Effect of muscle type, salt and pH on cooked meat haemoprotein formation in lamb and beef

The rate of cooked meat haemoprotein formation, measured as the rate of loss of myoglobin solubility, in lamb was dependent on the muscles anatomical location and temperature. Lamb longissimus dorsi musle at 55 to 70°C formed cooked meat haemoprotein more rapidly than the muscles in the shoulder and leg. The formation in lamb was more rapid than in beef. The rate in high pH beef (7.25) l. dorsi was lower than found in beef l. dorsi of normal pH but in low pH lamb (5.38) l. dorsi the rate was, at most temperatures, also slower than found in this muscle from lamb of normal pH. In the presence of NaCl the rate of cooked meat haemoprotein formation was faster (almost doubled at 2g/100g meat) than found in the corresponding salt free lamb and beef samples. Other additives commonly added to meat products (mechanically recovered meat, oil, polyphosphates, soya, whey and caseinate) had little effect on the rate of cooked meat haemoprotein formation, at the levels normally used in meat products. It is concluded that for lamb products little if any myoglobin will remain soluble, and the products will look cooked before the recommended thermal treatment to inactivate Escherichia coli O157:H7 has been achieved. ?     

Stability of haem pigments in model systems and cooked meat

The stability of sheep haemoglobin and myoglobin in aqueous solution at 80, 100 and 121°C for 1 h was measured by subjecting portions of the heated solutions to electrospray mass spectrometry (ESMS). ESMS dissociates haem proteins into the globin chains and the haem moiety and, with haemoglobin, degradation of the α-(15047·5 Da) and β-(16073·3 Da) chains was observed at all heating temperatures. Under the same conditions, sheep myoglobin dissociated into the globin (16923·2 Da) and haem parts but the globin was stable and few degradation products were observed in the ESMS trace (mass range 4-20 kDa) even after 1 h at 121°C. There did seem to be limited breakdown of the globin due to loss of 170 Da. From the amino acid sequence, it is postulated that this is due to loss of GLY-LEU from the N-terminus. Methods for extracting myoglobin from raw and cooked meat were then investigated. Water was adequate for myoglobin extraction from raw meat but urea solution was required for adequate extraction of cooked meat samples. Sheep meat was heated at 80, 100 and 121°C in sealed cans, extracted and the mass profile in the range 4-20 kDa measured. Myoglobin was the major peak when samples were heated for 10, 20, 30 and 40 min. After that time, other peaks appeared although the myoglobin globin chain was still apparent. The results are discussed in relation to using myoglobin as a marker for meat speciation.     

Lipid and haemoprotein oxidation in meat emulsions

Emulsions of refined additive-free lard, egg albumin and water were designed to study the effect of haemoproteins, iron salts and sodium chloride on lipid oxidation. It was found that ferric haematin pigments (metmyoglobin, methaemoglobin and heat denatured myoglobin and haemoglobin) were all catalysts of lipid oxidation whereas the oxy and carboxy derivatives were not effective. Emulsions prepared using meat of high and low metmyoglobin contents supported these findings. At the levels present in meat products, both ferrous and ferric salts were only very weak catalysts of the lipid oxidation compared with the ferric haematin complexes. Sodium chloride (1·5%) also possessed little or no pro-oxidant activity in these systems. Emulsions prepared from fresh meat and fats from various sources and of different histories indicated that although, in model systems, peroxidising lipids can catalyse the oxidation of myoglobin, in meat and meat-based emulsions the effect is of minimal importance.     

The role of non-haem proteins in meat haemoprotein digestion

The influence of additional protein on the in vitro digestion of haem compounds was investigated. When either (59)Fe-labelled haemoglobin in blood or unlabelled purified haemoglobin were digested in vitro, the formation of low molecular weight (< 10,000), dialysable, iron degradation products was very limited (<18% of the total iron) and consisted mostly of haematin compounds. The presence of additional protein, in the form of bovine serum albumen or gelatin, greatly increased the formation of low molecular weight (<10,000) degradation products; the increase being proportional to the concentration and type of added protein. In these systems approximately two-thirds of the low molecular weight iron compounds were non-haematin in character. However, the digestion of aqueous muscle extracts resulted in the greatest formation of low molecular weight (<10,000) iron degradation products (>70% of the total iron), nearly all of which were non-haematin compounds. A hypothesis is presented explaining how haemoprotein degradation occurs in meat and related systems during normal physiological digestion.     

