Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
2005
Volume 8
Issue 3
Topic:
Food Science and Technology
ELECTRONIC
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
Dolata W. , Krzywdzińska-Bartkowiak M. , Wajdzik J. 2005. TECHNOLOGICAL EFFECT OF PLASTIFICATION ON CHANGES IN THE MACROSTRUCTURE OF MEAT, EJPAU 8(3), #39.
Available Online: http://www.ejpau.media.pl/volume8/issue3/art-39.html

TECHNOLOGICAL EFFECT OF PLASTIFICATION ON CHANGES IN THE MACROSTRUCTURE OF MEAT

Włodzimierz Dolata, Mirosława Krzywdzińska-Bartkowiak, Jerzy Wajdzik
Institute of Meat Technology, The August Cieszkowski Agricultural University of Poznan, Poland

 

ABSTRACT

The aim of this study was to assess the range and dynamics of changes in the muscle tissue structure under the influence of the injection and plastification processes, using the macroscopic image computer analysis technique. Ham muscles (m. biceps femoris) were examined fresh, after being injected with curing brine, in the middle of the adopted massaging time, i.e. after 3 h and 20 min (a total of 1200 rotations of the massage machine drum), and after the massaging process was completed, i.e. after 6 h and 40 min of massaging (a total of 2400 rotations of the massage machine drum). The process of plastification caused changes in the structure on the surface of ham muscles, which resulted in an additional binding of the added brine by the muscle protein and facilitated increased extraction of muscle protein outside the muscle. The changes on the surface of the muscles could be observed thanks to the applied computer analysis of macroscopic images.

Key words: computer image analysis, muscle tissue structure, plastification.

INTRODUCTION

Plastification is a technological process improving the quality characteristics of cured meat [23, 25, 31]. It is a procedure changing the springy-elastic properties of meat into plastic-viscous ones. The process of meat massaging plays an especially important role in the processing of raw material at the early stage of post mortem changes. The muscle tissue at this stage of post mortem changes exhibits lowered technological properties. It is tough, springy, has low water holding capacity with considerable thermal drip losses. As a result of plastification the tenderness, water binding capacity and yield of products obtained from plastified muscles [14] or deboned meat raw materials are improved [14, 25].

Massaging meat consists in the continuous or periodical action of varying stresses on the muscle tissue in a massage machine. The raw material is subjected to the action of bending, torsional, impact and expansion forces. Generally it may be stated that during massaging the muscle tissue is subjected to the action of overpressure and partial vacuum, which alter properties of meat as a result of changes taking place in the protein compound of meat, primarily the myofibrillar protein fraction [7, 30, 38].

The process of plastification, while accelerating the degradation of protein structures in the muscle tissue, provides the so-called mechanical tenderization on masceration [30]. Muscles subjected to massaging absorb curing brine introduced during injection faster. Moreover, they absorb water more effectively and faster diffusion is facilitated through the increased migration of curing brine components as a result of the disrupted cell structure [13] and the ruptured muscle fiber sarcolemma [4]. While loosening and disrupting meat structure, massaging results in an increased brine sorption and the release of protein to the intercellular space [24, 37, 43]. During the process of massaging brine in the outer layer of muscles contains increasing amounts of protein, becoming more and more viscous, forming the so-called adhesive capable of binding muscles during thermal processing. Thus, the effect of binding is obtained in moulded ham [4, 28]. The obtained brine drip (exudate) contains fragments of muscle fibers and myofibrils [32, 33]. Studies conducted by Mozdziak and Cassens [20] on cured beef muscles (m. semimembranosus) confirmed that the massaging procedure has an effect on the amount of protein extracted in the outer layer of muscles. Extraction of muscle protein is enhanced by the chemical action of curing brine components (primarily sodium chloride and phosphates), which raise the pH value and ionic strength of the environment [28, 29]. The consequences of this procedure are changes both in the structure and texture of meat, increasing along with the time of massaging [15, 22, 28, 29, 32]. The process of plastification should facilitate maximum protein swelling, cause dissociation or disrupt the actomyosin complex and facilitate brine access to intracellular myofibrillar protein [35]. It may be concluded from the literature data that muscles of slaughtered animals differ in their texture [27] and structure [42], as well as their plasticability [21, 26]. Thus, it may be assumed that each type of muscle requires different massaging parameters, the measure of which is most frequently massaging time [16]. The time of muscle plastification may be reduced, or the effectiveness of the whole procedure may be improved by combining massaging with tenderization. The mechanism of the tenderization process consists in subjecting muscles to compression or crushing with the simultaneous scarification of their surface. The aim of tenderization, apart from the loosening of the muscle structure, is to disrupt cells and release protein to the intracellular space, to expand significantly the muscle surface and their opening to the access of curing brine components. This accelerates the diffusion process of salt and curing components, and facilitates the formation of brine solutions of myofibrillar protein. In the course of massaging bigger amounts of extracted protein, the basic adhesive of muscles, are released from the meat surface expanded in such a way [35, 36].

