R. G. Kauffman

The relationship of sarcoplasmic and myofibrillar protein solubility to colour and water-holding capacity in porcine longissimus muscle.

In order to investigate the relationship of sarcoplasmic and myofibrillar protein solubility to colour and water-holding capacity (WHC) in pork, 60 loins were selected to represent the quality classes: PSE (pale, soft, exudative), RSE (reddish-pink, soft, exudative), RFN (reddish-pink, firm, non-exudative) and DFD (dark, firm, dry). PSE samples exhibited lower (p<0.05) protein solubility (sarcoplasmic, myofibrillar and total) compared to the other quality classes. RSE samples exhibited lower (p<0.05) sarcoplasmic protein solubility compared to DFD samples. RSE, RFN and DFD samples had similar myofibrillar and total protein solubilities. Sarcoplasmic protein solubility explained 71% of the variation in lightness with a linear decrease in L* value. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) gels of the sarcoplasmic and myofibrillar samples distinctly showed the association of some sarcoplasmic proteins with the myofibrillar protein fractions in PSE and RSE samples. The sarcoplasmic proteins which precipitated were phosphorylase, creatine kinase, triose phosphate isomerase and myokinase for PSE and phosphorylase for RSE samples. Pork colour is highly correlated with precipitation of sarcoplasmic proteins while WHC is affected by denaturation of myofibrillar proteins (PSE samples) and lower ultimate pH (PSE and RSE samples).

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.

A comparison of methods to estimate water-holding capacity in post-rigor porcine muscle

Water-holding capacity (WHC) of muscle is important because it affects both qualitative and quantitative aspects of meat and meat products. For assessment of WHC under field and laboratory conditions, there are several methods available, but they have not been compared in a single experiment to determine accuracy and repeatibility. The Longissimus dorsi from each of 28 porcine loins representing three distinct levels of WHC (DFD, PSE, normal) was separated into eighteen parts that were randomly assigned to individual methods. The following methods were compared: Grau-Hamm and Braunschweiger-Gerät filter paper press techniques using five approaches of evaluation for each method; transmission per cent; swelling due to added water; centrifugation; 48-h fresh and cooked shrink: imbibition of surface fluids, kapillar volumeter, permittivity; and score or weight of surface fluids accumulating on filter paper. Results indicated that most methods separated the three muscle types. However, the cooking loss tests failed to differentiate between PSE and normal samples, and the transmission, imbibition and pressed fluid methods did not always distinguish between DFD and normal. The tests that appeared to be most reliable included drip loss originating from size-standardized samples, swelling of homogenized samples by added water and absorption of surface fluids on filter paper.

Early-postmortem cooling rate and beef tenderness

Four distinct early-postmortem cooling rates (as measured within the longissimus muscle) were obtained by exposing one side of each of five fat and five lean steers to moving air at -2° and the other to 9° static air. Loin steaks of the fastest cooling group were found to be the least tender and to have the shortest sarcomeres; the three remaining groups differed significantly from each other in tenderness but not in sarcomere length. For all twenty sides, regardless of treatment group, tenderness was highly dependent on, and almost linearly related to, the muscle temperature attained at 2 hours post mortem (27-40°), the relationship deteriorating rapidly as longer time intervals and lower temperature ranges were considered. The results indicate that (1) except in very rapidly chilled lean carcasses, cold shortening is not a significant determinant of tenderness; (2) the enhanced tenderness of slowly chilled beef is not due primarily to the relatively prolonged avoidance of shortening-inducive temperatures but to the accompanying retardation of cooling during the first 2-4 hours post mortem, when muscle temperatures are still far above those associated with cold shortening and (3) the generally recognised superior tenderness of well-finished beef is largely (and perhaps entirely) a consequence of slower cooling during this very early-postmortem period.

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.

Quality attributes of major porcine muscles : a comparison with the Longissimus lumborum

Quality attributes of the longissimus lumborum (LL) were compared to the attributes of the muscles semimembranosus (SM), rectus femoris (RF), biceps femoris (BF), gluteus medius (GM) and the lateral portion of the semitendinosus (ST) in the ham, the psoas major (PM) in the loin and the supraspinatus (SS), infraspinatus (IS) and triceps brachii (TB) in the shoulder. Carcasses were allocated to quality groups based on measurements of muscle exudate and lightness (CIE-L(∗)) in the LL. The SM, BF, GM and ST in the ham were similar to the LL (P > 0·05) in meat ultimate pH (pHu) and exudate and the GM, ST and LL were similar (P > 0·05) to the LL in lightness. The TB, RF, SS, PM and IS were similar (P > 0·05) in exudate, lightness and pHu and compared to the LL, were less exudative (P < 0·05) and darker (P < 0·05). When the LL was classed pale, and exudative, the GM, BF, SM and ST were also pale and exudative but the other muscles were darker and non-exudative. When the LL was classed dark and non-exudative, all other muscles were dark, non-exudative and the pHu was high. Therefore, the LL could serve as a reliable indicator of colour and exudate for all porcine musculature when the condition was dark and non-exudative (i.e. DFD). However, when the condition was pale and exudative (i.e. PSE), then the LL would serve as a reliable indicator only for the four major ham muscles, excluding the RF.

