Novel aspects of health promoting compounds in meat

Meat is an integral part of the human diet. Besides essential amino acids and nutritive factors of high quality and availability, meat provides often overlooked components of importance for human health. These are amino acids and bioactive compounds that may be very important in i) preventing muscle wasting diseases, such as in sarcopenia, ii) reducing food and caloric intake to prevent metabolic syndrome, iii) blood pressure homeostasis via ACE-inhibitory components from connective tissue, and iv) maintaining functional gut environment through meat-derived nucleotides and nucleosides. In addition, meat could be an important source of phytanic acid, conjugated linoleic acids and antioxidants. Further, it becomes increasingly apparent that design of in vitro meat will be possible, and that this development may lead to improved health benefits from commercially viable and sustainable meat products.

Influence of feeding intensity, grazing and finishing feeding on meat and eating quality of young bulls and the relationship between muscle fibre characteristics, fibre fragmentation and meat tenderness

Forty-one autumn-born Friesian bull calves were allocated to two production systems (Extensive='E'and Intensive='I'). In the E-system, animals were loose-housed and fed a roughage-based diet from October to May, followed by a grazing period from May to October. Ten animals were slaughtered directly from pasture in October [360 kg body weight (BW)] and 11 after a 10-week finishing period in tie-stalls (460 kg). The E-bulls were compared with intensively-fed tie-stall-housed young bulls (I) slaughtered at comparable weights (360 kg, n=11 and 460 kg, n=9). The myofibril fragmentation index (MFI) was measured 24 h post mortem in semitendinosus (ST), longissimus dorsi (LD), and supraspinatus (SU) muscles, and meat quality characteristics and sensory evaluation of LD were performed on aged meat. Intramuscular fat content was lower (P<0.001) in all three muscles of E- compared with I-bulls. MFI of ST and LD was lower in E-bulls compared with I-bulls, but only at 360 kg. In contrast, MFI of SU was higher in E- compared with I-bulls at 360 kg. In E- compared with I-bulls, shear force value of ST was higher (P<0.003) at 360 kg, but not at 460 kg. Panel scores for tenderness, taste and juiciness were all lower (P<0.006 to 0.001) and remarks for off-flavour higher in E- compared with I-bulls, the effects being most pronounced at 360 kg. A 10-week finishing period improved all meat and eating quality characteristics of E-bulls. In LD, the correlation between MFI and tenderness was 0.79 (P<0.001), which indicates a potential of MFI as an early predictor of tenderness.

An assessment of extraction and assay techniques for quantification of calpain and calpastatin from small tissue samples

Our objective was to evaluate whether small (biopsy-sized) samples could be used to measure calpain and calpastatin activities in skeletal muscle. The accuracy of different separation and assay methods for the quantification of calpains and calpastatin from small (1.0 and 0.2 g) skeletal muscle samples was tested. In Exp. 1, the LM was removed from six lambs, and a 50-g subsample was processed using the reference method (DEAE-Sephacel chromatography and casein assay). Subsamples (1.0 and 0.2 g) also were processed using the two-step separation (1 mL DEAE-Sephacel and bulk elution using 200 and 400 mM NaCl) and heated calpastatin methods; in both cases, fractions were assayed with Bodipy-labeled and [14C]-labeled casein microassays. Finally, casein zymography was used to separate and quantify the calpain proteases from 1.0-and 0.2-g samples. The values obtained after processing the 50-g sample using the reference method were judged most accurate, and the alternative approaches were compared with these. For each extraction and assay approach, we considered: 1) the effect of the sample size on the mean activity; 2) increased or decreased variation of data; and 3) the correlation relative to the reference method. Where possible, we compared the ratio of calpain to calpastatin activities determined using the alternative approaches with the ratios found using the reference method. These methodologies were further investigated in Exp. 2, where single homogenates from different tissues (heart, spleen, lung, and muscle) were assayed using the alternative approaches. Experiment 1 established that most of the approaches suffered from poor correlations and/or unacceptable variation. By using a large, homogenous sample in Exp. 2, however, we determined that this error was not due to the methodologies themselves. Therefore, the unacceptable variation found in Exp. 1 resulted from the small sample size, and we recommend that large tissue samples (e.g., 50 g) should be used for calpain and calpastatin activity measurements in skeletal muscle instead of small tissue biopsies (e.g., 0.2 and 1.0 g).

