Modelling the decline of pH in muscles of lamb carcases

Assuming an exponential decay model (EDM) for pH decline as a function of temperature, ideal shortening (i.e. neither hot nor cold shortening) for an individual carcase occurs if and only if that carcase's model parameters fall within a specific sub-region of three dimensional space. This paper demonstrates that simply fitting EDMs to a sample of carcases and using the proportion of sampled carcases with estimated parameters within the specific sub-region can lead to seriously biassed estimates for the proportion of carcases ideally shortened. This is particularly so if the EDMs are fitted separately to each sampled carcase but also remains the case, to a lesser extent, if the models are fitted jointly using random effects modelling. A preferred estimate is based on the probability that an independently selected carcase has model parameters within the specific region, based on the distribution of the EMD parameters. The distribution of EMD parameters is obtained via the fitted random effects exponential decay model.     

The measurement of pH in raw and frozen turkey Pectoralis superficialis muscle

The objective of this study was to validate a rapid method for muscle pH assessment. Early pH is a good indicator of turkey breast meat quality. The stabilisation of pH can be obtained by homogenising fresh muscle in iodoacetate, but it is time consuming and not appropriate to the rate of poultry slaughter line. To reduce the time required for pH assessment, we compared different methods (homogenisation in iodoacetate of fresh (reference method), frozen and freeze-dried samples, direct measurement in tissue). Freezing the samples in liquid nitrogen before homogenisation in iodoacetate buffer could be substituted to the reference method for the measurement of pH at 3 and/or 20 min post mortem. For ultimate pH, however, the relationships were not good enough to substitute a new procedure to the reference method.     

Selective production of lactic acid in continuous anaerobic acidogenesis by extremely low pH operation

The selective production of lactic acid by anaerobic acidogenesis with low pH control was examined using a chemostat culture. By decreasing culture pH to 3.5 in a chemostat culture containing mixed microbial populations for anaerobic acidogenesis, heterolactic fermentation became dominant, resulting in the selective production of lactic acid and ethanol. This phenomenon was reversible between the acidic and neutral conditions, and was not affected by the dilution rate. The extremely low pH operation was effective for selective lactic acid production in anaerobic acidogenesis.     

Catechins enhance skeletal muscle performance

Abstract

Muscle-related disorders, such as sarcopenia and cachexia, caused by aging and chronic diseases can lead to the loss of muscle mass and strength to different degrees, severely affecting human health. Globally, tea is one of the three most popular beverages, and its major active ingredient catechins have been reported to delay muscular atrophy and enhance movement. However, currently, there is no systematic review to elaborate its roles and the associated mechanisms. This article reviews the (1) functions and mechanisms of catechins in the differentiation of myogenic stem cells, biogenesis of mitochondria, synthesis and degradation of proteins, regulation of glucose level, and metabolism of lipids in muscle cells; and (2) effect of catechins on the blood vessels, bones, and nerves that are closely related to the skeletal muscles. Catechins could prevent, mitigate, delay, and even treat muscle-related disorders caused by aging and diseases.     

牛宰后肌肉生物电阻抗与pH值相关性研究

试验在多频(5～200kHz)条件下采用四电极法对30头肉牛宰后背最长肌肉(Longissimusdorsi,LD)的生物电阻抗和pH值进行了为期10d的连续检测。发现肉牛肌肉生物电阻抗同pH值有显著相关性(γ=-1.000～-0.999)。宰后第3天(48h),驱动电流频率为40～200kHz时,肌肉组织生物电阻抗达到最大值,pH值降到最小值。在不同频率下肌肉生物电阻抗表现的离散度不同,尤其是在5～100kHz范围内,肌纤维的生物电阻抗受频率影响较明显,并且和宰后肌肉的贮藏时间有关。在相同的环境条件下,肌肉的横向电阻抗(平行于肌纤维横截面方向)均大于纵向电阻抗(平行于肌纤维方向)。     

Chicken muscle homogenate gelation properties: effect of pH and muscle fiber type

Gelation properties of chicken breast and thigh muscle homogenates at a protein concentration of 4.5% under different pH conditions (5.80–6.60) and those of myofibrillar proteins at a protein concentration of 2% were compared to determine the influence of muscle fibre types on gelation. The optimal gelling pH for breast muscle homogenates (pH 6.30) was slightly higher than that for thigh muscle homogenates (pH 5.80–6.30), a similar trend was found for the isolated chicken myofibrillar proteins (pH 6.00 for breast and 5.50 for leg). Similarly, the pH values at which breast muscle homogenate gels were weaker (pH<6.20) or stronger (pH6.20) than thigh muscle homogenate gels were higher when compared with chicken breast and leg myofibrillar protein gels (pH<5.80 and pH>5.90, respectively).     

