Since the mid-twentieth century, there has been a rapid rise in the production and consumption of ultra-processed foods (UPFs) so that they now contribute up to 60% of dietary energy intake in several Western countries. Existing accounts emphasize economic, political, food-system, and socio-cultural drivers of this shift. In this conceptual article, we discuss whether from a historical perspective, UPFs are a unique category of foods or rather an intensified extension of a long-standing trajectory of humans using various methods, such as mechanical processing, fermentation and cooking, to improve the digestibility, energy availability and palatability of their foods. Hereto we identify the typical properties used to explain the appeal of UPFs, distinguishing (i) direct intake drivers: engineered palatability, food matrices that enable high eating rates, high energy density and high sensory variety and (ii) market-mediated product attributes: convenient and portable formats, low effective cost, branded and marketed, ubiquitous availability, and long shelf life. We show that for none of these, UPFs form a clearly distinct grouping, but that what sets them apart is that on average they score higher on these properties, and they combine more of them at the same time. We then propose a conceptual framework to assess whether UPFs are unique in the way that they appeal to our evolved food intake regulation system. Hereto we map the properties onto (quantifiable) characteristics of the food intake regulation system in a testable framework. We conclude that a property-based assessment of UPFs suggests them to be an extension, rather than a categorical break from historical traditions, and that understanding the contemporary prevalence of UPFs requires explicit consideration of their interaction with evolved food intake regulation mechanisms, alongside established structural explanations, and we outline implications for future empirical tests and multi-level interventions.

This study investigated mechanics, oral processing, and dynamic sensory perception of commercial plant-based burgers. A beef burger and four commercial green pea and soy-based samples with diverse contents of proteins, fats, carbohydrates, and fibers were selected for the study. The results of mechanical tests indicated complexity of matrix and crust formed due to grilling. A similar pattern was seen for all mechanical parameters; the beef burger mostly scored medium values, similar to an analog (B). Another analog (E) recorded the highest values for large and small deformation parameters, including load-to-deformation, elasticity, and fracturability. The opposite was analog D. The mastication results followed the trends as for the mechanical parameters, indicating the correlations between instrumental texture and eating behavior: the beef burger and analog B were consumed in similar dynamics, while analogs D and E scored extreme values. The differences between the products existed in the bolus particles of median size. Finally, attributes like chewiness, crumbliness, juiciness, and meat flavor were relevant to the beef burger dynamic sensory profile. Otherwise, plant flavor was the dominant attribute for the plant-based analogs. Texture and oral processing parameters were independent of the plant-protein source. However, soy-based burgers scored higher values of plant flavor dominance. Considering previously published studies and reports, commercial products’ quality improvement is evident but there is more room for texture and flavor improvements. Future studies should focus on these products’ preparation and serving to investigate possible strategies for texture improvement and plant flavor masking. Instrumental and eating quality of beef and plant-based burgers was studied. Mechanical results indicated patty deformation and structure failure complexity. Substantial correlations between mechanics and oral processing were observed. Beef burger and analog “B” were often similar and had medially positioned values.

Previous studies dealing with plant-based meat analogs confirmed the potential of oral processing methods to identify options for improving those products. Knowing that sensory perception can be influenced by adding condiments, this short communication aimed to investigate the texture and oral processing of four plant-based burger analogs and a beef burger when consumed in portions or as part of model meals with buns and sides. Texture profile analysis indicated that beef burgers and analog E were the toughest. Two analogs (B and S) showed textures close to beef, while one (analog D) displayed significantly lower values for hardness, toughness, cohesiveness, and springiness. The instrumental data was only partly reflected in the mastication parameters. Adaptations in mastication behavior were expected, but differences between the plant-based analogs were smaller than anticipated, although clear differences were observed for consumption time, number of chews and number of swallows. On the whole, mastication patterns concurred within different consumption scenarios (portions, model burgers), and significant correlations with instrumental texture were obtained.

Popularity of meat analogs is rising. Several causes for that were identified. On one side, more sustainable products with lower environmental impact are needed. Consumers also demand these products because of their ethical and health benefits. However, sensory perception is still a great obstacle for their wider acceptance.

