Factors Affecting Colour Development and Binding in a Restructuring System Based on Transglutaminase.
By: Eben van Tonder
1 June 2018

The articles on the complete bacon production system are available in booklet form:    https://tgrestructuringofmeat.pressbooks.com

INTRODUCTION

I started experimenting with Ajinomoto’s Activa almost 5 years ago.  In preparation for that, I wrote an article, Restructuring of whole muscle meat with Microbial Transglutaminase – a holistic and collaborative approach, which I updated over the years.

I have been approached by countless people from around the world with questions and insights which I did not address in my initial article.  I continued to gather bits of information, stored in mails to myself, learn from production managers I got to know in every part of the world and great articles I discovered over the years as I worked on a daily basis to do first-hand experiments at Woody’s and I tried to answer these questions for myself and for others while, always, working on improving the system.

It is time for a completely new follow up article where I address these issues systematically.  I look at heat treatment, colour development, moisture loss, protein denaturing, phosphates, salt, deboning, meat quality, pressure, freezing, chilling and gelation in relation to the use of TG.  I continued to look at what an optimal TG blend will look like and the aspects that our production systems must incorporate.  I also examine possible future developments in thermal processing and a few alternative ways to set up a production line where TG is incorporated into a grid system for the restructuring of large meat muscles, mainly for the production of bacon.

The number one question I was asked over the years is if TG affects meat colour.  Some researchers reported slight colour changes on fresh meat, but as far as processed meats are concerned, it is an irrelevant question since there are much more important factors affecting colour than the small impact that TG may or may not have.  Lets very briefly look at heating, colour development, and moisture loss to illustrate my point.

We begin with a review of the curing process and the effect of heat and smoke on colour development and moisture loss before we turn our full attention to a discussion of other factors affecting TG.

PROPER COLOUR DEVELOPMENT BEGINS WITH CURING:  THE IMPORTANCE OF RESTING, AFTER INJECTION, BEFORE SMOKING

 to  to NO 

When sodium nitrite is placed in solution in the brine preparation phase, the crystal structure breaks up and the ions separate into Na and .  Nitrous acid is formed.    This hydration of nitrous acid is an important time-consuming reaction (Krause, B. L.; 2009: 9).

After the formation of nitrous acid (), the next step “is the generation of either a nitrosating species or the neutral radical, nitric oxide (NO).”  (Sebranek, J., and Fox, J. B. Jn.; 1985:  1170)  A nitrosating species is a molecular entity that is responsible for the process of converting organic compounds into a nitroso (NO) derivatives, i.e. compounds containing the R-NO functionality.  During resting, the most important one is the formation of Nitrosyl Chloride (NOCl). This is one of the good reasons why leaving out salt from bacon curing is not advisable.  The time-consuming nature of these reactions is also the reason why a resting phase is vital.

In a large commercial high-throughput bacon curing plant we found that an optimal processing sequence has the following sequence.  A few variations of this basic model will be proposed in this article, but this is the model that I used with great effect for many years and other models, if they survive critical theoretical scrutiny, needs to be tested.

• injecting the meat,
• tumbling it,
• resting it for between 12 and 24 hours (depending on the curing room temperature),
• tumbling it again to pick up brine that leached out during the maturing or colour development stage and,  This time, add TG blend.
• grid filling
• smoking/Thermal Treatment
• de-gritting
• blast freezing
• equalizing
• slicing and packing

Lets now focus on colour development during smoking and thermal treatment to understand optimal smoker chamber temperatures.

PROPER COLOUR DEVELOPMENT:  THE IMPORTANCE OF SMOKING

Cold smoking is normally seen as smoking where the core temperature will remain below 35 deg C.  We use hot smoking where the core temperature riches > 35 deg C but < 45 deg C.  Smoking and thermal treatment are therefore considered jointly.  Temperature effects product taste, meat toughness, binding, coulour, and moisture loss.

Reddening

During reddening, the temperature is increased, extraction flaps in the smokehouse closed to maintain humidity, and sulfhydryl groups are released which is a reducing substance in meat and important in proper cured colour formation.  Fraczak and Padjdowski (1955) indicated that 80°C is the critical temperature for the decomposition of sulfhydryl groups in meat.” (Cole, 1961)  (Reaction sequence)

Smoking

During heating and smoking, there are several changes in the meat that has a direct effect on the colour development.  The nitrosating species that is more dominant than NOCl is smoke due to the presence of phenolic compounds.  In addition to the heat release of sulfhydryl groups, the pH is reduced in the meat.  Randall and Bratzler (1970) noticed an increase in the myofibrillar protein nitrogen fraction, pH and free sulfhydryl groups of pork samples that were only heated, and a decrease of these values in the samples that were subjected to heat and smoke. “Results of this study indicated that smoke constituents react with the functional groups of meat proteins.” (Randall, 1970)  These results seem to support a reddening step before smoke is applied due to the fact that heating would release the sulfhydryl groups and during the smoke steps, the pH will be reduced.  (Reaction sequence)

DENATURING VS COAGULATION

With our consideration of smoking on meat, we have also entered the discussion of the effect of heat on meat.  Before considering the effect of heat on the protein lets first see how the heat gets to it.

Mechanism of heat transfer

Heat is transferred during cooking through conduction, convection, and radiation.  “Spakovszky and Greitzer (2002) defined conduction as ‘transfer of heat occurring through intervening matter without bulk motion of the matter,’ convection as heat transfer due to a flowing fluid, either a gas or a liquid, and radiation as ‘transmission of energy through space without the necessary presence of matter.’   Radiation can also be important in situations in which an intervening medium is present, such as heat transfer from a fire or from a glowing piece of metal (Spakovszky and Greitzer 2002).”  (Yu, T.Y., et al, 2017)

“Meat cooking usually involves more than 1 mode of heat transfer (Bejerholm and others 2014).”   During cooking in a smokehouse, heat treatment is achieved through dry heat surrounding the meat, but during reddening and smoking the air is or become moist and moist-heat (hydrothermal) thermal processing uses hot steam. Smoke House thermal treatment, including smoking, is, in reality, a combination of dry heat and moist heat.  (Yu, T.Y., et al, 2017)

“Conventional cooking of meat results in heterogeneous heat treatment of the product on account of steep temperature gradients (Tornberg 2013). Emerging mild cooking techniques such as ohmic cooking can achieve a more homogeneous heating by heating the entire volume of meat at the same time (Tornberg 2013).”  (Yu, T.Y., et al, 2017)  THis is an important point for consideration in a continuous, fully automated system.

This is important in considering the effect of heat on the grid system with holes.   The present role to steel ratio is 1:1,8.  The exposed meat area is therefore approximately half (take the edging to be approximately 0.02 to give the total ratio of 1:2).  This amplifies the effect of heating, but by what factor? This needs to be determined experimentally between different smokehouses.  I have determined a variety of different options in smokehouse settings over the years.

