Spatial development of transport structures in apple (Malus x domestica Borkh.) fruit

The void network and vascular system are important pathways for the transport of gases, water and solutes in apple fruit (Malus x domestica Borkh). Here we used X-ray micro-tomography at various spatial resolutions to investigate the growth of these transport structures in 3D during fruit development of ‘Jonagold’ apple. The size of the void space and porosity in the cortex tissue increased considerably. In the core tissue, the porosity was consistently lower, and seemed to decrease towards the end of the maturation period. The voids in the core were more narrow and fragmented than the voids in the cortex. Both the void network in the core and in the cortex changed significantly in terms of void morphology. An automated segmentation protocol underestimated the total vasculature length by 9 to 12% in comparison to manually processed images. Vascular networks increased in length from a total of 5 meter at 9 weeks after full bloom, to more than 20 meter corresponding to 5 cm of vascular tissue per cubic centimeter of apple tissue. A high degree of branching in both the void network and vascular system and a complex three-dimensional pattern was observed across the whole fruit. The 3D visualisations of the transport structures may be useful for numerical modeling of organ growth and transport processes in fruit

X-ray microtomography provides new insights into vacuum impregnation of spinach leaves

Vacuum impregnation is used in the food industry to facilitate the impregnation of porous products with, e.g. firming, antioxidant, antimicrobial or cryoprotective agents. X-ray micro-tomography (CT) was used to study the process of vacuum impregnation in spinach leaves. Low (300 mbar absolute pressure) and mild vacuum (150 mbar absolute pressure) impregnation protocols were used to impregnate an isotonic solution of trehalose in the leaves and CT was used to make observations of the cross section of the impregnated samples and quantify their porosity. Results revealed that the free volume in the spongy mesophyll is easier to impregnate than the spaces around the palisade mesophyll. The low vacuum impregnation protocol provoked less impregnation close to the edge of the leaf than in its centre, probably accounting for an influence of the tissue structure on impregnation. The vacuum impregnation protocols tested in this investigation drastically decreased the proportion of large pores (>100 m) and increased the proportion of small pores (<50 m). The mild vacuum impregnation protocol, which was designed on the basis of measured apparent porosity, did not achieve full impregnation of the tissue.V. Panarese acknowledges the financial support from the Portuguese Foundation of Science (FCT). F. Gomez Galindo acknowledges the financial support from European Community's Seventh Framework Program (FP7/2007-2013) under grant agreement no. 245280, also known under the acronym PRESERF. Financial support of FWO Vlaanderen (project G.0645.13), the Flemish government agency for Innovation by Science and Technology (project IWT SBO120033 TomFood) and the University of Leuven (project OT 12/055) is gratefully acknowledged. Dennis Cantre is an IRO scholar of KU Leuven. We also acknowledge the Hercules foundation for supporting the X-ray CT facility (AKUL001(HER/09/016))

Microstructural understanding of chilling injury in mango in relation to fruit quality

