handbook of muscle foods analysis · electron microscope (sem) (figure 19.5). in both methods, the...

335

Chapter 19

Microstructure of Muscle Foods

I. Pérez-Munuera, V. Larrea, A. Quiles, and M.A. Lluch

Contents19.1 Introduction on Food Microstructure .............................................................................33519.2 Main Microscopy Strategies for Studying the Structure of Muscle Foods .......................33719.3 Th e Muscle Structure of Meat ........................................................................................ 34619.4 Infl uence of Postmortem Processing on Meat Microstructure ........................................ 34819.5 Infl uence of Processing on Meat Microstructure .............................................................35019.6 Microstructure of Model Systems Based in Meat Components .......................................351References ................................................................................................................................351

19.1 Introduction on Food MicrostructureTh e chemical components of a food are organized into a characteristic microscopic pattern that-constitutes its microstructure. Th e food’s microstructure is currently being presented as a new challenge in multidisciplinary studies of foods and a way of contributing to our understanding of scientifi c and technological progress.

In foods from animal and plant tissues, macromolecules such as proteins, lipids, and polysaccha-rides and their interactions with other chemical components, including water, perform important functional roles. Th ese chemical components constitute the fundamental structural components from which the characteristic microstructures of each food are built. For instance, within muscle foods such as Spanish “serrano” dry-cured ham, the organization of the muscle fi bers, with their

CRC_45296_Ch019.indd 335CRC_45296_Ch019.indd 335 7/7/2008 12:06:03 PM7/7/2008 12:06:03 PM

© 2009 by Taylor & Francis Group, LLC

336 � Handbook of Muscle Foods Analysis

myofi brils and free fat infi ltration among the fi bers, constitutes the microstructural basis for the characteristic texture and sensory quality that consumers appreciate.

Th e diff erent stages of the processing and storage of foods cause modifi cations that are mani-fested by macroscopic changes that impart the characteristic texture, color, fl avor, etc., to the fi nished food. Th e microstructure is directly aff ected by the chemical, biochemical, and physical changes undergone by the foods during processing, and the fi nal properties of the elaborated foods, desirable or not, depend on their microstructure. For example, there are foods where a total microstructural change is desired and all the original plant or animal tissue organization disappears (products such as patés or vegetable purees). In other cases, a predefi ned microstruc-ture is imitated to obtain processed foods such as surimi, artifi cially reproducing a particular tissue organization. However, the original submicroscopic structure in processed foods, where the appearance of a “fresh food” has to be retained, needs to be preserved as much as possible during the various treatments (fresh-cut fruits and vegetables, refrigerated fresh meat packed in inert atmospheres, marinated fi sh, and so on). It is also possible to seek an optimum microstruc-ture, which is defi ned both by the arrangement of the chemical components and by the size and distribution of the gaps or air bubbles, in bubble foods such as certain emulsions and foams or in bakery products, for example. Additionally, and always depending on the temperature, the physical state of the chemical compounds also aff ects the fi nal structure. For instance, the solidifi cation of the ingredients and the even distribution of the air bubbles in ice creams are key aspects of their microstructure. Th e presence of microscopic foreign bodies can occasionally lead to the detection of unsuitable practices or even fraud.

However, the microstructure of the food plays an important role in many processes where transport takes place within the food: (i) saline agents and other preservatives are carried through the intercellular spaces and through the cell walls and membranes when pickling vegetables, cur-ing hams, and salting and smoking fi sh, (ii) the heat transmission in thermal processes such as sterilization, blanching, freezing, etc., (iii) water/solutes move intra- and intercellularly during dehydration by hot air or by osmosis, and (iv) matter is transferred intra- and intercellularly in solid/liquid extraction of oils and fats from food tissues, etc. Th e establishment of mathematical transport models, which provides suffi ciently accurate predictions, requires a real understanding of the mechanisms that govern them. Th ese mechanisms are infl uenced by the chemical and biochemi-cal components and their structural distribution within the food. Consequently, a better under-standing of the microstructure of foods should, in turn, allow for better modeling of the processes.