“Heat may cause proteins to lose their native conformation (denature) by providing the polypeptides with kinetic energy, increasing their “thermal motion,” and thus rupturing the weak intramolecular forces (such as nonpolar interaction, various kinds of electrostatic interaction, and disulfide bonds) that hold the proteins together (Davis and Williams 1998). As the temperature increases, a protein starts to unfold. When almost all the tertiary and secondary structures are lost, the unfolded protein may aggregate, have its disulfide bonds scrambled, undergo side-chain modifications (Davis and Williams 1998), and cross-link with other polypeptides. Aggregation is the consequence of nonpolar interaction between heat-denatured proteins whose hydrophobic groups have turned outward into the surrounding water, in order to adopt a lower energy state (Davis and Williams 1998). A variety of side-chain modifications, such as those induced by oxidation or the Maillard reaction, have been characterized in proteins following heat treatment.”  As heat increases, the 3-dimensional structure of meat proteins change.  These changes manifest in a change in colour and gelation.  (Yu, T.Y., et al, 2017)

DEVELOPMENT OF NITROSYLMYOCHROMOGEN

“Upon thermal processing, globin denatures and detaches itself from the iron atom, and surrounds the hem moiety.  Nitrosylmyochromogen or nitrosylprotoheme is the pigment formed upon cooking and it confers the characteristic pink colour to cooked cured meats.”  (Pegg, R. B. and Shahidi, F; 2000: 42)

We also need to review the main muscle proteins found in the body.

SKELETAL MUSCLES

Skeletal muscles are bundles of muscle cells (also known as muscle fibers) embedded in connective tissue.  (Yu, T.Y., et al, 2017) These muscle proteins “are grouped into three general classifications: (1) myofibrillar, (2) stromal, and (3) sarcoplasmic. Each class of proteins differs as to the functional properties it contributes.”  (www.meatscience.org)

->  Myofibrillar Proteins

The first very important protein to take note off is the myofibrillar protein for the purpose of water binding and binding meat pieces together.  These muscle fibers are muscle cells, grouped into muscle bundles.  The structural backbone of the myofibrils is actin and myosin.  (Toldra, 2002) They are the most abundant proteins in muscle and are directly involved in the ability of muscle to contract and to relax.  (www.meatscience.org)  Myofibrils also include tropomyosin and troponin, regulatory proteins associated with muscle contraction.  Parallel to the long axis of the myofibril, are two very large proteins called titin and nebulin.  (Toldra, 2002)

Myosin is a protein which is described as the motor, and the structural protein, actin’s filaments are the tracks along which myosin moves, and ATP is the fuel that powers movement.  (Lodish, 2000)  Myosin “converts chemical energy in the form of ATP to mechanical energy, thus generating force and movement.”  (Cooper.  2000)

“Together, actin and myosin make up about 55-60% of the total muscle protein of vertebrate skeletal muscle, with the thicker myosin myofilaments yielding about twice as much protein as the thinner actin myofilaments. Actin alone does not have binding properties, but in the presence of myosin, acto-myosin is formed, which enhances the binding effect of myosin.” (Patterson, The Salt Cured Pig)  In meat processing, it is important to note that it is the myofibrillar proteins which are soluble in high ionic strength buffers.  (Toldra, 2002)

“Texture, moisture retention, and tenderness of processed muscle foods are influenced by the functionality of myofibrillar protein.”  (Xiong, Y. L.;1994)  The pork muscle that contains the most myosin is the longissimus dorsi or the eye-muscle or longissimus muscle on the loin.  “The muscle fiber bundles of the longissimus dorsi are arranged at an acute angle to the vertebral column.  The cross-sectional area of the longissimus dorsi increases towards the posterior part of the ribcage, but it has an approximately constant cross-sectional area through the loin.”  (Animal Biosciences)

-> Sarcoplasmic Proteins

“The sarcoplasmic proteins include hemoglobin and myoglobin pigments and a wide variety of enzymes.  Pigments from hemoglobin and myoglobin help to contribute the red colour to muscle.” (www.meatscience.org)  These proteins are water soluble.  Besides myoglobin and hemoglobin, this class of proteins also includes metabolic enzymes (mitochondrial, lysosomal, microsomal, nucleus or free in the cytosol).  (Toldra, 2002)

Very important to remember for the purpose of meat processing is that myoglobin is the protein pigment responsible for the red colour in meat.  The redness of meat is largely dependant on the concentration of myoglobin.  Myoglobin is the storehouse for oxygen in the muscle.  Because different muscles need different oxygen levels, the concentration of myoglobin will differ between muscles.  The loin muscles in pigs are for example used for support and posture and therefore contains low levels of myoglobin.  Myoglobin levels are further influenced by species, breed, sex, age (older animals generally have more myoglobin), training or exercise (this is why free-range pigs have more myoglobin than stall-fed animals), and nutrition. (Pegg and Shahidi, 2000)

-> Stromal Proteins

“Connective tissue is composed of a watery substance into which is dispersed, a matrix of stromal- protein fibrils; these stromal proteins are collagen, elastin, and reticulin.

Collagen is the single most abundant protein found in the intact body of mammalian species, being present in horns, hooves, bone, skin, tendons, ligaments, fascia, cartilage and muscle. Collagen is a unique and specialised protein which serves a variety of functions. The primary functions of collagen are to provide strength and support and to help form an impervious membrane (as in skin). In meat, collagen is a major factor influencing the tenderness of the muscle after cooking.  Collagen is not broken down easily by cooking except with moist—heat cookery methods. Collagen is white, thin and transparent. Microscopically, it appears in a coiled formation which softens and contracts to a short, thick mass when it is heated and helping give cooked meat a plump appearance. Collagen itself is tough; however, heating (to the appropriate temperature) converts collagen to gelatin which is tender.  In the consideration of a TG mix, collagen is one of our most important considerations.

Elastin (often yellow in colour) is found in the walls of the circulatory system as well as in connective tissues throughout the animal body and provide elasticity to those tissues.  Reticulin is present in much smaller amounts than either collagen or elastin. It is speculated that reticulin may be a precursor to either collagen and/or elastin as it is more prevalent in younger animals.”  (www.meatscience.org)

It is interesting that collagen has been used for centuries to create strings to bind things and for strings on musical instruments.  Catstring or catgut is made by twisting together strands of purified collagen taken from the serosal or submucosal layer of the small intestine of healthy ruminants (cattle, sheep, goats) or from beef tendon and has been in use for a long time 900’s AD.  (Wray, 2006)  Gut strings were being used as medical sutures as early as the 3rd century AD as Galen, a prominent Greek physician from the Roman Empire, is known to have used them.   (Nutton, 2012)

Abū al-Qāsim Khalaf ibn al-‘Abbās al-Zahrāwī al-Ansari (Hamarneh, et al., 1963)(Arabic: أبو القاسم خلف بن العباس الزهراوي‎;‎ 936–1013), popularly known as Al-Zahrawi (الزهراوي), Latinised as Abulcasis (from Arabic Abū al-Qāsim), was an Arab Muslim physician, surgeon and chemist who lived in Al-Andalus in the early 900’s CE. He is considered as the greatest surgeon of the Middle Ages (Meri, 2005), and has been described as the father of surgery.  (Krebs, 2004).  He became the first person to have used Catgut to stitch up a wound. He discovered the natural dissolvability of the Catgut when his monkey ate the strings of his musical instrument called an Oud. (Rooney, 2009)

Later, in 1818, the modern founder of surgery, Joseph Lister, and his former student William Macewen independently and quite remarkably, almost at the exact same time, reported on the advantages of a biodegradable stitch using “catgut”, prepared from the small intestine of a sheep.  Over the ensuing years, countless innovations have extended the reach of collagen in the engineering and repair of soft tissue in medicine and numerous other industrial applications. (Chattopadhyay, 2014)  The interesting point should not escape our notice that collagen is included in our TG mixes ta facilitate meat protein – TG – connective tissue – TG – meat protein binding structure.  Collagen is surface-active and is capable of penetrating a lipid-free interface.  (Chattopadhyay, 2014)

The other major constituent of meat is, of course, lipids or fat but I deal with this separately below.

