Kombination analytischer Strategien und multivariater Datenanalysen zur Beurteilung von Milch- und Molkereierzeugnissen

Milch und daraus hergestellte Erzeugnisse spielen eine zentrale Rolle in der Ernährung des Menschen. Infolge einer Optimierung der molkereitechnologischen Produktionsprozesse ist eine gesteigerte Qualität sowie eine verlängerte Haltbarkeit dieser Produkte erzielt worden, wobei dies das Fundament des bis heute beständig wachsenden, vielfältigen Produktspektrums an Milch und der daraus hergestellten Erzeugnisse bildet. Die Globalisierung der Märkte sowie die in den letzten Jahren stark ansteigenden Rohstoff- und Energiekosten haben dabei zu einer erheblichen Verschärfung des Konkurrenzdrucks auch zwischen Lebensmittelproduzenten geführt. Um kostensenkend zu produzieren werden zahlreiche Massnahmen ergriffen, welche vorwiegend auf dem Ersatz von Fett- und Proteinanteilen, der Mischung von Milchsorten unterschiedlicher Spezies, dem Zusatz billiger Füllstoffe auf Milchbasis zur Ausbeuteerhöhung sowie einer falschen Deklaration von Produkten geschützter geografischer Herkunft beruhen (De la Fuente et al. 2005). Der Einfluss des globalisierten Milchmarktes macht dabei auch vor Schmelzkäseerzeugnissen und Schmelzkäsen keinen Halt. Produzenten dieser Produkte wurden infolgedessen mehr und mehr dazu verleitet, die in diesen Erzeugnissen wertgebende Rohware Käse anteilig durch günstigere Füllstoffe auf Milchbasis zu ersetzen. Neben ernährungs-physiologischen und technologischen Aspekten spielen in diesem Zusammenhang vor allem ökonomische Interessen eine entscheidende Rolle. Dem Endprodukt Schmelzkäse ist dieser Qualitätsverlust, welcher durch den Austausch von Käse-Protein durch Nicht-Käse-Protein resultiert, dabei auf den ersten Blick nicht unbedingt anzusehen. Bislang existieren auch keine einfachen analytischen Marker zur qualitativen Unterscheidung, geschweige denn quantitativen Bestimmung, dieser Rohwaren in Schmelzkäsen. Die analytischen Herausforderungen welche sich aus der vorliegenden Problemstellung ergeben, sind dabei sehr vielfältig. Nicht nur, dass alle wertgebenden Zutaten von Schmelzkäsen einem gemeinsamen Ausgangsrohstoff Milch entstammen, welcher zudem noch natürlichen Schwankungen in der Zusammensetzung unterliegt, sondern auch die in der wertgebenden Rohware Käse sorten-, reifungs- und lagerungsabhängig ablaufenden Prozesse führen zu starken Schwankungen der Zusammensetzung dieser Produkte. Wie genau die große Gruppe der Käsesorten basierend darauf chemisch charakterisiert werden kann, erscheint aus analytischer Sicht äußerst anspruchsvoll. Darüber hinaus kann eine Beeinflussung der chemischen Zusammensetzung der fertigen Schmelzkäseprodukte auch durch die während des Herstellungsprozesses herrschenden Bedingungen hervorgerufen werden. Das Ausmaß einer solchen Veränderung in handelsüblichen Schmelzkäsen ist jedoch nur schwer abschätzbar und bislang wenig erforscht worden. Einer Irreführung und Täuschung der Verbraucher sowie einer Verzerrung des Wettbewerbs zwischen den einzelnen Schmelzkäseproduzenten ist somit Tür und Tor geöffnet. Dies wird letztlich auch durch den Gesetzgeber nicht unterbunden, da dieser die Deklaration der eingesetzten Menge und Sorte an Käse sowie der Menge an zugesetztem Proteinzusatz zur Herstellung von Schmelzkäsen und Schmelzkäseerzeugnissen nicht zwingend fordert. Das Ziel der vorliegenden wissenschaftlichen Arbeit besteht somit darin, ein Analysenportfolio verschiedenster, analytischer Parameter zur Bestimmung der kompositionellen Zusammensetzung von Schmelzkäseerzeugnissen zu erarbeiten, mit deren Hilfe eine Unterscheidung der am Markt erhältlichen Produktqualitäten möglich ist. Weiterhin soll anhand der Kombination dieser analytischen Messgrößen sowie deren mathematischer Auswertung mittels multivariater Datenanalyseverfahren eine Bewertung und Priorisierung hinsichtlich deren Aussagekraft vorgenommen werden. Neben der Analyse handelsüblicher Schmelzkäse werden im Rahmen dieser Aufgabenstellung auch verstärkt die Schmelzrohwaren und Proteinzusätze sowie Modell-Schmelzkäse hinsichtlich deren chemischer Zusammensetzung charakterisiert. Das Hauptaugenmerk liegt dabei auf der Unterscheidung der Rohwaren Käse und den zum Schmelzkäseprodukt weiterhin zugesetzten Proteinpulvern auf Milchbasis. Zu diesen zählen neben den Trockenmilch- und Trockenmolkeerzeugnissen (Magermilchpulver, Milchpulverkonzentrat, Molkepulver) auch Milcheiweiß-erzeugnisse (Säure- und Labcasein). Zusammen stellen diese mengenmäßig den größten Anteil in Schmelzkäsen dar und bestimmen somit maßgeblich deren technologische und sensorische Eigenschaften und damit verbunden die Qualität und den Preis der fertigen Schmelzkäseprodukte