Understanding the organization of chemical components is key to describing, predicting, or controlling the changes undergone by foodstuff s during processing. Conceptually, this adds a new viewpoint to the classic chemical or physical aspect of foods; microstructure is thus seen as a fundamental aspect of the combined, multidisciplinary study of food.

Nowadays, diff erent microscopy techniques, particularly electron microscopy (scanning or SEM, transmission or TEM), off er powerful tools for clarifying the microstructure of foods and establishing its interrelationships with their physical, chemical, and biochemical behaviors. Coupled with image analysis, it also allows the quantifi cation of the morphological changes that take place during food processing. Additionally, current X-ray detection systems (EDX, WDX) make it possible to microanalyze foods at submicroscopic levels. Above all, broad horizons have opened up in the fi eld of food microstructure and its multidisciplinary study. It could be interest-ing to take research carried out in this fi eld as a complement for solving problems and developing new products in the food industry. Furthermore, this could also be a very useful approach defi ning the properties of functional foods and the importance of their components for the health of the consumers.



Microstructure of Muscle Foods � 337

As the aim of this chapter is to give a brief overview of these issues, certain interesting aspects concerning the microstructure of diff erent foods of animal origin with, for example, native, modi-fi ed or altered, destroyed, restructured, or imitated tissue structures will be discussed.

19.2 Main Microscopy Strategies for Studying the Structure of Muscle Foods

Th e invention of the light microscope (LM) at the end of the sixteenth century provided food scientists with the fi rst tool that allowed them to observe samples magnifi ed up to 20 or 30 times their original size. LM uses visible light as its illumination source and was used to study food microstructure despite its low resolution, which is limited due to the wavelength of the light (Figure 19.1a). Nowadays, modern LMs have a resolution (200–500 nm) that is about 103 times that of the human eye and they produce an image that is magnified 4–1500 times (4–1500×) (Fig ure 19.2). Th e LM is a versatile and useful tool that works in diff erent applications such as bright fi eld, which is the most common application for muscle foods; phase contrast or diff erential interference contrast (Nomarski), where the contrast of unstained tissues is enhanced; polarizing microscopy, where a plane-polarized light is used to illuminate the sample (useful with birefringent structures); or fl uorescence microscopy, which is the basis of the modern technique of confocal laser scanning microscopy (CLSM). Th ere are diff erent ways of preparing samples for LM observation (Figure 19.3); the only essential requirement is that the sample be translucent, in other words, suffi ciently thin to allow light to pass through it when mounted in a suitable medium. Conse-quently, depending on the physical characteristics of the sample, diff erent methods are available [1]. Powdered foods (normally under 200 µm) are fi ne enough to be observed directly, mounted in an inert oil or an appropriate dye solution. Fluid foods such as emulsions and sauces are spread

(a)

(b)

�

�

Figure 19.1 (a) Visible light, high wavelength, only interferes with big objects. (b) Accelerated electrons, short wavelength, only interfere with very small objects.



http://www.crcnetbase.com/action/showImage?doi=10.1201/9781420045307.ch19&iName=master.img-000.jpg&w=216&h=91

http://www.crcnetbase.com/action/showImage?doi=10.1201/9781420045307.ch19&iName=master.img-001.jpg&w=217&h=94


on the slide as translucent fi lms. Lastly, solid foods are prepared in thin sections. Th e sections can be obtained after embedding the food in paraffi n or resins, but the simplest and quickest way is to use a cryotome, placed in a freezer, to obtain cryosections of samples after having frozen their constituent water along with their other chemical constituents. In this method, the solid water acts as the embedding medium. Th e use of a hot stage coupled to the microscope helps to reproduce food processes that include a heating step.

