Katja Rosenvold

Factors of significance for pork quality-a review.

This paper reviews current knowledge about factors of importance for pork quality with special emphasis on technological quality attributes. It is evident that production and slaughter factors can be used to control technological quality traits. However, most of the present knowledge is based on studies investigating the influence of a single or at the most two factors. This survey reveals that: -Most important, an understanding of how production and slaughter factors interact in relation to pork quality is a must to give the maximum number of tools to control pork quality and hereby meat quality demands of tomorrow. -The existence of a new genetic pool (elimination of the halothane and RN(-) genes in the commercial pig populations of tomorrow) force the meat science into a renaissance, as the influence of production and slaughter factors on pork quality may be fundamentally different in this new genetic pool. -A basic understanding on how muscle glycogen stores are influenced by genotype and feeding regime and the interaction with pre-slaughter handling might be the next major breakthrough in controlling technological pork quality. -Introduction of new production systems claim parallel studies to prevent unforseen negative effect on quality. -A holistic approach is needed to give an overall understanding of the influence of production, peri and post mortem factors on pork quality.

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.

The significance of pre-slaughter stress and diet on colour and colour stability of pork

The influence of pre-slaughter stress and a diet known to affect post mortem muscle metabolism or a standard diet (control pigs) on colour and colour stability of m. longissimus dorsi, m. biceps femoris and m. semimembranosus from 112 female pigs, free of the Halothane gene, was investigated. Pre-slaughter stress increased the early post mortem temperature in the three muscles, as well as the pH decline in control pigs, but not in pigs fed the experimental diet. Colour was measured on sliced samples after 0, 2 and 5 days retail display (1, 3 and 6 days post mortem, respectively) from the three muscles aged 1 day before cutting as well as on sliced m. longissimus dorsi samples aged 8 days before cutting (8, 10 and 13 days post mortem, respectively). Early post mortem pH was not a main determinant of the colour and colour stability, while the degree of pre-slaughter stress and especially its influence on temperature early post mortem was crucial in relation to colour development and colour stability. The discoloration rate was enhanced in m. longissimus dorsi aged for 8 days prior to retail display compared with samples aged for 1 day. However, the extent of the discoloration after 5 days of retail display was not inferior in muscle samples aged for 8 days due to a higher degree of blooming. Finally, present data indicate that 3-4 days ageing of pork prior to retail display results in the optimal colour stability.

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 T(2) relaxation data revealed the presence of three distinct water populations (T(20), T(21), T(22)) within the muscle during its conversion to meat. Comparison of T(2) relaxation patterns and contraction data indicates that rigor development affects the attributes of the T(21) water population and thereby contributes to myofibrillar water characteristics post mortem, as the T(21) water population is believed to reflect inter/intra-myofibrillar water. The volume of the water population believed to reflect extra-cellular water (T(22)) in the living muscle. Early post mortem T(22) 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 T(22) 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.

Manipulation of critical quality indicators and attributes in pork through vitamin E supplementation, muscle glycogen reducing finishing feeding and pre-slaughter stress.

The combination of a muscle glycogen reducing diet or a standard diet (control group) with normal (80 mg/kg) and high vitamin E levels (500 mg/kg) and exercise immediately prior to slaughter was used on 56 pigs to investigate the influence on meat quality indicators (pH and temperature) and attributes (drip loss, colour and Warner-Bratzler shear force). The drip loss was reduced in M. longissimus dorsi, M. biceps femoris and M. semimembranosus in pigs given the muscle glycogen reducing diet compared with the control groups, the greatest effect was seen in exercised pigs. These results can be explained by an early post mortem reduction in glycometabolism in pigs fed muscle glycogen reducing diets rather than by an increase in ultimate pH. Noticeably, high dietary vitamin E level increased muscle glycogen stores by about 10% on the day prior to slaughter but not on the day of slaughter in both dietary groups compared with the low dietary vitamin E level, which in fact reduced rather than improved the water-holding capacity, especially in pigs fed the standard diet.