During thermal processing, moisture loss will take place.  Let us predict the optimal temperature range that will give us the right moisture loss and colour development in the shortest possible time.  Countries such as Australia sell their bacon cooked but in the UK, New Zealand, Canada, the USA and South Africa, bacon is sold par-cooked.  I, therefore, consider temperatures which will be considered par-cooked and fully cooked.

DIFFERENCES IN MOISTURE LOSS

“Bendall and Restall (1983) systematically studied the physical changes occurring during heating of intact beef-derived single muscle cells, and also the very small myofiber bundles of 0.19 mm in diameter (containing 40 to 50 cells) at final temperatures between 40 and 90 °C. In addition, the authors also studied heating of larger bundles of 2 mm in diameter.”  (Yu, T.Y., et al, 2017)

According to their work, the stewing process progresses as follows:

From 40 to 52.5 °C

Denaturation of sarcoplasmic (include hemoglobin and myoglobin) and myofibrillar proteins occurs.  Related to colour development the denaturation will effect sarcoplasmic protein even though its denaturation probably occurs from at least 25 °C.   Related to moisture and the range of 40 to 52.5 °C, a slow loss of fluid from the myofibers into the extra-myofiber spaces occurs without shortening. (Yu, T.Y., et al, 2017)  The maximum activity observed for TG was at 40 °C for the commercial TG. At temperatures above 45 °C, TG suffered a rapid drop in its activity. (Ceresinoa, 2018)

Between 52.5 and 60 °C

At this temperature, there is “an increasingly rapid loss of fluid from the myofibers, reaching a maximum rate and extent at about 59 °C.”  There is no overall shortening at this temperature mainly due to heat shrinkage of the basement membrane collagen (type IV and perhaps type V as well) at about 58 °C.   (Yu, T.Y., et al, 2017)

Between 64 to 94 °C

“Considerable overall shortening and a decrease in cross-sectional area are noted, accompanied by increased cooking loss with heat shrinkage of the endomysial, perimysial, and epimysial collagen.”  (Yu, T.Y., et al, 2017)

Long Stewing

“Long periods of stewing causes partial or complete gelatinization of the epimysial collagen, followed by the peri- and endomysial collagen, resulting in the soft and tender feature of stews (Bendall and Restall 1983). It is worth mentioning that meat with a high pH (Zhang and others 2005) or fat content (Wood and others 1986; Jung and others 2016) has been shown to exhibit higher water-holding capacity.”  (Yu, T.Y., et al, 2017)

The important aspect for us is the key temperature of < 52.5 where moisture loss becomes “rapid”.  This gives us an important upper “meat temperature” limit above which rapid moisture loss occurs.

The following section confirms the conclusion of par-cooked bacon’s optimal thermal processing range of between 40 and 52 deg C.  Due to inconsistencies in the smoke chamber, it is suggested that a maximum internal core temperature of 40 deg C is set.

KINETICS OF THERMAL DENATURATION

Kajitani, et al, (2011) studied the kinetics of thermal denaturation of protein in cured pork meat related to each of the three protein classes of meat proteins namely myosin (from myofibrillar proteins), sarcoplasmic proteins and collagen (from stromal proteins).  Of great interest to us is the sarcoplasmic proteins which include the pigment containing myoglobin.

The first important consideration is that the “thermal denaturation of muscle proteins such as myosin, sarcoplasmic proteins and collagen, and actin, occurs at different temperatures. To describe those reactions during thermal processing, temperature dependency of the reaction rate constant is necessary.”  As the level of NaCl in the meat increased, “the thermal-denaturation rate constant of each protein increased.” (Kajitani, et al, 2011)

Adding salt to the sarcoplasmic proteins means that it starts to denature at a temperature of around 50 deg C, reaching a peak at around 68 deg C.  Adding Sodium Chloride moves the graph to the left.

Graph source:  (Kajitani, et al, 2011)

Having now considered thermal treatment and smoke in some detail, we can move to a consideration of TG in particular, but we will broadly keep looking at colour development, binding strength, and water loss.

TG is mixed into solution before added to the meat.  The TG mix contains connective proteins and the first important matter to take into account is the solubility of these proteins.

The maximum activity observed for TG was at 40 °C for the commercial TG. At temperatures above 45 °C, TG suffered a rapid drop in its activity.  Optimal pH for commercial TG was found to be between pH 5.5 and 6.0. (Ceresinoa, 2018)

DIFFERENCES IN SOLUBILITY

In terms of the use of Transglutaminase, different proteins are used in the TG mix as added connective protein to enhance the overall binding action.  When TG is mixed in a solvent before application, different solvents will provide different solubility which may concern operators.

For example, TG containing stromal proteins such as collagen which shows low solubility in a neutral aqueous solvent such as water but high solubility in a curing brine solution with phosphates and salts on account of the high ionic charge of this solution.

From Yu, T.Y., et al, 2017.

The solubility of different proteins under various ionic strengths further informs us of the importance of salt and phosphates in solubilizing myofibril protein.  Mixing the TG into a small brine solution has in my experience the best results.

MIXING AND TUMBLING – COLOUR LOSS AND BINDING

The system I developed over the years and used with great effect is to mix a batch of “stuffing meat” which I use in conjunction with whole muscles.  Whether such a mix is made or comminuted muscle meat prepared for sausages, researchers have found that mixing time has an effect on the color and will increase the deterioration of the desired color if conducted in excess of 12 min” (Sun, 2009).  Over the years I noticed a similar colour change if whole meat muscles have been over-tumbles, but if the meat is smoked, the colour change is immaterial.

The greatest benefit of the system relates to binding.  The reason why I use “stuffing meat” is that this combines modern binding systems such as transglutaminase with old-school meat processing techniques, such as chunking, flaking and tearing.  Bhaskar Reddy, et al. describes chunking and its benefits as “passing the meat through a coarse grinder plate leading to decrease in the particle size not greater than one and a half inch cubes.  This technique increases the surface for the extraction of myosin and aids in better binding during mixing.” (Bhaskar Reddy, et al.; 2015)  This describes the system I currently use to produce the stuffing meat.  Bhaskar and his colleagues refer to flaking and say that “high-speed dicing or slicing machine is being used for flaking and reforming of restructured meat products. Fine flakes produce more acceptable appearance, increase tenderness and decrease shear force value”, referencing Mandal et al., 2011; Reddy et al., 2015.  They add another category which they refer to as  “sectioned and formed meats” which are “primarily composed of intact muscle or section of muscle that are bound together to form a single piece”, quoting Pearson and Gillet, 1996; Mandal et al., 2011; Sharma et al., 2013.  This is the process then of taking the whole muscle meat and joining them together in the grid system.  My method combines then chunking with sectioned and formed meats.

