DIFFERENTIAL SCANNING CALORIMETRY CAN DETERMINE KINETICS OF THERMAL DENATURATION OF BEEF MUSCLE PROTEINS

Differential scanning calorimetry (DSC) of beef muscle produced three large endotherms occurring at 55–57°C, 65–67°C and 81–83°C. Based on earlier DSC research on isolated proteins (Privalov 1979), the concept of cooperative units participating in thermal transition phenomena was applied to beef muscle endotherms. Analysis of these endotherms by the van't Hoff relationship and Borchardt and Daniels kinetics analysis revealed reaction orders of ca. 0.6 to 2.1, 3.5 to 5.1 and 1.5 to 3.1, respectively, for the three muscle endotherms. The reaction orders for these endotherms were influenced by muscle type, fiber sarcomere length and conditioning. Aging led to an increase in reaction order whereas increased sarcomere length was accompanied by a decrease in reaction order or number of cooperative units. Changes in the number of cooperative units participating in the endotherms is discussed in the context of meat tenderization and conditioning. It appears reaction order analysis of the T₃ transition (81–83°C) may correlate with meat tenderness.     

Effects of Postmortem pH and Temperature Muscle Structure and Meat Tenderness

Bovine longissimus muscles with postmortem pH in the range 5.5 - 7.0 were subjected to different postmortem temperatures of 1°, 4°, 25° and 37°C. Intact beef sides with different postmortem pH were also subjected to two different environmental temperatures of 1° and 25°C. High pH muscles exhibited an extensive degradation of Z-lines, whereas low pH muscles showed a preferential degradation of M-lines and myosin heavy chains. Intermediate pH muscles did not show much degradation of muscle proteins, resulting in tougher meat than either low or high pH muscles. High postmortem temperatures enhanced the degradation of muscle proteins in excised and incubated muscle strips, but the delayed chilling of intact beef sides at 25°C for 8-hr did not affect either the structural changes or meat tenderness.     

Differential Scanning Calorimetry of Beef Muscle: Influence of Postmortem Conditioning

Differential scanning calorimetry (DSC) was used to follow the changes in the endothermic transitions of beef muscle during conditioning. Sternomandibularis muscle held at 5°C from 2–8 days postmortem resulted in a significant (P < 0.05) drop in the total heat of transition (ΔH) from 3.8 to 3.0 J/g. The myosin transition decreased from 57.8° to 55.2°C while the actin transition increased from 81.8° to 83.2°C (P < 0.05). Storage time and temperature were varied to generate a response surface of thermal data for psoas major and semimembraneosus muscle. The decrease in °H of psoas major was optimal between 10° and 13°C. Total ΔH of semimembraneosus (3.9 J/g) was significantly greater (P < 0.05) than that of psoas major (3.4 J/g).     

Effect of Cooking on the Thermal Conductivity of Whole and Ground Lean Beef

The probe method was used to measure thermal conductivity of beef through a temperature range of 30–120°C. Thermal conductivity of beef increases with temperature up to 70°C followed by a decrease during the denaturation of proteins and subsequent loss of water. The thermal conductivity of beef again increases with temperature after protein denaturation. The thermal conductivity of cooked beef is lower than raw beef up to about 80°C. The rate of increase for cooked meat thermal conductivity is fairly constant with temperature at a given moisture content. Models based on composition and temperature were found to predict the thermal conductivity of meat during cooking at an average standard percent error of 7%.     