Gridded maps of geological methane emissions and their isotopic signature

Methane (CH4) is a powerful greenhouse gas, whose natural and anthropogenic emissions contribute ∼20&thinsp;% to global radiative forcing. Its atmospheric budget (sources and sinks), however, has large uncertainties. Inverse modelling, using atmospheric CH4 trends, spatial gradients and isotopic source signatures, has recently improved the major source estimates and their spatial–temporal variation. Nevertheless, isotopic data lack CH4 source representativeness for many sources, and their isotopic signatures are affected by incomplete knowledge of the spatial distribution of some sources, especially those related to fossil (radiocarbon-free) and microbial gas. This gap is particularly wide for geological CH4 (geo-CH4) seepage, i.e. the natural degassing of hydrocarbons from the Earth's crust. While geological seepage is widely considered a major source of atmospheric CH4, it has been largely neglected in 3-D inverse CH4 budget studies given the lack of detailed a priori gridded emission maps. Here, we report for the first time global gridded maps of geological CH4 sources, including emission and isotopic data. The 1∘×1∘ maps include the four main categories of natural geo-CH4 emission: (a) onshore hydrocarbon macro-seeps, including mud volcanoes, (b) submarine (offshore) seeps, (c) diffuse microseepage and (d) geothermal manifestations. An inventory of point sources and area sources was developed for each category, defining areal distribution (activity), CH4 fluxes (emission factors) and its stable C isotope composition (δ13C-CH4). These parameters were determined considering geological factors that control methane origin and seepage (e.g. petroleum fields, sedimentary basins, high heat flow regions, faults, seismicity). The global geo-source map reveals that the regions with the highest CH4 emissions are all located in the Northern Hemisphere, in North America, in the Caspian region, in Europe and in the East Siberian Arctic Shelf. The globally gridded CH4 emission estimate (37&thinsp;Tg&thinsp;yr−1 exclusively based on data and modelling specifically targeted for gridding, and 43–50&thinsp;Tg&thinsp;yr−1 when extrapolated to also account for onshore and submarine seeps with no location specific measurements available) is compatible with published ranges derived using top-down and bottom-up procedures. Improved activity and emission factor data allowed previously published mud volcanoes and microseepage emission estimates to be refined. The emission-weighted global mean δ13C-CH4 source signature of all geo-CH4 source categories is about −49&thinsp;‰. This value is significantly lower than those attributed so far in inverse studies to fossil fuel sources (−44&thinsp;‰) and geological seepage (−38&thinsp;‰). It is expected that using this updated, more 13C-depleted, isotopic signature in atmospheric modelling will increase the top-down estimate of the geological CH4 source. The geo-CH4 emission grid maps can now be used to improve atmospheric CH4 modelling, thereby improving the accuracy of the fossil fuel and microbial components. Grid csv (comma-separated values) files are available at https://doi.org/10.25925/4j3f-he27.</p