The “old school” method relies on the combined effects of salt, phosphate and mechanical action.  Bhaskar Reddy, et al. (2015) references Boles and Shand, 1998 who found that “by using this technology, the product must be sold either precooked or frozen because the product binding is not very high in the raw state but high yields (25% above meat weight) are possible.

One of the benefits of the “old school” methods is the effect of meat particle size. “An increase in meat surface area and an increase in the availability of myofibrillar proteins for binding is the net consequence of comminution.” (Sun, 2009).

“In a study to evaluate mixing time on the binding effect of restructured meat, Booren, Mandigo, Olson, and Jones (1982) found that there was a significant linear increase in binding strengths up to 12 min of mixing at 28C.”  (Sun, 2009)

The excellent review article of Sun (2009) makes reference to a study by Ghavimi,
Rogers, Althen, and Ammerman (1986) where they assessed vacuum, non-vacuum, and nitrogen back flush processing conditions at 1–38C during tumbling of restructured cured beef.  Fascinatingly, they concluded that meat had higher cooked yields in a non-vacuum atmosphere. This, in the context of the application of Transglutaminase, is a very interesting observation.

I have long proposed a re-examination of the viability of vacuum tumbling, but I recognise the entrenched nature of this technology in modern meat processing plants and propose a new line set-up for investigation.

Injector -> vacuum tumbler -> 24 hours resting station -> add TG -> ribbon/ paddle mixer -> filling station -> smoking/ cooking -> de-gritting -> freezing – slicing -> packing.

This eliminates the re-routing of meat back to the tumblers which are expensive assets while it achieves the application of the TG, final pick-up of any brine that purged out of the meat during resting as well as the balancing brine added after injection.  In order to facilitate a proper pick up of this “loose brine”, some processors choose to add between 1 and 2% pork protein at this stage which will mean that the brine added during this step consists of the pork protein and the TG blend in a small amount of brine.

Lets first look at why a tumbler works.  The interaction of the meat, rubbing against the meat and the pressure created as the mass of meat falls to the bottom of the tumbler during the drum rotation causes pressure which then “activates” the protein by causing the highly swollen muscular protein cells to burst.  Bhaskar Reddy, et al., (2015) quotes Feiner, 2006 who stated that it is the “kinetic energy released during falling of meat pieces at bottom of the tumbler which serves to disrupt cellular membranes, which in turn causes protein extraction.  It is the baffles inside the tumbler which “move the injected pieces of meat up the wall of the tumbler and once the pieces of meat reach a certain height, gravity causes them to fall.”  (Bhaskar Reddy, et al., 2015)

This is, in my opinion far more aggressively and successfully achieved through a paddle mixer or a ribbon mixer than only the falling of the meat inside the tumbler.  Mixing in a paddle or ribbon mixer will, in my estimation, better develop the myosin protein to become “sticky.”  Remember that the aim of this step is to “solubilize the protein, creating a layer of activated protein on the surface of meat which is responsible for slice coherency in the cooked product.  The sarcolemma surrounding the tightly swollen muscle cells is, in my opinion, more likely to be destroyed by the impact of energy from paddles than only tumbling and myofibrillar proteins will be released and solubilized (which is the object of tumbling).  There is considerable academic and anecdotal support for this.  Dikeman and Devine state in their Encyclopedia of Meat science, second edition (2014), commenting on the fact that paddle mixers run at reduced revolutions per minute (rpm), that they “can be useful for applying mecahnical action to whole muscle pieces. . .  to produce a surface protein exudate without damaging muscle integrity.”  (Dikeman and Devine, 2014:  126, 127)

Meat must be mixed until they become tacky – almost furry.   “Rust and Olson (1973) found that the extraction of myofibrillar proteins on the surface of meat has two functions. One is to act as a bonding agent holding the meat surfaces together and the other is to act as a sealer when thermally processed and therefore, aid in the retention of water in the muscle tissue.”  “In addition, cellular disruption of the meat tissue occurs during tumbling which together with the curing additives allows the meat to improve the yield (Chow et al., 1986). Constraining connective tissue sheaths around muscle fibres are disrupted, allowing further myofibrillar swelling introduced by salt (Katsaras and Budras, 1993).  (Bhaskar Reddy, et al., 2015)

It is, of course, possible to mix the TG mix into the stuffing meat by hand, but one loses all the benefits listed above.  For the exact reason, I believe a more aggressive treatment of the whole muscle meat just prior to filling into the grids should yield far better reshaping and binding results.  Too little mixing will result in meat being “loose” and a failure to bind together.  Too much mixing, on the other hand, will result in a loss of tenderness and the product being “rubbery”.  (Pearson and Gillett, 1999)

The reason why mixing is essentially done in a tumbler under vacuum is mainly that, removing the oxygen, prevents oxidation.  This prevention of oxidation will, however, also be accomplished by maintaining a low temperature during mixing which is obviously also very good to control negative mirco-growth.  (Pearson and Gillett, 1999)

Bhaskar Reddy and colleagues state that tumbling or massaging (physical action upon the meat, in whatever form) “improves the speed of curing by increasing salt absorption.”  (Bhaskar Reddy, et al., 2015)  It is this reason why I still prefer the two-step tumbling.  The solubilization of the proteins by the fat and the phosphates are greatly enhanced if the meat is left to rest for 12 or 24 hours and re-tumbled/ mixed which of course will increase the protein bind.

Having made this statement, we get to a long-standing debate related to tumbling namely if one must tumble continually (uninterrupted) or if one must have intervals of rest periods.  For every study that intermitted tumbling is superior, there seems to be a study that shows continues tumbling is superior.  Why is the one preferred over the other?  Exactly because brine needs time to diffuse into the muscle.  (Krause et al., 1978)  One needs the drum to stop turning so that the meat can be immersed in the brine in order to absorb into it.  This is not achieved, as many believe, by the vacuum which presumably opens up the meat fibers and somehow pulls the brine into the meat.  The reason why this is done intermittently (tumble, rest, tumble, rest) and not in a two-step process of tumbling, unloading, resting in the chiller, loading into the tumbler and tumbled again, is presumably to eliminate the need to load and unload the tumbler twice.  In a high throughput factory, this should, in any event, be done with loading equipment and should not be a consideration.  I also doubt if the total time of resting in a tumbling program will be sufficient for the brine to be absorbed if one takes absorption rates into meat into account.

Whichever way I look at it, a two tumbling system is preferred over injection, resting, tumble, adding TG 15 minutes before the end of the program and grid filling (only one tumbling step).  There are simply too many advantages which are ignored which one will get in a system of injection, tumbling, resting, TG tumble, grid filling.

