Effects of pressure treatment on the ultrastructure of striated muscle

Pre- and post-rigor sheep semimembranosus muscles were subjected to a hydrostatic pressure of 100 meganewtons/m² at 25°C. The ultrastructure of the muscle fibres was compared with that of non pressure-treated samples. A conspicuous feature of pressure-treated post-rigor samples was the absence of the M-band in the central region of the A-band. Therefore it appeared that some, if not all, of the proteins in the M-line were very susceptible to disaggregation under high pressure. Another feature of the post-rigor pressure-treated sample was the loss of integrity and aggregation of I-band filaments which presumably involved an F-G transformation of actin. Pressure treatment of pre-rigor muscle resulted in extensive structural disruption with contraction band formation. It is suggested that a weakening of thin filaments and M-line bridges, when combined with a pressure-induced contraction, facilitates disruption of pre-rigor pressure-treated muscle.     

Heat-Induced Textural and Histological Changes of Ordinary and Dark Muscles of Yellowfin Tuna

When a fresh specimen of yellowfin tuna Neothunnus albacora was analyzed, the cross-sectional area of ordinary (white) muscle fiber was 3.5 times larger than that of dark muscle. As heating temperature was raised, the shear force of dark muscle became progressively larger than that of ordinary muscle. Simultaneously, the A band in the ultrastructure of both muscles was stained more densely. While the Z line in I band of dark muscle still remained, that of ordinary muscle disappeared completely by heat treatment at 60°C for 30 min. Therefore, the differences in toughness change during heat treatment correlated well with that fiber sizes and ultrastructures of the two types of muscle.     

The effects of the ultimate pH of meat on tenderness changes during ageing

A range of ultimate pH (pH(u)) values, from 5.4 to 7.2, was produced in the m. longissimus thoracicum et lumborum (LD) of 55 sheep by subcutaneous injections of adrenaline, or by injection and subsequent exercise. The rate constant of ageing for each of 47 animals was calculated from shear force measurements, taken at intervals for up to 5 days from the LD held at 12 dgC. The relationship between the ageing rate and pH(u) could be adequately described by the equation rate constant (k) = 4.109 - 1.349(pH) + 0.1111(pH)(2); r(2) = 0.707, with a minimum rate constant at pH 6.07. The loin muscles from eight carcasses were selected to determine the effects of ultimate pH on the initial, unaged toughness value. Calpain activity was inhibited by intramuscular injection of ZnCl(2) dissolved in saline, and the muscles were aged at 10-12 °C on the carcass for up to 6 days. At all values of pH(u) (5.4-6.7), tenderness as measured by shear force were equivalent, from which it was concluded that the initial toughness of unaged lamb was not affected by pH(u). In the contralateral, untreated muscle, ageing was measured using both shear force measurement and changes in the myofibrillar fragmentation index (MFI). After 1 day, the intermediate pH range (5.8-6.2) has the highest shear force and the lowest fragmentation index value. However, in contrast to the shear force values, the ultimate MFI value in aged muscle was lowest in the high pH(u) range (6.4-6.7; minimum value at 6.4). The highest fragmentation values were found at the low pH(u) range. These observations suggest that pH(u)-related tenderness differences in meat result from different rates of ageing in the post rigor period, and therefore that these differences disappear following a sufficient ageing period. The slowest rate of tenderization measured on cooked meat was observed at pH(u) values around 6.07, but the least fragmentation of raw meat was observed at pH(u) values around 6.4, a difference of almost 0.33 pH unit.     

Influence of pH on the Warner-Bratzler shear properties of mutton

Initial yield and peak shear force values obtained for stretched muscles cooked at 80°C for different times decreased linearly at a similar rate with increasing pH, which is consistent with the prime effect of pH being on the myofibrillar structure. The tenderising effect of pressure-heat treatment on stretched and cold-shortened muscle decreased rapidly with increase in ultimate pH until, at values near 7, the effect disappeared. Increased ultimate pH effectively eliminated the large increase in shear force values, occurring in cold-shortened muscle of normal pH and attributable to heat denaturation of myosin, as cooking temperature was increased above 60°C.     

