Bornimer Agrartechnische Berichte
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96
The application of cold atmospheric pressure plasma (CAPP) was suggested as an innovative nonthermal technology for inactivating undesirable microorganisms on the surface of heat-sensitive food products. Moreover, CAPP may offer a promising approach for the tailored modification of product properties along value-added chains of plant and animal related products. Therefore, this thesis puts emphasis on providing evidence for the possible utilization of plasma-induced surface and ingredient interactions as a tool for the selective modification of secondary metabolite profiles in plants and techno-functionality of flours and proteins from peas. Further, the knowledge gained on plasma assisted modification of plant-based materials was transferred to animal-based materials from edible insects taking additionally into account microbial decontamination as another key issue in insect processing. The thesis imparts the detailed characterization of selected raw materials, the identification of proper CAPP setups and corresponding product-specific process parameters by performing process accompanying monitoring of plasma characteristics required to achieve desired modifications. Detailed investigations of the plasma-induced effects were conducted following a top-down approach by using suitable analytical methods providing insights into possible underlying mechanisms from macroscopic to molecular level. The macroscopic level of analysis included quality (color/texture), compositional (protein/fat/dry matter contents) and microbial (surface/overall total viable counts) methods, followed by determining techno-functional (water/fat binding/emulsification) and protein (solubility/water/fat binding/emulsification) properties, as well as protein structure (surface hydrophobicity/fluorescence properties/CD spectroscopy) on the microscopic and structural level, down to analysis of the protein composition (SDS-PAGE/tryptophan content/amino acid composition) on the molecular level. The results provide a scientific basis regarding the targeted use of the CAPP technology for functionalization and modification of high-protein food components and could therefore contribute to the bio-economic and resource efficient production of dry high-value protein products, as protein functionality plays a key role in improving existing products, developing new products, and utilizing alternative protein sources as new ingredients. Consequently, feedback on the applicability of CAPP for tested raw materials was derived by evaluating the effectiveness of the treatment regarding the desired process goal, and by identifying product-specific characteristics allowing transferability of the CAPP process with the long-term goal of combining plasma treatments with existing unit operations in established product-specific process lines. Initial approaches regarding the CAPP treatment of complex food matrices by using a plasma device, which is promising for the application in industrial scale, aimed at the development of innovative process combinations with focus on “plasma-drying” as a prospective future unit operation, which may contribute to reducing the expected costs of CAPP treatments. The potential of CAPP processing to become a routine tool for the food industry in the coming years is also reflected throughout all parts of this work, and thus, it provides a substantial contribution to promoting the successful admission of the CAPP technology in the food sector.
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77
Microbial contamination of fruits and vegetables can lead to high economic losses as well as to foodborne diseases. Washing procedures, which are commonly applied, only reduce the microbial load by 0.5 to 2 log units. Conventional thermal inactivation processes cannot be applied to fresh fruit and vegetables because these products are physiologically active food systems and temperatures above 45 °C can result in unwanted deterioration. Since heat sensitivity of fruits and vegetables limits the application of thermal inactivation processes, new emerging inactivation technologies have to be established to fulfil the requirements of food safety without affecting the produce quality. On one hand an early detection of produce contamination is essential to enable a contamination-related process design and on the other hand the efficiency of inactivation treatments has to be ensured and monitored. Monitoring of inactivation effects is commonly performed using traditional cultivation methods which have the disadvantage of the length of time needed to obtain results. In this study, the potential of flow cytometry in short-time monitoring of inactivation effects (thermal treatment, treatment with peracetic acid, ozone, and atmospheric pressure plasma) was investigated. For this purpose morphological and physiological properties of bacteria (size, granularity, membrane integrity (thiazole orange & propidium iodide), esterase activity (carboxyfluorescein diacetate), pump activity (carboxyfluorescein efflux), and membrane potential (3,3'-diethyloxacarbocyanine iodide)) were determined by flow cytometry. In the initial step appropriate staining procedures had to be developed. Especially, Gram-negative bacteria restrict the dye uptake due to their cell membrane constitution. This limits the determination of esterase activity of Gram-negative bacteria. In this study, an adequate dye concentration (0.83 mmol l-1 carboxyfluorescein diacetate) and incubation time (45 min) at 37 °C were defined which enables a reliable determination of esterase activity of Gram-negative bacteria. This developed staining procedure was successfully applied to monitor inactivation treatments. It was shown that the test bacteria (E. coli, L. innocua, P. carotovorum) lose their culturability due to the applied inactivation treatments but physiological activities were still detectable using flow cytometry. The remaining physiological activities may still result in product spoilage and also may cause human diseases. For example, E. coli cells still showed esterase activity after 10 min of thermal treatment at 70 °C and also after 2 min treatment with 0.25 % PAA at 10 °C. Esterase activity of E. coli cells was also detected after 2 min plasma treatment with an operating power of 40 W. The degree of bacterial damage due to the inactivation processes is highly dependent on treatment parameters as well as on treated bacteria. This study clearly indicates the potential of flow cytometry to monitor the efficacy of inactivation processes within a short time. Additionally, important information regarding the inactivation mechanisms can be obtained by flow cytometric measurements and this enables the definition of critical process.
