Use of meat fluorescence emission as a marker of oxidation promoted by cooking

Accumulation of fluorescent pigments in cooked bovine meat (M. Longissimus thoracis) was studied in relationship with the heating parameters (time and temperature). Muscles were aged at 4 °C for 11 days under vacuum before cooking. Meat cooking was performed by applying jets of steam. Three different heating treatments were tested: two with constant surface temperatures of 65 and 96 °C for 300 s, and one with a continuously increasing surface temperature up to 207 °C. After extraction in water/dichloromethane/ethanol, fluorescence pigments were distributed between the apolar phase (emission 420–440 nm after excitation at 360 nm) and the polar phase, where two emission peaks were seen (emission 410–430 and 515 nm after excitation at 360 nm). Fluorescence in the two phases was little affected by heating at the two constant temperatures while it increased exponentially after 1 min of treatment, as the varying temperature reached 141 °C. The maximum fluorescence increases, measured in the extreme conditions of cooking (207 °C/300 s), were of 5000% in the apolar phase and 1700% in the polar phase. Thiobarbituric acid reactive substances (TBARS) and protein carbonyls were measured in parallel. The correlations between these two parameters and the fluorescence emission demonstrated that the interaction between proteins and aldehyde products of lipid peroxidation was mainly involved in the production of fluorescent pigments in cooked meat.     

肉蛋白烹调氧化及其对肉品与人体健康的影响

烹调加工会加剧蛋白质氧化,导致蛋白质结构、理化性质等发生变化,从而影响其功能特性与营养价值。本文介绍了肉类烹调过程中蛋白质氧化机制、表现形式,探讨了其对肉类感官品质与营养价值的影响及对人体健康的潜在危害,最后进行总结与展望。      

Use of a fluorescence front face technique for measurement of lipid oxidation during refrigerated storage of chicken meat

Lipid oxidation in chicken breast was measured during refrigerated storage in air by front face fluorescence and by thiobarbituric acid techniques. Three chicken genotypes were compared: Standard (fast-growing line), Certified (medium-growing line) and Label (slow-growing line). Lipid oxidation was stable during the first 3 days of storage and then increased in the certified and label animal groups. Standard animals were very stable towards lipid oxidation. This study showed a good correlation between fluorescence intensity and thiobarbituric acid reactive substances measurements. Front face fluorescence technique can be used as a valuable index of lipid oxidation in chicken meat.     

Lipid oxidation in chicken as affected by cooking and frozen storage

Oxidative rancidity in fresh, frozen and cooked chicken breast and leg meat was evaluated by measuring malondialdehyde (MDA) in fat from meat with an improved 2-thiobarbituric acid (TBA) assay with antioxidant protection, and by measuring the relative fluorescent products of organic and aqueous layers from Folch extracted meat. Fresh samples were frozen for 3 and 6 months at ?18 °C and cooked in convection and microwave ovens. Frozen storage for 3 and 6 months either before cooking or after convection and microwave cooking substantially increased MDA concentrations in fat from meat, whereas cooking was more effective in generating fluorescent products. There were no significant differences in free MDA concentrations or TBA numbers in chicken meat between convection and microwave cooking methods. The certain secondary fluorescent products were significantly higher in meat cooked by convection oven. The initial levels of either MDA or fluorescent products in meat are of primary importance in determining the final MDA and fluorescence levels after processing.     

Effect of cooking and storage on lipid oxidation and development of cholesterol oxidation products in water buffalo meat

Buffalo meat was subjected to two cooking methods viz. broiling and pressure cooking and two storage procedures viz. refrigerated (4 °C) storage for six days and frozen (-10 °C) storage for 90 days. Changes in lipid oxidation and development of cholesterol oxidation products were studied in raw as well as cooked meat samples. Total lipid, phospholipid, cholesterol, free fatty acid, glycolipid and glyceride contents increased significantly on cooking of meat but did not show any significant changes during either refrigerated or frozen storage except for free fatty acid content which showed an increase. The TBA values also increased during storage but not to the extent of indicating rancidity. Cholesterol oxidation products separated by thin layer chromatography were: cholestanetriol, 7-α-hydroxycholesterol, 19-hydroxycholesterol, 7-ketocholesterol, cholesterol-α-epoxide, cholesterol-β-epoxide and an unidentified fraction. All these fractions, except for the unidentified fraction, increased on cooking and storage. The cholesterol-β-epoxide fraction was resistant to changes. Changes in broiled meat were more pronounced compared to pressure cooked meat. Frozen storage did not prevent the development of cholesterol oxidation products in buffalo meat.     

