Influence of Postmortem Changes in Bovine Muscle on the Water-Holding Capacity of Beef. Postmortem Storage of Muscle at Various Temperatures Between 0 and 30°C

Bovine neck muscles were incubated between 0° and 30°C soon after slaughter. At different times postmortem biochemical and physical parameters and cooking loss in homogenates with or without salt were measured. The rate of pH fall in muscle depends on the incubation temperature. At 0.5°C the pH drops fast at first, leveling off afterwards but between 7° and 14°C there is an initial lag period of 2-3 hr. At 30°C no lag phase occurs. The increased rate of postmortem metabolism at 0.5°C is accompanied by cold shortening which occurs before onset of rigor and is followed by little rigor shortening. Above 16°C rigor shortening increases with rising temperature without prerigor contraction. Neither shortening nor development of rigor have an immediate influence of WHC of muscle and unsalted muscle homogenates; the small decrease of WHC postmortem is due to pH fall only and independent of temperature. Salted homogenates prepared from muscles at different time postmortem show above pH 6.0 a similar relationship between pH and WHC. At the onset of rigor mortis (pH 5.9), however, the WHC of the salted homogenate decreases strongly. The practical consequences of these results with regard to processing of beef are discussed.     

Effect of shortening during cooking on the tenderness and histology of beef

In muscles which have gone into rigor at 15°C or 37°C without shortening, prevention of cooking shortening leads to greater toughness than in samples cooked free. This tenderness difference is not seen in cold shortened muscles. A histological study showed that heat shrinkage of collagen imposes an irregular “cooking crimp” in unshortened muscle, cooked free. This is quite distinct from cold induced crimp. Cooking cold shortened muscle under restraint completely removes the cold crimp. A striking “crossed-diagonal” orientation of the perimysial collagen in the cooked meat is described.     

Tenderness in relation to the temperature of rigor onset in cold shortened beef

Beef sternomandibularis muscle was cold shortened at 2°C for 24 h and then transferred to 37°C until rigor mortis was complete. In spite of a final shortening of 33%, the mean shear value after cooking was identical with that of unshortened meat which had gone into rigor at 15°C. Meat sent into rigor at 2°C with the same degree of shortening had twice the shear value. Thus raising the temperature to 37°C in the final stages of rigor completely nullifies the toughness seen in cold shortened meat, without affecting the shortening. Small changes in cooking loss run parallel to tenderness. The effects are not due to ageing, and may arise from modification of actin–myosin bonding. It is concluded that conditions during the last stages of rigor onset are more important to tenderness than the rest of the post-mortem history of the muscle.     

Evaluation of shortenings based on various palm oil products

Several formulations based on blends of hydrogenated palm oil (MP 41·5°C) and palm stearin (IV 44) with other liquid oils, on direct blends of palm stearin with other liquid oils, and on 100% inter-esterified palm olein, were used as feedstocks in shortening production. The shortenings were stored at 20°C over a period of one month. Physicochemical characteristics, creaming properties and baking performance of the shortenings were evaluated and compared with the best shortening on the market. Slip melting point of the shortenings ranged from 41·5 to 46·4°C. Palm-cottonseed oil shortenings had higher solid fat contents at all temperatures than palm-soya bean or palm-low erucic acid rapeseed oil shortenings. The shortenings were rich in C₅₀, C₅₂and C₅₄ glycerides. Creaming power after 12 min of beating ranged from 1·55 to 1·77 cm³ g^?1. Palm stearin-cottonseed (3:2) oil shortening showed the best creaming performance. The specific volume of cakes ranged, for the experimental shortening, from 90% to 101% from the control, with low erucic acid-palm blends showing the best performance. In applications for both aerated cream and cakes, inter-esterified palm olein was excellent.     

Differential Scanning Calorimetry of Beef Muscle: Influence of Sarcomere Length

Contraction state of beef muscle at onset of rigor influences tenderness of cooked meat. Loss in tenderness during cooking has been related, through use of differential scanning calorimetry (DSC), to thermal denaturation of myofibrillar proteins. Contraction of beef sternomandibularis muscle was controlled at sarcomere lengths of 2.4, 2.1, 1.9, 1.7, and 1.4 μm. Samples were scanned from 25- 105°C at 10°C/min; ΔH (change in heat of transition) between 45° and 92°C dropped from ca. 4 J/g muscle at 2.4 μm to ca. 3 J/g at 1.4 μm. This difference (P < 0.05) amounts to less than 1% of the total energy resuired to heat meat from 45° to 92°C. The decrease is attributed to a greater actomyosin contribution to the overall thermal curve resulting from increased overlap of the filaments.     