Conflicting estimates of natural geologic methane emissions

Global bottom-up and top-down estimates of natural, geologic methane (CH4) emissions (average approximately 45 Tg yr–1) have recently been questioned by near-zero (approximately 1.6 Tg yr–1) estimates based on measurements of 14CH4 trapped in ice cores, which imply that current fossil fuel industries' CH4 emissions are underestimated by 25%–40%. As we show here, such a global near-zero geologic CH4 emission estimate is incompatible with multiple independent, bottom-up emission estimates from individual natural geologic seepage areas, each of which is of the order of 0.1–3 Tg yr–1. Further research is urgently needed to resolve the conundrum before rejecting either method or associated emission estimates in global CH4 accounting

Upward revision of global fossil fuel methane emissions based on isotope database

Methane has the second-largest global radiative forcing impact of anthropogenic greenhouse gases after carbon dioxide, but our understanding of the global atmospheric methane budget is incomplete. The global fossil fuel industry (production and usage of natural gas, oil and coal) is thought to contribute 15 to 22 per cent of methane emissions to the total atmospheric methane budget. However, questions remain regarding methane emission trends as a result of fossil fuel industrial activity and the contribution to total methane emissions of sources from the fossil fuel industry and from natural geological seepage, which are often co-located. Here we re-evaluate the global methane budget and the contribution of the fossil fuel industry to methane emissions based on long-term global methane and methane carbon isotope records. We compile the largest isotopic methane source signature database so far, including fossil fuel, microbial and biomass-burning methane emission sources. We find that total fossil fuel methane emissions (fossil fuel industry plus natural geological seepage) are not increasing over time, but are 60 to 110 per cent greater than current estimates owing to large revisions in isotope source signatures. We show that this is consistent with the observed global latitudinal methane gradient. After accounting for natural geological methane seepage, we find that methane emissions from natural gas, oil and coal production and their usage are 20 to 60 per cent greater than inventories. Our findings imply a greater potential for the fossil fuel industry to mitigate anthropogenic climate forcing, but we also find that methane emissions from natural gas as a fraction of production have declined from approximately 8 per cent to approximately 2 per cent over the past three decades.Published88-916A. Geochimica per l'ambienteJCR Journa

Intercomparison of detection and quantification methods for methane emissions from the natural gas distribution network in Hamburg, Germany

In August and September 2020, three different measurement methods for quantifying methane (CH4) emission from leaks in urban gas distribution networks were applied and compared in Hamburg, Germany: the “mobile”, “tracer release” and “suction” methods. The mobile and tracer release methods determine emission rates to the atmosphere from measurements of CH4 mole fractions in the ambient air, and the tracer release method also includes measurement of a gaseous tracer. The suction method determines emission rates by pumping air out of the ground using soil probes that are placed above the suspected leak location. The quantitative intercomparison of the emission rates from the three methods at a small number of locations is challenging because of limitations of the different methods at different types of leak locations. The mobile method was designed to rapidly quantify the average or total emission rate of many gas leaks in a city, but it yields a large emission rate uncertainty for individual leak locations. Emission rates determined for individual leak locations with the tracer release technique are more precise because the simultaneous measurement of the tracer released at a known rate at the emission source eliminates many of the uncertainties encountered with the mobile method. Nevertheless, care must be taken to properly collocate the tracer release and the leak emission points to avoid biases in emission rate estimates. The suction method could not be completed or applied at locations with widespread subsurface CH4 accumulation, or due to safety measures, and this sampling bias may be associated with a bias towards leak locations with low emission rates. The leak locations where the suction method could not be applied were the biggest emitters as confirmed by the emission rate quantifications using mobile and tracer methods and an engineering method based on leak’s diameter, pipeline overpressure and depth at which the pipeline is buried. The corresponding sampling bias for the suction technique led to a low bias in derived emission rates in this study. It is important that future studies using the suction method account for any leaks not quantifiable with this method in order to avoid biases, especially when used to inform emission inventories

Quantification of methane emissions in Hamburg using a network of FTIR spectrometers and an inverse modeling approach

