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Cows milk and derived products are important components in the Western diet. The composition of raw milk and the size distribution of suspended fat globules and casein micelles largely determine the nutritional, physicochemical and functional characteristics of the milk. Moreover, as these properties have a considerable impact on the general perception of the milk and the properties of derived products, they are important quality parameters for the dairy industry and the consumer. Additionally, the composition of the extracted raw milk and the size distribution of the suspended particles comprise valuable information on the metabolic, nutritional and general health status of the cow as there is a strong interaction between the cows blood circulation and the milk production. Therefore, techniques to measure the milk quality can help to improve cow health monitoring and enhance the efficiency and animal welfare on a dairy farm.^ Further on, the use of similar sensing-technology in a dairy plant could enable online monitoring of production processes to further reduce the variability and promote the development of new food products with improved properties.Optical measurement techniques are frequently used to monitor processes in industry and agriculture. Among them, spectroscopy studies the interaction between electromagnetic radiation and the product of interest. As the molecules of the product absorb this electromagnetic radiation at specific wavelengths, spectral analysis gives insight in the composition of the measured product. The molecular absorption of visible (Vis) and near-infrared (NIR) radiation is sufficient to be used for the analysis of the main sample components, while the penetration depth of Vis/NIR radiation is still adequate to reduce the need for extensive sample preparation. Nowadays, spectral detectors for this wavelength range are fast, robust and cost-efficient.^ Hence, it is widely used for non-destructive and online quality control in industry, food processing and agriculture. Several researchers have shown the potential of Vis/NIR spectroscopic analysis of raw milk in the lab. However, recent studies indicate that this technology might not be robust against changing scattering properties that are typical for on farm raw milk samples. Scattering is a process where the radiation is forced to deviate from a straight trajectory due to local non-uniformities. In milk, the fat globules and casein micelles are the main cause of Vis/NIR light scattering. This increases the travelling path of the Vis/NIR radiation to an unknown extent and seriously complicates the prediction of the sample composition from measured spectra. Accordingly, powerful and advanced techniques are needed to separate and extract pure absorption and scattering information from the obtained spectra.^ The pure absorption spectrum relates directly to the sample composition according to the Beer-Lambert law. Accordingly, prediction of the milk composition from the pure absorption spectrum with multivariate statistics would be more robust and independent of the effects of light scattering. The scattering properties, on the other hand, are determined by the physical microstructure properties (particle size distribution) of the sample. For milk, this primarily relates to the quantity and size of the suspended fat globules and, to a smaller extent, the casein micelles. Therefore, these scattering properties could be employed to extract this microstructure information, creating an added value for Vis/NIR spectroscopy on milk.Knowledge on the Vis/NIR optical properties of milk is essential for the design and optimization of a measurement configuration and model that would result in accurate and robust estimations for the composition and microstructure of milk.^ Accordingly, the measurement and study of these properties is the main objective of this dissertation. To this end, two sub-objectives were set: (1) the development of a measurement setup for accurate optical characterization of turbid media in the Vis/NIR wavelength range; and (2) to study the effect of quantity and size distribution of the suspended particles on the scattering properties of milk.The full optical characterization of turbid media is not straightforward and can only be achieved through an indirect method where multiple measurements, reflectance and/or transmittance, are combined with an inverted theoretical light propagation model. The samples total reflectance and total transmittance, as measured with double integrating spheres, together with an unscattered transmittance measurement are generally accepted as the golden standard method to estimate bulk optical properties (bulk absorption coefficient, bulk scattering coefficient and scattering anisotropy factor).^ Therefore, a dedicated measurement setup was designed and built to acquire these measurements with high signal-to-noise ratios for turbid and absorbing media in the Vis/NIR wavelength range. This setup consists of a flexible high-power light source, which produces a pre-dispersed narrow collimated light beam and allows for fast and automated wavelength and waveband selection, two integrating spheres with detectors and an unscattered transmittance measurement path. The bulk optical properties of the sample can be extracted from these measurements with an inverse adding-doubling algorithm adapted from literature and optimized for the setup. The measurement and estimation procedure to obtain the bulk optical properties for turbid media was thoroughly validated on a set of 57 liquid optical phantoms.