Bovine muscle 20S proteasome: I. Simple purification procedure and enzymatic characterization in relation with postmortem conditions

Over the last decade, several sets of evidence support a possible contribution of the 20S proteasome to the meat tenderizing process. This assumption was emphasized by recent investigations demonstrating that the 20S proteasome was active in the absence of activators and exhibited endo- and exoproteolytic activities, a status often strongly debated before. In the present work, we developed a new rapid and simple purification procedure for muscle 20S proteasome and revisited the physicochemical properties of this complex in relation with the postmortem muscle environmental conditions, i.e. temperature, pH, osmolarity, etc. From a crude extract obtained from freshly excised muscle tissue, reasonable amounts of highly pure proteasome were prepared within a maximum of 4 days using only three chromatography steps. This purified proteasome was used to investigate the effect of pH, temperature, ionic strength and sodium dodecyl sulphate (SDS) on the major hydrolytic activities of this complex, i.e. trypsin-like (TL), chymotrypsin-like (CL) and peptidylglutamyl peptide hydrolase (PGPH) activities. Taken together, the data obtained suggest that the 20S proteasome constitutes a high hydrolytic potential in postmortem muscle conditions. To attest this finding, the 20S proteasome was further quantified by ELISA in at death and postmortem muscles including Longissimus, Rectus abdominis, Diaphragma pedialis and Tensor fascia latae bovine muscles. The primary conclusion was that time course changes in proteasome concentrations were not dependent on the kinetics of the pH fall. Secondly, the proteasome concentration in conditioned meat was in good agreement with previously reported proteolytic activity. Furthermore, the decrease in the muscle proteasome concentration can be considered as slow and this is particularly true in type 1 muscles for which the decrease in the amount of this complex did not exceed 7% during the first three days postmortem. This would suggest that the 20S proteasome was relatively stable during meat conditioning, a feature supporting a potential role in the meat tenderizing process.     

PSK1 coordinates glucose metabolism and utilization and regulates energy-metabolism oscillation in Saccharomyces cerevisiae

Energy-metabolism oscillations (EMO) are ultradian biological rhythms observed in in aerobic chemostat cultures of Saccharomyces cerevisiae. EMO regulates energy metabolism such as glucose, carbohydrate storage, O₂ uptake, and CO₂ production. PSK1 is a nutrient responsive protein kinase involved in regulation of glucose metabolism, sensory response to light, oxygen, and redox state. The aim of this investigation was to assess the function of PSK1 in regulation of EMO. The mRNA levels of PSK1 fluctuated in concert with EMO, and deletion of PSK1 resulted in unstable EMO with disappearance of the fluctuations and reduced amplitude, compared with the wild type. Furthermore, the mutant PSK1Δ showed downregulation of the synthesis and breakdown of glycogen with resultant decrease in glucose concentrations. The redox state represented by NADH also decreased in PSK1Δ compared with the wild type. These data suggest that PSK1 plays an important role in the regulation of energy metabolism and stabilizes ultradian biological rhythms. These results enhance our understanding of the mechanisms of biorhythms in the budding yeast.     