欧姆加热过程对猪肉氧化和体外消化率动态变化的研究

本文研究了欧姆加热与水浴加热肉块到一定的终点温度（20¹00℃）时,脂肪和蛋白质氧化、蛋白质表面疏水活性和聚合度、胃蛋白酶、胰蛋白酶和α-凝乳蛋白酶体外消化率的动态变化。结果显示:随着肉块终点温度的升高,蛋白质羰基呈现先下降后上升的趋势,而胰、α-凝乳蛋白酶体外消化率呈现一定的下降趋势。当肉块温度为40℃时,欧姆加热组的蛋白质表面疏水活性显著低于（p<0.05）水浴加热处理组。当肉块温度为20℃时,欧姆加热组的胰、α-凝乳蛋白酶消化率显著高于水溶加热处理组（p<0.05）。当肉块温度为60℃时,欧姆加热组的羰基值和胃蛋白酶体外消化率显著低于（p<0.05）水浴加热处理组,而胰、α-凝乳蛋白酶体外消化率显著高于（p<0.05）水浴加热处理组。当肉块温度为80℃时,欧姆加热组的硫代巴比妥酸值显著低于（p<0.05）水浴加热处理组。其余各指标各处理组无显著差异（p>0.05）。蛋白质聚合度、蛋白质疏水活度与胃蛋白酶体外消化率呈现显著负相关关系（p<0.05）,因此欧姆加热肉品节约了总加热时间的1/2⁵/6,氧化、体外消化率各指标与水浴加热处理组整体上无明显区别。      

Laboratory measurements of the heterogeneous oxidation of condensed-phase organic molecular makers for meat cooking emissions

Multiphase oxidation of trace organic constituents inside of complex atmospheric particles is not well understood. In this study, organic aerosol formed from flash-vaporized residual grease from meat cooking was exposed to atmospherically relevant ozone concentrations in a smog chamber for 4-6 h. Changes in particle composition were measured to determine reaction rates for important molecular markers used for source apportionment analysis (oleic acid, palmitoleic acid, and cholesterol). Results are also presented for palmitic and stearic acids and likely reaction products. To quantify oxidation rates over a range of atmospheric conditions, separate experiments were conducted at low and high relative humidity and using particles mixed with and without secondary organic aerosol. Although particle composition, relative humidity, and secondary organic aerosol all influence the reaction rates, the unsaturated compounds were rapidly oxidized in every experiment. At typical summertime conditions, palmitoleic acid, oleic acid and cholesterol are estimated to have a chemical lifetime of about one day. The experimentally determined reaction rates are used in conjunction with the chemical mass balance model to investigate the effects of aging on source apportionment estimates. The results highlight that assumptions regarding the photochemical stability of molecular markers can lead to substantial biases in predictions of receptor models.     

Identification of hare meat by a species-specific marker of mitochondrial origin

Meat species identification in food has gained increasing interest in recent years due to public health, economic and legal concerns. Following the consumer trend towards high quality products, game meat has earned much attention. The aim of the present work was to develop a DNA-based technique able to identify hare meat. Mitochondrial cytochrome b gene was used to design species-specific primers for hare detection. The new primers proved to be highly specific to Lepus species, allowing the detection of 0.01% of hare meat in pork meat by polymerase chain reaction (PCR). A real-time PCR assay with the new intercalating EvaGreen dye was further proposed as a specific and fast tool for hare identification with increased sensitivity (1 pg) compared to end-point PCR (10 pg). It can be concluded that the proposed new primers can be used by both species-specific end-point PCR or real-time PCR to accurately authenticate hare meat.     

Effect of different cooking methods on lipid oxidation and formation of volatile compounds in foal meat

The influence of four different cooking methods (roasting, grilling, microwaving and frying) on cooking loss, lipid oxidation and volatile profile of foal meat was studied. Cooking loss were significantly (P < 0.001) affected by thermal treatment, being higher (32.5%) after microwaving and lower after grilling (22.5%) and frying (23.8%). As expected, all the cooking methods increased TBARs content, since high temperature during cooking causes increased oxidation in foal steaks, this increase was significantly (P < 0.001) higher when foal steaks were microwaved or roasted.     

