Effect of ultrasonic homogenization on the Vis/NIR bulk optical properties of milk

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The role of chloroplast movement in C4 photosynthesis: a theoretical analysis using a three-dimensional reaction-diffusion model for maize

18 Pág.Chloroplasts movement within mesophyll cells in C4 plants is hypothesized to enhance the CO2 concentrating mechanism, but this is difficult to verify experimentally. A three-dimensional (3D) leaf model can help analyse how chloroplast movement influences the operation of the CO2 concentrating mechanism. The first volumetric reaction-diffusion model of C4 photosynthesis that incorporates detailed 3D leaf anatomy, light propagation, ATP and NADPH production, and CO2, O2 and bicarbonate concentration driven by diffusional and assimilation/emission processes was developed. It was implemented for maize leaves to simulate various chloroplast movement scenarios within mesophyll cells: the movement of all mesophyll chloroplasts towards bundle sheath cells (aggregative movement) and movement of only those of interveinal mesophyll cells towards bundle sheath cells (avoidance movement). Light absorbed by bundle sheath chloroplasts relative to mesophyll chloroplasts increased in both cases. Avoidance movement decreased light absorption by mesophyll chloroplasts considerably. Consequently, total ATP and NADPH production and net photosynthetic rate increased for aggregative movement and decreased for avoidance movement compared with the default case of no chloroplast movement at high light intensities. Leakiness increased in both chloroplast movement scenarios due to the imbalance in energy production and demand in mesophyll and bundle sheath cells. These results suggest the need to design strategies for coordinated increases in electron transport and Rubisco activities for an efficient CO2 concentrating mechanism at very high light intensities.The work is supported by the Research Council of KU Leuven (project C1/16/002) and the Research Fund Flanders (project G.0645.13). Wageningen based authors have contributed to this work within the program BioSolar Cells. FJC was funded through the Spanish fellowship Ramon y Cajal (RYC2021-035064-I).Peer reviewe

