Food Microstructure Research Articles

Statistical Description of Food Microstructure. Extraction of Some Correlation Functions From 2D Images

Two algorithms able to compute lineal-path distribution function L(z) and two-point correlation function, S2(r1,r2) from 2D digital images of foods were developed and validated. Particularly, “Altamura” and “White” breads as well as “Napoli” sausages were studied. Lineal-path function was modeled by considering the foods as two-phase random systems composed from polydisperse overlapping disks. Instead, two-point correlation function was modeled by using a Debye’s equation. In all cases a good agreement between experimental and theoretical trend was obtained stating the high accuracy of the algorithms in the extraction of correlation functions as well as the possibility to model breads and sausages as two-phase random systems. Also, important morphological properties such as pores distribution, pore size homogeneity and their spatial distribution, were obtained. For instance, although the estimated radius of the pores was lower for “Altamura” bread rather that for “White”, its slowest decay of L(z) highlighted that the pores showed a high dimensional inhomogeneity.

Use of Lineal-Path Distribution Function as Statistical Descriptor of the Crumb Structure of Bread

The importance of the relation between food microstructure and their quality is recognized as crucial. In terms of bread quality, the precise characterization of the crumb structure is considered essential to evaluate its sensorial properties. A variety of different statistical correlation functions have been theoretically formulated in recent years to quantify the microstructure of general random heterogeneous materials but they have rarely been applied in food science. In this paper, we have developed a method to calculate the lineal-path distribution function L(x) for the void and solid matrix phases from two-dimensional (2D) images of bread. The method has been successfully employed here to characterize the microstructure for two type of commercial breads. Our results reveal that crumb structure may be modeled as a system of polydispersed overlapping disks. Moreover, we have quantified the dimensions of the voids and crumb phase statistically and differences in the homogeneity of crumb structure.

Innovative technologies in the control of lipid oxidation

AbstractTransition metal promoted oxidative degradation reactions impact quality, shelf‐life, and nutritional content of many packaged foods. When trace metals are present in packaged foods, they can initiate degradation of nutritional compounds such as unsaturated fatty acids, carotenoids, antioxidants, phytosterols, and many vitamins. These reactions occur at metal concentrations naturally occurring in foods (often in the low parts per billion range) therefore complete metal removal is not a practical solution to inhibit these reactions. Chelators such as EDTA can be added to inhibit metal‐promoted oxidation, however there is significant consumer and industry demand to eliminate EDTA from product formulations. Other natural chelators such as citric acid are ineffective in many foods and in some cases can actually increase oxidation rates by increasing metal solubility. An alternate approached to control transition metal reactivity is to utilize active packaging technologies. However, current approaches to antioxidant active packaging can impact packaging film mechanical properties and often exhibit low antioxidant activity. This review article surveys and critically reviews advances in the control of lipid oxidation, paying particular attention to novel advances in both food product formulation (e. g. additives, food microstructure) as well as food packaging. We introduce a new concept of active packaging in which metal ion chelation by non‐migratory active packaging materials may enable removal of synthetic food additives from product formulations while maintaining product quality and shelf‐life.

Application of MRI for tissue characterisation of ‘Braeburn’ apple

Magnetic resonance imaging (MRI) has become a well-established technique for non-destructive analysis of the internal (micro)structure of food, and the related heat, gas, water and solutes transport, which is of interest for food processing (e.g., drying), physical tissue damage assessment (e.g., bruising) for online sorting purposes or detection of internal defects (e.g., internal browning), amongst others. In contrast to previous MRI studies which predominantly analysed entire fruit, small samples (diameter ∼10−2m) of ‘Braeburn’ apple were investigated in this study with high-field MRI, providing very local, high-resolution information, in order to identify the capability of MRI for detecting differences in fruit tissue types. The focus was on MRI for tissue characterisation with respect to inner and outer cortex tissue, fertilisation treatment, storage time and internal browning (IB). For this purpose, the proton density (PD), T2 value and self-diffusion coefficient (DC) were measured. No clear distinction could be made between samples with different fertilisation treatments. Differences in storage times could be observed from an increased PD for longer storage times. Inner tissue clearly showed an increased PD, T2 value and DC, compared to the outer tissue. IB could be successfully detected, where the PD, T2 value and the DC of the affected tissue were clearly higher than those of the healthy tissue, but a dependency of these parameters on the degree of tissue degradation was identified. Especially, the DC seemed to be an appropriate parameter regarding IB detection.