Antimicrobial effect of natural preservatives in a cooked and acidified chicken meat model

The inhibitory effect of Microgard 100, Microgard 300, nisin, Alta 2002, Perlac 1902, sodium lactate and essential oil of mustard on microorganisms experimentally inoculated was screened in an acidified chicken meat model (pH = 5.0) and stored for 2 weeks at a none restrictive growth temperature of 22 degrees C. All antimicrobials tested were used at the highest concentration recommended by their manufacturer. Sausage batter made with mechanically deboned chicken was inoculated with a mixed culture of Escherichia coli ATCC 25922, Brochothrix thermosphacta CRDAV452, and a protective culture Lactobacillus alimentarius BJ33 (FloraCan L-2). A final cell concentration of 3-4 log CFU g (-1) was targeted after cooking at a core temperature of 55 degrees C for each microorganism in order to assess cell count variation effectively. Composition, water activity (a(w)), pH and redox potential of the sausage model was also evaluated. The E. coli population decreased steadily during storage and was close or below detection level (< 1 log CFU g (-1)) for all treatments, including the control, after 14 days. Sodium lactate was most effective against B. thermosphacta; population was 4 log lower than the control after 14 days of storage. When essential oil of mustard was used, aerobic mesophilic bacteria and lactic acid bacteria were significantly lower than the control after 2 days of storage (P < or = 0.05). The other antimicrobial agents tested had no significant effect on the aerobic mesophilic bacteria, E. coli, B. thermosphacta and lactic acid bacteria counts, when compared to the control.     

A comparison of the flavour volatiles from cooked beef and pork meat systems

The headspace volatiles from beef and pork cooked with and without added adipose tissue were entrained on Tenax GC before analysis by gas chromatography (g.c.) and combined gas chromatography-mass spectrometry. Lipid-derived volatiles dominated the headspaces of all samples and the only qualitative difference between beef and pork was an alkene of lipid origin which was peculiar to beef samples. A comparison of the areas of 37 g.c. peaks from replicate analyses of the different meat preparations using canonical variates and stepwise discriminant statistical techniques unambiguously distinguished the lean meats and the lean meats cooked with adipose tissue of either species. Adding adipose tissue to lean meat did not result in proportional increases in lipid-derived volatiles.     

Amylolytic activity in cooked luncheon meat

Glucose accumulated in chub packed luncheon meat cooked at 66°C. Glucose was also released from pork starch slurries, but not similar slurries prepared with beef or mutton. The amylolytic activity of pork was not inactivated by heating at 60°C, and this thermostable activity appears to account for the accumulation of glucose in pasteurized chub packed luncheon meat stored under conditions that preclude bacterial growth.     

Pink discoloration in cooked white meat

Abstract

Through the years various factors have been implicated in the pinking of cooked poultry and pork. The problem usually appears randomly and mysteriously disappears. Two of the most prominent precursors for the defect appear to be the presence of extraneous residual nitrates/nitrites and high cytochrome c levels.     

Hydrogen sulphide in cooked chicken meat

Summary. Precautions necessary for the determination of hydrogen sulphide in chicken meat are outlined and data given for its production during heating and subsequent disappearance on standing.     

The effect of pH on the formation of maillard-derived aroma volatiles using a cooked meat system

The effect of pH on the formation of volatile compounds was investigated using minced beef in which the pH was adjusted within the range 4.0–5.6, by the addition of hydrochloric acid before cooking. The strong buffering capacity of the meat ensured that the pH did not vary during heating. Volatiles were analysed using headspace concentration and gas chromatography-mass spectrometry. The total quantity of volatile compounds increased as the pH decreased. A number of furanthiols and their oxidation products were preferentially formed at acid pH; some of these compounds had strong meaty aromas. The formation of other heterocyclic compounds such as thiazoles and pyrazines were favoured by higher pH.     