Compensatory growth improves meat tenderness in gilts but not in barrows

Compensatory growth is a phenomenon observed in pigs given free access to feed following a period of restricted feeding that results in increased growth rates. Compensatory growth is believed to increase protein turnover and thereby the proteolytic potential at the time of slaughter, leading to faster tenderization rates of meat. Nine litters of three gilts and three barrows were allocated within litter and gender to three dietary treatment groups. Pigs had ad libitum access to feed from d 28 to slaughter at d 140 (ALA) or were restricted to 69% ad libitum from d 28 to d 80 or 90, and then given ad libitum access to the diet until slaughter at d 140 (RA80 and RA90, respectively). Pigs in the RA80 and RA90 treatment groups had a 9.7% higher (P < or = 0.001) fractional growth rate in the second feeding period than those in the ALA group. Growth rate was correlated to the activity of m-calpain (r = 0.37; P < or = 0.01), beta-glucuronidase (r = 0.48; P < or = 0.001), and cathepsins B (r = 0.47; P < or = 0.001) and B+L (r = 0.31; P < or = 0.04). The LM of RA80-gilts received higher tenderness scores than the LM of ALA gilts, but tenderness scores were similar among barrows regardless of treatment (gender x treatment; P = 0.02). Conversely, tenderness scores were higher for the biceps femoris of ALA barrows than either ALA gilts or RA90 barrows (gender x treatment; P = 0.02). Desmin and troponin-T degradation, as well as myofibrillar fragmentation index, of the LM were not (P > or = 0.24) affected by treatment. No dietary treatment effects were observed on the activities of mu-calpain (P = 0.15), m-calpain (P = 0.74), or calpastatin (P = 0.91) at slaughter. The cathepsin inhibitors, cystatins, tended to be increased (P = 0.06) in RA80 and RA90 pigs. Sarcomere length was longer (P = 0.003) in the LM of gilts than barrows. Barrows in the RA80 group had lower i.m. fat concentrations than ALA; however, no differences were found in the LM of gilts (gender x treatment; P = 0.03). The underlying hypothesis that compensatory growth leads to an increased proteolytic potential at the time of slaughter could not be verified in this study.

Changes in the muscle proteome after compensatory growth in pigs

Sixteen female pigs (Duroc x Landrace x Large White) were divided into 2 groups, which had either free access to the diet (control group) or were feed-restricted from d 28 to 80 and then had free access to the diet (compensatory growth group). The sensory analysis showed that the pigs exhibiting compensatory growth produced meat with increased tenderness compared with control pigs (P < 0.05). To gain further knowledge of the influence of compensatory growth on meat tenderness, the sarcoplasmic protein fraction of muscle tissue was studied at the time of slaughter and 48 h postmortem using proteome analysis. At slaughter, 7 different proteins were found to be affected by compensatory growth: HSC70, HSP27, enolase 3, glycerol-3-phosphate dehydrogenase, aldehyde dehydrogenase E2, aldehyde dehydrogenase E3, and biphosphoglycerate mutase. The HSC70 and HSP27 both belong to the heat shock family and are known to play a role during muscle development. Hence, they may be affected by compensatory growth and increased protein turnover. Forty-eight hours after slaughter, 8 different proteins were found to be affected by compensatory growth: myosin light chain (MLC) II, MLC III, sulfite oxidase, chloride intracellular channel 1, 14-3-3 protein gamma, elongin B, and phosphohistidine phosphatase 14. The changes observed on MLC II and MLC III could be a consequence of enzymatic cleavage in the neck region of the globular myosin head domain that causes the release of MLC II and MLC III from the actomyosin complex. It has previously been hypothesized that compensatory growth results in an increased postmortem proteolysis; thus it was presumed that the intensity of some protein fragments would be affected by compensatory growth. However, the peptides that were found to be affected at 48 h postmortem were all full-length proteins. The 14-3-3 protein gamma has been proposed to play a role in the contraction of muscle during rigor and may thereby have an effect on meat tenderness. This study reveals some very interesting changes in the muscle proteome affected by compensatory growth, which may be useful in understanding the relationship among compensatory growth, protein turnover, and meat tenderness.