Strategic finishing feeding as a tool in the control of pork quality

A standard diet and two finishing feeding strategies known to reduce muscle glycogen stores were investigated in combination with exercise immediately prior to slaughter in pigs. The objective was to determine the influence of muscle glycogen at slaughter on temperature and pH in post-mortem muscle, the colour, drip loss and Warner-Bratzler shear force of the meat. The muscle glycogen stores were reduced by strategic finishing feeding. In general, pH(45 min) was higher in muscles from strategically fed pigs compared with control pigs. Exercise also resulted in higher pH(45 min) in control pigs compared to non-exercised control pigs, while the opposite was seen in muscles from strategically fed pigs. Exercise resulted in higher muscle temperatures in the carcasses irrespective of feeding strategy. pH(24 h) were higher in M. biceps femoris and M. semimembranosus from exercised, strategically fed pigs compared with the corresponding controls. In contrast, irrespective of feeding strategy no difference in pH(24 h) was registered in the meat of non-exercised pigs. Drip loss was lower in meat of strategically fed pigs compared with meat of control pigs. Moreover the drip loss was lowest in the meat of non-exercised pigs. The present study shows that strategic finishing feeding has high potential for the control of pork quality.

Dietary creatine monohydrate affects quality attributes of Duroc but not Landrace pork

Increased creatine content in the muscle may delay post mortem lactate formation and postpone the pH decline, hence potentially improving the water-holding capacity (WHC). Duroc and Landrace pigs were supplemented with 0, 12.5, 25 or 50g creatine monohydrate (CMH)/d for 5 days prior to slaughter. Meat from Longissimus dorsi (LD) of Duroc pigs had a higher WHC and pH at all times, lower colour determinants; a* (redness), b* (yellowness), L* (lightness) and was more juicy compared to that of Landrace pigs. Furthermore, higher pH(2h), pH(24h) and decreased colour determinants were observed in carcass sides exposed to a faster cooling profile. Dietary supplementation with CMH increased the body weight gain of both breeds. However, only meat from Duroc pigs had higher pH(30min) and pH(45min) (at 50g CMH/d) and WHC, but reduced redness (reduced in both breeds) and juiciness when supplemented with CMH compared to non-supplemented controls.

Dietary creatine monohydrate has no effect on pork quality of Danish crossbred pigs

Creatine content in the muscle may delay postmortem lactate formation and postpone the pH decline, hence potentially improving the water-holding capacity (WHC) as shown in a previous study including purebred Duroc pigs, although the same study did not find any effect on meat from purebred Landrace pigs. In the present study Danish D(LY) crossbreeds were supplemented with 0 or 50g creatine monohydrate (CMH)/d for five days prior to the slaughter. CMH supplementation had no effect on meat quality indicators (pH and temperature), meat quality attributes (WHC and colour) or eating quality (juiciness and tenderness) of meat from the D(LY) crossbred pigs. As a consequence the D(LY) crossbreed was classified as a non-responder to CMH supplementation.

The calibration temperature of pH-glass electrodes: significance for meat quality classification

In this short communication we show important factors concerning pH measurements in pork. The purpose of the study was to investigate the effect of the calibration temperature of pH-buffer and of the pH-electrode on pH measured 1-120 min post mortem in pork, and to evaluate its significance for prediction of meat quality. The calibration temperature of pH-electrodes as well as the sample temperature is essential for pH measurements, as pH measurements are highly temperature-dependent. This is especially important when using pH measurement for prediction of meat quality or when different experiments are compared. We have used two calibration temperatures of 15xa0°C (normal) and 35xa0°C (modified) in the present investigation. Based on our findings, we therefore recommend a buffer and electrode temperature of 35xa0°C as a standard procedure for measuring pH early post mortem. As a minimum the pH should be presented along with the measuring and calibrating temperatures.