To increase the appeal of plant protein-based meat analogs, further progress needs to be made in their sensory perception. Given the limited number of studies on meat analogs, this review focuses on structure, oral processing, and sensory perception of meat and subsequently translates the insights to meat analogs. An extensive number of publications has built the current understanding of meat mechanical and structural properties, but inconsistencies concerning terminology and methodology execution as well as the wide variety in terms of natural origin limit solid conclusions about the control parameters for oral processing and sensory perception. Consumer-relevant textural aspects such as tenderness and juiciness are not directly correlated to single structural features but depend on an interplay of multiple factors and thus require a holistic approach. We discuss the differences in mastication and disintegration of meat and meat analogs and provide an outlook toward converting skeptical consumers into returning customers.

Nowadays, a growing offering of plant-based meat alternatives is available in the food market. Technologically, these products are produced through high-moisture shear technology. Process settings and material composition have a significant impact on the physicochemical characteristics of the final products. Throughout the process, the unfolded protein chains may be reduced, or associate in larger structures, creating rearrangement and cross-linking during the cooling stage. Generally, soy and pea proteins are the most used ingredients in plant-based meat analogues. Nevertheless, these proteins have shown poorer results with respect to the typical fibrousness and juiciness found in real meat. To address this limitation, wheat gluten is often incorporated into the formulations. This literature review highlights the key role of wheat gluten in creating products with higher anisotropy. The generation of new disulfide bonds after the addition of wheat gluten is critical to achieve the sought-after fibrous texture, whereas its incompatibility with the other protein phase present in the system is critical for the structuring process. However, allergenicity problems related to wheat gluten require alternatives, hence an evaluation of underutilized plant-based proteins has been carried out to identify those that potentially can imitate wheat gluten behavior during high-moisture shear processing.

The Doi-Edwards tube model, coupled with relaxation mechanisms, such as reptation, contour length fluctuation, and constraint release, allows us to quantitatively predict the linear viscoelastic properties of entangled polymers. However, for nonlinear elongational flows, large discrepancies between theoretical predictions based on the tube model and experimental results still persist today. This is in particular obvious for the experimentally observed strong qualitative differences in extensional flow of entangled polystyrene (PS) melts and solutions despite having the same number of entanglements and exhibiting the same linear viscoelastic behavior. The cause of this non-universality is often attributed either to a monomeric friction reduction or to an interchain pressure effect. In this work, we investigate the changes in extensional flow behavior going from polymer solutions to the melt state. For this purpose, we measure with a filament stretching rheometer the nonlinear extensional responses of differently long PS chains, both in the melt state and diluted in short-chain matrices of the same polymer at varying concentrations. These concentrations have been chosen sufficiently high, such that the chains stay entangled. This allows us to discuss the influence of concentration and molar mass on the steady-state elongational viscosity to highlight scaling relations. The purpose of the present work is to conduct well-defined experiments to further investigate how the steady extensional viscosity of polymer solutions and blends varies with the concentration and with the molecular weight of the chains.

This study provides an overview of over 50 publications exploring the consumers’ motives for choosing meat analogs over real meat, how they perceive them, and what can be learned from meat structure, mechanics, oral processing, and dynamic sensory analysis for meat analog design. Meat analogs’ sensory perception is their main lack, while ethics, health, and environmental statements might be used to boost their promotion. Methods for meat structure and mechanics’ analysis are well established and translated (to some degree) to meat analog’s quality analysis. However, limited information is present concerning meat and meat analogs’ oral processing and dynamic perception, which can be seen as a chance for future research and improvement.

