Microstructural characterization of multiphase chocolate using X-ray microtomography

In this study, X-ray microtomography (μCT) was used for the image analysis of the microstructure of 12 types of Italian aerated chocolate chosen to exhibit variability in terms of cocoa mass content. Appropriate quantitative 3-dimensional parameters describing the microstructure were calculated, for example, the structure thickness (ST), object structure volume ratio (OSVR), and the percentage object volume (POV). Chemical analysis was also performed to correlate the microstructural data to the chemical composition of the samples. Correlation between the μCT parameters acquired for the pore microstructure evaluation and the chemical analysis revealed that the sugar crystals content does not influence the pore structure and content. On the other hand, it revealed that there is a strong correlation between the POV and the sugar content obtained by chemical analysis. The results from this study show that μCT is a suitable technique for the microstructural analysis of confectionary products such as chocolates and not only does it provide an accurate analysis of the pores and microstructure but the data obtained could also be used to aid in the assessment of its composition and consistency with label specifications. PRACTICAL APPLICATION: X-ray microtomography (μCT) is a noninvasive and nondestructive 3-D imaging technique that has several advantages over other methods, including the ability to image low-moisture materials. Given the enormous success of μCT in medical applications, material science, chemical engineering, geology, and biology, it is not surprising that in recent years much attention has been focused on extending this imaging technique to food science as a useful technique to aid in the study of food microstructure. X-ray microtomography provides in-depth information on the microstructure of the food product being tested; therefore, a better understanding of the physical structure of the product and from an engineering perspective, knowledge about the microstructure of foods can be used to identify the important processing parameters that affect the quality of a product.     

基于X射线无损研究霉变对小麦籽粒三维结构的影响

食品微观结构在确定其最终产品性能方面起着至关重要的作用,霉菌又是粮食储藏期危害非常严重的微生物类群,目前对粮粒感染霉菌后的研究多是间接的、破坏性的,无损的研究食品感染霉菌后内部微观结构的变化非常困难。X射线断层扫描技术提供了一个极好的工具来无损的评估食品内部的组分,本文利用X射线断层扫描法实现了小麦籽粒发霉后内部特征的三维可视化和定量分析。利用图像滤波、阈值分割、重建算法对X射线断层扫描获取的图像进行重建和渲染,实现了感染籽粒及内部孔隙的三维可视化,除了可视化还获取了如籽粒体积、籽粒内部孔隙率等参数。X射线断层扫描是一种强有力的工具,可以用于粮食储藏期间易发霉部位如(粮仓墙壁附近、粮粒表层)以及粮食在深加工前是否霉变的区分检测,用于无损检测单颗小麦籽粒等生物材料的损伤和微观结构组织的变化。     

图像分析技术在谷物食品研究中的新应用

介绍了近几年来图像分析技术在谷物食品结构研究中的应用新进展。其中利用磁共振成像技术对面包孔洞组织进行2D平面的非侵入性扫描研究，分辨率高，并且可以对面包生产过程中气孔动态变化进行追踪和统计；X光计算机微观断层扫描技术在计算机辅助下可以将物体不同角度X光扫描图像进行重建组合，将物体内部3D立体结构重现，并对任意平面进行非侵入性统计研究。     

Microstructure evolution affecting the rehydration of dried mushrooms during instant controlled pressure drop combined hot air drying (DIC-HA)

This paper presents a study on the microstructure evolution providing good rehydration performance of shiitake mushroom after instant controlled pressure drop combined with hot air drying (DIC-HA). The effect of variations of DIC process parameters on the cell membrane was studied via the electrical conductivity of rehydration liquid as well as transmission electron microscopy (TEM). Microstructural properties of dried products, including porosity and connectivity, were studied by scanning electron microscopy (SEM) and X-ray micro-computed tomography (μCT). The results confirm that DIC pretreatment can facilitate a higher porosity of mushroom tissue, thus preventing collapse during subsequent hot air drying – provided that the product temperature remains below a critical temperature for retaining the integrity of the cell membrane. A new insight into the role of instant controlled pressure drop is to improve the microstructure of the samples. The porous structure implies potential innovative applications in the production of dry foods distinguished by good rehydration behavior.     

