Ultrasound velocity and attenuation of porcine soft tissues with respect to structure and composition: II. Skin and backfat

Ultrasound is regarded as a promising method to determine the intramuscular fat content of pork loin. At intact carcasses, the signal passes the backfat whose ultrasound parameters (sound velocity and attenuation) have not been fully investigated. This study intended to collect a dataset of ultrasound parameters for individual backfat layers and to elucidate relationships with structural and compositional characteristics. In-vitro measurements at 10 MHz were conducted on backfat samples of pork carcasses representative for German populations. The average sound velocity ranged from 1436 ± 9 to 1470 ± 37 ms(-1) for the fat layers, and 1682 ± 23 ms(-1) for skin. Velocity of the compound backfat decreased with overall thickness. Attenuation was not affected by thickness ranging between 1.6 ± 0.7 and 2.7 ± 1.5 dB MHz(-1)cm(-1) for all layers. Sound velocity was negatively correlated with fat content and dry matter. The obtained results are anticipated to improve signal correction prior to spectral analysis of ultrasound measurements at intact carcasses.     

Non-destructive estimation of the intramuscular fat content of the longissimus muscle of pigs by means of spectral analysis of ultrasound echo signals

The eating quality of porcine meat is supposed to increase with increasing intramuscular fat content (IMF). The aim of this study was to investigate the use of acoustic parameters obtained by spectral analysis of ultrasound echo signals to non-destructively predict intramuscular fat content of porcine longissimus muscle. Ultrasound is regarded as a promising non-destructive technique to characterize tissue. Ultrasound data acquisition was performed at slaughter with a clinical B-mode device equipped with a 3.5 MHz center-frequency transducer on 115 warm carcasses about 45 min postmortem. Acoustic parameters quantifying attenuation, backscattering and cepstral structure were calculated off-line from the recorded primary raw ultrasound echo signals. Their relationship to IMF content was investigated. IMF level significantly influenced powerspectrum amplitudes and backscatter parameters. With partial least-squares regression (PLS), the IMF content could be predicted with root mean standard error of prediction RMSEP of 0.36% IMF. The ultrasound parameters were able to correctly classify nearly 80% of the carcasses into HIGH and LOW level class, respectively. Results indicate the potential use of ultrasound spectral analysis for non-destructive evaluation (NDE) of pig carcasses in order to estimate the IMF content.     

In Situ Ultrasonic Characterization of Cocoa Butter Using a Chirp

Differences between tempered and untempered cocoa butter were investigated by an ultrasonic signal “chirp” generated by contact transducers. Polarized light microscopy and powder X-ray diffraction were used to characterize the morphology and polymorphism of tempered and untempered cocoa butter, whereas pulsed nuclear magnetic resonance was used to determine the amount of crystalline solids present. Ultrasonic wave velocity and attenuation data were collected simultaneously throughout the 5-h crystallization process for cocoa butter. Ultrasonic velocity and attenuation changed at the different solid fat contents (SFC): 4, 8, and 11 %. Untempered cocoa butter showed an attenuation of 3 dB/cm at 1.7 MHz and 4 % SFC, whereas tempered cocoa butter showed an attenuation of 4.5 dB/cm at 1.7 MHz and 4 % SFC. At 3 MHz, the attenuation was 2 dB/cm for untempered and 6 dB/cm for tempered cocoa butter. Under these conditions (4 % SFC, 3 MHz), the chirp wave of tempered sample showed a phase angle change of 0.5 rad, whereas the untempered sample showed ?0.5 rad relative to the canola oil that was taken as 0. The study suggests that an ultrasonic chirp can be effectively used to detect differences between tempered and untempered cocoa butter when measuring attenuation and ultrasonic wave phase angle changes as a function of frequency. The in-line characterization of chocolate “temper” using such nondestructive ultrasonic measurements could be applied to industrial chocolate manufacturing.     