^ The phantom set was designed to cover a wide range of absorption and scattering properties by mixing intralipid (scattering agent), methylene-blue (absorption agent) and water (dilution agent) in different ratios, similar to the phantoms often used to validate measurement systems in the field of biomedical optics. Intralipid is an oil-in-water emulsion which is, except for the much smaller fat globule size, very similar to raw milk. It was found that the followed approach resulted in very accurate estimation of the samples pure absorption and scattering propertiesThe obtained dataset was further explored to investigate the effect of an increasing concentration of scattering intralipid particles on the phantoms scattering properties. Furthermore, it was tested when the particle density is so high that individual scattering events start to influence each other, a phenomenon known as dependent or correlated scattering.^ It was found that dependent scattering has a significant impact on the scattering properties of intralipid-dilutions for particle volume concentrations above 2%. Additionally, semi-empirical equations were derived, describing the scattering properties as a function of the radiation wavelength and the volume concentration of scattering intralipid particles, taking into account dependent scattering.To study the effect of the size distribution of suspended spherical particles on the samples scattering properties, a simulation algorithm was developed that relates them. A generalization of the Mie solution for Maxwells equations was used to calculate the optical properties for a single spherical and scattering particle in an absorbing host medium. Accordingly, the optical properties were combined for multiple particles and polydispersity was supported by discretization of the provided particle size distribution.^ The number of discrete intervals is optimized automatically in an efficient iterative procedure. Finally, the developed microscale light propagation algorithm was validated by simulating the bulk optical properties for two aqueous nanoparticle systems and intralipid in the Vis/NIR wavelength range, taking into account the representative particle sizes. The simulated bulk optical properties matched closely with those obtained by the golden standard method.In a next step, the gathered knowledge, measurement techniques and models were employed to study the effect of the fat globule size distribution on the Vis/NIR bulk scattering properties of milk. Ultrasonic homogenization was performed on raw milk to create milk samples with different fat globule size distributions. Next, the Vis/NIR total reflectance and total and unscattered transmittance spectra of these samples were measured and their bulk optical properties were estimated as described earlier.^ Additionally, the actual particle size distribution of fat globules and casein micelles was measured for each sample and the obtained distribution was used as an input for the microscale algorithm, described earlier, to simulate the samples bulk optical properties. Consequently, the validity of the developed microscale algorithm could be tested for milk by comparing the measured and simulated bulk optical properties. The simulated values were very close to the measured ones as long as scattering was independent. Moreover, it was found that a reduction in the fat globule size results in a higher wavelength-dependency of both the Vis/NIR bulk scattering coefficient and the scattering anisotropy factor. Therefore, these scattering parameters are very suitable to estimate the fat globule size distribution from.^ However, this requires inversion of the microscale model.Finally, the Vis/NIR bulk optical properties were determined for a diverse set of 60 raw milk samples that are representative for individual milkings on a dairy farm. The observed variability was discussed and the relation between the obtained bulk optical properties and the raw milk composition and fat globule size was extensively studied. The bulk absorption coefficient spectra were found to mainly contain information on the water, milk fat and casein content, while the bulk scattering coefficient spectra turned out to be primarily influenced by the quantity and the size of the fat globules. Moreover, there was a strong positive correlation between the fat content in raw milk and the measured

Academic collection --- Theses

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Deze animatie werd gemaakt voor het Mastiman-project. De doelstelling van dit project is een paradigmashift teweegbrengen naar het behandelen van mastitis in functie van het herstel. Het project zal dit doen door het demonstreren van de werkelijke productieverliezen, het aanreiken van praktische tools en handleidingen (afgetoetst aan de praktijk in discussiegroepen) en het actief verspreiden van de verzamelde kennis via het Koesensor-kennisplatform (www.koesensor.be). Met de handleidingen en tools kunnen melkveehouders en bedrijfsdierenartsen onmiddellijk aan de slag.

