Development of technology for the early post mortem prediction of water holding capacity and drip loss in fresh pork

Two different technologies were tested on the slaughterline for their ability to predict drip loss at 24 h, namely near infrared reflectance (NIR) and impedance measurements using a tetra polar measuring geometry at a frequency of 1000 Hz. The results demonstrate that NIR measurements (900-1800 nm) acquired during a 6 min period starting only 30 min post exsanguination through a fibre optic probe in combination with multivariate data analysis can be used for predicting drip loss 24 h after slaughter. A correlation higher than 0.8 was observed for a trial on 99 carcasses measured at a commercial slaughterhouse. The tetrapolar impedance measurements did not perform as well as NIR yielding a correlation of 0.5 with 24 h drip loss.     

Muscle protein changes post mortem in relation to pork quality traits

The relationship between post-mortem traits of muscle proteins and water loss traits was investigated using 84 pork loins representing the four quality traits of PSE, RSE (reddishpink, soft, exudative), RFN (reddish-pink, firm, non-exudative) and DFD. Protein solubility measurements (sarcoplasmic, myofibrillar and total) were lower and myosin denaturation (quantified by myofibrillar ATPase activity) was higher for PSE samples compared with samples from the other quality classes. RSE samples were similar to RFN samples in protein solubility and myosin denaturation, although RSE had lower values then DFD samples for protein solubility measurements. RFN samples had lower drip, thaw, cook and total water loss than RSE samples and all water loss traits were lowest for DFD samples and highest for PSE samples. Insoluble phosphorylase was the only characteristic that differentiated among PSE, RSE and RFN samples. SDS-PAGE and Western blots indicated that in PSE and RSE samples, the myofibrillar protein titin was less degraded and nebulin was more degraded compared with RFN and DFD samples. SDS-PAGE of extracted and unextracted myofibrils showed that the reduced myofibrillar solubility of PSE samples was caused by decreased extractability of the myosin heavy chain in these samples. In conclusion, although RSE samples have unacceptably high water loss, muscle protein denaturation was minimal and did not explain the low water-holding capacity.     

Improving meat quality of organic pork through post mortem handling of carcasses: an innovative approach

This study was conducted to examine the best combination of post mortem chilling, suspension and ageing in order to optimize tenderness of organic pork at slaughter, which may be tougher than conventionally produced pork, because of lower daily gain. Combinations of stepwise chilling with a holding period of 6h at 10°C or traditional blast tunnel chilling, suspension in the pelvic bone or Achilles Tendon and ageing 2 or 4 days post mortem were tested. Stepwise chilling and ageing improved tenderness of the loin, and the effects were additive, whereas pelvic suspension was less effective in texture improvements, and non-additive to stepwise chilling. Stepwise chilling improved tenderness to a similar degree as can be obtained within 2-4 days of extended ageing, however, the minimum temperature during the holding period seems to be crucial in order to obtain a positive effect of stepwise chilling, and it should be above 7.5°C.     

Physiological and structural events post mortem of importance for drip loss in pork

Early post mortem metabolism and structural changes from 3 to 24 h, together with pH, temperature and impedance Py development were investigated in 37 Duroc×Landrace×Large White (DLY) pigs covering a range of drip loss from 2.2 to 12.6%. Multivariate statistical analysis was used to assess the impacts of different metabolites, pH and temperature, impedance, cytoskeletal protein degradation and extracellular cross-sectional area on drip loss. Taken as single factors, the concentration of lactate could explain 80% of the variation in drip, inosine monophosphate (IMP) and adenosine triphosphate (ATP) concentration explained 71 and 68%, respectively, whereas inosin and glycogen levels explained only 59 and 60%. The extracellular area was found to explain 39% of the variation in drip. The area between fibres provided more significant information than did the area between fibre bundles. The degradation of the cytoskeletal proteins was not related to drip loss. Impedance Py development over 24 h could explain 66% of the variation in drip, whereas pH and temperature explained 85 and 87%, respectively. A model including all measured variables could explain 83% of the variation in drip. However, only pH, temperature, impedance, [ATP]_{1 h} and [lactate]_{1 h and 2 h} were significant in relation to drip. By reducing the variables in the multivariate analysis, 89% of the variation in drip could be explained by a model containing only pH_{2 h} and temperature_{1 min}. To explain variation in drip loss, pH and temperature measurements at significant time points were sufficient. Variation in post-mortem metabolites did, however, explain why variation in pH and temperature occurred. Development of drip channels was ruled by pH and temperature while impedance development was highly correlated to pH. This multi-faceted study shows those parameters, which can best be used to indicate or predict WHC, as well as those indicating the basic mechanism underlying variations in drip.     