Mango is considered the king of tropical fruit due to its appealing color and flavor. It is also considered as the most important fruit of Asia. The fruit currently ranks fifth in the world production with the Philippines included among the ranks of top mango producers. Mango is recommended to be included in the daily diet of consumers due to its richness in antioxidants. Mango, however, has a short shelf life, which requires cold storage to preserve quality and extend shelf stability. In addition, application of cold storage is also very limited as storage below optimal temperature for a sufficient time induces chilling injury (CI). This condition limits the postharvest preservation and marketing potential of mango, which consequently affects the export potential of mango to distant markets. CI is classified as a physiological disorder, which is characterized by grayish scald like discoloration and pitting in the peel, followed by uneven ripening and poor flavor and color development. CI, like other physiological disorders, is the result of imbalances in metabolism which are greatly affected by respiration and gas transport. This underlines the importance of three-dimensional (3-D) microstructure and pore network in the development of CI. The absence of a technique to completely control CI reflects the lack of sufficient understanding on the changes prior to the visual appearance of the symptoms and the need to unravel the mechanism of tissue breakdown due to CI. Previous studies analyzed only 2-D images, not based on measurements of the whole volume and cannot be used for determining the changes in the 3-D microstructure. To this end, X-ray microtomography (μCT) protocols and image processing tools were developed to characterize the microstructure of mango. The protocols and tools were applied to obtain 3-D images of mango tissues at different stages during ripening of the fruit, and via 3-D image processing and multivariate statistics to investigate the changes in 3-D microstructure of a healthy fruit. This provided the basis for comparing the 3-D microstructural changes in the fruit during CI. 3-D analysis of structural parameters revealed changes in microstructure along the radial axis of the fruit and clear changes in the microstructure during ripening. Multivariate statistical analysis unveiled that ripening was associated with a decrease in pore size, and increase in pore fragmentation and pore specific surface area. An integrated understanding on the effect of these microstructural changes in the postharvest ripening of the fruit was presented by investigating the observed microstructural changes in relation to the evolution of quality during ripening. This was accomplished by monitoring the changes in 3-D microstructure at different stages of ripening and observing the concurrent changes in quality. Quality changes are known to be influenced by the postharvest metabolism, which is directly affected by the changes in microstructure. The changes in quality indices such as firmness, color, taste and aroma greatly affect price competitiveness and consumer acceptability, which are essential to the marketability of the fruit. Microstructural changes associated with cell leakage were supported by the increase in the electrolyte leakage measurement of the peel. In addition, possible effects of microstructure on respiration, color development, firmness and flavor development were identified. Multivariate statistics identified structural parameters, aroma volatiles and other quality parameters that are important to ripening. Next, we investigated the 3-D microstructural changes during CI. This was accomplished through the use of X-ray μCT of tissue obtained at different stages during cold storage, three-dimensional image processing and multivariate statistics in relation to changes in CI indicators. Microstructural changes observed during CI included a decrease in porosity, pore size and pore connectivity due to cell leakage and tissue breakdown, which was followed by an increase in pore size due to cavity formation. These changes contribute significantly to CI by drastically changing tissue aeration and water movement. Multivariate statistics identified pore connectivity and Euler number as the most important parameters in relation to CI. These changes were found to adversely affect the quality resulting in the expression of CI symptoms, increase of electrolyte leakage, limited respiration, less color development, impaired citric acid metabolism and aroma volatile production. Multivariate statistics identified structural parameters, aroma volatiles and other quality parameters that are important to CI. In conclusion, the study showed the feasibility of using μCT to characterize the microstructure of mango fruit. Automatic segmentation and analysis allowed quantification of individual cells and tissue breakdown due to CI. Microstructure analysis allowed identification of the role of intracellular water leakage in tissue breakdown, cavity formation and peel and lenticel discoloration. Microstructural changes during CI support the hypothesis that changes in tissue and pore structure in mango fruit contribute significantly to the development of postharvest tissue disorders by drastically affecting tissue aeration and water movement, identical to what has been observed in other fruit species. This study confirmed the effect of microstructure on aroma volatiles, due to its adverse effects on gas exchange properties, limiting the respiration and shifting the metabolism of the fruit. Multivariate statistics allowed identification of structural and quality parameters that are important to ripening and CI. It served as a tool to formulate a conceptual model to describe CI, revealing a complex and