Imaging food freezing using X-ray microtomography

Causal factors concerning the texture of French fries manufactured at industrial scale

In this paper, we review the physical/chemical phenomena, contributing to the final texture of French fries, as occurs in the whole industrial production chain of frozen par-fried fries. Our discussion is organized following a multiscale hierarchy of these causal factors, where we distinguish the molecular, cellular, microstructural, and product levels. Using the same multiscale framework, we also discuss currently available theoretical knowledge, and experimental methods probing the relevant physical/chemical phenomena. We have identified knowledge gaps, and experimental methods are evaluated in terms of the effort and value of their results. With our overviews, we hope to give promising research directions such to arrive at a multiscale model, encompassing all causal factors relevant to the final texture. This multiscale model is the ultimate tool to evaluate process innovations for effects on final textural quality, which can be balanced against the impacts on sustainability and economics.

Non-Destructive Assessment of Microstructural Changes in Kabuli Chickpeas during Storage

The potential of hyperspectral imaging (HSI) and synchrotron phase-contrast micro computed tomography (SR-µCT) was evaluated to determine changes in chickpea quality during storage. Chickpea samples were stored for 16 wk at different combinations of moisture contents (MC of 9%, 11%, 13%, and 15% wet basis) and temperatures (10 °C, 20 °C, and 30 °C). Hyperspectral imaging was utilized to investigate the overall quality deterioration, and SR-µCT was used to study the microstructural changes during storage. Principal component analysis (PCA) and Partial Least Squares Discriminant Analysis (PLS-DA) were used as multivariate data analysis approaches for HSI data. Principal component analysis successfully grouped the samples based on relative humidity (RH) and storage temperatures, and the PLS-DA classification also resulted in reliable accuracy (between 80 and 99%) for RH-based and temperature-based classification. The SR-µCT results revealed that microstructural changes in kernels (9% and 15% MC) were dominant at higher temperatures (above 20 °C) as compared to lower temperatures (10 °C) during storage due to accelerated spoilage at higher temperatures (above 20 °C). Chickpeas which had internal irregularities like cracked endosperm and air spaces before storage were spoiled at lower moisture from 8 wk of storage.

Ice crystallization and structural changes in cheese during freezing and frozen storage: implications for functional properties

Temperature-mediated preservation techniques offer a simple, scalable, effective, and fairly efficient method of long-term storage of food products. In order to ensure the uninterrupted availability of cheese across the globe, a critical understanding of its techno-functional properties as affected by freezing and frozen storage is essential. Detailed studies of temperature-mediated molecular dynamics are available for relatively simpler and homogeneous systems like pure water, proteins, and carbohydrates. However, for heterogeneous systems like cheese, inter-component interactions at sub-zero temperatures have not been extensively covered. Ice crystallization during freezing causes dehydration of caseins and the formation of concentration gradients within the cheese matrix, causing undesirable changes in texture-functional attributes, but findings vary due to experimental conditions. A suitable combination of sample size, freezing rate, aging, and tempering can extend the shelf life of high- and low-moisture Mozzarella cheese. However, limited studies on other cheeses suggest that effects and suitability differ by cheese type, in most cases adversely affecting texture and functional attributes. This review presents an overview of the understanding of the effects of refrigeration, freezing techniques, and frozen storage on structural components of cheese, most prominently Mozzarella cheese, and the corresponding impact on microstructure and functionality. Also included are the mechanism of ice formation and relevant mathematical models for estimation of the thermophysical properties of cheese to assist in designing optimized schemes for their frozen storage. The review also highlights the lack of unanimity in critical understanding concerning the effect of freezing on the long-term storage of Mozzarella cheese with respect to its functionality.

Different methods for textural evaluation of freeze-dried candies during storage

The textural changes during storage of two freeze-dried candies developed from blackcurrant fruits, unflavored yogurt, and different alternative sweeteners, one sweetened with honey/isomalt (HI) and another sweetened with isomalt/stevia (IS), were analyzed using three different methods (instrumental, sensory, and image analysis). Fresh candies were in the supercooled state and presented different structural and textural characteristics (HI: compact and homogeneous, and IS: porous and crunchy), with Fmax values of 139 ± 14 and 174 ± 16 N for HI and IS, respectively. After storage, the instrumental analysis showed approximately 60% average drop in Fmax and W values, in agreement with the decrease observed by sensory analysis in hardness, fracturability, and crispness. Image analysis showed an increase in parameters related to the homogeneity and the uniformity/smoothness for HI. Pearson's correlation coefficients analysis showed that there was a good correlation between the three techniques used, suggesting that the joint use of these methods could be performed for a better understanding of complex food texture.

