Applications of mechanically deboned meat in sausage mass

The use ofmechanically deboned meat (MDM) and its proportion in homogeneous sausage mass was investigated. A test Bologna containing 7.50% mechanically deboned meat was used. Two deboning machines, an Inject Star based on pressure and an auger-type Poss machine based on scraping, were used. The water contents of the masses varied between 28.36 and 43.36%. Test sausages containing the same amounts of meat recovered by the Inject Star and Poss deboners were surprisingly similar in colour. Calcium contents of samples were 0.11% 0.18%, and the corresponding ash contents 2.6 2.9%. The pH values of all the test sausages were similar, about 6.4. Fat contents in samples made using MDM recovered with the Inject Star deboner were lower than those in the samples made using MDM recovered with the Poss deboner. On the basis of chemical quality indices the shelf lives of all the test sausages were similar. Index words: mechanically deboned meat (MDM), use of MDM, sausage, shelf-life of sausage


Introduction
Mechanical deboning is an inexpensive and convenient method of recovering meat attached to bones. Many processed meats are finely minced, so mechanically deboned meat (MDM) can be used to economic advantage.
In the case of poultry products there is no limit to the amount of mechanically processed poultry meat that can be added for example in the USA, but for red meats the maximum quan-tity of mechanically separated beef, pork, or lamb meat is limited to 20 percent of the meat fraction (1). Field (2) reported that flavour not associated with rancidity, texture, or juiciness in products containing MDM may vary depending on the amount of red bone marrow in the MDM and on the amount of MDM in the finished product. Field (3) also observed 397 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND that sensory panels have not been able to de-Material and methods teet differences in juiciness or flavour when 10% mechanically deboned meat is added to formulations.
The bones from the vertebral column, ribs and sternum are most suitable for mechanical deboning because they usually have more lean meat attached and thus yield a greater percentage of mechanically separated tissue (4,5). Round bones are least suitable for mechanical deboning since they have very little lean meat attached and the marrow is primarily fat. Field et al. (6) also reported that the protein content in mechanically deboned meat was lower and the fat content higher than in similar hand deboned meat.
Gillet et al. (7) have shown that mechanical recovering removed approximately half of the connective tissue from beef and pork trimmings. The tendency for jellypockets to form in salami was reduced by using such material, and the texture and tenderness were improved by the recovering operation.
Marshall et al. (8) studied the effects of adding MDM from pork to frankfurter sausages on cooking loss and texture . They manufactured frankfurters comprising 10%, 25% and 40% MDM, calculated on total batch weight, and found that the cooking loss increased with increasing MDM concentration. However, when the sausages were judged for texture by sensory evaluation, the batch containing 10% MDM was ranked the best, followed by the control and the batch containing 25% MDM. The batch containing 40% MDM was rated 'very mushy'.
Microbial counts in frankfurters containing 15°70 mechanically deboned turkey meat after frozen ( -24°C) storage for 7 days were generally low (9). Joseph et al. (10) claimed that the microbial load in MDM can be as low as that of handboned trimmings if proper sanitation and temperature control are employed.
The aim of the present work was to study the use of mechanically recovered meat and its optimum proportion in homogeneous sausage meats.
Bologna sausage was chosen as the basic sausage, because it best reveals the benefits and disadvantages of the added mechanically recovered meat. The formulation of the basic sausage is presented in Table 1.
In preliminary trials, 2.5%, 5%, 7.5%, 10% and 12.5% MDM was used in the test sausages and on the basis of these tests the optimum proportion of 7.5% mechanically recovered meat was used in subsequent experiments. High concentrations of MDM in the formulation resulted in a very soft, dark and inelastic sausage.
The  Consistency Consistency was measured in an Instron testing apparatus (Model 4301), using a weight head with a diamter of 5.5 cm. A 6 cm slice was cut from the test sausage, the side of the slice was depressed to a depth of 0.5 cm. The compression force (kp) was measured as the maximum height of force-deformation curve. made using mechanically deboned meat recovered with the Inject Star deboner as presented in Table 2. In all the test sausages milk powder, potato flour, additives and spices were added in the same proportion as in the basic formulation. Test sausages in experiments 111 and IV were made using mechanically deboned meat recovered with the Poss deboner. In experiment V all the samples were made from MDP and MDB recovered by Inject Star and Poss as described in the following (see also Table 3). In all tests MDB and MDP were from mixed beef and pork bones and the MDM was separated in a freshly disinfected deboning machine. In experiments I-IV the sausages were in natural casings, whereas the sausages in Test V were prepared with cellulose casings. All experimental sausages were stuffed by hand. The technical quality of sausages was best in experiment V.