in-depth relation underlying the effect of CI on microstructure and quality.Acknowledgements i Abstract iii Abbreviations and Symbols xi Table of Contents xv 1 Introduction 1 1.1 Mango: the Philippine ‘Carabao’ cultivar 1 1.1.1 Botany 1 1.1.2 Economic importance 2 1.1.3 Postharvest quality and handling 4 1.1.4 Chilling injury (CI) 7 1.2 General problem statement 9 1.3 Objectives and outline 11 2 Mango: microstructure and quality during ripening and chilling injury (CI) 13 2.1 Mango fruit anatomy 14 2.2 Histology of mango fruit 14 2.2.1 Exocarp 14 2.2.2 Mesocarp 16 2.2.3 Endocarp 17 2.3 Mango quality 19 2.3.1 Color 19 2.3.2 Firmness 21 2.3.3 Sugars and acids 22 2.3.4 Aroma 24 2.4 Mango ripening 27 2.4.1 Physiology 27 2.4.2 Effect of ripening on quality attributes of mango 31 2.5 Chilling injury (CI) in mango 36 2.5.1 Symptoms 36 2.5.2 Effect of CI on quality attributes of mango 39 2.5.3 Factors affecting CI 42 2.6 Understanding the mechanism of CI 43 2.7 Microstructure imaging 45 2.7.1 Definition 45 2.7.2 Requirements 45 2.7.3 Imaging methods 46 2.7.4 Assessment of methods 48 2.8 X-ray microtomography (µCT) 50 2.9 Conclusion 55 3 Characterization of the 3-D microstructure of mango fruit (Mangifera indica L. cv. Carabao) during ripening using X-ray microtomography1 57 3.1 Introduction 58 3.2 Materials and methods 59 3.2.1 Mango fruit and treatments 59 3.2.2 X-ray microtomography 59 3.2.3 Image processing 61 3.2.4 Representative elementary volume analysis 65 3.2.5 Statistical analysis 65 3.3 Results 65 3.3.1 Image segmentation 65 3.3.2 Representative elementary volume analysis 67 3.3.3 3-D structural parameters of mesocarp cells 68 3.3.4 Pore network analysis 72 3.3.5 Partial least squares - discriminant analysis 79 3.4 Discussion 80 3.5 Conclusion 83 4 Evolution of quality in mango (Mangifera indica L. cv. Carabao) during ripening 85 4.1 Introduction 86 4.2 Materials and methods 86 4.2.1 Mango fruit 86 4.2.2 X-ray microtomography and image processing 87 4.2.3 Respiration and ethylene production 87 4.2.4 Color, firmness and density 87 4.2.5 Soluble solids content (SSC), pH and total titratable acidity 88 4.2.6 Aroma volatile extraction and analysis 88 4.2.7 Electrolyte leakage 89 4.2.8 Statistical analysis 90 4.3 Results 91 4.3.1 Microstructure analysis 91 4.3.2 Respiration and ethylene production 92 4.3.3 Color, firmness and density 93 4.3.4 SSC, pH and total titratable acidity 94 4.3.5 Electrolyte leakage 95 4.3.6 Aroma volatile compounds 96 4.3.7 Multivariate analysis 97 4.4 Discussion 106 4.4.1 Microstructure analysis 106 4.4.2 Respiration and ethylene production 106 4.4.3 Color, firmness and density 107 4.4.4 SSC, pH and total titratable acidity 107 4.4.5 Electrolyte leakage 107 4.4.6 Aroma volatile compounds 108 4.4.7 Multivariate analysis 109 4.5 Conclusions 113 5 Tissue breakdown of mango (Mangifera indica L. cv. Carabao) due to chilling injury1 115 5.1 Introduction 116 5.2 Materials and methods 117 5.2.1 Mango fruit and treatments 117 5.2.2 CI incidence and percent area chilling injured (CI area) 118 5.2.3 Color and fruit surface conductance 119 5.2.4 X-ray microtomography 119 5.2.5 Image processing and analysis 120 5.2.6 Statistical analysis 120 5.3 Results 120 5.3.1 CI incidence and percent area chilling injured (CI area) 120 5.3.2 Color and fruit surface conductance 121 5.3.3 Mango tissue pore network analysis 123 5.3.4 Analysis of tissue parameters during CI development 126 5.4 Discussion 130 5.4.1 CI affects peel and pulp color 130 5.4.2 Peel and lenticel discoloration is associated with intracellular water leaking from damaged cells in the outer mesocarp 130 5.4.3 Structural changes of CI are distinct from normal storage, but are similar to other physiological disorders 132 5.5 Conclusion 134 6 Deterioration of quality in mango (Mangifera indica L. cv. Carabao) due to CI 135 6.1 Introduction 136 6.2 Materials and methods 136 6.2.1 Mango fruit and treatments 136 6.2.2 CI incidence and percent area chilling injured (CI area) 137 6.2.3 X-ray microtomography 138 6.2.4 Respiration and ethylene production 139 6.2.5 Color, firmness and density 139 6.2.6 Soluble solids content (SSC), pH and total titratable acidity 139 6.2.7 Aroma volatile extraction and analysis 140 6.2.8 Electrolyte leakage 141 6.2.9 Statistical analysis 141 6.3 Results 142 6.3.1 CI incidence and percent area chilling injured (CI area) 142 6.3.2 Microstructure analysis 142 6.3.3 Respiration and ethylene production 145 6.3.4 Color, firmness and density 146 6.3.5 SSC, pH and total titratable acidity 148 6.3.6 Electrolyte leakage 149 6.3.7 Aroma volatile compounds 150 6.3.8 Multivariate analysis 153 6.4 Discussion 158 6.4.1 A distinct microstructural and senescence pattern was observed in CI and control fruit 158 6.4.2 Increased electrolyte leakage and permeability of the intercellular space indicates membrane damage due to CI 158 6.4.3 CI adversely affected respiration and induced ethylene production rate 159 6.4.4 Microstructure and ultrastructure changes may influence color development during CI 160 6.4.5 Firmness was less affected by CI, but may be influenced by microstructure 161 6.4.6 CI adversely affected citric acid metabolism 161 6.4.7 CI affected aroma volatile evolution 162 6.5 Conclusions 165 7 General conclusions and future perspectives 167 7.1 General conclusions 167 7.2 Conceptual model of CI in mango 168 7.3 Future research 173 8 References 175 9 List of publications 197 9.1 Articles in internationally reviewed academic journals 197 9.2 Papers at international scientific conferences and symposia, published in full in proceedings 198 9.3 Meeting abstracts, presented at international scientific conferences and symposia, published or not published in proceedings or journals 199nrpages: 221status: publishe

