Download Chapter 23: Meat Emulsions - FEA

23
Meat Emulsions
Violeta Ugalde-Benítez
CONTENTS
23.1 Introduction................................................................................................................................... 447
23.2 Emulsions...................................................................................................................................... 447
23.2.1 Emulsion Stability............................................................................................................ 448
23.2.2 Emulsion-Destabilization Mechanisms............................................................................ 449
23.2.2.1 Creaming........................................................................................................... 449
23.2.2.2 Flocculation...................................................................................................... 449
23.2.2.3 Coalescence...................................................................................................... 449
23.2.3 Emulsifiers........................................................................................................................ 450
23.3 Proteins as Emulsifiers.................................................................................................................. 450
23.3.1 Animal Proteins................................................................................................................451
23.3.2 Plant Proteins.....................................................................................................................451
23.3.3 Enzymatically Modified Proteins......................................................................................451
23.3.4 Muscle Proteins.................................................................................................................452
23.4 Meat Emulsions..............................................................................................................................453
23.4.1 Sliceable Products.............................................................................................................453
23.4.2 Spreadable Products..........................................................................................................453
23.4.3 Low-Fat Products............................................................................................................. 454
References................................................................................................................................................455
23.1 Introduction
A large amount of processed foods are emulsions. The wide diversity in physicochemical and sensory
characteristics of food emulsions is due to the variety of ingredients and processing conditions.
Emulsified meat products, also called meat batters, are complex systems in which fat is emulsified into
a viscous fluid mainly composed of solubilized myofibrillar proteins previously extracted from meat
from different animal species. The importance of these products is based on their wide consumption
throughout the world in a range of food items, from highly valued liver sausages and pâtés up to ­low-cost
sausages and bologna.
23.2 Emulsions
Emulsions are colloidal two-phase systems, in which a liquid is dispersed in another liquid of different
composition, the second liquid forming the continuous phase. The dispersed phase is also called internal
phase, and the continuous phase is referred to as the external phase. In many emulsions, there is an
­aqueous phase and a hydrocarbon or oil phase (Schramm 2005).
McClements (2005) defines an emulsion as a system formed by two immiscible liquids (usually oil and
water) in which one is dispersed as small spherical particles into the other. The mean particle diameter
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in most food emulsions is between 0.1 and 100 μm. Schramm (2005) reports that oil droplets of milk fat
usually have a mean diameter bigger than 0.2 μm, and even can be higher than 50 μm. In general, there
are two types of emulsions, depending on the continuous and dispersed phase composition: oil-in-water
emulsions (O/W) in which oil globules are dispersed in water; and water-in-oil emulsions (W/O) if water
droplets are dispersed in oil (Schramm 2005). Examples of oil-in-water emulsions are milk, dairy cream,
salad dressings, mayonnaise, fortified drinks, soups, and sauces. Butter and margarine are water-in-oil
emulsions (McClements 2005).
In addition to O/W and W/O, other emulsion forms are possible. Multiple, or double, emulsions are
complex dispersed systems characterized by low thermodynamic stability. These are “emulsions of
emulsions,” such as water droplets in oil-in-water (water-in-oil-in-water, W/O/W), or oil globules in
water droplets in oil (O/W/O). The use of multiple emulsions has been reported for controlled liberation
of the internal phase to the external phase, mainly for medical, pharmaceutical, cosmetic, and industrial
purposes. This type of systems also have potential application in food processing to encapsulate or protect food components, active or sensitive, from environmental factors such as oxidation; to control aroma
and flavor component release, or for low-lipid content food production. Multiple emulsion stability is
mainly affected by emulsion composition and emulsifying conditions (Muschiolik 2007).
The operation of converting two immiscible phases into an emulsion, or reducing oil globule average
size in a previously formed emulsion is called homogenization (McClements 2005). Globule resistance
to deformation and breakage is due to Laplace pressure, which increases when average globule diameter
decreases. As a result, a considerable amount of energy is necessary for emulsion formation. This energy
is supplied by vigorous agitation, generated by a sufficiently intense shear force in high-viscosity continuous phase; this is often the case when preparing W/O emulsions. As a result, droplet diameter is
reduced to a few micrometers. In an O/WE emulsion, the continuous phase viscosity tends to be low;
therefore, to disrupt oil globules the force is generated by rapid and intense pressure fluctuations of a
turbulent flow regime (Walstra 1996).