Optical measurements of pH in meat

Previous studies have shown that, provided cold-shortening conditions are avoided, increases in ultimate pH from a normal of about 5.5 for beef M. longissimus thoracis (LT) are associated with increased cooked meat shear forces to an intermediate pHu of about 6 and then decreases in shear force with further increases to 7. The current study with LT samples from 156 cattle (40 steers, 116 bulls) investigated this relationship following 1 and 20 days ageing at 1-2°C. The patterns of change in shear values with increasing pHu were similar for both ageing times with a peak at just under 6, but the difference between 20 and 1 day samples (1-20 days) varied so that the relationship between pHu and this difference also showed a peak at intermediate pHu values. In contrast to some previous studies, sarcomere length did not decrease as pHu increased from 5.5 to 6, indicating that it is not necessarily an important determinant of toughening over this pHu range. A myofibrillar fragmentation index (MFI) increased from 1 to 20 day ageing, but the extent of the change was similar as pHu increased from 5.5 to 6.2. Over the wider range in pHu from 5.5 to 7 MFI at 1 day remained essentially constant while that at 20 days, and consequently the increase from 1 to 20 days, increased. These results do not provide evidence that any one factor is responsible for the greater toughness of beef with an intermediate pH, and suggest that factors other than degree of muscle fibre contraction and extent of myofibrillar protein breakdown may be involved.     

Effect of muscle-type, stage of maturity and level of nutrition on the quality of meat from male buffalo calves

The effect of stage of maturity (8, 12 and 16 months), level of nutrition (100, 115 and 130% of both energy and protein) and muscle type, on the quality of selected muscles viz. longissimus dorsi (LD), biceps femoris (BF), triceps brachii (TB) and semi tendinosus (ST) from male buffalo calves was evaluated. The LD muscle gave higher values for pH, acidity and glycogen contents while ST gave higher values for cook release volume (CRV) and Warner Bratzler shear force. The TB muscle had higher expressible juice content (EJC). The 16 month old calves gave significantly higher values for the various parameters as compared to 8 and 12 month ones except EJC and CRV. A significant increase (P 0.05) in pH, EJC and shear force values was observed with increase in level of nutrition. The shear force values which are an indicator of toughness/tenderness increased with the stage of maturity. The 8–12 month old male buffalo calves reared on 130% level of nutrition had the best fresh meat quality (P 0.05) indicated by the various parameters evaluated.     

Pressure-heat treatment of meat: Changes in myofibrillar proteins and ultrastructure

The effects on muscle of a combined pressure-heat (P-H) treatment that overcomes myofibrillar toughness have been investigated using SDS gel electrophoresis and electron microscopy. Densitometer scans of polyacrylamide gels of muscle extracts revealed that P-H treatment caused greater degradation of connectin than did heat treatment alone. Breakdown of connection by P-H treatment was reduced in muscle that had been injected with the protease inhibitor pepstatin. However, pepstatin treatment did not reduce the effectiveness of P-H treatment for tenderizing meat, as would be expected if connectin was responsible for myofibrillar toughness. P-H treatment resulted in an increase in the intensity of a peak with M(r) ～ 150 000, but this peak was also produced by non-tenderizing pressure treatments. The ultrastructural studies revealed that P-H treatment disrupted the thick and the thin filaments, leaving voids at the M-line region. It is suggested that P-H treatment achieves most of its effect by an irreversible disaggregation of the myosin of thick filaments.     

Effect of High Pressure during heat Treatment on the Wamer-Bratzler Shear Force Values of Selected Beef Muscles

The effect on the Warner-Bratzler shear values of post-rigor beef muscles of heat treatments ranging from 40 to 80°C with or without concurrent pressure treatment at 150 MPa have been investigated. For muscles in a stretched condition, a decrease in shear values attributed to changes in the connective tissue was found to occur at a higher temperature in the pressure treated samples than in those not pressure treated. For muscles in a contracted condition, a steep increase in shear values with increase in cooking temperature (attributed to myofibrillar toughening) was prevented by pressure treatment. Instead, a decrease in shear values attributed to changes in connective tissue as found in stretched muscle, was then evident.     