In recent years, an important advance in the fi eld of food structure has been the introduction of CLSM. In this technique, as the muscle food materials of structural interest are not auto- fl uorescent, the sample should be stained with fl uorescent dyes before examination under the microscope. Optical sectioning is one of the major advantages of this technique, since physical slicing is not necessary. Th is leads to the possibility of generating three-dimensional (3D) images of biological cells and tissues [2]. In CLSM, the illumination of the sample is restricted to a

Illumination source(light source)

Condenser lens

Specimen

Objective lens

Projection lens

Image plane

Image

Light optical system

Figure 19.2 Diagram of a light microscope (LM).




Food

Specimen portions(slice, powder, pellet, …)

To prepare for slicing

Cold knife

Embedding withparaffin or resin

Freezing(CO2, liquid N2)

Semithin sections(0.1−2 µm)

Slice

Cold stubCryomicrotome

CO2

Microtome

Knife

Mounting inglass slides

Staining specimen

LM observation

1% toluidine blue,1% lugol, 1% red oil,…

14.5 µm

Figure 19.3 Preparation of samples for LM observation.




To computer

Photomultiplier

Detector pinhole

Dichroic mirror

Objective lens

Specimen

Condenser lens

Detector

Focus plane

Laser

Figure 19.4 Diagram of a confocal laser scanning microscope (CLSM).

single point (or an array of points), which is scanned to produce a complete image (Figure 19.4). Another major advantage of CLSM is the exclusion of out-of-focus blur, since the fl uorescence emissions from the illuminated regions of the sample above and below the focal plane are not allowed to reach the photomultiplier and form an image.

Th e development of electron microscopy (EM) has allowed food structure to be studied in greater detail. Th e electron microscope takes advantage of the much shorter wavelength of the accelerated electron compared to light (Figure 19.1b). Th is makes a 1000-fold increase in magnifi -cation possible, together with a parallel increase in resolution. Th ere are two microscopes that use electron beams as source of illumination: transmission electron microscope (TEM) and scanning electron microscope (SEM) (Figure 19.5). In both methods, the samples fi rst need to be prepared. Both the working conditions (the electron microscope works under high vacuum) and the nature of the sample itself (in the case of muscle foods, a biological tissue) make long and occasionally tedious sample preparation protocols essential.

Th e TEM projects accelerated electrons through a very thin slice of specimen [3]; the trans-mitted electrons produce a 2D image on a phosphorescent screen (Figure 19.6). TEM gives an image with better resolutions (0.2–1 nm) and higher magnifi cations (200–300,000×) than LM. Th e steps in the preparation of the sample (Figure 19.7) are primary fi xation, washing, secondary fi xation, dehydration, infi ltration with resin, embedding, cutting ultrathin sections (100–500 Å) in an ultramicrotome, and staining with heavy metals. Th e resin permeates the sample, replacing all the water within the structural components and making the sample fi rm enough for sections




TEM SEM

Electron beam

Electron beam

Specimen

Specimen

Viewing screen

Signaldetector

Figure 19.5 Two basic electron microscopes. TEM: image is formed from the electrons transmitted by the electron beam. SEM: image is formed from the signal (secondary electrons, etc.) emitted by the sample scanned by the electron beam.

High voltage

Illumination source (electron beam filament)

Condenser lens

Specimen

Objective lens

Projection lens

Projection lens

Image

Fluorescent screen

Figure 19.6 Diagram of a transmission electron microscope (TEM).




Food

Fixation

Specimen portions(slice, powder, pellet,…)

Dehydration

Infiltration andembedding in resin

Ultrathin sectioning(5−100 nm)

Section collectionUltrathin section staining

TEM observation

4% lead citrate2% uranyl acetate

KnifeGrid

Specimenblock face

Tweezers

Specimen block Trimmed blockUltramicrotome

Glass or diamond knife

Cured resinEpoxi resin, AralditeSpurr's, LR white

Ethanol (30%, 50%, 70%, 90%, 100%) Transition fluid

2.5% glutaraldehyde 2% Os O4

Figure 19.7 Preparation of samples for TEM observation.




to be cut. Th is technique is very useful for observing the characteristic banding of animal muscle fi bers and the ultrastructure of the cells, diff erentiating the cell organelles.