Evaluation of meat and sausage quality
Water holding capacity The method developed by Pohja (11) was used for determining the water holding capacity of the meat. Other analyses used for the evaluation of meat and sausage quality have been presented earlier Riikonen et ai. (12). Tables 4 and 5 show the analytical results of the meat recovered using the two different machines. Meat recovered in the Poss machine was organoleptically noticeably smoother, and lighter in colour, than that recovered in the Inject Star. The greatest differences between meat recovered using the Poss and Inject Star machines were in calcium and ash contents.

Results and Discussion
The water holding capacity was surprisingly low (P<0.05) in sample BP (Table 4). Other workers have reported that frozen, mechanically recovered meat has less water  holding capacity than unfrozen meat (7,8). Water holding capacity is influenced not only by the freezing rate but also by the pH of the meat, which is higher in mechanically recovered meat than in hand boned meat. More water exudes from the meat during slow freezing, thus lowering its water holding capacity. The water holding capacity of meat is also influenced by the the freezing time and temperature, the rate of thawing and the fat and collagen contents. Puolanne and Turkki (13) studied the effects of frozen storage on the water holding capacity of the raw materials of cooked sausage and concluded that frozen storage of ground meat results in a strong decrease in water holding capacity. In the case of pork the minimum level is reached after 6-9 months, but with beef the decrease is linear for at least 12 months. In this work the colour retention qualities of meats recovered by the two machines were also compared. Colour changes were rather similar, with the darkest mechanically deboned beef recovered in the Inject Star changing the least (P<0.05).
When examining the keeping qualities of meat during storage at +4°C using the free fatty acid (FFA%) and peroxide value, it was noticed that the FFA%-value changed more in the mechanically deboned beef and pork recovered in the Inject Star deboner than in the corresponding samples recovered in the Poss machine ( Figure 1).

Sausage analyses
Colour Before cooking, a colour difference was noticed between samples I -4 1 -4 and samples 5-6. This difference disappeared during cooking.
It was, however, observed that test sausages containing the same amount of meat and recovered in the Inject Star or Poss machines were surprisingly similar in colour (Figure 2). The colour change of stored sausages was caused than 90% of frankfurter-type sausages have by surface dehydration and oxidation of the a reddish colour, the rest being greyish-white meat pigments. It has been reported that more (14)  Sensory quality Figure 3 illustrates the results of sensory analysis. Sample 5 was judged somewhat better than the others in taste, smell, appearance and texture. FIELD (15) concluded that acceptability is for the most part based on sensory evaluation, i.e. colour, texture and flavour, although the suspicious attitude of consumers towards new products often plays an important, if subconscious part.

Consistency
Consistency proved to be best in samples 5 and 6 ( Table 5). These results are in agreement with those of Field (15) and Smith (16), who reported improved textural quality when mechanically deboned meat was added to ground beef and mutton in the range 5-25%.
Similarly, a more pleasing texture, which gives fresh sausage an extra bite, is often obtained when 5-10% mechanically deboned meat is added, but a grainy or gritty texture may result in products with more than 30% mechanically deboned meat.

Calcium content
The calcium contents of samples 2 and 3 were about 0.18%, significantly different (P<0.05) from those of samples 1 and 5-7, which were approximates 0.10% (Table 5). This result was logical, because the calcium content of meat recovered in the Poss machine was generally higher than that of meat recovered in the Inject Star (Table 4).

pH and fat
All test sausages had similar pH values of between 5.8 and 6.0. The fat content in samples 5-7 was lower than in samples I-3, because the fat contents of BP and PP were lower than those of BI and PI (Tables 4 and   5).

Microbiological keeping qualities
The microbiological keeping qualities of samples 1 and 3 were the best. When comparing the effects of meats recovered by the two machine types on the microbiological keeping qualities of sausages, no great differences were found. However sample 6, after 21 days of storage, had a lower lactic acid bacterial count than the other samples (Figure 4).

Chemical storage properties
Chemical storage properties were measured using the peroxide and free fatty acid values.
The results presented in Figure 5 indicate that the initially higher peroxide values in samples 5-7 did not increase proportionately during the two-week storage period in comparison with samples I -3 . 1 -3.
No significant differences were observed in the effects of the meats recovered by these two (pressure-based and auger) machine types. The differences between the non-homoge-  neous meat recovered using the Poss and Inject Star machines could not be detected in the finished sausages. The shelf life of the test sausages was two to three weeks. Storability of sausages containing 7.50% mechanically recovered meat did not differ significantly from that of the basic test bologna (2.02% MDM) made at the same time. Mechanically recovered meat accelerated the development rancidity of the sausage slightly, but this was not detected in the sensory evaluations.
Mechanically recovered meat gave the finished sausage a slightly darker colour.