Applications of tribology in studying food oral processing and texture perception

Effect and mechanism of calcium ions on the astringency in green tea infusion and epigallocatechin gallate solution: An in vitro oral soft tribology study

In this study, the effect of calcium ions (Ca2+) on the astringency sensation in green tea infusion was explored using sensory evaluation, in vitro oral soft tribology, and targeted metabolomics. Ca2+ enhanced the astringency intensity (from 2 to 6) and the turbidity (from 10.0 to 83.3), and decreased the particle size (from 1468.0 to 817.65) in cold-brewing tea. Catechins influenced the astringent sensation in the presence of Ca2+ and the content of (-)-Epicatechin, (-)-Epigallocatechin, and (-)-Epigallocatechin gallate (EGCG) solution in green tea infusion after oral processing all reduced. The friction coefficient of hot-brewed tea (μ, 1.6-2.8) was greater than that of cold-brewed tea (μ, 1.0-2.6), and EGCG increased with the enlarged Ca2+ concentrations. Ca2+ increased the astringency mainly through catechins and saliva lubrication. The in vitro soft oral tribology could be usefully explored the enlarged astringency sensation by Ca2+, and applied to the astringency regulation of beverages.

Methods and instruments for the evaluation of food texture: Advances and perspectives

Evaluation of food texture is crucial for product development and quality control in the food industry. To objectively evaluate the texture, the methods to characterize the texture attributes by instruments become increasingly important. This review mainly introduces the advances of instrumental methods by rheology and tribology in food texture studies, with a focus on the instrumental applications in four complex texture attributes, including thickness, astringency, creaminess, and graininess. It discusses the mechanism of food texture perception by finding the optimal instrumental method, but quantitatively correlating the instrumental parameters with sensory texture remains a challenge. Moreover, the perspectives of new cutting-edge technologies including micro-analytical, tactile sensing, and biomimetic techniques, are introduced. The review provides a possible direction that integrating the technologies not only by rheology and tribology, but also by multi-modal tactile sensing, will deepen the understanding of sensory texture perception and advance the instrument development for food texture evaluation.

Effect of Two-Stage Water Addition on Consistency of Processed Cheese: Physicochemical, Mechanical, Thermal, and Organoleptic Approach

The current study investigated the impact of two-stage water addition on the selected properties of processed cheese (PC). In particular, the above-mentioned novel approach involved adding water in two stages during the PC manufacturing process. The effects of this process on the physicochemical, viscoelastic, textural, tribological, thermal, and organoleptic properties of PC were evaluated. For all examined PC samples, the elastic modulus consistently dominated over the viscous modulus (G' > G″) across the entire frequency range. Moreover, it was observed that a smaller amount of initial water addition during the melting process resulted in a slight increase in the values of both viscoelastic moduli. The control sample exhibited the lowest lightness values, while it also showed the highest level of yellow coloring, suggesting that the two-stage addition of water affected the color of the PC samples. The results showed that the two-stage addition of water significantly influenced the physicochemical, viscoelastic, textural, tribological, thermal, and organoleptic properties of PC, leading to a modified texture, and thermal stability. Moreover, firmer PC products were obtained when a greater initial water level (first dosage; in the range of 60 to 90%) was utilized. This study could provide valuable information on the development of high-quality PC products with tailored functional properties, which can be important for the dairy industry.

Application of fat replacers in low-fat starch-based foods: Type, formulation and action mechanism on food quality

Fat is an essential component in the processing of starch-based products. However, excessive fat intake is not beneficial to human health. Therefore, the development of fat replacers (FRs) and healthy and delicious low-fat starch-based products has become a research focus. The regulation mechanisms of fat on the quality of starch-based products, and types and formulations of FRs used in starch-based products were summarized. Based on the interaction with starch, the regulation mechanism of FRs on the quality of starch-based products and main quality evaluation parameters of low-fat starch-based products formed by these FRs were discussed. Oil-free systems (particles, polymers, hydrocolloids) and oil-containing systems (emulsions, emulsion gels, oleogels) are the main FRs used in starch-based foods. Their formulations depend mainly on the interaction between the components (polysaccharides, proteins and fats). Regulation mechanisms of FRs on the quality of starch-based products are mainly due to that their addition changes the structure, physicochemical and functional properties of starch. Microstructure, textural, rheological and tribological properties, sensory evaluation, fat digestion and calories, and nutrition are main elements of quality evaluation of low-fat starch-based products containing FRs. Next, it is necessary to systematically explore the regulation mechanism of FRs with different structures and properties on the quality of starch-based products based on molecular simulation and machine learning. More interdisciplinary collaborations, such as molecular chemistry, nutrition and nanotechnology, need to be used to guide the design of FRs and the development of low-fat starch-based products.

