Dolly for dinner? Assessing commercial and regulatory trends in cloned livestock.

As cloning technologies become more widely established, will products enter the food chain sooner than regulatory agencies and the public might be prepared for?

The effects of breed and level of nutrition on whole-body and muscle protein metabolism in pure-bred Aberdeen angus and Charolais beef steers.

Eighteen pure-bred steers (live weight 350 kg) from each of two breeds, Aberdeen Angus (AA) and Charolais (CH), were split into three equal groups (six animals each) and offered three planes of nutrition during a 20-week period. The same ration formulation was offered to all animals with amounts adjusted at 3-week intervals to give predicted average weight gains of either 1.0 kg/d (M/M group) or 1.4 kg/d (H/H group). The remaining group (M/H) were offered the same amount of ration as the M/M group until 10 weeks before slaughter when the ration was increased to H. Data on animal performance, carcass characteristics and fibre-type composition in skeletal muscle are presented elsewhere (Maltin et al. 2000; Sinclair et al. 2000). On three occasions (17, 10 and 2 weeks before slaughter) the animals were transferred to metabolism stalls for 1 week, during which total urine collection for quantification of Ntau-methylhistidine (Ntau-MeH) elimination was performed for 4 d. On the last day, animals were infused for 11 h with [2H5]phenylalanine with frequent blood sampling (to allow determination of whole-body phenylalanine flux) followed by biopsies from m. longissimus lumborum and m. vastus lateralis to determine the fractional synthesis rate of mixed muscle protein. For both breeds, the absolute amount of Ntau-MeH eliminated increased with animal age or weight (P < 0.001) and was significantly greater for CH steers, at all intake comparisons, than for AA (P < 0.001). Estimates of fractional muscle breakdown rate (FBR; calculated from Ntau-MeH elimination and based on skeletal muscle as a fixed fraction of live weight) showed an age (or weight) decline for M/M and H/H groups of both breeds (P < 0.001). FBR was greater for the H/H group (P = 0.044). The M/H group also showed a lower FBR for the first two measurement periods (both at M intake) but increased when intake was raised to H. When allowance was made for differences in lean content (calculated from fat scores and eye muscle area in carcasses at the end of period 3), there were significant differences in muscle FBR with intake (P = 0.012) but not between breed. Whole-body protein flux (WBPF; g/d) based on plasma phenylalanine kinetics increased with age or weight (P < 0.001) and was similar between breeds. The WBPF was lower for M/M compared with H/H (P < 0.001) based on either total or per kg live weight0.75. Muscle protein fractional synthesis rate (FSR) declined with age for both breeds and tended to be higher at H/H compared with M intakes (intake x period effects, P < 0.05). Changing intake from M to H caused a significant increase (P < 0.001) in FSR. The FSR values for AA were significantly greater than for CH at comparable ages (P = 0. 044). Although FSR and FBR responded to nutrition, these changes in protein metabolism were not reflected in differences in meat eating quality (Sinclair et al. 2000).

Altered calpain levels in longissimus muscle from normal pigs and heterozygotes with the ryanodine receptor mutation.

The calpain proteolytic system was examined in the longissimus muscle (LD) of heterozygote pigs carrying a single copy of a mutation in the skeletal muscle ryanodine receptor gene (RyR1) that is associated with porcine stress syndrome and reduced meat quality. Conventional British White-type pigs (n = 30) were selected from a commercial line on the basis of slaughter weight, backfat depth, and pH at 45 min postmortem > 6.0; based on DNA analysis, 11 were heterozygous RyR1 mutants (Nn), and 19 were normal genotype (NN). The LD samples were taken from carcasses at 2, 4, and 24 h postmortem for calpain analysis with enzyme assay and immunoblotting, using specific antisera raised against recombinant polypeptides derived from calpain large subunits and calpastatin. Shear force (SF) was measured after conditioning for 8 d at 2 degrees C and did not differ between Nn and NN groups. The extractable activity of mu-calpain decreased over 24 h postmortem (P < .001), with no significant difference in activity between NN and Nn animals at any time. The activity of m-calpain also decreased with time (P < .001), but it was lower at all times in Nn than in normal genotypes (P < .001). After Western blotting, the immunoreactivity of mu- and m-calpain large subunit bands declined over 24 h postmortem (P < .001); values for mu-calpain were higher (P < .05) and for m-calpain were lower (P < .001) in heterozygotes than in normal animals at each sampling time. The calpastatin antibody detected a major band of 135 kDa that declined with time postmortem but did not differ between Nn and NN genotypes at any sampling time. These data indicate that the levels of extractable mu- and m-calpain, but not calpastatin, may be different in pigs that carry the RyR1 mutation.

Relationship between skeletal muscle-specific calpain and tenderness of conditioned porcine longissimus muscle.

