Food Mechanical Properties Research Articles

Food Rheology: An Introduction and Fundamentals Concepts

Food rheology is the study of the flow and deformation of food materials. It involves understanding the physical and mechanical properties of food, such as how it behaves when subjected to external forces or changes in temperature. Understanding food rheology is essential in various food processing and manufacturing industries as it helps in product development, quality control, and optimization of processing parameters. Some fundamental concepts in food rheology include as follows. Viscosity refers to a material’s resistance to flow. In food rheology, it is a measure of how easily a food material flows under an applied force. Food materials can exhibit different types of viscosity, such as Newtonian, pseudoplastic, dilatant, and viscoelastic behavior. Shear stress is the force per unit area applied to a food material, while the shear rate is the rate at which the food material deforms. In food rheology, these two variables are used to describe the flow behavior of food materials. Different food materials have different flow behaviors. Some foods, like water, exhibit Newtonian flow behavior, where the viscosity remains constant regardless of the applied shear rate. Other foods, like ketchup or mayonnaise, exhibit non-Newtonian flow behavior, where the viscosity changes with the shear rate. Elasticity refers to a material’s ability to regain its original shape after deformation. In food rheology, elasticity is important in determining the texture and shelf life of food products. Viscoelasticity refers to the combined properties of both viscosity and elasticity, where a material exhibits both liquid-like (viscous) and solid-like (elastic) behavior. Yield stress is the minimum amount of shear stress required to initiate flow in a material. Many food materials, such as gels or semisolid foods, exhibit yield stress where they behave like a solid until a certain stress threshold is reached. By understanding these fundamental concepts, food scientists and engineers can manipulate and control the rheological properties of food materials to achieve the desired texture, mouthfeel, and sensory attributes, as well as optimize processing conditions to improve the overall quality of food products.

The effects of feeding frequency on jaw loading in two lemur species.

Studies on oral processing are often snapshots of behaviors that examine feeding through individual bouts. In this study, we expand on our previous work comparing bite/chew variables per feeding bout to summed daily biting, chewing, and food intake to interpret loading that could have potential morphological effects. We observed sympatric Lemur catta and Propithecus verreauxi over two field seasons in the dry forest of Bezà Mahafaly Special Reserve in southwestern Madagascar. Bite and chew rates determined from videos filmed during observations were multiplied with time spent feeding on specific foods during focal follows to calculate daily values for each feeding bout. Food mechanical properties (FMPs) were tested on dietary items with a portable tester. We contrasted daily bite/chew numbers and intake with FMPs, species, season, and food shape. Daily bite and chew numbers increased with maximum, but not average, food toughness. Daily intake decreased with average and maximum toughness. Season had a strong effect on daily bites and chews, but not on intake. Food shape influenced intake and total bite and chew numbers. The lemur species did not differ in our models. Maximum food toughness impacted feeding behaviors and intake, which is consistent with higher loads having a greater effect on morphology. In contrast to feeding per bout, cumulative biting and chewing did not differ between species; taking feeding frequency into consideration affects interpretation of jaw loading. Finally, biting, as much as chewing, may generate strains that impact morphology.

Correlations of sensations of hardness and springiness of agar and gelatin gels with mechanical properties in human participants

ObjectivesIt is unclear which mechanical properties of foods cause the texture sensation in humans. This study aimed to investigate the relationship between unilateral compression measurements and the sensations of hardness and springiness in gels. MethodsThree different concentrations of agar and gelatin gels were prepared by the addition of agar (1%, 2%, and 3%) and gelatin (4%, 8%, and 16%) to water or apple juice. In a stress-rupture test, stress–strain curves were obtained by the application of uniaxial compression with a disc plunger at a compression rate of 10 mm/s. The hardness, springiness, and palatability of the gels were evaluated by 12 healthy volunteers using a visual analog scale. ResultsThe sensation of hardness was positively correlated with the sensation of springiness for the agar and gelatin gels. Palatability decreased as hardness increased for both gels. In terms of mechanical properties, the sensation of hardness was only significantly correlated with the initial elastic modulus, while the sensation of springiness was correlated with the late elastic modulus and other mechanical properties such as fracture strain, time, and stress. ConclusionsThese results suggest that sensations of hardness and springiness are produced in the initial and late stages, respectively, during the food-crushing process using the tongue, palate, and teeth.