Short wave infrared hyperspectral imaging for non-destructive quality assessment of mangoes

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X-ray microtomography of mango tissue breakdown development due to chilling injury

The study aims to provide an insight in the 3-D microstructural changes caused by chilling injury in mango. This was accomplished through the use of X-ray microtomography (μCT) of tissue of mango (cv. Carabao) during storage under chilling injury inducing conditions. X-ray μCT provided 3D visualization and quantification of the changes in tissue structure and pore networks during chilling injury development. The largest changes were observed in mango outer mesocarp, including significant changes in cell shape, pore size and shape and connectivity of the pores. Microstructural results provided support to the hypothesis that intracellular water leakage occurs, contributing to discoloration of the peel. Furthermore, water leakage adversely affects tissue aeration which inhibits respiration of the tissue aggravating tissue breakdown. To interpret the microstructural changes in relation to chilling injury development, multivariate statistics was applied. This analysis identified several microstructural descriptors related to the severity of chilling injury. This study will generate detailed understanding of the structural changes leading to the symptoms of chilling injury.status: accepte

Characterization of the 3-D microstructure of mango (Mangifera indica L. cv. Carabao) during ripening using X-ray computed microtomography

In this study, X-ray computed microtomography (X-ray μCT) was applied to investigate the changes in the 3-D microstructure of mango during ripening at 20 °C. X-ray μCT provided a unique insight of the undamaged tissue and pore network during ripening. Analysis of the pore and tissue network revealed differences in the microstructure along the radial axis of the fruit and microstructural changes during ripening. Multivariate statistical analysis unveiled that ripening was associated with a decrease in pore size, and increase in pore fragmentation and pore specific surface area. These structural parameters have the highest discriminating ability, correctly classifying unripe from ripe fruit samples. The study concludes that ripening can be successfully characterized on the basis of its 3-D microstructure using X-ray microtomography. Industrial relevance: This study identified important parameters to describe the ripening process on the basis of microstructure. As today's microtomography technology allows for scanning only a small tissue sample from the fruit, the pace at which tomography technology is advancing will allow for scanning whole fruit with sufficient resolution and without any need for sample preparation. Results from this study could be applied for non-destructive determination of fruit microstructure for assessing fruit quality in relation to the ripening process.publisher: Elsevier articletitle: Characterization of the 3-D microstructure of mango (Mangifera indica L. cv. Carabao) during ripening using X-ray computed microtomography journaltitle: Innovative Food Science & Emerging Technologies articlelink: http://dx.doi.org/10.1016/j.ifset.2013.12.008 content_type: article copyright: Copyright © 2013 Elsevier Ltd. All rights reserved.status: publishe

Visualizing 3D Food Microstructure Using Tomographic Methods: Advantages and Disadvantages

X-ray micro–computed tomography (micro-CT) provides the unique ability to capture intact internal microstructure data without significant preparation of the sample. The fundamentals of micro-CT technology are briefly described along with a short introduction to basic image processing, quantitative analysis, and derivative computational modeling. The applications and limitations of micro-CT in industries such as meat, dairy, postharvest, and bread/confectionary are discussed to serve as a guideline to the plausibility of utilizing the technique for detecting features of interest. Component volume fractions, their respective size/shape distributions, and connectivity, for example, can be utilized for product development, manufacturing process tuning and/or troubleshooting. In addition to determining structure-function relations, micro-CT can be used for foreign material detection to further ensure product quality and safety. In most usage scenarios, micro-CT in its current form is perfectly adequate for determining microstructure in a wide variety of food products. However, in low-contrast and low-stability samples, emphasis is placed on the shortcomings of the current systems to set realistic expectations for the intended users.status: publishe