Evaluation of protein aggregation in cooked meat

The effect of meat cooking on protein aggregation was measured in pig M.Longissimus dorsi. Muscles were aged 4 days in air and then cooked at 100 °C for 10 or 30 min. Meat was ground in a KCl solution and the whole extract was delipidated with a mixture of butanol and di-isopropyl ether in a 40:60 v/v ratio. Protein aggregation induced by cooking was evaluated with a laser granulometer, which enabled reliable and reproducible characterisation of particle size distributions, and particle shape distributions using automated imaging techniques. Cooking significantly decreased the level of big particles, while the number of small particles remained stable. Cooking also affected the form and size of the particles. In order to better understand the mechanisms implicated in the aggregation process the level of protein oxidation and the protein surface hydrophobicity were evaluated in parallel with the granulometry measurements. Significant correlations were observed between the granulometry parameters and some of the protein oxidation indices. The protein surface hydrophobicity was also correlated with the granulometry parameters demonstrating the impact of thermal denaturation on the aggregation process.     

Effects of precursor composition and water on the formation of heterocyclic amines in meat model systems

Model systems based on pressed meat from ox, pork and chicken were used to study the formation of carcinogenic/mutagenic heterocyclic amines (HAs). The composition of precursors (free amino acids, creatine and glucose) was examined and samples were heated in test-tubes under wet and dry conditions at 175 and 200°C for 30 min. Several HAs were detected, and the formation of DMIP (2-amino-1,6-dimethylimidazo[4,5-b]-pyridine), TMIP (2-amino-1,5,6-trimethyl-imidazo[4,5-b]-pyridine), IFP (2-amino-1,6-dimethylfuro[3,2-e]imidazo[4,5-b]-pyridine) and PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine) was found to be favoured by dry heating conditions. Highest amounts of PhIP and IFP were detected in heated meat juice from chicken breast, while more MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline) was found in heated meat juices from roast beef and pork chop. Norharman (9H-pyrido[3,4-b]-indole) and Harman (1-methyl-9H-pyrido[3,4-b]-indole) were also detected at high levels.     

Ropy slime formation in vacuum-packed cooked meat products caused by homofermentative lactobacilli and a Leuconostoc species

This paper deals with the cause of the formation of ropy slime on the surface of vacuum-packed cooked meat products. Two different homofermentative lactobacilli and a Leuconostoc strain were isolated from different ropy vacuum-packed meat products. The strains were able to produce slime experimentally on vacuum-packed cooked sausages. The slime had a molecular weight in the range of 70000-30000 and contained glucose and galactose in a ratio 10:1-10:2. The formation of ropy slime also occurred on sausages without added sugars.     

Antioxidant activity of Carob fruit extracts in cooked pork meat systems during chilled and frozen storage

The purpose of this study was to evaluate the effect of adding condensed tannins in the form of non-purified (Liposterine^®) or purified (Exxenterol^®) extracts obtained from Carob fruit to prevent lipid cooked pork meat systems from oxidising during chilling and frozen storage. The antioxidant activity of these extracts was compared with that of α-tocopherol. Meat lipid alteration was evaluated as thiobarbituric acid reactive substances content (TBARS) and polar material-related triglyceride compounds followed by high-performance size-exclusion chromatography (HPSEC). TBARS levels were lower (P < 0.05) in samples containing Liposterine (LM), Exxenterol (EM), and α-tocopherol (TM) than in control sample (CM) under chilled storage. TBARS formation was similar (P > 0.05) for LM and EM but lower (P < 0.05) than for TM. Polar material increased several times in all samples, but significantly less in TM and EM than in LM. Thermal oxidation compounds determined by HPSEC were lower (P < 0.05) in EM than in LM or TM. The changes in polar material were proportionally smaller after six months frozen storage than after chilled storage, with Exxenterol displaying the highest antioxidant protection. Therefore Carob fruit extracts can be successfully used to reduce fat alteration in cooked pork meat at chilled and frozen temperatures.     