In the food industry, this process is carried out using equipments known as homogenizers, usually
subjecting the liquid to intense mechanical agitation, such as high-speed stirrers, high-pressure
­homogenizers, and colloid mills (McClements 2005). High-pressure homogenizers, designed for milk
homogenization, are the most widely used because fine emulsions with texture and high stability can be
obtained. This type of equipment operates by forcing a coarse emulsion, previously obtained in a
­high-speed stirrer, through a narrow valve. The combination of high shear force, cavitation, and turbulent flow in the valve promote oil globule disruption. Globule diameter reduction decreases creaming and
increases emulsion stability (Desrumaux and Marcand 2002).
23.2.1 Emulsion Stability
An emulsion is formed when pure oil and pure water are homogenized. However, these two phases rapidly
separate into a system made of an oily layer in the upper part (low density) and an aqueous layer at the
­bottom (high density). This is due to the tendency of the oil globules to merge with neighboring globules as
soon as they collapse; eventually, this leads to a complete phase separation. This happens because the contact between oil and water molecules is thermodynamically unfavorable (McClements 2005). Therefore,
many emulsions are thermodynamically unstable systems, although some emulsions can be stable and
resist emulsion-destabilizing treatments; these emulsions can also be stable for considerably long time.
Metastable emulsions (kinetically stable) found in practice are made of oil, water, and an emulsifier (or
stabilizer) usually a surfactant, that is, macromolecules or a finely divided solid (Schramm 2005).
The ability of an emulsion to resist changes in its properties throughout time is known as emulsion
stability. The more stable the emulsion, the slower the changes occurring in its properties. An emulsion
can become unstable due to different physical and chemical processes. Physical instability is observed as
spatial distribution or alteration of the molecular structure organization; chemical instability occurs in
the molecules forming the emulsion (McClements 2005).
The factors favoring emulsion stability are (a) low interfacial tension, a low interfacial free energy
facilitates keeping a large interfacial area; (b) high surface viscosity and/or mechanically strong interfacial film, acting as a barrier against coalescence; adsorption of small solids improves this property;
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(c) large electric double layer and/or steric repulsion that prevents collisions and aggregation, hence,
­coalescence does not occur; (d) small dispersion attractive force decreasing aggregation and coalescence velocity; (e) small volume of the dispersed phase, reducing collision and aggregation frequency;
(f) small-size globules, in case they have electrostatic or steric interactions; (g) small density difference
between phases, reducing creaming and sedimentation velocity, therefore reducing collisions and
aggregation; and (h) high viscosity, reducing creaming and coalescence velocity (Schramm 2005).
23.2.2 Emulsion-Destabilization Mechanisms
The velocity at which an emulsion loses its stability, as well as the mechanisms leading to this breakdown,
depends on the emulsion composition and microstructure and environmental factors to which it is exposed,
such as temperature, mechanical stirring, and other storage conditions (McClements 2005). The main
emulsion-destabilization mechanisms are creaming, flocculation, and coalescence. Structural changes
occur in the emulsion during flocculation and creaming, but globule size distribution is not altered;
­conversely, during coalescence globule size distribution changes with time (Tcholakova and others 2006).
23.2.2.1 Creaming
This is a gravitational separation phenomenon occurring in emulsions when globules of lower density
than the surrounding liquid phase are displaced to the emulsion upper part. The density of most oils in
the liquid state is lower than water density; due to this, the oil tends to accumulate in the top and the
water in the bottom (McClements 2005). Therefore, globules in an O/W emulsion tend to cream.
Creaming velocity follows Stokes Law, it is directly proportional to the dispersed phase globule size, and
inversely to the continuous or dispersing phase viscosity. In the case of meat emulsions, the smaller the
fat globule size, the more stable is the formed emulsion (Nawar 1993).