rigor mortis in beef sternomandibularis muscle at 37°c

Beef Sternomandibularis muscle, restrained from shortening, was more tender if it entered rigor at 37°C than at 15°C. Raising the pre-rigor holding temperature of unrestrained muscle above 15°C resulted in progressively greater shortening above 28°C, and greater tenderness, particularly between 34 and 37°C. Muscles allowed to shorten during rigor at 37°C were actually more tender than if restrained. In M. rectus abdominis, the muscles shortened at 37°C were a little tougher, but much less so than the degree of shortening would indicate. A study of the time course of tenderness changes, and other evidence, indicated that these effects were not due to ageing. Muscles which went into rigor at 37°C showed a slightly higher cooking loss than the 15°C controls and were softer, and usually paler in colour. There was an increased tendency of fibres to slip over each other. Loading experiments with raw muscle strips showed that where rigor occurred at 37°C, the strips yielded and “flowed” at lower loads than the 15°C controls. The various physical changes described indicate that rigor at 37°C differs considerably from rigor at lower temperatures. Some of the changes appear to be a mild form of the “pale soft exudative” condition seen in pork.     

Effect of Temperature on the Crystalline Form and Fat Crystal Network of Two Model Palm Oil-Based Shortenings During Storage

Fat products experienced undesirable microstructural property changes due to the temperatures during transportation and storage. In this study, the lipid composition and solid fat content (SFC) of two model palm oil-based shortenings, which are denoted as shortening A (melting point of 35.1°C) and shortening B (melting point of 51.2°C), were evaluated, and their crystallization behavior and polymorphism during storage at various temperatures (?10 °C to 30 °C) was examined by X-ray diffraction (XRD) and polarized light microscopy (PLM). The fractal dimension (D _b) was calculated to qualify the change in the crystal network during storage. The aggregation of high-melting triacylglycerols (TAGs) nanostructure and the formation of the most stable β polymorph were observed in shortening at higher temperatures (≥0 °C) during storage. At the same temperature, the intensity of β crystals in the two samples increased as the storage time increased, and this trend was obvious at high temperatures (≥10 °C). In addition, the intensity of the β crystals in the two samples gradually increased as the temperature increased, and the size of the crystalline particles became larger. The crystal size in shortening A was larger than that in shortening B at high temperatures (≥10 °C). The crystal network of shortening B was denser than that of shortening A. The D _b value reached a maximum at 10 °C and 30 °C for shortening A and B, respectively. These findings have important implications on the storage stability and functional properties of palm oil-based shortenings.     

Electrical Stimulation of Mutton

Electrically stimulated ovine muscles, restrained from shortening during rapid chilling at 0-1 or 15-16°C, had lower Warner-Bratzler (WB) shear force values after 1 and 2 days aging at 0-1°C than un-stimulated controls, but were not significantly different at ≥4 days aging. Direct measurement of muscle fiber length showed that contraction values obtained for muscles assigned to go into rigor at 0, 15, 30 or 40°C were significantly less for stimulated muscles than for control muscles at 0°C, but of same magnitude or at rigor temperatures ≥15°C. WB shear force values indicated that, at temperatures ≥15°C, increase in tenderness due to stimulation became small after 7 days aging at 0-1°C, whereas at 0°C aging further increased improvement due to stimulation. Results were thus consistent with electrical stimulation reducing myofibrillar shortening at rigor temperature <15°C but at temperature ≥15°C stimulation had the same effect as a few days aging.     

