Technological quality and composition of the M . semimembranosus and M . longissimus dorsi from Large White and Landrace Pigs

Vladimir M. Tomović1*, Božidar A. Žlender2, Marija R. Jokanović1, Mila S. Tomović3, Branislav V. Šojić1, Snežana B. Škaljac1, Tatjana A. Tasić4, Predrag M. Ikonić4, Milena M. Šošo1 and Nevena M. Hromiš1 1University of Novi Sad, Faculty of Technology, Bulevar cara Lazara 1, 21000 Novi Sad, Serbia 2University of Ljubljana, Biotechnical faculty, Jamnikarjeva 101, 1000 Ljubljana, Slovenia 3Technical school “Pavle Savić”, Šajkaška 34, 21000 Novi Sad, Serbia 4University of Novi Sad, Institute for Food Technology, Bulevar cara Lazara 1, 21000 Novi Sad, Serbia


Introduction
The technological quality attributes of meat include: pH value, color, texture, water-holding capacity (WHC) and chemical composition (Rosenvold and Andersen 2003, Olsson and Pickova 2005, Sevón-Aimonen et al. 2007).These parameters are influenced by multiple interacting factors including breed, genetics, feeding, pre-slaughter treatment and stunning, slaughter method, chilling and storage conditions, as reviewed by Rosenvold and Andersen (2003).
It is believed that pH is one of the keys to understanding post-mortem muscle glycolysis.A number of authors report that the rate of post-mortem pH fall is an important determinant of colour and WHC.An abnormally rapid rate of glycolysis early post-mortem in the muscles produces poor pork quality (pale and exudative meat).On the other hand, higher ultimate pH is associated with darker colour and better WHC (Bendall and Swatland 1988, Brewer et al. 2001, Lawrie and Ledward 2006).
Fresh pork has been traditionally classified into three technological quality categories, according to the measurements of pH value, colour, firmness (texture) and drip loss (exudation): PSE (pale, soft, exudative), RFN (reddish-pink, firm, non-exudative or normal pork) and DFD (dark, firm, dry).The RFN meat is considered the ideal pork quality class (Kauffman et al. 1992, Joo et al. 2000a).Pork meat that is classified as RFN has a desirable color, normal texture and WHC.One of the most important and the most frequently found quality deviation of pork meat is a PSE defect (Bendall and Swatland 1988, Kauffman et al. 1992, Warner et al. 1997, Joo et al. 2000a, O'Neill et al. 2003, van de Perre et al. 2010).On the other hand, the incidence of DFD meat is low and less relevant to industry (Bendall and Swatland 1988, Kauffman et al. 1992, van Laack et al. 1994, O'Neill et al. 2003, van de Perre et al. 2010).

