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 T₂ relaxation data revealed the presence of three distinct water populations (T₂₀, T₂₁, T₂₂) within the muscle during its conversion to meat. Comparison of T₂ relaxation patterns and contraction data indicates that rigor development affects the attributes of the T₂₁ water population and thereby contributes to myofibrillar water characteristics post mortem, as the T₂₁ water population is believed to reflect inter/intra-myofibrillar water. The volume of the water population believed to reflect extra-cellular water (T₂₂) in the living muscle. Early post mortem T₂₂ 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 T₂₂ 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.     

Relationships between sensory perception and water distribution determined by low-field NMR T(2) relaxation in processed pork - impact of tumbling and RN(-) allele

The relationships between water distribution, measured with low-field NMR (LF-NMR) transverse (T₂) relaxometry and sensory properties in tumbled and non-tumbled cured-smoked loins from 30 female Hampshire crossbred pigs were investigated. Upon distributed analysis of the T₂ relaxation, three populations centred at about 2, 40 and 600–800 ms, respectively, were detected. Clear differences in the characteristics of the intermediate population (T₂₁) were observed between loins from carriers and non-carriers of the RN⁻ allele, which implies differences in water–protein interactions between the two genotypes. PLS regressions between NMR T₂ variables and sensory attributes revealed significant correlations between NMR T₂ variables and the sensory attributes juiciness, acidulous taste and meat taste, which mainly could be ascribed to the T₂₁ time constant. In addition, the number of unappealing pores assessed by the sensory panel was highly related to the relative T₂ populations, implying that the microstructure is directly reflected in the NMR T₂ populations. However, prediction of the processing yield from NMR T₂ variables was poor. The correlation improved when RN genotypes and tumbling conditions were included as predictors. Thus, other effects of tumbling treatments and RN genotypes unrelated to NMR T₂ relaxation were observed.     

Identification of PSE in the Longissimus muscle of pigs stunned by captive-bolt

Meat quality characteristics in the longissimus muscle of 57 pigs slaughtered at approximately 100 kg liveweight were studied. They were slaughtered by captive-bolt stunning and exsanguination. The incidence of pale, soft and exudative (PSE) meat was identified by muscle colour and water holding capacity 24 h post mortem (C₂₄ and WHC₂₄). The muscle pH value 45 min post mortem (pH₁), absorption ratio (R-value) of muscle acid extract, and colour and water holding capacity 1 h post mortem (C₁ and WHC₁) were also determined. The interrelationships among pH₁, R-value, C₁, WHC₁, C₂₄ and WHC₂₄ were studied and the multiple regressions of C₁, C₂₄, WHC₁ and WHC₂₄ with pH₁ and R-value were computed. The results of simple and multiple regression analysis showed that neither muscle pH₁ nor R-value could effectively predict colour or WHC at 24 h post mortem. Combining pH₁ and R-value provided little improvement in the prediction of the ultimate meat colour and WHC.     

Water status of cooked white salted noodles evaluated by MRI

Transverse relaxation time (T₂)-weighted images and T₂ maps of white salted noodles (WSN) were investigated by magnetic resonance imaging technique. T₂-weighted images and T₂ maps clearly showed the differences in water status between noodles. The migration of moisture from surface regions to central regions of boiled WSN at different migration rates were investigated during storage. The distribution of T₂ values changed differently depending on the cooking and storage times. The small differences in T₂ values between surface region and central region of noodles cooked for 5 and 15 min were attributed to the limited water absorption during short cooking time, which resulted in high firmness. The changes in starch granules morphology observed under scanning electron microscope and the increase of noodle firmness measured by texture analyzer were significantly affected by the water status in noodles. The water status can be controlled by the cooking time.     