Effects of freezing on cell structure of fresh cellular food materials: A review

BackgroundFresh cellular food materials including fruits and vegetables and animal tissues normally consist of fine organized cellular structures. Freezing is a common method to preserve the quality and safety of these cellular foods. However, the formation of ice crystals during food freezing may cause damage to the food microstructure, leading to the deterioration of food quality after thawing.Scope and approachThis review offers current knowledge on freezing damage to cell structure of fresh cellular food materials. Effects of cell structure and water distribution on the texture and sensory properties of fresh cellular foods are presented. Mechanisms of cell structure damages caused by freezing are discussed. Novel methods to control the formation of ice crystals and preserve cell structures are also provided.Key findings and conclusionsThe quality of cellular foods after frozen-thawed is highly correlated with the integrity and viability of tissue cells. The formation of ice crystals, water migration and the inherent characteristics of cell structure are regarded as the main factors affecting the cell structure during freezing. For obtaining better quality of frozen products, further investigation and understanding on freezing damage to cell structure of fresh cellular foods is necessary. It is hoped that the current review will provide more information on improving frozen food quality for the frozen food industry.     

Imaging food freezing using X-ray microtomography

X‐ray micro‐computed tomography (X‐ray micro‐CT) has been applied to visualise ice crystal structures formed during freezing of a number of foods. Materials were frozen unidirectionally at ?5 °C and then freeze‐dried to remove the ice crystal structure and leave voids that can be measured by the X‐ray. The system reconstructs the 3‐D image based on a set of 2‐D images, and is capable of micrometre‐scale visualisation. This study demonstrates the capability of the technique to characterise the internal ice crystal microstructure of a range of frozen materials; meat, fish, chicken, potato, cheese and carrot. Results show the voids corresponding to the ice crystals formed within these materials at different directions to the heat flux and various axial positions. Electron microscopy of the same materials, both fresh and frozen at ?5 °C, indicates the same shape of voids seen by the tomographic technique. Ice crystal parameters such as size, area and width can be quantified by the technique. Ice crystals in carrot were larger than in the other materials, while cheese and potato had the lowest values. The ice crystal distribution of all the experimental materials varied with axial distance from cooling surface; the closer the measurement was to the cooling surface, the smaller the crystal size. The results demonstrate that X‐ray micro‐CT might be useful in the analysis of frozen foods.     

Use of High-Resolution X-Ray Micro-Computed Tomography for the Analysis of Internal Structural Changes in Maize Infected with <Emphasis Type="Italic">Fusarium verticillioides</Emphasis>

X-ray micro-computed tomography (X-ray micro-CT) is a non-destructive, three-dimensional (3D) imaging and analysis technique for the investigation of internal structure of a large variety of materials, including agricultural produce. As a relatively new method in the field of food science, X-ray micro-CT has been applied successfully to obtain micro-structural information of foods undergoing different physical and chemical changes. In this study, high-resolution X-ray micro-CT was used for non-destructive analysis of the internal structure of maize kernels infected with Fusarium verticillioides. The major anatomical features of the maize kernel were identified based on their differences in X-ray attenuation, i.e. the germ, scutellum, vitreous and floury endosperm. Fungal infection caused changes in the internal structure of the kernels over time, which included a decrease in total kernel volume and an increase in total volume of void space, with more voids observed in the germ and floury endosperm regions. No significant (P > 0.05) difference was observed between the control and the infected kernels; it was apparent that the changes observed in the infected kernels were not solely as a result of fungal growth. The grey level histograms of the control and infected kernels shifted to the lower grey value intensity range over time indicating an increase in void space within the kernels. In the 3D images, the increase in total volume of void space with fungal progression was clearer and the effect of fungal damage on the internal structure was evident.     

A Novel Approach to Study Biscuits and Breadsticks Using X-Ray Computed Tomography

Abstract: In this study X-ray microtomography (μCT) was used for analysis of the microstructure of 6 different types of Italian biscuits and 3 types of Italian breadsticks. Appropriate quantitative 3-D parameters describing the microstructure were calculated, such as the structure thickness (ST), the object structure volume ratio (OSVR), the degree of anisotropy (DA), and the percentage object volume (POV). Sensory analysis was also performed to discriminate samples on the basis of texture characteristics. A correlation between microstructural data (OSVR for biscuits and OSVR, POV, and DA for breadsticks) and sample crunchiness was also found. Results obtained from the current study showed that analysis at a microscopic level could be useful to the food industry, as the accurate calculation of number, dimension, and distribution of pores in the products could be used to improve the sensorial properties of food. Further study by μCT could be carried out to correlate microstructure to specific ingredients and process conditions to allow obtaining more tailored food.     

