Psychrotrophic Clostridium spp. associated with 'blown pack' spoilage of chilled vacuum-packed red meats and dog rolls in gas-impermeable plastic casings.

'Blown pack' spoilage of vacuum-packed chilled beef, lamb and venison, and of a cooked meat product, chilled dog rolls packed in an oxygen-impermeable plastic casing, was characterised by sensory, chemical and microbiological analysis. Investigation of the probable causative agents led to the isolation of eight strains of psychrotrophic clostridia. Three strains have been provisionally identified as C. difficile, C. beijerinckii and C. lituseburense; the other five remain unidentified. In inoculation studies only one isolate produced significant amount of gas on meat, causing pack 'blowing'. It is, therefore, possible that 'blown pack' spoilage involves a synergism with one or more other organisms.

Pyridinoline in ovine intramuscular collagen.

Pyridinoline, a mature crosslink of collagen, was measured in intramuscular connective tissue isolated from ovine semimembranosus, a muscle noted for its highly insoluble collagen. Concentration ranged between 0·25 and 0·59 mol/mol of collagen, on the high side of concentrations reported in the literature for this and other muscles in various species. Pyridinoline concentration was inversely related to collagen solubility in muscle homogenates (P < 0·0). In a comparison between semimembranosus, biceps femoris and gluteus medius, pyridinoline concentration was again inversely related to collage solubility. For all these muscles, pyridinoline remained insoluble in a heat-dependent solubility test, but it is argued that pyridinoline does not explain all the solubility properties of ovine intramuscular collagen. Pyridinoline concentration was not significantly correlated with sensory or shear properties of cooked semimembranosus, confirming the importance of other heat-stable crosslinks.

The effects of antioxidative treatments on mutton flavour/odour intensity and species flavour differentiation.

This study examined the effects of curing and oxygen exclusion on the odour and flavour of sheepmeats. One series of experiments examined the effect of curing on the ability of panellists to distinguish between the flavours of lean mince from various species (mutton, beef, pork, chicken). Other experiments examined the effects of curing and of maintaining an anoxic storage/cooking environment on the intensity of mutton flavour and odour, particularly adipose tissue odour. Curing had no effect on panellists' abilities to distinguish between the flavour of mince from different species. Storage and cooking of uncured mutton adipose tissue samples under anoxic conditions limited lipid oxidation but enhanced mutton odour intensity. Nitride had a pro-oxidant effect on mutton adipose tissue stored in air. There was no corresponding effect on mutton odour intensity. These findings suggest that lipid oxidation products contribute very little to mutton odour from adipose tissue, and possibly also to species flavour differences in lean meats.

Tenderness of ovine semimembranosus: Is collagen concentration or solubility the critical factor?

The concentration and heat-dependent solubility of collagen were measured in the semimembranosus (36 animals) and, for comparison, the gluteus (108) muscles of sheep aged 4 months to 5 years. For both muscles, solubility declined with age but concentration remained unchanged. Compared to gluteus and other major ovine muscles, the semimembranosus had markedly insoluble collagen at a relatively low concentration. To assess the relative importance of collagen concentration and solubility on tenderness/texture for a muscle with this profile, the semimembranosus muscles contralateral to those used for collagen analysis were cooked to an endpoint of 75°C and assessed by sensory panel and Warner-Bratzler shear tests. The panel data showed that collagen concentration was the more important determinant of eating quality, whereas shear data were more clearly related to solubility. The implications of the sensory results are discussed for muscles that contain a different collagen profile.

Onset of insensibility at slaughter in calves: effects of electroplectic seizure and exsanguination on spontaneous electrocortical activity and indices of cerebral metabolism.

