Effects of Connective Tissue on Algin Restructured Beef

Different levels of connective tissues were examined in algin/calcium gel restructured beef tenderloin, riblifter and foreshank products. Foreshank meat, which contained a high level of collagen (4.83%), formulated with algin/calcium gel ingredients, exhibited relatively strong bind in the raw and cooked state. Addition of 5–10% undenatured or 5% denatured connective tissue to algin/calcium restructured riblifter meat resulted in products of acceptable bind and sensory quality. However, beef riblifter formulations containing 10% added denatured connective tissue had greater (P<0.05) discoloration and lower (p<0.05) bind than the other added connective tissue plus algin/calcium treatments. Algin/calcium binder improves quality of restructured meat formulated with increased concentrations of connective tissue.     

Thermal denaturation of proteins in Post rigor muscle tissue as studied by differential scanning calorimetry

Post rigor bovine M. semimembranosus was analysed by differential scanning calorimetry (d.s.c.). After extractive removal of sarcoplasmic proteins, subsequent pH adjustment and manual connective tissue removal, d.s.c. yielded reproducible thermograms which permitted investigation of the individual major myofibrillar proteins in various pH and salt environments without prior isolation. The positions of two major peaks, interpreted as myosin transitions, proved to be strongly pH dependent. At pH 5.4, the peak maxima occurred at 58 and 65°C, respectively, at a heating rate of 10°C min-¹. Above pH 6.5 their order of denaturation was reversed. In the pH range 5.4–6.5 the peak ascribed to actin had its maximum near 80°C in intact muscle. Above this pH range it was displaced to lower temperature. The thermal stability of actin was studied after treatment of the muscle tissue with different salt solutions. At equal ionic strengths (μ = 0.15) at pH 5.5, calcium chloride and sodium chloride caused 6.5°C and 4°C displacement to lower temperature, respectively. The thermograms of bovine semimembranosus muscle were compared to those of two red and two white muscle types (bovine cardiac and rabbit soleus muscles, chicken breast and rabbit semimembranosus muscles, respectively) at two pH levels. Greater myosin differences were found between red and white muscles than between muscles from different animal species. All muscles gave similar actin transitions, with exception of the heart muscle where the actin peak appeared at 3 °C lower temperature. The necessity of a strict pH control in order to obtain reproducible muscle thermograms is demonstrated.     

Thermal Denaturation of Hake (Merluccius hubbsi) Myofibrillar Proteins. A Differential Scanning Calorimetric and Electrophoretic Study

Denaturation of hake (Merluccius hubbsi) proteins was studied with DSC by monitoring T_max of transitions and denaturation enthalpies. Whole muscle free of connective tissue showed two transitions (T_max 46.5°C and 75.3°C), and ΔH of 4.27 cal/g. The exudative sarcoplasmic fraction showed three transitions (T_max 45.2°C, 59.0°C and 75.5°C) and ΔH of 3.92 cal/g. The sarcoplasmic proteins from whole hake muscle contributed to both denaturation peaks. Muscle depleted of sarcoplasmic proteins by chloride extraction showed a higher thermal sensitivity and a diminished denaturation enthalpy on the second transition. This suggested an additional effect of chloride upon actin in addition to sarcoplasmic protein extraction. pH had an effect upon the native conformation of thick filament proteins, specifically myosin.     

Binding, Sensory and Storage Properties of Algin/Calcium Structured Beef Steaks

Structured beef steaks formed with the algin/calcium binder and with or without glucono-delta-lactone were compared with 100% beef controls and with structured steaks formed with salt and phosphate. Algin/calcium-treated products exhibited better binding and color in the raw state, but had lower palatability scores in the cooked state than salt/phosphate controls. Shelf-life of both algin/calcium products under aerobic conditions was similar to the all-beef control. In vacuum packages, however, the algin/calcium products showed more rapid gas production and microbial growth than all-beef and salt/phosphate controls. The algin/calcium treatment will allow increased marketing alternatives for meat products.     