Effects of high-pressure treatment on the ultrastructure and thermal behaviour of beef intramuscular collagen

Effects of high-pressure treatment on the ultrastructure and thermal behaviour of beef intramuscular collagen were investigated to clarify the pressure effects on background toughness attributed to the presence of connective tissue in the muscle. No significant differences in the ultrastructure, electrophoretic pattern, thermal solubility and thermogram of differential scanning calorimetric analysis of the intramuscular collagen were observed among the control (untreated) and pressurized muscles. From the results, it is suggested that the pressurization has no significant effects on the connective tissue and the pressure-induced tenderization of meat could probably be caused only by the improvement of actomyosin toughness attributed to the myofibrillar proteins.     

THE EFFECTS OF DELAYED PICKING AND HIGH-TEMPERATURE CONDITIONING ON THE TEXTURE OF HOT- AND COLD-BONED BROILER BREAST MEAT

Four trials were conducted to evaluate the effects of delayed picking for 30 min versus normal picking, high temperature conditioning at 32°C versus low temperature conditioning at 0°C, and hot boning versus cold boning on broiler breast meat tenderness, pH, sarcomere length and R-values. None of the treatments affected cold-boned shear values. Within the hot-boned group, delayed picking significantly increased shear value (14.5 kg) compared with normally picked samples (12.5 kg). Conditioning at 32°C significantly lowered shear values (12.5 kg) compared with 0°C (14.6 kg). High-temperature conditioning lowered muscle pH immediately after evisceration, but delayed picking had no effect. Following 24 h aging, treatments had no effect on muscle pH or R-value. These results indicate that 32°C conditioning temperature and early picking significantly reduced meat toughness, but not to a commercially practical degree.     

The basal toughness of unaged lamb

Identification of the commencement of aging in relation to the rigor process was determined on lamb loin muscles by injecting a zinc-TRIS solution, which inhibits meat aging, into the muscle over the period when the pH was falling. Aging was evaluated by measuring the tenderness of cooked meat samples using a MIRINZ tenderometer. When zinc was injected into muscle above pH 6·5, the sarcomeres shortened and the cooked meat had an average shear force of 19 kgF (shear force is the force required to shear through at 1 cm cross-section sample). When sinc was injected into the muscle at pH values below 6·5 the sarcomeres did not shorten, and down to the ultimate pH, the shear force remained at approximately 15 kfF. Aging did not take place pre-rigor. The same relationships occurred for electrically stimulated muscle. The data indicate that the basal shear-force value of lamb loin prior to aging, i.e. the basal toughness level, is 15 kgF.     

Pressure-Accelerated Changes in the Proteins of Muscle and Their Influence on Warner-Bratzler Shear Values

The effect on cold-shortened post-rigor beef semitendinosus muscle of pressure treatment at 150 MPa for 6 or 16 hr at 30°C or for 1 hr at 60°C, on the presumed proteolytic breakdown of myofibrillar proteins (as revealed using sodium dodecyl sulfate (SDS) gel electrophoresis) and on Warner-Bratzler shear values, was studied. Production of a 145,000 dalton molecular weight component was much greater in the 30°C (for 6 hr or 16 hr) pressure treatments than in that at 60°C (for 1 hr). The pressure treatments at 30°C significantly decreased Warner-Bratzler shear values but to a lesser extent than did pressure treatment at 60°C. Therefore, although the mechanism by which the 145,000 dalton molecular weight component is produced may be associated with a degree of tenderization of cold-shortened muscle, it appears that another mechanism is primarily responsible for the tenderization achieved by pressure treatment at 60°C.     