Experimental and computational models for simulating the oral breakdown of food due to the interaction with molar teeth during the first bite

The first bite involves the structural breakdown of foods due to the interaction with teeth and is a crucial process in oral processing. Although in vitro experiments are useful in predicting the oral response of food, they do not facilitate a mechanistic understanding of the relationship between the intrinsic food mechanical properties and the food behaviour in the oral cavity. Computer simulations, on the other hand, allow for such links to be established, offering a promising design alternative that will reduce the need for time consuming and costly in vivo and in vitro trials. Developing virtual models of ductile fracture in soft materials, such as food, with random and non-predefined crack morphology imposes many challenges. One of the most important is to derive results that do not depend on numerical parameters, such as Finite Element (FE) mesh density, but only physical constants obtained through independent standard mechanical tests, such as fracture strain and/or critical energy release rate. We demonstrate here that this challenge can be overcome if a non-local damage approach is used within the FE framework. We develop a first bite FE modelling methodology that provides mesh independent results which are also in agreement with physical first bite experiments performed on chocolate. The model accounts for key features found in chocolate and a wide range of compliant media, such as rate dependent plasticity and pressure dependent fracture initiation strain. As a result, our computational methodology can prove valuable in studying food structure-function relationships that are essential in product development.

Effect of starch retrogradation on molecular dynamics of cooked rice by quasi-elastic neutron scattering

Starch retrogradation can be evaluated using X-ray diffraction (XRD) techniques, which can estimate the crystallinity of starch. It is well known that the crystallinity is reflected in the mechanical properties of foods and materials. Crystallinity should be also related to the structural dynamics of starch, but there are no reports on the relationship between these properties. In this study, we used quasi-elastic neutron scattering (QENS) to investigate changes in the molecular dynamics of cooked rice starch during retrogradation. The width of the measured QENS narrowed with retrogradation. The elastic incoherent structure factor (EISF) increased, which indicated that the molecular dynamics are spatially suppressed upon retrogradation. However, the width of the quasi-elastic scattering component was independent of retrogradation in the measured Q-range. Analysis of EISF with a bimodal continuous diffusion model, where low and high mobilities are assumed to correspond to crystalline and amorphous phases, respectively, showed that the fraction of the low-mobility component increases with retrogradation. The suppression of the molecular dynamics during retrogradation was correlated with the crystallinity evaluated by XRD. The molecular dynamics of the crystalline region that appeared after gelatinization and retrogradation were different from that of raw rice starch. These results suggest that molecular dynamics reflect the state of retrogradation and can be used to monitor retrogradation of starch in foods.

Microwear textures associated with experimental near-natural diets suggest that seeds and hard insect body parts cause high enamel surface complexity in small mammals

In mammals, complex dental microwear textures (DMT) representing differently sized and shaped enamel lesions overlaying each other have traditionally been associated with the seeds and kernels in frugivorous diets, as well as with sclerotized insect cuticles. Recently, this notion has been challenged by field observations as well as in vitro experimental data. It remains unclear to what extent each food item contributes to the complexity level and is reflected by the surface texture of the respective tooth position along the molar tooth row. To clarify the potential of seeds and other abrasive dietary items to cause complex microwear textures, we conducted a controlled feeding experiment with rats. Six individual rats each received either a vegetable mix, a fruit mix, a seed mix, whole crickets, whole black soldier fly larvae, or whole day-old-chicks. These diets were subjected to material testing to obtain mechanical properties, such as Young’s modulus, yield strength, and food hardness (as indicated by texture profile analysis [TPA] tests). Seeds and crickets caused the highest surface complexity. The fruit mix, seed mix, and crickets caused the deepest wear features. Moreover, several diets resulted in an increasing wear gradient from the first to the second molar, suggesting that increasing bite force along the tooth row affects dental wear in rats on these diets. Mechanical properties of the diets showed different correlations with DMT obtained for the first and second molars. The first molar wear was mostly correlated with maximum TPA hardness, while the second molar wear was strongly correlated with maximum yield stress, mean TPA hardness, and maximum TPA hardness. This indicates a complex relationship between chewing mechanics, food mechanical properties, and observed DMT. Our results show that, in rats, seeds are the main cause of complex microwear textures but that hard insect body parts can also cause high complexity. However, the similarity in parameter values of surface textures resulting from seed and cricket consumption did not allow differentiation between these two diets in our experimental approach.