Thermal Properties of Proteins in Chicken Broiler Tissues

The thermal behavior of breast and thigh muscles, blood and skin tissues of chicken broilers was evaluated by differential scanning calorimetry (DSC). Onset temperature of transition (T_o), maximum thermal transition (T_max) temperatures, and denaturation enthalpy (ΔH) were evaluated. Breast muscle exhibited a complex thermogram with five endothermic transitions at 57°C, 63°C, 67°C, 73°C, and 78°C at a heating rate of 10°C/min. Thigh muscle exhibited only three major transitions at 60°C, 66°C, and 76°C. Thermal curves of isolated protein fractions indicated that the thermal transitions in muscle corresponded to the denaturation of myosin, sarcoplasmic proteins, collagen and F-actin. An increase in the heating rate from 1.0° to 40°C/min significantly elevated the onset temperature of transition and major transition temperatures, as well as the enthalpy of denaturation. Enthalpy of the muscle system heated to various end-point temperatures, cooled and reheated, showed that myosin was completely denatured at 60°C, sarcoplasmic proteins at 70°C and actin at 80°C.     

Influence of Rate and Length of Cookery upon Product Attributes of Pre- and Post-Rigor Beef

Paired sides of 15 steer carcasses were used to determine the effects of low temperature, long duration cooking upon muscle (semimembranosus, SM; semitendinosus, ST) shortening, cooking and tenderness attributes of beef roasts that were removed 1 hr (hot-boned, HB) and 48 hr postmortem (cold-boned, CB). The cooking treatments were: (1) 1st hr at 47°C then raised 5.6°C/hr through the 5th hr (69°C); (2) 1st hr at 52°C then raised 5.6°C/hr through the 4th hr (69°C); and (3) 1st hr at 58°C then raised 5.6°C/hr through the 3rd hr (69°C) and thereafter at 80°C until an internal temperature of 66°C was reached. Shear values and panel ratings showed HB roasts to be slightly less tender than CB roasts. Cooking yields were higher for HB than CB roasts.     

Functional, Sensory, and Microbiological Properties of Restructured Beef and Emu Steaks

Beef and emu steaks were restructured with 5% fibrinogen/0.25% thrombin (F), 0.5% algin/0.5% calcium lactate (A), or 0.5% phosphate/1.5% salt (P). P and A treatments had higher cooked binding strengths and cook yields than the F treatments (P < 0.05). The pH and cook yields of restructured emu were higher than beef (P < 0.05). Binding strength of emu was lower than beef in all binding systems (P < 0.05). F solution had an aerobic plate count (APC) of 39,000/g and increased the microbial count in restructured emu steaks from 940 to 7500/g (P < 0.05). Cooking to 60°C reduced APC to < 250/g (P < 0.05) with progressively greater bacterial kill after cooking to 66°C or 75°C.     

Some Effects on the Mechanical Properties of Meat Produced by Cooking at Temperatures between 50° and 60°C

Peak force (PF) shear values obtained for stretched muscles from beef animals of three ages (2–3 months, 2–6 year and 12–17 years) decreased when heated for 1 hr at temperatures above 50°, 55° and 60°C respectively. PF values obtained for veal muscles were unaffected by heating at 50°C for up to 8 hr but rapidly decreased with increased time of heating at 55° or 60°C. The decrease in shear values with heating time was still evident after the connective tissue contribution was eliminated by a further cook at 80°C. Samples from the oldest animals required 24–48 hr at 60°C to produce a large decrease in the connective tissue contribution. Tenderization by prolonged cooking at 50–60°C was achieved by accelerated aging of the myofibrillar structure and, at ≥ 55°C, by a weakening of the collagenous connective tissue also.     

Differential Scanning Calorimetry of Beef/Kappa-Carrageenan Mixtures

The thermal properties of kappa-carrageenan (KC) and/or beef under various ionic conditions were evaluated using Differential Scanning Calorimetry (DSC). The single endotherm observed for 2% aqueous KC (Tmax at 53°C) shifted to 54–59°C with addition of 1–3% NaCl and 0.35% sodium tripolyphosphate. Three endotherms were observed for post-rigor bovine semimembranosus meat (Tmax at 57, 66 and 80°C). Addition of salt/phosphate to beef had greater effects on Tmax than did 2% KC. On rescanning following 24 hr refrigerated storage, beef samples showed no thermal response, while KC treatments and beef/KC mixtures showed single endotherms at 53–63 and 69–76°C, respectively, indicating a wide shift in melting temperature of KC both in the presence of meat and at higher ionic strength.     