Manuscript received September 2013
The development of PSE is caused by excessive protein denaturation due to a combination of a low pH and a high muscle temperature early post-mortem.The opposite of PSE is DFD muscle, which is caused by a depletion of glycogen content at the time of slaughter, resulting in a high ultimate pH 24h and a higher susceptibility to the microbiological spoilage (Bendall and Swatland 1988, Warner et al. 1997, Lawrie and Ledward 2006, Barbut et al. 2008).
Beside these three traditional categories, during the last two decades many authors introduced two additional intermediate quality variations: RSE (reddish-pink, soft, exudative) and PFN (pale, firm, non-exudative).RSE pork has normal color, but a soft texture and an exudative character similar to PSE, whereas PFN pork has the texture of meat of good quality, but has undesirable color, similar to PSE (Kauffman et al. 1992, van Laack et al. 1994, Warner et al. 1997, Joo et al. 2000a, O'Neill et al. 2003).Over the years RSE and PFN have also been recognized as serious quality defects (Kauffman et al. 1992, van Laack et al. 1994, Joo et al. 2000a, O'Neill et al. 2003, van de Perre et al. 2010).
Incidence of inferior muscle quality, especially with PSE and RSE defects, has an economic impact in the pork industry (Kauffman et al. 1992, Joo et al. 2000a, O'Neill et al. 2003, Huff-Lonergan and Lonergan 2005, Sevón-Aimonen et al. 2007).For this reason, evaluation of technological quality of pork represents an important step in meat production and processing.
In international practice the evaluation of pork quality is based on very different parameters and criteria.The most popular parameters, which enable identification of defective meat, include the pH value, measured in the muscle tissue 30-60 minutes (pre-rigor state) and 24 hours post-mortem (post-rigor state), meat colour (reflectance -lightness -CIEL* value) and WHC (numerous analytical methodologies: filter paper press, filter paper, bag, tray, EZ-DripLoss, absorption or centrifugation methods or determination of cooking loss), measured 24 hours postmortem (Bendall and Swatland 1988, Honikel 1998, 1999, Sevón-Aimonen et al. 2007).Moreover, other parameters like: electrical conductivity (Joo et al. 2000a, Lee et al. 2000) or impedance (Swatland 1995) help to identify defects in pork meat quality (Bendall andSwatland 1988, Honikel 1999).Characteristics should be easily measurable, what means that a destructive cutting of a carcass must not occur.Therefore, the easy accessible M. semimembranosus and M. longissimus dorsi are recommended as representative muscles (Honikel 1999).
The measurement of pH values is the most direct way to obtained information about meat quality characteristics.The pH 45min identifies potential PSE pork, especially if the value is less than 6.0 (Bendall and Swatland 1988, O'Neill et al. 2003, Lawrie and Ledward 2006).However, CIEL* value is probably the best overall indicator for PSE and DFD pork (Brewer et al. 2001).
The Autonomous Province of Vojvodina (the northern part of the Republic of Serbia) is a region where the number of animals of the porcine species and the production of pork meat are of high economic importance.The most common white purebreds of pigs used in Vojvodina, as well as in Serbia, for pork production are the Large White and the Landrace.Also, they are commonly used in crossbreeding programs.This cross is often used as the female line in commercial herds.Dark purebreds such as Duroc, Hampshire or Pietrain are often used as a male line (Lawrie and Ledward 2006, Sevón-Aimonen et al. 2007, The Danish Standard 2007, Barbut et al. 2008, Tomović et al. 2011).
The objective of this study was to determine the technological quality (pH, colour -CIEL*a*b* values and WHC -M/T value -filter paper press method) and composition (moisture, protein, total fat and total ash content) of two economically most important muscles (M.semimembranosus and M. longissimus dorsi) from two major white purebreds (Large White and Landrace) used for pork production in Vojvodina (Republic of Serbia).Based on the criteria for colour (CIEL* value) and WHC (M/T value), data of this study were used to classify pork quality into different categories.

Animals, sampling, slaughter and preparing
This study was carried out on 81 (females and castrated males) Large White (LW) and 83 (females and castrated males) Landrace (L) pigs.The pigs were fattened at the 4 production farms in Vojvodina under identical conditions (Tomović et al. 2011).The pigs were randomly selected from both purebreds at an individual live weight between 95 and 110 kg, and about 6 months old.Four to five pigs from both breeds fattened at the same farm were taken during one production day per week for a total of 20 weeks.All the pigs were slaughtered in the two biggest slaughterhouses in Vojvodina according to routine procedures.After transport, which took 1-2 hours, pigs were allowed to rest for about 2-3 hours in the abattoir.Stunning was performed electrically (220 V, 2 A, 8-12 seconds) in a V-restrainer with a pair of stunning tongs.After stunning, the animals were shackled by one hind leg and exsanguinated and scalded (5 minutes, 62 °C) vertically.Carcasses were then individually placed in a dehairer and any remaining hair was removed using flame and knife.The evisceration was finished about 45 minutes postmortem.Carcasses were conventionally chilled for 24 hours in a chiller at 0-4 °C.
M. semimembranosus (SM) and M. longissimus dorsi (LD) were excised from the right side of each carcass.Identification of the muscles was performed according to UNECE (2008).The meat samples were trimmed of visible adipose and connective tissue.Technological quality characteristics were measured on fresh muscles (SM muscle: central part, LD muscle: central part between 3rd and 4th from the last rib).After determination of technological quality characteristics, each muscle was homogenized (Waring 8010ES Blender, USA, capacity: 1 liter, speed: 18000 rpm, duration of homogenization: 10 seconds, temperature after homogenization: <10 °C), vacuum packaged in polyethylene bags and stored at -40 °C until determination of composition.Composition of SM and LD muscles for 40 pigs from each purebred was determined.

