Meat Protein

Non-meat proteins can be used to provide nutritional benefits by lowering the calorific and cholesterol contents (when used as fat replacers) and by increasing the protein level and balancing the amino acid profile.

From: Encyclopedia of Meat Sciences , 2004

Cantonese Sausage, Processing, Storage and Composition

Weizheng Sun , ... Mouming Zhao , in Processing and Impact on Active Components in Food, 2015

Protein Nutritional Change

Meat proteins are important nutritional sources for humans. Proteins must be broken down into amino acids or small peptides before passing through the small intestine wall and entering the bloodstream and, therefore, nutritional quality of meat proteins is largely dependent on their digestibility. Nevertheless, Cantonese sausage processes (salting, drying, sugar addition) can affect the meat proteins structure and, thus, their digestibility. Meat protein oxidation and aggregation have an influence on their degradation by enzymes of the digestive tract ( Sante-Lhoutellier et al., 2007).

The effect of the physicochemical changes of sarcoplasmic and myofibrillar proteins, especially oxidation behavior, on their mechanism of action on in vitro protein digestibility during Cantonese sausage processing has been evaluated (Sun et al., 2011b, d). For gastric pepsin, protein digestibility and rate of proteolysis of sarcoplasmic proteins increased to 26.77% and 0.0201 over the first 6   h drying, while it decreased over 6–72   h (Table 35.1). For pancreatic trypsin and α-chymotrypsin, protein digestibility and rate of proteolysis of sarcoplasmic proteins during processing showed significant decrease (p  <   0.05) from 53.26% and 0.0591 to 32.65% and 0.0350, respectively (Table 35.1). For gastric pepsin, the rate of proteolysis of myofibrillar proteins decreased during processing (Figure 35.2). For pancreatic trypsin and α-chymotrypsin, the rate of proteolysis of myofibrillar proteins increased significantly (p  <   0.05) firstly, then decreased (p  <0.05) at the final stage (Figure 35.2). Results from correlation analysis showed that protein physicochemical changes, especially protein oxidation and aggregation, influenced protein digestibility and thus resulted in a loss of nutritional quality.

TABLE 35.1. In Vitro Protein Digestibility of Sarcoplasmic Proteins from Raw Muscle and Cantonese Sausage at Different Processing Periods ∗

Protein Digestibility Rate of Proteolysis Standardized Coefficients
PEPSIN DIGESTIBILITY
Control 19.76   ±   1.13ab 0.0163   ±   0.0005bc 0.976   ±   0.007a
0   h 22.44   ±   1.68ab 0.0173   ±   0.0012bc 0.974   ±   0.016a
3   h 19.92   ±   1.88ab 0.0155   ±   0.0012ab 0.948   ±   0.024a
6   h 26.7   ±   1.07c 0.0201   ±   0.0012d 0.946   ±   0.029a
18   h 22.16   ±   1.93ab 0.0168   ±   0.0007bc 0.948   ±   0.018a
36   h 23.35   ±   1.77b 0.0183   ±   0.0010cd 0.957   ±   0.010a
54   h 20.39   ±   2.09ab 0.0152   ±   0.0017ab 0.918   ±   0.033a
72   h 18.48   ±   0.77a 0.0136   ±   0.0011a 0.909   ±   0.036a
TRYPSIN AND α-CHYMOTRYPSIN DIGESTIBILITY
Control 56.07   ±   2.22d 0.0599   ±   0.0014d 0.854   ±   0.010a
0   h 53.26   ±   2.63d 0.0591   ±   0.0027d 0.862   ±   0.004a
3   h 55.07   ±   1.25d 0.0602   ±   0.0016d 0.830   ±   0.041a
6   h 47.65   ±   2.24c 0.0518   ±   0.0037c 0.808   ±   0.069a
18   h 46.88   ±   2.79c 0.0521   ±   0.0026c 0.832   ±   0.019a
36   h 42.03   ±   0.86b 0.0455   ±   0.0018b 0.788   ±   0.044a
54   h 33.90   ±   1.20a 0.0368   ±   0.0011a 0.802   ±   0.021a
72   h 32.65   ±   3.07a 0.0350   ±   0.0022a 0.821   ±   0.027a
∗
Values in a column followed by different letters are significantly different (p  &lt;   0.05)

From Sun et al. (2011b).

