Studies on classification models to discriminate ‘Braeburn’ apples affected by internal browning using the optical properties measured by time-resolved reflectance spectroscopy

This work aimed at studying the feasibility of time-resolved reflectance spectroscopy (TRS) to nondestructively detect internal browning (IB) in ‘Braeburn’ apples through the development of classification models based on absorption (ua) and scattering (us') properties of the pulp.This research was carried out in two seasons: in 2009, apples were measured by TRS at 670 nm and inthe 740–1040 nm spectral range on four equidistant points around the equator, whereas in 2010 appleswere measured by TRS at 670 nm and at 780 nm on eight equidistant points. The values of the absorption coefficients measured in the 670–940 nm range increased with IB devel-opment. On the contrary, us'780 was higher in healthy fruit than in IB ones. The ua780 also significantlyincreased with IB severity, showing high values when IB affected the pulp tissues compared to the coreones. Also ua670 changed with IB development, but it was not able to clearly discriminate healthy fruitfrom IB ones because its value was also affected by the chlorophyll content of the pulp. The absorption and scattering coefficients were used as explanatory variables in the linear discriminant analysis in order to classify each apple tissue as healthy or IB; then the models obtained were used forfruit classification. The best classification performance was obtained in 2010 using ua780 and us'780and considering the IB position within the fruit: 90% of healthy fruit and 71% of IB fruit were correctly classified. By using all the ua measured in the 670–1040 nm range plus the us'780, IB fruit classification was slightly better while healthy fruit classification was worse. The better result of 2010 was due tothe increased number of TRS measurement points that allowed better exploration of the fruit tissues. However, the asymmetric nature of this disorder makes detection difficult, especially when the disorderis localized in the inner part of the fruit (core) or when it occurs in spots. A different TRS set-up (position and distance of fibers, time resolution) should be studied in order to reach the deeper tissue within the fruit in order to improve browning detection

A Continuum Model for Metabolic Gas Exchange in Pear Fruit

Exchange of O2 and CO2 of plants with their environment is essential for metabolic processes such as photosynthesis and respiration. In some fruits such as pears, which are typically stored under a controlled atmosphere with reduced O2 and increased CO2 levels to extend their commercial storage life, anoxia may occur, eventually leading to physiological disorders. In this manuscript we have developed a mathematical model to predict the internal gas concentrations, including permeation, diffusion, and respiration and fermentation kinetics. Pear fruit has been selected as a case study. The model has been used to perform in silico experiments to evaluate the effect of, for example, fruit size or ambient gas concentration on internal O2 and CO2 levels. The model incorporates the actual shape of the fruit and was solved using fluid dynamics software. Environmental conditions such as temperature and gas composition have a large effect on the internal distribution of oxygen and carbon dioxide in fruit. Also, the fruit size has a considerable effect on local metabolic gas concentrations; hence, depending on the size, local anaerobic conditions may result, which eventually may lead to physiological disorders. The model developed in this manuscript is to our knowledge the most comprehensive model to date to simulate gas exchange in plant tissue. It can be used to evaluate the effect of environmental stresses on fruit via in silico experiments and may lead to commercial applications involving long-term storage of fruit under controlled atmospheres

Multiscale modeling of equal channel angular extruded aluminium with strain gradient crystal plasticity and phenomenological models

peer reviewedThe Equal Channel Angular Extrusion process is used to modify the microstructure of an AA1050 aluminum alloy in order to produce an ultra fine grained material. Due to the severe plastic deformation undergone by the material during the ECAE process, the subsequent behavior of the material is non-conventional and difficult to model with classical constitutive laws (e.g. ECAE aluminum presents a large initial back-stress which must be adequately incorporated in the model). In this study, the evolution of the back-stress during the ECAE process is analyzed. Two different numerical models were investigated in this respect. The first one is a single crystal strain gradient plasticity model based on dislocation densities. The second model is the Teodosiu and Hu’s hardening model, which is a microstructuraly based phenomenological model at the macroscale. The results provided by the two models are obviously distinct. Nevertheless, some common trends can be pointed out, among which the amplitude of the back-stress that is similar. In agreement with the cyclic deformation mode of the studied route C ECAE process, the evolution of the predicted back-stress is also cyclic in both models