Technological quality measurements
Temperature was measured at the start 45 minutes (T 45min ) post-mortem and at the end 24 hours (T 24h ) post-mortem of the chilling process in the SM muscles, and in the LD muscles, on the right side of every carcass, using a portable digital thermometer with a 12 cm stem (Consort T651, Turnhout, Belgium).
The pH value was measured 45 minutes (pH 45min ) and 24 hours (pH 24h ) post-mortem using the portable pH meter (Consort T651, Turnhout, Belgium) equipped with an insertion glass combination electrode (Mettler Toledo Greifensee, Switzerland).The pH meter was calibrated before and between the measurements using standard phosphate buffers (pH values of calibration buffers were 7.00 and 4.01 at 25 °C) and adjusted to the expected temperature of measured muscles (ISO 2917 1999).Measurements were performed in triplicate.
Determination of the water-holding capacity (WHC) was based on measuring water released when pressure was applied to the muscle tissue (exudative juice).Exudative juice was assessed using a filter paper press method (Grau andHamm 1953, van Oeckel et al. 1999).A cube of 300±25 mg of meat from the inside of the muscle sample was placed on a filter paper (Schleicher & Schull No. 2040 B, Dassel, Germany) between two plexiglas plates.Plates were then screwed together tightly for exactly 5 minutes.The analysis was performed in triplicate.The WHC was expressed as the ratio of the area of pressed meat film (M) and the wet area on the filter paper (T), as determined by mechanical polar planimeter (REISS Precision 3005, Bad Liebenwerda, Germany).The WHC quality was calculated on the basis of all individual M/T values measurements, according to criteria for pork (exudative meat: M/T<0.35,non-exudative meat: M/T=0.35-0.45,dry meat: M/T>0.45) as defined by Hofmann et al. (1982).Thus, combining three criteria for colour and three criteria for WHC technological pork quality was classified into 9 quality classes.

Composition
Moisture (ISO 1442 1997), protein (nitrogen x 6.25, ISO 937 1978), total fat (ISO 1443 1973) and total ash (ISO 936 1998) contents of muscles were determined according to methods recommended by International Organization for Standardization.All analyses were performed in duplicate.

Statistical analysis
All data are presented as mean and standard deviation (SD).Data were analyzed statistically with factorial ANOVA and post-hoc test (Dunckan's test).Two-way analysis of variance was performed; 2 breeds x 2 muscles.Levels of significance p<0.05, p<0.01, and p<0.001 were used.Correlation coefficients among quality characteristics of pork were also calculated.Statistical analysis was conducted using Statistica software version 10 (StatSoft, Inc. 2011).