Tenderness of pre- and post rigor lamb longissimus muscle

Lamb longissimus muscle (n=6) sections were cooked at different times post mortem (prerigor, at rigor, 1dayp.m., and 7 days p.m.) using two cooking methods. Using a boiling waterbath, samples were either cooked to a core temperature of 70 °C or boiled for 3h. The latter method was meant to reflect the traditional cooking method employed in countries where preparation of prerigor meat is practiced. The time postmortem at which the meat was prepared had a large effect on the tenderness (shear force) of the meat (P<0.01). Cooking prerigor and at rigor meat to 70 °C resulted in higher shear force values than their post rigor counterparts at 1 and 7 days p.m. (9.4 and 9.6 vs. 7.2 and 3.7 kg, respectively). The differences in tenderness between the treatment groups could be largely explained by a difference in contraction status of the meat after cooking and the effect of ageing on tenderness. Cooking pre and at rigor meat resulted in severe muscle contraction as evidenced by the differences in sarcomere length of the cooked samples. Mean sarcomere lengths in the pre and at rigor samples ranged from 1.05 to 1.20 μm. The mean sarcomere length in the post rigor samples was 1.44 μm. Cooking for 3 h at 100 °C did improve the tenderness of pre and at rigor prepared meat as compared to cooking to 70 °C, but not to the extent that ageing did. It is concluded that additional intervention methods are needed to improve the tenderness of prerigor cooked meat.     

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.     

Differential Scanning Calorimetric Studies of Meat Protein-Alginate Mixtures

Differential scanning calorimetry thermal curves of beef semimembranosus muscle showed peaks at 58, 67 and 78°C. Addition of algin/calcium binder or 5-10% connective tissue increased magnitude of the 58°C peak. For crude myofibrillar, sarcoplasmic and connective tissue proteins thermal destabilization was lowered by 7.5, 23.6 and 8.6°C, respectively, with addition of algin/calcium binder. Destabilization of tendon by the binder from about 67°C to 58°C was similar in magnitude to the shift of the 67-68 and 58°C thermal transitions reported in semimembranosus and probably indicated collagen destabilization. Thermal destabilization by algin/calcium may indicate change in physical state of proteins which could influence texture of algin/calcium restructured meat products.     

Heat resistance of Escherichia coli O157:H7 in cook‐in‐bag ground beef as affected by pH and acidulant†

Summary The heat resistance of a four‐strain mixture of Escherichia coli O157:H7 was tested. The temperature range was 55–62.5 °C and the substrate was beef at pH 4.5 or 5.5, adjusted with either acetic or lactic acid. Inoculated meat, packaged in bags, was completely immersed in a circulating water bath and cooked to an internal temperature of 55, 58, 60, or 62.5 °C in 1 h, and then held for pre‐determined lengths of time. The surviving cell population was enumerated by spiral plating meat samples on tryptic soy agar overlaid with Sorbitol MacConkey agar. Regardless of the acidulant used to modify the pH, the D ‐values at all temperatures were significantly lower (P < 0.05) in ground beef at pH 4.5 as compared with the beef at pH 5.5. At the same pH levels, acetic acid rendered E. coli O157:H7 more sensitive to the lethal effect of heat. The analysis of covariance showed evidence of a significant acidulant and pH interaction on the slopes of the survivor curves at 55 °C. Based on the thermal‐death–time values, contaminated ground beef (pH 5.5/lactic acid) should be heated to an internal temperature of 55 °C for at least 116.3 min and beef (pH 4.5/acetic acid) for 64.8 min to achieve a 4‐log reduction of the pathogen. The heating time at 62.5 °C, to achieve the same level of reduction, was 4.4 and 2.6 min, respectively. Thermal‐death–time values from this study will assist the retail food processors in designing acceptance limits on critical control points that ensure safety of beef originally contaminated with E. coli O157:H7.     

Effect of Freezing Temperature on Weight Loss and Quality Characteristics of Beef Liver, Kidney, Heart, and Tongue

Temperature at which variety meats were frozen (—126°C, -34°C, - 18°C, -8°C) had little effect on weight loss, color, appearance, odor or tenderness of beef liver, kidney, heart and tongue, before, during or after thawing and retail display. Freezing of variety meats at -34°C, as opposed to -126°C: (a) appeared to minimize weight losses associated with thawing, retail display and/or application of pressure; (b) did not materially affect color of meat surfaces during retail display; (c) might improve overall appearance enough to increase retail caselife; and (d) did not affect off-odor incidence or tenderness of variety meats.     