Problems with Paranthropus

Carbon isotopic analysis has been challenging our ideas about hominin diet for nearly 30 years. The first study in 1994 revealed that Paranthropus robustus from South Africa consumed principally C3 foods (e.g., tree fruits and leaves) but also about 25% C4/CAM resources (e.g., tropical grasses and sedges). This result was largely consistent with morphological and dental microwear evidence suggesting P. robustus had a diet which included hard objects like nuts and seeds. Decades later, however, P. boisei from eastern Africa was shown to have eaten nearly 80% C4/CAM plants like the contemporaneous grass-eating primate Theropithecus. Moreover, dental microwear revealed no evidence of hard object consumption in P. boisei, suggesting a diet of tough foods such as grass or sedge leaf and stem. So Paranthropus presents us with two central problems: 1) Why do dietary proxies suggest different diets for the two robust australopiths despite their morphological congruity; and 2) How could P. boisei have consumed tough foods with teeth that seem unsuited to the task. Here we review these questions and more with a particular focus on new isotopic data from the Omo and insights that can be gleaned from mammals outside the haplorrhine primates. We argue that extant Primates do not capture the ecomorphological diversity of P. boisei and other extinct primates and should not narrowly circumscribe the behaviors we ascribe to extinct taxa. We also discuss possible digestive strategies for P. boisei in light of its morphology, dietary proxy data, food mechanical properties, and comparative data on mammalian digestive kinetics.

C. elegans PEZO-1 is a mechanosensitive ion channel involved in food sensation.

PIEZO channels are force sensors essential for physiological processes, including baroreception and proprioception. The Caenorhabditis elegans genome encodes an orthologue gene of the Piezo family, pezo-1, which is expressed in several tissues, including the pharynx. This myogenic pump is an essential component of the C. elegans alimentary canal, whose contraction and relaxation are modulated by mechanical stimulation elicited by food content. Whether pezo-1 encodes a mechanosensitive ion channel and contributes to pharyngeal function remains unknown. Here, we leverage genome editing, genetics, microfluidics, and electropharyngeogram recording to establish that pezo-1 is expressed in the pharynx, including in a proprioceptive-like neuron, and regulates pharyngeal function. Knockout (KO) and gain-of-function (GOF) mutants reveal that pezo-1 is involved in fine-tuning pharyngeal pumping frequency, as well as sensing osmolarity and food mechanical properties. Using pressure-clamp experiments in primary C. elegans embryo cultures, we determine that pezo-1 KO cells do not display mechanosensitive currents, whereas cells expressing wild-type or GOF PEZO-1 exhibit mechanosensitivity. Moreover, infecting the Spodoptera frugiperda cell line with a baculovirus containing the G-isoform of pezo-1 (among the longest isoforms) demonstrates that pezo-1 encodes a mechanosensitive channel. Our findings reveal that pezo-1 is a mechanosensitive ion channel that regulates food sensation in worms.

More Challenging Diets Sustain Feeding Performance: Applications Toward the Captive Rearing of Wildlife