Sugar-free aerated chocolate: Production,investigation of bubble features using X-ray computed tomography and image processing

In contrast to other imaging techniques, X-ray imaging does not destruct the internal structure of the sample being imaged. Furthermore, this technique is able to capture numerous images of the sample at a low slice thickness, which is almost impossible in other imaging techniques. In this study, sugar was replaced with inulin:maltodextrin mixtures at ratios of 25:75 (i25), 50:50 (i50), and 75:25 (i75). Then, nitrogen (N₂) and carbon dioxide (CO₂) were injected into the three mixtures as well as the sugar-containing sample (control) at pressures of 3, 4.5, and 6 bar to produce aerated chocolate. The images of the samples were captured using X-ray computed tomography (XCT). After processing, they were segmented using the Chan–Vese model. Image segmentation showed that the Chan–Vese method, compared with adaptive thresholding, was more able to segment the images and remove the noise. The bubble total volume (10440 ± 9206 mm³) and average diameter (1.30 ± 0.10 mm) of the control were larger than those of the other samples. The results also demonstrated that the sugar-free aerated samples had lower hardness than the corresponding unaerated ones. However, it was reversed in the case of the control. This research sheds light on the industrialization of the production of aerated chocolate and the application of XCT and image processing in the analysis of the microstructure of aerated products.     

Use of non-invasive X-ray microtomography for characterizing microstructure of extruded biopolymer foams

Understanding foam microstructure formation is important for a priori design and engineering of new biopolymer-based products for both food and industrial applications. However, this has been hindered by unavailability of an imaging technology to characterize the cellular structure of foams accurately. This study investigated a non-invasive imaging technology, X-ray microtomography (XMT), for visualization and measurement of microstructural features of biopolymer foams. Brittle corn starch foams with two levels (5% and 15%) of whey protein concentrate (34% protein) factorialized with two moisture contents (26% or 34%) were produced using extrusion. XMT allowed non-invasive imaging of sample cross-sections at various depths, and facilitated accurate and hitherto impossible measurements of features like true cell size distribution (bi-modal), average diameter (0.58 to 2.27 mm), open wall area fraction (0.068 to 0.099), cell wall thickness (0.09 to 0.15 mm), and true void fraction (0.63 to 0.84). Results indicated XMT is superior to conventional imaging techniques for characterizing foam microstructure.     

Synergistic effect of microwave 3D print and transglutaminase on the self-gelation of surimi during printing

To improve the molding quality of 3D printed surimi products under the disturbance of self-gravity and post-processing, the synergistic effect of a microwave 3D print (MW3DP) and transglutaminase (TGase) on the self-gelation process of surimi from fluid to solid gel state during 3D printing is investigated. Simulation and 3D printing results show that microwave power affected the extrudability by changing the temperature distribution of surimi in the nozzle. Rheological properties of the squeezed-out surimi were monitored while the gel properties, microstructure and self-gelation mechanism of products after printing were analyzed. Surimi exhibited shear-thinning behavior when microwave power was less than 60 W/g. After printing, the solid gels with better shape fidelity and large protein aggregates appeared at 40 and 50 W/g when TGase was added. Results indicate that hydrogen bonds and ɛ-(γ-Glu)-Lys are main forces to maintain molding quality, and TGase is activated by microwaves to promote the self-gelation process.Industrial relevance3D food printing, as an emerging technology in food industry, has great potential in meeting the individual needs of consumers for shapes and nutrition. One of the challenges that restricts the large-scale industrialization and commercialization of 3D food printing is that deformation will occur during printing and subsequent processing because most food materials are still flowing after printing. This study provided a synergistic method of MW3DP with a focused heating mode and TGase, realizing self-gelation of surimi during printing. A solid product with high resistance to deformation was obtained in this condition. Valuable guidance is provided to obtain heat-induced solid products with better shape fidelity. In addition, a more complex hollow shape can be printed to improve the personalization of food manufacturing, thus promoting further applications of 3D printing in food industry.     