Changes in lysosomal enzyme activities and shear values of high pressure treated meat during ageing

The effects of pressure treatment (520 MPa for 260 s at 10°C) on lysosomal enzyme activities, Warner-Bratzler (WB) shear values and physico-chemical parameters of post-rigor (day 2) beef (Biceps femoris and Longissimus dorsi muscles) were investigated immediately after treatment and during ageing. Activities of cathepsin D and acid phosphatase in pressurised meat samples were higher than in controls at 2 days post-mortem and throughout storage. This increase in activities was related to the breakdown of the lysosomal membrane and/or to enzyme activation. The WB peak forces were higher for pressurised samples of both muscles at 2 days than in the control and remained higher throughout ageing. The WB shear force deformation curves from pressurised samples showed that the increase in toughness was due to the increase in shear force of the myofibrillar component and not the collagen component. Pressurised muscle led to a significant decrease in sarcomere length and higher cooking loss. Post-rigor application of high pressure induced higher catheptic activity but no conclusive effect on the post-mortem rate of tenderization or tenderness of meat was observed.     

Interfacial behaviour of crayfish protein isolate

The interfacial behaviour of a crayfish protein isolate (CFPI) produced as by-product from the food industry has been studied at the air–water surface at two pH values (2 and 8). An analysis of the surface pressure and interfacial shear behaviour has been carried out as a function of CFPI content for the two mentioned pH values. The results indicate that CFPI shows higher surface pressure, smaller aggregates and higher interfacial viscoelasticity at pH 8 than at pH 2, being highly dependent on CFPI content. In fact, a transition from fluid-like behaviour to a gel-like behaviour have been obtained by increasing the protein content. These results are in agreement with the higher solubility and z-potential values and the longer emulsion stability found under alkaline conditions. Furthermore, usage of highly sensitive interfacial shear techniques, such as the magnetic rod interfacial stress rheometer or the double wall ring, both of them providing rather coincident results, has proven to be highly useful to study the viscoelastic properties of CFPI interfacial films at levels that cannot be detected by other methods.     

食品基质成分对瞬时高压杀灭枯草芽孢杆菌效果的影响

本文研究了瞬时高压对枯草芽孢杆菌的杀灭效果,以及不同pH和不同食品基质成分（蛋白质、蔗糖）对瞬时高压杀菌效果的影响。实验表明：瞬时高压作用对枯草芽匏杆菌具有一定的杀灭效果,随着处理压力的提高,枯草芽孢杆菌的致死率上升;提高进料温度对其杀灭效果也有所改善,但效果不明显;瞬时高压对枯草芽孢杆菌的致死率随着处理次数的增加而上升,且提高处理次数比提高压力的效果更明显。此外,酸性和碱性条件下较中性下更有利于瞬时高压杀菌;蛋白质和糖类对菌体有一定的保护作用,在一定浓度范围内,随着加入物浓度的提高,对菌体保护作用越强。     

Effect of cooking temperature and time on the physico-chemical, histological and sensory properties of female carabeef (buffalo) meat

The effect of cooking temperature (80-100°C) and time (30-60min) on collagen solubility of Semimembranosus muscle in carabeef were investigated. The pH, cooking loss, shear force value, collagen content, collagen solubility, sensory evaluation and histological observations of water bath cooked and pressure cooked Semimembranosus meat samples were measured. Increase in pH, cooking loss, collagen solubility and tenderness scores with decrease in shear force value and collagen content was observed with increases in cooking temperature and time. However, no statistical difference was observed for shear force values, collagen solubility values and tenderness scores in pressure cooked meat and meat cooked in a water bath at 100°C for 45min, inferring that cooking of buffalo meat at 100°C for 45min improved collagen solubility and tenderness to the same extent as that due to pressure cooking.     