The influence of temperature on shortening and rigor onset in beef muscle

At sufficient ATP concentration and temperatures below about 15°C, pre-rigor beef muscles (neck muscles) contract; this phenomenon is known as cold shortening. There is also a contracture at higher temperatures occurring just before rigor onset which is called rigor shortening. While rigor shortening starts in neck muscles at pH around 6·3–6·0 and at about 2 μMol ATP/g muscle, cold shortening can begin at pH around 7·0 and the full ATP concentration (4 μMol ATP/g) in the muscle. Shortening can take place as long as there is no irreversible formation of the actomyosin complex in the muscle, i.e. before rigor onset occurs, which can be measured by intermittent loading of the muscle. The degree of extensibility which follows starts to decrease at the moment of rigor onset. This irreversible loss of extensibility at temperatures between the freezing point (?1°C) and physiological temperatures (38°C) starts at various pH values and ATP concentrations in the muscle. At 38°C the rigor onset occurs at pH 6·25 and about 2 μMol ATP/g muscle, dropping at 15°C to pH 5·75 and 1 μMol ATP/g muscle. At 0°C, as at all temperatures below 10°C, the loss of extensibility at medium loads (about 250 g/cm²) begins shortly after cold shortening. This loss of extensibility is reversible by increasing the load or raising the temperature. The irreversible loss, or rigor onset, however, occurs at 0°C with pH of 6·1–6·2 and 1·8–2·0 μMol ATP/g muscle. Thus, the onset of rigor is influenced by more than one factor. Temperature, pH and ATP concentration each play a rôle.Maximum loss of extensibility or completion of rigor is reached between 10°C and 38°C at pH 5·5–5·6 and less than 0·5 μMol ATP/g muscle. At 0°C the completion of rigor takes place at pH 6·0, but still at 0·5 μMol ATP/g muscle. The latter fact shows that the completion of rigor is solely dependent on the ATP concentration in the muscle; nevertheless, the pH of rigor completion is higher in the extreme cold shortening range. This is apparently due to a different pH/ATP relationship in muscles at low temperatures.The results are discussed in terms of changes in the concentration of Ca²⁺ ions and ATP.The results are of particular interest for the handling of hot-boned meat; that is, for both the cooling of pre-rigor muscle and the use of hot-boned meat for processing.     

Dynamical Changes of Beef Intramuscular Connective Tissue and Muscle Fiber during Heating and their Effects on Beef Shear Force

Changes of meat shear force and its characteristics during cooking have been extensively studied, but great variability existed due to the cooking method among different studies. This study was designed to focus on the dynamic changes of beef intramuscular connective tissue (IMCT) and muscle fiber during water-bath heating and their effects on beef shear force. At 4 d postmortem, beef semitendinosus muscles were divided into 11 steaks and then cooked respectively to an internal temperature of 40, 50, 55, 60, 65, 70, 75, 80, 85, and 90°C (the remainder was not cooked as control). Collagen content and its solubility, transition temperature of perimysia and endomysia, fiber diameter, and Warner–Bratzler shear force values (WBSF) were determined. The results showed that fiber diameter decreased gradually during cooking, concomitant with the increases in filtering residue and WBSF. The maximum transition temperature (T _max) of endomysial components was lower than that of perimysial components (50.2 vs. 65.2°C). Muscle fiber and IMCT (especially perimysia) shrank during cooking, resulting in the increase of WBSF when the internal temperature was lower than 75°C, but further cooking led to the disintegration of perimysial structure, lowing up the increase of WBSF between 75 and 90°C. For beef semitendinosus muscle, the internal temperature of 65°C is a critical cooking point where meat gets tougher.     

The tenderness of cooked and raw meat from young and old beef animals

The shortening-toughness relationships for sternomandibularis muscles of young ox and large old bull have been compared. In both, toughness, measured by tenderometer, increases to a maximum at a shortening of 40%, and declines steeply from there at higher shortenings. This characteristic peaked relationship is obtained for ox and bull cooked both at 60 and 80 °C. However, toughness values for meat cooked to 60 °C are only about half those for meat cooked to 80 °C. In contrast to these similarities in the relationships for young and old animals, the rate of toughness increase with shortening in ox is considerably less than in bull. Thus toughness of ox at a given shortening and cooking temperature is considerably lower than that for bull, especially at high shortenings. A further distinction is made between the animals in that raw ox muscle does not give a peaked shortening-toughness relationship, whereas raw old bull does. The results have shown that for longissimus and sternomandibularis muscles a trained taste panel is only sensitive to variations in toughness in the lower half of the range of shear force values determined by tenderometer. In the light of this, live animal characteristics and muscle shortening are both important in determining toughness measured by taste panel.     

Thermal Gelation of Stretched and Cold-Shortened Bovine Sternomandibularis Muscle and Myofibrils

Muscle gels (10% protein) and myofibril gels (8% protein) were prepared at pH 6.0 with 2% NaCl and a heating rate of 0.7°C/min. No difference in gel strength occurred between stretched and cold-shortened muscles, but cooking loss was lower for stretched muscle. Stretched muscle sarcomeres were longer than those of cold-shortened muscle. The myofibril fraction from stretched muscle had higher gel strength, viscosity index, elasticity, and lower cooking loss than that from cold-shortened muscle. These results suggest that the contractile state of the muscle affects protein binding and water binding of the myofibrillar fraction.     