Th e SEM uses a spot of electrons that scans the surface of the specimen to generate secondary electrons, which are the primary signal emitted by the specimen and form a 3D image (Figure 19.8). SEM gives resolutions (3–4 nm) and magnifi cations (20–100,000×) that are intermediate between those of LM and TEM. Th e SEM method observes the surface of the sample, so there is no need to section it. Surface and internal structures can be observed, depending on the preparation techniques used, and these are much easier than the TEM. In essence, there are two ways of preparing samples for SEM: chemical fi xing and physical fi xing (Figure 19.9). In the former, the sample preparation steps are chemical fi xation, dehydration in a series of ethanol dilutions of increasing concentra-tion, change to a transition fl uid (acetone), critical point drying, mounting, and coating with a conducting metal or carbon. When physical fi xation is used, the sample is frozen in liquid nitrogen and then freeze-dried before being mounted, coated, and observed. In recent years, considerable progress has been made in the fi eld of SEM through vitrifi cation techniques. In cryo-SEM, the sample is frozen in slush nitrogen and quickly transferred to a cold stage fi t on a microscope where the frozen sample is coated and observed (Figure 19.10); in this way, the sample can be observed with all its constituent water.

High voltage

Illumination source(electron beam filament)

Condenser lens

Condenser lens

Deflection coils

Signaldetector

PhotomultiplierVideo amplifier

Specimen

Figure 19.8 Diagram of a scanning electron microscope (SEM).




Food

Fixation

Specimen portions(slice, powder, pellet,…)

Dehydration

(To transformer)(To pumps)

CO2

Physical fixation Chemical fixation

Quick freezingin liquid N2

2.5% glutaraldehyde 2% Os O4

Sublimated H2O

(To vacuum)

Freeze dryerCritical point dryer

P T

Sputter metal coater (or evaporation coater)

SEM observation

Coating(Au, Pd, for SEM imaging)

(C, for X-ray)

~200 µm

Figure 19.9 Preparation of samples for SEM observation.




Figure 19.10 Preparation of samples for cryo-SEM observation.

Food

Specimen portions

Freezing

Transfer tocryo-SEM

Specimen fracturing (into cryo-SEM)

Etching(into cryo-SEM)

Coating (Au, C, …) (into cryo-SEM)

Cryo-SEM observation

(−130°C, vacuum)

Au deposition

Specimen "heating"(−90°C, vacuum)

Sublimated H2OSpecimen fracturing(−180°C, vacuum)

Knife

Specimen transfer

Quick freezing in slush N2 (T <−210°C)

~200 µm

Besides the secondary electrons, other emanations or signals such as X-rays and backscattered electrons may be generated as a result of the electron beam striking the specimen [3]; the diff erent signals can be captured by the appropriate detector in each case. In this way, ions or molecules can be identifi ed and quantifi ed in situ using specifi c detectors coupled to the electron microscope




(X-ray microanalysis) (Figure 19.11); this can be useful, for example, in meat products where the curing process involves the use of salts, such as Spanish “serrano” ham.

Finally, image analysis relies heavily on computer technology to obtain quantitative results from microscopy observation [4], for example, shortening or lengthening of muscle fi bers during meat processing.

19.3 The Muscle Structure of MeatTh e muscle structure of meat is similar in all species. Although meat includes a number of diff er-ent tissues, the majority is skeletal muscle tissue. Th e muscle mass is elongated and covered by a connective tissue termed the epimysium which binds both individual fi ber bundles and groups of muscle bundles together [5]. It tapers into a tendon that connects the muscle to the skeletal struc-ture. Th e perimysium forms partitions within the muscle at irregular intervals to form both pri-mary and secondary muscle bundles. Within the perimysium, the sarcolemma or cell membrane retains the sarcoplasmic fl uids, which bathe each muscle fi ber. Th e muscle fi ber is surrounded by a connective tissue called the endomysium, and inside the cells there are numerous myofi brils (Figure 19.12).