Dietary-induced changes of muscle growth rate in pigs: effects on in vivo and postmortem muscle proteolysis and meat quality

The effects of various growth rates in pigs induced by four different feeding strategies on the activity of the calpain system and on postmortem (PM) muscle proteolysis and tenderness development were studied. An increased growth rate may be caused by an increased protein turnover, which results in up-regulated levels of proteolytic enzymes in vivo that, in turn, possibly will affect PM tenderness development. It can be hypothesized that increased proteolytic activity pre-slaughter will increase the PM tenderization rate. From postnatal d 28 to d 90 (phase 1) the pigs were divided into two groups, given either ad libitum (A) or restricted (R, 60% of ad libitum) access to feed. The two groups were then divided into two subgroups, given either restricted or ad libitum access to feed from d 91 to slaughter at d 165 (phase 2). Measurements of the activity of mu-calpain, m-calpain, and calpastatin; concentrations of total collagen and the percent of soluble collagen; and RNA, DNA, and elongation factor-2 where made at slaugther. Myofibrillar fragmentation index (MFI) was determined at slaughter and 24 h PM. Warner-Braztler shear force was determined 1 d and 4 d PM. Pigs fed restricted diets in phase 1 and fed ad libitum in phase 2 (RA pigs) had increased growth rates in the last phase compared to pigs fed ad libitum during both phase 1 and phase 2 (AA pigs). The increased growth rate (compensatory growth) was followed by an increased proteolytic potential (mu-calpain:calpastatin ratio), increased MFI values, and higher tenderization rates. There was a positive correlation between the activities of m-calpain and growth rates (r = 0.35, P = 0.03), and between RNA levels and growth rates (r = 0.43, P = 0.006). The proposed hypothesis is largely supported by the results. The activities of both mu- and m-calpain at slaughter were highest in fast-growing pigs. The calpain activity was highest in RA pigs, which in turn also had the fastest growth rates prior tslaughter among the four groups. This implies that the synthesis of these enzymes was up-regulated during the second feeding period to a larger extent in RA pigs. The proteolytic potential and the MFI values indicate that the up-regulated in vivo calpain activity had an effect on PM protein degradation, which also is supported by the higher tenderization rate in RA pigs.

Muscle glycogen stores and meat quality as affected by strategic finishing feeding of slaughter pigs

The aim of the present study was to investigate whether muscle glycogen stores in slaughter pigs could be decreased through strategic finishing feeding before slaughter. Moreover, preliminary meat quality traits were measured to see whether such a regulation of muscle glycogen stores affected ultimate pH, color, and tenderness in the meat. The strategic finishing feeding was carried out the last 3 wk prior to slaughter. Seven experimental groups with eight animals per group were fed diets low in digestible carbohydrates. A control group with four animals was fed a traditional grower-finishing diet. The muscle glycogen stores were reduced in longissimus muscle (LM) 11 to 26% at the time of slaughter in pigs that were fed the experimental diets compared with the control group. Meat quality measured as ultimate pH and color on LM muscle in half the pigs 24 h postmortem showed that ultimate pH in LM was not affected by the reduction in glycogen stores in the muscles from pigs fed any of the experimental diets. However, the meat from pigs fed the experimental diets was darker than the meat from pigs that were fed the control diet with two of the experimental diets, resulting in significantly lower L* values. Activities of key enzymes in the glycolytic pathway, glycogen phoshorylase a and b, phosphofructokinase, and the fatty acid oxidative pathway, beta-hydrozyacyl-CoA-dehydrogenase, were not affected by the strategic feeding. In contrast, the activity of the proteolytic enzyme calpain as well as its inhibitor calpastatin was influenced by the strategic feeding. Lower activity of mu-calpain and greater activity of calpastatin in the muscle samples from the strategically fed pigs indicate a lesser muscle protein degradation in the muscles compared with muscles of control animals. The present study showed that the muscle glycogen stores in slaughter pigs can be reduced at the time of slaughter through strategic finishing feeding with diets low in digestible carbohydrate without compromising growth rate.