SynopsisThe rescue and rehabilitation of young fauna is of substantial importance to conservation. However, it has been suggested that incongruous diets offered in captive environments may alter craniofacial morphology and hinder the success of reintroduced animals. Despite these claims, to what extent dietary variation throughout ontogeny impacts intrapopulation cranial biomechanics has not yet been tested. Here, finite element models were generated from the adult crania of 40 rats (n = 10 per group) that were reared on 4 different diet regimes and stress magnitudes compared during incisor bite simulations. The diets consisted of (1) exclusively hard pellets from weaning, (2) exclusively soft ground pellet meal from weaning, (3) a juvenile switch from pellets to meal, and (4) a juvenile switch from meal to pellets. We hypothesized that a diet of exclusively soft meal would result in the weakest adult skulls, represented by significantly greater stress magnitudes at the muzzle, palate, and zygomatic arch. Our hypothesis was supported at the muzzle and palate, indicating that a diet limited to soft food inhibits bone deposition throughout ontogeny. This finding presents a strong case for a more variable and challenging diet during development. However, rather than the “soft” diet group resulting in the weakest zygomatic arch as predicted, this region instead showed the highest stress among rats that switched as juveniles from hard pellets to soft meal. We attribute this to a potential reduction in number and activity of osteoblasts, as demonstrated in studies of sudden and prolonged disuse of bone. A shift to softer foods in captivity, during rehabilitation after injury in the wild for example, can therefore be detrimental to healthy development of the skull in some growing animals, potentially increasing the risk of injury and impacting the ability to access full ranges of wild foods upon release. We suggest captive diet plans consider not just nutritional requirements but also food mechanical properties when rearing wildlife to adulthood for reintroduction.

Impact of the particle-polymer interface on small- and large-scale deformation response in protein- and carbohydrate-based food matrices

Interfaces are important regarding the mechanical behavior of foods. In particle-polymer-based food systems, the rheological effect of interface characteristics between microscopic particles and viscoelastic polymers is controversial. By using a new approach of presenting defined glass beads surfaces, which imitate functional groups of starch particle surfaces, the adhesiveness and the adsorption mechanism between particle and polymeric food matrix (protein-/carbohydrate-based) can be controlled. The combination of defined particle-polymer interfaces with a comprehensive rheological analysis gives new insights into the effect of particle-polymer interfaces on the mechanical properties of food. Independent of the matrix-type, non-adhesive particles show the strongest network at low stress (protein-based: network strength Af = 2.02 ± 0.16 ∗ 104 Pas1/z), but the fastest network breakdown under higher stress (fracture strain protein-based 4.40 ± 0.08). Adhesive particles behave inverse (Af = 1.02 ± 0.24 *104 Pas1/z; fracture strain 5.38 ± 0.32). Consequently, particle supplemented protein-/carbohydrate-based matrices have properties similar to particle reinforced rubbers and exhibit a more or less pronounced Payne effect depending on the adhesiveness. Besides the adhesiveness, the adsorption mechanism affects the deformation behavior of particle-polymer based system. The highly adhesive but unspecific adsorption of carbohydrate-based polymers at cyano-functionalized surfaces shows a similar relaxation behavior as non-adhesive surface functionalization.

Flexibility of intraoral food processing in the salamandrid newt Triturus carnifex: effects of environment and prey type.

Intraoral food processing mechanisms are known for all major vertebrate groups, but the form and function of systems used to crush, grind or puncture food items can differ substantially between and within groups. Most vertebrates display flexible mechanisms of intraoral food processing with respect to different environmental conditions or food types. It has recently been shown that newts use cyclical loop-motions of the tongue to rasp prey against the palatal dentition. However, it remains unknown whether newts can adjust their food processing behavior in response to different food types or environmental conditions. Newts are interesting models for studying the functional adaptation to different conditions because of their unique and flexible lifestyle: they seasonally change between aquatic and terrestrial habitats, adapt their prey-capture mode to the respective environment, and consume diverse food types with different mechanical properties. Using X-ray high-speed recordings, anatomical investigations, behavioral analyses and mechanical property measurements, we tested the effects of the medium in which feeding occurs (water/air) and the food type (maggot, earthworm, cricket) on the processing behavior in Triturus carnifex We discovered that food processing, by contrast to prey capture, differed only slightly between aquatic and terrestrial habitats. However, newts adjusted the number of processing cycles to different prey types: while maggots were processed extensively, earthworm pieces were barely processed at all. We conclude that, in addition to food mechanical properties, sensory feedback such as smell and taste appear to induce flexible processing responses, while the medium in which feeding occurs appears to have less of an effect.

