Salt (sodium chloride) is used to improve texture, enhance the flavor, and extend the shelf life of meat products that include ham, bacon, sausage, frankfurters, and bologna. Salt is commonly found in meat products at a 2% inclusion level (Offer and Trinick 1983). However, frankfurters and bologna typically include salt at inclusion levels greater than 2% (Smith and Hui
2004). Matulis et al. (1995) found that lowering salt levels to less than 1.3% in frankfurters
resulted in incomplete protein extraction and allowed water to escape. Protein extraction with the
use of salt is important in the meat industry to obtain desirable textural properties. Salt changes
the ionic strength and allows the proteins to be exposed within a meat batter. The hydrophilic
ends of the protein bind to water, whereas the hydrophobic ends of the protein bind with fat
stabilizing an emulsion. The concept of fat being encapsulated by solubilized proteins is
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important for emulsion stability in meat batter matrices, where the solubilized proteins swell up
with free water (Lan et al. 1993).
Bind strength, water-holding capacity, break strength, and cook loss are influenced by the
amount of salt-soluble proteins present and affect the overall texture of a product. Foegeding
(1987) reported that positive effects of texture and water-holding capacity of processed meat are
attributed to myofibrillar proteins within the matrix of a meat batter. Myofibrillar proteins, which
include myosin and actin, are two of the major proteins that are extracted from muscle tissue by
salt. Binding strength of a meat product is increased with salt soluble proteins (Swift and Ellis
1956; Mandigo et al. 1972, Acton 1972, Rhee et al. 1983). Break strength is measured by
breaking meat products. If it takes more force to break a meat patty, then there is more bind
within the product. Thus, data from break strength evaluation provides information in regards to
the amount of bind strength between the meat particles and fat within a product (Herrero et al. 2008). Bind strength is important in uniformity and slicability of meat products like bologna. If
bind strength is weakened, particles within meat products crumble, which is detrimental in
further processing. In addition to bind strength, water-holding capacity and cook loss affect
texture. If water-holding capacity is reduced and cook loss is increased in meat products, an
undesirable texture is created. Meat is dry and overall palatability is reduced. Gelabert et al.
(2003) demonstrated that water-holding capacity increased with salt inclusion, while cook loss is
reduced in meat when salt is added (Huffman et al. 1981).
In addition to textural properties, salt is also used as a flavor precursor in meat products
and for extending shelf life. The amount of water activity within a meat product impacts
microbial growth. Lower water activity extends the shelf life by reducing microbial growth.
Marsh (1983) found that water activity in fermented meat products is lowered with the use of
salt. Overall, flavor and functional properties of meat determine if consumers will accept the
product (Bourne 1978; Herrero et al. 2008).
Issues Surrounding Salt Use in the Meat Industry
Although salt has functionality purposes in the meat industry, it can also be detrimental to
meat products by accelerating lipid oxidation, which is undesirable in food products and leads to
oxidative rancidity. Furthermore, accumulation of lipid peroxides in the diet has been linked
with certain human diseases such as atherosclerosis (Kanazawa and Ashida 1998). Lipid
oxidation is an auto-catalytic reaction involving free radical formation. Lipid oxidation consists
of three stages that include initiation, propagation, and termination within the phospholipid
bilayer of the muscle tissue. Initiation of the process occurs when a methylene hydrogen atom is
removed from the double bond on the unsaturated fatty acid. Free radicals are generated from the unsaturated fatty acids as a result. The fatty acid free radical connects with a molecule of oxygen
to create a peroxyradical during propagation (Damodaran et al. 2008). Hydroperoxides are
formed during the primary change of lipid oxidation (Coxon 1987). Termination of free radical
formation occurs when there is a combination of two radicals to form a nonradical species
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(Damodaran et al. 2008). Secondary products such as aldehydes, ketones, and alcohols result
when primary products are broken down with accelerated oxidation. These secondary products
are responsible for the production of off favors and off odors. (Ahn et al. 1993b). Meat products
containing a higher degree of polyunsaturated fatty acids are more susceptible to lipid oxidation
than products containing saturated fatty acids (Dawson and Gartner 1983) because free radical
formation increases with the degree of unsaturation. Exposure to oxygen, grinding during
processing, and transition metals such as iron and copper enable the primary radicals to form and
accelerate oxidation (Asgar et al. 1988; Kanner and Rosenthal 1992). Light and increased
temperatures can accelerate the process as well, as cooked meat is known to oxidize faster than
raw meat (Rhee et al. 1983) .