23.2.2.2 Flocculation
Flocculation is the process in which two or more globules approach each other to form an aggregate, but
the globules keep their individual integrity. It is the result of electric charge removal and subsequent
inhibition of electrostatic repulsions. Globules merge but remain separated for a thin layer of continuous
phase. The number of globule aggregates increases as flocculation proceeds, and, therefore sedimentation rate also increases. The globules move as a group and not individually. Flocculation implies disruption of the interfacial film surrounding the globule; therefore, changes in the original globule size are not
expected (McClements 2005).
23.2.2.3 Coalescence
It is induced by disruption of the thin film that separates neighboring globules. This is a random process,
leading to several consequences: (a) coalescence probability, when occurring, is proportional to the time
the globules remain next to each other; for this reason, creaming is more likely to occur in aggregates or
in clogged milk; (b) it is a first-order rate process, conversely to aggregation which is, in principle, a
second-order rate process with respect to time and concentration; and (c) film disruption probability is
proportional to its area; this means that as the area increases, the globules flatten as they approach each
other, promoting coalescence. Fat globules generally present in food emulsions do not become flat as the
Laplace pressure is too high. Coalescence is less probable in the following situations:
• With the smallest droplets. These have a very small area, therefore, the probability of disruption is also low. Higher coalescence is necessary to produce larger droplets; cream removal
velocity decreases. In practice, the leading variable usually is the average globule size.
• With thick film separating globules. A thick film requires more intense repulsive forces or
forces with more effect extension that provide better stability against coalescence. Steric repulsion is specifically efficient to prevent coalescence as it keeps globules relatively distant.
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• With high interfacial tension (γ). It could be a paradox; to formulate an emulsion, a surfactant
is necessary, and surfactants reduce the interfacial tension. In addition, small γ values mean
lower surface free energy. However, the key matter is how much activation free energy to disrupt is present; this increases with high γ. High γ values make film deformation difficult, and
film deformation leads to disruption.
These principles suggest that proteins are the most suitable compounds to prevent coalescence; this is
confirmed by experience. Proteins do not greatly decrease γ and frequently promote considerable electric
and steric repulsions (Walstra 1996).
Although many of the factors involved in emulsion stability are of thermodynamic and chemical
nature, meat emulsion stability can be reached by increasing the continuous phase viscosity by foodgrade emulsifier addition and adjusting the average particle size of the dispersed phase (McClements
2005). Van Ruth and others (2002) reported that the better stability of meat is a function of colloidal
­factors, such as ionic strength, particle form, particle surface charge, and particle size distribution.
23.2.3 Emulsifiers
An emulsifier is a surface-active molecule that adsorbs to the surface of globules recently formed during
homogenization; it forms a membrane that protects the globules against aggregation when they come
close to each other (McClements 2005). In a number of cases, emulsifiers are necessary to facilitate
emulsion formation (Schramm 2005). Many emulsifiers are amphiphilic molecules, with polar and
­nonpolar regions within the same molecule (McClements 2005). The ability of fat emulsifier to form an
emulsion is related to how easily it adsorbs to the water-in-oil interface. Emulsifiers reduce surface tension and work necessary to create new surfaces (Zhang and others 2009). They are not only necessary
for emulsion formation, but also to stabilize the emulsions already prepared. It is important to distinguish
between these two basic functions, as they are not interrelated. An emulsifier can be suitable for small
globule formation but not to prevent coalescence for a given time, or vice versa (Walstra 1996).
Some of the emulsifiers commonly used in the food industry are small surfactant molecules, phospholipids, proteins, or polysaccharides (McClements 2005). Natural or modified soy lecithin is an example
of phospholipids used as food stabilizer and emulsifier, giving products with acceptable attributes (Pand
and others 2004). For food O/W, the most widely used emulsifiers are proteins (Walstra 1996) as the
main functional property of these molecules is the ability to disperse in the aqueous phase (Mu and others 2009), they are edible, tensoactive, and provide resistance against coalescence. Emulsified oil globules are stabilized by protein accumulation in the surface, forming a protective barrier against coalescence
and subsequent emulsion breakdown.
An emulsifier success also depends on its ability to maintain the emulsion structure in further processing steps, such as cooking and canning. However, in low-protein concentration or low protein/oil ratios,
protein is not enough to cover the interface formed during emulsification; the resulting emulsion is highly
unstable and flocculation is likely to occur.