Role of AMP‐activated protein kinase in the glycolysis of postmortem muscle

AMP‐activated protein kinase (AMPK) is a newly identified kinase controlling energy metabolism in vivo. The objective of this study was to show the role of AMPK in postmortem glycolysis. Rapid and excessive postmortem glycolysis is directly related to the incidence of PSE (pale, soft and exudative) meat in pork, chicken and turkey, while insufficient glycolysis leads to dark cutters in beef and lamb, which causes significant loss to the meat industry. A total of 24 two‐month‐old C57BL/6J mice were assigned to three treatments: (1) wild‐type mice without pre‐slaughter treatment; (2) wild‐type mice with a 2 min swim before slaughter; and (3) wild‐type mice intraperitoneally injected with AICAr (50 mg kg⁻¹), a specific activator of AMPK, to stimulate the activity of AMPK. In addition, 16 two‐month‐old C57BL/6J mice with AMPK knockout were assigned to two treatments: (4) AMPK knockout mice without pre‐slaughter treatment; and (5) AMPK knockout mice with a 2 min swim before slaughter. The longissimus dorsi muscle was sampled at 0, 1 and 24 h postmortem for pH and enzyme activity measurements. Results showed that AMPK activity had a major role in determining the ultimate muscle pH. Pre‐slaughter stress induced by swimming significantly accelerated the glycogenolysis in postmortem muscle through activating glycogen phosphorylase. AMPK is important for maintaining the activity of glycogen phosphorylase and pyruvate kinase, and glycogenolysis/glycolysis in postmortem muscle. Thus, AMPK has an important role in the control of postmortem glycolysis and is crucial for a lower ultimate pH in postmortem muscle. However, the activation of AMPK cannot fully account for the initial rapid glycogenolysis/glycolysis induced by stress and another mechanism must exist for the accelerated glycolysis induced by pre‐slaughter stress. Copyright © 2005 Society of Chemical Industry     

Revisiting the conversion of muscle into meat and the underlying mechanisms

The conversion of muscle into meat is a complex process in which all mechanisms responsible for the development of meat qualities are very likely interdependent. Colour and flavour are thus both dependent on oxidative mechanisms. Oxidation and proteolysis are probably two processes involved in the development of meat tenderness. This paper reviewed the consequences of programmed cell death or apoptosis on muscle cells structure and biochemistry and on meat qualities as well. We therefore look at different new hypothesis susceptible to highlight the meat science field and provide new supports for a more dynamic meat research. One of them which would have appeared evident for our purpose since a decade, deals with the fact that, after animal bleeding, muscle cells have no other alternative to only enter the programmed cell death procedure or apoptosis. If we introduce an early phase corresponding to apoptosis, taking place before the rigor onset and overlapping it, we will see that the known consequences of that process bring forward possible answers to still unexplained observations. After an overview of the actual state-of-the-art in meat science, we will introduce the programmed cell death and its underlying mechanisms. We then described the strong analogies between the known consequences of apoptosis and the postmortem changes affecting a set of different muscle characteristics.     

Modelling coating quality in fluidised bed coating: Spray sub-model

Fluidised beds are widely used in industrial applications for the coating of particles. Little research has been performed in developing a model that is able to predict the quality of the coating process in terms of the coating thickness and uniformity and the occurrence of unwanted side-effects, including agglomeration, attrition and spray loss. The quality of the coating process in a fluidised bed is largely determined by the spray characteristics and the particle motion. As a first step in the development of a new model for the coating process in a top-spray fluidised bed, an accurate spray sub-model that describes the movement and the heat and mass transfers of the droplets in the coating process was created and experimentally validated.     

酪蛋白酸钠溶液粘度变化的数学模型

研究了浓度为１２－２０％酪蛋白酸钠溶液在６６－９０℃的粘度变化。在ＰＨ值为６．８－７．５的范围内，ＰＨ值对酪蛋白酸钠的粘度没有显著的影响。酪蛋白酸钠溶液粘度的和与溶液的浓度和温度都叶线性关系（Ｒ＾２〉９５％）。酪蛋白酸钠溶液的粘度浓度方程的斜率和截距都与温度呈二次方程的关系（Ｒ＾２＝９４．９１％，Ｒ＾２＝９３．５９％），并由此推导出关于浓度和温度对酪蛋白酸钠溶液粘度相互 半对数方程（Ｒ＾２＝９４．     