Quantitative 3D Shape Description of Dust Particles from Treated Seeds by Means of X‑ray Micro-CT

Crop seeds are often treated with pesticides before planting. Pesticide-laden dust particles can be abraded from the seed coating during planting and expelled into the environment, damaging non-target organisms. Drift of these dust particles depends on their size, shape and density. In this work, we used X-ray micro-CT to examine the size, shape (sphericity) and porosity of dust particles from treated seeds of various crops. The dust properties quantified in this work were very variable in different crops. This variability may be a result of seed morphology, seed batch, treatment composition, treatment technology, seed cleaning or an interaction of these factors. The intra-particle porosity of seed treatment dust particles varied from 0.02 to 0.51 according to the crop and generally increased with particle size. Calculated settling velocities demonstrated that accounting for particle shape and porosity is important in drift studies. For example, the settling velocity of dust particles with an equivalent diameter of 200 µm may vary between 0.1 and 1.2 m s-1, depending on their shape and density. Our analysis shows that in a wind velocity of 5 m s-1, such particles ejected at 1 m height may travel between 4 and 50 m from the source before settling. While micro-CT is a valuable tool to characterize dust particles, the current image processing methodology limits the number of particles that can be analyzed.status: publishe

Tissue breakdown of mango (Mangifera indica L. cv. Carabao) due to chilling injury

Chilling injury (CI) presents a major problem in postharvest preservation and marketing potential of mango. In this study, tissue breakdown caused by chilling injury was investigated using X-ray computed microtomography (X-ray μCT). This provided a unique insight in 3-D changes in tissue structure and pore networks during chilling injury development. Evidence of cell collapse and cavity formation in severely chill injured fruit was apparent. In addition, microstructural evidence supporting the occurrence of intracellular water leakage was found. Quantitative analysis revealed that chilling injury was associated with, first, a decrease in porosity, pore size and pore connectivity due to cell leakage and tissue breakdown, which was followed by an increase in pore size due to cavity formation. Multivariate statistics identified pore connectivity and Euler number as the most important parameter in relation to chilling injury. The results support the hypothesis that changes in tissue and pore structure in mango fruit contribute significantly to the development of postharvest tissue disorders by drastic changes in tissue aeration and water movement, identical to what has been observed in other fruit species.publisher: Elsevier articletitle: Tissue breakdown of mango (Mangifera indica L. cv. Carabao) due to chilling injury journaltitle: Postharvest Biology and Technology articlelink: http://dx.doi.org/10.1016/j.postharvbio.2016.11.009 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved.status: publishe

Effect of oven and forced convection continuous tumble (FCCT) roasting on the microstructure and dry milling properties of white maize

The effect of oven and forced convection continuous tumble (FCCT) roasting on the microstructure of whole maize kernels was characterised and quantified using X-ray micro-computed tomography (μCT). The three dimensional(3-D) volumes, reconstructed from the two-dimensional (2-D) images, were segmented into regions of interests (ROIs), i.e. air, germ, floury and vitreous endosperm, and each region quantified. Oven roasting was associated with a larger increase in total kernel volume (10.8%) than FCCT roasting (3.4%) as well as a significant(P≤ 0.05) decrease in whole kernel relative density (oven =6.3%; FCCT=1.9%). FCCT roasting had almost no effect on material density, in contrast to a significant (P ≤0.05) decrease of 5.0% during oven roasting. Subsequent validation of the dry milling properties, i.e. percentage hominy chop, milling yield and hectolitre mass (HLM), indicated no significantly (P > 0.05) detrimental effect by either of the roasting methods. Industrial relevance: Roasting of maize can improve sensory, shelf life, nutritional and antioxidant properties with subsequent use in ready-to-eat foods and breakfast cereals. Roasting will inevitably affect the structure of maize, which in turn will affect the quality of the end product. This prompted the demand for non-destructive techniques that directly measure microstructural properties of food in order to link structure with quality. X-ray μCT in combination with image analysis uniquely illustrated the microstructural changes occurring during conventional oven and innovative FCCT roasting respectively. Furthermore, dry milling properties are important indicators of quality characteristics for the dry milling industry. The method described in this article can be applied to any food material to investigate structural properties.status: publishe