FIGURE 35.2. In vitro proteolysis rate of myofibrillar proteins from raw muscle and Cantonese sausage at different processing periods by gastric pepsin (A), pancreatic trypsin   +   α-chymotrypsin (B), previously treated with pepsin. Values in a column followed by different letters are significantly different (p   &lt;   0.05).

 Adapted from Sun et al. (2011d).

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Functional meat products

K. Arihara , M. Ohata , in Functional Foods (Second Edition), 2011

21.4.2 Utilization of meat protein-derived peptides

Meat protein-derived peptides are a group of bioactive components of meat ( Arihara, 2006a; Arihara and Ohata, 2008). Studies show that numerous bioactive peptides are generated from food proteins, such as milk, soy, fish and meat proteins (Gobbetti, et al., 2007; Korhonen and Pihlanto, 2003, 2007; Mine and Shahidi, 2005; Pihlanto and Korhonen, 2003). As representative bioactivities of such peptides, antihypertensive, antioxidative, antithrombotic, hypocholesterolemic, antimicrobial, mineral binding, prebiotic, immunomodulatory and opioid activities have been studied. Angiotensin I-converting enzyme (ACE) inhibitory peptides are the most extensively studied of these bioactive peptides (Meisel et al., 2005; Vermeirssen et al., 2004). Since some of these peptides have antihypertensive effects by oral administration, they have been utilized for functional foods (Arihara, 2004, 2006a). However, functional meat products with bioactive peptides, including ACE-inhibitory peptides, have not been developed.

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Industrial cooking

P.J. Fellows , in Food Processing Technology (Fourth Edition), 2017

Meat proteins have three groups: myofibrillar proteins (50–55%, mostly myosin and actin), sarcoplasmic proteins (30–34%, mostly enzymes and myoglobin) and connective tissue (10–15%, mostly collagen and elastin fibres embedded in mucopolysaccharides). When heated, the myofibrillar proteins contract, causing the muscle fibres to shrink transversely between 40–60°C and longitudinally above 60–65°C. Most of the water in meat is held within the myofibrils between thick myosin filaments and thin actin filaments, and the water-holding capacity of meat is affected by the shrinkage of myofibrils. Transverse shrinkage widens the gaps between fibres and longitudinal shrinkage causes substantial water loss, which increases with temperature.

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Meat protein ingredients

R. Tarté , in Handbook of Food Proteins, 2011

4.5 Hydrolysates and flavors

4.5.1 Obtainment and manufacture

Meat protein hydrolysates encompass a broad family of products that can be obtained from meat by-products such as bone residues, mechanically separated meat (MSM), bone residues from mechanical separation, trimmings ( Fonkwe and Singh, 1996; Webster et al., 1982), blood plasma (Wanasundara et al., 2002), and red blood cells (Shahidi et al., 1984; Synowiecki et al., 1996), as well as from skeletal muscle and connective tissue. The possibilities and opportunities in this area are potentially great, given the different kinds of potential raw material sources available which can, in turn, be hydrolyzed to varying extents to yield different types of functional products. Therefore, although some hydrolysates have already been discussed (i.e., gelatin and gelatin hydrolysates), this topic is worth expanding and discussing further.

Hydrolysis can be achieved by treatment with enzymes, acids, or alkali (Lahl and Braun, 1994), but for many applications the enzymatic process is preferred due to its faster reaction rates, mild process conditions, and high specificity (Hamada, 1992), and because it allows for more precise control of the degree of hydrolysis (DH) and, as a result, of the peptide and amino acid profile of the resulting hydrolysates (Lahl and Braun, 1994). Degree of hydrolysis, usually expressed as the ratio of amino nitrogen to total nitrogen (AN/TN), or percent of peptide bonds cleaved, is a measure of the extent of hydrolytic degradation of proteins (Mahmoud, 1994). It is both a practical and effective way of monitoring and controlling the hydrolysis process, and a good indicator of a hydrolysate's functional properties (e.g., solubility, gelation, water holding, emulsification, flavor, etc.).

