F.J.M. Smulders

The effectiveness of examining early post-mortem musculature to predict ultimate pork quality

Variations in pork quality reflect value differentials. However, only when they can be easily, accurately, rapidly and cost-effectively detected, can swine producers expect to eliminate poor quality from their herds through genetic selection, and can the industry be expected to take the necessary environmental precautions to prevent poor quality. This study was designed to assess the effectiveness of various techniques thought to predict ultimate pork quality through the examination of the physical and chemical properties of early post-mortem (PM) musculature. Based on stiffness and pH 30, 285 carcasses were selected. This selection procedure ensured a wide variation in ultimate quality. Using 12 instruments simultaneously, temperature, stiffness, electrical properties, lightness properties, and pH 45 of the early PM longissimus thoracis et lumborum were recorded to predict ultimate quality. Based on post-rigor light reflection and water-holding capacity (WHC), quality was assigned to one of five arbitrary groups. Of all techniques tested, the only one with any potential for adequate prediction of quality categories was pH 45. Combination of different techniques did not significantly increase predictive values. For predicting quality of single carcasses, pH 45 should not be considered satisfactory. However, based on our success in selecting carcasses representing quality variation for this study and the results obtained from the study, using pH 45 and muscle stiffness to select groups of carcasses is feasible. We conclude that the techniques used early post mortem are not appropriate for predicting ultimate pork quality for single carcasses. At present we recommend that only post-rigor muscle be considered, and that ultimate pH, light reflection and a measure of WHC should be used.

The effect of high and low voltage electrical stimulation on beef quality

Meat bulls were assigned to three treatment groups-high voltage intermittent electrical stimulation, low voltage electrical stimulation and no stimulation. Both stimulation methods resulted in a significantly more rapid pH fall in the longissimus and adductor muscles during the first 8 h post mortem. Carcass cooling rates were relatively slow, since temperatures of the longissimus and adductor muscles were 15°C, respectively, at 8 h post mortem. Samples of stimulated longissimus, cut at 24h post mortem and vacuum stored at 3°C for 6 days, had a brighter red colour, higher drip and heating loss, lower shear force values and scored better in taste panels, compared with samples from control carcasses. No significant differences were observed between high and low voltage electrical stimulation in quality traits measured. Although the combined result of pH and temperature measurements during the first 8 h post mortem suggest an absence of cold shortening conditions in control carcasses, a lower sarcomere length was found in samples of the longissimus muscle taken from these carcasses at 24 h post mortem.

Effect of electrical stimulation on veal quality

In three experiments involving a total of eighty-eight veal calves raised in groups and with access to straw, plasma hemoglobin (Hb) levels were determined at one week ante mortem. In each experiment, animals with similar Hb levels were paired. One animal of each pair was stimulated electrically (ES) post mortem whereas the other remained non-stimulated (NS). ES resulted in a more rapid pH fall in longissimus and semi-membranosus muscle. Carcass lean colour scores were improved at 24h, but not at 40 min, post mortem. At 24h post mortem longissimus muscle from ES carcasses showed a brighter colour, lower sarcomere length and lower protein solubility. No significant differences were observed in total haem pigment. After vacuum storage at 3°C for 6 days, samples from ES carcasses had a brighter colour, higher drip and heating loss, lower maximum shear force values, and better ranking and scoring in taste panel preference tests than NS samples. The data indicate that a certain degree of denaturation of the sarcoplasmic proteins may be responsible for the observed effects of ES on water retention and muscle colour, while the improvement of tenderness in the present experiment was due to the prevention, by the treatment, of cold shortening. It is suggested that ES may possibly contribute to the introduction of alternative veal production methods, and thus improve animal welfare.