Relationships between muscle type and some traits influencing veal colour

The influence of the muscle type on some compositional and qualitative traits of veal was studied in two experiments, each including 20 Friesian-Holstein veal calves. Metabolic type, pigment content, glycolytic potential, buffering capacity and pH (at slaughter and ultimate) were determined on muscles longissimus dorsi, psoas major and triceps brachii caput laterale in experiment 1. Pigment content, glycolytic potential and pH (at 5 h after slaughter and ultimate) were determined in experiment 2. In both experiments, reflectance spectra were obtained from m longissimus dorsi and m psoas major at 3 and 9 days after slaughter. Reflectance at 630 nm, lightness, redness (a) and difference between reflectances at 630 and 580 nm (ΔR) were calculated from the spectra. Muscle type strongly influenced the rate of pH fall and most colour traits. Pigment content, reflectance, a and ΔR were higher in m psoas major than in m longissimus dorsi. The ultimate pH was related to the glycolytic potential but not to the buffering capacity. The relative influence of the pigment content and the rate of pH fall on the colour traits depended on the muscle. Colour of m psoas major was affected to a larger extent by the rate of pH fall than by the pigment content. Conversely, pigment content played the more important role in m longissimus dorsi.     

Characterisation of myoglobin from sardine (Sardinella gibbosa) dark muscle

Myoglobin from the dark muscle of sardine (Sardinella gibbosa) with the molecular weight of 15.3 kDa was isolated and characterised. The different myoglobin derivatives exhibited varying thermal unfolding characteristics. Deoxymyoglobin showed a single distinct endothermic peak at 74.5 °C, whereas two transition temperatures were noticeable for oxymyoglobin (64.5 and 78.4 °C) and metmyoglobin (59.0 and 76.0 °C). The spectrum of deoxymyoglobin and oxymyoglobin had absorption bands at 739, 630, 575, 500 and 405 nm, while the disappearance of the peak at 575 nm was found in the spectrum of metmyoglobin. The soret peak of all derivatives was noticeable at 405 nm. The autoxidation of myoglobin became greater at very acidic or alkaline conditions as evidenced by the formation of metmyoglobin, the changes in tryptophan fluorescence intensity as well as the disappearance of soret absorption. The higher temperature, particularly above 40 °C, and the longer incubation time induced the higher metmyoglobin formation as well as the conformational changes.     

Influence of muscle type on rheological properties of porcine myofibrillar protein during heat-induced gelation

The gelation characteristics of myofibrillar proteins are indicative of meat product texture. Defining the performance of myofibrillar proteins during gelation is beneficial in maintaining quality and developing processed meat products and processes. This study investigates the impact of pH on viscoelastic properties of porcine myofibrillar proteins prepared from different muscles (semimembranosus (SM), longissimus dorsi (LD) and psoas major (PM)) during heat-induced gelation. Dynamic rheological properties were measured while heating at 1 °C/min from 20 to 85 °C, followed by a holding phase at 85 °C for 3 min and a cooling phase from 85 to 5 °C at a rate of 5 °C/min. Storage modulus (G′, the elastic response of the gelling material) increased as gel formation occurred, but decreased after reaching the temperature of myosin denaturation (52 °C) until approximately 60 °C when the gel strength increased again. This resulted in a peak and depression in the thermogram. Following 60 °C, the treatments maintained observed trends in gel strength, showing SM myofibrils produced the strongest gels. Myofibrillar protein from SM and PM formed stronger gels at pH 6.0 than at pH 6.5. Differences may be attributed to subtle variations in their protein profile related to muscle type or postmortem metabolism. Significant correlations were determined between G′ at 57, 72, 85 and 5 °C, indicating that changes affecting gel strength took effect prior to 57 °C. Muscle type was found to influence water-holding capacity to a greater degree than pH.     

Modelling the effect of asparaginase in reducing acrylamide formation in biscuits

The influence of asparaginase on acrylamide formation, as well as colour development, in short dough biscuits was studied. In particular, asparaginase concentration, incubation time and temperature were changed according to an experimental design. As acrylamide formation was found to vary significantly between biscuits obtained by using the same ingredients and process, a mixed effect model was used to model variation of acrylamide concentration. By contrast a fixed effect model was used for colour polynomial analysis. Within the range of study, the overall results allowed the best conditions for minimising acrylamide formation to be found. It can be suggested that acrylamide development was at a minimum at intermediate asparaginase concentrations, as well as at the lowest time and temperature of incubation. Asparaginase addition did not significantly affect the colour of the final product, although the quadratic term of the incubation temperature did slightly.