The aim of this study was to assess the range and dynamics of changes in the muscle tissue structure under the influence of the injection and plastification processes, using the macroscopic image computer analysis technique.

MATERIALS AND METHODS

The experimental material consisted of ham muscles (m. biceps femoris) trimmed 48 h after slaughter. Meat temperature did not exceed 5°C and the pH value was 5.8 – 6.2. The concentration of hydrogen ions (pH) was determined using the microcomputer pH-meter CP-315M combined with the combination electrode type OSH-1201. The pH-meter was calibrated using reference buffers with pH = 4 and pH = 7, respectively.

Temperature was measured using a microcomputer CP-315M meter combined with a MT AM ½ temperature probe.

Muscles obtained during the trimming process were injected with curing brine containing sodium chloride, sodium nitrite, vitasol K-6 and water.

Brine was cooled to the temperature below 0°C using flake ice. Next it was injected into ham muscles using a low pressure (0.25 – 0.30 MPa) stitch pumping, with the use of an Inject Star Twin 424 multineedle injector, type New Twist. The application of pressure exceeding 0.4 MPa during injection could result in a destruction of muscle structure. Injection was performed in the diagonal system with the crossing method at the level of 60% of meat weight.

Injected muscles were subjected to the plastification process. This process was performed in a massage machine by Lutetia (France), type 4 with the drum capacity of 2000 kg, equipped with a helicoid blade. The massage machine drum was filled to 70% of its capacity. During the massaging process constant partial vacuum of 88 – 90 kPa and drum rotations at the level of 6 r.p.m. were applied, which made it possible to reach the total number of drum rotations of 2400, after 6 h and 40 min of continuous massaging. With the application of plastification in the continuous system extreme conditions were created for the increase in the temperature of the massaged material. The application of the machine by Lutetia made possible systematic control of the partial vacuum and temperature inside the drum during the massaging process. Such conditions facilitated the penetration of brine and water binding by the muscles [1].

The muscle tissue structure was examined using computer image analysis [6, 19]. Ham muscles (m. biceps femoris) were examined fresh, after being injected with curing brine, in the middle of the adopted massaging time, i.e. after 3 h and 20 min (a total of 1200 rotations of the massage machine drum), and after the massaging process was completed, i.e. after 6 hours and 40 minutes of massaging (a total of 2400 rotations of the massage machine drum). Thanks to the application of the converter (the camera) transmitting information on the image, pictures were taken in visible light.

The pictures were taken using a Hitachi 3 CCD HV C20 camera with the TV 12-mm lens with the aperture of 1 : 1.2, lighted with a Kaiser RB 5000DL lamp.

The Lucia 326 Versien 4.11 software package was applied for the computer image analysis.

RESULTS AND DISSCUSION

The quality of raw material for the production of cooked hams depends on three main factors: the concentration of hydrogen ions (pH), pre-slaughter handling of animals, storage temperature and the related thermal state of meat (cooled or frozen). During the process of meat freezing ice crystals are formed, which cause an increase in the ionic strength of the unfrozen solution and disrupt the sarcolemma. As a result of osmosis the water content in cells decreases resulting in protein denaturation and as a consequence – a lowered water binding capacity of meat.