Effect of temperature, pressure and calcium soaking pre-treatments and pressure shift freezing on the texture and texture evolution of frozen green bell peppers (Capsicum annuum)

The firmness of green bell pepper (Capsicum annuum) was studied under different processing conditions. Thermal texture degradation kinetics of pepper tissue between 75 and 95 °C could be accurately described by a fractional conversion model. The firmness of pre-processed pepper increased when the samples were submitted to several heat, pressure, and combinations of heat/pressure and calcium soaking pre-treatments. Pre-heating at 55 °C during 60 min and mild heat/high-pressure treatments (200 MPa at 25 °C, 15 min) yielded the best results, which were further improved when combined with calcium soaking. These pre-treatments significantly slowed down thermal texture degradation of pepper at 90 °C, a typical temperature used for pepper blanching prior to freezing. The above-mentioned pre-treated samples showed a significant reduction in firmness when frozen by regular freezing at 0.1 MPa. The same samples showed no changes in firmness when frozen by high-pressure shift freezing at 200 MPa. When freezing was carried out by high-pressure shift and after frozen storage (−18 °C) for 2.5 months, pressure pre-treated pepper showed a better retention of texture than thermal pre-treated pepper.     

A Comparison of Isometric Tension and Differential Scanning Calorimetry Measurements on Meat

The isometric tension developed in strips of stretched and cold-shortened muscle samples while heated up to 85°C showed six transitions. Preheating at 50°C or 60°C eliminated most transitions in samples from very young animals except for those near 80°C. Differential scanning calorimetry results obtained for samples from young and old animals were similar, but the peak assigned to connective tissue changed from 61°C to 65°C with age. The age effect indicated some of these differences were due to collagenous connective tissue. The transitions near 80°C were effectively eliminated by a pressure treatment known to denature actin—an indication that actin might still be structurally viable at temperatures under or close to 80°C.     

Effect of Electrical Stimulation on the Tenderization of Mutton by Aging

The effect of high voltage electrical stimulation (800V RMS, 10 ms pulse width, 14.3 Hz for 90 sec) on the tenderization due to aging of meat at 0— 1°C has been studied by obtaining Warner-Bratzler shear force deformation curves of cooked longissimus dorsi and semimembranosus muscles from young and old sheep. For muscles restrained from myofibrillar shortening stimulation did not result in any significant improvement in shear parameters nor was the aging process affected. For muscles able to shorten, stimulation produced a substantial reduction in shear force values to the level obtained for restrained muscle. Shear force measurements on samples pressure-heat treated, to minimize myofibrillar strength, indicated that major structural changes in connective tissue, due to electrical stimulation, were unlikely.     

Effect of Algin/Calcium Binder Levels on Various Characteristics of Structured Beef

Six levels of algin/calcium binder (0, 0.28, 0.57, 0.85, 1.13, 1.42%) were evaluated in raw and cooked structured beef. Binder levels of 0.57% gave higher cook yield and greater cooked product bind scores than products without binder. Sensory evaluation scores for product bind and hardness increased (P< 0.05) with higher binder level for raw samples, but hardness showed no differences for cooked samples. Force required to penetrate raw samples increased up to the 0.85% binder level, but snowed no difference (P>0.05) among cooked samples. Raw product bind scores increased with higher levels of binder, while cooked product bind scores were similar with binder levels above 0.57%.     

IONIC INTERACTIONS IN ALGIN/CALCIUM/ MYOFIBRILLAR PROTEIN GELS

Algin/calcium/myofibrillar protein gel interactions were investigated by modifying protein basic amino acids to an unreactive state and evaluating Instron texture profile (TP) of gels. Gels analyzed were: 1% algin and 0.075% CaCl₂; 1% algin, 0.075% CaCl₂ and 1.5% porcine myofibrillar protein (A/C/P); and A/C/P with lysine, histidine or arginine modified. The modification of amino acids reduced (P<0.05) gel TP parameters of hardness, hardness 2, gumminess and chewiness. Similar TP data for protein modified gels indicated that each basic amino acid was involved in algin/protein gelation. Results provided evidence that ionic bonds between protein basic amino acids and algin carboxylate groups may be important for algin/myofibrillar protein gelation.     

