A. Talmant

Influence of intramuscular fat content on the quality of pig meat — 1. Composition of the lipid fraction and sensory characteristics of m. longissimus lumborum

The present study is part of a project which aimed to examine the influence of intramuscular fat (IMF) content on the sensory attributes and consumer acceptability of pork. Two experiments were conducted to evaluate the influence of IMF level on the composition of the lipid fraction and on the sensory qualities of muscle longissimus lumborum (LL). Each of these experiments used 32 castrated male pigs selected after slaughter either from 125 Duroc×Landrace (Experiment 1) or 102 Tia Meslan×Landrace (Experiment 2) crossbred animals, and showing large variability in LL IMF content: from <1.5 to >3.5% in Experiment 1 and from 1.25 to 3.25% in Experiment 2. Results from lipid analyses indicate that in both experiments, an increase in IMF content is almost entirely reflected by an increase in the triglycerides content of the muscle. In Experiment 2, higher IMF content was associated with higher free fatty acids. Marbling score was significantly affected by IMF level in Experiment 1 but not in Experiment 2. In Experiment 1, a trend towards a favourable effect of high IMF levels on flavour (p=0.09) and tenderness (p=0.055) was observed. In experiment 2, increased IMF level was associated with significantly higher juiciness and flavour scores. The results from the present study indicate that the variability in IMF level of LL muscle was almost entirely due to the variability in triglyceride contents. Favourable effects of increased IMF levels on the sensory attributes of pork were demonstrated in both experiments using different types of animals, but the nature and the magnitude of these effects depended on the experiment considered.

Influence of intramuscular fat content on the quality of pig meat : 2. Consumer acceptability of m. longissimus lumborum

The present study is part of a project which aimed to examine the influence of intramuscular fat (IMF) content on sensory attributes and consumer acceptability of pork. Two experiments were conducted to evaluate consumer acceptability of pork chops with varying IMF level in muscle Longissimus lumborum (LL). Each experiment used 32 castrated male pigs selected after slaughter either from 125 Duroc × Landrace (Experiment 1) or 102 Tia Meslan × Landrace (Experiment 2) crossbred animals, and showing large variability in LL IMF content: from <1.5 to >3.5% in Experiment 1 and from 1.25 to 3.25% in Experiment 2. A group of 56 consumers evaluated various items on rib-eye (LL muscle trimmed of backfat) (Experiment 1) and on entire chops trimmed of backfat (Experiment 2). Data from Experiment 1 indicate that an increase in IMF level is associated with an increase in visual perception of fat and a corresponding decrease in the willingness to eat and purchase the meat, when expressed before tasting. The latter effect disappeared after the consumers had tasted the meat, probably due to a positive effect of increase IMF, up to 3.5%, on the perception of texture and taste. In Experiment 2, where entire chops were evaluated, the perception of visible fat was not affected by IMF level, probably due to the lack of variation in the level of intermuscular fat between the four IMF groups. The willingness to eat and purchase the meat were unaffected by IMF level, whereas the perception of texture and taste was enhanced with increased IMF levels up to 3.25%. The present data suggest that the acceptability of pork may be improved by increasing IMF level but: (1) this effect disappeared for IMF levels higher than 3.5%, which are associated with a high risk of meat rejection due to visible fat and (2) the positive effect of increased IMF probably holds true as long as it is not associated with an increase in the level of intermuscular fat.

Calpains and calpastatin distribution in bovine, porcine and ovine skeletal muscles.

The concentration of calpain II and calpastatin was determined in various beef, lamb and pork muscles showing very different metabolic and contractile types as assessed by measurement of lactic dehydrogenase (LDH), citrate synthetase (CS) and ATPase activities. The calpain II: calpastatin ratio, which is a good index of the efficiency of this proteolytic system, was also determined. A species comparison revealed that while calpastatin level was lowest in pork, the ratio of calpain II to calpastatin was highest in this species. For both determinations, lamb was intermediate followed by beef. Conversely, the amount of calpain II was very similar in the three species. In beef and pork, calpain II content decreased as muscle ATPase and LDH activities rose; and conversely increased with CS activity; whereas in lamb, the amount of this enzyme was highest in red muscles regardless of their speed of contraction. Except for masseter muscle, a comparable distribution was observed for calpastatin in beef and pork muscles. In lamb, the calplastatin concentration was highest in slow-twitch red muscles, intermediate in fast-twitch red muscles and lowest in fast-twitch white muscles. Variability of the calpain II: calpastatin ratio with muscle ATPase, LDH and CS activities appeared to be both muscle and species dependent. As results for masseter muscle are rather unexpected, especially in beef and lamb, this muscle was considered separately. The present findings are discussed with regard to the conditioning rate of meat from different species and, within one species, from different muscles. It was concluded that the conditioning rate may be correlated positively to calpain II: calpastatin ratio and negatively to calpastatin content. In contrast, no relationship seems to exist between meat ageing rate and calpain concentrations.

