lag phase of bacterial growth in frozen/thawed pork was
shorter than for fresh meat, but that the time to develop spoilage
odours was not affected. Literature on the microbial quality and
shelf-life post freeze/thaw is scarce for all species of meat, but that
which is available seems to indicate that the microbiological shelf-
life of fresh and frozen/thawed samples is similar.
3. Mitigation of the effects of freezing and thawing on meat quality
3.1. Novel freezing and thawing methods that increase the rate of phase
transition
Novel methods for freezing and thawing have been investigated
on a laboratory scale, however, these are generally more expensive
than their conventional counterparts (reviewed by Bing & Sun,
2002). One such novel method is high-pressure freezing, which
results in instantaneous and homogenous ice crystal formation
throughout the product due to the high supercooling effect achieved
on pressure release. The result of the increased pressure causes a shift
in the type of ice crystals that are formed from type I (lower density
than liquid water) to type IV ice crystals. Type IV ice crystals are
smaller and denser than water and do not cause the product to
swell by 9–13%, the normal expansion that occurs with type I crystals.
The theory is that, with type IV ice crystals, there is less mechanical
damage to the cell structures, which results in a superior quality
product. The drawback of this method is the capital layout and the
product size limitation. Currently only products that are able to fit
into the product chamber (0.15 ml to 3000 ml) can be frozen in this
manner (Chevalier, Sequerira-Munoz, Le Bail, Simpson, & Ghoul,
2001; Fernandez et al., 2007; Martino, Otero, Sanz, & Zaritzky, 1998).
High pressure thawing has received less attention than high-
pressure freezing. In the former case, it has been noted that the
phase transition time can be reduced by ca. 50–60% compared to
the traditional atmospheric thawing practices. This translates into
less microbial spoilage, a firmer product and less thaw drip losses.
Nonetheless, the drawbacks of this method are reported to include a
loss in colour, a decrease in water-binding capacity post-thawing
and protein denaturation (Schubring, Meyer, Schlüter, Boguslawski,
& Knorr, 2003; Zhao, Flores, & Olson, 1998). Novel methods of
freezing and thawing have been comprehensively reviewed by Li
and Sun (2002).
3.2. Anti-freeze proteins
The addition of anti-freeze proteins can control the structure and
size of ice crystals in frozen foods. Anti-freeze proteins lower the
temperature at which freezing is initiated and retard recrystallisation
during frozen storage. Payne, Sandford, Harris, and Young (1994)
and Payne and Young (1995) administered anti-freeze glycoproteins
(AFGP) from Atlantic cod to chilled meat prior to freezing and intra-
venously ante mortem before slaughter and subsequent freezing.
Administration of the AFGP post mortem at a concentration of 1 ng/ml
to 1 mg/ml in a phosphate buffered saline, led to a considerable
reduction in the size of the ice crystals formed. The administration
of the AFGP intravenously at 1 or 24 h before slaughter led to
reduced drip loss and smaller ice crystal size. The major drawback
of this mitigation method is the cost-effectiveness and the mode
of application as the consumer acceptance of an additive needs to
be established.
97C. Leygonie et al. / Meat Science 91 (2012) 93–98
3.3. Ante and post mortem vitamin E supplementation
The ante mortem supplementation of vitamin E has been shown
to reduce the rate of oxidation in the meat post mortem (Guidera,
Kerry, Buckley, Lynch, & Morrissey, 1997; Lanari, Cassens, Schaefer,
& Scheller, 1993, 1994; Lanari, Schaefer, Cassens, & Scheller, 1995).
Vitamin E is partitioned into the cellular membranes where it acts
as an antioxidant, protecting the phospholipids from free radicals
and thereby decreasing the rate of lipid and pigment oxidation.
Therefore, as freezing and thawing increase the rate of oxidation
post thawing, the supplementation ante mortem increases the antiox-
idant levels in the meat. Experimentally, this practice has been shown
to retard oxidation, leading to improved quality in the final product
(Guidera et al., 1997; Lanari et al., 1993, 1994, 1995). This is also a
simple and relatively inexpensive means of mitigating the delete-
rious quality effects of freezing and thawing on meat quality, and
has proven successful in lamb and beef. Studies on vitamin E supple-
mentation of fresh meat have been successful for chicken, turkey and
pork, but further studies are required to confirm the effectiveness of
such treatments in relation to freezing and thawing (Morrissey,
Buckley, & Galvin, 2000).
3.4. Brine injection
In the poultry industry, salt and phosphate solutions (brine) have
been injected into the meat prior to freezing to promote the tender-
ness, juiciness and flavour of the final product. Pietrasik and Janz
(2009) recently evaluated the use of brine injection to combat the
exudate loss upon thawing of beef. They found that the purge loss
was significantly lower in injected samples compared to the non-
injected control, but the tenderness and colour (CIE a*) of the former
samples were significantly decreased. In this study it was reported
that the injection of beef with brine solutions prior to freezing
increased the consumer's purchase intent and degree of liking of the
products. Therefore, this mitigation method appears to be an inex-
pensive and commercially applicable solution to decreasing purge
losses upon thawing.