Eulerian-Lagrangian finite element modelling of food flow-fracture in the stomach to engineer digestion

Highly processed foods tend to form weak structures which breakdown rapidly in the gastrointestinal (GI) tract, often causing negative effects on human metabolism and health. Developing healthier foods has been limited by the lack of understanding of how foods are digested. Through computational modelling we reveal mechanical gastric food breakdown phenomena and relate food mechanical properties with performance during critical initial digestion stages. Our model relies strictly on a viscoplastic-damage constitutive law, calibrated via rheological experiments on an artificial biscuit bolus and validated by simulating cutting tests. Simulations suggest that bolus separation during bolus backward extrusion and/or indentation by peristaltic waves, and, bolus agglomeration due to hydrostatic compression near the pylorus, are two competing phenomena that can influence the bolus free surface to volume ratio. This showcases the importance of including mechanical aspects of breakdown when designing foods for controlled chemo-mechanical breakdown and associated nutrient release rates.

Effect of foods on selected dynamic parameters of mandibular elevator muscles during symmetric incisal biting

The paper focuses on research that enables the relationship between food and selected mechanical parameters do be determined. The main aim of the study was to designate, depending on the food: (1) the work of a single muscle (i.e. masseter, medial pterygoid, temporalis), and (2) the energy balance of mandibular elevator muscles based on the dynamic patterns of muscles. In turn, the indirect goal was to determine: (1) the muscle contraction, and (2) the average muscle contraction velocity based on the specified kinematic parameters, i.e. incisal biting velocity and incisal biting time.A hybrid model, consisting of a phenomenological model of the masticatory system and a behavioural model of incisal biting, was used in the calculations. The phenomenological model was based on an anatomically and physiologically normal mandible and healthy muscles, while the behavioural model was represented by the dynamic patterns of food.Calculations showed that muscle force is an important, but not the only, parameter that enables the quantitative and qualitative assessment of the functioning of the mandibular elevator muscles during symmetric incisal biting. Based on the obtained results, it can be stated that the dynamic patterns of muscles are a very important parameter, because on their basis, among others, muscle contraction, contraction time, work, and energy can be determined. The conducted calculations and analyses showed that the above-mentioned parameters depend on the mechanical properties of food (the dynamic patterns of food).

Preparation of Antimicrobial Collagen Casings with High Mechanical Properties

Tea Polyphenols (TP) has received much attention for their excellent antioxidant and antibacterial activities. Some additives (such as sodium alginate and sodium pyrophosphate) have good hydrophobicity which have influence on the mechanical properties of food. The effect of TP on the antibacterial activity of collagen casing was investigated, the effect of addition of TP, sodium pyrophosphate and sodium alginate on mechanical properties including tensile force, tensile strength and elongation at break were also studied. Results from the single factor experiments demonstrated that TP showed strong antibacterial activities against Escherichia coli, Staphylococcus aureus and Salmonella according to the Minimum Inhibitory Concentration (MIC) and the inhibition zone method. Moreover, the mechanical properties of collagen casings were obviously influenced by the addition of TP and two food additives including sodium alginate and sodium pyrophosphate. This work would be useful for application of collagen casings with TP in food package to extend shelf-life of sausage during processing, transportation and storage.

Internal architecture of the mandibular condyle of rabbits is related to dietary resistance during growth.

Although there is considerable evidence that bone responds to the loading environment in which it develops, few analyses have examined phenotypic plasticity or bone functional adaptation in the masticatory apparatus. Prior work suggests that masticatory morphology is sensitive to differences in food mechanical properties during development; however, the importance of the timing/duration of loading and variation in naturalistic diets is less clear. Here, we examined microstructural and macrostructural differences in the mandibular condyle in four groups of white rabbits (Oryctolagus cuniculus) raised for a year on diets that varied in mechanical properties and timing of the introduction of mechanically challenging foods, simulating seasonal variation in diet. We employed sliding semilandmarks to locate multiple volumes of interest deep to the mandibular condyle articular surface, and compared bone volume fraction, trabecular thickness and spacing, and condylar size/shape among experimental groups. The results reveal a shared pattern of bony architecture across the articular surface of all treatment groups, while also demonstrating significant among-group differences. Rabbits raised on mechanically challenging diets have significantly increased bone volume fraction relative to controls fed a less challenging diet. The post-weaning timing of the introduction of mechanically challenging foods also influences architectural properties, suggesting that bone plasticity can extend well into adulthood and that bony responses to changes in loading may be rapid. These findings demonstrate that bony architecture of the mandibular condyle in rabbits responds to variation in mechanical loading during an organism's lifetime and has the potential to track dietary variation within and among species.