Chemical and structural changes in dry-cured hams (Bayonne hams) during processing and effects of the dehairing technique

Pigs of similar genetic backgrounds and feeding regimes were slaughtered in two abattoirs, one carrying out dehairing by scalding and the other by singeing. One ham from each of 80 carcasses was retained. Sixteen fresh hams (8 from each dehairing technique) were used for analysis while 64 hams were processed into dry-cured ham. Sixteen hams (8 from each dehairing technique) were taken for analysis at end of salting (day 14), end of rest (day 78), mid-processing (day 127) and end of processing (day 251). During processing, the water content of all muscles decreased while the salt content increased. The salt concentration in muscle water tended to equalize in all muscles. The nitrogen content of desalted dry matter (i.e. dry muscle tissue) decreased in both Biceps femoris and Semimembranosus. The content of every free amino acid increased with time, except for taurine and glutamine. Electrophoresis of the low ionic strength-soluble fractions showed all protein bands decreased during processing. Electrophoresis of the myofibrillar fractions indicated changes in all bands except actin (42kDa). These changes were more marked in the Semimembranosus than the Biceps femoris in the earlier processing steps. Ultrastructural changes were more marked in Semimembranosus than Biceps femoris. Hardness and chewiness increased in both muscles during the first half of processing then returned to values close to the initial ones in Semimembranosus but changed little in Biceps femoris. The scalded hams lost more weight than the singed ones during processing. The salt content was higher in scalded hams. Water-soluble nitrogen and NPN were higher in singed hams at the end of processing. The scalded hams were saltier and pungent. They had more pronounced aromas of dry ham, rancidity and hazelnut, and less aroma of fresh meat. Their texture was drier and less mellow.

Comparison between the three porcine RN genotypes for growth, carcass composition and meat quality traits

A three-step experimental design has been carried out to add evidence about the existence of the RN gene, with two segregating alleles RN- and rn+, having major effects on meat quality in pigs, to estimate its effects on production traits and to map the RN locus. In the present article, the experimental population and sampling procedures are described and discussed, and effects of the three RN genotypes on growth and carcass traits are presented. The RN genotype had no major effect on growth performance and killing out percentage. Variables pertaining to carcass tissue composition showed that the RN- allele is associated with leaner carcasses (about 1 s.d. effect without dominance for back fat thickness, 0.5 s.d. effect with dominance for weights of joints). Muscle glycolytic potential (GP) was considerably higher in RN- carriers, with a maximum of a 6.85 s.d. effect for the live longissimus muscle GP. Physico-chemical characteristics of meat were also influenced by the RN genotype in a dominant way, ultimate pH differing by about 2 s.d. between homozygous genotypes and meat colour by about 1 s.d. Technological quality was also affected, with a 1 s.d. decrease in technological yield for RN- carriers. The RN genotype had a more limited effect on eating quality. On the whole, the identity between the acid meat condition and the RN- allele effect is clearly demonstrated (higher muscle GP, lower ultimate pH, paler meat and lower protein content), and the unfavourable relationship between GP and carcass lean to fat ratio is confirmed.

31P NMR study of post mortem changes in pig muscle

The rate and the extent of post mortem pH changes in pig muscle largely determine pork quality. Fast pH fall combined with low ultimate pH leads to pale soft exudative (PSE) meat; high ultimate pH leads to dark firm dry (DFD) meat. Post mortem metabolism was studied in pig muscle using(31)P NMR. Fifteen pigs, i.e. 7 Large White pigs and 8 Pietrain pigs, were used. Five pigs of each breed were slaughtered, taking care to minimize preslaughter stress. The other pigs (3 Large Whites and 2 Pietrains) were injected with 0·1 mg adrenaline per kg liveweight before slaughter, in order to increase meat ultimate pH. All the animals were killed by electronarcosis and exsanguination. Three of the adrenaline-treated pigs (1 Large White and 2 Pietrains) gave meat with ultimate pH above 6 (DFD meat). The pigs with normal muscle ultimate pH, i.e. 6 Large Whites and 6 Pietrains, had very variable rates of post mortem muscle metabolism (pH at 30 min after slaughter: 6·17-6·85 in Large Whites; 6·04-6·23 in Pietrains). The relationships between pH and ATP changes were similar in all pigs showing normal muscle ultimate pH, whereas ATP disappeared at a high pH value (on average pH 6·4) in pigs with high ultimate pH. The course of post mortem biochemical changes in a given animal could be predicted rather well by examination of a single(31)P NMR spectrum obtained around 30 min after death. At this time, muscle with a low rate of metabolism simultaneously showed medium to high pH, high ATP content (4-6·8 μmol/g) and rather low Pi content (6-14 μmol/g); muscle with a fast rate of metabolism (PSE-prone muscle) had low pH, low to medium ATP content (1·1-4 μmol/g) and generally high phosphomonoester (PME) content (9-23 μmol/g); muscle with high ultimate pH (DFD-prone muscle) had high pH, low PME content (4-8 μmol/g) and high Pi content (22-27 μmol/g).