The pH value of ham muscles (m. biceps femoris) used in this study fell within the 5.8 – 6.2 range (Tables 7 and 8). According to Tyszkiewicz [35], raw material for the production of ham subjected to thermal processing should have pH > 5.8, however not exceeding pH = 6.2. The concentration of hydrogen ions (pH) of the raw material determines its water binding capacity and thus – the production yield, binding and consistency of cooked ham, and brine absorption capacity, i.e. the diffusion of salt and curing agents. Such a selected material ensures a compromise between the water holding capacity, salt and curing agent absorption capacity, and shelf life. It also has an effect on the proper color of the product and its stability, understood as the conditions for the development of bacterial microflora, and the sensory quality of the product. At the same time, the selection of ham muscles in such a range of pH values made it possible to eliminate muscles with defects such as PSE and DFD changes. At the normal course of glycolysis after slaughter muscles acidify within 6 – 12 hours to the value pH = 5.4 ÷ 5.8. If acidification progresses too fast, the effect is a PSE muscle (pale, soft, exudative). Such ham muscles reach pH 45 min values below 5.8, whereas normal muscles have pH 45 min > 6.2. In DFD ham muscles delayed glycolysis results in high pH45 min of such muscles, reaching the value of approx. 6.5 [5], whereas normal muscles have pH45 min= 6.3. Such muscles, exhibiting DFD symptoms (dark, firm, dry), have compact consistency and a structure hindering effective absorption of salt and curing agents. In such muscles the nitrite reduction is limited and salt diffusion deteriorates [17, 18]. The effect of pH values of the material on the yield of hams was also investigated by Műller [22]. He found that at the concentration of hydrogen ions in the material amounting to 5.6 the production yield of hams was approx. 84%, whereas at the pH values of the material amounting to 6.6, the production yield was 102%.

As results from the data presented in Table 1, the mean pH value of muscles used in the investigations was similar to the mean pH value of the curing brine. Injection brine used in this study had the mean temperature of – 2.0°C (Table 2). Brine chilled in this way using ice flake made it possible to conduct the process of injection and plastification at optimum temperature conditions. Knipe et al. [12] showed that the temperature of massaging has an effect on the color of hams, their contrast, cohesiveness and the yield of the finished product. That the optimum temperature during the plastification of ham muscles is approx. 0°C. In the opinion of those authors such a temperature ensures the shortening of the plastification process by approx 40%, an increase in the yield of the finished product, improved sliceability, color fastness and an improvement of hygienic conditions during the whole production process [10].

Table 1. The pH values of raw ham muscles (m. biceps femoris) and injection curing brine

Investigated material

pH value

Ham muscles (m. biceps femoris)

6.0

Injection brine

6.0

From the results of the investigations presented in Table 2 it can be seen that the final temperature of plastified muscles did not exceed 5°C. Such a temperature limits to the minimum the development of microorganisms, which could result in a reduced shelf life of meat [10, 22]. At the temperature over 5°C proteolytically active psychrophilic microorganisms were observed along with cocci from the genus Staphylococcus, exhibiting high resistance to salinity [34]. Maintaining the temperature below 5°C inhibits the development of bacteria from the family Enterobacteriaceae [11].

Higher temperatures of the massaged raw material also result in a deterioration in the binding, shelf life, color and yield of cooked hams [10]. Studies by Brauer [3] showed that the application of temperatures below 5°C makes it possible to obtain a product with an appropriately high quality.

Table 2. Temperatures of ham muscles (m. biceps femoris) and injection brine

Investigated material

Temperature [0C]

Fresh muscles immediately after trimming

4.5

Muscles after injection

1.2

Muscles after massaging

4.8

Injection brine

-2.0

The dynamics of histological changes occurring during plastification is affected primarily by the design of the massage machine, the duration of the process and the programmed massaging cycle. Along with the progress in the mechanical disruption of the natural structure of muscles, the plasticity and water binding capacity of meat increase, and during thermal processing – the dynamics of collagen thermohydrolysis. In the opinion of Siegel et al. [28], destructive changes in muscle fibers caused by the massaging process occur faster in the presence of salts and phosphates. However, excessively long massaging may lead to the destruction of the tissue structure of meat and the formation of large amounts of pulp. It is connected with the extraction of large quantities of protein, the content of which in the brine drip in the 12th h of massaging may reach 12% [29]. On the other hand, massaging for a too short period of time, or an insufficient intensity of the unitary load do not change the properties of the raw material to obtain the desired tenderness and juiciness of the finished product. An optimally performed massaging process results in such a level of destruction in the protein of the muscle tissue that it increases appropriately its rehydration and water binding during thermal processes, it has slightly disrupted external structures, and myofibrillar protein released from these structures bind individual pieces into a uniform meat block, which maintains the fibrous structure of the whole.