Improved surface plasmon resonance biosensing using silanized optical fibers

© 2015 Elsevier B.V. Abstract Coupling surface plasmon resonance (SPR) to optical fiber (FO) technology has brought tremendous advancements in the field by offering attractive advantages over the traditional prism-based SPR platforms, such as simplicity, cost-effectiveness and miniaturization. However, the performance of the existing FO-SPR sensors widely depends on the adhesion of the gold (Au) layer to the FO silica core, thereby often representing a major limiting factor in achieving the properties of the benchmark SPR systems. In this paper, we used (3-marcaptopropyl)trimethoxysilane (MPTMS) as an adhesion promoter for developing robust Au surfaces on the three-dimensional (3D) FO-SPR sensing probe. Carefully prepared FO substrates were first silanized using a wet chemistry approach, with MPTMS concentrations ranging from 2.5 to 24 mM, and subsequently exposed to a drying treatment at room temperature (RT) or at 100 C, before coating them with a ∼50 nm Au plasmonic film. Differently prepared silanized FOs were next used for evaluating their sensitivities, by performing refractive index (RI) measurements in sucrose dilutions. Advanced statistical analysis of the obtained data indicated that using 8 mM MPTMS solution coupled with a RT post-drying treatment is an efficient way of producing FOs with dramatically improved Au adhesion properties. The role of the MPTMS underlayer was further investigated by exposing the reference and silanized FOs to stress conditions, such as strong mechanical (adhesion tape tests), chemical (piranha solution treatments) and thermal variations. Although additional studies using scanning electron microscopy (SEM) revealed changes in the Au film morphology after these endurance tests, the silanized FOs exhibited an enhanced robustness while retaining the overall sensor's capabilities. In contrast, the reference FOs consistently failed the mechanical and chemical tests, while only resisting under thermal variations. Moreover, the improved resistance of the silanized FO-SPR probes allowed them to be reused up to three times with no significant loss in the sensor performance, while implementing bioassays based on two types of bioreceptors (a DNA aptamer against thrombin protein and a polyclonal antibody against human immunoglobulin E - hIgE). All these results might represent a step forward in the fabrication of more robust and reusable FO-SPR biosensors, featuring great potential for developing highly-sensitive biochemical assays.publisher: Elsevier articletitle: Improved surface plasmon resonance biosensing using silanized optical fibers journaltitle: Sensors and Actuators B: Chemical articlelink: http://dx.doi.org/10.1016/j.snb.2015.04.069 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved.status: publishe

Multiscale modeling of equal channel angular extruded aluminium with strain gradient crystal plasticity and phenomenological models

The Equal Channel Angular Extrusion process is used to modify the microstructure of an AA1050 aluminum alloy in order to produce an ultra fine grained material. Due to the severe plastic deformation undergone by the material during the ECAE process, the subsequent behavior of the material is non-conventional and difficult to model with classical constitutive laws (e.g. ECAE aluminum presents a large initial back-stress which must be adequately incorporated in the model). In this study, the evolution of the back-stress during the ECAE process is analyzed. Two different numerical models were investigated in this respect. The first one is a single crystal strain gradient plasticity model based on dislocation densities. The second model is the Teodosiu and Hu's hardening model, which is a microstructuraly based phenomenological model at the macroscale. The results provided by the two models are obviously distinct. Nevertheless, some common trends can be pointed out, among which the amplitude of the back-stress that is similar. In agreement with the cyclic deformation mode of the studied route C ECAE process, the evolution of the predicted back-stress is also cyclic in both models.status: publishe

Automatic analysis of the 3-D microstructure of fruit parenchyma tissue using X-ray micro-CT explains differences in aeration

Background: 3D high-resolution X-ray imaging methods have emerged over the last years for visualising the anatomy of tissue samples without substantial sample preparation. Quantitative analysis of cells and intercellular spaces in these images has, however, been difficult and was largely based on manual image processing. We present here an automated procedure for processing high-resolution X-ray images of parenchyma tissues of apple (Malus × domestica Borkh.) and pear (Pyrus communis L.) as a rapid objective method for characterizing 3D plant tissue anatomy at the level of single cells and intercellular spaces. Results: We isolated neighboring cells in 3D images of apple and pear cortex tissues, and constructed a virtual sieve to discard incorrectly segmented cell particles or unseparated clumps of cells. Void networks were stripped down until their essential connectivity features remained. Statistical analysis of structural parameters showed significant differences between genotypes in the void and cell networks that relate to differences in aeration properties of the tissues. Conclusions: A new model for effective oxygen diffusivity of parenchyma tissue is proposed that not only accounts for the tortuosity of interconnected voids, but also for significant diffusion across cells where the void network is not connected. This will significantly aid interpretation and analysis of future tissue aeration studies. The automated image analysis methodology will also support pheno- and genotyping studies where the 3D tissue anatomy plays a role.status: publishe