The degree of emulsion flocculation is a function of the adsorbed film structure, as well as thermodynamic characteristics of the solvent. The factors affecting this phenomenon are: dispersed and continuous phase viscosity, globule deformability and size, interglobular forces, surface tension, and mobility of
the adsorbed film. If the interfacial oil/water film is disrupted, coalescence occurs and oil globules combine to form a larger spherical globule (Eleousa and Doxastakis 2006). Proteins cannot be applied in
W/O emulsions due to their low solubility in the oily phase (Walstra 1996).
23.3 Proteins as Emulsifiers
Many proteins, including casein, soy, muscle, and egg proteins are used in several foods as emulsifiers
(Mine and others 1991). Walstra (1996) pointed out that proteins vary in their emulsification efficiency,
mainly due to their molecular mass. Low-molecular mass proteins should be more efficient emulsifiers,
however the application of these proteins is not always a good choice as very small peptides can be
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formed, leading to rapid coalescence. It must be taken into consideration that different protein preparations, mainly at industrial levels, contain molecular aggregates of various sizes that considerably increase
the effective molecular mass and decrease the emulsification efficiency. Protein solutions difficult to dissolve are not good emulsifiers. As a general rule, highly soluble proteins facilitate emulsion formation (or
globule formation) almost to the same extent if the concentration is too low.
Another important variable is the protein surface charge. If the protein is highly charged, more
­concentration will be necessary to obtain a stable emulsion. A protein surface charge also depends on
how the emulsion is prepared.
23.3.1 Animal Proteins
Egg white proteins are in fact composed of different chemical entities; they are of great importance for
the food industry, possessing highly desirable characteristics for the preparation of a wide variety of
foods. Ovalbumin, the most abundant protein in egg white, is highly functional, with properties related
to emulsification, foaming, and stabilization (Mine and others 1991). This protein is composed of 385
residues (44 kDa), a carbohydrate chain, none to two phosphoryl groups, four free sulfhydryl groups,
and one disulfide linkage (–S–S–) (Galazka and others 2000). Mine and others (1991) concluded that
the emulsifying activity of ovalbumin in soy oil as the dispersed phase was higher at acidic pH than at
neutral pH due to its high surface hydrophobicity and molecular flexibility when exposed to acidic
conditions. In addition to egg white proteins, hen’s egg yolk is an excellent food emulsifier for bakery
products, sauces, and dressings. Fresh egg yolk contains around 40–50% dry matter, 80% water soluble
and 20% formed by insoluble granules. The plasma is composed of 85% low-density lipoproteins (LDL)
and globular glycoproteins, known as a, b, and g-livetins. LDL apoproteins are known as lipovitelins,
these are the main egg yolk components, close to 68% total dry matter (Daimer 2009). Guilmineau and
Kulozik (2006a,b) showed that egg yolk emulsification behavior is highly dependent on the environmental conditions (pH and ionic strength); thermal treatment can improve these properties. Partially
denatured proteins are adsorbed in the oil/water interface and stabilize the emulsion more efficiently
than egg yolk native proteins. In addition, emulsions prepared with heat-treated egg yolk are less sensitive to pH and ionic strength variations. This positive effect could be due to an increase in steric repulsion between oil globules when denatured protein aggregates cover the oil/water interface. Bovine
serum globin has been known to be a good emulsifier and a stabilizer in acidic conditions (pH 3–6),
where this protein is highly soluble (Bizzotto and others 2005). Milk whey proteins and concentrate are
an important source of food ingredients due to their nutritional, sensory, and functional properties.
Among others are their abilities to absorb water, form gels, to be used as emulsifiers and as foaming
agents.
23.3.2 Plant Proteins
Several plant proteins are also excellent emulsifiers. Adebowale and Adebowale (2008) reported that
protein isolates obtained from Mucuna bean play an important role in emulsification, as they favor W/O
emulsion formation and stabilize the emulsion once formed. Being surface-active compounds, these
protein isolates displace oil/water interfaces, decreasing the surface tension and facilitating emulsion
formation. The high solubility within a wide pH range of Mucama bean protein isolates and the seed
flour shows that this bean can be applied in protein-enriched soft drinks, sausages, salad dressings, mayonnaise, and other foods. Lima bean protein concentrates were studied by Akintayo and others (1998);
these authors pointed out that the obtained material was a better emulsifier than pigeon pea protein concentrates; it can be an option for low-viscosity emulsion formulation; African yam bean protein concentrate is another option of a good emulsifier that can be applied in high-viscosity emulsions.