Effects of Low-Frequency Electromagnetic Field on the Physicochemical Properties of Freeze-Thawed Mongolian Cheese

To verify whether a low-frequency electromagnetic field (LFE field) can help reduce structural damage during the freeze-thaw process and maintain shelf life, Mongolian cheese was frozen at -10, -20, and -30 °C, then thawed at microwave or room temperature. Results showed that LFE field-assisted frozen treatment could reduce ice crystal size and protect the protein matrix structure of cheese. Frozen-thawed cheese retained 96.5% of its hardness and showed no significant difference from the fresh one in elasticity, cohesion, and chewiness. Frozen cheese showed similar but slower ripening behavior during storage, suggesting a potential application of the LFE field in the frozen storage of high-protein foods.

Effect of freezing raw meat on the physicochemical characteristics of beef jerky

The effect of freezing raw meat on the quality characteristics of beef jerky was evaluated in the present study. Jerky was made using different types of raw beef (fresh, frozen, and frozen-thawed) with different curing times (6 h and 12 h). Frozen-thawed beef had a lower moisture content than fresh or frozen beef due to higher exudate loss (P < 0.05). Jerky made using frozen and frozen-thawed beef showed lower drying yield and higher shear force than jerky prepared using fresh beef (P < 0.05). Freezing raw beef decreased the fat content and increased the redness, yellowness, chroma, and hue values of jerky (P < 0.05). The microstructure of beef jerky was showed to increase the deformation and contraction of muscle fibers due to freezing. Longer curing times increased the moisture content of jerky made using frozen meat (P < 0.05). Jerky made using frozen or frozen-thawed meat was tough due to excessive fat and moisture loss.

Synchrotron tomography applications in agriculture and food sciences research: a review

Synchrotron imaging is widely used for research in many scientific disciplines. This article introduces the characteristics of synchrotron X-ray imaging and its applications in agriculture and food science research. The agriculture and food sector are a vast area that comprises of plants, seeds, animals, food and their products; soils with thriving microbial communities; and natural resources such as water, fertilizers, and organic matter. These entities have unique internal features, structures and compositions which differentiate them from each other in varieties, species, grades, and types. The use of a bright and tuneable monochromatic source of synchrotron imaging techniques enables researchers to study the internal features and compositions of plants, seeds, soil and food in a quick and non-destructive way to enhance their use, conservation and productivity. Synchrotron's different X-ray imaging techniques offer a wide domain of applications, which make them perfect to enhance the understanding of structures of raw and processed food products to promote food safety and security. Therefore, this paper summarizes the results of major experiments carried out with seeds, plants, soil, food and relevant areas of agricultural sciences with more emphasis on two synchrotron X-ray imaging techniques: absorption and phase-contrast imaging and computed tomography.

The Effect of Multiple Freeze-Thaw Cycles on the Microstructure and Quality of Trachurus murphyi

Temperature fluctuation in frozen food storage and distribution is the perpetual and core issue faced by the frozen food industry. Ice recrystallisation induced by temperature fluctuations under cold storage causes microstructural changes in fish products and irreversible damages to cells and tissues, which lower the frozen fish quality in the food chain. This study is intended to explore how repeated freezing-thawing affected the microstructure and quality of Trachurus murphyi during its frozen storage. The results showed the consistency between the increase in ice crystal diameter, volume, and porosity in frozen fish and the increase in centrifugal loss (from 22.4% to 25.69%), cooking loss (from 22.32% to 25.19%), conductivity (from 15.28 Ms/cm to 15.70 Ms/cm), TVB-N (from 16.32 mg N/100 g to 19.94 mg N/100 g), K-value (from 3.73% to 7.07%), and amino acid composition. The muscle structure change observed by Fourier-Transform Infrared spectroscopy (FT-IR) showed that the content of α-helix reduced from 59.05% to 51.83%, while the β-sheet fraction grew from 15.44% to 17.11%, β-turns increased from 5.45% to 7.58%, and random coil from 20.06% to 23.49%. Moreover, muscular structure exhibited varying degrees of deterioration with increasing cycles of freezing and thawing as shown by scanning electron microscopy (SEM). We studied the muscular morphology, which included the measurement of porosities (%) of pore that increased (from 1.4% to 4.3%) and pore distribution, by X-ray computed tomography (uCT). The cycles of the freeze-thaw resulted in structural changes, which seemed to be closely associated with ultimate quality of frozen fish products.