The effect of RN gene on yields and quality of extended cooked cured hams

The effect of RN(-) allele on minimally processed hams as manufactured in France is now well established. In the present study, meat from 35 rn(+) and 51 RN(-) pigs on the basis of their glycolytic potential (GP) was used to assess the effect of the RN(-) allele on a model system and on yields and quality of cooked hams cured with a 40% brine addition containing the most common meat processing ingredients. Quality parameters were also measured on the fresh loins and a glucose assay was carried out on meat juice from both hams and longissimus dorsi (LD) muscles. With respect to GP, glucose content of LD juice gave the best prediction of RN status with 10% misclassified samples in comparison with 20% as determined from ham juice. Lower pH and higher drip loss and L* values were measured on the LD from RN(-) pigs (p⩽0.001). Technological yields obtained on the model system and on extended cooked cured hams were lower in meat from RN(-) pigs (p⩽0.001). However, pH value was more influential on the yield of the model system while protein content and particularly the amount of extractable sarcoplasmic proteins were more determinative on cured hams probably due to the effect of tumbling. All other quality traits were lower in hams from RN(-) pigs (p⩽0.001). Meat from RN(-) pigs can be used for the manufacture of extended cured products, but under similar processing technologies, quality and yield will remain inferior to what would provide pork of normal quality.

Muscle glycogen level and meat quality in pigs of different halothane genotypes

The halothane genotype of 22 Polish landrace pigs was determined using halothane test and blood typing. Eight homozygous normal (NN), eight hetero-zygotes (Nn) and six homozygous recessive (nn) were identified. The levels of glycogen and lactate were measured in biopsy samples taken from the longissimus lumborum using a shot biopsy technique. pH (pH(1)) and IMP/ATP ratio (R) were determined at 30 min after slaughter, while pH, meat colour and water holding capacity were determined on the day after slaughter. The halothane genotype did not affect intra vitam glycogen level. The nn pigs had a higher R value and lower pH(1) than both Nn and NN animals. Heterozygous animals were intermediate between both homo-zygotes for biopsy lactate level and meat colour. The lactate content of biopsy samples was significantly correlated with pH(1) (r = -0·68; P < 0·01), R (r = 0·68; P < 0·01), meat colour (r = 0·57; P < 0·01) and water holding capacity (r = 0·45; P · 0·05).

Evaluation of halothane sensitivity and prediction of post-mortem muscle metabolism in pigs from a muscle biopsy using 31P NMR spectroscopy

Phosphorus nuclear magnetic resonance ((31)P NMR) measurements were made on biopsy samples from pig muscles. Two experiments were performed, one in France and one in Czechoslovakia. In experiment 1, the muscle samples were obtained by surgery from the Biceps femoris muscle of 10 pigs with various genetic types (5 Large White, 1 Large White × Landrace, 4 Pietrains). In experiment 2, the muscle samples were obtained by shot biopsy from the Longissimus dorsi muscle of 11 Belgian Landrace × Duroc pigs, of which 6 were halothane-negative and 5 halothane-positive. The pigs were slaughtered by electrostunning and exsanguination respectively 3 weeks and 1 week after the biopsy, and meat quality traits (pH(1), reflectance and water holding capacity) were determined. The changes in adenosine triphosphate (ATP), creatine phosphate (CP), inorganic phosphate (P(i)) and pH, as deduced from NMR, were faster in Pietrains than in Large Whites, and in halothane-positive than in halothane-negative pigs. The value of the CP/P(i) ratio at 40 min after taking biopsy allowed discrimination between halothane-positive and halothane-negative pigs. The values of pH, creatine phosphate and adenosine triphosphate, as measured at definite times on the biopsies, were correlated with the rate of post-mortem metabolism (r approx 0·8) and with meat quality traits. (31)P NMR measurements combined with a rapid and efficient biopsy technique appear as an alternative tool for assessment of both halothane sensitivity and prediction of meat quality in pigs.

Meat quality as influenced by halothane sensitivity and ultimate pH in three porcine breeds

Abstract The technological qualities of the meat from 45 Large White (LW), 42 Pietrain (P) and 58 Belgian Landrace (BL) pigs were assessed by criteria measured on fresh meat and cooked Paris ham processing ability. There were 9 halothane-negative (HN) and 33 halothane-positive (HP) animals among P pigs and 16 HN and 42 HP among BL pigs, whereas all LW pigs were HN. Glycolytic potential and enzyme activities of 3 muscles of various metabolic types were measured on a subsample of 101 pigs. As a general rule, the traits under study were much more affected by breed than by halothane phenotype. The LW breed, free from halothane sensitivity, exhibits a relatively slow pH fall and gives meat with the most satisfying technological qualities. The P breed combines a fast pH fall (owing to the high incidence of HP animals) with a rather low ultimate pH (presumably owing to a slightly higher muscle glycolytic potential). Since the post-mortem acidification of muscle is both rapid and extensive, the meat from P pigs presents the worst technological qualities. In the BL breed, the unfavourable effects of halothane sensitivity are counter-balanced to some extent by a higher level of ultimate pH compared with the 2 other breeds in most muscles studied: BL pigs are consequently intermediate between LW and P pigs in meat quality.