Th e contractile unit of the myofi bril is known as sarcomere. Th e dark band is called the A-band, the light band is called the I-band, and the dark line bisecting the light band is called the Z-disk. Th e sarcomere is the distance from one Z-disk to the next (1.5–2.5 µm in length, depending on the state of contraction) and is made up of two sets of interdigitating fi laments: thin and thick. Th e thin fi laments are predominantly composed of actin molecules, wrapped around one another, and of tropomyosin and troponin, connected to the Z-disk; the thick fi laments are composed of densely packed myosin proteins, running from the center of the sarcomere toward the Z-disk (Figure 19.12). Th e myofi brils are linked to the sarcolemma by fi lamentous structures called costameres; the protein constituents of the costameres (desmin, actin, vinculin, talin, etc.) extend into the muscle cell where they encircle the myofi brils at the Z-disk and run from myofi bril to myofi bril and from myofi bril to sarcolemma [6].

Secondary electrons

Backscattered electrons

X-rays

Incident electron beam

Heat

Figure 19.11 Different signals emitted by the sample when scanned by the electron beam.




Epimysium

Perimysium

Endomysium

Muscle fiber(longitudinal section)

Muscle fiber (transverse section)

Myofilaments

Myofibril

Myofilaments

Myofibril

Sarcolemma

Sarcolemma

Costameres(desmin, γ-actintalin, vinculin, etc.)

I band

One sarcomere

A band

H zone

M-Line

Z-Disk

Thin filament (actin)

Thick filament(miosin) (titin)

Tendon

(a)

(b)

(c)

Figure 19.12 Schematic representation of the skeletal muscle. (a) A transverse section of the muscle bundles and the connective tissues: epimysium, perimysium, and endomysium. (b) Longitudinal muscle fi ber composed of myofi brils, which are composed of groups of myofi laments and surrounded by the sarcolemma. (c) Muscle proteins organized into ultrastructural features or sarcomeres. Costameres are protein fi laments anchored in the Z-disk and run from myofi bril to myofi bril and from myofi bril to sarcolemma. (From Lluch et al., Chemical and Functional Properties of Food Proteins, Technomic, Lancaster, PA, 2001. With permission.)




19.4 Infl uence of Postmortem Processing on Meat Microstructure

Diff erent microscopy techniques have been used to characterize meats and to analyze the changes in muscle tissue that take place under diff erent postmortem storage or cooking conditions. Some authors [7,8] have observed the microstructure of rabbit semimembranosus muscles by LM. Th ey found that the muscle tissue of the dead animal presented a type of structure in which the myo-fi brils were perfectly packed and the intercellular connections of the connective tissue remained unchanged; as the postmortem progressed, the structure of the muscle fi bers and endomysial connective tissue gradually broke down. Transverse sections of rabbit semimembranosus muscle showed the typical muscle tissue structure (Figure 19.13a); at 24 h postmortem, gaps caused by the destruction of the perimysium were observed in the muscle bundles in some zones and the fi bers inside each cell bundle appeared fairly separate due to degradation of the endomysial connective tissue (Figure 19.13b).

SEM was employed by Palka [9] to study the infl uence of postmortem aging of bovine semi-tendinosus muscle. Th e structure of the intramuscular connective tissue and myofi brillar structure of the meat after fi ve days of aging was regular. In 12-day-old samples, the fi brous and myofi brillar structures were less distinct, damage appeared in the endomysium tubes, and the fi bers of the perimysium were swollen.

CLSM was used by Straadt et al. [10] to study aging-induced changes in microstructure and water distribution in fresh pork. At day 1 (24 h postmortem) a few muscle fi bers appeared to be swollen.

