Genotype effect on the palatability of the pork loin

 

 Introduction

The consumption of meat and meat products decreased in the last years in Hungary; however the rate of pork consumption is still important. In the year 2003 the total average meat consumption was 68.6 kg per capita. In the same year, as far as the whole meat market is concerned first was the poultry consumption (33.2 kg per capita per year), and the second was the pork consumption (27.1 kg per capita per year). The average beef consumption reached 4.1 kg while the fish purchase was only 3.4 kg. Pork industry decreased 2.7 per cent whilst pork export increased with 8.3 per cent.

Mainly the lean and the quality of muscle affect the pork quality - according to the actual market and consumer requirement (Andersen, 2000). However, consumers are to take into consideration some other characteristics of pork, such as color, smell and intramuscular fat content. Tenderness was also found as important quality attribute to consumers (Enfalt et al. 1997). Tenderness is not considerable at the purchase its measure can be tasted only as a result of some culinary procedures.

There are two main possibilities to measure tenderness: either test panel with subjective error or objective mechanical measurement. During test panel meat is appreciated by panelist's impression during chewing. The equipment for mechanical measurement is established to simulate chewing process. The result from mechanical measurement is the shear force. The palatability of the meat is determined as the average of the shear force (kg) of the sample cores taken from the slice. The shear force of the meat is the maximum force required to shear the core. To measure shear force the standard Warner-Bratzler (WB) method is used (Wheeler et al., 1995).

Several studies were carried out to determine the relationship between shear force (palatability) and tenderness. In a study dealt with beef, showed that these two parameters had a high, negative correlation (r= -0.6 to -0.85) (Pearson, 1963), which means lower shear force means better palatability. Eikelenboom et al. (1996) found similar correlation (r= -0.67). Other researcher described much higher differences (r= -0.32 to -0.94) in the coefficients of correlation between beef tenderness and palatability (Szczesniak, 1968).

Numerous factors before slaughtering have influence on the pork tenderness, such as genetic factors (species, breed, sex, stress-resistance, intramuscular fat content, etc.) or nutrition. There are additional factors in the slaughtering such as chilling technology, slaughter weight, suspension method etc. Many studies were established to determine the mode of action and importance of the above mentioned parameters which are affecting palatability. Various and sometimes controversy results came up to light depending on the species breed of the examined animal.

There has been a controversy in the literature with regard the effect of intramuscular fat content of pork on palatability. Some of the studies suggest positive relation (DeVol et al., 1988, Eikelenboom and Hoving-Bolink, 1994, Goodwin and Burroughs, 1995), however others did not find any significant correlation between intramuscular fat content and tenderness (Rhodes, 1970, Skelley et al., 1973, Göransson et al., 1992).

Circumstances of the age at slaughtering and chilling conditions (temperature, velocity) have measurable effects on myofibril toughness. Bouton et al. (1975) studied the mechanical properties of stretched, normal and cold-shortened muscles, using WB shear test and tensile measurements. They found that increased sarcomer lenght of muscle in raw meat significantly involved in the higher shear force values, nevertheless this affect is terminated when meat is cooked above 60 ºC. Locker and Hagyard (1963) were the first who detected that m. sternomandibularis showed the lowest (10 %) shortening at 15-20 °C.

The velocity and the chilling process affect the palatability of the meat, as well. In a study, dealt with porcine m. longissimus lumborum, pointed out that ultra-rapid chilling parallel with high velocity (4m/s) increase shear force value (van der Wal, 1994).

Medium-lean genotype and high-lean genotype were compared by different weight of slaughter (104 kg and 127 kg). Results from this study suggested that high-lean genotype barrows should be slaughtered at lighter weight (104 kg), because higher slaughter weight (127 kg) involves higher shear force. Medium-lean genotype pigs can be fattened up to 104 kg or 127 kg, because it does not affect remarkably quality-related traits (Unruh, 1996). In the same slaughter weight (104 kg or 127 kg) medium-lean genotype had lower WB shear force then high-lean genotype.

Several experiments were carried out to detect the differences of the lean shear force among pig breeds. As far as results are concerned controversy exists in the literature, as well. According to Frank et al. (1997) there are statistical differences among different pig genotypes: Yorkshire × Landrace cross, European Terminal Sire derived. Although neither Jukna et al. (2005) nor Faucitano et al. (2004) found any significant difference among modern breeds and hybrids. Jukna et al. (2005) investigated Litvanian White, Large White, Landrace and Yorkshire while Faucitano et al. (2005) studied Large White, Meishan derived Dam Line and Syntethic genex 3000.

Pork samples of 91 pigs were investigated to determine the effect of genotype and cooking loss of palatability. Pigs were grown in official fattening performance and carcass yield test till 105±2 kg, in a Central Testing Station of the National Institute of Agricultural and Quality Controll in Atkár. Pigs were raised, fed and slaughtered under same conditions. The samples were taken from six typical Hungarian breeds and hybrids: Hungarian Large White (n=16), Dalland (n=19), Pannon Hybrid (n=16), Hungahib 39 (n=14), Közép-Tiszai Hybrid (n=19), and Swallow-Belly Mangalitza (Mangalitza) (n=7).