Use of X‐ray micro tomography to study the microstructure of loose‐packed and compacted milk powders

The use of X-rays to evaluate food microstructure has developed considerably in recent years. In this work we used X-ray micro tomography (XMT) to visualize the microstructure of loose-packed and compacted samples of spray-dried skim milk powder (SMP) and whole milk powder (WMP) and to quantify the proportion of both interstitial and occluded air voids in each sample. Visual scrutiny of the acquired XMT images showed details of the microstructure of the milk powders such as the spherical morphology of the particles, the size of the particles and internal air voids of various sizes. Within loose-packed powders, the proportion of air voids was higher (13% average) in WMP than in SMP. This was reversed in the compacted powders, in which the proportion of air voids was higher in SMP. The disparity in the proportion of air voids in both loose-packed and compacted samples of SMP and WMP was attributed to the size, shape and surface properties of the particles.

CUTTING EDGE TECHNOLOGIES IN POSTHARVEST RESEARCH: JOURNEY TO THE CENTRE OF THE FRUIT

Food microstructure is at the base of many food quality roperties. The EU project InsideFood focuses on the pplication of high technological techniques to inspect internal quality of fruit. Tomographic techniques such as magnetic resonance imaging, X-ray computed tomography, optical coherence tomography and confocal microscopy can be used to obtain information about the 3-D microstructure of the fruit which is believed to affect quality attributes such as texture. Optical techniques such as spatially or time resolved reflectance spectroscopy may also be used to obtain information about fruit microstructure. This microstructural information can be incorporated in multiscale simulation models to predict the cellular gas concentrations in fruit. Such models aid towards a better understanding of, for instance, controlled atmosphere storage of apple and postharvest behaviour of fruits and vegetables in general.

Interrelations among physical characteristics, sensory perception and oral processing of protein-based soft-solid structures

Oral processing is essential in breaking down the physicochemical structure of the food and thus important to the sensory perception of food in the mouth. To have an understanding of protein-based, soft-solid texture perception, a multidisciplinary approach was applied that combined studies of food microstructure with mechanical properties, sensory evaluation, and oral physiology. Model foods were developed by combining ion-induced micro-phase separation and protein-polysaccharide phase separation and inversion. Activities of masseter, anterior temporalis and anterior digastric muscles during oral processing were recorded by electromyography (EMG), while jaw movement amplitudes, durations, and velocities were simultaneously collected by a three-dimensional jaw tracking system (JT-3D). Changes in the microstructure of mixed gels significantly altered the characteristics of the chewing sequence, including the muscle activities, number of chews, chewing duration and chewing frequency. Mechanical attributes related to structural breakdown and sensory perception of firmness were highly correlated with the amount of muscle activity required to transform the initial structure into a bolus ready for swallowing. Chewing frequency was linked to mechanical properties such as recoverable energy, fracture strain and water holding capacity of the gels. Increased adhesiveness and moisture release also resulted in slower chewing frequency. Evaluation of oral processing parameters at various stages (i.e., first cycle, first 5 cycles, and last 3 cycles) was found to be a useful method to investigate the dynamic nature of sensory perception at first bite, during chewing and after swallowing. The study showed that muscle activity and jaw movement can be used to understand the links between physical properties of foods and sensory texture.

Influence of the Addition of Dietary Fiber on the Drying Curves and Microstructure of a Dry Fermented Sausage (Sobrassada)

The formulation of a dry fermented sausage has been modified by the addition of carrot dietary fiber (CDF; 3, 6, 9, and 12% [w/w]), and the influence of this change on the drying curves and food microstructure has been studied. The CDF content influenced the initial moisture content as well as the drying rate. A diffusion model taking into account the change in the product formulation has been proposed to simulate the drying curves. A constant mass transfer coefficient of 2.53 × 10−8 m/s was obtained and the effective water diffusivity varied exponentially with the CDF content from 0.99 × 10−11 m2/s (0% CDF) to 2.08 × 10−11 m2/s (12% CDF). The simulation of the drying curves was satisfactory (mean relative error of 0.5 ± 0.1%). No differences in the microstructure related to the proteolytic process were found among samples with different CDF contents.