3.5. Modified atmosphere packaging
Modified atmosphere packaging (MAP) has proven to be success-
ful in extending the shelf-life of fresh meat by the inclusionof oxygen
(>13%) to prolong its bloomed, cherry-red appearance and the inclu-
sion of carbon dioxide to decrease the microbial activity (McMillin,
2008). Carbon monoxide has also been shown to improve the colour
of meat by binding to myoglobin to form a bright pink red colour. The
carbon monoxide also acts to decrease the redox potential of the
environment in which the meat is packaged, thus decreasing micro-
bial activity (Mancini & Hunt, 2005). However, there is a huge contro-
versy about the use of CO in packaging with a number of countries not
allowing the use thereof (Anonymous, 2004). Nitrogen has also been
used as a filler gas, as it is inert and helps inhibit package collapse
as the carbon dioxide and the oxygen are absorbed and utilised by
the meat and the microbes (McMillin, 2008). Therefore, MAP holds
potential in mitigating the negative effects on the colour stability of
meat brought about by freezing and thawing. The inclusion of high
concentrations of oxygen or low concentrations of carbon monoxide
could restore or maintain the bloomed cherry red appearance of the
meat (Leygonie et al., 2011).
The major drawback of oxygen inclusion (>21%) in MAP is
increased oxidation of the lipid and protein fractions. As freezing
and thawing lead to accelerated oxidation under refrigerated storage
post thawing, research is required to establish the levels at which
oxygen should be included in order to improve the colour, but not
to cause accelerated lipid and protein oxidation. Nevertheless, meat
purchasing decisions are influenced more by colour than any other
quality factor(s). Therefore, if meat colour can be enhanced, the
market demand for the product is likely to simultaneously improve
(Mancini & Hunt, 2005). Carbon monoxide does not increase oxida-
tion but the EU has limited its use due to health risks to the consumer
and meat plant workers (Anonymous, 2004).
The use of carbon dioxide during thawing and post thawing might
mitigate the increased rate of spoilage due to the decreased lag phase
of the spoilage organisms and the abundance of nutrients from the
purge loss, because of the antimicrobial action of the gas (McMillin,
2008). Carbon dioxide gas has been proven to be very effective
against the most common meat spoilage bacteria, Pseudomonas and
Achromobacter (Gill & Tan, 1980). Therefore, the correct composition
of modified atmospheric packaging could result in a significant
improvement in the physicochemical properties of frozen/thawed
meat under refrigerated storage conditions.
4. Summary
The production of meat that is of a high quality and which is ap-
pealing to consumers is expected to translate into increased revenue
for meat producers and consequently boost the entire meat industry.
As global trade increases and the distance between producer and con-
sumer expands, the need to freeze meat for transportation increases.
Beef, lamb/mutton and chicken are the meat products that are pro-
duced world-wide in the greatest quantities and hence the majority
of the research to date in the meat science discipline has focussed
on these species. The effects of the freezing rate have been studied
in detail and the link between the rate of freezing and moisture loss
is well documented. Nonetheless, many inconsistencies exist in the
literature regarding the combined effect of freezing and thawing on
the colour, oxidation susceptibility, tenderness and the microbiologi-
cal shelf-life post freeze/thaw. More research into the combined
effect of freezing and thawing is thus essential.
In recent years, the main focus of research into freezing and
thawing mitigation mechanisms has been concentrated on the devel-
opment of high-pressure freezing and thawing methods. The com-
mercial application of these processes is still disputed, however,
even though scientific research indicates that they lead to an increase
in the quality of meat. Ante mortem supplementation with anti-freeze
proteins and vitamin E appears promising in reducing the effects of
freeze/thaw on meat quality, especially vitamin E in retarding myo-
globin, lipid and protein oxidation during long term frozen storage.
The use of brine injection has also been shown to decrease moisture
losses in frozen/thawed meat, likely due to the fact that the salts in
the brine aid in improved binding of water. Similarly MAP could mit-
igate the colour deterioration of frozen/thawed meat, but a balance is
necessary to minimise the rate of oxidation envisaged with such
treatments. More research into these areas is necessary, especially
relative to the application of these to the more exotic meat species
such as ostrich, crocodile, kangaroo and African antelope species as
these are increasingly being exported from their native countries to
Europe and the United States.
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	Impact of freezing and thawing on the quality of meat: Review
	1. Introduction
	2. Meat quality attributes affected by freezing and thawing
	2.1. Moisture
	2.2. Protein denaturation
	2.3. Oxidation of lipids and protein
	2.4. Colour (myoglobin proteins)
	2.5. pH
	2.6. Tenderness (shear force)
	2.7. Microbial count
	3. Mitigation of the effects of freezing and thawing on meat quality
	3.1. Novel freezing and thawing methods that increase the rate of phase transition
	3.2. Anti-freeze proteins
	3.3. Ante and post mortem vitamin E supplementation
	3.4. Brine injection
	3.5. Modified atmosphere packaging
	4. Summary
	References