Tenderization of skeletal muscle in meat animals has been closely linked to the postmortem activity of the calpain proteolytic enzyme system, which includes the specific inhibitor calpastatin. Increased understanding of the skeletal muscle-specific calpain isoform p94 has prompted suggestions as to whether it too could have a role in the tenderization process. In this study, two groups of pigs were identified in which shear force measurements after 8 d of conditioning indicated a large variation in the tenderness of longissimus muscle. The quantity of p94 in the muscle was monitored by immunoblotting, using a porcine-specific polyclonal antibody raised against a recombinant peptide fragment generated as a fusion protein. The antiserum recognized a 94-kDa protein associated with myofibrils in skeletal but not cardiac muscle, as expected for this calpain isoform, although it could not be tested with the native protein because of the extreme instability of p94. In the first experiment, the mean shear force for the tough group was 6.71 +/- .28 kg (n = 12, SEM) and that of the tender group was 3.87 +/- .12 kg (n = 12), but there was no difference in the normalized absorbance of the immunopositive 94 kDa band on Western blots from samples collected at approximately 40 min postmortem. In the second experiment, the stability of p94 in chilled carcasses was investigated over 24 h, using a further two groups of 10 tough and 10 tender pigs of mean shear force values 5.36 +/- .14 kg and 2.81 +/- .15 kg, respectively. In tough and tender animals, there was a decline (P < .05) in the 94-kDa immunostaining material of mean half-lives of 13.8 and 12.9 h, respectively, although there was considerable variability. Despite this variability in half lives and shear force values, no correlation was seen between these factors. Thus, in porcine longissimus muscle, the variability in tenderness after 8 d of conditioning cannot be attributed to an underlying variability in p94.

The effect of dietary oil containing (n-3) fatty acids on the fatty acid, physicochemical, and organoleptic characteristics of pig meat and fat.

An investigation was made to alter the fatty acid composition of pork and a pork product in line with human dietary advice while not adversely affecting factors controlling consumer acceptability. Pigs (n = 150) were assigned to three dietary treatments with 25 intact male-female pairs per treatment. Diet A (control) contained 3% of a 4:1 (wt/ wt) tallow-soybean oil mixture. Diets B and C contained 2% rapeseed oil plus 1% fish oil. Diets A, B, and C were supplemented with 100, 100, and 250 mg of all-rac-alpha-tocopheryl acetate/kg of diet, respectively. Pigs were given ad libitum access to feed from 52 kg live weight until 95 kg (slaughter). Sausages were prepared from the resulting cuts. Tissues of pigs were evaluated in terms of fat firmness, color, fatty acid composition, and contents of alpha-tocopherol and thiobarbituric acid-reactive substances (TBARS). Organoleptic characteristics of chops and sausages were evaluated by a trained taste panel. Pigs fed Diets B and C had improved feed conversion ratios (P < .05) and ADG compared with control pigs. The levels of n-3 (omega-3) polyunsaturates were significantly increased in the tissues and sausage from pigs fed Diets B and C with associated alterations in n-6 to n-3 fatty acid ratios that accorded with contemporary human dietary recommendations. Levels of alpha-tocopherol and TBARS were significantly altered in the tissues. There were no appreciable differences between treatments in carcass characteristics, including color. The overall organoleptic acceptability of chops and sausages was not different between the treatments.

Pig muscle fibre characteristics as a source of variation in eating quality.

Despite the application of the MLC Blueprint specifications there is still unacceptable variation in meat eating quality. Evidence from the literature suggests that the intrinsic characteristics of the muscle may be an important source of variation, but there is no indication as to what extent these characteristics may explain the residual variation in eating quality. The purpose of the present study was to quantify the role of muscle fibre characteristics in accounting for eating quality variability. In the study, evaluation of samples from 125 pigs from eight breeding company populations indicated that fibre characteristics, particularly the diameter of the fast twitch oxidative glycolytic fibres, contributed to variation in instrumental texture of meat. In addition, the data suggest that there are genetic differences in fibre type distribution which can be used to segregate populations.

Collagen cross-linking in porcine m. longissimus lumborum: Absence of a relationship with variation in texture at pork weight.

The determination of all currently known intermolecular cross-links present in intramuscular collagen of porcine m. longissimus lumborum is described in relation to the texture of the meat as determined both objectively by instrumentation and subjectively by sensory panel. The variation in texture observed in the m. longissimus lumborum of pork weight pigs has been shown to be unrelated to the total collagen content or to the nature of the collagen intermolecular cross-links. We have also demonstrated a considerable error in the colorimetric method for quantitation of hydroxyproline when determining the very low values of collagen present in pig meat. During this study we have established a sound protocol for the determination of all the known cross-links in intramuscular collagen of meat from any meat animal species.

Improving pork quality by electricalstimulation or pelvic suspension ofcarcasses.