72
Der Erfolg einer präzisen Düngung der Grundnährstoffe (P, K, Mg, Kalk) hängt wesentlich von dem Aufwand ab, der für die Erzeugung genauer Ausbringekarten erforderlich ist. In diesem Projekt wurden Daten, die in einem großen landwirtschaftlichen Betrieb (3000 ha) verfügbar waren bzw. durch zusätzliche Untersuchungen gewonnen wurden, genutzt, um den Einfluss der Probenahmedichte und verschiedener Interpolationsmethoden auf die Genauigkeit der Ausbringekarten zu untersuchen. Eine Simulation der on-the-go Erfassung des pH-Wertes sowie der Grundnährstoffe zeigte, dass diese Technik in der Lage ist, die Mängel, die mit der traditionellen Probenahme verbunden sind, zu überwinden. Außerdem wurden die Wirtschaftlichkeit sowie die potentielle Über- und Unterdüngung verschiedener Varianten der teilflächenspezifischen Düngung kalkuliert. Das beste Ergebnis wurde für die kleinste untersuchte Teilfläche von 1 ha ermittelt.
98
Abstract
Broccoli (Brassica oleracea var. italica) is a highly perishable crop. The aim of the work presented here is to find ways to predict storability of broccoli shortly after harvest. Several methods are examined regarding their suitability for predicting broccoli storability.
The non-destructive, optical measuring devices used in this work represent some of the common methods used for scientific quality assessment (color determination, chlorophyll fluorescence analysis). In addition, spectral data from diffuse reflection measurements, from both spot measurements and hyperspectral images, was evaluated. The generative development of broccoli curds was studied using diameters both of single buds and of whole curds, and was related to subsequent storability.
The concentrations of the chlorophylls a and b, green chlorophyll catabolites chlorophyllide a (Chlide), pheophytin a (Pheoin), pheophorbide a (Pheoide) and carotenoids ß-carotene (ß-Car), lutein (Lut), neoxanthin (Nx) and violaxanthin (Vx) were determined in floral buds of broccoli through the use of high pressure liquid chromatography (HPLC). The goal was to determine if chlorophyll catabolites may function as indicators of broccoli storability and, furthermore, to relate the concentrations of photosynthetic pigments to the color change of broccoli during storage.
In order to investigate effects from the field on the subsequent storability of broccoli, cultivation methods were altered. Plants were partly covered with covers of different materials, which affected the quantity and quality of incident global radiation. The application of fertilizers was specifically varied in one broccoli batch. Additionally, the influence of climatic events on the shelf life of broccoli was analyzed by querying an established database.
The non-destructive indexes that proved to be most sensitive to changes during storage were the levels of photosynthetic efficiency (Fv/Fm, ΦPSII), the CIELAB color space coordinate on a blue to yellow scale (b*) and the inflection point of reflection spectra in the transition region from dark red to infrared electromagnetic wavelength range (REIP). However, based on parameter sensitivity, the prediction of value levels after four days of storage at 16 °C and high relative humidity (RH) (~ 95 %) was unfeasible. Quality indexes that changed on the same storage day did not necessarily end up at the same value level. Additionally, values of both Fv/Fm and ΦPSII did not adequately reflect the quality status of broccoli when different harvest batches were compared.
In hyperspectral images, early quality changes were effectively rated based on Euclidean distances within broccoli curds and were displayed using reflection intensities at three wavelengths within the visible electromagnetic spectrum as RGB channels. The observed variation within broccoli curds was related to differences in the degree of senescence of single floral buds. However, the diameters of floral buds did not correspond to a rating of storability. In contrast, curd diameters within individual harvest batches were related to subsequent yellowing.