After slaughtering carcasses were chilled conventionally, at 6 ºC for 24 hours. At 24 hours post-mortem carcasses were ribbed at the 13^th and 14^th rib. Samples with 2.5 cm width were taken from m. longissimus dorsi (MLD) from the same anatomical point. Samples were stored in freezer (-20ºC) till the analysis. Those were thawed at 4 ºC for 12-14 hours, Chops were weighted and grilled in a contact grill machine (Cucina HD 2430, Philips, Germany) till 72 ºC internal temperature which was determined by contact thermometer (TESTO 926, TESTO AG., Germany). After a 1.5 h cooling period at room temperature samples were re-weighted. About six 1.27 cm diameter cores were taken from each slice except chops from Mangalitza loin. Only three cores were taken from Magalitza because of the small size of loin. Cores were removed with a mechanical coring device parallel to muscle fibers. Shear force was measured by WB shear blade attached to TA.XT2 Plus texture analyzer (Stable Micro System Ltd., USA). The percent of cooking loss was calculated: (thawed chop weight - cooked chop weight)/thawed chop weight * 100.

Statistical analysis was performed with SPSS 14.0 software, using one-factor ANOVA and LSD methods, furthermore two-tailed correlation was also calculated.. The statistical significance level was accepted at 95%.

Palatability results are given in Figure 1. As shown, Pannon Hybrid (3.17±0.88 kg) and Hungarian Large White (3,17±0,74 kg) showed the highest, and Mangalitza (2.54±0.58 kg) the lowest shear force. Palatability of modern breeds and hybrids showed very similar values, about 3 kg.

 

Figure 1: Average and standard deviation of shear force values per studied genotypes

 

 

The statistic proof of the differences of shear force per genotypes is affected by methods ANOVA and LSD. The results from ANOVA test (not shown) indicated that genotype effect palatability in porcine loin. LSD test related to differences measured per genotypes gave that there was no significant statistic difference between the values of the shearing force of the modern breeds and hybrids involved in the analysis with the exception of shearing force in case of Mangalitza and the other examined genotypes (Table 1.).

Table 1. Least Significant Differences among the shear force of MLD per studied genotypes

     NS: no significant, **: P≤ 0.01, ***: P≤ 0.001

The lowest cooking loss was observed at the average of the Mangalitza loin with a value of about 14% (Figure 2).

 

Figure 2. Average and standard deviation of cooking loss values per studied genotypes

 

 

The statistical proof of the differences of cooking loss per genotypes calculated by the methods ANOVA and LSD. The results from ANOVA test (data not shown) indicated that genotype effect cooking loss in porcine loin. Results of the LSD test are shown in the Table 2.

 

Table 2. Least Significant Differences among the cooking loss of MLD per studied genotypes

  NS: no significant, *: P≤ 0.05, **: P≤ 0.01, ***: P≤ 0.001

Based on these results, there are statistical differences among the genotypes concerning the average cooking loss. As shown in Figure 2, and proved by statistical analyses according to the average cooking loss the genotypes could be ordered into three loss categories.

Mangalitza and Hungarian Large White showed the lowest cooking loss with a value of about 14-15%. There was no significant difference between these values, however those significantly differ from other genotypes were investigated.

Pannon Hybrid, Közép-Tiszai Hybrid and Dalland had a cooking loss of about 16-17 %. No significant difference could be observed among these values although those had statistically proved difference, as compared to the other three genotypes were investigated.

Hungahib 39 had the highest value in cooking loss - >18% - which significantly differs from the data of all other genotypes.

The correlation analysis showed a positive, moderate (r=0.40) relation between palatability and cooking loss which can be considered proved by statistical analysis (p≤ 0.001).

According to the correlation of tenderness and palatability which was established by Pearson (1963) and the results of present study suggest that loin from Mangalitza has more tenderness than loin from other breeds and hybrids, which were investigated. Modern breeds and hybrids showed similar palatability without any significant difference among them. Despite of the low number of cores (3 cores per MLD slice) of Mangalitza loin, this number of repetition represented the whole surface. Furthermore the results of Wheeler et al. (1996) proved with this number of cores taken from the same slice a high repeatability (r=0.70) can be reached.

Although no international standard categories of palatability in pork were established till now, Van Oeckel et al. (1999a) evaluated a threshold on the basis of their own study. The maximum of 3 kg shear force for tender porcine loin is suggested; therefore the loin of Mangalitza (2.54 kg) and Közép-Tiszai Hybrid (2.98 kg) are tender. However the other examined genotypes have slightly higher shear force values, it can be consider them also as acceptable tender meat.

The cooking loss in the examined breeds and hybrids are influenced by genotype as showed by the statistical analysis (p≤ 0.001). There are relatively higher cooking loss values can be found in the literature. For instance Unruh et al. (1996) carried out a similar investigation for detecting cooking loss in medium- and high-lean genotype, and they found higher percentage (20-28%). Furthermore Brewer et al. (2002) studied other breeds (Berkshire, Hampshire, Pietrain, Duroc and a synthetic line) and they also found slightly higher cooking loss (18-22 %). In their investigation Duroc showed the lowest cooking loss among the different genotypes.

Palatability and cooking loss show moderate and positive but significant correlation r=0.40 (p≤0.001). Likewise De Smet et al. (1998) found moderate, significant correlation between these two meat quality parameters (r=0.43).

From the outstanding results of shear force and cooking loss of Mangalitza, this loin can be suggested to consume as a steak.

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