Larrea et al. [11,12] have used several techniques to observe muscle in pork meat. No structural differences were observed between the biceps femoris and semimembranosus muscle tissues. A cross section of the semimembranosus muscle from a sample of pork meat observed by SEM shows the perimysial connective tissue that separates the bundles of fi bers (Figure 19.14a). Th e cells are surrounded by endomysial connective tissue, a reticular structure primarily composed of collagen, which keeps the muscle fi bers fi rmly attached to one another. Th is technique provides a clearer picture of the myofi brils inside the cells, where they are strongly attached to one another and to the sarcolemma (Figure 19.14b).

e

p2.76 µm 2.64 µm

(b)(a)

Figure 19.13 Transverse sections of rabbit meat at 1 h postmortem (a) and 24 h postmor-tem (b) observed by light microscopy (LM); e: endomisyal conjuctive tissue; p: perimysial conjuctive tissue. (From Sotelo, I., Pérez-Munuera, I., Quiles, A., Hernando, I., Larrea, V., and Lluch, M.A., Meat Sci., 66, 823, 2004. With permission.)




(b)

s

e

m

∼20 µm

(d)

Zc

H

M

A

I

1 µm

(c)mt

sr

2 µm

(a)

p

∼200 µm

Figure 19.14 Cross section of semimembranosus muscle of raw ham observed by SEM (a: 250× and b: 1500×) and longitudinal section of biceps femoris muscle of raw ham observed by TEM (c: 10,000× and d: 25,000×). A: A band; c: costameres; e: endomysial connective tissue; H: H-zone; I: I band; M: M-line; m: myofi brils; mt: mitochondria; p: per-imysial connective tissue; S: sarcolemma; sr: sarcomere; Z: Z-disk. (From Larrea, V., Pérez-Munuera, I., Hernando, I., Quiles, A., Llorca, E., and Lluch, M.A., Meat Sci., 76, 574, 2007. With permission.)

When ultra-thin sections of pork muscle tissue are studied by TEM, it is possible to observe ultrastructural details that pass unnoticed with other methods. Figure 19.14c shows the inside of a muscle fi ber with perfectly bundled myofi brils. In this fi gure, several mitochondria can be observed between the myofi brils. Figure 19.14d shows a more detailed view of a number of myo-fi brils; it is even possible to distinguish their component sarcomere fi laments.

Th e microstructure of broiler chicken muscles was studied by Wattanachant et al. [13] using SEM. Th e thickness of the perimysium directly contributes to the texture of raw chicken muscles, whereas the cross-linked collagen content does not.

Th e amount of fat in diff erent meats and muscles depends on a wide range of factors. Fat is located in the adipocytes, in the adipose tissue. Figures 19.15a and 19.15b show the intramuscular fat of pork meat observed by SEM and cryo-SEM [11]. As observed by SEM, it is made up of spheri-cal adipocytes closely arranged and surrounded by a membrane, with perimysial connective tissue fi bers among them.

Nishimura et al. [14] used SEM to investigate changes in the structures and mechanical prop-erties of intramuscular connective tissue during the fattening of steers. Th ey observed that the




development of adipose tissue in longissimus muscle appears to disorganize the structure of the intramuscular connective tissue and contributes to tenderization of highly marbled beef during the late fattening period.

19.5 Infl uence of Processing on Meat MicrostructureTh e eff ect of cooking on diff erent types of meat has been studied by several authors [9]. Roasting to an internal temperature of 50°C slightly aff ected the structure of bovine meat. During roast-ing to an internal temperature of 60–90°C, signifi cant changes occurred both in the myofi brils and in the intramuscular connective tissue. Th e degree of postmortem aging of meat had a sig-nifi cant eff ect on the thermal stability of tissue structures. Th e changes in myofi bril structure during roasting were considerably smaller in meat aged for 5 days than in that aged for 12 days postmortem.