Monitoring Tempered Dark Chocolate Using Ultrasonic Spectrometry

Ultrasonic spectrometry was used to distinguish between properly tempered and untempered commercial dark chocolate. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to characterize the polymorphic state of tempered and untempered chocolate, results that were correlated to those of ultrasonic spectrometry. Four different kinds of dark chocolate samples with different amounts of sugar (7.5–50 %), fat (30–50 %), and cocoa mass (70–90 %) were subjected to two different tempering protocols. The tempering was achieved using cocoa butter seeds under static cooling from 50 to 14 °C. The ultrasonic generator and analyzer SIA-7 (V.N. Instruments) was used to monitor the crystallization process. The instrument generated a chirp signal with a bandwidth of 0.5 to 3 MHz and was set to work in a four-pathway configuration with two transducers and a center frequency of 2.25 MHz. Spectrometric analysis was carried out with chocolate samples containing 2, 4, and 6 % solid fat content (SFC). The SFC was obtained from DSC measurements. Ultrasonic signals for attenuation, reflection, and velocity were compared between tempered and untempered chocolates. It was shown that seed-tempered chocolate with 30 % sugar and 47.5 % fat attenuated 2.5 MHz of ultrasonic waves by 0.8, 1.7, and 2.0 dB/cm at 2, 4, and 6 % SFC, respectively. On the other hand, untempered chocolate attenuated the ultrasound signal by 3.5, 3.6, and 4.3 dB/cm. Furthermore, it was found that ultrasound reflection signals were stronger and ultrasonic velocity was higher in chocolates with high sugar content.     

Composition and estimation of intramuscular and subcutaneous fatty acid composition in Spanish young bulls

Sixty Pirenaica yearling intact bulls were raised and slaughtered at 519±50kg live weight and 371±18 days of age. Fatty acid composition of intramuscular lipids in longissimus dorsi muscle and subcutaneous fat were determined by capillary gas chromatography. Carcass conformation and fatness, carcass weight, ether extractable intramuscular fat percentage, marbling, dorsal fat thickness, and ultrasonic parameters were recorded to study the relationship between these traits and fatty acid profile. Lipids of subcutaneous adipose tissue had higher monounsaturated fatty acids (MUFA) percentage (49% vs. 33%) but lower saturated fatty acids (SFA) (51% vs. 46%) and polyunsaturated fatty acids (PUFA) (16% vs. 5%) percentages than intramuscular fat depots (p<0.001). Fatter carcasses had higher MUFA percentage and lower PUFA percentage (p<0.01) in intramuscular fat. Carcass weight and conformation would contribute to explain the fatty acid profile of subcutaneous fat (p<0.05). Ultrasound readings reflected the effect of fatness on fat composition.     

Elastography of beef muscle

Elastography, a technique that uses ultrasonic pulses to track the internal displacements of small tissue elements in response to an externally applied stress, has been applied to beef muscle. Beef longissimus (1 day post mortem) and semimembranosus (5 days post mortem) muscles were obtained from A maturity beef carcasses. Samples were vacuum-packaged and frozen to -20°C. For elastography measurements, muscles were equilibrated to a constant temperature (30° C± 0·5) in a water tank. Custom transmitters and receivers were used in conjunction with a 2·25 MHz medical transducer. The transducer was driven by a 286 PC, and the radio-frequency echoes digitized at 50 MHz and 8 bits. The pre- and post- compression echo trains (A-lines) were subjected to cross-correlation analysis. Visual interpretation of beef elastograms demonstrate circular areas of relatively inelastic tissues and smaller, banding areas of elastic tissues in the cross-section of beef longissimus muscle. The dark inelastic areas from the elastograms may be related to myofibrilar areas from the same muscle sections; the light, elastic band areas from the elastograms may be related to perimysiaal connective tissue or intramuscular fat. Fatty septa and a calcified abscess could be easily identified on the elastogram. These preliminary results demonstrate that elastography may have potential as a non-intrusive method of visualizing tissue components of beef muscle.     

Prediction of the intramuscular fat content in loin muscle of pig carcasses by quantitative time-resolved ultrasound