Overall technological quality of pork
No significant (p>0.05)interaction effect between breed and muscle type was found for all determined technological parameters (Table 1).
The initial (45 minutes post-mortem) mean temperatures in the SM muscles of both LW and L breeds were 40.2 and 40.1 °C, respectively (Table 1).At the same time, in the LD muscles significantly lower mean temperatures (p<0.001) were found than those in the SM muscles, within each breed, i.e. initial temperature was significantly influenced by the type of the muscle.Difference between mean temperatures in SM and LD muscles for both breeds was identical, 1.5 °C.Similarly, at the end of chilling (24 hours post-mortem), mean temperatures in LD muscles were significantly lower (p<0.001)than those in the SM muscles.Ultimate temperature was also significantly (p<0.001)influenced by the breed.Mean ultimate temperatures ranged from 2.9 (LD of L) to 5.0 °C (SM of LW).All the individual ultimate temperatures were lower or equal 7 °C.According to EU Council Directives (ECC No. 433/1964), as well as Serbian Regulation (2011), pork must not be cut and deboned before reaching 7 °C in the deep leg.Initial pH value was significantly influenced (p=0.008) by the type of the muscle (Table 1).In the SM muscles initial pH values were significantly (LW breed, p<0.05) or numerically (L breed, p>0.05) higher than those in the LD muscles.In SM muscles from LW and L breeds, the mean initial (45 minutes post-mortem) pH values were 6.26 and 6.20, respectively, while in LD muscles these values were 6.16 and 6.14, for LW and L breeds, respectively.Similarly, at the end of chilling (24 hours post-mortem), mean ultimate pH in SM muscles were numerically higher than those in LD muscles within each breed.However, ultimate pH was not significantly influenced (p>0.05) by the type of muscle.All mean ultimate pH values, which ranged from 5.70 (LD of L) to 5.78 (SM of LW), were in the characteristic range for pork (5.3-5.8;Smulders et al. 1992, Honikel 1999).As expected (Table 2), in the present study the pH 45min was significantly positively correlated with the pH 24h (r=0.42 for LW and r=0.48 for L, p<0.001).

