Review: Quality of animal-source foods.

This article critically reviews the current state of knowledge on the quality of animal-source foods according to animal production and food processing conditions, including consumer expectations-behaviours and the effects of consumption of animal-source foods on human health. Quality has been defined through seven core attributes: safety, commercial, sensory, nutritional, technological, convenience, and image. Image covers ethical, cultural and environmental dimensions associated with the origin of the food and the way it is produced and processed. This framework enabled to highlight the priorities given to the different quality attributes. It also helped to identify potential antagonisms and synergies among quality attributes, between production and processing stages, and among stakeholders. Primacy is essentially given to commercial quality attributes, especially for standard commodity animal-source foods. This primacy has strongly influenced genetic selection and farming practices in all livestock commodity chains and enabled substantial quantitative gains, although at the expense of other quality traits. Focal issues are the destructuration of chicken muscle that compromises sensory, nutritional and image quality attributes, and the fate of males in the egg and dairy sectors, which have heavily specialised their animals. Quality can be gained but can also be lost throughout the farm-to-fork continuum. Our review highlights critical factors and periods throughout animal production and food processing routes, such as on-farm practices, notably animal feeding, preslaughter and slaughter phases, food processing techniques, and food formulation. It also reveals on-farm and processing factors that create antagonisms among quality attributes, such as the castration of male pigs, the substitution of marine-source feed by plant-based feed in fish, and the use of sodium nitrite in meat processing. These antagonisms require scientific data to identify trade-offs among quality attributes and/or solutions to help overcome these tensions. However, there are also food products that value synergies between quality attributes and between production and processing phases, particularly Geographical Indications, such as for cheese and dry-cured ham. Human epidemiological studies have found associations between consumption of animal-source foods and increased or decreased risk for chronic non-communicable diseases. These associations have informed public health recommendations. However, they have not yet considered animal production and food processing conditions. A concerted and collaborative effort is needed from scientists working in animal science, food process engineering, consumer science, human nutrition and epidemiology in order to address this research gap. Avenues for research and main options for policy action are discussed.

Characterization of Longissimus thoracis, Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 1. Microscopic analysis of muscles.

Three porcine muscles (Longissimus thoracis, Semitendinosus, Masseter), known to have large differences in biochemical and histological traits, were fully characterized and the link between muscle structure and quality evaluated. The oxidative Masseter had more pigment, higher content of metmyoglobin, haem iron, protein and collagen, and was redder with higher fibre numbers, fibre circularity, pH and water holding capacity than the glycolytic Longissimus. Fibre type distribution showed predominance of type IIB in Longissimus and Semitendinosus white, type I in Semitendinosus red and IIA in Masseter. Type I fibres were larger than type IIB and IIA in Semitendinosus and Masseter, respectively, but not in the Longissimus, indicating that fibre size is muscle dependent. Muscle redness was positively correlated with type I fibre traits, haem iron and metmyoglobin, and negatively associated with type II fibre characteristics, non-haem iron and oxymyoglobin. Expressible juice had positive correlation with fibre size and negative with fibre number and connective tissue.

Kinetics of protein physicochemical changes induced by heating in meat using mimetic models: (2) effects of fibre type, peroxides and antioxidants.

Heating-induced changes in meat proteins were investigated using models made of aqueous suspensions of myofibrils according to muscle fibre types and cellular compounds (oxidants and antioxidants). These changes were evaluated by measurements of carbonyl groups and protein surface hydrophobicity. Model results were compared to trial results obtained on pork meat (M. Longissimus dorsi) heated under the same conditions (45 and 75°C, from 5 to 120 min). Myofibrillar proteins from α-white fibres were more sensitive to oxidation and thermal denaturation than those from ß-red fibres. At 45°C, there were negligible differences due to peroxide or antioxidant types. At 75°C, organic peroxides (ROOH) were less oxidative than hydrogen peroxide (H2O2), and antioxidant enzymes were less efficient than vitamin E and carnosine at protecting proteins against oxidation. Protein oxidation observed in meat is lower than in the mimetic models and the increase in hydrophobicity remained limited in meat.

The fusion of lipid droplets is involved in fat loss during cooking of duck "foie gras".

Fat loss during cooking of duck "foie gras" is the main quality issue in processing plants. To better understand this phenomenon, a histological and ultrastructural study was conducted. The aim was to characterize changes in lipid droplets of duck "foie gras" related to fat loss during cooking. Ten fatty livers were sampled before and after cooking and prepared for optical and transmission electron microscopy. In raw livers, the lipid droplets were nearly spherical while after cooking, they were larger and lost their spherical shape. We also observed a decrease in the number of droplets after cooking, probably due to droplet fusion caused by the heat treatment. Before cooking, there were fewer lipid droplets and a higher osmium tetroxyde staining intensity in the fatty liver, which later gave a lower technological yield. Fat loss during cooking was higher when there was more fusion of lipid droplets before cooking.