Methane (CH4) is a potent greenhouse gas, and anthropogenic CH4 emissions contribute significantly to global warming. In this study, the CH4 emissions of the second most populated city in Germany, Hamburg, were quantified with measurements from four solar-viewing Fourier transform infrared (FTIR) spectrometers, mobile in situ measurements, and an inversion framework. For source type attribution, an isotope ratio mass spectrometer was deployed in the city. The urban district hosts an extensive industrial and port area in the south as well as a large conglomerate of residential areas north of the Elbe River. For emission modeling, the TNO GHGco (Netherlands Organisation for Applied Scientific Research greenhouse gas and co-emitted species emission database) inventory was used as a prior for the inversion. In order to improve the inventory, two approaches were followed: (1) the addition of a large natural CH4 source, the Elbe River, which was previously not included in the inventory, and (2) mobile measurements were carried out to update the spatial distribution of emissions in the TNO GHGco gridded inventory and derive two updated versions of the inventory. The addition of the river emissions improved model performance, whereas the correction of the spatial distribution with mobile measurements did not have a significant effect on the total emission estimates for the campaign period. A comparison of the updated inventories with emission estimates from a Gaussian plume model (GPM) showed that the updated versions of the inventory match the GPM emissions estimates well in several cases, revealing the potential of mobile measurements to update the spatial distribution of emission inventories. The mobile measurement survey also revealed a large and, at the time of the study, unknown point source of thermogenic origin with a magnitude of 7.9 ± 5.3 kg h-1 located in a refinery. The isotopic measurements show strong indications that there is a large biogenic CH4 source in Hamburg that produced repeated enhancements of over 1 ppm which correlated with the rising tide of the river estuary. The CH4 emissions (anthropogenic and natural) of the city of Hamburg were quantified as 1600 ± 920 kg h-1, 900 ± 510 kg h-1 of which is of anthropogenic origin. This study reveals that mobile street-level measurements may miss the majority of total methane emissions, potentially due to sources located within buildings, including stoves and boilers operating on natural gas. Similarly, the CH4 enhancements recorded during the mobile survey from large-area sources, such as the Alster lakes, were too small to generate GPM emission estimates with confidence, but they could nevertheless influence the emission estimates based on total column measurements

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

The 2015 Paris Agreement of the United Nations Framework Convention on Climate Change aims to keep global average temperature increases well below 2 °C of preindustrial levels in the Year 2100. Vital to its success is achieving a decrease in the abundance of atmospheric methane (CH4), the second most important anthropogenic greenhouse gas. If this reduction is to be achieved, individual nations must make and meet reduction goals in their nationally determined contributions, with regular and independently verifiable global stock taking. Targets for the Paris Agreement have been set, and now the capability must follow to determine whether CH4 reductions are actually occurring. At present, however, there are significant limitations in the ability of scientists to quantify CH4 emissions accurately at global and national scales and to diagnose what mechanisms have altered trends in atmospheric mole fractions in the past decades. For example, in 2007, mole fractions suddenly started rising globally after a decade of almost no growth. More than a decade later, scientists are still debating the mechanisms behind this increase. This study reviews the main approaches and limitations in our current capability to diagnose the drivers of changes in atmospheric CH4 and, crucially, proposes ways to improve this capability in the coming decade. Recommendations include the following: (i) improvements to process‐based models of the main sectors of CH4 emissions—proposed developments call for the expansion of tropical wetland flux measurements, bridging remote sensing products for improved measurement of wetland area and dynamics, expanding measurements of fossil fuel emissions at the facility and regional levels, expanding country‐ specific data on the composition of waste sent to landfill and the types of wastewater treatment systems implemented, characterizing and representing temporal profiles of crop growing seasons, implementing parameters related to ruminant emissions such as animal feed, and improving the detection of small fires associated with agriculture and deforestation; (ii) improvements to measurements of CH4 mole fraction and its isotopic variations—developments include greater vertical profiling at background sites, expanding networks of dense urban measurements with a greater focus on relatively poor countries, improving the precision of isotopic ratio measurements of 13CH4, CH3D, 14CH4, and clumped isotopes, creating isotopic reference materials for international‐scale development, and expanding spatial and temporal characterization of isotopic source signatures; and (iii) improvements to inverse modeling systems to derive emissions from atmospheric measurements—advances are proposed in the areas of hydroxyl radical quantification, in systematic uncertainty quantification through validation of chemical transport models, in the use of source tracers for estimating sector‐level emissions, and in the development of time and spaceresolved national inventories. These and other recommendations are proposed for the major areas of CH4 science with the aim of improving capability in the coming decade to quantify atmospheric CH4 budgets on the scales necessary for the success of climate policies. Plain Language Summary Methane is the second largest contributor to climate warming from human activities since preindustrial times. Reducing human‐made emissions by half is a major component of the 2015 Paris Agreement target to keep global temperature increases well below 2 °C. In parallel to the methane emission reductions pledged by individual nations, new capabilities are needed to determine independently whether these reductions are actually occurring and whether methane concentrations in the atmosphere are changing for reasons that are clearly understood. At present significant challenges limit the ability of scientists to identify the mechanisms causing changes in atmospheric methane. This study reviews current and emerging tools in methane science and proposes major advances needed in the coming decade to achieve this crucial capability. We recommend further developing the models that simulate the processes behind methane emissions, improving atmospheric measurements of methane and its major carbon and hydrogen isotopes, and advancing abilities to infer the rates of methane being emitted and removed from the atmosphere from these measurements. The improvements described here will play a major role in assessing emissions commitments as more cities, states, and countries report methane emission inventories and commit to specific emission reduction targets. </div