My only concern of using paddle mixers for the second step and not tumblers relates to the formation of foam.  If foam is created, this may lead to protein denaturation and the binding strength will be compromised (Kerry et al., 2002)  This will have to be evaluated.  In my own experience, when using a blender to do the stuffing meat, this has never in 2 years of using the technique created foam.  Whole muscles will have to be tested for foam formation which I know happens in a tumbler if only a partial vacuum is pulled.  I suspect the paddle mixer will work very well.

DIFFERENT GELLING ABILITY OF DIFFERENT PORK MUSCLES

A matter of interest is the different gelling strengths of different proteins.  Between poultry, beef, fish, milk, and pork, but also between different pork muscle groups.  This is of interest to me for choosing the best muscle to produce the stuffing meat.  Robe and Xiong (1993) reports that pork longissimus dorsi muscles (predominantly white) formed stronger gels when compared to pork serratus ventralis muscles (predominantly red).

One would not use the longissimus dorsi muscles to produce stuffing meat, but there may be muscle groups in the leg with similar visual characteristics.  Is there an advantage in using some of these muscle groups for the stuffing meat?  It is an interesting question that must be investigated.  Robe and Xiong (1993) concluded that their work indicates that “red and white muscle types (in pork) should undergo different processing treatments for optimum quality meat products.”

PRESSURE – COLOUR AND BINDING

Contrary to popular belief, pressing of the meat does not facilitate the binding or the effect of TG in any way.  (Pearson, and Gillett, 1999)  Pressing into moulds have a few important functions.  In the first place, it ensures the meat, particularly large meat pieces, are forced into a regular shape which is the key behind improved slicing yields.

The second reason for pressing relates to surface area and meat contact.  If there are cavities in the meat log, binding at those locations will obviously be compromised and the appearance of the meat slices, especially when bacon is sliced, will be undesirable.

SALT – COLOUR AND BINDING

Sun (2009) points out that “discoloration of restructured steaks can be caused by salt. A decrease in color desirability with increased salt levels has been observed by some researchers (Huffman & Cordray, 1979; Schwartz & Mandigo, 1976). The raw color could be improved by sodium tripolyphosphate (STP), which helps to compensate for the effect of salt (Schwartz & Mandigo, 1976).  As a matter of interest, Huffman, Ly, and Cordray (1981b) as cited by Sun, “showed that addition of salt at all levels increased thiobarbituric acid (TBA) values and decreased color levels.”  No such effect has however been noticed with heat treated, smoked and cured meat.

Salt and phosphates during the mixing/ tumbling step are essential in that it aids the extraction of myofibrillar proteins which in turn aids in the overall binding.  (Pearson and Gillett, 1999)

The interaction of salt and TG is a key consideration.  Sun reports that “in cooked restructured meat products, gel firmness and water-holding capacity (WHC) have been reported to increase by the addition of TG in high-salt (2%) products but not in low-salt products (Pietrasik & Li-Chan, 2002b). TG was able to improve consistency (firmness) but not cooking loss of the product in a low salt (1%) system (Dimitrakopoulou, Ambrosiadis, Zetou, & Bloukas, 2005).”  (Sun, 2009)

“Kuraishi et al. (1997) investigated the effect of salt on binding strength and indicated that provided there was addition of salt (NaCl), TG treatment caused effective binding of meat pieces. Their result showed that an increase in binding strength caused by adding salt (1.0–3.0%) with TG when compared to TG alone.”  (Sun, 2009)

PHOSPHATES – BINDING

Phosphate generally enhances the effect of salt.  Sun (2009) reports that “a variety of phosphates in different combinations, concentrations, and with concomitant salt concentrations were evaluated by Trout and Schmidt (1984). They found that tetrasodium pyrophosphate had the greatest binding effectiveness, which was followed by sodium tetrapolyphosphate, and then sodium hexametaphosphate.

They concluded that most of the changes in binding could be explained by the ionic concentration of the phosphates. STP also delays development of rancidity and is added at a level of about 0.25% for adequate protein extraction and flavor development (Pearson & Gillett, 1996). Nielsen, Peterson, and Møller (1995) observed optimum effects of STP on the texture at a concentration of 0.2%. (Sun, 2009)

COMBINATION OF STROMAL PROTEINS WITH ALGIN/ CALCIUM OR TG

I include this in a separate heading, due to the low-cost stromal proteins of collagen, elastin, and reticulin and muscles with a high percentage of it.  The protein is of huge interest in TG formulations.  How will the inclusion of pork gelatin aid the binding system with TG?

In considering connective tissues, it is astounding to recognise the monumental presence of K. B. Lehmann.  In terms of the curing reaction in meat, it was this German hygienist and bacteriologist from the Hygienic Institute at Würzburg, Germany who confirmed Polenski’s suspicions (Saltpeter) that nitrite is the key in the cured colour formation and not nitrate as was believed.  He further importantly identified its colour spectrum when diluted in alcohol.  (Fathers of Meat Curing)  It was probably based on his work and that of his student, Karl Kißkalt, that the German government allowed the use of nitrite in curing brines during the first world war.

It was Lehmann and his coworkers who showed that “the toughness of different cuts of meat, measured mechanically, was closely related to their content of connective tissue, and that the decrease in toughness resulting from cooking was related to the collagen of connective tissue rather than to the elastin.”  (Mitchell, et al.; 1926)

They found that “under the influence of moist heat the collagen is readily changed to gelatin, thus losing its toughness. In the raw condition, white fibrous connective tissue (mainly collagen) is almost twice as tough as yellow elastic connective tissue (mainly elastin), but when cooked, the former loses most of its toughness while the latter remains practically unchanged in this respect.”  (Mitchell, et al.; 1926)

“Ensor, Sofos, and Schmidt (1990) concluded that the use of high-connective-tissue meat or addition of concentrated forms of connective tissue in algin/calcium gel restructured meats could improve product texture and reduce formulation costs.”  (Sun, 2009)  Gelatin is the ideal thickening agent to accompany transglutaminase since it contains a variety of different amino acids, including our old friends Glutamine and Lysine which are now cross-linked by the action of transglutaminase.  (Aguilar, M. R. and Román, J. S.; 2014:  186)  It is important to use the right kind of gelatin.  Fish and pork gelatin will be objectionable for either religious or allergen concerns by various processors in various parts of the world and it is an important consideration.

I am aware of tests underway in Chili where pork protein is tested in conjunction with TG to replace MDM.  The viability of this must be tested.

WHAT ABOUT FAT?

We skipped over fat when we looked at the constituents of muscles and now returns to it.  Many people refer to fat as lipids, but fats are only a subgroup of lipids called triglycerides.  Lets set some basic concepts up, to begin with.  Human body fat, animal, and vegetable fats have triglycerides as its main constituent.  Their function in blood is to facilitate bidirectional transference of adipose fat which is the fat layer under our skin, around internal organs), in bone marrow, intermuscular and in the breast tissue.  

Let’s look closer at the adipose tissue.  It is “composed of a loose collection of specialized cells, called adipocytes, embedded in a mesh of collagen fibers.  We looked briefly at collagen when we reviewed the stromal proteins.  The main role of adipose tissue in the body is its role as a fuel tank for the storage of lipids and triglycerides.

