Source apportionment of molecular markers and organic aerosol. 3. Food cooking emissions

The chemical mass balance model is applied to a large dataset of organic molecular marker concentrations to apportion ambient organic aerosol to food cooking emissions in Pittsburgh, Pennsylvania. Ambient concentrations of key cooking markers such as palmitoleic acid, oleic acid, and cholesterol are well correlated, which implies the existence of well-defined source profiles. However, significant inconsistencies exist between the ambient data and published source profiles. Most notably, the ambient ratio of palmitoleic-acid-to-oleic-acid is more than a factor of 10 greater than essentially all published source profiles. This problem is not unique to Pittsburgh. The reason for this discrepancy is not known but it means that both acids cannot be fit simultaneously by CMB. CMB analysis is performed using three different combinations of food cooking source profiles and molecular markers. Although all three solutions have high statistical quality, the amount of OC apportioned to food cooking emissions varies by a factor of 9. Differences in fitting species and source profile marker-to-organic-carbon ratios cause most of the large systematic biases between the different solutions. The best CMB model includes two alkanoic acids as fitting species in addition to other cooking markers, which helps constrain the source contribution estimates. It also includes two meat cooking source profiles to account for the variability in the ambient data. This model apportions 320+/-140 ng-C m(-3) or 10% of the study average ambient organic carbon to food cooking emissions. Although these results illustrate the significant challenges created by source profile variability, the strong correlations in the ambient dataset underscore the significant promise that molecular markers hold for source apportionment analysis.     

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 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.     

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.     

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。      

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.     

Influence of electrostatics on the oxidation rates of organic compounds in heterogeneous Fenton systems

Electrostatic effects influence the oxidation rates of charged dissolved organic compounds in systems where the hydroxyl radical (*OH) is produced by the iron oxide-catalyzed decomposition of hydrogen peroxide (H2O2). Experiments were performed using goethite and the *OH probes 14C-labeled formic acid, 2-chlorophenol (2-CP), and nitrobenzene. At pH 4 and an ionic strength of 0.01 M, formic acid (pKa = 3.745) detected a steady-state concentration of *OH ([*OH]ss, calculated as a solution average) approximately 50 times higher than the two neutral probes did in the same systems, indicating significant enrichment of formate at the surface of the positively charged iron oxide where the *OH is being produced. Increasing the pH and ionic strength decreased formic acid oxidation rates by factors consistent with predicted decreases in electrostatic effects. In the presence of high 2-CP concentrations, the [*OH]ss measured by formic acid decreased with time, and goethite coagulation increased, due to loss of positive charge on the oxide surface as the oxidation products of 2-CP complexed surface Fe species. The [*OH]ss detected by 2-CP did not change significantly, indicating that neither goethite coagulation nor surface complexation of 2-CP oxidation products interfered with the rate of *OH generation; however, such an effect could have occurred in experiments using dissolved Fe instead of goethite. Model predictions of organic compound oxidation rates in mineral-catalyzed Fenton-like systems were improved by taking electrostatic effects into account.     

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.     

Time-resolved characterization of diesel particulate emissions. 2. Instruments for elemental and organic carbon measurements

The measurement of elemental carbon (EC) and organic carbon (OC) mass for particles emitted by diesel vehicles is currently accomplished using particle collection on filters, followed by analysis using the thermal/optical reflectance carbon analysis method (TOR) or one of its variations. Such filter methods limit time resolution to a minimum of several minutes, making it impossible to study emissions during transient operating conditions. Testing of five different measurement methods has demonstrated that fast response measurement of diesel exhaust particulate EC and OC concentrations, consistent with TOR filter measurements, is feasible using existing technology. EC mass concentrations are best measured through determination of particulate light absorption with a photoacoustic instrument or determination of light extinction with a smoke meter. The photoacoustic instrument has the better dynamic range and sensitivity, whereas the smoke meter is a simpler instrument. Fast response OC measurements cannot be made with any single instrument tested. However, a combination of real time weighing as implemented in the tapered element oscillating microbalance with the photoacoustic instrument has been shown to be capable of determining OC concentrations with good time response. The addition of a nephelometer to the OC measurement could potentially improve time resolution, freedom from interferences, and sensitivity.     

Influence of cooking methods on the nutritive value of turkey meat

Selected culinary parts of turkey meat were subjected to a differentiated cooking method. The chemical composition and -SH group levels were studied in both raw and cooked turkey meat and indices of nutritive value were determined. The turkey meat was shown to be characterized by a high nutritive value, irrespective of any cooking method. A slightly unfavourable effect was found to be exerted on the nutritive value of meat by microwaves. Fried and roasted meat was characterized by high values of PER (3.1) and BV (83.8). Lower index values were found for microwaved meat [PER (2.8); BV (82.2)].     