Meat hydrolysates can be classified as either primary (partially hydrolyzed) or secondary (extensively hydrolyzed). Primary hydrolysates result from hydrolysis by one or more endopeptidases of animal (e.g., pepsin, trypsin, chymotrypsin), vegetable (e.g., papain, bromelain), bacterial (e.g., subtilisin from Bacillus subtilis, Bacillus amyloliquefaciens, or Bacillus licheniformis), or fungal (endoprotease from Aspergillus oryzae) origin (Piette, 1999; Pinto e Silva et al, 1999). A secondary hydrolysis may be necessary in order to break down bitter peptides that may form as a result of partial hydrolysis (Pedersen, 1994). In these cases, exopeptidases are utilized, which can also be of animal, bacterial (e.g., Bacillus spp.), or fungal (e.g., aminopeptidases from Aspergillus spp.) origin, and are generally more effective after endopeptidases have reduced the average peptide size.

4.5.2 Functional properties

In general, properties such as emulsion stability, viscosity, and gel-forming ability decrease with increasing DH, due to the smaller molecular weight and to the increased net charge that results from hydrolysis (Mahmoud, 1994). Conversely, as DH increases, the hydrolysates' flavor contribution increases, primarily owing to the presence of low-molecular weight flavor components (e.g., amines, amino acids, and small peptides) and flavor precursors (e.g., organic acids and nucleotides). Therefore, extensive hydrolysis will result in products of such low rheological functional quality that they become strictly limited to use as flavors and flavor enhancers, and for protein supplementation (Synowiecki et al., 1996). In many cases this is desirable. Meat flavor notes can also be obtained from meat stocks and broths, as discussed previously, either by enzymatic hydrolysis or by reacting them with certain Maillard reactants (e.g., reducing sugars). Other factors that will affect the end-product obtained include the specificity of the hydrolytic enzymes used, the physicochemical nature of the intact parent protein, and processing conditions (Mahmoud, 1994).

4.5.3 Uses and applications

Knowledge of the extent and type of the hydrolytic reactions involved in the manufacture of meat protein hydrolysates allows the process to be manipulated and controlled to yield products with specific functional attributes, as described previously. The choice of meat protein hydrolysate is thus dictated by the specific functional properties desired for each particular application and may also be limited by commercial availability. Commercially, meat protein hydrolysates can be concentrated and used as added ingredients in liquid or powder form (Piette, 1999).

4.5.4 Regulatory aspects

In the US, the Food and Drug Administration (FDA) requires that '[t]he common or usual name of a protein hydrolysate shall be specific to the ingredient and shall include the identity of the food source from which the protein was derived' [21 CFR 102.22] (CFR, 2010j ). For meat protein hydrolysates this requirement is also mandated by 9 CFR 317.8(b)(7)(ii), which states that 'ingredients of livestock and poultry origin must be designated by names that include the species and livestock and poultry tissues from which the ingredients are derived' ( CFR, 2010b). Consistent with these regulations, the USDA requires that 'hydrolyzed protein of slaughtered animal species and tissue of origin, other than gelatin, must be indicated, e.g. 'hydrolyzed beef plasma,' 'hydrolyzed pork stock,' and 'hydrolyzed pork skin' (USDA-FSIS, 1995a). The degree of hydrolysis of the material also has labeling implications. Proteins with AN/TN ratios greater than 0.62 are considered by the FDA to be 'highly' hydrolyzed and must be declared as 'hydrolyzed (source protein).' Proteins with AN/TN   <   0.62 are not considered highly hydrolyzed and may therefore be declared as 'partially,' 'mildly,' or 'lightly' hydrolyzed (e.g., 'partially hydrolyzed [source protein]') (USDA-FSIS, 1995a).

Regarding usage limits, partially hydrolyzed proteins are permitted in the US in various meat and poultry products at a maximum level of 3.5% (USDA-FSIS, 2010).