Effects of housing conditions of slaughter pigs on some post mortem muscle metabolites and pork quality characteristics

The results of two experiments studying the effects of housing conditions on post mortem muscle metabolism and meat quality are presented. In the first experiment slaughter pigs (n=71) from two different crossings, were raised at a density of 0.7 m²/animal (10 pigs/pen) either with (enriched) or without (conventional) a bedding of daily fresh straw. In the second experiment, animals (n=60) were reared under either conventional or free range housing (1.25 m²/animal, 30 pigs per pen) conditions. Main differences between conventional and enriched housed pigs were found in the biceps femoris (BF) muscle, and related to temperature, drip loss and colour. Association studies revealed that there were significant correlations between early (0–4 h) post mortem muscle pH and glycogen and lactate concentrations and between muscle pH measured at 1 h post mortem and muscle rigidity, expressed as the rigor value. There were significant differences with respect to meat quality and post mortem metabolism of the longissimus lumborum (LL), between conventional and free-range pigs. Early post mortem pH (0–4 h) was highest in the free-range pigs, due to low lactate concentrations. The relatively fast pH decline in the conventionally housed group resulted in increased amounts of water exuding from the meat, as measured by the filter paper method. The ultimate pH, was lowest in the free-range animals. The differences in ultimate pH, however, had no effect on drip or cooking losses. It can be concluded from these results that enrichment of the housing system has little effect on the course of the post mortem metabolism and meat quality. However, increasing the freedom of movement by applying lower stocking densities, affects the post mortem muscle metabolism, resulting in reduced water exudation. Correlations up to 0.7 between energetic parameters are not sufficiently high to be useful to predict meat quality of individual carcasses.     

Prediction of pork quality with near infrared spectroscopy (NIRS): 1. Feasibility and robustness of NIRS measurements at laboratory scale

The objective was to study prediction of pork quality by near infrared spectroscopy (NIRS) technology in the laboratory. A total of 131 commercial pork loin samples were measured with NIRS. Predictive equations were developed for drip loss %, colour L*, a*, b* and pH ultimate (pHu). Equations with R(2)>0.70 and residual prediction deviation (RPD)≥1.9 were considered as applicable to predict pork quality. For drip loss% the prediction equation was developed (R(2) 0.73, RPD 1.9) and 76% of those grouped superior and inferior samples were predicted within the groups. For colour L*, test-set samples were predicted with R(2) 0.75, RPD 2.0, colour a* R(2) 0.51, RPD 1.4, colour b* R(2) 0.55, RPD 1.5 and pHu R(2) 0.36, RPD 1.3. It is concluded that NIRS prediction equations could be developed to predict drip loss% and L*, of pork samples. NIRS equations for colour a*, b* and pHu were not applicable for the prediction of pork quality on commercially slaughtered pigs.     

Prediction of pork quality with near infrared spectroscopy (NIRS) 2. Feasibility and robustness of NIRS measurements under production plant conditions

Longissimus dorsi samples (685) collected at four processing plants were used to develop prediction equations for meat quality with near infrared spectroscopy. Equations with R(2)>0.70 and residual prediction deviation (RPD)≥2.0 were considered as applicable for screening. One production plant showed R(2) 0.76 and RPD 2.05, other plants showed R(2)<0.70 and RPD<2.0 for drip loss %. RPD values were ≤2.05 for drip loss%, for colour L*≤1.82 and pH ultimate (pHu)≤1.57. Samples were grouped for drip loss%; superior (<2.0%), moderate (2-4%), inferior (>4.0%). 64% from the superior group and 56% from the inferior group were predicted correctly. One equation could be used for screening drip loss %. Best prediction equation for L* did not meet the requirements (R(2) 0.70 and RPD 1.82). pHu equation could not be used. Results suggest that prediction equations can be used for screening drip loss %.     