Incidence of different technological quality classes of pork
According to criteria for initial pH (pH 45min <6.0), in this study, the percentage of potential PSE pork was 14.8% for SM of LW, 28.4% for LD of LW, 24.1% for SM of L and 27.7% for LD of L (Table 3).Overall, based on criteria for pH 45min , 23.8% of investigated muscles were potentially classified as PSE.In addition, the percentage of DFD pork with pH 24h ≥6.0 (Kauffman et al. 1992, Warner et al. 1997, Joo et al. 2000a2000b, O'Neill et al. 2003) was 13.6% for SM of LW, 14.8% for LD of LW, 12.0% for SM of L, and 15.7% for LD of L. Overall, based on criteria for pH 24h , 14.0% of investigated muscles were classified as DFD.
In this study, the colour of SM and LD muscles was defined as pale when ultimate CIEL*>50, reddish-pink when ultimate CIEL*=43-50 or dark when ultimate CIEL*<43 (Table 3).The highest incidence of the pale (43.4%) and dark (10.8%) colour and lowest incidence of reddish-pink (45.8%) colour was found in LD muscles of L breed.The incidence of pale, reddish-pink and dark colour in other three investigated groups of muscles were similar, i.e. the incidence of pale colour ranged from 29.6% (SM of LW) to 33.3% (LD of LW), reddish-pink ranged from 60.5% (LD of LW) to 62.7% (SM of L) and dark ranged from 6.2% (LD of LW) to 8.6% (SM of LW).Overall, based on criteria for CIEL*, 34.1% of investigated muscles were classified as pale pork (CIEL*>50), 57.6% as reddish-pink pork (CIEL*= 43-50), and 8.2% as dark pork (CIEL*<43).
Combining criteria for pH 45min and CIEL* value to define pork quality of each individual SM and LD muscle, it was calculated that 62.8% of muscles with pH 45min <6.0 had CIEL* value higher than 50 (calculated data are not shown).Also, the incidence of pale (CIEL*>50) colour in all investigated groups of SM and LD muscles was higher than the incidence of the initial pH below 6.0 (Table 3).In addition, combining criteria for pH 24h and CIEL* value to define pork quality on each individual SM and LD muscle, it was calculated that 34.8% of muscles with pH 24h ≥6.0 had CIEL* value lower than 43 (calculated data are not shown).Also, the incidence of dark (CIEL*<43) colour in all investigated groups of SM and LD muscles was lower than the incidence of the ultimate pH above 6.0 (Table 3).
In this study, according to WHC, SM and LD muscles were defined as exudative when M/T value <0.35, non-exudative when M/T value between 0.35-0.45or dry when M/T value >0.45 (Table 3).The incidence of non-exudative pork in SM and LD muscles from both breeds was very similar (53.1% of SM : 37.0% of LD from LW versus 51.8% of SM : 37.3% of LD from L).Compared to incidence of non-exudative pork, the incidence of exudative pork in SM muscles was 34.8% lower for LW and 13.9% for L, while the incidence of exudative pork in LD muscles was 60.3% higher for LW and 64.6% for L. The highest incidence of dry pork was found in SM muscles of LW breed (12.3%), and the lowest in LD muscles of L breed (1.2%).Overall, based on criteria for M/T value, 50.0% of investigated muscles were classified as exudative pork (M/T<0.35),44.8% as non-exudative pork (M/T=0.35-0.45)and 5.2% as dry pork (M/T>0.45).
Combining criteria for pH 45min and WHC to define pork quality of each individual SM and LD muscles, it was calculated that 71.8% of muscles with pH 45min <6.0 had M/T value lower than 0.35 (calculated data are not shown).
Further, the incidence of exudative pork (M/T<0.35) in all investigated groups of SM and LD muscles was higher than the incidence of the initial pH below 6.0 (Table 3).In addition, combining criteria for pH 24h and WHC to define pork quality of each individual SM and LD muscles it was calculated that 13.0% of muscles with pH 24h ≥6.0 had M/T value higher than 0.45 (calculated data are not shown).Also, the incidence of dry pork (M/T>0.45) in all investigated groups of SM and LD muscles was lower to the incidence of the ultimate pH above 6.0 (Table 3).
The results of this study are in accordance with the conclusion of Bendall andSwatland (1988), van Laack et al. (1994), Joo et al. (1999) and Joo et al. (2000aJoo et al. ( 2000b) that the initial and ultimate pH values were not always a reliable predictor for ultimate pork quality and its relation to both color and WHC of pork muscle should be more carefully investigated, although it is evident that pH values are significantly related to both colour and WHC (Table 2).
The detection of different pork quality is an important issue for meat industry in order to reduce economic losses and to proportionate the best destination to fresh meat.Generally, PSE/DFD meat is identified on the base of pH value, colour (CIEL* value) and WHC.While in some cases PSE/DFD meat is identified only on the base of colour (CIEL* value) and WHC (van Laack et al. 1994, Joo et al. 1999, Joo et al. 2000a2000b).
With these seven categories of pork quality (Table 3) it is evident that although colour and WHC are significantly related (Table 2) their specific biochemical properties vary independently.This results are is in accordance with the conclusions of Bendall andSwatland (1988), van Laack et al. (1994), Joo et al. (1999) and Joo et al. (2000aJoo et al. ( 2000b)).The results of this study show high percentage of pale meat (PE + PN = 34.1%)and exudative meat (PE + RE = 50.0%),i.e. the high percentage of pale and/or exudative meat (PE + PN + RE = 60.7%) in SM and LD muscles (Table 3).Similar incidences of PSE, PFN and RSE pork were obtained in other studies (Kauffman et al. 1992, van Laack et al. 1994, Joo et al. 2000a, O'Neill et al. 2003, van de Perre et al. 2010).It has been estimated that as much as 50% or more of the pork produced has unacceptably high purge or drip loss (Kauffman et al. 1992, Huff-Lonergan andLonergan 2005).

Composition of pork
No significant (p>0.05)interaction effect between breed and muscle was found for composition (Table 4).Also, moisture, protein, total fat and total ash content were neither affected by the breed nor by the type of muscle.
The mean moisture content ranged from 75.63 (LD of L) to 75.72% (SM of L), and the mean protein content ranged from 21.62 (SM of L) to 21.79% (LD of LW).Furthermore, the mean total fat content ranged from 1.35 (SM of LW) to 1.48% (LD of L), and the mean total ash content ranged from 1.12 (LD of LW and L) to 1.14% (SM of LW  5), in the present study, moisture content was significantly negatively correlated with protein (r=-0.74,for LW, p<0.001; r=-0.43, for L, p<0.001), total fat (r=-0.35,for LW, p<0.01; r=-0.38, for L, p<0.01) and total ash content (r=-0.44,for LW, p<0.001; r=-0.23, for L, p<0.05).Additionally, protein content was significantly negatively correlated with total fat content (r=-0.30,for LW, p<0.01; r=-0.60, for L, p<0.001).According to Keeton and Eddy (2004) the content of moisture, protein and ash decrease with increasing amounts of fat in the tissues.