23.3.3 Enzymatically Modified Proteins
Enzymatic treatments of several proteins increase their functional properties even further. Enzymatic
hydrolysis of the milk whey fatty fraction considerably improves its interfacial properties; air/water
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interfacial adsorption rate is increased, thereby decreasing the equilibrium between surface tension and
increasing the compressibility modulus of films formed at the water surface. The overall result improves
the emulsion properties; the enzymatically treated whey can also be used to improve the food texture
(Blecker and others 1997).
Pancreatine hydrolysis of soy protein alters the molecular weight of an isolate, increasing surface
hydrophobicity and improving the functional properties, especially solubility and emulsifying activity. The resulting hydrolysis products can also be used as emulsifiers in meat products (Qi and
others 1997).
23.3.4 Muscle Proteins
The various technological properties of meat proteins play an important role in emulsified meat products.
Among the various proteins of this type, those in the myofibrils have the best emulsifying properties.
Their high solubility and interactions with other compounds positively affect the oil-binding ability,
water-holding capacity, stability, viscosity, density, and other emulsion characteristics. Myofibrillar
­proteins also take part in gel formation promoted by heat treatment; gelling contributes to texture development and stabilized water/oil systems in the emulsified meat products (Zorba 2006). On the other
hand, the effect of sarcoplasmic proteins on emulsification is relatively low, as reported by Zorba (2006);
the effect of these proteins in oil binding and water holding occurs when ionic strength is below 0.4 M,
but decreases even further above this value. The effect of connective tissue proteins in emulsification is
negligible.
Meat emulsion formation includes the activation of most of the proteins present in the muscle by
­disrupting the sarcolemma to release myosin and actin, subsequently solubilized by salts and phosphates.
Myofibrillar proteins, with fibrous structures, turn into a viscous fluid during protein activation. This
fluid is responsible for fat emulsification and immobilization of added water. Changing fibrous proteins
into a viscous fluid is relatively easy with pork and chicken meat, but more difficult with beef and lamb
(Feiner 2006). This is because different animal species may present a wide variety of protein characteristics, probably due to interaction effects (Zorba 2006). These differences in functional properties can
also derive from intrinsic factors such as protein structure, molecular mass, and amino acid composition
(Liu and others 2008).
According to Feiner (2006) meat hardness, as a result of fiber thickness variation among meat type and
cuts, is also related to protein solubility variation within the same animal species. Westphalen and others
(2006) agree in this respect and also report that the final characteristics of an emulsified meat product
are due to muscle type. This is observed from the fact that myosin extracted from a red muscle consistently produces weak gels, as compared to proteins obtained from white muscles. It is also reported that
gels made with myofibrillar proteins from hen’s leg (red) have lower storage moduli, as compared to gels
made with proteins from chicken breast; this variation in storage moduli was independent of pH, ionic
strength, or antioxidant content.
Fish myofibrillar proteins have excellent functional properties, including emulsion formation. In fact,
several marine products are preferred as raw materials due to their myofibrillar protein functionality, as
well as for religious and health reasons. However, fish myofibrillar proteins are less stable to thermal
and chemical treatments as compared to proteins from other vertebrates. Combinations of these ­proteins
with other chemical species such as alginate oligosaccharides have shown to improve the functional
properties, in particular, emulsion formation (Sato and others 2003). Proteins from other marine
sources, such as invertebrates, are also of interest in food product development. The thick filaments in
mollusks are formed by nuclei of paramyosin, surrounded by a cortical layer of myosin; paramyosin is
the protein responsible of the considerable texture alterations in emulsified muscle of these marine
animals (Mignino and Paredi 2006). Physicochemical and functional property analysis of myofibrillar
proteins of scallops, mollusks, and squid by these authors showed that paramyosin in the muscles of
these marine animals is different to similar proteins in vertebrates. Mollusk actomyosin has considerably higher viscosity, and lower hydrophobicity and water retention than other species, whereas
­actomyosin functionality varies depending on the anatomical regions of origin; the highest values were
observed in the squid mantle muscle.