Modelling the effect of a temperature shift on the lag phase duration of Listeria monocytogenes

The aim of this work is to study and model the effect of a temperature shift on h₀, the product of the growth rate by the lag phase duration (μλ). Our work is based on the data of Whiting and Bagi [Int. J. Food Microbiol. 73 (2002) 291], who studied the influence of both the pre-incubation temperature (T_prior) and the growth temperature (T_growth) on λ values of Listeria monocytogenes. We introduce a new model to describe the evolution of the parameter h₀ as a function of T_prior and T_growth, and compare it to Whiting and Bagi's published polynomial model that describes the influence of T_prior and T_growth on λ independently of μ. For exponential as well as stationary phase cells, h₀ increases almost linearly with the magnitude of the temperature shift. A simple linear model of h₀ turns out to be more suitable to predict λ values than a polynomial model of λ.     

Effects of halothane genotype and pre-slaughter treatment on pig meat quality. Part 1. Post mortem metabolism, meat quality indicators and sensory traits of m. Longissimus lumborum

Forty-eight castrated F₂ offspring of Piétrain and Large White pigs were allocated to a 3 × 2 factorial design in order to study the interactive effect of halothane genotype (NN, Nn and nn) and pre-slaughter treatment [referred to as ‘Experimental’ (EXP) and ‘Commercial-like’ (COL) conditions; the latter combining short transportation, mixing unfamiliar pigs and slaughtering shortly after transport] on muscle post mortem changes and meat quality. The pigs were slaughtered over 4 days. Pre-slaughter glycogen depletion in M. longissimus lumborum (LL) was greater in the nn pigs, compared with the two other genotypes. Lactate accumulation post mortem in LL muscle was greater and the pH value at 40 min post mortem was lower in nn compared with NN pigs. Nn pigs were close to nn pigs for lactate accumulation and showed intermediate pH values in the LL muscle. In the M. semimembranosus (SM), NN and Nn pigs showed the same rate of post mortem changes, as evidenced by similar glycogen, lactate, creatine phosphate and ATP levels, and pH values at 40 min post mortem. Pre-slaughter treatment did not affect the rate of post mortem changes in both muscles and no interactive effect with halothane genotype was found. The pigs slaughtered under the ‘COL’ conditions had a significantly higher ultimate pH in the LL and SM muscles than those slaughtered under the ‘EXP’ conditions. The LL muscle from nn pigs was paler (higher L*) than that of NN and Nn pigs. In SM muscle, Nn pigs showed a significantly higher L* value than NN pigs. Drip loss of the LL muscle was significantly higher in nn compared with NN pigs, the heterozygous pigs being intermediate. Sensory evaluation of the LL muscle showed that nn pigs had a lower colour intensity and colour homogeneity of raw meat than NN and Nn pigs. Tenderness was significantly lower in nn compared with NN pigs, the Nn pigs being intermediate. Pre-slaughter treatment significantly increased ultimate pH in both muscles (LL and SM) but did not affect significantly the rate of pH fall (pH₄₀). It did not affect any of the meat quality traits and no interactive effect with halothane genotype was found. These results confirmed the influence of the halothane gene on the kinetics of muscle post mortem changes and related meat quality traits. They also confirmed the intermediate position of heterozygous pigs in terms of meat quality.     

Effect of cooling rate upon processing characteristics of pork meat of different glycolysis type during post mortem ageing

Rapid chilling was applied to porcine longissimus dorsi muscles at 1 h post mortem in order to observe its effect on the quality of canned products prepared from those of different pH₁ values.

The muscle from one side of each animal was removed from the carcase 50 minutes post mortem and divided into two longitudinal strips. One was chilled immediately to 13–15°C (1 h post mortem): the other after a further hour (2 h post mortem) acted as control. After the centre temperature had reached 10°C the muscles were stored in a refrigerator at 3–5°C.

Compared with the control samples (chilled at 2 h p.m.), rapid chilling from 1 h p.m. caused an improvement in the water-holding capacity and the texture of pork meat, which had higher pH₁ values and was processed at 2, 4 and 48 h p.m. There was minimum brine retention and texture score if samples—both rapidly chilled and control—were processed at 24 h p.m.

Although brine retention of PSE pork meat could not be increased even by rapid chilling, the texture of heat treated PSE pork showed an improvement during storage, which was more pronounced after ageing for 48 h, if PSE samples were chilled at 1 h p.m.     

