Xavier Fernandez

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.

Skeletal muscle fibres as factors for pork quality

Interaction between muscle fibres, perimortem energy metabolism and different environmental factors determine postmortem transformation from muscle to meat. Muscle fibres are not static structures, but easily adapt to altered functional demands, hormonal signals, and changes in neural input. Their dynamic nature makes it difficult to categorise them into distinct units. It must be realised that some properties may change without affecting others or without changing histochemical appearance of a given fibre such as species specificity, developmental or adaptive processes or pathological conditions, and that transient fibre types exist. Therefore, a distinction between specific types must strictly refer to the method that has been used for the typing. Theoretically, there will be at least as many fibre types as there are motor units in a muscle, and within a muscle a fibre type may show a continuum of structural and functional properties which overlap with other fibre types. Histochemical and biochemical properties of a muscle, such as fibre type composition, fibre area, oxidative and glycolytic capacities, and glycogen and lipid contents, are factors that have been found to influence meat quality. An important factor for post-mortem changes and meat quality is the metabolic response that takes place in the different fibre types pre-slaughter. Selection for leaner pigs and for a higher proportion of large muscle fibres, especially of type IIB, can result in poor capillarisation and consequently an insufficient delivery of oxygen and substrates and elimination of end products, such as CO2 and lactate, and thereby a reduced pork quality. In the future, fibre types in pig muscle will probably be investigated with more advanced and sensitive techniques, which makes it is possible to look at adaptations in different contractile, sarcoplasmic proteins as well as other muscle proteins that are of importance for cell differentiation and muscle cell metabolism. Furthermore, single fibre dissection and quantitative biochemical analyses may increase the knowledge about metabolic and contractile properties of the muscle fibre. The literature indicates possibilities to include muscle fibre characteristics in breeding schemes for improved meat quality, while preserving optimal production traits. In order to use muscle fibre characteristics in a beneficial way for future breeding programmes, further investigations are needed to better understand the physiological mechanisms. Selection experiments based on biochemical and histochemical characteristics determined in biopsies or otherwise and study of the correlated selection responses, may possibly provide better tools to study these relationships.

Nutritional and hormonal regulation of energy metabolism in skeletal muscles of meat-producing animals

In meat-producing animals, skeletal muscle is a tissue of major economic importance. Energy metabolism of skeletal muscle should be assessed in relation to its main physiological functions which are growth as well as posture, physical activity and thermogenesis. These functions have specific energy requirements which may entail competition in the utilization of energy-yielding nutrients, and modify the efficiency of ATP production and use. In this review, the energy requirements of muscles will be presented as well as the main metabolic pathways involved in the utilization of carbohydrate and lipids for energy supply and deposition. Regulation of metabolism will also be tackled in relation to the major physiological functions of skeletal muscle in various domestic species. Special focus will be given to the energy metabolism of growing muscle and its interactions with meat quality. The question will be asked whether the optimization of the efficiency of ATP production and utilization in muscle for nitrogen retention is compatible with an improvement of meat quality (as partly determined by glycogen and lipid deposition)? For this purpose, the interactions between muscle carbohydrate, lipid and protein metabolism will be reviewed.

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.

Agonistic behavior, plasma stress hormones, and metabolites in response to dyadic encounters in domestic pigs: Interrelationships and effect of dominance status