In the EU, protein hydrolysates and their salts are not classified as food additives (European Parliament and Council, 2006) and are, therefore, not subject to food additive legislation. They are not considered meat and must, therefore, be declared separately.

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Producing low-fat meat products

J.F. Kerry , J.P. Kerry , in Improving the Fat Content of Foods, 2006

14.7.4 Non-meat proteins

Non-meat proteins employed in low-fat meat processing are usually sourced as isolates (>80% protein) and concentrates (30–80% protein) and are incorporated into meats at optimum residual powder levels of 2–3% and 4–6%, respectively. Addition of non-meat proteins in low-fat meat formulations is believed to partially compensate for the potential loss of some water-binding properties due to higher water addition rates and reduced salt levels in such products. Perhaps the most widely reported non-meat protein employed in meat processing is that of soya protein ( Dexter et al., 1993; Sofos and Allen, 1977; Yang et al., 2001). However, use of soya isolate in emulsion type products in excess of 3% has been reported to increase hardness and off-flavour, and decrease juiciness, saltiness and flavour intensity (Matulis et al., 1995b). Other non-meat protein sources that have been assessed in low-fat meat processing include: pea, wheat, dairy (whey proteins, caseinates, total milk protein, etc.) and oat flours as highlighted in Table 14.5. Incorporation of non-meat proteins in low-fat meat processing usually results in elevated protein levels together with improvements in product yield, product stability (water fat and meat binding), formulation costs and product textural properties (organoleptic issues) as well as a reduction in calorific values and improvement in nutritional status (Troy et al., 1999).

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TENDERIZING MECHANISMS | Enzymatic

E. Huff-Lonergan , in Encyclopedia of Meat Sciences (Second Edition), 2014

Abstract

Degradation of meat proteins is an important mechanism to improve the tenderness of meat. This degradation can be initiated by enzymes that are intrinsic to the muscle, or by those that are exogenous and are added to the meat with the specific goal of improving tenderness. Intrinsic enzymes include calpains, cathepsins, and caspases. Exogenous enzymes are typically of plant origin and include bromelain, ficin, and papain. Intrinsic enzymes are most active against myofibrillar proteins, whereas the exogenous plant enzymes can degrade both myofibrillar and connective tissue proteins. Optimizing the activity of these enzymes is the key to improving meat tenderness.

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Measuring chemical deterioration of foods

Lingling Liu , Fanbin Kong , in Chemical Changes During Processing and Storage of Foods, 2021

13.2.4.1 Protein oxidation

Oxidation of meat proteins can occur after overexposure to oxygen, which may cause meat color change from bright red to brown ( Steele, 2004). Hydroperoxides or peroxides and other short-lived intermediates can form upon the oxidation of proteins at the backbone and side chains (Jacobsen et al., 2010). Protein oxidation can also occur upon light exposure. For instance, light-induced oxidation of oxymyoglobin results in metmyoglobin formation in meat products (Bekbölet, 1990). Photoreduction of essential amino acid methionine to methional could cause activated flavor in milk (Bekbölet, 1990). In addition, degradation of tryptophan and tyrosine may contribute to the discoloration of milk upon light exposure (Bekbölet, 1990). An in-depth discussion of protein oxidation is presented in Chapter 3, Oxidation of Proteins.

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COOKING OF MEAT | Physics and Chemistry

K. Palka , E. Wesierska , in Encyclopedia of Meat Sciences (Second Edition), 2014

Effects of Heating on Meat Microstructure

When the meat proteins are exposed to heating, they first lose their tertiary structure and undergo several changes in configuration. In general, thermal denaturation leads to a loss in protein solubility. These chemical changes are also associated with changes in the physical character of the meat tissues. Elastin, however, is not susceptible to effects of heat. The transverse shrinkage to the fiber axis occurs at 40–60  °C, which widens the gap already present at rigor between the fibers and their surrounding endomysium. There is a controversy regarding these observations. Some authors found no changes in the cross-sectional area on cooking of the neck muscle, whereas others found that the transverse shrinkage of both fibers and fiber bundles of bovine psoas major muscle starts at approximately 40   °C. There is also a disagreement between the results presented in the literature with regard to the temperature, in which the longitudinal shrinkage of the fiber starts. Some observations indicate that fibers do not shorten below 60   °C, and the others, that both sarcomere shortening and fiber shortening usually begin at temperatures of 40–50   °C. The divergence in the results may be due to the large biological diversity within a muscle as well as between different muscles. At 60–70   °C the connective tissue network and the muscle fibers shrink. This is mainly based on the fact that the perimysial collagen shrinks at approximately 64   °C.