Variation in post-mortem rate of glycolyis does not necessarily affect drip loss of non-stimulated veal

In this study the effect of the rate of post mortem pH fall on the water-holding capacity of meat from moderately chilled veal carcasses was investigated. Also the relationship between muscle protein denaturation and drip loss of veal was examined. Three groups of 10 Friesian Holstein male veal calves each were selected on the basis of their pH in M. longissimus thoracis et lumborum (LTL) at 3 hr post mortem (pH₃): (1) fast pH-fall, pH₃ < 6.2; (2) intermediate pH-fall, 6.5 < pH₃ < 6.6; (3) slow pH-fall, pH₃ > 6.7. After 48 hr of chilling the LTL was excised from the carcass and sampled for determination of drip loss, filter paper wetness, sarcomere length, protein solubility and transmission value. Differences in pH₃ were not associated with differences in drip loss, filter paper wetness or differences in protein denaturation. It is suggested that at the relatively high veal carcass chilling rate the effect of rate of pH-fall on protein denaturation and thus on drip loss is negligible. Drip loss of veal was highly correlated with both solubility of sarcoplasmic (r = −0.67; p < 0.001) and total muscle protein (r = −0.54; p < 0.01) and with transmission values (r = 0.66; p < 0.001). These results indicate that protein denaturation measurements may be a good predictor for drip loss of veal.     

Identification of halothane genotypes by calcium accumulation and their meat quality using live pigs

The three halothane genotypes (NN, Nn, and nm) were identified by measuring the capacity for Ca²⁺ accumulation by sarcoplasmic reticulum in whole muscle homogenate preparations of M. longissimus dorsi with a Ca²⁺ specific electrode at 35°C. Significant differences (P < 0·001) in deterioration (%) of Ca²⁺ accumulation, 12% for NN, 35% for Nn, and 81% for nn pigs, were observed after ageing the whole muscle homogenate preparations for 24 h in ice.

Predictions of meat quality in live pigs (n = 34) based on the values for water-holding capacity, assessed as fluid (g/0·5 g wet wt LD), and pH (fluid) by using small biopsy LD samples (Cheah et al. 1993) were performed on all the halothane genotypes. The halothane genotype NN (n = 11) showed a fluid value of 0·37 ± 0·01 and a pH (fluid) value of 6·62 ± 0·03 as compared with 0·61 ± 0·02 and 5·84 ± 0·04, respectively, for the halothane genotype nn (n = 13). The Nn pigs (n = 10) showed fluid (0·49 ± 0·03) and pH (fluid) (6·19 ± 0·11) values between those values observed for the two homozygotes (NN and nn). Predictions of meat quality in live pigs from biopsy LD muscles were confirmed from assessments on post-mortem LD muscles based on pH₁ and fibre optic probe (FOP) measurements.

The extent of deterioration (%) in Ca²⁺ accumulation showed high correlations with fluid (r = −0·861) and pH (fluid) (r = −0·831) in the biopsy LD samples, and with pH₁ (r = 0·663), FOP (r = −0·812), and drip (%) loss (r = −0·777) in the post-mortem LD samples.     

NMR relaxometry and differential scanning calorimetry during meat cooking

By combining simultaneous nuclear magnetic resonance (NMR) T₂ relaxometry and differential scanning calorimetry (DSC) on pork samples heated to nine temperature levels between 25 and 75 °C, the present study investigates the relationship between thermal denaturation of meat proteins and heat-induced changes in water characteristics. Principal component analysis (PCA) on the distributed ¹H NMR T₂ relaxation data revealed that the major changes in water characteristics during heating occur between 40 and 50 °C. This is probably initiated by denaturation of myosin heads, which however, could not be detected in the DSC thermograms obtained directly on the meat. In contrast, the DSC thermograms revealed endothermic transitions at 54, 65 and 77 °C, probably reflecting the denaturation of myosin (rods and light chain), sarcoplasmic proteins together with collagen and actin, respectively. Simultaneous modelling of DSC and NMR data by partial least squares regression (PLSR) revealed a correlation between denaturation of myosin rods and light chains at 53–58 °C and heat-induced changes in myofibrillar water (T₂ relaxation time 10–60 ms) as well as between actin denaturation at 80–82 °C and expulsion of water from the meat. Accordingly, the present study demonstrates a direct relationship between thermal denaturation of specific proteins/protein structures and heat-induced changes in water mobility during heating of pork.     