Development of an on-line optical method for assessment of the bubble size and morphology in aerated food products

The quality of whipped products of the food industry is closely linked to the characteristics of the dispersed gas phase, such as the bubble morphology, the mean bubble size and the uniformity of the bubble size distribution. Here, an on-line method based on imaging techniques was developed for measuring these quantities in food foams manufactured in a continuous foaming device. On-line image acquisition was based on a quartz visualization cell that ensured a continuous renewal of the samples. The mean bubble size and the bubble size distribution were obtained using a semi-automated image analysis procedure. The method was validated on four kinds of aerated food emulsions (ice cream, whipped cream, aerated fresh cheese and a foamed sauce), corresponding to a large range of overrun (30–180%). The σ/d₃₂ ratio of bubble size distributions of dairy foamed emulsions was shown to be nearly constant, regardless of the recipe and of operating conditions.     

Granulometry of bread crumb grain: Contributions of 2D and 3D image analysis at different scale

Six bread crumbs were prepared from three different recipes and three baking procedures. Images of crumb were acquired in 2D at a macroscopic scale by using a flat bed scanner (resolution 85 μm) and in 3D at a local scale by X-ray tomography (resolution 10 μm). The cellular structure was assessed by mathematical morphology. 2D image analysis was completed by principal component analysis. The first principal component was found to reflect crumb fineness, in agreement with the mean cell size determined in 3D at a local scale. 3D mean cell wall size were about 220 μm and were not significantly different. The second principal component was linked to the 2D macroscopic heterogeneity of the crumb and to the macroscopic cell wall thickness. 2D images can be applied to the rapid control of crumb grain and could be used to quantify the cellular structure for the calculation of mechanical properties.     

Microscopic deformation mechanisms of unidirectional fiber bundles under transverse compressive stresses

The high-performance filament yarns, such as carbon fiber yarn, glass fiber yarn, and Kevlar fiber yarn, have characterized as unidirectional,high parallel filament in fiber bundle. However, due to the difficulties in statistically analyzing the micro-structural characteristics of high-performance fiber bundles comprising of thousands of filaments, Nylon (PA6) filament yarns were chosen as the substitute of high-performance fiber bundles to study the deformation micro-mechanisms of fiber bundles under transverse compressive stresses. In order to evaluate the effects of different compressive stresses on the deformation properties, the synchrotron radiation X-ray micro-computed tomography (micro-CT) was used to obtain cross-section images of the fiber bundle during the compression testing. In particular, the influences of compressive stress on the fiber volume fraction, fiber distribution, fiber contact, and fiber orientation were studied. Results indicate a strong dependence of the microstructure of fiber bundles on the compressive stress.     

Stabilising emulsion‐based colloidal structures with mixed food ingredients

The physical scientist views food as a complex form of soft matter. The complexity has its origin in the numerous ingredients that are typically mixed together and the subtle variations in microstructure and texture induced by thermal and mechanical processing. The colloid science approach to food product formulation is based on the assumption that the major product attributes such as appearance, rheology and physical stability are determined by the spatial distribution and interactions of a small number of generic structural entities (biopolymers, particles, droplets, bubbles, crystals) organised in various kinds of structural arrangements (layers, complexes, aggregates, networks). This review describes some recent advances in this field with reference to three discrete classes of dispersed systems: particle‐stabilised emulsions, emulsion gels and aerated emulsions. Particular attention is directed towards explaining the crucial role of the macromolecular ingredients (proteins and polysaccharides) in controlling the formation and stabilisation of the colloidal structures. The ultimate objective of this research is to provide the basic physicochemical insight required for the reliable manufacture of novel structured foods with an appealing taste and texture, whilst incorporating a more healthy set of ingredients than those found in many existing traditional products. © 2012 Society of Chemical Industry     

Microstructure of minerals and yerba mate extract co-crystallized with sucrose

Co-crystallization with sucrose is an interesting alternative for handling and preservation of different active compounds used in the food industry. Sucrose products containing different active compounds (calcium lactate, magnesium sulphate and yerba mate extract) were obtained by co-crystallization. The microstructure of these products and raw materials was analyzed by Differential Scanning Calorimetry (DSC), X-rays Diffraction (XRD) and Scanning Electron Microscopy (SEM). The co-crystallized products showed the basic crystalline structure of the treated sucrose without active compound. Mineral distribution in the co-crystallized products was uniform as seen by Energy Dispersive X-rays (EDX). DSC and X-rays analysis showed that the salts were partially dehydrated during the process, yielding products with a crystalline sucrose matrix and, both, anhydrous and hydrated forms of the salts. This characterization helped understanding macroscopic behaviour of the products.     