Thus, the time of effective massaging needs to be adopted to the type of the raw material, the programmed massaging cycle and the applied equipment, i.e. its design, size and operating parameters [8].

Investigations of the muscle structure showed that fresh muscles, after being injected with curing brine, vary during massaging and after this process is completed. The surface of fresh muscles is relatively dry, smooth, with an undisrupted structure. Muscle fibers visible on the cross-section of ham are compact and dry (Photo. no 5). As a result of the injection process a thin layer of unbound curing brine appeared on the surface of the muscles and between muscle fibers, visible on the cross-section of meat (Photos. 2 and 6). Moreover, traces left after the insertion of the injector needles were visible on the surface of the muscle (Photo. 2). It may be explained by the fact that a preliminary swelling of protein occurs already in the injection process, mainly as a result of the action of phosphates introduced into the muscles along with brine [29]. One of the functions of phosphates is to induce the dissociation of actomyosin, to activate myosin ATP-ase, to enhance the ionic strength of the environment, to change the buffering and to complex metals. A result of such activity of phosphates is increased water binding by meat and a decrease of the thermal drip loss and improved tenderness [9, 39]. Phosphates have an advantageous effect on the microbiological quality of cooked products [2, 40, 41]. In the photograph presenting a ham muscle after injection with curing brine a loosening of muscle fibers may be observed. It is probably the effect of an increase in the homogenous electric charge as a result of the chloride ion adsorption, which causes a longitudinal loosening of myofibrils [35].

Photo 1. Ham muscle – fresh

Photo 2. Ham muscle after injection with curing brine

Photo 3. Ham muscle in the middle of the massaging process

Photo 4. Ham muscle after the completion of the massaging process

Photo 5. Cross-section of fresh ham muscle

During the plastification process advanced changes in the muscle structure were observed on their surface. The surface of muscles became uneven, and fibers formed a polyhedral form and became rounded. Such changes were also observed by Tyszkiewicz [37].

As a result of the increase in porosity, in the free spaces and on the muscle surface a granular protein mass appeared, formed from the diffused sarcoplasm protein and extracted myofibrillar protein (Photos 3, 4). It results from the analysis of Photos 3 and 4 that the amount of the forming protein mass increases along with the time of massaging. While analyzing the photographs in detail it may also be seen that that the forming viscous protein substance fills the openings created during injection. It indicates that the amount of protein in the unbound brine in the outer layer of the muscle increases along with the time of the process and brine becomes increasingly viscous [4, 28].

Photo 6. Cross-section of ham muscle after injection with curing brine

Photo 7. Cross-section of ham muscle in the middle of massaging process

Photo 8. Cross-section of ham muscle after the completion of the massaging process

Comparing the images of muscles obtained using the computer image analysis system it may be stated that this method is useful in the investigation of changes in muscles. While analyzing images obtained during macroimaging and their recording using the computer image analysis system it is possible to observe changes in muscle structure (Photo 1-8). They are manifested in the loosening of the muscle fibers and the extraction of muscle protein, the amount of which increases along with the time of plastification. On the photographs presented above it is clearly seen how the muscle structure changes in the course of the massaging process. The image of the muscle after plastification is completed, i.e. after the total of 2400 revolutions of the massage machine drum, clearly shows how the viscous protein substance formed during plastification caps openings produced by needles in the course of the injection process. At the same time the surface of the muscle becomes uneven and muscle fibers become rounded and form a polyhedral structure.

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Włodzimierz Dolata
Institute of Meat Technology,
The August Cieszkowski Agricultural University of Poznan, Poland
Wojska Polskiego 31, 60-624 Poznan, Poland
ph (+48 61) 848 72 59
fax (+48 61) 848 72 54

Mirosława Krzywdzińska-Bartkowiak
Institute of Meat Technology,
The August Cieszkowski Agricultural University of Poznan, Poland
Wojska Polskiego 31, 60-624 Poznan, Poland
ph (+48 61) 848 72 59
fax (+48 61) 848 72 54
email: mirkakb@onet.pl

Jerzy Wajdzik
Institute of Meat Technology,
The August Cieszkowski Agricultural University of Poznan, Poland
Wojska Polskiego 31, 60-624 Poznan, Poland
ph (+48 61) 848 72 59
fax (+48 61) 848 72 54

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