Breakdown of connectin during cooking of meat

Light-scattering studies on extracts of meat have confirmed the heat-induced breakdown of connectin previously observed by SDS gel electrophoresis. Because of the high subunit MW (～10(6)) of connectin, the weight-average molecular weight of whole muscle undergoes a relatively large decrease when connectin is broken down during heating of meat. In cold-shortened muscle, breakdown of connectin by proteolysis was as rapid as in control samples, suggesting that connectin exists in an exposed environment rather than as a core to thick filaments. The breakdown of connectin during heating at 60 or 80°C for 40 min was more extensive than during ageing for 3 weeks at 2°C. Hence, the partial proteolysis of connectin during storage at 2°C is unlikely to be responsible for tenderisation induced by ageing.     

Meat cooking shrinkage: Measurement of a new meat quality parameter

Chemical, physical and sensory aspects of quality were compared on encased rolls (1kg) prepared from single muscle beef (biceps femoris) cooked in a steam oven (80°C) or by radio frequency (RF) heating (500W, 27.12MHz) under recirculating water at 80°C. The RF protocol reduced cooking times to 23 and 31% of steam cooking times, respectively, in non-injected meat (PG1) and in rolls prepared with curing brines possessing similar dielectric properties (PG2-4). Compared to steam heating, cooking yields were significantly higher (P<0.05) and instrumental texture measurements related to toughness significantly lower (P<0.05) for RF cooked PG1 rolls and for meat injected with brines containing water binding dielectrically inactive additives (PG4) but not for brined rolls lacking the latter ingredients (PG2 and PG3). Participants in a 50 member untrained sensory panel were unable to detect texture differences which had been indicated by instrumental analysis for PG1 and PG4.     

A critical evaluation of fluorescence as a potential marker for the Maillard reaction

During storage of foods and biological systems, fluorescent products are developed through the Maillard reaction, along with the brown pigments. Fluorescent products have been proposed as early indicators of this reaction. The aim of present work was to compare the kinetics of fluorescence and pigment development in order to define adequate early markers. Model glucose–aminoacid systems were prepared in several salts and buffers and stored at 55 °C. Pigment and florescence development was evaluated as a function of time. The results showed that, under unfavourable conditions for the reaction (low pH, presence of retardant salts), fluorescence was detected after important colour changes had occurred. However, under favourable conditions for the reaction (neutral pH, accelerating salts) fluorescent products could be considered as adequate markers because they sensitively reflected early steps of the reaction. Compositional factors and/or environmental conditions are the key factors for defining the performance of fluorescence as an adequate early marker.     

Decomposition kinetics of umami component during meat cooking

We developed a kinetic model for the decomposition reaction of inosine monophosphate (IMP), which is a umami component, and obtained kinetic parameters based on the amount of IMP in an isothermal experiment. The amount of remaining IMP decreased with heating time, and its reduction rate was the highest at 40 °C. We assumed that the activity of IMP decomposition enzyme is temperature-dependent above 40 °C, and constant below 40 °C. The predicted results using this kinetic model are in good agreement with the experimental ones. Unsteady-state three-dimensional heat transfer analysis of meat during sous-vide cooking was conducted, and the distribution of remaining IMP was predicted. By the end of sous-vide cooking, the ratio of the amount of IMP in the interior of the meat decreased, whereas at the surface region, it was almost the same as the initial value, because the surface temperature reached the inactivation temperature immediately.     

Influence of thermal treatment on formation of volatile compounds,cooking loss and lipid oxidation in foal meat

The influence of four different cooking methods (roasting, grilling, microwaving baking and frying with olive oil) on volatile compounds profile (using solid phase microextraction coupled to GC–MS), lipid oxidation (by TBARs measurement) and cooking loss of foal meat was studied. Cooking losses were significantly (P < 0.001) affected by thermal treatment, being higher (29.9%) after microwaving and lower after grilling (19.1%) treatments. As expected, all the cooking methods increased TBARs content, since high temperature during cooking seems to cause an increase of the oxidation processes in foal steaks, being this increment significantly (P < 0.001) higher when foal steaks were roasted or microwaved.     

Simulation of the temperature of a meat loaf during the cooking process

A mathematical model of heat and mass transfer in the cooking of a meat loaf has been derived in order to simulate the changing temperature profile in the product. The model is a further development of the authors' earlier work. The loaf was considered as comprising two parts, the crust and the crumb, because of their different physical properties.Heat transfer coefficients have been calculated from the amount of energy supplied under different air conditions.Weight losses were monitored and, from these, mass transfer rate curves were drawn. Mechanisms for mass transfer in this type of product are discussed.     

