High early post-mortem temperature induces activation of AMP-activated protein kinase and development of pale, soft and exudative characteristics in turkey muscles.

This study investigated the effect of early post-mortem temperature on development of a turkey muscle's pale, soft and exudative (PSE) characteristics. Muscles obtained at 20 min post-mortem were incubated at 0, 20 and 40 °C until 4 h post-mortem and then stored at 4 °C. During incubation, the 40 °C group had greater rate of pH decline, lactate accumulation and R-values increase than other groups. Moreover, AMP-activated protein kinase (AMPK) activation at 1h post-mortem was higher in the 40 °C group than the other groups. At 24 h post-mortem, the 40 °C group had higher L* values and drip loss; SDS-PAGE and western blotting indicated that lower protein solubility (sarcoplasmic, myofibrillar) in the 40 °C group resulted from phosphorylase denaturation and further adhere to myofibrillar fraction. These results suggest that high temperature early post-mortem could induce AMPK activation, which results in rapid glycolysis, thus affecting protein solubility and generating PSE characteristics.

Gas composition in controlled atmosphere stunning affects turkey meat quality traits.

1. Investigations were made into the breast and leg muscle energy metabolism, and the quality of breast meat of turkeys after controlled atmosphere stunning or stun-killing (CAS) with various gas mixtures. In addition, the effect on meat quality of an increase in the chilling rate of turkey breast meat after hypercapnic or anoxic stun-killing was studied. 2. A total of 35 turkey toms within two replicate pens were individually stunned during consecutive weeks using one of 4 CAS methods. The stunning gases tested were high CO(2) concentration (60% CO(2) in air), high N(2) concentration (98% N(2), < 2% O(2)), a mixture of 76% N(2) and 24% CO(2), and a biphasic method (first minute in mixture containing 40% CO(2), 30% N(2), and 30% O(2;) followed by two minutes in a mixture containing 60% CO(2) in air). 3. The birds stunned with N(2) displayed the highest initial reduction in muscle pH, but after 4 h post mortem there were no differences in pH values associated with the various CAS methods. 4. The CAS method alone had no statistically significant effect on the quality of turkey breast muscle when the chilling speed was rapid (0°C for 4 h, followed by storage at 4°C). When the chilling rate was slowed (20°C for 4 h followed by storage at 4°C), a significant decrease in cooking loss and in Warner-Bratzler shear force was recorded for birds stun-killed with CO(2). 5. This study shows that anoxic stun-killing with N(2) had no adverse effects on meat quality despite the rapid post mortem pH decrease. The CAS with N(2) allows rapid cooling of carcases without the risk of cold shortening, whereas with CO(2)-stun-killing of turkeys, the rate of chilling should be slower. Concerning meat quality, all the CAS methods tested were suitable for stunning turkeys.

Expression of CD147 and monocarboxylate transporters MCT1, MCT2 and MCT4 in porcine small intestine and colon.

Lactate, formed mainly in the stomach and small intestines, and short-chain fatty acids (SCFAs) formed in the colon, are ionised and require transporter proteins such as monocarboxylate transporters (MCTs) for absorption. The amounts of MCT1, MCT2, MCT4 and CD147, an ancillary protein for MCT1 and MCT4, were measured by immunoblotting the small intestine and colon of 40 pigs (Landrace, Yorkshire and LandracexYorkshire). MCT1 and MCT4 were found in both small intestine and colon, but MCT2 only in the small intestine. In both small intestine and colon, Yorkshire pigs had more CD147 than Landrace pigs, while no interbreed differences were found in MCT isoforms. Since CD147 is essential for the activity of MCT1 and MCT4, the breed difference suggests that MCT activity is higher in Yorkshire than in Landrace pigs. The absence of MCT2 in the colon suggests that it is mainly a lactate transporter, while MCT1 and MCT4 facilitate the transport of both lactate and SCFA.

Thermal stability of connective tissue from porcine muscles.

Connective tissue of three porcine muscles (M. infraspinatus, IS; M. longissimus dorsi, LD; M. semimembranosus, SM) from 27 animals [populations A (n=13, reared in Ireland) and B (n=14, reared in Finland)] was studied by measuring the collagen content, collagen solubility and thermal shrinkage temperature of the connective tissue. Colour and pH were also determined. Collagen solubility was highest in IS (p<0.05) and lowest in SM (p<0.05) although no difference between LD and SM was found in population B. The onset and peak temperatures of thermal shrinkage (T(o) and T(p)) were highest in IS (p<0.05). The lowest T(o) and T(p) were found in SM from population B whereas no differences were seen between LD and SM muscles in population A. It was concluded that the thermal stability of the connective tissue in the three porcine muscles differ. IS, as a dark muscle has high thermal shrinkage temperatures and high collagen solubilities in comparison to the lighter LD and SM muscles which have lower thermal shrinkage temperatures and collagen solubilities. Collagen contents were highest in IS and lowest in LD.

A 7-week reduction in salt intake does not contribute to markers of bone metabolism in young healthy subjects.