Effect of high‐pressure treatments prior to cooking on gelling properties of unwashed protein from barramundi (Lates calcarifer) minced muscle

Heat‐induced gelling properties of barramundi minced muscle with 1.5% and 2% added salt were assessed after application of pressures at 300, 400 and 500 MPa at 4 °C (initial temperature) for 10 min and subsequent cooking at 90 °C for 30 min. Whiteness, gel‐forming ability, water‐holding capacity, hardness and springiness of the barramundi gels increased as applied pressure and salt concentration increased. At 2% salt concentration, high‐pressure treatment results in barramundi gels with higher gel strength, mechanical properties and smoother texture as compared to conventional heat‐induced gels (0.1 MPa, 90 °C for 30). At a reduced salt concentration (1.5%) and pressure ≥ 400 MPa, the quality (gel strength, water‐holding capacity, hardness and springiness) of pressurised cooked gels is comparable to those heat‐induced gels with 2% added salt, but the microstructure is smoother. Scanning electron microscope images of pressurised cooked gels showed dense and compact network with smoother surface than those of heat‐only‐induced gels. Thus, application of high‐pressure treatment prior to cooking could be an effective method to enable reduced salt concentration in barramundi gels.     

Influence of Postmortem Changes in Bovine Muscle on the Water-Holding Capacity of Beef. Postmortem Storage of Muscle at 20°C

Rigor mortis occurs in bovine neck muscles as soon as pH 5.9 and an ATP level of about 1 μMol/g are reached. At 20°C muscle contraction does not occur before the onset of rigor. Postmortem changes in water-holding capacity (WHC) were followed by measuring the cooking loss of unsalted and salted (2% NaCl) muscle homogenates prepared after storage of the intact muscle tissue at 20°C for different periods postmortem. At tissue pH above 5.9 addition of salt causes a strong increase of WHC of muscle homogenates. There is a small decrease of WHC of both unsalted and salted homogenates during the prerigor phase which is apparently caused by the postmortem fall of pH. Rigor mortis does not influence the WHC of unsalted muscle homogenates but causes a strong decrease of WHC of salted homogenates. The reason for this difference is discussed. No more than one-third of the total postmortem decrease of WHC and protein solubility in salted muscle homogenates was attributed to the fall of pH, so at least two-thirds were due to the development of rigor.     

Effect of Storage Temperature on Rigor-Mortis and ATP Degradation in Plaice Paralichthys olivaceus Muscle

Live specimens of the plaice Paralichthys olivaceus were spiked at the brain, stored at various temperatures ranging from 0° to 20°C and examined for changes in rigor tension and ATP degradation in the muscle. The ATP degradation rate was clearly slower at 5–15°C than at WC, resulting in retardation of rigor- mortis onset at the former temperatures. Lactic acid accumulation in the muscle correlated well with the decrease of ATP. The muscle showed an ATP concentration of 3 μmol/g and “rigor index” (full rigor = 100%) at 30% when lactic acid increased up to 30 μmol/g at most storage temperatures. The muscle showed full rigor when ATP completely disappeared and lactic acid attained the maximum plateau (40–50 μmol/g).     

Modulation of thermal resistance of ascospores of Neosartorya fischeri by acidulants and preservatives in mango and grape juice

Minimal thermal processing is desirable for near natural organoleptic and nutritional qualities of fruit based products. In the present investigation, the effect of heat (85°C) in combination with acidulants or common preservatives on inactivation of ascospores of Neosartorya fischeri, a heat resistant mould isolated from grapes, has been studied in mango and grape juice. The ascospores were found to survive for >300 min of heating at 70, 75 and 80°C in these fruit juices and complete inactivation required 120 min of heating at 85°C. The synergistic effect of heat and organic acids or preservatives in fruit juices was noticed. The thermal death rate (1/k_85°C) values did not vary much in the presence of lactic (20), malic (20) and citric (19) acids, but tartaric acid showed least inactivation effect (1/k_85°C=54 min) in mango juice. The 1/k_85°Cvalues for ascospores of N. fischeri in mango juice containing 0·1% of potassium sorbate or sodium benzoate or combination of both at 0·05% were found to be 44, 35 and 29 min respectively. These values were respectively, 32, 13 and 14 min in grape juice. Nearly 50 and 67% of the heating time was reduced by the use of potassium sorbate and sodium benzoate (0·05% each) in mango and grape juice to inactivate 3 log number of ascospores of N. fischeri. These results may be useful in thermal processing of fruit juices.     