The current coarse-grained picture to represent polymer chain dynamics under uniaxial extensional flow (based on the Doi–Edwards model) fails to predict some scaling dependencies of material properties on deformation rate observed experimentally, specifically the monotonic thinning behavior of polymer melts. Recently, new mechanisms based on the concept of monomeric friction reduction have been proposed to explain this peculiar behavior; however, it is difficult to include them in the framework of the standard tube model. Therefore, in this work, we propose an alternative treatment which does not rule out friction reduction but uses a different approach. It considers that the chain can stretch up to a certain level that we determine based on the Pincus blob picture, in place of determining to which extend the chain stretch is reduced compared to its finite extensibility. To this end, we revisit the extensional rheological data of polystyrene melts and see how the specificities of chains under strong elongational flow can be integrated into a tube model. This requires accounting for possible flow-induced chain orientation, stretching, and disentanglement. In particular, we extend the picture of Pincus blobs and define different levels of stretch that a chain can reach as a function of the extensional rate by invoking a rate-dependent blob picture. While this approach requires introducing an additional parameter to describe the stretch relaxation time, the results are in good agreement with the experimental observations. This alternative but sound approach should contribute to the on-going discussion on the elongation of entangled polymers.

To predict in-mouth perception of semi-solid foods like yogurt, their lubricating behavior needs to be understood. In food industrial applications of oral tribology, it is preferable and more efficient to use a material with a hydrophilic surface to mimic the tongue in the in vitro setup. We investigated and compared whey protein isolate (WPI) gel and polydimethylsiloxane (PDMS), based on their physicochemical characteristics and their ability to discriminate the friction behavior of a set of commercial yogurts known to elicit different mouthfeels. Stiffness and wettability of WPI gel were more similar to the human tongue than PDMS. The friction factors of Newtonian fluids measured on WPI gel allowed to construct a master Stribeck curve; this was not the case for PDMS. The yogurts could be clearly discriminated when measured on WPI gel. Their friction factors in the mixed regime correlated to the fat content and to perceived creaminess. Yogurts' discrimination was not optimal on PDMS. The measurements on WPI gel, done in the speed range 1-0.001 m/s, were compared to a second speed range (0.2-0.002 m/s), believed to be more relevant for in-mouth conditions. Yet, the first speed range gave the best discrimination, also between samples with small differences in fat content (semi vs full-fat). Statistical analyses were performed on the datasets obtained using WPI gel, for a detailed characterization of its discriminative predictive power, demonstrating that the average friction in the mixed regime, and the slope in the mixed regime are the most discriminating features for tribological behavior.

It is now established that the huge qualitative difference in flow behavior between entangled polymer melts and solutions in nonlinear elongational flows cannot be explained in the framework of the "standard" tube model. Instead, the additional relaxation mechanism of alignment-induced friction reduction, acting primarily in melts, has shown its interesting potential to explain the experimental data. Here, we critically assess this mechanism by means of a systematic experimental investigation of the extensional response of long polystyrene chains diluted in short chain matrices of varying molar mass, varying the interaction between long chains and their molecular environment. We find that, surprisingly, all polystyrene blends exhibit different transient strain hardening properties but the same apparent steady-state elongational viscosity; i.e., the long chains reach the same final stretch state as long as the short chain exceeds a critical molar mass of about 4 kg/mol, well below the entanglement limit, and do not significantly contribute to the strain hardening. This observation contradicts, in part, the basic assumption according to which the elongation state of a chain depends on its molecular environment, and raises new fundamental questions, in particular on the relationship between transient strain hardening and the stretch state of the chains and its consequences on the nonuniversal behavior of melts and solutions in strong flows.

We investigate the molecular features of high-performance gel-spun ultrahigh-molecular-weight polyethylene UHMWPE fibers (SK75, invented and manufactured by DSM) and propose a multiscale structural model that describes the organization of molecules from the unit cell to the filament level, based on X-ray diffraction in static and dynamic conditions (during tensile testing). The model emphasizes the discontinuous nature of the crystalline phas e, which is embedded in a percolating amorphous phase and connected by tie molecules running through the amorphous phase. The tie molecules play a critical role in the tensile properties (e.g., Young's modulus and sonic modulus) of the material. We analyze the micromechanics of the material during tensile deformation and show that, in the elastic regime, the stress-transfer mechanisms (e.g., tie molecules) are so efficient to realize a homogeneous stress distribution through the various length scales (from filament level to unit cell level). Plastic deformation of filaments begins with shear break-up of crystals that triggers or is triggered by an unusual, not well explored, deformation mode of the orthorhombic unit cell (contraction of the a-axis with simultaneous expansion of the b-axis). We also show that the morphological model with discontinuous crystalline phase provides a logical base for the interpretation of the sonic modulus of UHMWPE fibers. Realignment of molecules in the noncrystalline regions of the material can explain the remarkable increase of the sonic modulus measured during tensile tests.

