Electron Microscopy for the Microstructure Analysis of Bovine Treated Muscles

GONZALEZ CLAUDIA B.; SZERMAN NATALIA; VAUDAGNA SERGIO R.

Rio de Janeiro

Congreso; 17th International Congress of Microscopy (IMC17); 2010

One of the most important factors that influence meat quality is the water holding capacity (WHC) of muscle tissue. It is associated to tenderness and juiciness of cooked products, having important commercial implications. However, when meat pieces are cooked under vacuum (sous vide system), the juice released is retained inside the package, affecting negatively the visual appearance. An alternative to increase the muscle WHC, is the incorporation of functional additives. In that context, the injection and massaging (tumbling) treatments to improve distribution and action of the additives are relevant. Nevertheless, the application of tumbling in excess can severely affect muscle structure, losing its fibrous appearance. Hence, the use of scanning electron microscopy (SEM) technique appears an interesting alternative to describe the effect of different processing steps on muscle structure. The aim of this study was to evaluate the effect of the combined treatments and addition of water binder compounds by means of SEM. Treatments applied were pre-injection (PreIT) and postinjection (PostIT) tumbling and sous vide cooking. The additives used were whey protein concentrate (WPC, 80% protein content, ArlaFoods) and sodium chloride (NaCl). Bovine Semitendinosus muscles (120 h post-mortem) were added with the WPC and NaCl by automatic injection of 30% (w/w) to achieve tissue concentrations of 3.5% and 1% (w/w), respectively. Tumbling treatments were applied to pieces according to a factorial design (PreIT: speed = 8.5 rpm, time = 0, 0.5 and 1.5 h; PostIT: speed = 8.5 rpm, time = 0, 2, 5 and 10h). For SEM analysis, pieces of 2x2x10 mm were excised from the central area of each muscle. Samples were immediately fixed in glutaraldehyde solution (2% w/w). Then, three successive washes were made with sodium phosphate buffer 0.1 M pH 7, followed by dehydration in ethanol solution (15 min each) at increased concentrations (50% to 100% w/w). Afterwards, samples were immersed in ethanol:acetone solution (50:50), and acetone. Specimens were mounted on holders and coated with gold (Balzer, SCD004). The chosen areas were view at 1000-10000 times magnification. Microscopic evaluation was performed using a Jeol, JSC, 6400 (Akishima, Tokyo, Japan) electron microscope at 20 kV. A large number of micrographs were taken and the most representative ones selected. Muscles non-submitted to tumbling treatments (NPreIT + NPostIT) showed a more conserved structure (Figure 1-a), with high interfiber spaces and without myofibril separation or fragmentation compared to massaged muscles (Figures 1- b,c). It can be also seen the presence of sarcolemma, endomysial collagen and other granular materials coagulated onto the fibers and spaces in between. When muscles were submitted to PreIT 0.5h + PostIT 10h, the microstructure presented higher cellular damage. It was also observed less separation between fibers probably due to the presence of material coming from myofibrillar fragmentation (Figure 1-b). By increasing PreIT time to 1.5 h, the increment of the myofibrils fragmentation was more pronounced and, as a consequence, the presence of material in the interfiber spaces was higher (Figure 1-c). Also, the damage produced in the tissue was even more intense. This damage induced a lower water retention which was demonstrated by the lower yield obtained (92.6%) when compared to muscles submitted to PreIT 0.5h + PostIT 10h (94.4%) or NPreIT + NPostIT (95.2%).