Gas exchange model using heterogeneous diffusivity to study internal browning in ‘Conference’ pear

Internal gas gradients in pear fruit during controlled atmosphere storage depend on the effective gas diffusivity of the tissue. The diffusivity varies over the fruit organ due to the heterogeneous tissue microstructure across the fruit. This study implemented effective diffusivity maps reflecting the heterogeneous structure to predict internal gas gradients and relate the result to the occurrence of internal browning. Diffusivity maps of different pears were calculated from X-ray CT based porosity maps. Internal oxygen (O2), carbon dioxide (CO2) and respiratory quotient (RQ) levels were computed using a reaction-diffusion model incorporating the heterogeneous effective diffusivity map. Critical O2 and RQ levels for the shift from respiration to fermentation were defined based on the respiratory-fermentative energy balance of the cells. The model was indirectly validated by comparing RQ level contours with non-destructive 3D images of the internal browning of the pears after storage at 1.0 kPa and 0.5 kPa O2, combined with 0.7 kPa CO2 at 1 degrees C. The distribution of the internal gas concentrations and RQ was affected by the heterogeneity of the diffusivity. The results also confirmed the incidence of internal browning when the O2 and RQ were under or above critical O2 and RQ limits, respectively. The fermentation process was indicated to be dominant when the tissue's RQ limit (RQ*) went above 2.12 (or at 0.044 kPa O2). The tissue volumes where O2 and RQ levels were critical corresponded reasonably well to browning-affected tissues of pears with different shapes. The pear with more shallow gas gradients showed less symptoms of browning

Non destructive detection of brown heart in ‘Braeburn’ apples by time-resolved reflectance spectroscopy

AbstractBrown Heart (BH) is an internal disorder which is visible only when fruit are cut open. The aim of this work was to test whether time-resolved reflectance spectroscopy (TRS) can be used to detect BH in intact ‘Braeburn’ apples stored for 3 and 6 months in BH inducing (1% O2 + 5% CO2) and not-inducing (2.5% O2 + 0.7% CO2) conditions. At each storage time, at d0 and d14 of shelf life at 18°C, thirty apples were measured by TRS at 670nm and in the spectral range 740-1100nm on four points (A-D) around the equator. Afterwards, each fruit was cut open and evaluated for BH (position and severity), firmness, intercellular space volume (RISV), and pulp colour (in correspondence of TRS points). Fruit affected by BH showed significantly higher μa in the 740-900nm spectral range than healthy ones, with the highest difference recorded at 740nm. The μa740 and a* increased and L* and H decreased in fruit with moderate and severe BH and when BH was localized in the pulp. In parallel, RISV showed the lowest percentage in healthy apples and the highest when cavities were associated to browning. High correlations were found between μa740 and pulp L*, a* and H°; considering the correlation with L*, at μa740<0.038cm−1 only healthy pulp can be detected, while at μa740>0.08cm−1 only severely browned pulp can be found

Down-regulation of respiration in pear fruit depends on temperature

The respiration rate of plant tissues decreases when the amount of available O2 is reduced. There is, however, a debate on whether the respiration rate is controlled either by diffusion limitation of oxygen or through regulatory processes at the level of the transcriptome. We used experimental and modelling approaches to demonstrate that both diffusion limitation and metabolic regulation affect the response of respiration of bulky plant organs such as fruit to reduced O2 levels in the surrounding atmosphere. Diffusion limitation greatly affects fruit respiration at high temperature, but at low temperature respiration is reduced through a regulatory process, presumably a response to a signal generated by a plant oxygen sensor. The response of respiration to O2 is time dependent and is highly sensitive, particularly at low O2 levels in the surrounding atmosphere. Down-regulation of the respiration at low temperatures may save internal O2 and relieve hypoxic conditions in the fruit.status: publishe