A novel method for non-destructive intramuscular fat (IMF) estimation via spectral ultrasound backscatter analysis of signals obtained from pig carcasses early post mortem is described. A commercial hand-held ultrasound device (center frequency: 2.7 MHz) was modified to focus the sound beam to the longissimus muscle at the 2nd/3rd last rib. Time-resolved ultrasound backscatter signals of loin muscle were recorded 45 min p.m. on 82 pig carcass sides. Backfat width (d_BF = 18.9 ± 3.8 mm) and muscle attenuation (α_muscle = .77 ± .15 dB MHz^− 1 cm^− 1) were assessed from the measured pulse echo data. Other propagation properties of skin, backfat and muscle tissue obtained in a previous investigation were incorporated into the signal pre-processing to minimize parameter estimation artifacts. Spectral and cepstral parameters were derived from time-gated backscattered signals measured in the central muscle region. The range of intramuscular fat (IMF) determined by ether extraction was representative for German pig populations (.7% ≤ IMF_chem ≤ 3.6%, coefficient of variation CV(IMF_chem) = 44.8%). Variations of IMF were associated with variations of backfat width (CV(d_BF) = 20.2%), muscle attenuation (CV(α_muscle) = 19.3%), and slope of the backscattered amplitude spectrum (CV(m) = 28.8%). A full cross validated multiple linear regression model using these parameters resulted in good predictability of IMF_chem (R² = .76, RMSEP = .34%). Among all tested carcasses, 73% could be correctly classified into one of three IMF classes (LOW: < 1%, MID: 1-2%, HIGH: > 2%). Using a single threshold (2% IMF), about 92% of all carcasses were correctly classified. With respect to the inherent variability of IMF within a single muscle and the different tissue volumes used for the chemical and ultrasound based IMF estimations the remaining prediction errors are acceptable. Compared to previous ultrasound based studies, the number of acoustic parameters used for the IMF prediction could be reduced. Moreover, the used parameters are based on time-of-flight and spectral slope estimations, which are i) more robust with respect to measurement artifacts and ii) have a causal link to structural variations associated with IMF variations in pork loin.     

Composition analysis of beef rib sections by dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DXA) was used as a non-invasive method to measure composition of 9, 10,11 - rib sections obtained from 80 beef carcasses. The weights of the rib sections ranged from 2986 g to 6394 g. Each rib section was scanned twice by DXA, once in a horizontal or standing rib position (DXA-1) and once in a vertical position (DXA-2). After scanning, each rib section was dissected into fat, muscle and bone. The intramuscular fat content of the longissimus muscle was measured chemically. Dissected lean and fat values were adjusted for the amount of intramuscular fat. DXA lean values were adjusted for amount of bone (less bone mineral content). Both DXA measurements consistently overestimated the amount of fat relative to dissection. The DXA-1 scan position measured more lean and less fat than did DXA-2. The correlation (r) between the amount of dissected lean and DXA-1 and DXA-2 lean was 0.91 and 0.85, respectively and between the amount of dissected fat and DXA-1 and DXA-2 fat was 0.94 and 0.92, respectively. The high correlations between DXA and dissection results indicate that DXA could be used as a non-destructive method for evaluating composition of cuts of beef; however, attention must be given to orientation of the cut during the DXA scan.     

Effects of Carcass Maturity on Collagen Solubility and Palatability of Beef from Grain-Finished Steers

Samples from steers fed a high-energy diet for 185 days prior to slaughter were used to compare collagen solubility and palatability of beef from youthful and mature carcasses. Carcasses representing the two maturity classes were selected specifically to have similar levels of intramuscular and subcutaneous fat, but distinctly different maturity indicators. Under the conditions of this study, maturity class had no effect on sensory properties or shear force values of cooked rib steaks. Total collagen content of samples from the longissimus muscle was higher for mature carcasses, but maturity class means for percentage of soluble collagen were not different. The relationships of these findings to preslaughter feeding regimen and collagen metabolism are discussed.     

Fatty acid and triglyceride profiles of intramuscular and subcutaneous fat from fresh and dry-cured hams from Hairless Mexican Pigs

The study was designed to compare the fatty acid profiles and triglyceride composition of subcutaneous and intramuscular fat of raw and cured hams from Hairless Mexican Pigs. Curing (180 days) was developed throughout several ordered steps: salting, stabilization, drying and ripening. For the salting step, hams were rubbed with nitrate salt, and kept on salt 1 day per kilogram at 0-4?°C and at relative humidity of 80-85%. The rest of the process consisted of small increments of temperature (from 0-24?°C) and small decrements of relative humidity (from 82-68%). The curing process decreased (P<0.05) significantly the proportion of unsaturated fatty acids (raw: 59.2±0.3% and cured: 55.3±0.4%) and increased the saturated ones (raw: 34.4±0.3% and cured: 39.4±0.5%). Subcutaneous and intramuscular fat had similar (P>0.05) percentages of unsaturated (57.60±0.3 and 56.88±0.4%, respectively) and saturated fatty acids (37.5±0.33 and 38.3±0.4%, respectively). With the exception of the monopalmitate, the curing process decreased (P<0.05) the levels of all acylglycerols studied.     