Effects of housing conditions of slaughter pigs on some post mortem muscle metabolites and pork quality characteristics

The results of two experiments studying the effects of housing conditions on post mortem muscle metabolism and meat quality are presented. In the first experiment slaughter pigs (n=71) from two different crossings, were raised at a density of 0.7 m²/animal (10 pigs/pen) either with (enriched) or without (conventional) a bedding of daily fresh straw. In the second experiment, animals (n=60) were reared under either conventional or free range housing (1.25 m²/animal, 30 pigs per pen) conditions. Main differences between conventional and enriched housed pigs were found in the biceps femoris (BF) muscle, and related to temperature, drip loss and colour. Association studies revealed that there were significant correlations between early (0–4 h) post mortem muscle pH and glycogen and lactate concentrations and between muscle pH measured at 1 h post mortem and muscle rigidity, expressed as the rigor value. There were significant differences with respect to meat quality and post mortem metabolism of the longissimus lumborum (LL), between conventional and free-range pigs. Early post mortem pH (0–4 h) was highest in the free-range pigs, due to low lactate concentrations. The relatively fast pH decline in the conventionally housed group resulted in increased amounts of water exuding from the meat, as measured by the filter paper method. The ultimate pH, was lowest in the free-range animals. The differences in ultimate pH, however, had no effect on drip or cooking losses. It can be concluded from these results that enrichment of the housing system has little effect on the course of the post mortem metabolism and meat quality. However, increasing the freedom of movement by applying lower stocking densities, affects the post mortem muscle metabolism, resulting in reduced water exudation. Correlations up to 0.7 between energetic parameters are not sufficiently high to be useful to predict meat quality of individual carcasses.     

Measurement by MRI of storage changes in commercial chocolate confectionery products

Storage of chocolate confectionery products was monitored non-invasively by Magnetic Resonance Imaging. Using a Carr–Purcell–Meiboom–Gill–(CPMG) sequence, 20 echo images (first echo 5 ms, subsequent echo every 5 ms) were acquired with a 2 s repetition time in a total 8-min scan time. Images were processed to give spatial maps of the proton density (M₀) and the transverse relaxation times (T₂-values) within the samples. In every case the T₂-values were successfully used to follow the migration of lipids from the fillings into the chocolate. The MR images also provided spatial information on the lipid migration.     

The effects of electrical stunning and percussive captive bolt stunning on meat quality of cattle processed by Turkish slaughter procedures

The effects of electrical and percussive captive bolt stunning both on initial and up to 14 days post mortem meat quality of Friesian young bulls were studied. The first group (NS; n=10) were slaughtered without stunning under Turkish slaughter procedure (these animals were slaughtered under conditions acceptable to the appropriate ethics committee) in a modern abattoir. In the second group (ES; n=10) animals were electrically stunned. In the third group (PS; n=10) animals were stunned with percussive captive bolt. Meat quality was assessed by examining muscle glycogen concentration, pH and WHC. Also cooking loss, texture parameters and consumer sensory properties were assessed at 24 h, 4, 7 and 14 days post mortem. Meat colour as L^*, a^*, b^*, C^*, h^* values were evaluated at 0, 48 h, 3, 5, 7, 9 and 14 days post mortem. Pre-slaughter handling affected muscle glycogen concentration (P<0.05). Animals in electrical and percussive captive bolt stunned groups had higher muscle glycogen concentrations compared to animals in the non-stunned group (P<0.05). Although pre-slaughter handling did not affect significantly pH_{24 h} and WHC, differences were significant for cooking loss, colour coordinates and texture parameters at some storage times. For all sensory attributes (odour, flavour, tenderness and overall acceptability) at all ageing periods (24 h, 4, 7 and 14 days) the percussive stunned (PS) group was significantly superior to the non-stunned (NS) group. The electrically-stunned (ES) group also tended to be superior to the NS group although not all differences were statistically significant. These results indicate that percussive captive bolt stunning of cattle improved meat quality compared with cattle electrically stunned using head only tongs and those non stunned under approved Turkish slaughter procedure.     