Lack of effects of hyperkalemia on the metabolism of normoxic or anoxic rabbit triceps brachii muscle.

Rabbit triceps brachii muscle was perfused with bovine red cells medium. Changes in phosphorus compounds and intracellular pH were followed using (31)P NMR during 15 min in the perfused muscle and during 50 min in muscle made anoxic by perfusion stop. Potassium levels in perfusate was maintained at 4 mM (normal plasma concentration at rest) during all perfusion in one muscle and at 4 mM for 10 min then 10 mM during 5 min before perfusion stop in the contralateral muscle. The intracellular pH and phosphorylated compounds content remained stable in the perfused muscle whatever the potassium concentration of the perfusate. Five min after perfusion stop a decrease in phosphocreatine (P<0.05) and pH (P<0.01) and an increase in sugar-phosphates (P<0.01) were observed independently of potassium concentration. The lack of effect of increasing circulating potassium indicates that hyperkalemia does not affect, by itself the muscles energetic metabolism.

Effects of the rate of muscle post mortem pH fall on the technological quality of turkey meat.

1. This experiment evaluated the influence of the rate of post mortem pH fall on the processing ability of turkey meat. 2. Four hundred and twenty male turkeys from a selected pure line (grand-parental female line, BUT Ltd) were slaughtered at 16 weeks of age in a commercial plant and pH was measured in the Pectoralis superficialis (PS) and Ilio tibialis (IT) muscles, at 20 min post mortem. Three groups of PS muscle differing in pH20 and two groups of IT muscle differing in pH20 were constituted and processed as cured-cooked white meat and turkey ham, respectively. 3. The technological yield was lower in the groups showing the lowest pH20 (97.4% at pH20 5.90 vs 98.6 and 98.3% at pH20 6.24 and 6.55, respectively, for white meat and 97.2% (pH20 6.28) vs 98.3% (pH20 6.56) for turkey hams). The groups showing the lowest pH20 also showed higher drip loss in commercially packed products. 4. Acceptability tests of processed products were carried out in the commercial plant. Texture and taste of white meat were better in the highest pH group but the overall impression was similar in the lowest and the highest pH groups (mean scores of 4.2 and 4.1, respectively), due to better colour in the former (mean scores of 4.4 for the lowest pH20 group vs 4.0 and 3.9 for the medium and highest pH20 groups, respectively). 5. For turkey hams, the meat processed from the highest pH group got the best score for all items.

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 F(2) 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 (pH(40)). 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.

Temperature and catecholamine effects on metabolism of perfused isolated rabbit muscle.

Biceps brachii muscle was isolated from anaesthetized New Zealand rabbits and perfused for 30 min with bovine red cells, while electrically stimulated at 0.1 Hz, 50 V. Temperature was maintained at 34 (physiological temperature of this muscle), 36 or 38 °C in the first experiment (Exp 1). In the second experiment (Exp 2), temperature was maintained at either 34 or 38 °C and the muscle was perfused with 2 ng/ml adrenaline and 10 ng/ml noradrenaline for 5 min during the perfusion. Whatever the temperature, twitch force decreased (P<0.01) during perfusion indicating muscular fatigue. Total turnover rate of "energy-rich" phosphate was higher at 38 °C than at 34 °C (P<0.05) during the first 30 min after the perfusion was stopped in Exp 1 and tended to be higher between 30 and 60 min (P<0.10) in Exp 2. Catecholamine perfusion had no effect on contraction and on muscle metabolism whatever the temperature. Our results show that an increase in temperature of 4 °C above the physiological temperature decreases the resistance of oxygenated rabbit muscle to fatigue. In anoxic muscle, temperature increase accelerates the turnover of "energy-rich" phosphate compounds, which is known to be detrimental to meat quality.

Post mortem muscle metabolism and meat quality in three genetic types of turkey.

1. A standard (FG, fast-growing), a black local or 'label', type (SG, slow-growing) turkey line, and the crossbreed between these two lines were compared for muscle post-mortem metabolism and related meat quality traits. 2. Ninety male turkeys (30 of each genetic type) were raised under the same experimental conditions until slaughter at 16 weeks of age. 3. Live weights at 16 weeks of age differed significantly (7.8, 6.0 and 4.2 kg, for the FG, crossbred and SG lines, respectively). Collagen content of Pectoralis superficialis (PS) muscle was higher in SG birds than in the other two types. 4. The rate of post-mortem glycogen depletion and lactate accumulation in PS and Ilio tibialis (IT) muscles were similar in the 3 lines, as were the rate and extent of post-mortem pH fall in PS muscle. In IT muscle, however, SG birds showed a slight but significantly faster pH decline. 5. Colour measurements indicated a paler breast muscle and a higher degree of myoglobin oxidation in SG birds at 24 h post mortem, than in both other lines. But these differences had disappeared after 4 and 7 d post mortem 6. SG birds showed higher drip loss and instrumentally-assessed toughness in breast muscle, compared with crossbred and FG birds. FG birds, however, had the lowest yield of breast meat after curing-cooking. 7. No marked differences in post-mortem metabolism were found between the three lines. However, differences in water-holding capacity of fresh and cured-cooked meat suggest that factors other than the rate and extent of post-mortem pH fall may contribute to the respective characteristics of these lines.