Using SEM, Wattanachant et al. [13] have studied the eff ect on broiler muscle fi bers after cooking (80°C/10 min). Th e broiler muscle fi bers shrank more in a parallel than in a transverse direction to the fi ber axis and expanded transversally after cooking, resulting in increasing muscle tenderness.

Sorheim et al. [15] have studied the eff ects of carbon dioxide on the microstructure of cooked beef by LM. Beef meat, previously stored in an environment containing 20–100% CO2, had higher cooking losses compared to meat stored in 100% N2 and under vacuum. Decreases in the pH of raw meat and the formation of small pores and microstructural changes upon heating due to CO2 exposure were likely to cause the increased cooking losses. During cooking, structural changes in the meat protein matrix showed an increase in water loss due to pores and gaps in the matrix created by heat denaturation of the myofi brillar proteins and collagen.

Ueno et al. [16] have studied the eff ect of high-pressure treatments on intramuscular con-nective tissue from beef using SEM; it seems that high pressure may have a diff erent eff ect from aging on the intramuscular connective tissue membrane structure. Structural changes in the endomysium and perimysium occurred and disruption of the honeycomb-like structure of the endomysium was observed.

(b)(a) ∼100 µm∼50 µm

Figure 19.15 Transversal section of intramuscular fat in biceps femoris of raw ham observed by cryo-SEM (a) and SEM (b) a: adipocytes; ct: connective tissue; m: muscular tissue. (From Larrea, V., Pérez-Munuera, I., Hernando, I., Quiles, A., and Lluch, M.A., Food Chem., 101, 1327, 2007. With permission.)




19.6 Microstructure of Model Systems Based in Meat Components

In recent years, a huge number of works have focused on the eff ects of using diff erent ingredients in meat product processing, employing model systems. Th ese lines of research help to elucidate the interactions between the ingredients and the main meat components.

Iwasaki et al. [17] have studied the eff ect of hydrostatic pressure pretreatment on thermal gelation of chicken myofi brils using SEM and TEM. Th e structure of the myofi brils observed by SEM was disrupted at 200 MPa and the myofi laments were dispersed. Th e myofi bril debris was observed at 300 MPa and the aggregated structures were observed in the debris periodi-cally. Th e dispersed myofi laments became short at 300 MPa. Th e structures and characteristics of pressure/heat-induced gels of chicken myofi brils were investigated by TEM. Th e M-line and the Z-line in the chicken myofi bril in the 0.2 M NaCl treatment were seen to be disrupted, and both the thin and the thick fi laments were dissociated by the pressure treatment. Th e microstructure of pressure/heat-induced chicken myofi brillar gel was composed of a 3D matrix of fi ne strands.

Chen et al. [18] investigated the microstructure of salt-soluble meat protein (SSMP) and fl ax-seed gum (FG) mixtures by using SEM. Th e addition of FG changes the microstructure of SSMP gels. SEM observations showed that an interaction between FG and SSMP might occur. Th e results of adding a destabilizer to SSMP gels indicated that electrostatic forces seemed to be the primary force involved in the formation and stability of a protein-polysaccharide gel. Th e structure of SSMP gels showed a granular aggregated structure of large open spaces within the matrix, which seemed to show less linkage and be somewhat discontinuous between protein strands. Th e struc-ture of SSMP–FG gels showed a well-structured matrix with a highly interconnected network of strands that may cause more resistance to applied stress and impart great water-holding capacity. Th ese microstructural changes helped to explain functionality diff erences among the gels. A fi ne, uniform structure with numerous small pores would probably result in a higher absorption capac-ity and better retention of fat and water compared to a coarse structure with large pores.