TBARS (Thiobarbituric acid reactive substances) and sensory characteristics
Lipid oxidation is evaluated to assess food quality and is associated with sensory
characteristics such as off flavor that are produced from the decomposition of hydroperoxides.
There are various assays to measure lipid oxidation. The peroxide value determination method is
used to quantify hydroperoxides. Secondary products can be measured by the TBA test
(Tarladgis et al. 1960; Witte et al. 1970) or by hexanal values (Shahidi and Pegg 1994). The
TBA Test is the most common method used to measure lipid oxidation and is also referred to as
the TBARS (thiobarbituric acid reactive substances) method. This assay measures the pink (red)
chromophore that is formed by the reaction of 2-Thiobarbituric Acid (TBA) with secondary products, such as malondialdehyde, by using spectrophotometry (Sørensen and Jørgensen 1996).
TBARS values are reported as milligrams of malondialdehyde equivalents per killigram of tissue
or samples and have been correlated with off flavor scores (Nolan et al. 1989). There are two
main methods for conducting TBARS which include the extraction method and the distillation
method. The extraction method has higher and more accurate yields than the distillation method
in non-cured meat products, as well as in ground chicken, pork, beef, veal, and lamb (Sørensen
and Jørgensen 1996; Wang et al. 1997).
Salt as a prooxidant
Salt at varying levels has been proven to be a prooxidant in meat products. Anderson and
Skibsted (1991) found that salt acted as a prooxidant at a 1% inclusion level in pork patties. In
another study conducted by King and Bosch (1990), sodium chloride at a 2% inclusion level was
more prooxidant compared with potassium chloride (2%) in turkey patties, even when the levels
of copper and iron were held constant. There are many postulations as to how sodium chloride
acts as a prooxidant. Kanner and Rosenthal (1992) argue that sodium chloride acts as a
prooxidant by displacing the iron ions with sodium in the heme pigments of the muscle tissue,
whereas others recognize the chloride ion acting upon the lipid as the source (Ellis et al. 1968) .
The metal impurities, particularly iron, within salt are also thought to cause lipid oxidation
(Chang and Watts 1950; Denisov and Emanuel 1960; Salih 1986b). Tichivangana and Morrissey
(1985) discovered that iron was more prooxidant than copper and cobalt in fish, turkey, chicken,
pork, beef, and lamb. Salih et al. (1989) agree with these results, as they found that when
different salt varieties at a 2% inclusion level were used with added metal contaminants that
included copper, iron, and magnesium in turkey breast and thigh meat mixtures, the combination
of sodium chloride with copper and iron was the most prooxidant. Rock salt, with no added
levels of copper and iron, was no more of a prooxidant than pure salt. However, when 50 ppm of
iron and 50 ppm of copper was added to pure salt, the sodium chloride with the added iron was
found to be more prooxidant than the sodium chloride with the same amount of copper added
(Salih et al. 1989). Farouk et al. (1991) investigated the effects of salt in combination with added
iron after storage time and found that TBARS in ground beef were significantly increased by
iron. Further investigation, however, is needed to evaluate the effects of sodium chloride with
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varying levels of trace metals such as iron and copper.
Lipid oxidation: Other factors
Even though salt acts as a prooxidant, storage, species, and muscle type influences
TBARS values as well. As storage time is increased, TBARS values will increase. Huffman et al.