EFFECTS OF COOKING CONDITIONS AND POST-PREPARATION PROCEDURES ON THE QUALITY OF BATTERED FISH PORTIONS

The effects of different cooking conditions and postpreparation handling on quality of battered fish portions for fast food services were investigated. As the frying temperature increased from 300 to 400°F (149–204°C), the cooking time of battered fish portions decreased from 276 to 202 s. Crude lipid content in the batter decreased as the temperature of the frying oil increased. Holding times (10, 20 min) affected crude lipid contents of the batter depending on the cooking temperature and were lower than an unheld product. Crude lipid contents in the fish fillets were generally higher after frying by 2–3%. The crude lipid uptake by the batter coating differed significantly for the three frying shortenings (partially hydrogenated soybean, V-S oil; animal fat-vegetable blend, A-V Fat; and vegetable-palm oil blend, V-P oil;) compared in this study. This finding contrasts with previously published results. The amount of crude lipid uptake by the fish varied with shortening type and holding times. No consistent trend was observed to occur. Peroxide values increased after 3 days in the V-S Oil and A-V Fat. Flavor scores on battered fish portions cooked in V-S Oil, V-P Oil, and A-V Fat were not statistically different immediately after cooking and after holding for 10- +20-min on the first day. By the second day, differences were observed among the three shortenings. Both shortening type and postpreparation holding times affected the perceived greasiness.     

Thermal inactivation of polyphenoloxidase and peroxidase in green coconut (Cocos nucifera) water

Coconut water is an isotonic beverage naturally obtained from the green coconut. After extracted and exposed to air, it is rapidly degraded by enzymes peroxidase (POD) and polyphenoloxidase (PPO). To study the effect of thermal processing on coconut water enzymatic activity, batch process was conducted at three different temperatures, and at eight holding times. The residual activity values suggest the presence of two isoenzymes with different thermal resistances, at least, and a two‐component first‐order model was considered to model the enzymatic inactivation parameters. The decimal reduction time at 86.9 ^°C (D_{86.9 °C}) determined were 6.0 s and 11.3 min for PPO heat labile and heat resistant fractions, respectively, with average z‐value = 5.6 °C (temperature difference required for tenfold change in D). For POD, D_{86.9 °C} = 8.6 s (z = 3.4 °C) for the heat labile fraction was obtained and D_{86.9 °C} = 26.3 min (z = 6.7 °C) for the heat resistant one.     

Heat resistance in Escherichia coli and its implications on ground beef cooking recommendations in Canada

This study assessed the adequacy of the current cooking recommendations in relation to heat resistant Escherichia coli by evaluating eight potentially heat resistant E. coli strains (four generic and four E. coli O157:H7) along with AW1.7. The D_60°C-values for these strains varied from 1.3 to 9.0 min, with J3 and AW1.7 being the least and most heat resistant strains, respectively. The D_60°C-values for E. coli 62 and 68 were similar and were not affected by growth medium, while the heat resistance of C37, J3, and AW1.7 varied with the growth medium. When heated in extra lean ground beef (100 g) in vacuum pouches, the mean D_54°C, D_57°C, and D_60°C-values were 44.8, 18.6, and 2.9 min for C37, 13.8, 6.9, and 0.9 min for J3, and 40.5, 9.1, and 6.1 min for AW1.7. Burger temperatures continued to rise after being removed from heat when the target temperature was reached, by 3–5°C, and resting of 1 min would result in a destruction of 133, 374 and 14 log C37, J3 and AW1.7. These findings along with the very low occurrence of heat resistant E. coli expected in ground beef show that cooking ground beef to 71°C should be adequate.     

Thermal Transitions of Salt-soluble Proteins from Pre- and Postrigor Chicken Muscles

Salt-soluble protein (SSP) was extracted from pre- and postrigor chicken muscles at various pH values, and protein thermal denaturation was studied using several techniques. Heating at 1°C/min from 20 to 70°C induced a three- to fourfold increase in breast and leg hydrophobicity. Differential scanning calorimetry of breast and leg SSP showed a major transition occurring within the range 55 to 64°C, with the value dependent on rigor state and pH. Protein-protein association, as measured by turbidity change upon heating, underwent two transitions for leg SSP and two or three for breast SSP. The specific transition temperature and rate were dependent on pH, muscle type and rigor state. However, muscle type and pH had a greater effect than muscle rigor state on SSP denaturation.