Imaging techniques for the study of food microstructure: a review

Structural formation during bread baking in a combined microwave-convective oven determined by sub-second in-situ synchrotron X-ray microtomography

A new concept has been developed for characterizing the real-time evolution of the three-dimensional pore and lamella microstructure of bread during baking using synchrotron X-ray microtomography (SRµCT). A commercial, combined microwave-convective oven was modified and installed at the TOMCAT synchrotron tomography beamline at the Swiss Light Source (SLS), to capture the 3D dough-to-bread structural development in-situ at the micrometer scale with an acquisition time of 400 ms. This allowed characterization and quantitative comparison of three baking technologies: (1) convective heating, (2) microwave heating, and (3) a combination of convective and microwave heating. A workflow for automatic batchwise image processing and analysis of 3D bread structures (1530 analyzed volumes in total) was established for porosity, individual pore volume, elongation, coordination number and local wall thickness, which allowed for evaluation of the impact of baking technology on the bread structure evolution. The results showed that the porosity, mean pore volume and mean coordination number increase with time and that the mean local cell wall thickness decreases with time. Small and more isolated pores are connecting with larger and already more connected pores as function of time. Clear dependencies are established during the whole baking process between the mean pore volume and porosity, and between the mean local wall thickness and the mean coordination number. This technique opens new opportunities for understanding the mechanisms governing the structural changes during baking and discern the parameters controlling the final bread quality.

Automatic segmentation for synchrotron-based imaging of porous bread dough using deep learning approach

In recent years, major capability improvements at synchrotron beamlines have given researchers the ability to capture more complex structures at a higher resolution within a very short time. This opens up the possibility of studying dynamic processes and observing resulting structural changes over time. However, such studies can create a huge quantity of 3D image data, which presents a major challenge for segmentation and analysis. Here tomography experiments at the Australian synchrotron source are examined, which were used to study bread dough formulations during rising and baking, resulting in over 460 individual 3D datasets. The current pipeline for segmentation and analysis involves semi-automated methods using commercial software that require a large amount of user input. This paper focuses on exploring machine learning methods to automate this process. The main challenge to be faced is in generating adequate training datasets to train the machine learning model. Creating training data by manually segmenting real images is very labour-intensive, so instead methods of automatically creating synthetic training datasets which have the same attributes of the original images have been tested. The generated synthetic images are used to train a U-Net model, which is then used to segment the original bread dough images. The trained U-Net outperformed the previously used segmentation techniques while taking less manual effort. This automated model for data segmentation would alleviate the time-consuming aspects of experimental workflow and would open the door to perform 4D characterization experiments with smaller time steps.

Investigation of food microstructure and texture using atomic force microscopy: A review

We review recent applications of atomic force microscopy (AFM) to characterize microstructural and textural properties of food materials. Based on interaction between probe and sample, AFM can image in three dimensions with nanoscale resolution especially in the vertical orientation. When the scanning probe is used as an indenter, mechanical features such as stiffness and elasticity can be analyzed. The linkage between structure and texture can thus be elucidated, providing the basis for many further future applications of AFM. Microstructure of simple systems such as polysaccharides, proteins, or lipids separately, as characterized by AFM, is discussed. Interaction of component mixtures gives rise to novel properties in complex food systems due to development of structure. AFM has been used to explore the morphological characteristics of such complexes and to investigate the effect of such characteristics on properties. Based on insights from such investigations, development of food products and manufacturing can be facilitated. Mechanical analysis is often carried out to evaluate the suitability of natural or artificial materials in food formulations. The textural properties of cellular tissues, food colloids, and biodegradable films can all be explored at nanometer scale, leading to the potential to connect texture to this fine structural level. More profound understanding of natural food materials will enable new classes of fabricated food products to be developed.

The effect of infrared drying to the microstructural structure and texture of whole Duku intact skin by means of scanning electron microscopy (SEM) technique

The Infrared method has the potential to extend the shelf life of duku fruit by drying the duku’s skin into "shell likeness". Duku’s skin drying using infrared method could change the shape and characteristics of duku’s skin which would significantly affect the length of fruit shelf life. The texture of duku’s skin for the treatment of infrared emitter distance of 6 cm, temperature of 400 °C and exposure time of 80 seconds was increasing with the storage time which made the fruit inside the skin to experience a passive modified atmosphere and increase the shelf life of duku. The 3D visual depiction of the optimization result on drying process using infrared had the largest porosity and cavity value in the treatment of infrared emitter distance of 10 cm, temperature of 300 °C, and exposure time of 80 seconds. At the magnification of 2500 times, with a resolution of 10 mm, it was found that the porosity and thickness of the duku’s void were greater than duku fruit without treatment. The result of the porosity also found that drying process with the infrared emitter distance of 6 cm at temperature of 400 °C, and exposure time of 80 seconds has more stable porosity (without collapsing) which confirmed the result found on the texture of the skin. The results of scanning electron microscopy analysis and 3D visual analysis confirmed the results of optimization that had previously performed in the drying process of duku fruit using infrared method.