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The high nutritional value and health benefits of citrus fruit make it a widely consumed food. To maximize customer satisfaction and minimize food waste, the citrus industry demands for non-destructive and efficient quality detection methods. Optical techniques have been proposed as interesting candidates to build detection models for quality monitoring of citrus fruit. However, these detection models have been reported to lack robustness against the biological variability between fruit from different growing seasons, production regions and even orchards. One way to increase this robustness would be to include more samples with different attributes to cover a wider variability and thus enhance the robustness of the detection model. However, this turns out to be challenging in practice. Tracing back to the nature of the light-matter interaction, it can be found that the light propagation in citrus fruit and the acquired spectra are the result of a complex interplay between chemical components-related absorption and physical structures-related scattering phenomena. Therefore, it is hypothesized that separating the bulk optical properties (BOP) that are related to the chemical and physical quality of citrus tissues will contribute to building more robust quality detection models and exploring the light propagation in citrus fruit to optimize the design of optical sensors for citrus fruit quality measurement.In a first experiment, the BOP were characterized for different citrus fruit species, including grapefruit, orange, lemon and lime. Since citrus fruit is composed of different tissue layers: flavedo, albedo and juice vesicles, the BOP measurements were performed on each of these tissue layers. The diffuse reflectance and total transmittance measured from double integrating spheres (DIS), together with the unscattered transmittance measurement, were combined with the inverse adding-doubling (IAD) routine to estimate the BOP. Simultaneously, the size of the oil glands in flavedo, the soluble solids content (SSC) and the titratable acidity (TA) in juice vesicles were respectively measured with traditional destructive methods. Based on these measurements, the relationships between the BOP and the quality properties were investigated. The bulk absorption coefficient (μa) spectra in the near-infrared (NIR) range were found to be dominated by the absorption peaks of water around 980, 1200 and 1450 nm for all the species and tissue layers. In the visible (Vis) range, absorption peaks attributed to carotenoids were found at around 480 nm for all the species, while a specific absorption peak attributed to chlorophyll was also found for lime at around 680 nm. Differences in the bulk scattering coefficient (μs) were observed among different tissue layers, with the μs value of peel (flavedo and albedo) much higher than the flesh (juice vesicles). The changes in anisotropy factor (g) with wavelength varied among different tissue layers. However, the differences in μs and g between different species were typically smaller than the variation among different tissues. A negative correlation was found between the average value of μs and the diameter of the oil glands in the flavedo. The best prediction models for SSC and TA were respectively achieved based on the attenuation coefficient (μt) and μa of juice vesicles.After obtaining the BOP of different tissue layers, the light propagation in citrus fruit was investigated with Monte Carlo multi-layered (MCML) simulations. The light propagation was traced in the wavelength range from 490 nm to 1880 nm for source-detector distances up to 1 cm. The simulated light energies in different detection modes (including diffuse reflectance, absorption and transmittance), absorbed by different tissue layers and their contributions to the diffuse reflectance profiles were recorded. Next, the simulated spatially resolved diffuse reflectance profiles for the intact fruit were compared to those extracted from hyperspectral laser scatter images to validate the accuracy of the simulations. Apart from the deviations caused by the rough surface and nearby oil glands, the simulated results generally matched well with the measurements. Simulation results indicated that most of the light was reflected and absorbed by the flavedo. Around 15 % of the light was absorbed by the albedo for all the wavelengths outside the absorption bands of water and flavedo pigments. Compared to the flavedo and albedo, the light absorbed by juice vesicles was extremely low with fractions mostly below 3 %. The flavedo and albedo layers were found to contribute mostly to the diffuse reflectance spectra at 800 nm and their contributions respectively decreased and increased with increasing source-detector distance. Although the contribution of the juice vesicles increased with distance, the maximal diffuse reflectance intensity contributed by juice vesicles was located within 0.56 cm from the illumination point. Based on these results, the combination of the power intensity and the source detector distance can be optimized to obtain maximal information about the layer of interest.In a next phase, the influences from harvest time, fruit size and cultivar on the BOP of Satsuma mandarin tissues were investigated. As the diffuse reflectance profiles mostly reflected the properties of the outmost flavedo layer while many qualities of interest (e.g., sugar and acid contents) are related to the innermost juice vesicles layer, the variation of the BOP in relation to these influencing factors was explored for both the inner (juice vesicles) and outer (flavedo) tissue layers. Satsuma mandarin of three different cultivars (Iwasaki, Okitsu and Goku Wase) harvested at three different times around the recommended harvest date were used as the samples for this experiment. Similar to the above measurements on the citrus fruit with different species, the BOP, SSC, TA as well as the color parameters (L*, a* and b*) and Brix minus acid (BrimA) were measured for the Satsuma mandarins. Along the harvest time, the absorption peak related to carotenoids in the μa spectrum was found to increase in both tissue layers, while the values attributed to chlorophylls decrease in the flavedo. Moreover, a slightly increasing trend over the harvest time was observed in the μs spectra of juice vesicles, especially at the early stage. The μa values of both tissue layers and the μs values of juice vesicles deviated among different fruit sizes, which can be related to the development stage. Smaller fruit presented a higher carotenoids content in juice vesicles, an advanced color change in flavedo throughout the maturation stages and higher μs values in juice vesicles at earlier maturation stages. The μa differences in pigment absorption among different cultivars were related to the maturation order. Earlier maturing cultivars possessed higher μa values related to carotenoids absorption in juice vesicles and advanced color changes in flavedo. The μs values of the flavedo differed among the cultivars and these differences were enhanced during maturation.BOP values can also be extracted from the non-destructive hyperspectral laser scatter images using a metamodel to link the BOP with the diffuse reflectance profiles. While measurement-based metamodels have been reported to provide a good match with the measured data, simulation-based metamodels would provide more flexibility in designing the search space. Therefore, the mismatches between measurements and simulations were explored by studying the influences from light source, the incident angle and the detection angle on the diffuse reflectance profiles as measured with a hyperspectral laser scatter imaging setup. Results indicated that the diffuse reflectance intensity was in proportion with the light source power and the influence from the size of the light beam diminished with increasing source-detector distance. The profiles extracted from the sides perpendicular to the illuminating beam were found to be less influenced by the incident angle. Moreover, taking into account the correct region of interest and incident angle, the mismatch between measurements and simulations could be reduced further. Within a detection angle range from 0 ° to 30 ° relative to the normal of the sample surface, the relative deviations between measurements and simulations at source-detector distances from 0.04 to 0.07 cm were below 6 %. After reducing the mismatches caused by the factors mentioned above, the simulated diffuse reflectance profiles matched well with the measurements, with R2-values above 0.99. Successively, metamodels were respectively built based on the measured and simulated profiles to link the BOP with the diffuse reflectance profiles. The prediction performance of the inverse simulation-based metamodel was comparable with the one based on the measurements, obtaining R2 values above 0.96. Proper correction for these sources of mismatches between measurements and simulations thus allows to build a simulation-based metamodel with a wide range of desired optical properties that is applicable to different measurement configurations.Early puffing is one of the dominant postharvest disorders in easy-peeling citrus cultivars such as Satsuma mandarin. To obtain more insight in this disorder, the structural properties (tissue thickness, surface/volume, percent volume and surface/tissue volume) of the flavedo and albedo tissue layer in the peel were calculated from X-ray CT scans of both healthy and puffy mandarin. The thickness of both flavedo and albedo tissue layers was found to be lower in the puffy mandarin. No differences were observed in the size of the oil glands in the flavedo, but the pore size in the albedo of puffy mandarin was found to be larger at a later harvest time. Next, the BOP of the individual tissue layers in the 530 nm - 970 nm wavelength range were quantified from the DIS and unscattered transmittance measurements, while those for the intact fruit were estimated from laser scatter images with the measurement-based metamodel. The reduced scattering coefficient (μs') values for the intact fruit were found to be lower in the puffy mandarins compared to the corresponding healthy fruit. The sizes of both the oil glands in the flavedo and the air pores in the albedo were negatively correlated with the μs' values of the respective tissue layers. The μs' values of the intact fruit were found to be dominated by the scattering properties of the flavedo layer and positively correlated with the size of the oil glands. However, as no differences in the size of the oil glands were observed between the healthy and puffy mandarins, the observed differences in the μs' values of the intact fruit could be attributed to changes in the scattering properties of the albedo and were negatively correlated to the size/percentage of the air pores. This provides a solid basis for the non-destructive optical detection of puffing disorder at an early stage.In general, the measurements on the BOP of citrus tissues provided an insight into the optical differences among tissues and the explorations of the relationship between the BOP and quality properties. The study on the influences of harvest time, fruit size, cultivar and puffing disorder on the BOP investigated the possible sources of variations in practice, which better promoted the development of the quality detection. By simulating the light propagation in citrus fruit, the obtained signal is well linked with the properties of the different tissue layers, which laid the foundations for designing and optimizing quality detection sensors for citrus fruit. The measurement-based and simulation-based metamodels of deriving BOP from spatially resolved diffuse reflectance profiles offered a non-destructive method for the BOP detection, moreover, the probe into the mismatch between these two metamodels further facilitated their applications on measurements.