The thickness and quality of backfat in various pig breeds and their relationship to intramuscular fat and the setting of joints from the carcasses

The characteristics of backfat were measured in carcasses from 233 pigs representing eleven breeds. Animals were fed ad libitum and killed at an average live weight of 62 kg. In breeds in which the backfat was thicker it was also firmer and contained less water. In leaner breeds there was reduced cohesiveness of fat and muscle components of the loin joint so that the fat separated more easily from the underlying lean. This contributed to joints which were subjectively assessed as less firm and well set. Fatter breeds tended to have Longissimus muscles which contained more intramuscular fat. However, the relationship between muscle fat and carcass fat was poor suggesting that, if it was thought desirable to select for increased intramuscular fat in the interests of meat palatability, then this could be achieved without making carcasses undesirably fat. Differences in fat characteristics between breeds were apparently largely attributable to differences in fatness rather than inherent breed factors.     

Phenotypic variations of muscle fibre and intramuscular fat traits in Longissimus muscle of F(2) population Duroc×Berlin Miniature Pig and relationships to meat quality

In Longissimus muscle from a F(2) population of Duroc×Berlin Miniature Pigs, micro-structural fibre traits and fatty acid composition were investigated to calculate correlation coefficients between these traits and meat quality. The animals of the F(2) population exhibited low carcass weight (55.7±11.2 kg), low meat percentage (35.0±8.4%) but a relatively high intramuscular fat content (3.52±1.44%) compared to pure bred animals (F(0)). No unacceptable meat quality was observed. The variation coefficients of carcass composition, muscle fibre traits, and fat traits were high enough to allow the analysis of candidate genes which influence the growth of muscle fibres, fat cells, and meat quality. Phenotypic correlation coefficients between muscle fibre characteristics and meat quality traits were low whereas fatty acid composition and meat quality were more closely related. The correlation coefficients between muscle fibre traits and fatty acid composition ranged from 0.10 to 0.40. The relationship between a low quotient of n-6/n-3 fatty acids in muscle and greater fibre sizes, higher percentages of the oxidative fibre type and higher capillary density was noteworthy indicating good conditions for muscle growth and meat quality.     

Effects of crossbreeding Mexican Pelibuey sheep with Rambouillet and Suffolk on carcass traits

Fifty nine lambs: Pelibuey (P), Suffolk×Pelibuey (SP) and Rambouillet×Pelibuey (RP), were used to evaluate the effect of crossbreeding on carcass characteristics and composition. Following carcass evaluation, muscle, bone, subcutaneous, seam, internal, total fat and other tissues were dissected. Carcass dressing percentage was similar across the three genotypes. The genetic group did not influence the percentage of cuts, except for shoulder percentage. Pelibuey carcasses had less fat thickness than RP and more kidney, pelvic and heart fat than SP. Muscle percentage was lower for RP (51.27±0.68) compared to P (54.01±0.61) and SP (53.78±0.58) carcasses, respectively. Consequently, the RP group showed the highest proportion of total fat (19.66±1.00). In general, RP carcasses had the lowest meat cutability. In conclusion, carcass yield of Pelibuey lambs was not improved by the cross with either Rambouillet or Suffolk breeds.     

Ether-Extractable Fat in Longissimus Muscles From Beef Carcasses with the Same Marbling Scores but Different Yield Grades

Ether-extractable fat in beef longissimus muscles–completely trimmed of all subcutaneous fat, epimysium and peripheral muscles–from 383 heifer and steer carcasses of A and B maturity was compared to determine whether the fat content of muscle was the same when marbling was held constant but yield grade of carcasses differed. Yield grade was a significant source of variation in intramuscular fat content of trimmed steaks within marbling scores (P < 0.001); as yield grade increased, total fat content of the ribeye muscle increased very slightly, even though marbling score was held constant. These data indicated that marbling score alone did not account for all of the variation in the fat content of totally-trimmed beef longissimus steaks.     