Intercomparison of detection and quantification methods for methane emissions from the natural gas distribution network in Hamburg, Germany

In August and September 2020, three different measurement methods for quantifying methane (CH4) emissions from leaks in urban gas distribution networks were applied and compared in Hamburg, Germany: the “mobile”, “tracer release”, and “suction” methods. The mobile and tracer release methods determine emission rates to the atmosphere from measurements of CH4 mole fractions in the ambient air, and the tracer release method also includes measurement of a gaseous tracer. The suction method determines emission rates by pumping air out of the ground using soil probes that are placed above the suspected leak location. The quantitative intercomparison of the emission rates from the three methods at a small number of locations is challenging because of limitations of the different methods at different types of leak locations. The mobile method was designed to rapidly quantify the average or total emission rate of many gas leaks in a city, but it yields a large emission rate uncertainty for individual leak locations. Emission rates determined for individual leak locations with the tracer release technique are more precise because the simultaneous measurement of the tracer released at a known rate at the emission source eliminates many of the uncertainties encountered with the mobile method. Nevertheless, care must be taken to properly collocate the tracer release and the leak emission points to avoid biases in emission rate estimates. The suction method could not be completed or applied at locations with widespread subsurface CH4 accumulation or due to safety measures. While the number of gas leak locations in this study is small, we observe a correlation between leak emission rate and subsurface accumulation. Wide accumulation places leaks into a safety category that requires immediate repair so that the suction method cannot be applied to these larger leaks in routine operation. This introduces a sampling bias for the suction method in this study towards the low-emission leaks, which do not require immediate repair measures. Given that this study is based on random sampling, such a sampling bias may also exist for the suction method outside of this study. While an investigation of the causal relationship between safety category and leak size is beyond the scope of this study, on average higher emission rates were observed from all three measurement-based quantification methods for leaks with higher safety priority compared to the leaks with lower safety concern. The leak locations where the suction method could not be applied were the biggest emitters, as confirmed by the emission rate quantifications using mobile and tracer methods and an engineering method based on the leak's diameter, pipeline overpressure, and depth at which the pipeline is buried. The corresponding sampling bias for the suction technique led to a low bias in derived emission rates in this study. It is important that future studies using the suction method account for any leaks not quantifiable with this method in order to avoid biases, especially when used to inform emission inventories.</p

U.S. CH4 emissions from oil and gas production: Have recent large increases been detected?

Recent studies have proposed significant increases in CH4 emissions possibly from oil and gas (O&G) production, especially for the U.S. where O&G production has reached historically high levels over the past decade. In this study, we show that an ensemble of time-dependent atmospheric inversions constrained by calibrated atmospheric observations of surface CH4 mole fraction, with some including space-based retrievals of column average CH4 mole fractions, suggests that North American CH4 emissions have been flat over years spanning 2000 through 2012. Estimates of emission trends using zonal gradients of column average CH4 calculated relative to an upstream background are not easy to make due to atmospheric variability, relative insensitivity of column average CH4 to surface emissions at regional scales, and fast zonal synoptic transport. In addition, any trends in continental enhancements of column average CH4 are sensitive to how the upstream background is chosen, and model simulations imply that short-term (4 years or less) trends in column average CH4 horizontal gradients of up to 1.5 ppb/yr can occur just from interannual transport variability acting on a strong latitudinal CH4 gradient. Finally, trends in spatial gradients calculated from space-based column average CH4 can be significantly biased (>2-3 ppb/yr) due to the nonuniform and seasonally varying temporal coverage of satellite retrievals.CC-BY 4.