Physical changes of significance for early post mortem water distribution in porcine M. longissimus

The post mortem changes in water mobility and distribution were followed in porcine muscle (M. longissimus dorsi) samples using continuous low-field NMR relaxation measurements and simultaneous measurement of changes in muscle impedance as an indirect measure of membrane integrity as well as muscle contraction measurements using a rigormeter instrument. Distributed exponential fitting analysis of NMR T₂ relaxation data revealed the presence of three distinct water populations (T₂₀, T₂₁, T₂₂) within the muscle during its conversion to meat. Comparison of T₂ relaxation patterns and contraction data indicates that rigor development affects the attributes of the T₂₁ water population and thereby contributes to myofibrillar water characteristics post mortem, as the T₂₁ water population is believed to reflect inter/intra-myofibrillar water. The volume of the water population believed to reflect extra-cellular water (T₂₂) in the living muscle. Early post mortem T₂₂ decreased slightly within the first 2–3 h post mortem followed by an increase and a change in its characteristic time constant. This was ascribed to an initial muscle cell swelling followed by water being expelled from the cellular space into the extra-myofibrillar space. Comparison of changes in the T₂₂ water population and impedance characteristics within the muscle during its conversion to meat revealed close relationship between progresses in the two attributes. Obtained data strongly support that the post mortem reorganization of water is closely associated with membrane properties, which moreover was found to affect the final water-holding capacity of the meat. Finally, a model for early post mortem events leading to changes in the distribution of water within muscles is proposed.     

Effect of cooling rate upon processing characteristics of pork meat of different glycolysis type during post mortem ageing

Rapid chilling was applied to porcine longissimus dorsi muscles at 1 h post mortem in order to observe its effect on the quality of canned products prepared from those of different pH₁ values.

The muscle from one side of each animal was removed from the carcase 50 minutes post mortem and divided into two longitudinal strips. One was chilled immediately to 13–15°C (1 h post mortem): the other after a further hour (2 h post mortem) acted as control. After the centre temperature had reached 10°C the muscles were stored in a refrigerator at 3–5°C.

Compared with the control samples (chilled at 2 h p.m.), rapid chilling from 1 h p.m. caused an improvement in the water-holding capacity and the texture of pork meat, which had higher pH₁ values and was processed at 2, 4 and 48 h p.m. There was minimum brine retention and texture score if samples—both rapidly chilled and control—were processed at 24 h p.m.

Although brine retention of PSE pork meat could not be increased even by rapid chilling, the texture of heat treated PSE pork showed an improvement during storage, which was more pronounced after ageing for 48 h, if PSE samples were chilled at 1 h p.m.     

Objective evaluation of pork quality: Results of on-line measurements

Research has been conducted on objective pork quality evaluation on line in an industrial slaughterhouse. The investigation, which involved more than 5000 pigs, lasted for 12 working days spread over four consecutive weeks between October and November. Measurements performed were Fat-o-Meat'er carcass classification (lean content, fat and muscle thicknesses), cold carcass weight, 24-h pH of Semimembranosus and Biceps femoris muscles and 24-h colour of Semimembranosus muscle. The results show that cold carcass weight and lean content are only slightly related to meat quality as evaluated by pH and colour. Cluster analysis has confirmed the importance of pH and colour parameters, such as L(?), a(?) and hue angle, for the evalaution of pork quality on line in an industrial context.     

Objective measurements of pork quality: Evaluation of various techniques

Research has been undertaken in which various methods for meat quality evaluation were compared. The measures used were pH (by homogenization and by combined electrode), light scattering conductivity, dielectric loss factor and colour. A very low incidence of PSE (Pale, Soft, Exudative) and DFD (Dark, Firm, Dry) cases was observed and the correlation between pH, as measured by homogenization and by combined electrode, did not appear to be completely satisfactory. Dielectric loss factor, as measured by the MS tester, seems to be specifically suited for PSE diagnosis. On the other hand, higher values of light scattering and conductivity measured at 24 h post mortem, are found to be linked to the rate of pH fall, even outside the range for PSE. Colour measurements, especially of the parameters L(?), a(?) and hue angle, have given interesting information. In fact, meat could be classified by colour intensity (a(?), psychometric chroma), by type of colour (hue angle) and by exudative phenomena (L(?)). No marked effects of rearing techniques have been observed, whereas the genetic background appears to influence some colour parameters. Slaughter conditions, on the other hand, could affect markedly all the meat quality parameters measured in this research.     

