EFFECT OF CURING BY INJECTION METHOD, MASSAGING AND PASTEURIZATION ON HISTOLOGICAL CHANGES OF BOVINE MUSCLES

Mirosława Krzywdzińska-Bartkowiak, Hanna Gajewska-Szczerbal
Institute of Meat Technology, The August Cieszkowski Agricultural University of Poznan, Poland

ABSTRACT

The objective of the investigations was to compare changes in the structure elements of selected cattle muscles taking place under the influence of the injection with curing brine, massaging and pasteurization with the assistance of the computer image analysis. The experimental material comprised: the semi-membranous muscle (musculus semimembranosus) and the lumbar part of the longest muscle of the back (musculus longissimus lumborum) which derived from carcasses of mature cows 5 years old. The analysis of the muscle structure was conducted on the basis of the following parameters of muscle fibres: the surface and circumference, Feret’s H and V diameter, percentage proportion of muscle fibres and their quantity in the analysed field of view. The fibre shape was determined on the basis of the H/V ratio. It was found that the closer its value was to one, the more regular was the shape of fibres. The performed analysis of the elements of the examined cattle muscle structure: musculus semimembranosus and musculus longissimus lumborum showed that they depended on the type of muscles. The brine injection processes and massaging increased the cell volume in the semi-membranous muscle. The cells of the longest muscle of the back underwent contraction following the injection with the curing brine, whereas the plasticisation process increased their surface in relation to the untreated muscles.

Key words: muscle structure, curing, plasticization, pasteurization, computer image analysis.

INTRODUCTION

The basic principle of production of food articles is the alteration of the raw material structure affecting the sensory and rheological properties of the finished product. That is why knowledge about the origin and course of structural changes is of crucial importance for the development of new technologies and products [25]. Individual operations that take place during the technological processes of food production cause not only the development of the structure or texture expected by the consumer but, equally importantly, they also cause significant changes in chemical constituents. That is why it is essential to combine all research disciplines of food analytics with the microscopic analysis, since only such combination provides wide and comprehensive basis for the development of new products and modem production processes. The main task of food microscopy is to apply the obtained information in food technology, in other words, it provides a bridge between food science and technology. This role requires a complete mastery over the microscope and good knowledge of the technological processes with the aim to recognise and explain the significance of microscopic observations to food technologists [7].

The knowledge of the effect of individual technological parameters on the course of the process allows its further improvement. It requires ever more accurate information about the value of the produced raw materials in order to obtain from them the best food articles using modern production technologies. From among many methods which are employed to achieve this goal, histological and histochemical methods adopted to light and electron microscopy find increasingly wide application. Histological methods allow indicating structural properties of the examined raw material, tracing changes and responses generated in the tissues and cells by pathological stimuli, effect of the action of the employed technological processes as well as indicating interrelationships between structural and biochemical properties taking place in plant and animal tissues [11].

One of the visual systems is the computer image analysis which is becoming increasingly common in the food industry [1, 14, 15, 19, 20].

Product texture is one of the most important properties of meat products affecting their quality. It is understood as a set of traits resulting from elements of its structure, their mutual arrangements and interactions [3, 6]. The structural unit is muscle fibres and their thickness, quantity and type exert influence on the meat texture [10, 30]. Muscle fibres are among many different structure elements which are associated with ham quality [1]. Numerous researchers maintain that muscles characterized by larger muscle fibres are tougher [19]. The final product quality depends not only on the muscle structure but also on a number of such technological treatments as: injection with the curing brine, plasticization processes and pasteurization [5, 31,32, 33].

The aim of the presented investigations was to compare changes of structural elements of selected cattle muscles taking place following their injection with the curing brine, plasticization processes and pasteurization employing for this purpose the computer image analysis.

MATERIAL AND METHODS

Experimental material
The experimental material comprised the semi-membranous muscle (musculus semimembranosus) and the lumbar part of the longest muscle of the back (musculus longissimus lumborum) which derived from carcasses of mature cows 5 years old. After cutting them out from chilled carcasses, experimental muscles were divided into 4 portions. One of the portions was treated as the control. The remaining three parts were injected with the curing brine applying low-pressure (0.3 MPa) injection using for this purpose a multi-needle, two-head injector. The applied treatment allowed 30% weight increase of experimental samples. One part of the injected muscles was taken for analyses, while the remaining two parts were placed in a tightly sealed plastic bag and subjected to the plasticization process. The effective massaging time was 6 h and 20 min. Again, one of the two samples after massaging was taken for analyses, while the last one was placed in steel cans and pasteurized at the temperature of 72°C and then cooled.

Preparation of histological specimens
Cuboids measuring 10x10x30 were cut out from the collected muscle samples: the control, injected with the brine, massaged and pasteurized. Next, they were fixed in neutralised formalin to prevent tissue destruction. Fixed muscle samples were embedded in paraffin and cut into 10 ·m slices which were placed onto micro slide glass, dried, dewaxed and prepared for staining. A combined slice staining was used applying Delafield haematoxylin and eosin.