One gets white and brown adipose tissue with white tissue being the most numerous.  “The main role, or function, of white adipose tissue is to collect, store and then release lipids.  However, because of the properties of the lipids being stored, the adipose tissue also acts as a protective cushion (resists knocks) and also as a layer of insulation against excessive heat loss.

Lipids conduct heat very poorly (only about a third of the rate of other materials) so even a small layer of adipose cells (about 2 mm) will keep a person warm at 15 degrees centigrade, whereas a person with only a 1 mm layer of protection will be feeling quite uncomfortable.

About 80% of average white adipose tissue is lipid, and of that, about 90% is made up of the six triglycerides: stearic, oleic, linoleic, palmitic, palmitoleic and myristic acid.  Also stored are free fatty acids, cholesterol, mono- and di-glycerides.”  (brooklyn.cuny.edu)

“Each adipocyte cell has a large, central, uniform, lipid packed central vacuole which, as it enlarges, pushes all the cytoplasm, the nucleus, and all the other organelles to the edge of the cell, making it look a bit like a band or ring under the microscope.

These cells can vary in size from about 30 microns to over 230 microns, and, despite their distorted appearance, contain all the necessary biochemical machinery of other cells.

Every adipose cell must touch at least one capillary or blood vessel (an artery or vein).  From this the cells draw all their needed supplies, including lipids.

Fatty foods, with high lipid content, often provide more lipids than can be digested and used right away.  The excess is stored in the adipose tissue.  Excess carbohydrate and protein taken in with meals can also be converted to fat (usually in the liver) and then moved to the adipose tissue for longer-term storage.

Lipids are the major fuel reserve for humans and most mammals.  These molecules are very efficient at storing needed energy.  One gram of fat stores about 9 kcal per gram, compared to carbohydrate or protein (4 kcal per gram).  For mobile animals, this means that less bulk has to be carried around and a normal sized body that is about 20% fat has enough stored energy to last about 20 – 30 days without eating!”  (brooklyn.cuny.edu)

Let’s look more closely at triglyceride.  There are many types of triglycerides.  We are all familiar with the two main groups of triglycerides, namely saturated and unsaturated types. Saturated fats are “saturated” with hydrogen — all available places where hydrogen atoms could be bonded to carbon atoms are occupied. the importance to us for meat processing is its melting point which is higher and are more likely to be solid at room temperature.  It is this saturated fats that, when ingested, raises the level of cholesterol in your blood.  (daa.asn.au)

On the other hand are the unsaturated fats which have double bonds between some of the carbon atoms, reducing the number of places where hydrogen atoms can bond to carbon atoms. For our purposes, the net result is that they have a lower melting point and are more likely to be liquid at room temperature.  These fats help reduce the risk of high blood cholesterol levels and have other health benefits when they replace saturated fats in the diet. (daa.asn.au)

When one works with pork fat, it is important to keep an eye on the temperature.  During processing, highly unsaturated fats will start to melt and form a fat coating on the product which is visually unappealing. (Toldra, 2010)  Beef fat is firmer with a more intense flavour in comparison with pork or chicken.  Beef fat’s melting point is comparable to pork kidney fat due to the low content of collagen and saturated fats.  The reason why pork fat is popular is that it is largely tasteless and flavourless.  The rules for making meat emulsions are based on fat choice and temperature. “Pork backfat gives the best suitable product for slicing.  Jowl and belly fat can also be used.  The endpoint chopping temperature should remain below 18 deg C, 12 deg C, and 8 deg C for beef, pork, and poultry fat respectively to avoid fat melting.”  (Toldra, 2010)

“To make spreadable products fat must be dispersed in the liquid state at “hot” temperatures.  The endpoint chopping temperatures should be above the fat melting point (i.e., 35 deg C).  To achieve this final temperature, fat is usually pouched in water at temperatures above 80 deg C before being mixed with protein (liver or lean meat).  The object is to reach a final internal temperature between 50 and 60 deg C for ham fat and between 70 and 75 deg C for jowl fat.  Fat poaching also causes contraction of the connective tissue which will facilitate the grinding; it eliminates low melting fats, which can cause weight losses during cooking and it lowers the microbial content.  Thus, for hot emulsions, low melting fat is preferred such as ham and jowl fat remain firm during cooking at high temperatures.”  (Toldra, 2010)

Triglycerides are composed of three fatty acids.  The fatty acid content in animals depends on age, type of feed and the environment.  Diet plays an important role, especially in pork which is one of the reasons why pork, raised in informal settlement environments are very poor substitutes for commercially farmed animals where feed are strictly controlled.   The properties of the fat will generally be determined by the composition of the fatty acids.  “It will be soft (oily appearance) and prone to oxidation when there is a high percentage of polyunsaturated fatty acid linoleic (typical of feed rich in corn, for instance) and linolenic acids.”  (Toldra, 2002)

There are two main groups of lipids in the body.  The one is triglycerides which we just had a look at.  The other is phospholipids.  They are present in very small amounts but have a strong key role in flavour development and the oxidation of postmortem meat.  They also have a relatively high proportion of polyunsaturated fatty acids in comparison to neutral lipids.  Some of the major constituents are phosphatidylcholine (lecithin) and phosphatidylethanolamine.  Phospholipids vary depending on the genetic type of the animal and anatomical location of the muscle.  Therefore, the amount of phospholipids tends to be higher in red oxidative muscles than in white glycolytic muscles.  (Toldra, 2002)

The interaction of fat and protein is a very important consideration in restructuring meat. “The fat level clearly influenced the structure of the gel/ emulsion network, as reflected by the differences in the type of protein molecular interactions involved in its formation, and this, in turn, affected the fat binding properties and the texture of the end product.” (Sun, 2009)

It is difficult to bind fat effectively to meat.  De NG, Toledo, and Lillard (1981) found that water and fat binding by meat batters diminish when temperatures exceed 16°C during comminution.  This speaks directly to the preparation of stuffing meat and it requires for the meat temperature to be kept as low as possible, but not so low that it makes it impossible for workers to use it in the restructuring process.

Secondly, when one talks about fat and stuffing meat, one must consider the interaction between a TG blend containing pork gelatin and fat in the meat mix which is less than optimal.  TG by itself is not a good binder for fat.  The easiest way of handling fat in stuffing meat is to avoid it.  I have found pork fillet to be particularly suited due to its lean nature.

Remember that gelatin “works by creating a very fine mesh of proteins, between which the (hydrophilic) liquid gets trapped.  A mixture of fat and water isn’t a liquid. It can be either a rough two-phase mixture, with visible fat droplets swimming around in the water, or it can be an emulsion, with invisibly small fat droplets dispersed through the water. Emulsions appear smooth, e.g. milk.”  (cooking.stackexchange.com)  Fat in the stuffing meat will interfere with the binding.

As far as the whole meat muscles are concerned, it is important to lay the meat pieces fat down in the mold to minimize contact between added meat and fat.

FREEZING/ CHILLING

After thermal treatment, the meat must be frozen as soon as possible.