Determinants of tenderisation in beef Longissimus dorsi and Triceps brachii muscles

Tenderisation of bovine Mm. longissimus dorsi and triceps brachii and factors impacting tenderisation were studied. Mm. longissimus dorsi and triceps brachii of 12 Friesian-Holstein cows (age 3-11 years; 212-349 kg carcass weight) were sampled at various times post mortem (p.m.) for determination of pH, temperature, fibre type and morphology, connective tissue distribution, SDS-PAGE of myofibrillar proteins, Warner-Bratzler shear force, sarcomere length and osmolality. The stretched position of the M. triceps brachii (sarcomere length 2.35 ± 0.24 μm) resulted in a relatively low shear force at 1 day p.m. (6.2 ± 0.9 kg/cm(2)) with further storage having little additional effect. M. longissimus dorsi entered rigor in a more contracted state (sarcomere length 1.65 ± 0.11 μm), resulting in a relatively high shear force at 1 day p.m. (10.3 ± 2.3). Stepwise linear regression was used to calculate the best 1- to 3-variable equations for shear force of M. longissimus dorsi at 1, 7 and 14 days p.m. and the decrease in shear force between 7 and 14 days p.m. Shear force at 1 day p.m. appeared to be determined mainly by the speed of pH- and temperature-decline. Proteolysis of myofibrillar proteins and animal age appeared to be the main determinants for shear force at 1 and 14 days p.m. The average surface area of type I fibres could explain part of the variation in the decrease in shear force between 1 and 14 days p.m.

The effect of dietary vitamin E supplementation on drip loss of bovine Longissimus lumborum, psoas major and Semitendinosus muscles

The effect of dietary vitamin E supplementation (2150 IU/head/day) on drip loss and related quality traits of bovine M. longissimus lumborum M. psoas major and M. semitendinosus was examined. The effect of vitamin E supplementation on drip loss seemed to depend on muscle studied. Drip loss of longissimus muscles was not significantly influenced, whereas supplemented semitendinosus muscles lost significantly less (p < 0.05) and supplemented psoas major muscles significantly more (p < 0.05) drip than did control counterparts. In both supplemented and control samples, sarcolemma failure occurred. No ultimate pH differences were detected between control and supplemented samples regardless of the muscle considered. In supplemented semitendinosus muscles, the decrease in drip loss was accompanied by an increase of sarcoplasmic protein solubility and sarcomere length. It is discussed that both these variables may be related to the stability of mitochondria and sarcoplasmic reticulum, as affected by dietary supplementation of vitamin E. However, this view deserves further investigation and more evidence is needed to establish the mechanism by which vitamin E influences drip loss.

The effect of storage temperature on drip loss from fresh beef

The effect of post rigor storage temperature on drip loss of two bovine muscles (M longissimus thoracis and M semimembranosus) was examined using 12 Dutch Friesian Holstein bulls. Drip loss of both longissimus and semimembranosus muscles was influenced by post rigor storage temperature. Higher storage temperatures resulted in increased drip losses, probably caused by a decrease in viscosity of the drip. The increase was most marked for the M longissimus thoracis. The relationship between drip loss and storage temperature was not linear; drip loss was found to be less affected by storage temperature as the latter was increased. The observed relationship could not be explained by a decrease in viscosity of the drip at higher temperatures alone. It was thought that faster ageing of the meat at elevated temperatures might increase the myofibrillar water-holding capacity, resulting in a decreased drip loss. However, this hypothesis requires further research.

Survival of pathogenic bacteria on pork loins as influenced by hot processing and packaging

The impact of hot and cold processing on the survival and/or growth of Salmonella , Listeria monocytogenes , pathogenic Yersinia enterocolitica , Aeromonas hydrophila , and Campylobacter spp. On inoculated pork loins was studied. Loin pieces were inoculated with pathogen-containing feces, then vacuum packaged directly after hot boning (hot packaging), vacuum packaged after chilling for 1 d, or left unpackaged. Pathogen numbers were assayed after storage at 1 + 1°C for 0, 1, 2, 5, and 9 d. Campylobacter numbers decreased during the storage period, but the organisms could still be recovered after 9 d storage. A lower Campylobacter survival rate was observed on unpackaged pork loin pieces. The other pathogens were less affected by packaging treatment. Numbers of L. monocytogenes increased by approximately 1-log10 CFU/cm2. Survival and growth of A. hydrophila during refrigerated storage varied between trials. In Experiment 1, numbers increased by ca. 2-log10 CFU/cm2, while levels were stable or decreased slightly in Experiment 2. Salmonella levels decreased during storage, with the greatest survival observed on hot-packaged pork. Despite the fact that pork loins were inoculated with ca. 102 CFU pathogenic Y. enterocolitica per cm2, the organism was recovered only sporadically during the storage period. This may be due to competition with the natural microflora. Existing procedures are often inadequate for recovering small numbers of pathogenic Y. enterocolitica in the presence of large numbers of competing flora. Until recovery procedures are improved, the effect of packaging treatment on pathogenic Y. enterocolitica cannot be determined.