Enthalpy-Entropy compensation in food vapor adsorption

Enthalpy-entropy compensation was analysed for sorption isotherms of potatoes, macadamia nuts, apricots, figs, currants, prunes and raisins. Plots of (ΔH_dif)_T vs (ΔS_dif)_T for potatoes and macadamia nuts presented two isokinetic temperatures: T_B1 = 272.0 ± 57.7 K (− 1 °C) for potatoes, T_B1 = 265.0 ± 18.8 K (− 8 °C) for macadamia nuts and T_B2 = 382.5 ± 7.3 K (109.5 °C) for both products. The first isokinetic temperature (T_B1) appeared only at the upper portion of the temperature range tested (50, 60 and 70 °C for potatoes and 50 and 60 °C for macadamia nuts). The two isokinetic temperatures observed for potatoes and macadamia nuts suggested that during the initial stages at low a_w T_B1 is controlled by changes in the entropy of water, whereas the second isokinetic temperature (T_B2) is considered to be enthalpy-controlled. Dried fruits presented only one isokinetic curve T_B = 315.7 ± 3.5 K (42.7 °C), for raisins, currants and figs (75.2–82.3% d.b. sugars) and T_B = 317.7 ± 4.6 K (44.7 °C) for prunes and apricots (51.5–54.5% d.b. sugars), indicating an enthalpy-controlled adsorption process for the whole range of moisture contents covered.     

Differences of post-mortem ATP turnover in skeletal muscle of normal and heterozygote malignant-hyperthermia pigs: Comparison of (31)P-NMR and analytical biochemical measurements

Energy metabolism of the biceps femoris muscle of normal and heterozygote malignant-hyperthermia pigs was studied post-mortem after in-vivo exposure to a combination of halothane and succinylcholine. The pigs were anaesthetized with halothane and subsequently captive-bolt-stunned immediately after intravenous administration of succinylcholine. Cardiac arrest occurred within one minute after the depolarizing neuromuscular blocking with succinylcholine. During the following 2-5 hours post mortem, the level of several metabolites, reflecting the rate of muscle glycogenolysis and glycolysis, was measured by analytical biochemical techniques and by in situ (31)P-NMR spectroscopy. Both techniques demonstrated more than three-fold-accelerated PCr decay, matched by a similar increase of P(i) in heterozygotes compared with normal pigs. The rate of pH decrease and of lactate accumulation was also three to five times higher in the heterozygotes, all-in-all demonstrating a significantly increased ATP turnover post mortem in these animals when exposed to a combination of halothane and succinylcholine. The results are consistent with the notion of increased excitability of skeletal muscle due to a genetically altered calcium-channel protein. In addition, the results suggest that NMR identification of heterozygote malignant-hyperthermia pigs is possible.     

Comparing predicting models for heat inactivation of Listeria monocytogenes and Pseudomonas aeruginosa at different pH

Under the same experimental conditions it has been demonstrated that whereas survival curves of Listeria monocytogenes in the range of temperatures from 54 to 62 °C followed a first-order kinetic, those of Pseudomonas aeruginosa in the range of temperatures from 50 to 56 °C were not linear showing a shoulder followed by a linear region. The first order kinetic model did not describe survival curves of P. aeruginosa. A model based on the Weibull distribution (Log₁₀(N_t/N₀)=(1/−2.303)*(t/b)ⁿ)) accurately described the inactivation kinetics of both microorganisms at the three pHs of 4, 5.5, 7.4 investigated. For both microorganisms, the b value depended on the treatment temperature and the pH of the treatment medium. Whereas for L. monocytogenes the n value was independent of the treatment conditions, for P. aeruginosa the n value depended on the pH of the treatment medium.