BACKGROUND: Sodium intake increases urinary calcium excretion and may thus lead to negative calcium balance and bone loss. OBJECTIVE: We hypothesised that reducing sodium intake would reduce urinary calcium excretion and have a beneficial influence in bone metabolism. DESIGN: A total of 29 subjects, 14 males and 15 females, were divided into two study groups. One group (low-sodium group (LS)) reduced sodium intake for 7 weeks by substituting low-salt alternatives for the most important dietary sources of sodium. The other group, serving as a control group (C), was given the same food items in the form of normally salted alternatives. Fasting serum samples as well as 24-h urine samples were obtained in the beginning and at the end of the study. Urinary sodium, urinary calcium, urinary creatinine, serum calcium, serum phosphate, serum creatinine, serum parathyroid hormone (s-PTH), serum C-terminal telopeptides of Type-I collagen and serum bone alkaline phosphatase (s-B-ALP) were analysed. RESULTS: The LS group showed a significant decline (P = 0.001) in urinary sodium/creatinine ratio without a significant effect on urinary calcium/creatinine ratio. In the LS group, s-PTH increased (P = 0.03). The C group showed an increase in s-PTH (P = 0.05) and in s-B-ALP, but no differences were observed between the study groups in the changes of serum markers of calcium and bone metabolism. CONCLUSIONS: We have shown that reducing the sodium intake of young, healthy people with adequate calcium intake over a 7-week period does not affect the markers of bone metabolism.

Distribution of monocarboxylate transporter isoforms MCT1, MCT2 and MCT4 in porcine muscles.

AIM: Monocarboxylate transporters (MCT), which cotransport lactate anions and protons across cell membranes, are important for regulation of muscle pH. We measured amounts of MCT1, MCT2 and MCT4 by immunoblotting in five different porcine muscles, to study MCT-isoform distribution both in oxidative and highly glycolytic muscles. METHODS: Samples from the longissimus dorsi, gluteus superficialis, semimembranosus, infraspinatus and masseter were taken from 18 slaughtered pigs. RESULTS: Oxidative capacity, estimated on the basis of the activities of lactate dehydrogenase (LDH), citrate synthase (CS) and 3-OH-acyl-CoA dehydrogenase (HAD), was highest in the infraspinatus and masseter, and was very low in the gluteus, semimembranosus and longissimus dorsi. In all muscles, the amount of MCT1 was small but variable. The amount of MCT2 was more abundant in the glycolytic than in the oxidative muscles, while MCT4 was found in equal amounts in all muscles. MCT2, but not MCT4, correlated negatively with CS and HAD. CONCLUSIONS: The results together with measured concentrations of lactate suggest that MCT2 may function as the housekeeping lactate transporter, preventing acidification especially in highly glycolytic muscles in which the capacity to oxidize lactate is low. The results also support the view that, as in other species, MCT4 would be important at high lactate concentrations that occur during stress.

Combined effects of NaCl and raw meat pH on water-holding in cooked sausage with and without added phosphate.

The intake of sodium in diets is of concern in many industrialized countries. Attempts have been made to lower sodium intake via meat products. The keeping quality, taste and water-holding/firmness of meat products have usually been impaired. The water-holding in cooked sausage was determined by a laboratory sausage method. Beef and pork with varying natural post-rigor pH-values (range: pork 5.50-6.12 and beef 5.60-6.48) were used as mixtures, and 0.5-2.5 % NaCl was used with or without added commercial sausage phosphate (2,5 g/kg determined as P(2)O(5)). The pH-values of raw batter increased to a level 0.0-0.7 units higher than the pH-values of the respective meat mixtures. The increase was higher in lower pH-values, with higher salt levels and with added phosphate. The cooking caused an additional increase of about 0.0-0.2 units, and the increase was again higher at lower pH-values. Maximum in water-holding was reached in 2.5% NaCl in all pH-values, both with and without added phosphate. The pH-value of meat raw materials for the maximum water-holding was ca. 6.3. The combined effect of salt and pH is important in high salt contents and low pH-values. By 2.5% NaCl , where the maximum in water-holding was obtained, raw meat pH has the largest effect, but in low NaCl contents, below 1.0%, only a minor effect in pH-values below 5.9, and above that, almost no effect. Approximately the same water-holding as with 2.5% NaCl in pH 5.7 can be reached with 1.5% NaCl in pH 6.1 and above. The effects of the variables were similar with pork and beef. It was concluded that when lowering the salt content in cooked sausages, the pH of the batter should be increased by using high-pH meat mixtures and/or pH-raising phosphates in order to reach a high enough level of water-holding.

Bovine muscle glycogen concentration in relation to finishing diet, slaughter and ultimate pH.