Applicability of Confocal Raman Microscopy to Observe Microstructural Modifications of Cream Cheeses as Influenced by Freezing

Confocal Raman microscopy is a promising technique to derive information about microstructure, with minimal sample disruption. Raman emission bands are highly specific to molecular structure and with Raman spectroscopy it is thus possible to observe different classes of molecules in situ, in complex food matrices, without employing fluorescent dyes. In this work confocal Raman microscopy was employed to observe microstructural changes occurring after freezing and thawing in high-moisture cheeses, and the observations were compared to those obtained with confocal laser scanning microscopy. Two commercially available cream cheese products were imaged with both microscopy techniques. The lower resolution (1 µm/pixel) of confocal Raman microscopy prevented the observation of particles smaller than 1 µm that may be part of the structure (e.g., sugars). With confocal Raman microscopy it was possible to identify and map the large water domains formed during freezing and thawing in high-moisture cream cheese. The results were supported also by low resolution NMR analysis. NMR and Raman microscopy are complementary techniques that can be employed to distinguish between the two different commercial formulations, and different destabilization levels.

High pressure-assisted vacuum-freeze drying: A novel, efficient way to accelerate moisture migration in shrimp processing

High pressure processing (HPP), as nonthermal processing technology, has the potential to increase the drying rate due to its improvement of heat and mass exchange in different processes. In this study, the moisture migration in shrimps during HPP-vacuum-freeze drying (HPP-VFD) processes has been monitored by using low-field nuclear magnetic resonance and magnetic resonance image (MRI) in comparison with hot air-drying and VFD. Based on the T₂ relaxation spectra, three water fractions corresponding to bound water (hydrogen-bonded water), immobile water (water trapped by organization structure or cell member), and free water were observed. For group B, with increasing drying time (4 to 22 hr), the transverse relaxation times of T₂₁ , T₂₂ , and T₂₃ were significantly decreased (76.79%, 57.78%, and 40.9%) (P < 0.05). The content of immobile water (A₂₂ ) and free water (A₂₃ ) decreased (81.55% and 89.07%), whereas the bound water (A₂₁ ) increased (7.26%). In comparison with group B, the T₂₁ , T₂₂ , and T₂₃ of group C showed greater decrease (83.12%, 87.12%, and 89.57% for group C) so that HPP pretreatment could shorten the relaxation time. MRI analysis further proved that HPP-VFD drying has improved drying efficiency, and moisture migration was from the exterior to the interior part with increasing drying time. SEM analysis demonstrated that no significant damage of muscle fibers with narrower gaps was observed for groups B and C. Overall, HPP, as a pretreatment technology, could accelerate the moisture migration and improve the drying efficiency of VFD process for shrimp. PRACTICAL APPLICATION: High pressure processing (HPP) is now well known as a nonthermal processing technology and becoming increasingly acknowledged. However, there is limited information about its application in shrimp-drying process and the moisture dynamic of shrimp subjected to high pressure processing-assisted vacuum-freeze drying. This study could provide valuable information regarding the moisture status and migration in HPP-VFD shrimp monitored by LF-NMR and MRI methods. The results showed that HPP processing at 550 MPa for 10 min can be used as an interesting method for drying pretreatment, increasing its drying rate and consequently reducing its process time, and it demonstrated that the methods used in this study had good correlation coefficient with physicochemical properties of shrimp, which may be real-time and nondestructive monitoring methods for shrimp-drying process.

Nuclear magnetic resonance and chemometrics to assess geographical origin and quality of traditional food products

In this globalization era, the opening of the markets has put at almost everybody's disposal a wide variety of foods, allowing everybody to taste food flavors and aromas from different nations. Notwithstanding this opportunity, countries try to preserve their markets by developing protection policies. A few countries have adopted different denominations to label their "typical food" products in order to give them additional value. Besides, the term "typical food" is widely thought of as something anchored to the local traditions, with geographical meaning and made with typical raw materials. Then a "typical food" starts to be considered "traditional" when it is made following specific and old recipes. As a matter of fact, these products acquire particular organoleptic characteristics that are not reproducible when produced in different places. In this review, NMR studies coupled to multivariate statistical analysis are presented with the aim of determining geographical origin and key quality characteristics.