The viscoelastic properties of wheat flour dough are known to be very sensitive to small changes in water content and mixing time. In this study the simple scaling law originally proposed by Hibberd (1970) [Rheol. Acta 9, 497-500] to capture the water dependency of the dynamic moduli in small amplitude oscillatory shear, was also applied to creep-recovery shear tests and extensional tests. The scaling law turns out to be valid not only in the linear region, but to a certain extent also in the non-linear region. At sufficiently high water levels, a ‘free’ water phase exists in dough, which attenuates the starch-starch and gluten-starch interactions. Dough characterisation after different mixing times shows that overmixing may cause a disaggregation or even depolymerisation of the gluten network. The network breakdown, as well as the subsequent (partial) recovery, are clearly reflected in the value of the strain-hardening index, for which a maximum is reached at a mixing time close to the optimum as determined with the Mixograph. Finally, the gluten proteins turn out to be much less susceptible to overmixing in an oxygen-lean environment, which demonstrates the significant role of oxygen in the degradation process.

The enzymes glucose oxidase and transglutaminase are frequently used to improve the breadmaking performance of wheat flours, as they have the ability to considerably alter the viscoelastic nature of the gluten network. To evaluate a flour’s breadmaking performance, rheological tests offer an attractive framework. In this study, the rheological impact of adding glucose oxidase or transglutaminase to wheat flour dough is investigated by means of linear oscillatory shear tests, creep-recovery shear tests and startup extensional tests. The former tests reveal that the enzymes render the dough stiffer and enhance its elastic character, until saturation is reached. In the breadmaking process, the use of excessive amounts of enzyme is known to be counterproductive. The strain-hardening index clearly reveals this overcross-linking effect. Besides enzymes, the gluten network can also be reinforced by adding supplementary gluten, which was indeed found to enhance the extent of strain-hardening.

There is still considerable debate in the literature about the respective roles of starch and gluten in both the linear and non-linear rheology of wheat flour dough. Hence, to elucidate the individual contributions of gluten and starch to the overall dough behaviour, the rheological properties of dough and mixtures of different gluten-starch ratios were studied systematically in shear and extension, by means of an adequate rheological toolbox consisting of linear small amplitude oscillatory shear tests and non-linear tests such as creep-recovery in shear and uniaxial extension. The starch component plays a pivotal role in linear dough rheology. With increasing starch content, the linearity limit observed in oscillatory shear tests decreases as a power-law function. Starch also clearly affects the extensional viscosity at small strains. Consequently, in the linear region differences between different gluten systems may become obscured by the presence of starch. As breadmaking qualities are known to be intrinsically linked to the gluten network, it is imperative to probe the non-linear behaviour of dough in order to expose differences in flour quality. The quality differences between a strong and a weak flour type were revealed most clearly in the value of the strain-hardening index in uniaxial extension and the total recovery compliance in non-linear creep-recovery tests. Notwithstanding its earlier successful application to pure gluten gels, the accuracy of the critical gel model in predicting the linear rheological properties of dough was found to be limited, due to dough having a small linearity limit and a finite longest relaxation time.

Despite extensive research, there is still no consensus in the literature about the roles of starch and gluten in both the linear and non-linear rheology of wheat flour dough. To elucidate the contributions of gluten and starch to the dough behavior, the rheological properties of dough and mixtures of different gluten-starch ratios were studied in shear (small amplitude oscillatory shear tests) and uniaxial extension. The breadmaking quality of a given wheat flour is mostly linked to the gluten network. In the linear region, starch has the potential to obscure differences between different gluten systems. Hence, only non-linear rheological tests are able to distinguish strong from weak flour dough. Changes in water content mostly affect the gluten-starch and starch-starch interactions, whereas the mixing time has a strong impact on the gluten network itself.