Extrusion,structure and mechanical properties of complex starchy foams

Wheat-based extruded foams were generated according to different conditions of barrel temperature (120, 140 and 160 °C), feed moisture content (20%, 22% and 24%), screw speed (400, 600 and 800 rpm), die opening (0.75, 1 and 1.25 mm) and addition of sucrose and sodium bicarbonate at different levels (0%, 3%, 6% and 0%, 0.2%, 0.4%, respectively). Their cellular structure, analyzed by micro-computed X-ray tomography, was linked to the bulk expansion properties and enabled to explain the discrepancies in stress at rupture values obtained with a 3-point bending test. Samples with a wide range of relative densities (0.09–0.48), mean cell sizes (240–2710 μm), mean cell wall thicknesses (195–396 μm) and cell densities (430–37670 cm⁻³) were obtained. Most of the samples showed an anisotropic expansion with a favoured radial expansion, resulting in cellular structures with larger and less numerous cells and shapes closer to ellipsoids than to spheres that would be expected for isotropic expansion. A good fit with the Gibson and Ashby model was observed for mechanical properties. For similar relative densities, slight but significant differences in the stress at rupture might be explained by differences in cellular structure.     

3D Microstructure of supercritical fluid extrudates. II: Cell anisotropy and the mechanical properties

The mechanical properties of biopolymeric cellular foams are often governed by their microstructure. 2D and 3D microstructural data of supercritical fluid extrudates were obtained with X-ray microtomography and correlated with the mechanical properties determined using compression and three-point bending tests. Cell size from transverse cross-sections of SCFX extrudates decreased with radial distance from the center. In the longitudinal direction, the cell shapes were more elliptical than spherical and were aligned along the extrusion direction. These findings indicated the presence of a certain degree of anisotropy in SCFX extrudates in both directions. Both piece density and the ratio of cell wall thickness to cell diameter were observed to be good predictors of compressive and flexural mechanical properties, including jaggedness parameters. Compressive modulus data suggested that cell shape anisotropy due to cell elongation in the longitudinal direction actually affected the mechanical properties of SCFX extrudates. X-ray microtomography was found to be useful to investigate 2D and 3D morphology of SCFX extrudates, including cell shape and cell size anisotropy.     

Application and challenges of 3D food printing technology in manned spaceflight: a review

Three-dimensional (3D) food printing is a digital food engineering method that has a remarkable application potential in long-term manned spaceflight. Extrusion-based 3D food printing, among the available 3D food printing techniques utilised in the food industry, is one of the most suitable printing methods for manned spaceflight. Extrusion-based 3D food printing could suffice most of the energy and personalised nutritional requirements of astronauts during long-term stay in space by utilising fruits, vegetables, meat products, and nutrients as printing materials. However, 3D food printing in manned spaceflight is still limited by technologies and costs such as printing materials, microgravity, post-processability of food, and engineering transportation under the existing technical conditions. Therefore, this article reviews the 3D food printing and manned spaceflight technologies that are currently available and discusses the challenges involved in 3D food printing in manned spaceflight, thus providing a theoretical basis for future 3D food printing for space missions.     

Supplementation of extruded foams with wheat bran: Effect on textural properties

The objective of this study was to investigate the effect of wheat bran concentrations on the mechanical properties determining the texture of extruded carbohydrate matrices. For this wheat flour was extruded under different conditions with an increasing concentration of wheat bran. The mechanical properties were assessed using a threepoint bending test and the cellular structure was determined by micro-computed X-ray tomography. Regardless of the bran concentration, the stress at rupture of the extruded foams was positively correlated with their relative density according to the Gibson-Ashby model. At same relative densities and bran concentration, finer structures with higher density of small cells led to a higher mechanical strength of the foams. Expanded foams with added bran at an intermediate level showed increased mechanical strength. This was attributed to the finer cellular structures obtained.The effect of increasing the bran to a higher concentration on the mechanical properties was depending on the cell wall thickness and bran particle dimensions.