Formation of heterocyclic amines during cooking of duck meat

Heterocyclic amines (HAs) are an important class of food mutagens and carcinogens produced in meat cooked at high temperature. In the present study, the effects of various cooking methods: boiling, microwave cooking, charcoal-grilling, roasting, deep-frying and pan-frying on the formation of HAs in duck breast were studied. The various HAs formed during cooking were isolated by solid-phase extraction and analysed by HPLC. Results showed that both the varieties and contents of HAs and the cooking loss of duck breast increase along with increasing cooking temperature and time. Pan-fried duck breasts contained the highest amount of total HAs, followed by charcoal-grilling, deep-frying, roasting, microwave cooking and boiling. 9H-pyrido[3,4-b]indole (norharman) and 1-methyl-9H-pyrido[3,4-b]indole (harman) were detected in all of the cooked duck meat, with levels in the range of 0.1–33?ng?g^?1. 2-Amino-1-methyl-6-phenylimidazo[4,5-f]pyridine (PhIP) was formed easily in duck meat cooked by pan-frying and charcoal-grilling in the range of 0.9–17.8?ng?g^?1. 2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) was identified in duck meat cooked by charcoal-grilling and pan-frying, in the range of 0.4–4.2?ng?g^?1. 2-Amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline (MeIQx) was detected in amounts below 4.5?ng?g^?1 in duck meat cooked by charcoal-grilling, roasting, deep-frying and pan-frying. The other HAs were detected in amounts below 10?ng?g^?1. Colour development increased with cooking temperature, but no correlation with HAs’ content was observed.     

Heat transfer during contact cooking of minced meat patties

Experimental results on heat transfer during heating of four types of minced meat patties by contact with hot plates are given. Experimental equipment, method of measurement and experimental values of heat flux from heating plate to heated product surface during 4 min contact cooking are described. Simultaneous measurements of product and heating plate temperatures as a function of time were used to determine the contact heat transfer coefficient between heating plate and product surface. The results show that the heat flux varied during the heating process. The magnitude of the heat flux as a function of time varies with the type of material heated and the heating plate temperature. The heat transfer coefficients measured were in the range 200 to 1200 W m^?2 K^?1, depending on product type, contact plate temperature, contact pressure and stage in the heat treatment.     

Proximate and fatty acid composition and cholesterol content of different cuts of guinea fowl meat as affected by cooking method

BACKGROUND: Poultry is one of the leading meat products in South Africa, and its nutritional composition can be affected by the cut and cooking method. Limited food composition data are available for typical South African poultry products. This study investigated the effect of different cuts and cooking methods on the proximate and fatty acid composition as well as the cholesterol content of guinea fowl (Numida meleagris) meat. RESULTS: The open‐roasting method produced the highest moisture content for all cuts, and the baking bag method the lowest. The baking bag method resulted in the highest protein content. Cooking method had no effect on fat content, although breast had the lowest and thigh the highest fat content. Ash content was highest in the open‐roasted drumstick. All cuts, regardless of cooking method, had a favourable polyunsaturated/saturated fatty acid (P/S) ratio (>0.4). Their n‐6/n‐3 ratio was also within the recommended beneficial range (<4:1). Both cooking method and cut affected cholesterol content. CONCLUSION: Different cuts of guinea fowl vary in proximate and fatty acid composition as well as in cholesterol content, which in turn is affected to varying degrees by cooking method. Copyright © 2012 Society of Chemical Industry     

Influence of cooking conditions on cooking loss and tenderness of raw and marinated chicken breast meat

The influence of different cooking treatments on tenderness and cooking loss, as main quality characteristics of chicken breast meat, was investigated. Industrial skinless chicken breast meat samples were designated as raw and marinated and cooked in the oven by hot air and hot air-steam mixture at 130, 150 and 170 °C, for 4, 8 and 12 min. Cooking losses were evaluated by weight changes before and after cooking, and tenderness changes were determined on cooked samples by measuring shear force using instrumental texture analysis. Results showed that marination, followed by air-steam cooking is the best combination to obtain the most tender chicken breast slices. The time and temperature of cooking showed similar effects on cooking loss and tenderness: short cooking time (4 min) and temperatures of 130–150 °C resulted in lower cooking losses and best meat tenderness, in both not marinated and marinated meat. Statistically significant correlations between tenderness and cooking loss indicated that the cooking loss correlated better with cooking time than with cooking temperature. An opposite phenomenon was observed for meat tenderness.