Changes in meat quality characteristics of bovine meat during the first 6 days post mortem

The development of some quality parameters in bovine meat during the first 6 days of post mortem ageing was studied in two commercial groups (heifer and bull). In the first day bull meat is harder and springier. Meat pH falls during the first 24 h post mortem in both groups, reaching values around 5.5, and it did not change during the next 5 days. Water-holding capacity (expressed as percentage of expelled water) increased in heifer meat. Instrumental texture measures (texture profile analysis, TPA) showed a decrease in hardness, springiness and chewiness in bull raw meat. Sensory analysis showed that assessors perceived a decrease in hardness and in springiness in bull meat and a decrease in juiciness and in chewiness (number of chewings before swallowing) in heifer meat. Ageing showed no effect on assessors’ pleasantness either in heifers’ or in bulls’ meat. During the first 3 days, heifer meat was juicier. Heifers’ meat produced a greater pleasantness on the sixth day. Both meats were not very different for most quality parameters studied in this work.     

The measurement of light scattering and electrical conductivity for the prediction of PSE pig meat at various times post mortem

Measurements of light scattering and electrical conductivity were made in the Longissimus dorsi (LD) and Semimembranosus (SM) muscles using the Fibre Optic Probe (FOP) and Quality Meter (QM), respectively, to assess their ability to estimate pig meat quality, particularly the occurrence of PSE meat. One-hundred-and-fifty-three gilt carcasses were measured on three occasions post mortem (pm): 45 min (FOP(45) and QM(45)), 2h (FOP(2) and QM(2) and 24 h (FOP(u) and QM(u)). Measurements of pH were taken in the same anatomical position and at the same times. At 24 h pm muscle reflectance (GOFO value) and subjective colour assessments were made on the cut surface of the LD at the level of the last rib. Water-holding capacity (WHC) was estimated in a sample taken from the exposed surface of the LD by the solubility of sarcoplasmic and myofibrillar proteins. The FOP(45) predicted most accurately the WHC (R(2) = 0·49). Neither of the other quality measurements improved the prediction at 45 min pm. However, at 2h, adding QM(2) as a second independent variable improved prediction of WHC (R(2) = 0.58). At 24 h the combination of FOPu, QMu and GOFO did not improve the prediction of WHC (R(2) = 0.58). The best prediction used measurements of FOP(45), QM(2) and GOFO (R(2) = 0·62). The best relationship between subjective colour scores and the quantitative measurements of meat quality using discriminant analysis was obtained with the FOPu with an error-count estimate of 15·1% followed by FOP(2) (17%), GOFO value (18·7%), pH(2) (19·7%) and QMu (20·2%). With combination measurements of two instruments, pH(2) and FOP(2) had the lowest error-count estimate (10·9%). No further precision was obtained with combinations of three instruments. These results suggest that FOP and QM can be used to predict PSE and normal pig meat at different times pm and can replace traditional pH muscle measurements.     

On-line prediction of fresh pork quality using visible/near-infrared reflectance spectroscopy

Visible/near-infrared (Vis/NIR) spectroscopy was tested to predict the quality attributes of fresh pork (content of intramuscular fat, protein and water, pH and shear force value) on-line. Vis/NIR spectra (350–1100 nm) were obtained from 211 samples using a prototype. Partial least-squares regression (PLSR) models were developed by external validation with wavelet de-noising and several pre-processing methods. The 6th order Daubechies wavelet with 6 decomposition levels (db6–6) showed high de-noising ability with good information preservation. The first derivative of db6–6 de-noised spectra combined with multiplicative scatter correction yielded the prediction models with the highest coefficient of determination (R²) for all traits in both calibration and validation periods, which were all above 0.757 except for the prediction of shear force value. The results indicate that Vis/NIR spectroscopy is a promising technique to roughly predict the quality attributes of intact fresh pork on-line.     

猪肉肉质和风味的提高与改善

介绍了影响猪肉肉质的因素和改善肉质的方法,主要有营养调控和管理方式的改善。