Computational optimization of an optical sensor design

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mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} It is interesting for the food industry to determine the microstructure of food products. Although several equipments already exist which can determine this microstructure, they’re only applicable to ‘simple’ structures (powders, emulsions or suspensions). An interesting technique to derive information over biological tissues is Vis/NIR spectroscopy. When light propagates through a biological tissue, photons will interact with the existing microstructure. The absorption of photons gives an idea about the chemical composition. Variations in the microstructure can however result into erroneous concentration estimations with classical Vis/NIR spectroscopy. This is the result of light scattering due to the microstructure. This light scattering is a dominant effect in biological tissues. In classical Vis/NIR spectroscopy one evaluates how light is fading away in the tissue, as a consequence of the interaction with the biological tissue. This results in a single measurements: reflection or transmission. It does not allow, however, to make a distinction between information about the chemical composition (absorption) and the microstructure (scattering). Advanced methods have arose, which perform multiple measurements, resolved over time or space. These methods employ light propagation models which allow to simulate the reflection or transmission of a sample with specific optical properties. Optical properties of a tissue can be estimated by iteratively comparing simulated spectra with measured ones. When determining the optical properties of a complex biological tissue, one needs an adapted sensor. The most efficient probe is therefore the result of an iterative development procedure, where improvements are being made after testing a previous prototype. Becauseof the significant investment necessary for building the prototypes,every step of this iterative process implies an increase in time andmoney. As a result, one can only justify building a small number of different prototypes. The result is a suboptimal probe design. If onewould be able to do this process computationally, this would be a large improvement. Light propagation models are a necessary tool for this computational sensor design. This research is subdivided into 4 parts. At first, a light propagation model will be developed. Starting from optical parameters, one should be able to derive the light distribution in a biological tissue. In the next step, an inverted algorithm will be developed. Starting from SRS-measurements, the optical properties of tissues will be estimated. Finally, a connection will be made between the optical properties – which characterize a tissue on a mesoscale – and the microstructure of the tissue. This will be done by estimating the particle size distribution of the tissue. Starting from this research, one will develop a computational optimization of the sensor design. This algorithm will make usage of the light propagation model, in combination with the inverse algorithm.Preface – Voorwoord i Samenvatting iii Abstract – Summary ix List of Symbols xiii Table of Contents xvii Chapter 1: General introduction 1 1.1 Importance of quality in food industry 1 1.2 Importance of food microstructure and composition 2 1.3 Applications of Vis/NIR spectroscopy in the food industry 4 1.4 The study of Vis/NIR light propagation in biological media 5 1.5 Problem statement and research objectives 6 Chapter 2: Light Propagation in Biomaterials: state of the art 9 2.1 Introduction 11 2.2 Electromagnetic spectrum 11 2.3 Theoretical principles of light propagation 12 2.3.1 Reflection and refraction 12 2.3.2 Absorption 14 2.3.3 Scattering 20 2.3.4 Bulk optical properties 23 2.4 Modeling propagation of electromagnetic radiation in turbid media 26 2.4.1 Radiative transfer theory 26 2.4.2 Adding-Doubling 29 2.5 Monte Carlo modeling of the light propagation in biomaterials 33 2.5.1 Introduction 33 2.5.2 Tracing photons through a biomaterial 35 2.5.3 Improving computational speed 44 2.5.4 Improving accuracy 49 2.6 Spectral fitting in tissue optics 51 2.7 Measurement of the bulk optical properties of turbid media 52 2.7.1 Unscattered transmittance measurements 52 2.7.2 Nephelometer measurements 54 2.7.3 Double integrating sphere measurement and inverse adding-doubling 55 2.7.4 Spatially resolved reflectance spectroscopy 58 2.7.5 Hyperspectral scatter imaging 60 2.8 Summary 61 Chapter 3: Estimation of optical properties – robust estimation using prior scattering information 63 3.1 Introduction 65 3.2 Materials and methods 68 3.2.1 Optical characterization of liquid phantoms 68 3.2.2 Metamodeling approximation of light propagation models 69 3.2.3 Light propagation metamodel 79 3.2.4 Inverse light propagation model 81 3.2.5 Validation of estimator 85 3.2.6 Wavelength-dependency 85 3.3 Results and discussion 87 3.3.1 Bulk optical properties of liquid phantoms 87 3.3.2 Visualization of the metamodel 88 3.3.3 Results of the estimation procedure on the calibration and validation set 91 3.3.4 Results for the estimation in the wavelength dependency test 95 3.4 Conclusions 97 Chapter 4: Computational optimization of spatially resolved spectroscopy sensor configuration design 99 4.1 Introduction 101 4.2 Materials and methods 102 4.2.1 Optical characterization of milk samples 102 4.2.2 Metamodeling 102 4.2.3 Simulating realistic SRS “measurements” of milk samples 103 4.2. 4 (Inverse) light propagation model 103 4.2.5 Optimization of sensor configuration: definition of a cost function 105 4.2.6 Genetic algorithm for optimizing a milk sensor configuration 106 4.3 Results 108 4.3.1 Bulk optical properties of milk samples 108 4.3.2 Estimation of milk BOP: the 30 fiber case 109 4.3.3 Optimization of a milk sensor design: overview of the different cases 110 4.3.4 Optimization of a milk sensor design: the optimal number of fibers 113 4.4 Conclusion and future perspectives 115 Chapter 5: Microscale light propagation modeling – linking microstructural information to optical properties in Monte Carlo simulations 119 5.1 Introduction 121 5.2 Materials and methods 122 5.2.1 Phase functions in MC simulations 122 5.2.2 Classical computation of the HG phase function 123 5.2.3 Example of a modified HG phase function 124 5.2.4 Simulating the bulk optical properties of polydisperse spherical particles in an absorbing host medium 125 5.2.5 Incorporating alternative phase functions in MC simulations 138 5.2.6 Testing the fpf-MC code 141 5.2.7 Comparing different MC algorithms: statistical analysis 144 5.3 Results 146 5.3.1 Effect of phase function resolution on accuracy of fpf-MC 146 5.3.2 Comparison with MCML 148 5.3.3 Effect of the second moment in the modified HG phase function 150 5.3.4 Introducing arbitrary phase functions derived from particle size distributions 150 5.4 Conclusions 151 Chapter 6: Microscale light propagation modeling – Monte Carlo modeling in realistic tissue structures 153 6.1. Introduction 155 6.2. Materials and methods 156 6.2.1 MMC-fpf algorithm 156 6.2.2 In silico validation 160 6.2.3 Experimental validation 164 6.3 Results and discussion 168 6.3.1 In silico validation 168 6.3.2 Experimental validation on tomato leaves 171 6.3.3 Absorption profiles of tomato leaf tissues 172 6.4 Discussion 174 6.5 Conclusions 177 Chapter 7: General conclusions and future perspectives 179 7.1 General conclusions 181 7.2 Future perspectives 183 7.2.1 Improving (inverse) light propagation modeling 183 7.2.2 Improving sensor design computation 186 7.2.3 Advanced chemometrics to predict composition 188 7.2.4 Inverse microscale models 188 Reference List 191 Curriculum vitae 209 Publication List 211 Appendix A: Mie expansion coefficients 213nrpages: 217status: publishe