(1981) evaluated restructured pork chops constructed from hams and Boston butts under frozen
storage (-15 ° C) for 0 days and 30 days. At 0 days of storage the TBARS values were 0.18 mg
malonaldehyde (MDA)/ kg sample, whereas the TBARS values at 30 days were 0.26 mg
MDA/kg sample. In another study conducted by Rhee et al. (1983), ground beef samples were
stored for 30 days and 60 days in frozen storage at -20 °C. The TBARS values for 30 days after
frozen storage were reported as 2.46 mg MDA/kg tissue and 2.58 mg MDA/kg at 60 days (Rhee
et al. 1983).
In addition to storage time, species affects the rate of oxidation. Different species contain
different levels of polyunsaturated fatty acids. Tichivangana and Morrissey (1985) found that
species containing more polyunsaturated fatty acids have higher TBARS values. Fish oxidized
quicker than turkey, chicken, pork, beef, and lamb, where lamb was the least oxidized. Within
species, muscle type impacts oxidation. Turkey breast meat oxidizes in a slower manner than
thigh meat, as indicated by higher TBARS values in thigh meat (Salih 1986a; Botsoglou et al.
2003). This is attributed to the fact that breast meat contains less fat than thigh meat (Salih et al.
Packaging and the use of antioxidants can delay the onset of the oxidation reaction when
salt is included in processed products. The type of packaging used for a product is dependent
upon how quickly the product will be used. Vacuum packaging, modified atmosphere packaging
with the use of nitrogen or carbon dioxide gases, and polyvinylchloride overwrap are often used
to minimize lipid oxidation in meat products. Overwrapping and modified atmosphere packaging
are used for products undergoing retail display, whereas vacuum packaging is used for meat
products that are going to be stored for extended periods of time. Nolan et al. (1989) found that
cooked pork and turkey was less oxidized when stored in vacuum packaging compared to storage
in modified atmospheric packaging (carbon dioxide or nitrogen), or exposed to the air. Cooked
turkey patties with added iron, hemoglobin, salt, or with a combination of those had lower
TBARS values when they were vacuum packaged compared to loose, oxygen-permeable
packaging (Ahn et al. 1993a). Matlock et al. (1984) observed similar results in precooked frozen
pork sausage patties stored over 8 weeks.
In addition to packaging, antioxidants are used in the food industry to interrupt the free
radical mechanism involved in lipid oxidation before the process is catalyzed. Some antioxidants
used in the meat industry include alpha-tocopherol, herbal extracts and oils. Chen et al. (1984)
report that TBARS values of beef with salt (2%) and added alpha- tocopherol were higher than
the unsalted control groups after 2 days of storage, yet were significantly lower than the TBARS
values of beef with only salt (2%). This implies that the salt was prooxidant, but the alpha-tocopherol slowed the process of lipid oxidation when salt was included. Although alpha-
tocopherol serves as an antioxidant when salt is used in food products, research has been
conducted on grape seed, oregano, and rosemary extract to evaluate their effectiveness as an
antioxidant in meat. Rojas and Brewer (2007) found that TBARS values and off flavor scores
were most improved when grape seed extract was used in combination with sodium chloride in
beef and pork patties compared to oregano or rosemary.
Antioxidants can also be added to the animal's diet to delay the onset of rancidity in the
meat products that will be obtained from them. Botsoglou et al. (2003) found that turkeys fed
with alpha-tocopherol acetate and oregano oil resulted in less lipid oxidation compared to
turkeys that were not provided with antioxidants. They determined the combination of oregano
oil and alpha-tocopherol provided the best protection against oxidation. Another study
conducted by Wen et al. (1996) is in agreement with these results, as it was determined that
incorporating alpha-tocopherol in turkey diets lowered TBARS values in raw and cooked
samples that had been stored in refrigeration and during frozen storage. Adding higher levels of
alpha-tocopherol can further prevent oxidative rancidity from occurring in turkeys. Higgins et al.
(1999) discovered that turkeys fed with 600 mg alpha-tocopherol/kg feed for 21 weeks prior to
harvest were less oxidized compared to meat from turkeys fed with lower levels of alpha-tocopherol. Also, TBARS values were higher for the samples containing meat from the turkeys
fed 600 mg alpha-tocopherol/kg and 1 % salt, confirming previous evidence that salt acts as a