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.     

马氏珠母贝肉蒸煮液主要呈味成分分析

采用高效液相色谱法、自动氨基酸分析仪、原子吸收光谱等方法分析了马氏珠母贝全脏器、闭壳肌和内脏团蒸煮液的主要呈味物质。结果表明:蒸煮液中游离氨基酸含量丰富,与呈鲜味和甜味相关的天门冬氨酸、谷氨酸、甘氨酸和丙氨酸4种氨基酸含量占到50%以上;ATP及其关联化合物含量中HxR的含量最高;内脏团蒸煮液中甜菜碱的含量最高,达到191.00 mg/100mL;琥珀酸在全脏器和内脏团蒸煮液中的含量较高,分别达到了125.00 mg/100 mL和124.00mg/100 mL;内脏团蒸煮液中糖原含量最高,达到了105.34 mg/100 mL,与呈味有着密切关系的阳离子K+、Na+在3种样品蒸煮液中的含量均较高,而阴离子PO43-在闭壳肌蒸煮液中含量最高、Cl-在内脏团蒸煮液中含量最高。     

常压蒸煮工艺对包装扣肉品质的影响

采用感官评价、质构仪全质构分析和微生物测定等方法进行包装扣肉制品的口感、蒸煮异味、白油凝结现象和卫生状况的分析,评价常压蒸煮对包装扣肉品质的影响。结果表明:常压蒸煮下扣肉肥肉和瘦肉部分的硬度、胶黏性和咀嚼性指标数据值均随着热处理时间的延长而明显降低,在100℃90min的蒸煮条件下可获得较佳的扣肉口感;随着包装后二次杀菌时间的延长增加了包装扣肉的蒸煮异味和成品冷藏后出现的白油凝结现象;采用先100℃蒸煮60min,然后真空包装并进行100℃30min二次杀菌的加工工艺,可以获得具有原汁原味,无明显蒸煮异味和较少白油凝结的包装扣肉制品,达到我国熟肉制品的卫生要求。     

The heat pipe and its potential for enhancing the cooking and cooling of meat joints

The rate of cooking and cooling of meat is limited by its poor thermal conductivity. Providing a high conductivity path to the thermal centre of the meat is a potential method of overcoming this problem. The aim of this research was to investigate the feasibility of using heat pipes to increase cooking and cooling rates in meat joints. Three diameters of heat pipe were inserted into 1 kg bacon joints, which were then cooked and cooled under catering/domestic conditions. These results show that the use of heat pipes in the cooking and cooling of meat joints has substantial potential. Heat pipes can halve the cooking time and help guarantee that joints are cooked to a safe internal temperature. They can also reduce the cooling time of joints by over 25%.     

烹调方式对不同肉及其制品中杂环胺的影响概述

杂环胺(heterocyclic aromatic amines,HAAs)是一类杂环芳香族化合物,是富含蛋白质的食物(如肉类和鱼类等)在高温和长时间烹饪过程中产生的一类有害物质.目前已经从高温加工的肉及其制品中发现有超过30种的杂环胺.国际癌症研究机构已把2-氨基-3-甲基咪唑并[4,5-f]喹啉(IQ)等杂环胺列为...     

Effects of different cooking methods on the formation of food mutagens in meat

Hamburgers and chicken fillets were cooked in convection ovens, deep‐fried or contact fried and analysed for mutagenic activity using the Ames test. For the three different convection ovens, the cooking parameters studied included the presence of steam, air velocity, air temperature and holding time. For deep‐frying and contact frying, the cooking parameters included cooking temperature and cooking time. In cooked hamburgers, mutagenic activity was only detected in those that had been deep‐fried. In chicken fillets, mutagenic activity was detected in samples prepared with all cooking methods, being highest in the deep‐fried samples. Factorial analysis indicated that heat transfer was the most important factor affecting mutagenic activity. High temperature and high air velocity in the convection ovens enhanced mutagenic activity. The presence of steam reduced the mutagenic activity, except when high temperature was used in combination with high air velocity. In chicken fillets, high mutagenic activity correlated to high weight loss during cooking. Pan‐fried chicken fillets were analysed using high performance liquid chromatography (HPLC) and the mutagenic/carcinogenic heterocyclic amines 2‐amino‐3,8‐dimethylimidazo[4,5‐f ]‐quinoxaline (MeIQx), 2‐amino‐1‐methyl‐6‐phenylimidazo‐[4,5‐b]‐pyridine (PhIP) and the co‐mutagenic heterocyclic amine Norharman (9H‐pyrido[3,4‐b]‐indole) were identified. The HPLC fractions were tested for mutagenic activity and, apart from the mutagenic fractions corresponding to MeIQx and PhIP, several mutagenic fractions were detected that did not correspond to known heterocyclic amines.     