A Handheld Multispectral Sensor for the Separation of Scattering and Absorption Properties

Optical measurements are influenced by both the effects of light absorption and scattering. In this research, spatially resolved spectroscopy (SRS) was used in combination with a metamodel approach to separate scattering and absorption information in a non-destructive way. To this end, a cost-efficient, portable and robust multispectral sensor was designed. Four laser modules at carefully selected wavelengths (533.3 nm, 674 nm, 800.7 nm and 981.1 nm) were mounted on four sides of a CCD camera, while a light-weight lithium-ion battery was used as power supply. Using this sensor, 49 liquid optical phantoms, based on Naphthol Blue Black and Intralipid, were measured. As a reference, the bulk optical properties (BOP) were measured accurately using a double integrating spheres (DIS) setup. Combining these reference optical properties with the corresponding SRS measurements, a metamodel was built and validated on a separate test set of 7 liquid phantoms. The bulk absorption coefficient µa and the reduced scattering coefficient µs’ were successfully estimated based on SRS measurements, with R2V values of 0.97 and 0.94 for respectively µa and µs’. This type of portable sensor could be used for on-field or on-site measurements in the agro-food sector to measure the absorption and scattering properties and extract information on the physical and chemical product properties.status: accepte

Optical characterization of biological material: A multiscale approach

The change of Vis/NIR radiation when propagating through biological material is the result of a complex process of molecule-specific absorptions and multiple light scattering caused by the interaction of the photons with the microstructure. In addition, many biological products, such as fruit or skin tissue are characterized by a layered structure. Therefore, multiple measurements are needed to separate the information on the different layers. In this research, reflectance measurements at different distances from the incident light beam are combined with multiscale light propagation models to extract the compositional and microstructure properties of biological products. First, the biological material is modelled at the macroscale (∼mm) as a set of uniform layers, where the light propagation in each layer is defined by 3 bulk optical properties. Using these 3 bulk properties the reflectance spectra at different distances from the incident light beam are calculated by Monte Carlo simulations for the radiative transport equation. The bulk optical properties of one or two tissue layers in a biological material are then estimated by comparing the measured spatially resolved reflectance profiles to a library of profiles simulated for a wide range of combinations of optical properties. In a second step, the estimated scattering and absorption properties are then related to the chemical composition and microstructure of the different layers. This approach has been applied for the optical characterization of microstructure in food products such as food gels, food foams and chocolate mousse.status: publishe

Effect of maturation on the bulk optical properties of apple skin and cortex in the 500 to 1850 nm wavelength range

To facilitate the design of new optical measurement systems for biological systems, the knowledge of light propagation properties is essential. Therefore, the bulk optical properties of skin and cortex of three apple cultivars were studied during maturation, in the 500 nm to 1850 nm range. A clear absorption signature was observed with absorption peaks which can be related to present anthocyanins, chlorophyll, carotenoids and water. During maturation, the skin absorption at 550 nm increased in the bicolored cultivars ‘Braeburn’ and ‘Kanzi’, while the absorption at 680 nm decreased in the cortex. Both the bulk scattering coefficient and the anisotropy factor were larger for the skin compared to the cortex tissue. Also during maturation, the skin scattering increased in the two bicolored cultivars, while a general decrease was seen in the apple cortex. Physiological changes during maturation, like cell growth, the formation/degradation of pigments and the formation of a cuticle layer on the skin, may explain the observed evolutions. As a result, using the bulk optical properties, these physiological changes can be monitored and linked to the maturity stage in the orchard, supporting the selective harvest of apples.status: publishe