Virucidal Effectiveness of Flexible Pouch Processing of Meat Products Prepared from Foot-and-Mouth Disease-Affected Cattle

Thermal processing of ground beef, beef cubes or beef slices in commercially popular flexible pouches, effectively inactivated foot-and-mouth disease (FMD) virus that had resulted from infection of cattle. Cooking the meat products at 75°C for 20 min or 80°C for 15 min was virucidal; however, FMD virus survived in ground beef products processed for shorter time periods and/or at lower temperatures. The processing schema described were limited to 200g samples of these meat products. Postmortem decrease of pH due to electrical stimulation of carcasses inactivated the virus in skeletal muscle but not in lymph mode tissue.     

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.     

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.     

Determination of the previous maximum temperature of heat-treated minced meat by near infrared reflectance spectroscopy

Determination of the heat treatment given to minced meat has been explored on a preliminary basis by near infrared reflectance (NIR) analysis. Minced meat samples from beef were heated at five different temperatures from 50 to 95°C. Correlating NIR-determined temperatures ranging against actual laboratory treatment temperatures gave correlation coefficients of 0.987 for ‘wet’ meat and 0.992 for freeze dried meat samples. The minimum root mean square of determination errors obtained were 3.9°C for ‘wet’ meat and 2.5°C for freeze dried meat samples.     

Effects of Antemortem Injected Crude Papain in Chicken Muscle

The effects of antemortem injected crude papain in chicken muscle on muscle protein hydrolysis were investigated. White Leghorn hens were injected intravenously prior to slaughter with crude papain or heat denatured crude papain. Collagen solubility (hydroxyproline) at 60°C was 210% of the heat denatured crude papain control. SDS-PAGE revealed no difference between treatments. Crude papain was unable to penetrate intact cells at physiological temperatures. A small but significant increase in muscle TCA soluble tyrosine was observed due to antemortem papain treatment. Postmortem papain treatment resulted in a 14 fold increase in tyrosine. Little if any intracellular muscle protein hydrolysis occurred as a result of antemortem papain treatment. Collagen hydrolysis may be the major contributor to antemortem papain induced meat tenderness.     

THE INFLUENCE OF HOT-BONING AND DELAY CHILLING ON TENDERNESS OF MATURE COW CARCASSES HUNG BY THE OBTURATOR FORAMEN

Carcasses of six mature cows (4 years plus) were investigated to evaluate the effect of hot boning with delay chilling on various muscles. Both sides of the carcasses were suspended by the obturator foramen before the muscle systems were fabricated. One side of each carcass was assigned at random to be delay chilled with hot-boning (experimental treatment). This experimental side was held for 4 hours postmortem at 16°C before various muscle systems were excised and stored at 1 °C for an additional 44 h. The conventionally processed side was held at 1 °C for 48 h before fabrication into muscle systems. Meat tenderness was objectively estimated by the use of the Warner-Bratzler Shear (WB). Subjective evaluation of meat tenderness was by a trained panel. The muscles studied were the longissimus (LD), quadriceps femoris (QF), and psoas major (PM). Shear force values were statistically different (P < 0.01) for the LD and QF and (P < 0.001) for the PM muscles. The taste panel detected variations in tenderness between the two treatments and found steaks from conventional chill muscles to be significantly (P < 0.001) preferred over the delay chilled steaks. Preference and hedonic scale scores all supported findings indicated by WB that delay chill processing for 4 h postmortem with hot-boning did not provide beef of greater tenderness than conventional chill when both sides were suspended through the obturator foramen.     

TENSILE PROPERTIES OF BEEF SEMITENDINOSUS MUSCLE AS AFFECTED BY HEATING RATE AND END POINT TEMPERATURE

The effects of heating rate and end point temperature on tensile properties of beef semi-tendinosus muscle were studied. Samples of meat heated in glass tubes in a water bath to simulate oven roasting at 93 °C had lower (P < 0.01) shear values than those heated to simulate oven roasting at 149 °C. Samples heated to 60 and 70°C had lower (P < 0.001) shear values than samples heated to 50°C. Instron breaking strength values varied (P < 0.001) with end point temperature, but were not significantly affected by the rate of heating. Significant (P < 0.001) interactions between the end point temperature and heating rate, as well as between the end point temperature and fiber direction suggested that Instron breaking strength measurements may be more sensitive to changes in tenderness than Warner Bratzler shear measurements.     