Computer image analysis
Investigations of the muscle tissue structure were carried out employing the system of computer image analysis [4, 22] with the assistance of the MultiScan program. An identical procedure of object identification and analysis was developed for all preparations. The preparation structure was studied at constant microscope magnification (x200) and 10 fields of constant area were analysed from each preparation. The characterization of the obtained images was conducted on the basis of the following parameters of muscle fibres: area, circumference, Feret’s diameter H and V, percentage proportion of muscle fibres and their quantity in the analysed field of view. The shape of fibres was determined on the basis of the ratio of H : V diameters. The closer was the value of the quotient to 1, the more regular was the shape of fibres.

Statistical analysis
The obtained numerical data were subjected to statistical analyses using for this purpose the STATISTICA program. The significance of differences was determined by the Fisher test at the level of significance p ≤ 0.05.

RESULTS AND DISCUSSION

The results of analyses of changes in the structures of the experimental cattle muscles: musculus semimembranosus and musculus longissimus lumborum are presented in Figures 1-4, Photographs 1-4 and in Table 1. On the basis of the results obtained with the assistance of the applied visual system, it was found that changes in the bovine muscles: musculus semimembranosus and musculus longissimus lumborum depended on the muscle type. Differences in the meat histological structure depend, among others, on the animal species or the kind of the muscle [9, 21, 24]. Shackelford et al. showed that muscles from slaughtered animals differed with regard to their texture [27]. Numerous other researchers reported also differences in the muscle structure [12, 13, 17, 34], whereas still others showed that muscles differed with regard to their sensitivity to the plasticisation process [8, 23, 26]. According to Lachowicz and co-workers [19], each type of muscles requires other massaging parameters with the massaging time as the most common measure. Analysing microstructural parameters of Turkey muscles, Kłosowska et al. [13] concluded that the type of muscle fibres, their diameter and quantity may be responsible for the physicochemical differences between breast and thigh muscles.

The cells of the cattle semi-membranous muscle, both raw and injected, were characterised by a fairly regular shape (1.01 and 0.99) (Table 1). The process of injection with the curing brine as well as massaging resulted in the increase of the cell volume in the semi-membranous muscle in relation to the raw muscle (Photos 1, 2 and 3). This is clear from mean measurement results of the cross section area and circumference of muscle fibres carried out in the raw muscles as well as in the injected and massaged muscles between which statistically significant differences were found (Figs 1 and 2). Statistically significant differences were also observed between the amounts of muscle cells calculated in the field of view of the examined images. The increase of the area in the semi-membranous muscle resulted in a simultaneous decline in their quantity (Fig. 3). The applied pasteurization process resulted in muscle contraction (Photo 4).

In contrast to the semi-membranous muscle, cells of the longest muscle of the back underwent shrinkage as a result of the injection with the curing brine. On the other hand, massaging caused some increase of the area and circumference in relation to the raw muscles as well as decrease of their quantity (Fig. 3). This may indicate that the penetration of the majority of brine into the cells of the musculus semimembranosus took place already after its injection with the curing brine, while in the case of the musculus longissimus lumborum – only during the massaging process. During the absorption of the curing brine by the muscle fibres they become rounded and lose their multilateral form [35]. This is caused by increased swelling of proteins part of which passes into the solution of the curing brine [2, 28]. The remaining part of the brine located itself in cell spaces together with the extracted muscular proteins (Photo 3A).

Using the image analysis technique, Lachowicz et al. [17] showed differences in the PSE and normal meats [17]. They found that the PSE meat was characterised by fibres of larger area and diameter as well as smaller quantities of intramuscular fat. The same researcher and his co-workers (1998) applied the above-mentioned technique to show differences in structural properties of pork meat of different genotypes [16]. On the other hand, Sobczak et al. [29] reported differences in the muscle structure of pigs of Pietrain and Duroc breeds and wbp x pbz crossbreds. It was found that harder, more elastic, rubbery and sticky muscles were characterised by coarser connective tissue, greater area of the muscle fibre and smaller content of intramuscular fat.

Comparing the structure of smoked loin obtained from the PLW pork meat and meat of crossbreds of the Czech J_HYB breed and CVM using the computer image analysis it was found that the larger the fibre diameter and its area, the less intramuscular fat is found in the raw meat [20].

CONCLUSIONS

The performed investigations revealed that the semimembranosus muscle was characterised by a greater dynamics of changes of the structural elements on the process of injection and plasticisation than the longissimus lumborum muscle. It was found that processes of injection with the curing brine and massaging increased the volume of cells in the semimembranosus muscle. Cells of the longest muscle of the back underwent compression following their injection with the curing brine and it was only the massaging process which increased their area in comparison with the raw muscles. This may imply that in the case of the semimembranosus muscle, the brine penetrated inside cells already during the process of injection with the curing brine, while in the case of the musculus longissimus lumborum – only during the plasticization process.

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Accepted for print: 26.04.2007

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