Alternatives to Meat and Dairy

The increasing size and affluence of the global population have led to a rising demand for high-protein foods such as dairy and meat. Because it will be impossible to supply sufficient protein to everyone solely with dairy and meat, we need to transition at least part of our diets toward protein foods that are more sustainable to produce. The best way to convince consumers to make this transition is to offer products that easily fit into their current habits and diets by mimicking the original foods. This review focuses on methods of creating an internal microstructure close to that of the animal-based originals. One can directly employ plant products, use intermediates such as cell factories, or grow cultured meat by using nutrients of plant origin. We discuss methods of creating high-quality alternatives to meat and dairy foods, describe their relative merits, and provide an outlook toward the future.

Radiological characterization of gilthead seabream (Sparus aurata) by X-ray computed tomography

In recent years, the increasing use of fish as new animal models in scientific research and the growth of fish farming (mainly for human consumption) have highlighted the need for advanced technology to deepen our knowledge of fish biology. Hence, the present study was carried out to radiologically analyse the whole body of gilthead seabream (Sparus aurata) specimens using X-ray computed tomography (CT). Images were acquired in an Albira SPECT/PET/CT tri-modal preclinical-scanner. Segmentation, measurements and three-dimensional reconstruction were made using the Carestream Molecular imaging Albira CT system in conjunction with Pmod, AMIDE and Amira software packages. The results showed that the density values of gilthead seabream are in the range -700 to +2500 HU for the whole body. We also determined the density ranges that topographically coincide with the swim bladder, soft tissues, fat, skin and skeleton. This work describes, validates and demonstrates the application of a fully automated image analysis technique to study and quantify fish body composition, whether segmented or as a whole. In addition, the basis for applying this image technique in other in vivo studies is established.

X-ray computed tomography for quality inspection of agricultural products: A review

The quality of agricultural products relates to the internal structure, which has long been a matter of interest in agricultural scientists. However, inspection methods of the opaque nature of internal information on agricultural products are usually destructive and require sample separation or preparation. X-ray computed tomography (X-ray CT) technology is one of the important nondestructive testing (NDT) technologies without sample separation and preparation. In this study, X-ray CT technology is used to obtain two-dimensional slice images and three-dimensional tomographic images of samples. The purpose of the review was to provide an overview of the working principle of X-ray CT technology, image processing, and analysis. This review aims to focus on the development of the agricultural products (e.g., wheat, maize, rice, apple, beef) and its applications (e.g., internal quality evaluation, microstructure observation, mechanical property measurement, and others) using CT scanner. This paper covers the aspects regarding the advantages and disadvantages of NDT technology, especially the unique advantages and limitations of X-ray CT technology on the quality inspection of agricultural products. Future prospects of X-ray CT technology are also put forward to become indispensable to the quality evaluation and product development on agricultural products.

CO₂ processing and hydration of fruit and vegetable tissues by clathrate hydrate formation

CO2 hydrate can be used to preserve fresh fruits and vegetables, and its application could contribute to the processing of carbonated frozen food. We investigated water transformation in the frozen tissue of fresh grape samples upon CO2 treatment at 2-3 MPa and 3°C for up to 46 h. Frozen fresh bean, radish, eggplant and cucumber samples were also investigated for comparison. X-ray diffraction indicated that after undergoing CO2 treatment for several hours, structure I CO2 hydrate formed within the grape tissue. Phase-contrast X-ray imaging using the diffraction-enhanced imaging technique revealed the presence of CO2 hydrate within the intercellular spaces of these tissues. The carbonated produce became effervescent because of the dissociation of CO2 hydrate through the intercellular space, especially above the melting point of ice. In addition, suppressed metabolic activity resulting from CO2 hydrate formation, which inhibits water and nutrient transport through intercellular space, can be expected.