Intermediate length amylose increases the crumb hardness of rice flour gluten-free breads

Consumers of Gluten Free Bread (GFB) seek soft, cohesive and resilient crumbs. However, the combined effect of amylose (AM) content and chain length, as opposed to only AM content, on crumb hardness have not been studied, neither the synergies of multiple starch molecular features (i.e., amylopectin, AP, and AM fine structures) are understood. In this work, kernels from 5 different rice varieties (Basmati, Thai, Waxy, Sushi and Bomba) were milled after tempering to result in rice flours with less than 8% starch damage varying in AM and AP fine structure, as measured by HPSEC. Dynamic rheology of rice flour gels revealed that Basmati flour exhibited a six-fold higher propensity to form internal Physical Junction Zones (PJZ), those that contribute to the food mechanical properties, than the rest of the starches. Frequency and temperature sweeps revealed AM-AM and AM-AP interactions, respectively, as the internal PJZ. Since Basmati and Bomba exhibited similar AM content and AP fine structure, the intermediate length amylose (699 DP) of Basmati is proved to be the responsible for a greater amount of AM-AM and AM-AP internal PJZ. Interestingly, GFB crumbs made with Bomba flour were 20% softer than those made with Basmati flour. For the first time, AM length is suggested to be a crucial parameter to attain breads with softer and more cohesive crumbs. In fact, results provide strong evidence that the AM length could play a major role than its content in the texture of GFBs crumbs.

Shear-induced molecular fragmentation decreases the bioaccessibility of fully gelatinized starch and its gelling capacity

This work provides information on the feasibility of molecular shear scissions that promote interactions resulting in slowly digestible foods. Extrusion using nine different Specific Mechanical Energy (SME) was performed to obtain amylose and amylopectin with different hydrodynamic radius (Rh) and molecular weight (Mw) from banana starch. The work also aims to find a potential size threshold that decreases starch bio-accessibility through the formation of structural assemblies. Shear-induced fragmentation enabled molecules to get in closer proximity promoting interactions that caused a 36% reduction in their digestion rate. Results suggested that the nature of the structurally-driven slowly digestible starch is mostly due to molecular interactions involving amylopectin, which do not necessarily worsen the food mechanical properties. The Rh and Mw threshold to significantly decrease starch bio-accessibility was estimated to be in the range of 54.3–58.9 nm and 9.9 × 106–17.1 × 106 g/mol, respectively, which was attained in the SME range of 177–274 kJ/kg.

MOLECULAR GASTRONOMY – NEW TREND IN RESTAURANT BUSINESS

Modern trends in catering are focused on various aspects including gastronomic trends, which are the most obvious to users of services. One of the most interesting contemporary trend in gastronomy is molecular gastronomy. This modern trend in the restaurant, which is very complex and insufficiently known to the general public due to the fact that it is a relatively new direction in the preparation of food in the restaurants. In such circumstances, there are numerous disagreements between scientists and chefs, and especially the disputed term is "molecular" that points to some microscopic size. Molecular gastronomy is a direction that involves the preparation of food in a new specific way, which is significantly different from the traditional one. It is often defined as a kind of application of science in practice, while some chefs consider it to be a style of cooking. The specificity of this type of gastronomy is the equipment used in the preparation of food such as rotary evaporators, sintered glass, filters, ultrasonic probes. It is not an equipment typical of classic kitchens, but equipment that is primarily found in scientific laboratories. In addition, the preparation of food in molecular gastronomy involves the use of specific ingredients that are typical of the food industry. Such ingredients are: calcium lactate, sodium alginate, flavors, ascorbic acid, phenols extracted from grape juice, etc. In addition to equipment and ingredients that characterize molecular cuisine, food preparation techniques are also specific. These techniques are based on controlling the cooking temperature, the use of liquid nitrogen and ultrasound, sperring and other specific features that are not used in traditional food preparation. Cooking temperature control is very important and depends on it on the structure, color and mechanical properties of food, where for each type of food the optimal cooking temperature is precisely determined. Very popular is the use of liquid nitrogen, which allows quick icing of food without creating large ice crystals, which is most often used for grinding plants and preparing ice cream. However, when using liquid nitrogen in the kitchen it should be very careful because of the potential hazards to the cook and the guests if it comes into contact with the eyes or in the disabling tract. In addition, molecular gastronomy also uses ultrasound that can be used to control viscosity. A good side of the use of ultrasound is that its use avoids the use of additives and chemicals, and such treatment does not lead to significant chemical changes in food. The classification is used to form a liquid into small edible beads in calcium-alginate capsules that resemble caviar. All of the mentioned specific molecular cuisines require specific innovative cooking skills, so such a kitchen can not be applied to any restaurant, but is typical for exclusive and well-equipped restaurants. Molecular gastronomy as a new trend in food preparation is most represented by European restaurants, but it is increasingly popular in other parts of the world.