Visible and near-infrared bulk optical properties of raw milk

The implementation of optical sensor technology to monitor the milk quality on dairy farms and milk processing plants would support the early detection of altering production processes. Basic visible and near-infrared spectroscopy is already widely used to measure the composition of agricultural and food products. However, to obtain maximal performance, the design of such optical sensors should be optimized with regard to the optical properties of the samples to be measured. Therefore, the aim of this study was to determine the visible and near-infrared bulk absorption coefficient, bulk scattering coefficient, and scattering anisotropy spectra for a diverse set of raw milk samples originating from individual cow milkings, representing the milk variability present on dairy farms. Accordingly, this database of bulk optical properties can be used in future simulation studies to efficiently optimize and validate the design of an optical milk quality sensor. In a next step of the current study, the relation between the obtained bulk optical properties and milk quality properties was analyzed in detail. The bulk absorption coefficient spectra were found to mainly contain information on the water, fat, and casein content, whereas the bulk scattering coefficient spectra were found to be primarily influenced by the quantity and the size of the fat globules. Moreover, a strong positive correlation (r ≥ 0.975) was found between the fat content in raw milk and the measured bulk scattering coefficients in the 1,300 to 1,400 nm wavelength range. Relative to the bulk scattering coefficient, the variability on the scattering anisotropy factor was found to be limited. This is because the milk scattering anisotropy is nearly independent of the fat globule and casein micelle quantity, while it is mainly determined by the size of the fat globules. As this study shows high correlations between the sample's bulk optical properties and the milk composition and fat globule size, a sensor that allows for robust separation between the absorption and scattering properties would enable accurate prediction of the raw milk quality parameters.status: publishe

The potential of optical measurement techniques for the evaluation of meat quality

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Effect of maturation on the bulk optical properties of apple skin and cortex in the 500 to 1850 nm wavelength range

To facilitate the design of new optical measurement systems for biological systems, the knowledge of light propagation properties is essential. Therefore, the bulk optical properties of skin and cortex of three apple cultivars were studied during maturation, in the 500 nm to 1850 nm range. A clear absorption signature was observed with absorption peaks which can be related to present anthocyanins, chlorophyll, carotenoids and water. During maturation, the skin absorption at 550 nm increased in the bicolored cultivars ‘Braeburn’ and ‘Kanzi’, while the absorption at 680 nm decreased in the cortex. Both the bulk scattering coefficient and the anisotropy factor were larger for the skin compared to the cortex tissue. Also during maturation, the skin scattering increased in the two bicolored cultivars, while a general decrease was seen in the apple cortex. Physiological changes during maturation, like cell growth, the formation/degradation of pigments and the formation of a cuticle layer on the skin, may explain the observed evolutions. As a result, using the bulk optical properties, these physiological changes can be monitored and linked to the maturity stage in the orchard, supporting the selective harvest of apples.status: publishe

Evolution of the bulk optical properties of bovine muscles during wet aging

The bulk optical properties (BOP) of two bovine muscles were studied in the 500nm to 1850nm wavelength range. Over a two-week period of wet aging, the BOP of the biceps femoris (BF) and longissimus lumborum (LL) were determined and related to moisture content, tenderness and cooking loss. The absorption by myoglobin and reduced scattering coefficient were higher in the BF compared to the LL. The scattering anisotropy factor was relatively high (>0.95 for LL), representing dominant forward scattering. Two-toning effects in the BF could be attributed to significant scattering differences, as no differences in absorption properties were observed. During wet aging, the anisotropy factor decreased, while tenderness increased. It was hypothesized that this might be related to proteolysis of cytoskeletal proteins. The results show the potential use of BOP to monitor tenderization and the cause of color differences in beef muscles. Moreover, this information could be used to develop and optimize optical sensors for non-destructive meat quality monitoring.status: publishe