Heat Transfer to Foods: Ensuring Safety and Creating Microstructure

Heat transfer in foods is commonplace in the home and restaurant, but is also the basis for a very large industry. Foods are complex non-Newtonian soft solids or structured liquids whose thermal behavior is difficult to model; engineering understanding is needed to develop processes that are safe and products that are attractive to the consumer. The increasing incidence of obesity in the developed world, and of food shortage elsewhere, demands that the industry adopts processes that give nutritious products in environmentally acceptable ways. Heat transfer is often limited by the low thermal conductivity of foods and increasing heating and cooling rates is critical in maximizing product quality. This paper briefly reviews the heat transfer problems found in food processing, with particular reference to the modeling of heating to ensure safety, problems found in the fouling and cleaning and process plant, and how heating and cooling are used to generate food microstructure. Research challenges for the future are outlined.

3D-characterization of three-phase systems using X-ray tomography: tracking the microstructural evolution in ice cream

The microstructure of food is key to its sensorial perception, and methods to characterize the microstructure are of crucial importance in food engineering. Ice cream is a special example whose microstructure changes dramatically in response to temperature variations. Since ice cream is a multiphase material, the complex interactions among the phases and the physical mechanisms that drive the evolution of microstructure are not yet well understood. This is mostly due to the fact that observing the microstructure with traditional microscopic methods is destructive and does not allow the study of undisturbed samples. With X-ray micro-tomography, it is possible to overcome these limitations and carry out time lapse studies of the evolution of the microstructure of ice cream. Using iodine as a contrast agent, we measured the three-dimensional distribution of the three main phases (air, unfrozen sugar solution, and ice crystals) with a voxel size of 6 μm. An automated routine was developed that allows for the segmentation of the three phases. Based on the three-dimensional data we calculated the temporal evolution of air bubble sizes and ice crystal sizes during cyclic variations of temperature. Under the given temperature variations we find strong hints that for ice crystal coarsening a melt refreeze mechanism and for air microstructure coarsening coalescence are the dominating underlying mechanisms. This method—which can be applied to a plethora of soft multiphase materials—provides new insights into the coarsening mechanisms of multiphase materials and could contribute to a better understanding of complex materials.

8A46 食感のバイオメカニクス : スナック菓子の微細構造と食感の官能評価(OS09 デンタルバイオメカニクス)

8A46 食感のバイオメカニクス : スナック菓子の微細構造と食感の官能評価(OS09 デンタルバイオメカニクス)

High Pressure Homogenization Increases the In Vitro Bioaccessibility of α‐ and β‐Carotene in Carrot Emulsions But Not of Lycopene in Tomato Emulsions

The correlation between food microstructure and in vitro bioaccessibility of carotenes was evaluated for tomato and carrot emulsions (5% olive oil) subjected to high pressure homogenization (HPH) at varying degrees of intensity. The aim was to investigate whether additional mechanical disruption of the food matrix could be utilized to further increase the carotene bioaccessibility of an already pre-processed material. The carotene bioaccessibility of the samples was measured after simulated in vitro digestion, carotene release to the oil phase was estimated by Confocal Raman spectroscopy and, to measure active uptake of carotenes, Caco-2 cells were incubated with the digesta of selected samples. HPH did not notably affect the retention of carotenes or ascorbic acid but significantly increased both the release and micellar incorporation of α- and β-carotene in carrot emulsions 1.5- to 1.6-fold. On the other hand, in vitro bioaccessibility of lycopene from tomato was not increased by HPH under any of the conditions investigated. Instead, the results suggested that lycopene bioaccessibility was limited by a combination of the low solubility of lycopene in dietary lipids and entrapment in the cellular network. Carotene uptake by Caco-2 cells appeared to be mainly dependent upon the carotene concentration of the digesta, but cis-trans isomerization had a significant impact on the micellarization efficiency of carotenes. We therefore conclude that HPH is an interesting option for increasing the bioaccessibility of carotenes from fruits and vegetables while maintaining a high nutrient content, but that the results will depend on both food source and type of carotene. A better understanding of the correlation between the processing of fruits and vegetables, microstructure and nutrient bioaccessibility can be directly applied in the production of food products with an increased nutritional value.