This investigation compared the separate and combined effects on meat quality of electrical stimulation (ES) and pelvic suspension of pig carcasses chilled rapidly or conventionally. Sides from 80 pigs, 80-90 kg live weight, were allocated to one of four treatments followed by either conventional chilling (1°C for 24 h) or rapid chilling (-20°C for 2-3 h, before 1°C until 24 h post-slaughter). The four treatments were: Achilles suspended, with and without high voltage ES, and pelvic suspended, with and without ES. The quality attributes: pH, colour and opacity, drip loss, instrumental and sensory texture were measured in M. longissimus thoracis et lumborum, at 10 days post-slaughter. Rapid chilling reduced the evaporative weight loss by 0·5% There were no significant effects of treatment on colour or opacity, although ES samples were slightly paler. Drip loss was also slightly greater with ES, particularly when combined with pelvic suspension, but in no case was the meat classified as PSE. Instrumental measurements of 'texture showed improved tenderness from both ES and pelvic suspension, even after 10 days ageing. The improvement was less pronounced when ES and pelvic suspension were combined Taste panelling confirmed that samples treated by ES or pelvic suspension, separately or combined, were significantly more tender than samples from non-ES, Achilles hung sides. ES and pelvic suspension were equally effective in improving the tenderness of pork loin. Pelvic suspension did not suffer the disadvantage of increased drip loss that occurred with ES in this study.

The effect of chilling, electrical stimulation and conditioning on pork eating quality.

The effect of three different post-slaughter treatments and subsequent conditioning times on the eating quality of pork was studied, using a total of 72 pigs (80-90 kg live wt). The treatments were: (A) holding in air at > 10°C for 3 h, followed by chilling in air at 1°C; (B) chilling in air at 1°C; (C) high voltage electrical stimulation (ES) at 20 min post-slaughter, followed by Treatment B. The quality attributes were measured in M. longissimus thoracis et lumborum (LTL) and in M. semimembranosus (Sm). There was little difference in cooling rate between the three treatments; the major effect on quality came from the use of ES in Treatment C. ES reduced pH at 45 min by approximately 0·3 units, and achieved pH values at 3 h post-slaughter of 5·64 (LTL) and 5·87 (Sm) but did not produce PSE meat. Drip losses were generally low, but were slightly higher with Treatment C. By all three instrumental texture parameters, LTL from Treatment C was significantly more tender than from A and B at 4, 7 and 12 days post-slaughter, suggesting that either some cold toughening with A and B was overcome by ES in treatment C or that ES had some other beneficial action. Conditioning at 1°C improved the tenderness of LTL from 4 to 7 days and further to 12 days. Taste panelling of loin chops and Sm roasts confirmed that Treatment C gave significantly more tender meat than A and B, and that ageing from 4 to 7 days and further to 12 days significantly improved tenderness. High voltage electrical stimulation at 20 min post-slaughter followed by cooling in air at 1°C (Treatment C) produced loin muscle which was more tender at 4 days than at 12 days with the other treatments.

Structural and mechanical changes in raw and cooked single porcine muscle fibres extended to fracture.

Tensile tests on single muscle fibres from raw and cooked porcine longissimus thoracis muscle were performed to explore the structural mechanisms responsible for their deformation and fracture properties. Measurements of load and deformation were made simultaneously with light microscopy observations of the structural changes which occur on extension. On extending the fibres to fracture, an r-shaped stress-strain curve was observed and the structural changes which occurred during this process could be divided into three phases. Phase one, was characterised by a rapid increase in stress with little change in strain and ended at the yield point. Sarcomere length was uniform along the fibre in this initial phase. Raw fibres yielded at strains of between 2 and 5% of their resting lengths and cooked fibres at strains of between 10 and 20%. In phase two, there was rapid increase in strain with minimal changes in stress. In most fibres this phase was characterised by multiple cracks on the fibre surface and unequal sarcomere stretching. Sarcomeres in the regions where the surface had ruptured extended faster than those in areas still covered by the surface membrane, where sarcomere length remained relatively unchanged. In some cooked fibres, there was little or no surface cracking and all the sarcomeres in these fibres extended almost uniformly. Phase three was characterised by a rise in stress as strain increased and then a final fall in stress at the breaking point. This was accompanied by myofibrillar failure and finally breakage of the whole fibre. The myofibrils did not always fail as one unit; a progressive snapping of small bundles of myofibrils was seen in some raw fibres. Muscle fibres could be stretched to 10·9 ± 1·45% of their resting length before breaking when raw, but to 130 ± 42% of their rest lengths after they were cooked for 1 h at 80°C. Where multiple surface cracking was observed in phase two, sarcomeres in some cracked areas lengthened faster than others and the cracked areas which extended fastest were usually the focus of the eventual failure of the fibre. In raw fibres, sarcomeres in the areas where the fibre surface had ruptured could be stretched up to 107·7% before failure, while those in areas of the fibre with an intact surface remained relatively unchanged. In cracked areas of cooked fibres the sarcomeres were more extensible and could be stretched to 169·7% before breaking. The order-of-magnitude increase in overall extension to failure of fibres resulting from cooking is only partially due to this increase in sarcomere extensibility in cracked areas. Mechanically demembranating raw fibres depressed the stress at which yielding occurred and doubled their breaking strain. However, this process had no effect on the stress at which the fibres fractured. The results show that deformation is not uniform along individual fibres, especially in the raw case and that the endomysium has an important contribution to this non-uniform deformation.