High pressure–low temperature processing of beef: Effects on survival of internalized E. coli O157:H7 and quality characteristics

High pressure–low temperature (HPLT) processing was investigated to achieve Escherichia coli O157:H7 inactivation in non-intact, whole muscle beef while maintaining acceptable quality characteristics. Beef semitendinosus was internally inoculated with a four strain E. coli O157:H7 cocktail and frozen to − 35 °C, then subjected to 551 MPa for 4 min (HPLT). Compared to frozen, untreated control (F), HPLT reduced microbial population by 1.7 log colony forming units (CFU)/g on selective media and 1.4 log on non-selective media. High pressure without freezing (551 MPa/4 min/3 °C) increased pH and lightness while decreasing redness, cook yield, tenderness, and protein solubility. Aside from a 4% decrease in cook yield, HPLT, had no significant effects on quality parameters. It was demonstrated that HPLT treatment reduces internalized E. coli O157:H7 with minimal effect on quality factors, meaning it may have a potential role in reducing the risk associated with non-intact red meat.Industrial relevanceIn the current work, high pressure (551 MPa, 4 min) was applied to beef semitendinosus while it was at subfreezing temperatures (<− 30 °C). Most studies utilizing this high pressure–low temperature (HPLT) process employ subzero capable thermostatic high pressure equipment, which currently has no commercial equivalent. Successful HPLT runs were completed in this study using more conventional temperature control (1–3 °C) on pilot scale (20 L) high pressure processing equipment. The process yielded E. coli O157:H7 reductions of 1.4–1.7 log colony forming units (CFU)/g, which, while lower than conventional high pressure processing (HPP), may be sufficient to eliminate O157 populations typical of non-intact, whole muscle beef. Various quality factors, including color, purge losses and cooked tenderness, were unaffected by HPLT, while an equivalent HPP process at nonfreezing temperatures (551 MPa, 3 °C) induced color change (loss of redness), increased cook losses and decreased cooked tenderness compared to the control and HPLT beef. Producers of non-intact, whole muscle (blade tenderized or brine injected) meat, especially those that ship and sell frozen products, may look to HPLT processes to improve food safety.     

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.     

THE DETERMINATION OF THE TENDERNESS ATTRIBUTE OF HOT BONING AND DELAY CHILLING OF MATURE COW CARCASSES

Recent research has suggested the potential for upgrading some muscles from the mature cow carcass to be used as steak and roasts. With the application of modern processing techniques, beef from mature cow carcasses shows a potential to be utilized as salable retail roast and steak. The advantages of such processing techniques could minimize labor and energy usage. This study was undertaken to compare tenderness of mature cow steak and roast which were “hot” or “cold” boned. Six mature cow carcasses were utilized in this study. One side of each carcass was randomly assigned to be delay chilled at 16°C for 4 h before fabrication into muscle and muscle systems. The remaining side was assigned the conventional treatment with muscle excision after a 48 h chilling period at 1°C. Meat tenderness was objectively evaluated by the use of the Warner-Bratzler Shear. Subjective evaluation of meat tenderness was by a trained taste panel. Muscles utilized in this investigation were the longissimus (LD), psoas major (PM), and quadriceps femoris (QF). Shear force values were generally small with less than .98 kg of shear force between treatments. Taste panelists were unable to distinguish between treatment, supporting the findings indicated by the mechanical measure.     

Glass Transition Values of Muscle Tissue

Reports of glass transition (Tg') values for frozen muscle tissue are not common and reported values are mostly much lower than would be expected. Tg’ values for muscle tissue and isolated proteins were studied using differential scanning calorimetry. Apparent Tg's of mackerel, cod and beef were similar (ca ?11 to ?13°C) and substantially higher than most published values (?15 to ?77°C for tuna and beef), but in accord with expectations for substances of high molecular weight. Dialyzed insoluble and soluble protein fractions from mackerel yielded apparent Tg’ values (ca ?7°C) that were similar, with both being higher than those for whole muscle. Apparent Tg’ values of ca ?7°C were determined for aqueous samples of gelatin and collagen, but none was detected for zein.