Image Analysis of Foods

The structure of foods, both natural and processed ones, is controlled by many variables ranging from biology to chemistry and mechanical forces. The structure also controls many of the properties of the food, including consumer acceptance, taste, mouthfeel, appearance, and so on, and nutrition. Imaging provides an important tool for measuring the structure of foods. This includes 2-dimensional (2D) images of surfaces and sections, for example, viewed in a microscope, as well as 3-dimensional (3D) images of internal structure as may be produced by confocal microscopy, or computed tomography and magnetic resonance imaging. The use of images also guides robotics for harvesting and sorting. Processing of images may be needed to calibrate colors, reduce noise, enhance detail, and delineate structure and dimensions. Measurement of structural information such as volume fraction and internal surface areas, as well as the analysis of object size, location, and shape in both 2- and 3-dimensional images is illustrated and described, with primary references and examples from a wide range of applications.

Studying the morphology of lyophilized protein solids using X-ray micro-CT: effect of post-freeze annealing and controlled nucleation

The objective of this study was to determine how different techniques used during the freezing step of lyophilization affect morphology of the dried protein solids. Aqueous solutions containing recombinant human albumin, trehalose, and sodium phosphate buffer were dried after their freezing by shelf-ramp cooling, immersion in liquid nitrogen, or controlled ice nucleation. Some shelf-frozen solutions were heat treated (annealed) before the vacuum drying. We used three-dimensional (3D) X-ray micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) to study the morphology of solids. The X-ray micro-CT images of the lyophilized microporous solids showed traces of varied size and structure ice crystals that were comparable to corresponding SEM images. A post-freeze heat treatment and a controlled nucleation both induced larger ice crystal ghosts in the solids. The variations in the structure of walls surrounding ice crystals, formed by the different freezing procedures, should affect the water vapor transition during the primary and secondary drying. Some solids also showed higher-density layer in the upper surface. Overall, the simple sample preparation procedures and the ample morphological information make the X-ray micro-CT appropriate for analyzing lyophilized pharmaceuticals.

X-ray imaging methods for internal quality evaluation of agricultural produce

A number of non-destructive methods for internal quality evaluation have been studied by different researchers over the past eight decades. X-ray and computed tomography imaging techniques are few of them which are gaining popularity now days in various fields of agriculture and food quality evaluation. These techniques, so far predominantly used in medical applications, have also been explored for internal quality inspection of various agricultural products non-destructively, when quality features are not visible on the surface of the products. Though, safety of operators and time required for tests are of concern, the non-destructive nature of these techniques has great potential for wide applications on agricultural produce. This paper presents insight of X-ray based non-destructive techniques such as X-ray imaging and Computed Tomography (CT). The concepts, properties, equipment and their parameters, systems and applications associated with the use of X-rays and CT for agricultural produce have been elaborated.

Effect of frozen storage conditions (temperature and length of storage) on microbiological and sensory quality of rustic crossbred beef at different states of ageing

The effect of frozen storage conditions on meat from 36 Morucha×Charolais crossbred yearlings was studied. Slices of M. Longissimus thoracis were randomly assigned to groups arising from the combination of experimental factors. These factors were: ageing extent (3 and 10days), length of frozen storage (0, 30, 75 and 90days) and temperature (-20 and -80°C). Regarding microbiological counts, although values were acceptable in all cases, longer storage time and longer previous ageing extent provided higher phychrotrophic bacteria counts. As frozen storage period increased, colorimetric parameters L(∗), a(∗) and C(∗) decreased, but H(∗) increased. Regarding Warner-Braztler shear force and tenderness values, an interaction (p<0.05) between frozen storage and post-mortem ageing resulted from larger differences between frozen storage periods at shorter ageing periods than those at longer ageing periods. Frozen storage for 90days resulted in a reduction in water holding capacity, without differences in juiciness. No effect of freezing temperature was observed in any of the parameters studied.