Conclusion
Investigating the effect of pig breed (Large White and Landrace) in combination with muscle (M.semimembranosus and M. longissimus dorsi) on technological quality and composition of pork, the following was concluded: (i) T 24h was significantly (p<0.001)influenced by breed, (ii) T 45min , T 24h , pH 45min , and WHC (M/T value) were significantly (p<0.01 or <0.001) influenced by the type of muscle, (iii) the pH values were not a reliable predictor for ultimate pork quality, (iv) based on the lightness (CIEL* value) and M/T value (WHC) M. semimembranosus and M. longissimus dorsi were classified into seven quality classes: PE (pale and exudative, 23.5%), PN (pale and non-exudative, 10.7%), RE (reddish-pink and exudative, 26.5%), RN (reddish-pink and non-exudative, 27.7%), RD (reddish-pink and dry, 3.4%), DN (dark and non-exudative, 6.4%), and DD (dark and dry, 1.8%) pork, (v) composition was in the characteristic range for modern lean pigs.
of the pressed meat film; T = wet area on the filter paper.

Table 1 .
Mean values (±SD) of the technological quality of M. semimembranosus (SM) and M. longissimus dorsi (LD) of Large White (LW) and Landrace (L) pigs.
abc indicates significant difference within raw at p<0.05, opq indicates significant difference within raw at p<0.01, vwx indicates significant difference within raw at p<0.001.M = area of the pressed meat film; T = wet area on the filter paper.
Joo et al. 1999, Joo et al. 2000a2000b, Tomović et al. 2008, Tomović et al. 2013)n values were found in LD and SM muscles of L breed.These values were 49.31 for the LD and 47.99 for the SM muscle.According to the mean values for lightness (CIEL* value), the colour of all investigated groups of SM and LD muscles represent normal meat quality (reddish-pink colour: CIEL*=43-50,Joo et al. 1999, Joo et al. 2000a2000b, Tomović et al. 2008, Tomović et al. 2013).Furthermore, the mean CIEa* values (redness) ranged from 10.12 (LD of L) to 11.04 (SM of L).Almost identical mean CIEb* values were determined in all investigated groups of muscles.The mean CIEb* value ranged from 6.31 (LD of LW) to 6.78 (SM of L).
Hofmann et al. 1982)significantly influenced (p<0.001) by the type of muscle (Table1).For both breeds, SM muscles had significantly better WHC (M/T=0.38 for LW and 0.36 for L, a bigger M/T ratio indicating a better WHC) than LD muscles (M/T=0.33,forbothbreeds).According to the mean M/T values, the WHC of both SM groups of muscles represent normal meat quality (non-exudative meat: M/T=0.35-0.45,Hofmannetal.1982), while both LD groups of muscles represent poor pork quality (exudative meat: M/T<0.35,Hofmannetal. 1982).

Table 2 .
Overall correlation coefficients (r) among technological quality parameters of Large White (LW) and Landrace (L) pigs.
***indicates significant difference at p<0.001.M = area of the pressed meat film; T = wet area on the filter paper.

Table 3 .
Incidence of different M. semimembranosus ). Composition of all investigated groups of SM and LD muscles analyzed in the present study were in agreement with the values reported for pork (Lawrie and Ledward 2006, Australia: Greenfield et al. 2009, Denmark: National Food Institute 2009, Finland: National Institute for Health and Welfare 2009, Italy: INRAN 2009, USA: The US Department of Agriculture's 2011).As expected (Table

Table 5 .
Overall correlation coefficients (r) among pork composition of Large White (LW) and Landrace (L) pigs.