On the assessment of water-holding capacity of hot- vs cold-boned pork

The effects of time of boning and storage period on creatine kinase (CK) activity, transmission value, drip losses and water-holding capacity (WHC) measured by various methods was investigated. At 40 min post-mortem 30 pig carcasses with pH values > 6·2 in the loin were selected. The right loin of each carcass was hot boned and vacuum packaged immediately. The left loin was cold boned and packaged after overnight chilling at 2 ± 2°C. After 1, 5 and 12 days of storage at 0 ± 1°C, 10 hot- and cold-boned loins were unpacked and sampled. Time of boning did not affect drip losses. At 1 day post-mortem the CK activity was higher in hot- than in cold-boned pork. Sarcomere lengths were not affected by time of boning. The WHC was investigated by two controlled methods. A filter-paper press method was not sensitive enough to assess differences in WHC of hot- vs cold-boned pork. The results of a gravimetric method depended on the sample location. Results of the gravimetric test decreased with increasing storage periods. The results suggest that under the experimental conditions the chilling rates of hot-boned vs carcass-attached muscles were similar.

Electrical stimulation during exsanguination: Effects on the prevalence of blood splash and on sensory quality characteristics in veal

Twenty-four veal calves were stunned with a captive bolt. Twelve calves were shackled by the left, the other twelve by the right hindleg. Approximately 1 min after sticking, six carcasses of each of these subgroups were stimulated electrically with equipment relying on a combined high (3000 V, 0·83 pulses s(-1), 1·5 ms duration) and low 35 V, 14 pulsess(-1)) voltage action. The remaining carcasses were left unharmed. At 24 h post-mortem hindquarters were boned to commercial primal cuts. Surrounding connective tissue and cut-up surfaces of primals as well as certain locations vulnerable for blood splash were further dissected. Neither electrical stimulation nor shackling by either of the hindlegs significantly affected the prevalence and severity of blood splash. Post-mortem factors promoting blood splash and possibly related to electrical stimulation and shackling are discussed. At 7 days post-mortem the sensory meat quality was assessed. In general, electrical stimulation did not significantly affect waterbinding and colour characteristics in longissimus (M. longissimus dorsi) and semimembranosus samples. Sarcomere lengths were similar in stimulated and control groups in longissimus but not in semimembranosus muscle. In both muscles shear force values were lower after electrical stimulation. In general, neither longissimus nor semimembranosus samples excised ipsilaterally from the shackled leg side exhibited differences in tenderness and sarcomere length. It is concluded that shackling by one leg or the other does not interfere with the tenderising effect of electrical stimulation.

Variation in post-mortem rate of glycolyis does not necessarily affect drip loss of non-stimulated veal

In this study the effect of the rate of post mortem pH fall on the water-holding capacity of meat from moderately chilled veal carcasses was investigated. Also the relationship between muscle protein denaturation and drip loss of veal was examined. Three groups of 10 Friesian Holstein male veal calves each were selected on the basis of their pH in M. longissimus thoracis et lumborum (LTL) at 3 hr post mortem (pH(3)): (1) fast pH-fall, pH(3) < 6.2; (2) intermediate pH-fall, 6.5 < pH(3) < 6.6; (3) slow pH-fall, pH(3) > 6.7. After 48 hr of chilling the LTL was excised from the carcass and sampled for determination of drip loss, filter paper wetness, sarcomere length, protein solubility and transmission value. Differences in pH(3) were not associated with differences in drip loss, filter paper wetness or differences in protein denaturation. It is suggested that at the relatively high veal carcass chilling rate the effect of rate of pH-fall on protein denaturation and thus on drip loss is negligible. Drip loss of veal was highly correlated with both solubility of sarcoplasmic (r = -0.67; p < 0.001) and total muscle protein (r = -0.54; p < 0.01) and with transmission values (r = 0.66; p < 0.001). These results indicate that protein denaturation measurements may be a good predictor for drip loss of veal.