References 1. Flint, O., in Food Microscopy: A Manual of Practical Methods, Using Optical Microscopy, Acribia S.A.,

Ed., Bio Scientifi c Publishers Limited, Zaragoza, 1994, chap. 4. 2. Sheppard, C.J.R. and Shotton, D.M., Confocal Laser Scanning Microscopy, Bio Scientifi c Publishers

Limited, Springer-Verlag, New York, 1997, chap. 1. 3. Bozzola, J.J. and Russell, L.D., Electron Microscopy, Jones and Barlett, Boston, MA, 1992, chap. 1. 4. Aguilera, J.M. and Stanley, D.W., Microstructural Principles of Food Processing and Engineering, 2nd

ed., Aspen Publishers, Inc., Gaithersburg, MD, 1999, chap. 1. 5. Hulting, H.O., Characteristics of muscle tissue, in Principles of Food Science I. Food Chemistry,

Fennema, O.R., Eds., Marcel Dekker, New York, 1976. 6. Lluch, M.A., Pérez-Munuera, I., and Hernando, I., Proteins in food structures, in Chemical and

Functional Properties of Food Proteins, Sikorski Z.E., Eds., Technomic, Lancaster, PA, 2001, chap. 2. 7. Pérez-Munuera, I., Sotelo, I., Hernando, I., and Lluch, M.A., Degradación postmorten en músculo

de conejo: Evolución de la microestructura, Alimentaria, 99, 19, 1999. 8. Sotelo, I., Pérez-Munuera, I., Quiles, A., Hernando, I., Larrea, V., and Lluch, M.A., Microstructural

changes in rabbit meat wrapped with Pteridium aquilinum fern during postmortem storage, Meat Sci., 66, 823, 2004.




9. Palka, K., Th e infl uence of post-mortem ageing and roasting on the microstructure, texture and collagen solubility of bovine semitendinosus muscle, Meat Sci., 64, 191, 2003.

10. Straadt, I.D., Rasmussen, M., Andersen, H.J., and Bertram, H.C., Aging-induced changes in micro-structure and water distribution in fresh and cooked pork in relation to water-holding capacity and cooking loss—a combined confocal laser scanning micrsocopy (CLSM) and low-fi eld nuclear magnetic resonance relaxation study, Meat Sci., 75, 687, 2007.

11. Larrea, V., Pérez-Munuera, I., Hernando, I., Quiles, A., and Lluch, M.A., Chemical and structural changes in lipids during the ripening of Teruel dry-cured ham, Food Chem., 101, 1327, 2007.

12. Larrea, V., Pérez-Munuera, I., Hernando, I., Quiles, A., Llorca, E., and Lluch, M.A., Microstructural changes in Teruel dry-cured ham during processing, Meat Sci., 76, 574, 2007.

13. Wattanachant, S., Benjakul, S., and Ledwardt, D.A., Microstructure and thermal characteristics of Tai Indigenous and broiler chicken muscles, Poultry Sci., 84, 328, 2005.

14. Nishimura, T., Hattori, A., and Takahashi, K., Structural changes in intramuscular connective tissue during the fattening of Japanese black cattle: Eff ect of marbling on beef tenderization, J. Anim. Sci., 77, 93, 1999.

15. Sorheim, O., Ofstad, R., and Lea, P., Eff ects of carbon dioxide on yield, texture and microstructure of cooked ground beef, Meat Sci., 67(2), 231, 2004.

16. Ueno, Y., Ikeuchi, Y., and Suzuki, A., Eff ects of high pressure treatments on intramuscular connective tissue, Meat Sci., 52, 143, 1999.

17. Iwasaki, T., Noshiroya, K., Saitoh, N., Okano, K., and Yamamoto, K., Studies of the eff ect of hydro-static pressure pretreatment on thermal gelation of chicken myofi brils and pork meat patty, Food Chem., 95, 474, 2006.

18. Chen, H.H., Xu, S.Y., and Wang, Z., Interaction between fl axseed gum and meat protein, J. Food Eng., 80, 1051, 2007.



handbook of muscle foods analysis · electron microscope (sem) (figure 19.5). in both methods, the...

Documents