The model based on the Weibull distribution was capable of accurately predicting the treatment time to inactivate five Log₁₀ cycles of both microorganisms at the three pHs investigated.     

Thermal inactivation of the frozen thawed traditional meat starter culture, Pediococcus pentosaceus, in a meat model system

The equation, y_(t) = y₍₀₎e^kt, was fitted (R = 0.9281, 0.9220 and 0.9117, respectively) to thermal inactivation data (55, 60 and 65 °C) of the traditional meat starter culture Pediococcus pentosaceus (10⁷ cfu/ml) in a meat model system. The population reduction constant (‘k’) increased (about 2.5- and 3-fold) with an increase in the treatment temperature (from 55 to 60 °C and from 60 to 65 °C, respectively). The Q₁₀ (55–65 °C) for ‘k’ was 7.63. Thermal treatments of 19.1, 9.0 and 3.1 min (55, 60 and 65 °C, respectively) reduced the population of P. pentosaceus by 2.0 logs. The value of ‘k’ and the duration of the thermal treatment played an important role in the extent of the inactivation of the culture. The “zero inactivation” temperature (T₀) for P. pentosaceus was 49.9 °C. About 5 logs of the culture would be destroyed at 63 and 68 °C within about 15.5 and 6.5 min, respectively.     

Influence of post-mortem treatments on turkey and chicken meat texture

Toughness of poultry breast muscle was influenced by the rate of rigor onset, the rate of cooling and chilled storage time. The pH of the breast muscle at 20 min after stunning (pH₂₀) in 52-day-old chickens varied from 5.9 to 6.9, and in 70-day-old turkeys from 6.2 to 6.8. In turkey meat with pH₂₀ > 6.4, toughening was induced by immersion chilling to 7°C within 65 min post mortem and subsequent 'tanking' in iced water. Unaged, thawed meat from chicken carcasses, in which freezing commenced about 2 h after stunning was tougher than that from carcasses chilled for 16 h before freezing. Both were tender after 7 days chilled storage. Electrical stimulation of carcasses using 94 V decreased pH₂₀ by an average of 0.3 unit in turkey, with no overall increase in tenderness. In chicken, it decreased the pH₂₀ by 0.5 unit, but caused an overall toughening due to increased rigor shortening in carcasses with pH₂₀ < 5.8.     

Effect of electrical stunning on meat quality of lamb

The effects of stunning on both initial and up to 2 weeks post mortem storage meat quality of Spanish Manchega breed lamb were studied. Twenty-four lambs were distributed into two groups. The first group (US; n =12) were slaughtered without previous stunning. In the second group (ES; n =12) animals were electrically stunned. Meat quality was assessed by examining pH, colour as L*, a*, b* values, water holding capacity (WHC) and shear force (SF). Stunning did not affect any parameter studied in the first 24 h post mortem. There were increasing differences between groups in pH (P<0.001) from 5 days onwards. In general stunning did not have an effect on WHC, SF and colour parameters. Ageing of meat affected SF in the ES group but not in the US one; however, there were no significant differences between treatments at any of the ageing times.     

Dietary vitamin E supplementation and discoloration of pork bone and muscle following modified atmosphere packaging

The effects of modified atmosphere (80% O₂: 20% CO₂) and illumination on the discoloration rate of pork bone (lumbar vertebrae) and muscle (longissimus lumborum), and on muscle lipid stability were studied in vitamin E-supplemented and unsupplemented pigs. Bone-in pork chops were placed in 80% O₂: 20% CO₂ at 0 °C and stored for 5 days in the dark. The chops were then displayed under (a) fluorescent light in air or modified atmosphere or (b) in air with or without illumination. Lipid oxidation was increased by the modified atmosphere packaging but this detrimental effect was offset by vitamin E supplementation. Higher supplementation levels (198 and 207mg/kg) improved bone color stability regardless of the packaging atmosphere or the lighting conditions. Although vitamin E supplementation improved muscle color stability during display in air or modified atmosphere, the benefit of supplementation on muscle color was detectable only for illuminated storage.