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23.4 Meat Emulsions
Basically, a meat emulsion is a biphasic system composed of fat globules (dispersed phase) suspended in a
matrix made of proteins solubilized in a salt solution (continuous phase). The droplet or fat globule diameter
in a true emulsion is between 0.1 and 100 μm (McClements 2005); the fat globule diameter of the dispersed
phase in a meat emulsion is larger than 100 μm; therefore, meat emulsions such as finely ­comminuted sausages or pâté are not considered true emulsions, but pastes or batters. Insoluble proteins, connective tissue,
meat particles, and other material are also dispersed in the continuous phase (Rust 1994) although this is,
in fact, a viscous fluid or exudate (Feiner 2006). Fat globules are suspended in the liquid bulk due to the
formation of a protein film. The protein hydrophilic groups are oriented toward the aqueous phase and the
hydrophobic groups, toward the fat (or lipid) phase, hence stabilizing the suspension.
As indicated before, myofibrillar as well as sarcoplasmic proteins can act as emulsifiers. However,
myofibrillar proteins are preferably adsorbed to the water/fat interface, in particular to free myosin. Once
the fat globules are surrounded by protein, the emulsion is formed; on further processing, the system is
stabilized by protein denaturation caused by heat treatment. Myofibrillar proteins produce a strong gel;
conversely, sarcoplasmic proteins do not contribute to the stabilization of the product because the gel
they produce is very weak. Water retention is, therefore, a fundamental characteristic that must be promoted in meat aimed for emulsified product production. The amount of water bound depends, to a large
extent, on the spatial arrangement of actin and myosin fibers, which in turn is due to the pH. At pH above
and below the isoelectric point an increase in water retention occurs, resulting in higher water holding.
Addition of sodium chloride solution modifies the muscle electric charge, increasing the water retention.
The positive charges of sodium binds weakly to the protein’s negative charges; whereas the negative
chloride ions strongly bind to the positive charges of the protein. The net result is a shift in the isoelectric
point, and more water molecules to interact with the proteins (Feiner 2006).
In the context of this chapter, emulsified meat products can be classified into two groups: sliceable
products, such as wieners, frankfurters, mortadella, and bologna; and spreadable products, such as
pâté, terrine, galantine, and roulade. Pork and beef are extensively used in emulsified meat products;
although poultry meat has also been processed into emulsions due to its nutritional characteristics
(Zorba 2006).
23.4.1 Sliceable Products
Sliceable sausages are emulsified cooked meat products of finely comminuted pork, beef, or poultry,
mixed with fat, water and ice, and additives (salt, nitrate, phosphate seasonings, flavorings, and so on).
The meat is emulsified in a cutter (or homogenizer), myofibrillar proteins acting as emulsifiers, although
additives such as skimmed milk to increase the cohesiveness and sliceability are generally added. The
added salt extracts the muscle proteins that emulsify the fat, forming a gel; this is further stabilized by
heat treatment, changing into a solid material. Fat content in an emulsified sausage depends on regional
legislation; it can range from 15% to 30%. After mixing the ingredients, the meat is stuffed into natural
or synthetic casings. Finally, the ground ingredients are heated in an oven, or smoked/cooked in smokehouses. After cooking/smoking, sausages are cooled down in showers or dipped in a slush tank. For some
sausage fabrication, such as wieners or hot dog frankfurters, the synthetic casing is removed. In others,
such as Polish and breakfast sausages, edible hog casings are used and remain in the product. The basic
textural characteristic of sliceable sausages is cohesiveness; it is measured by a two-cycle compression
test using a texturometer or compressimeter (Rosenthal 2010).