Changes in the Tenderness of Meat Cooked at 50–65°C

Warner-Bratzler (WB) shear force values obtained for stretched veal muscles decreased as cooking temperatures were increased from 50 to 60°C. Increased proteolytic enzyme activity at these temperatures to give accelerated aging did not appear to explain the effects since there was still a substantial decrease in shear force with increase in cooking temperature from 50 to 60°C, even when well aged (7 wk at 5–6°C) meat and meat cooked for 24 hr was used. A more likely explanation was that, even at these relatively low temperatures, changes in connective tissue were involved since (a) the magnitude and direction of the change in shear force with increasing temperature was dependent on animal age and cooking time; (b) the effect of recooking at 80°C was dependent on animal age; and (c) the effects of increasing the cooking temperature and/or time on adhesion between the meat fibres was significantly greater for the samples from the younger animals.     

Effect of Cooking Temperature and Time on the Shear Properties of Meat

The effect of cooking temperature in the range 40–95°C on Warner-Bratzler shear force-deformation curves, obtained for stretched and cold-shortened meat samples from young and old bovine animals, has been investigated. The results were interpreted as indicating that the relative contributions of the connective tissue and myofibrillar structures to the peak shear force values were markedly altered as cooking temperature was increased. The changes of the myofibrillar structure were reflected by the changes in initial yield force values. In general, the initial yield force increased about three- to fourfold between 40°C and 60°C for both stretched and cold-shortened meat but between 60°C and 80°C the increase was about twice for the former and about fivefold for the latter. The connective tissue contribution decreased as cooking temperature was raised above 50°C for meat for young animals and above 60°C for very old animals–the contribution at temperatures above 70°C being very small for the former but still relatively large for the latter.     

Thermal Denaturation of Perimysial Collagen in Meat Measured by Polarized Light Microscopy

The feasibility of using the de Sénarmont method to study the loss of birefringence in septa of perimysium as transverse sections of meat were heated with a hot stage was shown. Samples were from beef, pork and turkey from 1 to 5 days postmortem. Although there were considerable differences between different types of samples, from 20°C to 67°C, there was generally only a slight decrease in path difference (overall mean, ? 0.04 nm/°C). From 67°C to about 85°C all samples had a sharp and largely irreversible decrease in path difference (overall mean, ?0.58 nm/°C) concurrent with thermal denaturation.     

Heat‐induced coagulation of whole milk by high levels of calcium chloride

This study investigated the interaction of calcium ions and milk proteins during heat‐induced coagulation of milk. Addition of 20–200 mM calcium chloride to milk caused coagulation on heating to 70 °C. Preheating milk at 90 °C for 10 min or ultra‐high temperature treatment at 140 °C for 6 s increased the sensitivity of milk proteins to coagulation. The former treatment was more effective than the latter in coagulating proteins. A maximum of 98% of the protein in milk preheated at 90 °C for 10 min was coagulated by 50 mM added calcium chloride at 70 °C with holding for 5 min.     

DIMENSIONAL CHANGES IN MEAT DURING COOKING

Continuous measurements of changes in meat fiber length with increasing temperature during cooking showed three zones where rates of length change are significantly different. The first (> 40°C) is attributed to myofibrillar change. The second (> 55 °C) is thought to be related to connective tissue shrinkage and shows differences with myofibrillar contraction state attributable to changes in spatial orientation of collagen fibers. The third zone (> 70 °C) is believed to be due to the interaction between myofibrillar and connective tissue contraction. Measurements of changes in cooking loss, length and cross-sectional area of samples of contracted and stretched muscle showed that cooking losses and the decrease in the cross-sectional area were greater in contracted samples, whilst length changes were greater in stretched samples. This has been attributed to differences in spatial orientation of connective tissue.     

Properties of Dark and Light Tissue from Horse Mackerel (Trachurus murphyi)

Mechanical and physical properties of light and dark tissues from horse mackerel (Trachurus murphyi) were determined for tissue separation. Raw dark tissue was 1.8 times harder than raw white (1.4 and 0.79 kg-f/g, respectively). Hardness after heating to 20°C decreased slightly but it increased sharply to a value of about 2.4 kg-f/ g at 40°C. Tensile strength of the skin was highest at 30°C and a large reduction in the shearing force of the interfibrillar matrix (connective tissue) was also attained at that temperature. Pieces of light muscle were denser (d =1.082) than those of dark tissue (d = 1.059) and relative separation was attained based on terminal velocities. Heating at 30°C appeared adequate to implement future mechanical disruption processes.