In the bovine ST muscles aged for 5 or 12 days and roasted to internal temperatures in the range of 50–90   °C and then visualized using SEM, no significant structural changes are seen at the internal temperature of 50   °C. However, in the range between 60 and 90   °C, significant changes occur both in the myofibrils and in the intramuscular connective tissue, and this is further affected by the degree of postmortem ageing. The changes in the connective-tissue structure of perimysium and endomysium during roasting of the 5-day-aged bull ST muscles to 70   °C are shown in Figure 1(a) and to 90   °C in Figure 1(b), for the 12 day-aged muscle, the changes are shown in Figure 1(c) and (d), respectively. The granulation of perimysium and the cracks of endomysium tubes are observed in 5 day-aged meat roasted to an internal temperature of 80–90   °C (Figure 1(b)), however, in 12 day-aged meat after roasting to 60–70   °C (Figure 1(c)). The changes in the myofibrillar structure during roasting of the 5-day-aged bull ST muscles to 70   °C are shown in Figure 2(a) and to 90   °C in Figure 2(b), whereas for the 12 day-aged muscle in Figure 2(c) and (d). In the 5 day-aged samples the disintegration of the myofibrillar structure starts at 70   °C (Figure 2(a)) and is considerable at 90   °C (Figure 2(b)). In the 12 day-aged meat roasted to 70   °C (Figure 2(c)), the degree of structural destruction is similar to that of 5 day-aged meat roasted to 90   °C (Figure 2(b)). At 90   °C complete disintegration of the myofibrillar structure of 12 day-aged meat is observed (Figure 2(d)).

Figure 1. Connective tissue changes on heating. SEM micrographs of perimysium and endomysium from bull ST muscle: after ageing for 5 days at 4   °C and roasted to 70   °C (a) and to 90   °C (b); after ageing for 12 days at 4   °C and roasted to 70   °C (c) and to 90   °C (d).

 Reproduced from Palka, K., 2003. The influence of post-mortem ageing and roasting on the microstructure, texture and collagen solubility of bovine semitendinosus muscle. Meat Science 64, 191–198.

Figure 2. Myofibrillar changes on heating. SEM micrographs of myofibrils from bull ST muscle: after ageing for 5 days at 4   °C and roasted to 70   °C (a) and to 90   °C (b); after ageing for 12 days at 4   °C and roasted to 70   °C (c) and to 90   °C (d).

 Reproduced from Palka, K., 2003. The influence of post-mortem ageing and roasting on the microstructure, texture and collagen solubility of bovine semitendinosus muscle. Meat Science 64, 191–198.

As the endpoint temperature increases from 50 to 60   °C, there is a significant decrease in the fiber diameter. As the heating temperature is raised, the sarcomere length decreases, the effects being greater in the aged meat. The larger structural changes observed during roasting of the more aged meat may be a consequence of the changes during ageing in both the cytoskeletal proteins and the intramuscular connective tissue, leading to a weakening of the transversal and longitudinal integrity of the muscle fibers. In general, the microstructural changes are considerably less in the meat heated after 5-day ageing in comparison with the meat heated after 12-day ageing.

There is a high negative correlation (r=-0.97) between changes in the sarcomere length and the cooking losses during heating of the bovine ST at the temperature range of 50–120   °C (Figure 3).

Figure 3. Effect of heating temperature on cooking losses (–) and sarcomere length (– – –) of beef ST muscle samples retorted after 5 days ageing at 4   °C.

 Reproduced from Palka, K., Daun, H., 1999. Changes in texture, cooking losses, and myofibrillar structure of bovine M. semitendinosus during heating. Meat Science 51, 237–243.