Impact of sol-gel transition on the ultrasonic properties of complex model foods: Application to agar/gelatin gels and emulsion filled gels

Quantitative ultrasound (US) techniques have an attractive potential for the non-invasive and real-time characterization of the structural and mechanical properties of food. The objective of the present study is to unravel the determinants of the variations of US properties during sol-gel transition of emulsion filled gels of agar and gelatin, due to the relative contributions (i) of their individual components and (ii) of their combined interactions. Nine model foods were designed, accounting gradually for the complexity of an emulsion filled gel composed of water, sucrose, agar, gelatin and sunflower oil. A quantitative US device was designed to monitor the sol-gel transition of the model foods. US velocity, reflectivity and attenuation were measured at 50 °C (sol-state) and 20 °C (gel-state) with a 1 MHz transducer in pulse-echo mode. US data were then compared to visco-elastic shear moduli and density measurements. Bulk elastic modulus was shown to prevail over density for explaining the variations of US velocity and reflectivity during sol-gel transition, while high gelatin concentration and interactions between agar and gelatin had an impact on US attenuation. In addition to the fact demonstrated here that US reflectivity is easier to measure compared to velocity and attenuation, the literature reports that this parameter also highly depends on the mechanical coupling of interfaces. Therefore, this study is a baseline for future investigations on the potential of US reflectivity for the characterization of physical interactions between food and more complex surfaces, so that to mimic tongue-food interaction during oral processing.

Physical and Mechanical Properties of Selected Common Beans (Phaseolus vulgaris L.) Cultivated in Tanzania

The physical and mechanical properties of foods are important, if not essential, in the design of suitable systems, machines, and structures for planting, harvesting, handling and processing of agro-products. Phaseolus vulgaris L. is a popular legume species that play an important role in human diet and among easily available sources of plant protein. However, despite its important roles, there is a lack of information on the physical and mechanical properties of common beans cultivated in Tanzania. The objective of this study was therefore focused on experimental determination of physical and mechanical properties for Uyole-96, Kablanketi, and Wanja, common beans cultivars grown in the Southern Highlands of Tanzania. Experimental results showed that the average length, width, and thickness were 19.96 mm, 8.97 mm, and 7.6 mm at a moisture content of 17.15% dry basis (db.), 13.92% db., and 14.64% db. for Uyole-96, Kablanketi, and Wanja, respectively. The results further show that the average mean diameters (Da) were 10.93, 9.35, and 9.55 mm for Uyole-96, Kablanketi, and Wanja, respectively. The geometric mean diameters (Dg) were 9.66, 8.35, and 8.80 mm for Uyole-96, Kablanketi, and Wanja, respectively, whereas sphericity was found to be 53, 64, and 58% for the same types of beans. Repose angle measuremnts were experimentally determined as 40, 36, and 35 degrees for Uyole-96, Kablanketi, and Wanja, respectively. Weight for apparent density analysis was 709.27, 686.30, and 766.10 kg/m3 for Uyole-96, Kablanketi, and Wanja, respectively, whereas the apparent densities were determined as 1142, 1158, and 1327 kg/m3, respectively, for the same types of beans. Results from the study showed that physical and mechanical properties for Uyole-96, Kablanketi, and Wanja differ significantly from other common beans cultivars cultivated in other countries. Data on physical and mechanical properties determined in this study establishes a convenient reference table for the mechanization and processing of Tanzanian common beans cultivars .