23.4.2 Spreadable Products
In addition to traditional emulsified meat products, such as frankfurters or wieners, spreadable
­sausages are emulsion-type sausages fabricated in many parts of the world. Spreadable sausages are
available in a wide variety of products, according to seasonings and adjuncts used in their formulations, such as spices, herbs, and other materials. Liver sausages are usually commercialized in
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p­ ackages; pâté de foie is packed in a crust or croûte, and or molded or terrine; these are made of
­different components and various structures, including meat chunks or a pureé-like structure such as
terrine de foie de volaille. Although many of these products are made with liver, other pâtés are formulated only by meat and fat. In general, the ingredients for liver sausages and pâté (meat and fat) are
precooked; liver acts as an emulsifier. Basic ingredients for pâte can vary, although in general it is
made of beef, pork, poultry liver, or shellfish, venison, rabbit, or even vegetables. The most widely
commercialized liver pâtés are pork liver followed by duck liver pâtés (Totosaus and Pérez-Chabela
2005; Feiner 2006). For liver pâté fabrication, a meat paste similar to an emulsion is formed; hot water
and hot liquid fat is mixed to the meat paste (Feiner 2006). Different pâté products are high caloriecontaining foods, in addition to saturated fats, sodium, and cholesterol. Therefore, oxidation is one of
the main problems in shelf-life reduction in this type of products.
Fabrication of a spreadable emulsified meat product starts with cooking coarsely ground or chopped
ingredients. Previously scalded fat (45–50% total formulation) is then added, or fat substitutes are
included in the formulation. The meat block is then homogenized with hot broth (Totosaus and PérezChabela 2005). Nonmeat proteins, such as skim milk powder or soy protein concentrates are included in
the formulation as stabilizers. The paste is then homogenized together with the liver, if included in the
formulation, as well as spices, herbs, and other additives. Although the main emulsifiers are liver proteins, in commercial operations, other emulsifiers and plasticizers are added to improve spreadability.
The batter is finally stuffed into casings or canned, avoiding air trapping, as air reduces heat transference
and promotes lipid and pigment oxidation. Heating changes the gel into a spreadable emulsion, which,
together with the high fat content accounts for the characteristic of this product (Guerrero-Legarreta
2010). Some attempts have been made to change these product formulations. Martin and others (2008)
prepared pork liver pâté partially replacing pork fat by conjugated linoleic acid and olive oil. The authors
reported that the products were stable to lipid oxidation for 71 days in refrigerated storage. Pâté and similar products are semisolid foods, therefore they are consumed as that is expected to be consumed as a
spread; spreadability is the most important physicochemical characteristic. It is a subjective texture characteristic related to the material yield stress, that is, the minimum shear stress required to initiate flow
(σ0) (Guerrero-Legarreta 2010).
23.4.3 Low-Fat Products
In low-fat products, the dispersed phase has been totally or partially replaced by other material that
contributes to the formation of a two-phase system similar to an emulsion. Fat substitutes are starches,
hydrocolloids, skimmed dried milk, gums (pectin, carrageenan, gelan, xanthan), and plant proteins.
Other carbohydrates, such as pregelatinized starch, develop instantaneous stable viscosity. These
ingredients also provide gelling properties and texture, bind liquids, control syneresis, improve slicing, and increase product yield. Cogelling ingredients, such as protein–polysaccharides also allow fat
reduction in formulations. Kaack and others (2006) studied the effect of high cellulose-containing
fiber in reducing fat in liver pâté; they found that the product had better flavor and texture as compared
to original pâté.
One of the main problems in developing low-fat spreadable meat batters is to keep good extensibility
characteristics. Patel and Gupta (2006) described a spreadable product formulation including soy and
skimmed dried milk, as well as sodium citrate to reduce oil release in the final product and to increase
the flowing ability. Carrageenan and guar gum effectively increase extensibility, plasticizers such as
sorbitol and glycerol favor viscosity, flavor, and texture, and annatto and β-carotene are used as ­colorants.
The paste had improved extensibility properties and kept its quality for close to 3 months under refrigeration conditions. An American patent (5693350, Fernández and others 1997) describes a process to fabricate low-fat meat pâté; the patent refers to a product with <10% fat as a low-fat pâté; the formulation
includes 40–80% lean meat (3–8% fat), up to 15% fat substitute, 15–50% added water, 1.2–2.4% nitrate
salts, and up to 0.3% phosphate. The authors reported that the meat emulsion is treated for proteolytic
digestion and further cooking; and hydrostatic pressure (>400,000 kPa) for enough time to obtain <4.5
protease units/g pâté. The product had better extensibility and spreadability than traditional pâtés.
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