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Sausage processing and production

Steven M. Lonergan , ... Dennis N. Marple , in The Science of Animal Growth and Meat Technology (Second Edition), 2019

Sarcoplasmic Proteins

Another class of meat proteins is called sarcoplasmic proteins. They are water soluble, and the muscle pigment, myoglobin, is located in the sarcoplasmic protein fraction. Myoglobin is responsible for the color patterns in meat. For example, beef has the most myoglobin and has the darkest color. Pork has less myoglobin and has a lighter color than beef. Poultry breast and wing meat has the least myoglobin and is lighter in color than pork. The darker poultry meat from legs has more myoglobin and is darker than breast meat. Therefore the sarcoplasmic protein traits will influence the color of processed meat. The sarcoplasmic proteins, however, have very limited binding capacity when compared with the myofibrillar proteins. More detailed information on sarcoplasmic proteins can be found in Chapter 9 and Fig. 9.6.

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HEAT EFFECTS ON MEAT | Physics and Chemistry

K. Palka , in Encyclopedia of Meat Sciences, 2004

Chemical Changes in Meat Protein Systems

Thermal denaturation of meat proteins occurs over the range from 50 to 85 °C; α-actinin is most labile and becomes insoluble at 50 °C, myosin at 55 °C, sarcoplasmic proteins at about 65 °C, actin between 70 and 80 °C, and tropomyosin and troponin above 80 °C. The changes in denaturation of meat collagen start at its shrinkage temperature over the range from 56 to 65 °C and gelatinization occurs at about 80 °C. The amount of collagen shrinkage also increases with the quantity of mature links. The shrinkage temperature of the epimysium is usually higher than that of other connective tissue around the muscle. Differences in thermal stability of muscle connective tissue is a consequence of differences in the proportion of collagen types, level of heat-stable cross-linking, and level of glucosaminoglycans (GAG) in the structure. The highest thermal stability occurs in collagen of the endomysium, because of the large contribution of disulfide bonds in type IV collagen.

Differences in collagen solubility of different muscles may be a result of the degree of post-mortem ageing and the proportion of endomysium collagen in the connective tissue and the internal temperature in the range 50–90 °C. For example, 5-day-aged and 12-day-aged M. semitendinosus muscle samples retorted at 70 °C has almost twice the quantity of soluble collagen as that of muscle heated to 80 °C. In the case of roasting, these changes occur at 80 °C rather than at 70 °C. When the temperature is increased further, the 12-day-aged muscle has unchanged collagen solubility, but the 5-day-aged muscle collagen has lower solubility. In other words, the method of heating influences the rate of denaturation of intramuscular collagen.

The other alterations occurring when meat is heated include changes in pH, reducing activity, ion-binding properties and enzyme activity. Slight upward changes of pH (approximately 0.3 unit) result from exposure of reactive groups of histidine. Increased reducing activity develops as a result of unfolding of protein chains and exposed sulfhydryl groups. Conformational changes in proteins alter their ability to bind various ions, such as Mg2+ and Ca2+. Although elevated temperatures inactivate enzymes, there are differences between muscles.

Severe heating of proteinaceous foods leads to development of colour and flavour compounds due to Maillard reactions (see: HEAT EFFECTS ON MEAT | Maillard reaction and browning) and to thermal degradation of methionine and cysteine residues and other low-molecular-weight compounds in proteins.

Very severe heating of meat and meat products at much higher time–temperature levels than those required for sterilization may lead to formation of isopeptide cross-links between the free NH2 group of lysine and the carboxylic group of aspartic or glutamic acids. These reactions cause tightening of the structure of the products and may decrease the biological availability of lysine as well as the digestibility of the meat proteins.

Beef fat melts at 40–50 °C. Solubilization of collageneous connective tissue provides channels through which melted fat may diffuse. Cooking thus results in movement and possibly emulsification of fat and soluble proteins. At internal meat temperatures of 80 °C, a movement (thermal leak) of fat through the tissues is observed due to the destruction of the perimysium and endomysium.

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