Cerebral venous and femoral arterial blood samples were collected from 21 young calves either during electrical stunning and recovery or electrical stunning and slaughter by carotid severance or slaughter without stunning. The blood samples were analysed for PO2, PCO2, pH, glucose and lactate. The results were compared with simultaneous recordings of spontaneous electrocortical (ECOG) activity. Calves subjected to head-only electrical stunning and slaughter became permanently insensible at the time of the stun. The six calves slaughtered without stunning lost sensibility within 10 seconds. One calf, in which a clot formed in the carotid arteries inhibiting bleeding, maintained some evidence of cortical activity beyond 52 seconds; this was high amplitude low frequency activity and analysis by Fast Fourier Transform showed sensibility was not regained. In the remaining calves the ECOG activity was lost on average within 49 +/- 3.5 (SEM) seconds after slaughter. The cerebral extraction of metabolites increased after carotid severance, indicating inadequacy of cerebral bloodflow after slaughter. No correlations were found between indices of cerebral metabolism and the time of loss of cortical function.

Human liver cytosolic malate dehydrogenase: purification, kinetic properties, and role in ethanol metabolism.

Cytosolic malate dehydrogenase from human liver was isolated and its physical and kinetic properties were determined. The enzyme had a molecular weight of 72,000 +/- 2000 and an amino acid composition similar to those of malate dehydrogenases from other species. The kinetic behaviour of the enzyme was consistent with an Ordered Bi Bi mechanism. The following values (microM) of the kinetic parameters were obtained at pH 7.4 and 37 degrees C: Ka, 17; Kia, 3.6; Kb, 51; Kib, 68; Kp, 770; Kip, 10,700; Kq, 42; Kiq, 500, where a, b, p, and q refer to NADH, oxalacetate, malate, and NAD+, respectively. The maximum velocity of the enzyme in human liver homogenates was 102 mumol/min/g wet wt of liver for oxalacetate reduction and 11.2 mumol/min/g liver for malate oxidation at pH 7.4 and 37 degrees C. Calculations using these parameters showed that, under conditions in vivo, the rate of NADH oxidation by the enzyme would be much less than the maximum velocity and could be comparable to the rate of NADH production during ethanol oxidation in human liver. The rate of NADH oxidation would be sensitive to the concentrations of NADH and oxalacetate; this sensitivity can explain the change in cytosolic NAD+/NADH redox state during ethanol metabolism in human liver.

Kinetics of malate dehydrogenase and control of rates of ethanol metabolism in rats.

The theory that the rate of ethanol oxidation is governed by rates of NADH reoxidation is based in part on the observation that the ratio of free cytosolic [NADH]/[NAD+] increases during ethanol metabolism. However, it has recently been suggested that the amount of alcohol dehydrogenase governs rates of ethanol metabolism, which then leaves the change in cytosolic redox state unexplained. In this paper the kinetic parameters for rat liver malate dehydrogenase, determined at 37 degrees C and pH 7.4, are used to provide an explanation for the change in cytosolic redox state that is compatible with rate control by alcohol dehydrogenase.

The effects of high ethanol doses on rates of ethanol oxidation in rats. A reassessment of factors controlling rates of ethanol oxidation in vivo.

1. Ethanol was oxidised more slowly by rats which were given an ethanol dose of 5.1 g/kg than by rats which were given an ethanol dose of 1.4 g/kg. 2. A positive correlation was found between [lactate]/[pyruvate] ratios and rates of ethanol oxidation. 3. Acetaldehyde concentrations varied widely between rats, but in some cases were high enough to influence rates of ethanol oxidation. 4. Liver alcohol dehydrogenase levels were just sufficient to account for ethanol oxidation rates observed in vivo. 5. Pre-administration of a large ethanol dose (6.5 g/kg) did not alter mean [lactate]/[pyruvate] ratios or ethanol oxidation rates during metabolism of test doses of 2.5 g/kg. 6. Injection of pyruvate did not increase rates of ethanol oxidation. 7. The results do not support suggestions that a high-Km ethanol oxidising system plays an important role in vivo, that increased rates of ethanol oxidation can be induced by large, acute ethanol doses or that the rate of NADH reoxidation controls rates of ethanol metabolism. 8. The results support other evidence which has indicated that the level of alcohol dehydrogenase is the major factor limiting rates of ethanol oxidation in vivo.