Use of electrical conductivity to predict water-holding capacity in post-rigor pork

This study was designed to re-examine the interrelationships among ultimate pH (pH(u)), electrical conductivity (EC) and water-holding capacity (WHC), and to test if EC, using one of two EC instruments, and pH(u) can be used to predict WHC. The % drip (PD) was used as measure of WHC. Forty-seven pork loins were classified either as PSE (pale, soft, exudative), RSE (reddish-pink, soft, exudative), RFN (reddish-pink, firm, non-exudative) or DFD (dark, firm, dry), based on L* values, PD and pH(u.) The measurement of EC, conducted using the instrument developed at the University of Wisconsin-Madison (UW-EC) was highly correlated to PD at 24 h post mortem (CD=66%), but the pH (NWK) measure of EC was not as highly related to WHC as UW-EC. The predictive value of pH(u) and EC for WHC were similar. When 47 samples were divided into three different groups, such as low (< 2% drip), medium (2-6% drip) and high (> 6% drip) drip loss, UW-EC alone grouped 80% of the samples correctly. Thus, EC seemed to be an accurate predictor of WHC in pork muscle when measured at 24 h post mortem. It is conceivable that EC can be used independently, or with even better success in combination with pH(u), to classify WHC of pork carcasses.

Low voltage electrical stimulation of lamb carcasses: effects on meat quality.

The effects of an early post mortem low voltage electrical stimulation (28 V, 60 Hz) on biochemical changes and on final tenderness in muscles Longissimus thoracis et lumborum and Semimembranosus from lamb carcasses were studied. It was shown that electrical stimulation accelerated the glycolytic process resulting in a significant fall in pH during the first 6 h post mortem in both muscles examined and in a significant reduction in adenosine triphosphate (ATP) content in muscle Longissimus thoracis et lumborum. The effect of electrical stimulation on tenderness was recorded by measuring shear force values 2 and 7 days post mortem. Tenderness was significantly improved by electrical stimulation for the Longissimus thoracis et lumborum both at 2 and at 7 days post mortem, while for Semimembranosus electrical stimulation significantly increased tenderness just at 7 days post mortem.

The relative effect of dietary energy density on repleted and resting muscle glycogen concentrations

The aim of this study was to assess the effect of dietary energy density on the glycogen concentration of bovine gluteus medius (GM) and longissimus thoracis et lumborum (LTL) muscles in castrated and intact males. Cattle received diet C (90% whole corn and supplement: 10% alfalfa haylage) or diet AH (100% alfalfa haylage) in three experiments involving a 2×2 factorial cross-over design. Cattle fed an AH diet for 70 days prior to the first experiment had high glycogen concentrations in the GM (129±9.9 mmol/kg) and LTL (108±7.6 mmol/kg) at the first biopsy session. These concentrations are similar to GM (133±6.2 mmol/kg) and LTL (105±5.8 mmol/kg) glycogen concentrations when these cattle subsequently received diet C for 30 or 37 days. Diet C increased muscle glycogen concentration, but the consistency of the increase in glycogen was dependent on the initial concentration. When the initial glycogen concentration was depleted to 50 μmol/g with one subcutaneous injection of adrenaline, repleted glycogen concentration was higher for diet C than AH (P<0.01) in all comparisons involving GM and LTL muscles of both steers and bulls. For resting muscle glycogen, the GM of bulls was more sensitive to the effect of diet C than the bull LTL or either muscle in steers. Diet was not a major determinant of resting muscle glycogen concentration. The ultimate pHs of GM, LTL and semimembranosus (SM) were not affected by diet and residual glycogen was lower in LTL of bulls fed either diet than for LTL of steers fed AH. Diet and male status did not affect residual glycogen in GM or SM.

Effect of ion fluid injection on beef tenderness in association with calpain activity.

Sodium pyrophosphate plus sodium chloride (PPi) was injected into pre-rigor, hot boned biceps femoris (BF) and semimembranosus (SM) muscle from 12 heifer carcasses. The PPi injection caused higher pH values between 10 and 48 h post-mortem than found in the controls for both muscles (P<0.05). PPi injection resulted in faster decreases in the activities of μ-calpain and calpastatin than in the control for both muscles with time post-mortem (P<0.05). There were significant differences between treatments in both the BF and SM (P<0.05). There was evidence that PPi-injection elevated pH, and accelerated activation of calpains, resulting in improved tenderness. The rates of degradation of titin and troponin-T as well as the appearance of 95 and 30 kDa peptides were faster in the PPi-injected muscles than the controls. PPi-injection elevated muscle pH, which was attributed to acceleration of the calpain activation. It is concluded that PPi-injection improved beef tenderness by accelerating activation of calpain.