Sun (2009) reports that “although most of the studies using TG for restructuring meat conducted by incubation meat at optimum temperature (37–508C) of MTG or by cooking to obtain sufficient binding strength, some researchers obtained good binding effect by using cold binding (2–58C), with the combination of TG and sodium caseinate, without addition of salt or cooking (Kuraishi et al., 1997; Serrano, Cofrades & Jimenez Colmenero, 2004). Kuraishi et al. (1997) indicated that the TG reaction condition of 58C for 2 h would not enable any bacteria present to increase much and discoloration of the meat was not observed in the raw, refrigerated state. In my experience, IT binds very well at lower temperatures.

The maximum activity observed for TG was at 40 °C for the commercial TG. At temperatures above 45 °C, TG suffered a rapid drop in its activity.  Optimal pH for commercial TG was found to be between pH 5.5 and 6.0. (Ceresinoa, 2018)

DIFFERENT BACTERIA PRODUCE TG WITH DIFFERENT PROPERTIES

It has been found that different strains of bacteria that produce the enzyme TG, produce it with different yield and properties.  Different TG producing bacteria strains are still being identified from different environments. “The isolation of a strain of Streptomyces mobaraense was the first step towards the extensive commercial exploitation of this enzyme. Thereafter, a number of various microbial strains, such as Streptomyces lydicus, Streptomyces cinnamoneum CBS 683.68, Streptomyces sp. CBMAI 837, have been found being able to biosynthesize TG extracellularly.  How the TG is produced definitely impacts its application.  TG’s of various origins and in different concentrations have different functionality.  (Ceresinoa, 2018)

Generally, increased TG concentration produces a better binding of meat.  The optimum pH for the commercial TG was found to be between pH 5.5 and 6.0, but TG from different strains have a different optimal pH.  TG from Bacillus circulans BL32, for example, has been reported to have an optimal pH of 7.2.  (Ceresinoa, 2018)

“As to temperature influence on TG activity, minor differences were seen between the enzymes, with a maximum activity observed at 40 °C for the commercial TG and at 35–40 °C for SB6. At temperatures above 45 °C, both enzymes suffered a rapid drop in their activities.  These findings are consistent with studies of TG derived from other streptomycetes such as Streptomyces hygroscopicus and Streptomyces sp. CBMAI 837. (Ceresinoa, 2018)

DEBONING

Sinew and excess fat must be removed in the trimming stage to maintain product quality and consistency.  The use of a grid system allows the deboning department to trim to exact product specifications.  In regular bacon production, leaving the silverskin and membrane on the meat is advisable since it will prevent excess moisture loss during thermal processing.  In a restructuring scenario, it will have to be removed during trimming because it will interfere with the binding.

WHAT ABOUT PSE MEAT?

PSE pork meat is a scourge in the Western Cape during the summer and using TG does not resolve PSE.  An excellent article on an evaluation of factors impacting on meat quality in relation to PSE is Differentiation of pork longissimus dorsi muscle regarding the variation in water holding capacity and correlated traits.

It is possible to address PSE.  The first option will be so source meat during the summer from non-Western Cape sources, but this presents difficulty for the farmers who are the backbone of the industry and may go against strategic alliances.  A second strategy will be to work closely with farmers and the local abattoirs because much can be done pre and immediate post slaughtering.  These are, however matters that are notoriously difficult to implement.

What can be done from a processing perspective? Motzer, Carpenter, Reynolds, and Lyon (1998) successfully used pale, soft and exudative pork to manufacture restructured hams.  The problem with producing bacon from PSE meat is that “due to the rapid pH drop while muscle temperature remains high, the proteins in the myofibrillar fraction become partially denatured and lose their functionality.  Denaturation of myosin in PSE muscle ultimately affects the water holding capabilities of the meat system. As a consequence, products manufactured with PSE may be expected to lose higher amounts of water.”  (Motzer, et al., 2006)  The unfortunate reality is that 100% PSE meat cannot be utilized in high quality processed products (Marriott, et al. 2006).

Motzer and coworkers (2006) report on Shand et al. (1994) who evaluated the effects of various levels of salt, temperature and kappa carrageenan on the bind of structured beef rolls and reported that as salt or levels of kappa carrageenan increased, the bind increased.  They found that kappa carrageenan was the only binder different that when adequately solubilized improved adhesion of PSE meat.

As far as water holding capacity, they found that adding modified food starch (MFS) and isolated soy protein (ISP), enhanced the water holding capacity of hams produced from PSE pork meat.  They noted that isolated soy protein (ISP) “resulted in a thicker adhesion than normal for the meat pieces. Manual stuffing became difficult and often resulted in air pockets within the meat log.”  (Motzer, et al., 2006)  This will, however, be overcome by a proper press system.

Even though there were improvements in the ham, the fact remained that “due to loss of structural integrity, PSE meat will lose considerable water “, especially after thermal processing.  Most of the water is released due to the partially denatured myofibrillar proteins.”  (Motzer, et al., 2006)

The complete article can be found at PSE Meat Treatment.  Without reformulating a brine for the summer in Cape Town, incorporating kappa carrageenan, MFS, and ISP, losses in bacon production will remain material for pork procured locally.  It will manifest in excessive purge in the final product stage, excessive moisture loss during and after thermal processing and poor binding of restructured parts of the bacon logs.

Of course, a strategy will be to produce ham with the badly affected meat.  “Motzer et al. (1998) revealed that utilizing 50% PSE pork in a restructured product with either modified food starch or carrageenan yielded better quality pork than 100% PSE treatments.  Schilling et al. (2002) later demonstrated that combining 25% PSE and 75% RFN (red, firm, and non-exudative) pork in a chunked and formed ham was similar in quality to a 100% RFN pork sample when soy protein concentrate and modified food starch were incorporated together at 2 and 1.5%, respectively. Similarly, Torley et al., (2000) reported that increasing the ionic strength and utilization of polyphosphates resulted in increased cooking yield similar to that of a product manufactured from RFN pork.”  (Marriott, et al. 2006)

It is my suggestion that all these be tested in a summer mix of products to compensate for the extraordinary level of PSE prevalent in regions like the Western Cape during the summer.  “This research makes it clear that PSE pork can be incorporated into processed products, but it can be unsatisfactory to use formulations with more than 25% PSE. Samples formulated with 25% PSE pork exhibit acceptable texture, but those formulated with 75 or 100% PSE often sustain cracking.”  (Marriott, et al. 2006)  This relates to cooked hams. Bacon is a different matter and mixing PSE and non-PSE meat cannot be part of the solution. Producing hams instead of bacon with such meat is an option.

The bottom line is that solutions exist and an effective strategy is possible but will require focus and cooperation.

INCLUSION OF OTHER PRODUCTS

I have for some time considered the inclusion of a  blood-based binding system with TG which “can be used for binding comminuted and large pieces of meat (Boles & Shand, 1998, 1999). The binding mechanism of restructured meats is based on the blood clotting action between fibrinogen, thrombin, and TG. Cross-linking and gelation between fibrin itself and between meat collagen and the fibrin are induced by TG (Sheard, 2002).”  (Sun, 2009).