Review: Starch Matrices and the Glycemic Response

Starch is the most important source of energy for humans, and it is present in many products derived from cereals, legumes and tubers. Interestingly, some of these food products can have different metabolic effects (e.g. change of postprandial blood glucose concentration) although the total amount of starch is the same. This review focuses on a microstructural perspective of the glycemic response, in search of an alternative and complementary explanation of this phenomenon. Several starch and food microstructures are responsible for the change in starch bioaccessibility. Aspects such as the characterization of the microstructure of starchy products and, its relation to the metabolic problem, the crucial role of the food matrix and other components in the ingested meal, and the gaps in our present knowledge are discussed.

Food structure engineering for nutrition, health and wellness

Many of today's food products addressing specific nutritional, health and wellness needs of human and animal consumers are often very complex structures. Consequently, it is of utmost importance in food engineering research to develop a detailed understanding of the time-dependent transient changes in all of the structural aspects of food matrices from raw material harvesting, to product processing, to the point of breakdown during shelf-life, consumption and final digestion. Food structural understanding and control needs to be mastered on a broad range of length scales including: the molecular, supra-molecular, micro- and macro-structural level. At the same time, the mechanical, physical and chemical properties of the food need to be considered. Only in this manner can a tailor- made build-up and controlled breakdown of food products be achieved, and subsequently, can specific nutritional, physical and sensorial properties be engineered. Reducing fat and sugar content in order to reduce the energy density of food requires a particular micro- and macro-structural design in order to compensate for resultant sensorial changes. Specific structures can improve the stability and bioavailability (ultimately bioefficacy) of bioactive compounds and probiotics. Improving the nutritional profile of food by increasing the overall content of (plant) proteins, dietary fibres or whole grains can be achieved by certain means of structuring. Specific health care products exhibiting a particular rheological behaviour at very high protein content, for example, can only be realised by targeted modification of their supra-molecular structure. Finally, food microstructures can be designed in such a way that their modulated digestion behaviour triggers different physiological responses.

The Role of Dietary Fiber in the Bioaccessibility and Bioavailability of Fruit and Vegetable Antioxidants

Antioxidants are abundant compounds primarily found in fresh fruits and vegetables, and evidence for their role in the prevention of degenerative diseases is continuously emerging. However, the bioaccessibility and bioavailability of each compound differs greatly, and the most abundant antioxidants in ingested fruit are not necessarily those leading to the highest concentrations of active metabolites in target tissues. Fruit antioxidants are commonly mixed with different macromolecules such as carbohydrates, lipids, and proteins to form a food matrix. In fruits and vegetables, carbohydrates are the major compounds found, mainly in free and conjugated forms. Dietary fiber, the indigestible cell wall component of plant material, is considered to play an important role in human diet and health. Most studies on antioxidant bioavailability are focused on foods and beverages from which antioxidants are easily released. There is evidence indicating that food microstructure affects the bioaccessibility and bioavailability of several nutrients, referring mostly to antioxidants. Nevertheless, the specific role of dietary fiber in the absorption of antioxidants has not been widely discussed. In this context, the purpose of the present review is to compile and analyze evidence relating to the association between dietary fiber and antioxidants, and the physical and chemical interactions that modulate their release from the chyme in the gastrointestinal tract.

Developing novel 3D measurement techniques and prediction method for food density determination