Comparative oxidation and net emissions of methane and selected non-methane organic compounds in landfill cover soils

The surface emissions of methane (CH4) and non-methane organic compounds (NMOCs) were determined at two different areas at a French landfill: a permanently covered and fully vegetated area (40 cm coarse sand + 80 cm of loam) and a temporarily covered area (40 cm of coarse sand). The 37 NMOCs quantified in the landfill gas samples included alkanes (C1-C10), alkenes (C1-C4), halogenated hydrocarbons (including (H)CFCs), and aromatic hydrocarbons. Both positive and negative CH4 fluxes ranging from -0.01 to 0.008 g m(-2) d(-1) were measured from the permanently covered cell. However, high spatial variation was observed, and a hot spot with a high flux (10 g m(-2) d(-1)) was identified. A higher CH4 emission occurred from the temporarily covered cell (CH4 flux of 49.9 g m(-2) d(-1)) as compared to the permanently covered cell. The NMOC fluxes from the permanently covered zone were all very small with both positive and negative fluxes in the order of 10(-7) to 10(-5) g m(-2) d(-1). Higher and mainly positive NMOC fluxes in the order of 10(-5) to 10(-4) g m(-2) d(-1) were obtained from the temporarily covered zone. The lower emission from the permanently covered and fully vegetated cell was attributable to the thicker soil layer, which functions as microbial habitat for methanotrophic bacteria. The NMOC oxidation capacity was investigated in soil microcosms incubated with CH4. Maximal oxidation rates for the halogenated aliphatic compounds varied between 0.06 and 8.56 microg (g of soil)(-1) d(-1). Fully substituted hydrocarbons (tetrachloromethane, perchloroethylene, CFC-11, CFC-12, and CFC-113) were not degraded in the presence of CH4 and O2. Benzene and toluene were rapidly degraded, giving very high maximal oxidation rates (28 and 39 microg (g of soil)(-1) d(-1)). On the basis of the emission measurements and the batch experiments conducted, a general pattern was observed between emissions and biodegradability of various NMOCs. The emissions mainly consisted of compounds that were not degradable or slowly degradable, while an uptake of easily degradable compounds was registered. As an example, perchloroethylene, trichloromethane, CFC-11, and CFC-12 were emitted, while atmospheric consumption of aromatic hydrocarbons and lower chlorinated hydrocarbons such as vinyl chloride, dichloromethane, and chloromethane was observed. This study demonstrates that landfill soil covers show a significant potential for CH4 oxidation and co-oxidation of NMOCs. Under certain conditions, landfills may even function as sinks for CH4 and selected NMOCs, like aromatic hydrocarbons and lower chlorinated compounds.     

Measurement of emissions from air pollution sources. 4. C1-C27 organic compounds from cooking with seed oils

The emission rates of gas-phase, semivolatile, and particle-phase organic compounds ranging in carbon number from C1 to C27 were measured from institutional-scale food cooking operations that employ seed oils. Two cooking methods and three types of seed oils were examined: vegetables stir-fried in soybean oil, vegetables stir-fried in canola oil, and potatoes deep fried in hydrogenated soybean oil. The emission rates of 99 organic compounds were quantified, and these include n-alkanes, branched alkanes, alkenes, n-alkanoic acids, n-alkenoic acids, carbonyls, aromatics, polycyclic aromatic hydrocarbons (PAH), and lactones. Carbonyls and fatty acids (n-alkanoic and n-alkenoic acids) make up a significant portion of the organic compounds emitted from all three seed oil cooking procedures. The compositional differences in the organic compound emissions between the different cooking operations are consistent with the differences in the organic composition of the various cooking oils used. The distribution of the n-alkanoic acids between the gas and particle phases was found to be in good agreement with gas/particle partitioning theory. The relative importance of emissions from commercial deep frying operations to the total emissions of C16 and C18 n-alkanoic acids in the Los Angeles urban area was estimated using the available information and is estimated to account for approximately 7% of the total primary emissions of these acids. Additional emissions of these n-alkanoic acids from stir-frying and grill frying operations are expected. Estimates also indicate that seed oil cooking may make up a significant fraction of the emissions of lighter n-alkanoic acids such as nonanoic acid.