Postmortem Calcium Chloride Injection Alters Ultrastructure and Improves Tenderness of Mature Chinese Yellow Cattle Longissimus Muscle

ABSTRACT: This study was conducted to test the hypothesis that postmortem calcium injection could activate the calpain system in mature Chinese Yellow Cattle muscle, thereby promoting meat tenderization through disruption of the myofibril structure during aging. A 10% (w/w) injection of CaCl₂ (300 m M ) solution lowered the Warner-Bratzler shear values of longissimus muscle by more than 30% ( P < 0.05), even with only 24 h postmortem storage when compared with noninjected or water-injected controls. The accelerated meat tenderization by the Ca²⁺ treatment paralleled the changes in myofibril fragmentation index and fracture of the myofibril ultrastructure throughout the sarcomere but most notably around the I-bands and the Z-disks. Injection of ZnCl₂ (50 m M ) largely inhibited these proteolytic changes. The colorimetric L * and a * values were not affected by CaCl₂ nor by ZnCl₂ injection. The results suggest that postmortem CaCl₂ injection can be used to help resolve the toughness problem of mature Chinese Yellow Cattle meat and shorten the aging time required to achieve adequate tenderness.     

Nanomechanical Characteristics of Meat and Its Constituents Postmortem: A Review

Tenderness/toughness are two important factors in meat evaluation and can be well explained by their mechanical and nanomechanical characteristics, which in turn are highly affected by the complex arrangement of meat numerous constituents and the influence of endogenous enzymes on this biological structure. It has been also revealed that post-slaughter variations in muscle characters that make muscle to transform to meat are a consequence of changes in the nanomechanical properties of myofibrillar proteins through linkage with each other or even through their breakdown. However, background toughness that is related to the connective tissues exists just at the time of slaughter and does not change over the time. The most famous instruments that measure the mechanical characters of myofibrils in pico/nano scale are atomic force microscopy, also known as scanning force microscope, optical tweezer, and glass microneedle. In this regard, mechanical terms such as torsional strength, rotational Brownian motion, elastic modulus, viscoelasticity, flexibility, etc. are generally used to show different behavior of meat ultrastructure and the changes that usually occur in postmortem muscle. It is expected that the evaluation of nanomechanical properties of muscle cells and connective tissues, particularly when the muscle undergoes different changes, be useful in order to justify many features of meat postmortem.     

Differences in quality characteristics of normal, PSE and DFD pork

Differences in water-holding capacity, colour and tenderness/toughness were studied in 21 pork loins belonging to three quality categories, i.e. dark firm dry (DFD), normal and pale soft exudative (PSE). The division into the three groups was based upon the ultimate pH-values of the loins (< pH 5·5, pH 5·5-6·0, pH > 6·4). The PSE loins were characterized by a poor waterholding capacity, higher cooking loss and paler colour in contrast to the DFD category. The normal loins took an intermediate position. Neither sarcomere length, determined on fresh muscle tissue, nor Armour tenderometer values showed significant differences between the various quality categories. This was in contrast to the Warner-Bratzler (W-B) shear force values, determined on cooked loins, which had the lowest values in the DFD category. A strong relationship between the W-B values and the cooking losses was found. It was concluded that neither sarcomere length nor Armour tenderometer measurements were able to predict the shear force values of cooked pork loins.     

Effect of meat ultimate pH on rate of titin and nebulin degradation

The processes involved in the tenderisation of meat were studied on muscles with a range of ultimate pH values (5.4–7.0), produced by subcutaneous injection of various doses of adrenaline and exercise. The m. longissimus thoracicum et lumborum (LD) was removed from carcasses stored at 10 °C and held for 1, 3 or 6 days after slaughter, then frozen until tenderness assessment. The tenderness of meat cooked from the frozen state was determined as the force to shear samples of 10 mm × 10 mm cross-section using a MIRINZ tenderometer. The maximum toughness of 15 kgF occurred at an ultimate pH (pH_u) of about 6.0, resulting in a curvilinear relationship between tenderness and pH_u at 1 day post-slaughter. By 6 days post-slaughter, all meat had reached the same low shear value of approximately 3 kgF. SDS-PAGE patterns obtained from samples at 12, 24 and 48 hr post-slaughter showed increasing titin and nebulin degradation over time, with the slowest rate of degradation occurring at pH_u values 6.0–6.3. Titin and nebulin are known to play an important role in the stabilisation of myofibril structure, and it is suggested that the curvilinear relationship results when pH-dependent titin and nebulin degradation occurs.