Application of biomimetic tongue substrate to investigate the role of friction and vibration in sensory texture perception

This study proposed a novel biomimetic tongue substrate to better understand food texture perception, expanding the scope of this mechanism from merely friction to also include vibration in oral lubrication. With our bioinspired setup, friction and vibration signals were simultaneously acquired using the polyvinyl alcohol (PVA) hydrogel substrates fabricated with different parameters of surface roughness and thickness. Results showed that the feature parameters of friction coefficient and vibration amplitude were positively correlated to surface roughness, while substrate thickness had little effect on these features. Characterization tests were conducted for the PVA biomimetic tongue substrate with featured filiform papillae and fungiform papillae, whose surface roughness, Young's modulus, and friction coefficient were 70.94 ± 8.44 μm, 12.11 ± 1.15 kPa, and 0.17, respectively, showing similar properties and friction responses to the human tongues. Focusing on the typical texture attributes of slipperiness, astringency, and graininess, rheological, friction, and vibration response were further measured using the food samples mixed with artificial saliva. Sensory analysis was also conducted to demonstrate the essential roles of tactile features in sensory texture perception. Results of correlation analysis revealed that sensory slipperiness and astringency had linear correlations with friction coefficient (r = 0.89 and 0.899, respectively), while sensory graininess was linearly correlated with vibration amplitude (r = 0.905, higher than r = 0.819 with friction coefficient). The findings highlighted the crucial role of oral friction and vibration sensation in sensory texture perception. Meanwhile, this work provided a new biomimetic setup for oral lubrication studies, paving the way for a better understanding of the food texture perception mechanism.

Surfactant-free W/O high internal phase emulsions co-stabilized by beeswax and phytosterol crystal scaffold: A promising fat mimetic with enhanced mechanical and mouthfeel properties

Water-in-oil high internal phase emulsions (W/O-HIPEs) typically rely on large amounts of surfactants to disperse water droplets and usually use crystalline saturated triacylglycerides (TAGs) to enhance processing properties. However, these practices conflict with consumer demands for 'natural' ingredients. This study seeks to develop novel crystal fractions similar to saturated TAGs for the preparation of W/O-HIPEs as low-calorie fat mimetics, focusing on their mechanical and mouthfeel properties, which have received little attention thus far. This study explored using an all-nature crystal scaffold to stabilize W/O-HIPEs as fat mimetics under surfactant-free conditions, featuring multi-sensorial attributes. The crystal scaffold was designed by varying the ratios (10:0, 8:2, 6:4, 4:6, 2:8, and 0:10, w/w) of beeswax (BW) and phytosterol (PS), two sustainable crystal fractions. The optimal stabilization of W/O-HIPEs (φ = 0.75) was achieved at a BW/PS ratio of 6:4, with only a slight increment in droplet size for either static storage (30 days) or freeze-thaw (3 cycles) treatment. Crystal particles of BW and PS performed a synergistic effect to stabilize W/O-HIPEs by forming a network in the bulk phase and adsorbing onto droplet surfaces as a Pickering stabilizer. The crystalline layer on the droplet surfaces also generated bridging networks, providing a dual stabilization mechanism for W/O-HIPEs. Incorporating 3.0 wt% of BW and PS (BW/PS = 6:4, w/w), W/O-HIPEs exhibited the required modulus of 1 × 105 Pa to mimic fat. Moreover, these W/O-HIPEs exhibited superior lubrication behavior (friction coefficients below 0.06) compared to pure liquid oil at low sliding speeds (0-2.5 mm/s), enhancing mouthfeel. However, increasing the BW and PS crystals content to 4.0 wt% led to increased brittleness, with a reduction in the emulsion's lubricity at the hydrodynamic region. These findings highlight the potential of natural crystals to develop low-calorie W/O-HIPEs as fat mimetics in the food industry.

Older adults and prepared meals: The influence of comfort, nostalgia, and texture preferences on acceptance

This study's objective was to develop desirable, safe, and nutritious dairy-rich breakfasts and desserts for older adults while identifying the influence of comfort, nostalgia, and texture preferences. Participants (n = 81, mean age = 71 ± 7.3 years) evaluated two breakfast meals (meat-containing, vegetarian) and two desserts (chocolate, vanilla puddings) for acceptance; they also answered inquiries concerning texture preferences and reported their feelings of comfort and nostalgia experienced during evaluation. Mean participant liking was 6.2 for the meat breakfast, 5.7 for the vegetarian breakfast, 5.8 for the chocolate pudding, and 4.3 for the vanilla dessert (along a 9-point scale). Meal liking was mediated by flavor intensity, sweetness intensity, and texture preference. Texture preference results indicated that older adults both like and are comfortable with orally handling textures typically deemed concerning for this population. Liking of the meals also increased if a higher experience of comfort was elicited during meal consumption (p < 0.05); perceived comfort decreased if there was insufficient flavor. Increased nostalgia experienced during meal consumption also increased overall liking. This study provided guidance on acceptable textures for potential product development while highlighting the importance of understanding the perception of nostalgia and comfort for older adults' meal acceptance. PRACTICAL APPLICATIONS: Focusing on older adults, this study showed that nostalgia, comfort, and texture variety are all important elements of an older adult's diet. This research is useful for product developers who can use these elements in designing and testing the acceptance and healthfulness of prepared meals by older adults.