Agonistic behavior, neuroendocrine, and plasma metabolite changes were studied in 16 domestic Large White pigs (100 +/- 5 kg) submitted to dyadic encounters (30 min) in a neutral environment. The animals had been housed individually for 2 months prior to the experiment. Aggressive and submissive behaviors were recorded for each animal during the encounter. Surgically implanted catheters allowed collection of blood samples at selected times. Plasma levels of cortisol, catecholamines, and metabolites were determined and compared with data obtained on eight control pigs kept under resting conditions. Resting plasma cortisol levels tended to be higher in subordinate compared to dominant subjects, suggesting a relationship between baseline adrenocortical activity and submissive behavior during aggressive encounters in domestic pigs. Plasma norepinephrine and epinephrine levels did not differ between dominants and subordinates, but they were linearly correlated with aggressive behaviors. Metabolic state changed in response to the encounters, as evidenced by increased plasma levels of free fatty acids, glucose, and lactate at the end of the dyads. Dominance status did not significantly affect plasma metabolite levels. Plasma lactate and glucose levels were linearly correlated with both aggressive behaviors and plasma catecholamines. The present results provide evidence suggesting that stimulation of the sympathetic nervous system and physical activity are both involved in the control of the mobilization of body energy sources in response to aggressive encounters in domestic pigs.

The effect of high post-mortem temperature on the development of pale, soft and exudative pork: Interaction with ultimate pH

The effects of post-mortem temperature and ultimate pH (pH(u), 24 h post mortem) on the development of the pale, soft and exudative (PSE) characteristics in pig longissimus dorsi muscle were studied. Ten out of the 13 pigs used received pre-slaughter injections of adrenaline in order to deplete muscle glycogen stores. The two muscles from each pig were held at 12 or 35°C during rigor mortis development. Results from covariance analysis, using pH(u) as covariate, showed that a high temperature (35°C) resulted in a dramatic increase in internal light scattering (FOP) 24 h post mortem and a significant decrease in water- and salt-soluble proteins. Cooking loss, sarcomere length and drip loss did not vary significantly with rigor temperature. Interaction between temperature and pH(u) was estimated by assessing the relationship between pH(u) and the difference between the two rigor temperatures for selected traits. The best predictive model was a segmented quadratic model with a plateau which gave significant results for FOP, drip loss, water- and salt-soluble proteins. The effect of temperature decreased curvilinearly when pH increased until a constant value above which no noticeable difference was recorded (drip loss, water- and salt-soluble proteins) or a constant difference was reached (FOP). The pH values corresponding to the convergence points differed from one trait to another. They ranged from 5·72 to 6·22. These results illustrate the importance of muscle glycogen content at slaughter and subsequent pH(u) with regard to the development of temperature-induced PSE meat.

Effects of halothane genotype and pre-slaughter treatment on pig meat quality. Part 1. Post mortem metabolism, meat quality indicators and sensory traits of m. Longissimus lumborum

Forty-eight castrated F(2) offspring of Piétrain and Large White pigs were allocated to a 3 × 2 factorial design in order to study the interactive effect of halothane genotype (NN, Nn and nn) and pre-slaughter treatment [referred to as Experimental (EXP) and Commercial-like (COL) conditions; the latter combining short transportation, mixing unfamiliar pigs and slaughtering shortly after transport] on muscle post mortem changes and meat quality. The pigs were slaughtered over 4 days. Pre-slaughter glycogen depletion in M. longissimus lumborum (LL) was greater in the nn pigs, compared with the two other genotypes. Lactate accumulation post mortem in LL muscle was greater and the pH value at 40 min post mortem was lower in nn compared with NN pigs. Nn pigs were close to nn pigs for lactate accumulation and showed intermediate pH values in the LL muscle. In the M. semimembranosus (SM), NN and Nn pigs showed the same rate of post mortem changes, as evidenced by similar glycogen, lactate, creatine phosphate and ATP levels, and pH values at 40 min post mortem. Pre-slaughter treatment did not affect the rate of post mortem changes in both muscles and no interactive effect with halothane genotype was found. The pigs slaughtered under the COL conditions had a significantly higher ultimate pH in the LL and SM muscles than those slaughtered under the EXP conditions. The LL muscle from nn pigs was paler (higher L*) than that of NN and Nn pigs. In SM muscle, Nn pigs showed a significantly higher L* value than NN pigs. Drip loss of the LL muscle was significantly higher in nn compared with NN pigs, the heterozygous pigs being intermediate. Sensory evaluation of the LL muscle showed that nn pigs had a lower colour intensity and colour homogeneity of raw meat than NN and Nn pigs. Tenderness was significantly lower in nn compared with NN pigs, the Nn pigs being intermediate. Pre-slaughter treatment significantly increased ultimate pH in both muscles (LL and SM) but did not affect significantly the rate of pH fall (pH(40)). It did not affect any of the meat quality traits and no interactive effect with halothane genotype was found. These results confirmed the influence of the halothane gene on the kinetics of muscle post mortem changes and related meat quality traits. They also confirmed the intermediate position of heterozygous pigs in terms of meat quality.