The yellowing of broccoli was based on the decomposition of chlorophyll, which unmasked the carotenoids present. No accumulation of chlorophyll catabolites was found during storage. A trend towards rapidly increasing chlorophyll a/b ratios was observed in a broccoli batch with particularly high storability.
Different N-fertilization of broccoli curds closely corresponded both with values of initial lightness L* of the CIELAB color space (R² = 0.70) and normalized difference vegetation index NDVI (R² = 0.73). Yet, N-fertilization had no impact on further storability. A negative impact on storability was observed when the spectrum of incident radiation on the field was temporarily reduced by using plastic covers with limited transmittance (λ = 400-500 nm). In a similar way, an increased number of hours with high solar radiation intensity (> 600 W m-2) during cultivation had a negative impact on broccoli storability (R² = 0.47). The impact of high irradiation partly corresponded with temperatures higher than 25 °C (R² = 0.29). A strong predetermination of curd storability was observed based on the water availability for broccoli plants in the last two weeks before harvest (R² = 0.71).
A successful prediction of broccoli storability is therefore most likely to be conducted by looking at effects during cultivation. For early non-destructive evaluation of the current quality status of broccoli, both the parameter b* and the spectral index REIP were highly suitable. Therefore, through the help of monitoring systems throughout cultivation (database of climate and cultivation incidents) in combination with reflection-based, hand-held devices during storage, the prediction and rating of broccoli storability can certainly be improved.
67
Die Produktion von Biogas aus landwirtschaftlichen Primärprodukten oder Reststoffen stellt einen wesentlichen Beitrag zur Reduktion des Co2-Ausstoßes sowie zur Entwicklung einer nachhaltigen Landbewirtschaftung dar. Im Rahmen dieses Projektes soll daher die Artenzusammensetzung der methanogenen Mikroflora in ausgewählten Praxis-Biogasanlagen anhand ihrer 16S rDNA analysisert werden.
87
In dieser Studie wurde die Entwicklung methanogener Biofilme in meso- und thermophilen ein- und zweistufigen Biogasreaktoren bei der Vergärung von Maissilage untersucht. Ziel war neben der kultivierungsunabhängigen Charakterisierung von Struktur und Dynamik der mikrobiellen Lebensgemeinschaften und ihrer Stoffwechseleigenschaften insbesondere auch die Entwicklung von Strategien zur Ansiedlung solcher Biofilme.
84
Der anaerobe Abbau von Biomasse zu Biogas erfolgt durch eine komplexe mikrobielle Lebensgemeinschaft aus fermentativen Bakterien und methanogenen Archaeen. Der Großteil der daran beteiligten Arten ist bislang jedoch noch unbekannt, ebenso ihr jeweiliger Einfluss auf die Reaktorleistung. In den letzten Jahren konnten in der mikrobiologischen Analytik jedoch gewaltige technologische Durchbrüche erzielt werden, welche die Analyse von komplexen Lebensgemeinschaften auch für höheren Probenzahlen ermöglichen. Im Rahmen des im Folgenden dargestellten Forschungsvorhabens sollten diese neuartigen Techniken gezielt eingesetzt werden, um die Auswirkungen verschiedener Betriebsweisen von Biogasanlagen auf die Prozessmikrobiologie in der Praxis zu untersuchen. Weiterhin sollten Zusammenhänge zwischen der Prozessmikrobiologie sowie der Reaktorleistung ermittelt werden. Übergreifendes Ziel war die Ermittlung besonders prozessrelevanter Arten oder Organismengruppen.
Das Verbundprojekt umfasste die Teilvorhaben (1) Mikrobiologisches Monitoring (Leibniz-Institut für Agrartechnik Potsdam-Bornim e.V. Abt. Bioverfahrenstechnik), (2) Taxonomisches Profiling (Universität Bielefeld, Centrum für Biotechnologie), (3) Metaproteom-Analytik (Otto-von-Guericke-Universität Magdeburg, Bioprocess Engineering) und (4) Biostatistische Prozessdatenauswertung (Universität Hohenheim, Institut für Lebensmittelwissenschaft und Biotechnologie).
Die Schlussberichte aller vier Teilvorhaben sind in diesem Band der Bornimer Agrartechnischen Berichte in ungekürzter Form enthalten.