A national survey of the microbiological quality of beef carcasses and frozen boneless beef in Australia

The third national baseline microbiological survey of Australian beef carcasses and frozen boneless beef was conducted in 2004. Carcasses (n=1155) sampled at 27 slaughter establishments had a mean aerobic plate count (at 25 degrees C) of 1.3 log CFU/cm2. Escherichia coli was isolated from 8.0% of the cacasses, with a mean count of -0.8 log CFU/cm2 for positive samples. On samples from 24 boning (fabrication) plants (n=1082), the mean aerobic plate count for frozen boneless beef was 1.3 log CFU/g, and the mean count for the 1.8% of samples with detectable E. coli was 1.5 log CFU/g. E. coli O157: H7 was isolated from 1 of 1,143 carcasses and from 0 of 1082 boneless samples. Salmonella was isolated from 0 of 1155 carcasses and from 1 of 1082 samples of boneless product. No Campylobacter spp. were isolated from carcasses or boneless beef. Coagulase-positive staphylococci were isolated from 28.7% of beef carcasses and 20.3% of boneless beef samples, and positive samples had a mean count of 0.3 log CFU/cm2 and 0.8 log CFU/g, respectively.     

Effects of porcine MC4R and LEPR polymorphisms, gender and Duroc sire line on economic traits in Duroc × Iberian crossbred pigs

Polymorphisms MC4R c.1426 A>G (p.Asp298Asn) and LEPR c.2002 C>T (p.Leu663Phe) have been associated in pigs with feed intake, growth and fatness. Our aims were to analyze how these polymorphisms influence production and quality traits in Duroc × Iberian crossbred pigs, and moreover evaluate how the effects of gender and Duroc line were affecting these traits. Significant effects of gender, Duroc sire line and LEPR c.2002 C>T mutation, were detected on the main traits. LEPR c.2002 T allele increased body weight (2.5 ± 0.7 kg), backfat thickness (1.5 ± 0.4mm), loin intramuscular fat (0.7 ± 0.2 %), and lightness (1.0 ± 0.3); however it was decreasing premium cuts yield (-0.9 ± 0.2%). Allele c.2002 T increased SFA (0.60 ± 0.12 %), and decreased MUFA (-0.35 ± 0.12%) and PUFA (-0.25 ± 0.06%). No significant effects of MC4R c.1426 A>G SNP were identified. A genetic test based on the LEPR c.2002 C>T SNP may be useful to select Duroc sires to reduce undesirable heterogeneity of carcasses and premium cuts of crossbred animals.     

Estimation of lamb carcass composition from measurements of the speed of ultrasound in the soft tissues of live animals and carcasses

The application of the velocity of sound (VOS) technique to lamb carcasses in a previous study (Fisher & Page, 1986) measured composition at a hind limb and neck site but was not as precise as fat scores in predicting lean proportion. This study examines VOS measurements made at sites in the hind limbs and along the vertebral column in live sheep and carcasses. A group (A) comprising five breeds of males and females (n = 61) and a sub-group (B) of Scottish Blackface castrated males (n = 34) were studied, and the reciprocal velocity of ultrasound (RV) was measured on the live sheep immediately behind the shoulder and over the last rib using a fixed-distance transducer assembly operating at 5 MHz, and in the hind limbs at 2·25 MHz using the apparatus described by Miles et al. (1984). Corresponding measurements were made on the carcasses which were classified by a Meat and Livestock Commission fatstock officer and then dissected. Standard deviations of lean proportion were 4·48% (A) and 3·39% (B). The residual standard deviations (rsds) for groups A and B respectively were obtained using the following predictors: live mass (LM) 4·27% and 2·96%; LM + breed (B) 3·08% (group A only); LM + mean RV 2·36% and 2·07%; LM + B + mean RV 1·99% (group A only). Using carcass measurements: carcass mass (CM) 4·25% and 2·90%; CM + MLC fat score 2·99% and 2·12%; CM + RV last rib 2·89% and 2·02%. These data show that VOS measurements through dorsal sites of live sheep provide encouragingly precise estimates of carcass lean proportion. For carcasses, dorsal sites provide a less precise estimate of carcass lean but when carcass mass is included in multiple regression the precision of the correlation is comparable with that of multiple regression of fat score with carcass mass.     