Isoelectric variants of actin in raw and cooked meat

Isoelectric focusing of myofibrillar proteins from raw meat gave one major and several minor actin bands. Extending the time, or raising the temperature, of a heat treatment progressively increased the proportion of variants of isoelectric point lower than the primary component. Because of the concomitant release of ammonia on heating, it was concluded that these variants arose from the hydrolysis pf amide groups of asparagine and/or glutamine. Determination of the relative proportion of deamidated actin components may provide a measure of the severity of heat treatment given to a sample of cooked meat.     

预测微生物学及其在熟肉制品贮藏中的应用

熟肉制品中微生物的活动会引发产品品质劣变,利用预测微生物学的研究方法,通过总结不同加工、包装、贮藏条件下微生物活动的变化规律,建立回归线性方程作为预测模型,可随时了解熟肉制品中微生物的活动状况,确保熟肉制品的品质和储藏安全。     

Occurrence of heterocyclic amines in cooked meat products

Heterocyclic amines (HCAs), potent mutagens and a risk factor for human cancers, are produced in meats cooked at high temperature. The aim of this study was to determine the HCA content in cooked meat products (beef, chicken, pork, fish) prepared by various cooking methods (pan frying, oven broiling, and oven baking at 170 to 230 °C) that are preferred by U.S. meat consumers. The primary HCAs in these samples were PhIP (2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine) (1.49-10.89 ng/g), MeIQx (2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline) (not detected-4.0 ng/g), and DiMeIQx (2-amino-3,4,8-trimethyl-imidazo [4,5-f]quinoxaline) (not detected-3.57 ng/g). Type and content of HCAs in cooked meat samples were highly dependent on cooking conditions. The total HCA content in well-done meat was 3.5 times higher than that of medium-rare meat. Fried pork (13.91 ng/g) had higher levels of total HCAs than fried beef (8.92 ng/g) and fried chicken (7.00 ng/g). Among the samples, fried bacon contained the highest total HCA content (17.59 ng/g).     

Shelf life of modified atmosphere packed cooked meat products: a predictive model

The effect of temperature, concentration of dissolved CO2 and water activity on the growth of Lactobacillus sake was investigated by developing predictive models for the lag phase and the maximum specific growth rate of this specific spoilage organism for gas-packed cooked meat products. Two types of predictive model were compared: an extended Ratkowsky model and a response surface model. In general, response surface models showed a slightly better correlation, but the response surface model for the maximum specific growth rate showed illogical predictions at low water activities. The concentration of dissolved CO2 proved to be a significant independent variable for the maximum specific growth rate as well as for the lag phase of L. sake. Synergistic actions on the shelf life-extending effect were noticed between temperature and dissolved CO2, as well as between water activity and dissolved CO2. The developed models were validated by comparison with the existing model of Kant-Muermans et al. (1997) and by means of experiments in gas-packed cooked meat products. Both developed models proved to be useful in the prediction of the microbial shelf life of gas-packed cooked meat products.     

Creatinine,creatine and protein in cooked meat products

The accuracy of the results obtained with a flow injection (FI) system for the simultaneous determination of creatinine and creatine in cooked meat products was evaluated in 30 samples by comparison with those obtained by reference methods. The FI method was then applied to 52 different samples (cooked ham, 14; frankfurters, 11; wieners, 9; chopped, 10; mortadella, 8) and the protein content was also determined. From % creatinine of total creatine (creatine + 1.159 creatinine) an estimation of the heat treatment applied in the processing was made. Cooked ham, mortadella and chopped had the highest values, indicating that the cooking conditions were more severe for these products than those used in the sausages. The ratio of total creatine/protein permitted an estimation of muscular protein to be made. According to the mean value for this ratio, the products were ordered as: cooked ham, 21.9 > chopped, 17.7 > wieners, 15.9 > mortadella, 13.0 > frankfurters, 12.3mg total creatine per gram of protein.