Interactive effect of food deprivation and agonistic behavior on blood parameters and muscle glycogen in pigs

Agonistic behavior, neuroendocrine and plasma metabolite changes, and muscle glycogen content were studied in 16 fed and 16 24 h-fasted domestic Large White pigs (100 +/- 5 kg) submitted to dyadic encounters (30 min) in a novel environment. Comparisons were made with corresponding control pigs (eight fed and eight 24 h-fasted animals) kept under resting conditions. At rest, fasting resulted in a significant decrease in plasma insulin, increase in plasma-free fatty acids, and decrease in glycogen content in the predominantly red Semispinalis muscle. Fasted pigs displayed significantly more submissive acts than fed ones. In response to dyadic encounters, fed and fasted pigs showed similar rise in plasma levels of cortisol, catecholamines, and lactate, but stress-induced hyperglycemia was suppressed in food-deprived animals. Fasting enhanced stress-induced glycogen depletion in the predominantly white Longissimus muscle but this effect was significant only in fast-twitch glycolytic fibres (alpha W). In the Semispinalis of fasted pigs, however, dyadic encounters did not induce further glycogen depletion. The present findings suggest that in response to dyadic encounters, fasting-induced changes in glucose metabolism lead to a higher dependence on endogenous energy reserves, i.e., glycogen, in working muscles.

Paris ham processing: Technological yield as affected by residual glycogen content of muscle.

The aim of the present experiment was to study the relationships between pH, protein and residual glycogen content of pig muscle on the one hand, and technological yield (TY) of Paris ham processing on the other (Paris ham is a type of cured cooked ham). Fifty-two pigs were slaughtered at 100 kg liveweight in a commercial abattoir, in four slaughter series. Ultimate pH, protein and glycogen were determined around 24h post mortem. Two days after slaughter, the right hams were processed to Paris ham. Residual glycogen levels varied from 0 to 78 μmol/g of fresh tissue. All correlations between TY and the other traits under study were significant at the P < 0·05 level. Correlation between glycogen and TY was by far the highest one (r = 0t-0·60, P < 0·01). Protein content and both pH values gave similar but lower correlations with TY (r around 0·4, P < 0·01). It is concluded that the results of the present study agree with the hypothesis that the residual glycogen content of muscle has a direct effect on the technological yield of cooked ham processing.

Glycogen depletion according to muscle and fibre types in response to dyadic encounters in pigs (Sus scrofa domesticus)-relationships with plasma epinephrine and aggressive behaviour

Changes in glycogen content according to fibre type were assessed in a predominantly white (Longissimus) and a predominantly red (Semispinalis) pig muscle, in response to dyadic encounters involving aggressive interactions. Tested animals showed significantly lower glycogen levels than the control in the Semispinalis, but not in the Longissimus muscle. Histological treatment of muscle serial cuts followed by computerized image analysis showed that the observed decrease in muscle Semispinalis glycogen level occurred only in fast-twitch fibres. Total glycogen and glycogen contents in fast-twitch fibres of the Semispinalis muscle were closely and negatively related to aggressive behaviour, but not with plasma epinephrine levels during and at the end of the encounters. The present results provide indirect evidences suggesting a major influence of fighting-induced physical activity on muscle glycogen depletion in response to aggressive interactions in pigs.