A novel approach to grading pork carcasses: computer vision and ultrasound

A Computer Vision System prototype for grading pork carcasses was developed at the Lacombe Research System. The system consists of two components: ultrasound imaging to scan a cross-section of the loin muscle and video imaging to capture two-dimensional (2D) and three-dimensional (3D) images of the carcass. For each of the 241 carcasses (114 barrows and 127 gilts), salable meat yield was determined from a full cutout. Linear, two- and three-dimensional, angular and curvature measurements and carcass volume were derived from each image. Muscle area and fat thickness (7 cm off the mid-line) measured by ultrasound at the next to last rib site, together with 2D and 3D measurements provided the most accurate model for estimating salable meat yield (R²=0.82 and RSD=1.68). Models incorporating fat thickness and muscle depth measured at the Canadian grading site (3/4 last rib, 7 cm off the mid-line) with the Destron PG-100 probe, had the lowest R² and highest residual standard deviation (RSD) values (R²=0.66 and RSD=2.15). Cross-validation demonstrated the reliability and stability of the models; hence conferring them good industry applicability. The Lacombe Computer Vision System prototype appears to offer a marked improvement over probes currently used by the Canadian pork industry.     

Investigation of bovine serum albumin denaturation using ultrasonic spectroscopy

The ability of ultrasound spectroscopy to characterise protein denaturation at relatively high concentrations and under conditions found in foods, is examined. Measurement of longitudinal sound velocity against concentration and frequency (20–160 MHz) for the bovine serum albumin monomer at pH 7.0 gave a frequency independent value for molecular compressibility of κ′ = 2.05 × 10⁻¹⁰ Pa⁻¹ at 25 °C, corresponding to a sound velocity for the BSA molecule of 1920 m s⁻¹. At 160 MHz, the longitudinal sound attenuation in BSA molecules is ∼5200 Np m⁻¹, a factor of 10 higher than in water. The excess attenuation of the solution over water was nearly 90 Np m⁻¹ at the highest measured volume fraction of 0.03 (or 3% v/v). Concentration-dependent ultrasound velocity (20–160 MHz) and attenuation (2–120 MHz) spectra were obtained over time for heated bovine serum albumin (BSA) solutions up to 40 mg/mL at neutral pH and at 25 °C. An acoustic scattering model was used which considered the solute molecules as scatterers of ultrasound, to determine the molecules’ sound velocity, compressibility, and attenuation properties. Mild heat treatment caused the molecule to organise into dimers and trimers, without change in sound velocity; implying that there is little or no change in secondary structure. Changes in attenuation spectra correlated with estimated molecular weight as determined through DLS and SEC measurements. During oligomerisation, the BSA molecules continue to behave acoustically as monomers.     

Influences of anatomical location and muscle quality on porcine lipid composition

Carcasses of sixty Lacombe and Lacombe cross swine fed the same high concentrate ration were selected to equally represent three muscle quality groups (pale soft exudative (PSE), normal and dark firm dry (DFD)). These carcasses were utilised to supply back and belly fat samples for the evaluation of the influences of muscle quality and anatomical location on fatty acid composition. Back fat samples had lower percentages of palmitic (C16:0) and stearic (C18:0) acids, long (≥ C18), and short (≤ C16) chain saturated fatty acids and total saturated fatty acids and higher percentages of oleic (C18:1) and linoleic (C18:2) acids, polyunsaturated fatty acids and total unsaturated fatty acids than belly fat samples. They also had a higher unsaturated fatty acid to saturated fatty acid ratio than belly fat samples. Carcasses with DFD hams and loins had lower percentages of palmitoleic (C16:1) and linoleic (C18:2) acids and polyunsaturated fatty acids in their back fat than those with PSE hams and loins. They also had higher (P < 0·05) percentages of myristic (C14: 0) and stearic (C18:0) acids and long chain saturated fatty acids (≥ C18) and lower percentages (P < 0·05) of palmitic (C16:0) and palmitoleic (C16:1) acids in their back fat than carcasses with normal hams and loins. Moreover, they had lower (P < 0·05) percentages of palmitoleic (C16:1) and linoleic (C18:2) acids and poly-unsaturated fatty acids in their belly fat than carcasses with normal and PSE hams and loins. The fact that the lipid composition of carcasses differed significantly among muscle quality groups is of considerable importance, since it implies that factors (stress) producing differences in muscle quality may also significantly influence the fatty acid composition-and thereby the physical properties of carcass lipids.