Density is a physical characteristic which depends on the experimental technique used and structural properties of food. True, apparent, and bulk are different types of densities based on the way volume is measured. For porous foods such as grain food products, accurate measurement of density is challenging. Current measurement techniques for food density are inconsistent and nutrient databases do not have sufficient density data. Computed tomography (CT) and magnetic resonance imaging (MRI), laser scanners are non-destructive diagnostic tools for characterizing food microstructure. The objectives of this study were to 1) optimize the parameters of CT, MRI, and laser scanner to determine food density and compare the corresponding values with other traditional techniques, and 2) to develop neural networks as a prediction method for apparent and bulk densities. MicroCT 40 (Scano Medical Inc.), Lightspeed QX/i clinical CT (GE Healthcare), and 3 Tesla Signa HDx MRI (GE Healthcare) were used to acquire 3D images of foods for true density. A 3D laser scanner (NextEngine, Inc) was used to scan the foods items for apparent density. Neural networks were used in conjunction with the data collected from laser scanner and using food composition and processing conditions to generate a black-box prediction scheme. The results of CT, MRI, and laser scanner showed great potential to estimate density in comparison to traditional techniques. Porosity was estimated from the CT and MRI scanned image data. Laser scanner was successful in acquiring 3D images and calculating apparent density. Neural networks provided reliable density prediction power and were comparable to the other empirical equations in terms of accuracy. The ability to predict food density based on composition and processing conditions is necessary to fill gaps in nutrient databases and account for new foods.

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. 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.

Cell surface properties affect colonisation of raw milk by lactic acid bacteria at the microstructure level

Cell localisation in the matrix microstructure of fermented food is important for microbial activity and ripening. To evaluate the importance of physicochemical factors in these phenomena, the physicochemical behaviour of four strains of lactic acid bacteria were investigated after inoculation of raw milk or milk fractions. To discriminate between physicochemical and metabolic properties, media were (i) rapidly acidified to avoid cell division or (ii) bacteria were allowed to ferment milk. To evaluate the impact of milk components, cells were dispersed in protein or fatty globule fractions. From two Lactococcus lactis subsp. lactis biovar. diacetylactis strains selected from their different surface properties investigated in previous studies, after rapid acidification one was encountered in fatty globules and protein gels whereas the other was found in serum and on the surface of globules. After fermentation, the first one formed colonies in the lipid phase or next to it in the whey and the second formed colonies in the protein gel. Strains forming long chains (Lactobacillus bulgaricus and Streptococcus thermophilus) were always found in contact with fatty globules, where they developed. Our results suggest that localisation and subsequent spatial colonisation depend on the physicochemical properties of cell surfaces, on the structure in chains as well as on the metabolic ability to develop on proteins or lipids.

Addition of ice-nucleation active bacteria: Pseudomonas syringae pv. panici on freezing of solid model food

Ice-nucleation active bacteria (INAB), Pseudomonas syringae pv. panici, were cultured at 26 °C in a nutrient broth and harvested at late log phase. The ice-nucleation activity unit per unit volume of the bacterial culture measured by the droplet-freezing assay developed by Vali was 3.29 × 10 4 INA/mL. A differential scanning calorimetry (DSC) analysis of 77 g/100 g Tylose samples showed that the addition of bacteria had no obvious effect on the glass transition temperature and heat of fusion of the samples. Freezing operations carried out at −20 °C showed that the addition of INAB produced no obvious change in the freezing time. The scanning electronic microscope (SEM) observation of microstructure of the model food indicated that the mean ice crystal size was reduced from 25.7 μm to approximately 15 μm by the addition of INAB.

Image Analysis of Representative Food Structures: Application of the Bootstrap Method

Images (for example, photomicrographs) are routinely used as qualitative evidence of the microstructure of foods. In quantitative image analysis it is important to estimate the area (or volume) to be sampled, the field of view, and the resolution. The bootstrap method is proposed to estimate the size of the sampling area as a function of the coefficient of variation (CV(Bn)) and standard error (SE(Bn)) of the bootstrap taking sub-areas of different sizes. The bootstrap method was applied to simulated and real structures (apple tissue). For simulated structures, 10 computer-generated images were constructed containing 225 black circles (elements) and different coefficient of variation (CV(image)). For apple tissue, 8 images of apple tissue containing cellular cavities with different CV(image) were analyzed. Results confirmed that for simulated and real structures, increasing the size of the sampling area decreased the CV(Bn) and SE(Bn). Furthermore, there was a linear relationship between the CV(image) and CV(Bn) (.) For example, to obtain a CV(Bn) = 0.10 in an image with CV(image) = 0.60, a sampling area of 400 x 400 pixels (11% of whole image) was required, whereas if CV(image) = 1.46, a sampling area of 1000 x 100 pixels (69% of whole image) became necessary. This suggests that a large-size dispersion of element sizes in an image requires increasingly larger sampling areas or a larger number of images.