Other products to consider for inclusion are crude myosin, extract, surimi (Chen, Huffman, & Egbert, 1992), egg white powder, raw egg white, egg powder, bovine, porcine, lamb, broiler plasma powders, broiler breast meat powder, gelatine (Lu & Chen, 1999), dried apples, corn crumbs, mushrooms (Marriott, Graham, Schaffer, & Boling, 1986c), rice bran oil and fiber (Kim, Godber, & Prinaywiwatkul, 2000), and walnut (Jime´nez Colmenero et al., 2003; Serrano et al., 2006).

CONCLUSION

TG represents one of the most exciting developments in meat processing from the perspective of the large-throughput meat factories.  The optimal utilization of the technology is still in its infancy, despite the many decades that passed since it was first made available from the shores of Japan.

References:

Aguilar, M. R., and Román, J. S..  2014.  Smart Polymers and their Applications.  Woodhead Publishing.

http://animalbiosciences.uoguelph.ca/~swatland/ch4_1.htm

Bhaskar Reddy, G. V., Mandal, P.K., Sen, A.R. and Reddy, K.S..  2015. Developments in Science, Technology, Quality and Constraints of Restructured Meat Products-A Review. International Journal of Meat Science, 5: 14-48.  DOI: 10.3923/ijmeat.2015.14.48 URL: https://scialert.net/abstract/?doi=ijmeat.2015.14.48

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C4d/C4d_adipose.html

Ceresinoa, E. B.,  de Meloa, R. R.,  Kuktaiteb, R.,  Hedenqvistc, M. S., Zucchid, T. D.,  Johanssonb, E.,  Satoa, H. H..  2018.  Transglutaminase from newly isolated Streptomyces sp. CBMAI 1617:  Production optimization, characterization and evaluation in wheat protein and dough systems.  Food Chemistry 241 (2018) 403 – 410. Science Direct, Food Chemistry.

Chattopadhyay S, Raines RT.  2014. Collagen-Based Biomaterials for Wound Healing. Biopolymers. 2014;101(8):821-833. doi:10.1002/bip.22486.
Cooper GM.  2000.  The Cell: A Molecular Approach. 2nd edition.  Sunderland (MA): Sinauer Associates.

https://cooking.stackexchange.com/questions/15077/how-does-gelatin-interact-with-grease-fat

https://daa.asn.au/smart-eating-for-you/smart-eating-fast-facts/nourishing-nutrients/the-ins-and-outs-of-unsaturated-fats/

De NG, J. C.,  Toledo, R. T., Lillard, D. A..  1981.  Protein‐Protein Interaction and Fat and Water Binding in Comminuted Flesh Products.  First published: July 1981.

Dikeman, M., and Devine, C..  2014.  Encyclopedia of Meat Science.  Second edition.  Elsevier, Academic Press.

Hamarneh, Sami Khalaf; Sonnedecker, Glenn Allen (1963). A Pharmaceutical View of Abulcasis Al-Zahrāwī in Moorish Spain: With Special Reference to the “Adhān,”. Brill Archive. p. 15.

Kajitani, S., Mika Fukuoka, M., and Sakai, N..  2011.  Kinetics of Thermal Denaturation of Protein in Cured Pork Meat.  Japan Journal of Food Engineering, Vol. 12, No. 1, pp. 19 – 26, Mar. 2011Lodish H, Berk A, Zipursky SL, et al.  2000.  Molecular Cell Biology. 4th edition.  New York: W. H. Freeman; 2000.

Kerry, J., J. Kerry and D. Ledward, 2002. Meat Processing: Improving Quality. CRC Press, Boca Raton, USA., ISBN-13: 9781855735835, Pages: 464.

Krause, R.J., H.W. Ockerman, B. Krol, P.C. Moerman and R.F. Plimpton, 1978. Influence of tumbling, tumbling time, trim and sodium tripolyphosphate on quality and yield of cured hams. J. Food Sci., 43: 853-855.

Lehmann, K. B., Sitzungsber. physik.-med. Ges. WURZBURG, 1897, 35; Arch. Hyg., 1907, Ixiii, 134.

Marriott, N. G., Schilling, M. W.,  reviewed by Sebranek, J..  2006.  Utilization of Pale, Soft, and Exudative Pork.  http://porkgateway.org/resource/utilization-of-pale-soft-and-exudative-pork/

http://www.meatscience.org/TheMeatWeEat/topics/fresh-meat/article/2015/07/31/does-muscle-tissue-contain-different-types-of-protein

Meri, Josef W. (2005). Medieval Islamic Civilization: An Encyclopedia. Routledge. p. 783.”The greatest surgeon of the medieval ages was Abu’l-Qasim az Zahrawi (d. 1010), a most important representative of the Andalusian school.”

Mitchell, H. H.,  Zimmerman, R. L., and Hamilton, T. S..  1926.  The Determination of the amount of connective tissue in Meat.  (From the Division of Animal Nutrition, Department of Animal Husbandry, University of Illinois, Urbana.) (Received for publication, October 16, 1926)

Motzer, E. A., Carpenter, J. A., Reynolds, A. E., Lyon, C. E..  2006.  Quality of Restructured Hams Manufactured with PSE Pork as Affected by Water Binders.  First published: 20 July 2006. https://doi.org/10.1111/j.1365-2621.1998.tb15843.x

Nutton, Dr Vivia (2005-07-30). Ancient Medicine. Taylor & Francis US. ISBN 9780415368483. Retrieved 21 November 2012.

Patterson, John, The Salt Cured Pig:  http://thesaltcuredpig.com/Porkopedia/index.php?title=Myosin

Pearson, T. A., Gillett, T. A..  1999. Processed Meats.  3rd edition.  A Chapman & Hall Food Science Book.  Aspen Publishers.

Pegg, R. B. and Shahidi, F..  2000.  Nitrite Curing of Meat.  Food & Nutrition Press, Inc.

RANDALL, C. J. and BRATZLER, L. J. (1970), CHANGES IN VARIOUS PROTEIN PROPERTIES OF PORK MUSCLE DURING THE SMOKING PROCESS. Journal of Food Science, 35: 248–249. doi:10.1111/j.1365-2621.1970.tb12149.

Rooney, Anne (2009). The Story of Medicine. Arcturus Publishing. ISBN 9781848580398.

Robe, G. H., and Xiong, Y. L. (1992). Phosphates and muscle fiber type influence thermal transitions in porcine salt-soluble protein aggregation. Journal of Food Science, 57, 1304 – 1304.

Sun, X. D..  2009.  Utilization of restructuring technology in the production of meat products: a review, CyTA – Journal of Food, 7:2, 153-162, DOI:  10.1080/19476330903010193 To link to this article: https://doi.org/10.1080/19476330903010193

Toldra, F..  2002.  Dry-Cured Meat Products.  Food & Nutrition Press, Inc.

Toldra, F.. (Editor) 2010.  Handbook of Meat Processing.  Blackwell Publishing.

Wray, David B., ed. (2006). “Sutures and Suture Materials: Absorbable Sutures: Surgical Gut”. Remington: The Science and Practice of Pharmacy (21st ed.). Baltimore, Maryland; Philadelphia, Pennsylvania: Lippincott Williams & Wilkins. p. 1974. ISBN 0-7817-4673-6.