The aim of this study was to investigate the effects of a high-energy diet provided for a rather short time prior to transportation to slaughter on muscle glycogen concentration on farm, after transportation and after refrigeration of the carcasses. The experiment involved 60 Ayrshire bulls which were fed either a low energy diet of 100% grass silage or a compound feed based diet providing 10.8 and 12.9 MJ of metabolizable energy per kg of dry matter, respectively. Identical setup of 30 bulls was carried out in spring and in summer. Three muscle samples were obtained from the longissimus dorsi and gluteus medius muscles: a biopsy prior to initiation of experimental feeding (B1); another biopsy after 14 days on diet (B2); a post mortem sample at 48 h after slaughter (3) (also M. semimembranosus). Initial resting muscle glycogen concentration affected the responsiveness of glycogen to diet. The more glycogen there was initially the less glycogen increased (r=-0.678, p<0.0001). However, compared to the low energy diet the high energy diet seemed to protect cattle from potentially glycogen-depleting stressors such as high temperatures and transportation. The cattle on high energy lost 7±4.0 (se) mmol/kg and 23±3.9 mmol/kg during transportation in spring (cool weather) and in summer (hot weather), respectively, whereas the cattle on low energy diet lost 16±3.8 mmol/kg in spring and 33±4.1 mmol/kg in summer. The overall protective effect of high energy diet corresponded to 0.65 pH units. The effects of diet were reflected all the way to ultimate pH values [5.69±0.03 (high energy); 5.93±0.03 (low energy)] (p<0.0001) and residual glycogen concentrations (p<0.0001). It seems indeed that providing a diet high in energy for a couple of weeks prior to transportation to slaughter is one of the many appropriate measures to take in the fight against bovine dark-cutting.

Some effects of residual glycogen concentration on the physical and sensory quality of normal pH beef.

The aim of this study was to assess the effects of residual glycogen concentration on the physical and sensory quality of normal-pH beef. Longissimus thoracis et lumborum muscles (n=42) having ultimate pH (48 h) between 5.50 and 5.75 were excised, assayed for residual glycogen concentration and divided into three categories according to the residual glycogen concentration. The categories were ⩽25 mmol/kg, 25.1-49.9 mmol/kg and ⩾ 50 mmol/kg. One half of every LTL muscle was aged for 28 days. All samples were evaluated for fresh meat colour, drip loss, shear force, thawing and frying losses and fried steak colour as well as sensory attributes of tenderness, juiciness, flavour and overall palatability. The independent significant effects of increasing residual glycogen concentration on the physical and sensory quality of normal-pH-beef were, although numerous, quite modest in magnitude. The water holding variables in the form of decreasing drip loss (p<0.061), increasing thawing loss (p<005), increasing sum of losses in thawing and frying (p<0.05), and decreasing sensory juiciness (p<0.05) were somewhat affected as were decreasing fresh meat redness (Minolta a*) (p<0.005), decreasing shear force (p<0.05) and increasing yellowness (Minolta b*) of the steak (p<0.0001). Beef of the lowest and highest glycogen category were the ones behaving slightly differently from each other, the intermediate category mostly followed the pattern of one or the other.

Comparison of histochemical properties of different pig breeds.

The study involved 158 pigs: 51 Hampshire (H), 54 Landrace (L) and 53 Yorkshire (Y). The aim of the study was to compare muscle histochemical properties of M. longissimus dorsi and adductor between muscles from pigs of purebred Hampshire, Landrace and Yorkshire lineages. The following histochemical properties were determined: 1) the percentage of type I, IIA and IIB fibers in number (calculated on the basis of the number of different fiber types) and area (calculated on the basis of the area of different fiber types) as analyzed with the myosin ATPase method using an acid preincubation solution of pH 4.6; 2) the cross sectional area of each fiber type; 3) the percentage of oxidative fibers on the basis of the NADH-TR method; and 4) the capillary density of the muscles. The cross-sectional area of type IIB fibers was the largest in Landrace. The highest capillary density (capillaries per mm(2)), 254 ± 38, was in longissimus of Hampshire. A positive correlation between M. longissimus dorsi and M. adductor was found in the percentage of type I, IIA and IIB fibers in number and area, cross-sectional area of each fiber type, and capillary density. The differences in histochemical properties between breeds were, however, smaller in M. adductor than in longissimus dorsi muscle. In addition, the variation in muscle fiber composition in pigs within the breeds was larger than the average variation between the breeds.

The properties of connective tissue membrane and pig skin as raw materials for cooked sausage.

Pig skin and epimysial membrane from young bulls were comminuted in a colloid grinder and mixed with water and additives. The resultant mixture was heated in a water bath to give an internal temperature of 72°C, and centrifuged while still hot. Such variations in the amount of water added, the salt content, the phosphate content and the pH value as are possible in cooked sausage heated to over 65°C during processing did not cause marked changes in the amount of water bound by the connective tissues, the amount of dissolved protein or the gel strength of the liquid released from the connective tissues. As the temperature rose the amount of bound water dropped, but the amount of dissolved protein and the gel strength increased. The liquid released from the connective tissue membranes formed a gel at 32°C and re-melted at 49°C. For pig skin, the corresponding temperatures were 23°C and 47°C. On the basis of this study it appears that connective tissue may be important for the water-binding capacity and firmness of cold sausage. The connective tissue membranes obtained from young bulls and pig skin are of roughly equal value in this respect, although the gel formed from connective tissue membrane is tougher.