Tenderization of beef by lactic acid injected at different times post mortem.

The potential to tenderize beef muscles by the injection of lactic acid (0.5 M, 10% w/w) was studied using the pectoralis profundus muscle from cull cows. The injection was performed either 1 h (pre rigor) or 24 h (post rigor) post mortem, and the meat was stored for 2 or 14 days post mortem. Both treatments caused a rapid pH drop to around 5.0 within 4 h of injection. Other effects were: (1) an accelerated release of lysosomal enzymes into the cytosol; (2) a greater degradation of myosin heavy chains; (3) ultrastructural alterations of the myofibrils which included a general weakening or rupture in the M-lines and, to a lesser extent, in the I-bands; (4) a decreased heat stability of perimysial collagen indicated by a lower insoluble collagen content, lower differential scanning calorimetry transition temperature, and lower transition temperatures in isometric tension tests on muscle strips. The lactic acid injections improved significantly the textural traits of the meat (shear value, tensile strength, sensory scores) at 2 days post mortem with little further improvement when storage was extended to 14 days post mortem. Changes in texture were of similar amplitude at both post mortem injection times. The tenderization mechanisms of lactic acid injection are discussed.

Effect of stunning current frequency on carcass downgrading and meat quality of turkey.

The objective of this study was to determine the effect of frequency of a 150 mA water-bath stunning current on turkey hen carcass and meat qualities. Fifty turkey hens were subjected to water-bath stunning with alternating current of various frequencies: 50 Hz (n = 12), 300 Hz (n = 14), 480 Hz (n = 12), and 600 Hz (n = 12); the duration of stunning was 4 s for each bird. Carcass defects such as engorged wing veins, red wing tips, and hemorrhages were recorded. Turkey meat quality traits (M. Pectoralis major) were assessed based on rigor mortis development, color, drip loss, cooking loss, tenderness, and cooking yield of cured products. The data showed that frequencies of 480 Hz and 600 Hz are associated with an increased rate of postmortem pH decline (during bleeding). This effect is most likely due to the occurrence of vigorous wing flapping during the first 3 min poststunning. Under the experimental conditions of the present work, the increase in rate of pH decline after stunning at 480 and 600 Hz did not induce carcass and meat quality defects. However, before any recommendation is given, the influence of stunning frequency on turkey meat quality needs to be evaluated under industrial conditions.

Effects of high-intensity high-frequency ultrasound on ageing rate, ultrastructure and some physico-chemical properties of beef.

High-intensity and high-frequency ultrasound was tested for its ability to accelerate meat ageing and increase beef tenderness. Samples (≈50g) of semimembranosus muscles from 8 cull cows were assigned to ultrasonic treatment (2.6MHz; 10W/cm(2); 2 ×15s) either pre-rigor (day 0, pH 6.2) or post-rigor (day 1, pH 5.4). When applied pre-rigor, ultrasound induced a slight delay in rigor mortis onset, a stretching (12-15%) of the sarcomeres (p<0.05), an ultrastructural alteration in the Z-line region and an immediate increase (around 30%) in the release of calcium in the cytosol (p<0.05). However, no conclusive effect on meat ageing rate was observed. Post-rigor ultrasonic treatment did not induce any structural modification but slightly improved the ageing index after 6 days (p<0.05). However, no improvement in the final (day 14) ageing index was observed compared to the controls. As ultrasound had also no effect on the thermal stability of collagen, at both postmortem times, no improvement in meat tenderness can be expected under the conditions used.

Estimation of the muscle to bone ratio of the bovine pelvic limb using a morphometric method.

Conformation is an indicator of carcass composition. The aim of this study was to derive an equation for estimating the composition of the bovine pelvic limb using morphometric variates. From a mixed group of 38 French bred bovines, the sample was chosen to have a wide range of conformation. The muscle to bone ratio (M B ) was used as an index of composition. The carcasses were weighed and the other variates of the equation were measured on carcass photographs: M B = 6.2 + 0.005W - 0.62EF AB + 12GH with W: carcass weight (kg); GH: medio-lateral diameter of the distal part of the leg (cm); EF AB : medio-lateral diameter of thigh (cm)/leg length(cm); (R(2) = 0.91 and rsd = 0.27).