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Precise knowledge of milk composition on a frequent base can help to monitoring dairy cow’s health and detect potential disease in a daily routine. This is not only crucial for a profitable dairy farm, but also meaningful for cows’ welfare. 349 raw milk samples are collected, with NIR spectra acquired in both transmittance mode and reflectance mode. The wavelength ranges between 943.17 nm to 1701.3 nm. Several innovative preprocessing chemometrics including optical path length estimation and correction (OPLEC), extended multiplicative scattering correction (EMSC), extended inverse scattering correction (EISC) are tested, their prediction performance are compared with the one obtained by the basic chemometrics. Excellent results are obtained with regard to the coefficient of determination, R^2 equals to 0.99 for fat using EISC corrected reflectance spectra, 0.98 for protein using EISC corrected transmittance spectra, 0.91 for lactose using EISC corrected transmittance spectra. It has been proven that EISC, EMSC, EMSCL all have the good ability to estimate and correct multiplicative scattering effect. It is also found that prediction for lactose based on reflectance spectra is always less satisfactory through all the techniques used in this thesis.

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Om de gezondheid van melkkoeien op te volgen maakt men vandaag de dag gebruik van melkanalyses die worden uitgevoerd in daarvoor uitgeruste labo’s. De tijd tussen het afname van het te onderzoeken staaltje en de vrijgave van de resultaten van het labo is ongeveer een week. In die tijd kan de gezondheid van de koe al sterk achteruit gegaan zijn. Om deze reden is de ‘Livestock Technology’ onderzoeksgroep op de campus in Geel een sensor aan het ontwerpen die kan gebruikt worden op de melkveebedrijven zelf. Deze sensor zou via een optische analyse van de melk de gezondheidstoestand van een koe kunnen bepalen. De masterproef is daarom ook in samenwerking met de onderzoeksgroep Livestock Technology in Geel. Het doel van deze thesis is om de mechanische en fysische problemen die zich voordoen in het analyse systeem op te lossen of te omzeilen. De vier problemen die centraal staan hierbij zijn: verminderen van de kans op luchtbellen in de cuvette die de analyse beïnvloedt, repetitieve melktemperatuur bekomen bij iedere melkanalyse, reinigingsklep ontwikkelen om plaatselijk bederf van melk te voorkomen en de demping van trillingen die zich voordoen in een lineair translatie systeem. De masterproef focust zich vooral op de vermindering van de kans op luchtbellen in de cuvette. De oplossing hiervoor is gebaseerd op het herontwerp van een peristaltische pomp. De pomp doet dan zowel dienst als peristaltische pomp en als knijpventiel. Om dit te bekomen zal de klep van de peristaltische pomp automatisch moeten kunnen openen en sluiten. Dit wordt gedaan op basis van een solenoïde actuator met veer die de benodigde kracht uitoefenen op de gevraagde momenten. Deze kracht is wetenschappelijk onderzocht, zodat de bestelde solenoïde en veer zeker zouden voldoen aan deze vereisten. Verder is er ook een assemblage van de sensor gemaakt in Autodesk InventorTM om dit te simuleren. Dit zou mogelijke problemen later kunnen visualiseren tijdens een eventuele aanpassing aan het systeem. De grootste focus van de masterproef lag op dit gedeelte. Het ontwerp van het verwarmingselement om een repetitieve melktemperatuur te bekomen tussen de verschillende analyses, zat nog in de testfase. De verwarming zou gebeuren op basis van het joule-effect. Om deze verwarming optimaal te laten gebeuren, zijn er verschillende manieren besproken om het warmteverlies te minimaliseren en om een zo groot mogelijk warmteaandeel te verkrijgen. Verder dient hierbij nog een code te programmeren die de regelaar van de verwarming aanstuurt. Omtrent de demping van het translatie systeem en het ontwerp van de reinigingsklep zijn er verschillende methodes onderzocht. De voorgestelde oplossingen hiervan zijn nog niet geïmplementeerd in de melk sensor. Verder zijn op een USB-stick nog CAD bestanden toegevoegd, waaronder de assemblage van de sensor zelf.