Citrus fibers improve rheology of OSA starch-based high internal phase emulsion for 3D printed elderly foods

3D printing ready-to-eat emulsions using trans-fat-free edible oil, presents a significant challenge due to the complexities involved in achieving the necessary material structure, rheological properties, and stability. This study fabricated High Internal Phase Emulsions (HIPEs) stabilized with citrus fibers and octenyl succinic anhydride (OSA) modified waxy starch, serving as the printable inks for 3D-printable elderly foods. These printable inks exhibited a pseudoplastic gel structure, which provided enhanced extrudability and improved shape retention. The incorporation of citrus fiber, water, OSA starch, sunflower oil at a concentration of 0.3 wt%, 22.7 % wt %, 2 % wt%, 75 wt% in the 3D-printed HIPEs resulted in optimal addition, yielding the highest level of shape accuracy. Compared to the addition of OSA-modified starch, microstructural analysis and rheological testing (using Lissajous-Bowditch plots) indicated that the addition of citrus fiber had a greater impact on the rheological and textural properties of the HIPEs, which improved shape retention and fluidity of the HIPEs, and ensure the stability of continuous extrusion printing. Additionally, bionic tribological properties demonstrated that tribological properties of the prepared HIPEs were very close to the ones of mayonnaise, which indicating that the prepared HIPEs had smooth texture and easy-to-chew properties for the elderly. These findings offered a comprehensive understanding of the structure-function relationship between the molecular structures of HIPEs and their 3D printability, providing technical insights for the development of 3D-printed emulsion-based ready-to-eat elderly food products. This study provided a good industrialized method for HIPEs stabilized with only fruit dietary fiber and modified starch, and facilitated the development of emulsion-based ready-to-eat food products with 3D printability.

Changing the Oral Tribology of Emulsions Through Crystallization of the Dispersed Triglyceride Phase

Suspoemulsions are used for food, cosmetic and pharmaceutical products, including food such as dairy products and non-dairy alternatives. Product properties, such as flow behavior or sensory perception of non-dairy products differ from those of dairy products and are therefore perceived by consumers as products of inferior quality. One reason for this may be the crystallization behavior of the added triglycerides leading to differences in solid fat content in comparison to cow milk. This is discussed with the solidity of the dispersed phase as a parameter of suspoemulsions. The solidity was varied by using low and high melting triglycerides and measuring at different temperatures. The dispersed phase fraction is φ = 30%. The droplet size distribution showed a x50,3 of 1.2 and 3.66 μm, mimicking the droplet sizes of milk and dairy cream. Rheological frequency sweeps were carried out within a temperature range from 5°C to 50°C. The differences in solidity of the dispersed phase caused no changes in viscosity at each temperature. In contrast, oral tribology distinguished different solidities of the dispersed phase with changes in the friction coefficient. The friction coefficient was determined for increasing rotational speeds (0.01-100 mm/s), to compare the so called Stribeck curves with each other. In general, with increasing solidity of the dispersed phase, the friction coefficient increases. Comparing the Stribeck curves of pure butter fat suspoemulsion with those of plant-based fat suspoemulsions, different plant-based fats can be mixed, to mimic the friction profile of milk products in plant-based alternatives.

Bacterial cellulose infusion: A comprehensive investigation into textural, tribological and temporal sensory evaluation of ice creams

The study examines how adding bacterial cellulose also referred to as Symbiotic Culture of Bacteria and Yeast (SCOBY) to ice cream affects the textural, tribological, and sensory attributes, particularly texture and mouthfeel perception. Analytical assessments were performed on three types: SCOBY-added ice cream and two reference samples (control and guar gum-added ice creams). Evaluations included physicochemical properties, textural and tribological characteristics, and dynamic sensory mouthfeel using the temporal dominance of sensation (TDS) methodology. SCOBY ice cream showed higher probiotics content, lower pH, and higher acidity than reference samples. The addition of SCOBY increased hardness and altered the textural properties. TDS analysis highlighted distinct temporal dominance patterns, with guar gum ice cream presenting a pronounced mouth/residual coating pre-swallowing, while SCOBY and control ice cream exhibited a thin/fluid perception. The frictional factor at 37 °C was positively correlated with the melting rate, graininess, and thin/fluid perception while negatively correlated with firmness, smoothness and mouthfeel liking. Additionally, the mouthfeel liking was higher with firm, smooth and mouth/residual coating sensations and lower with grainy and thin/fluid perception. In summary, incorporating SCOBY in ice cream formulations can provide health benefits and meet consumer preferences for natural ingredients, while ensuring careful optimization of mouthfeel.

Development of Oleogel-in-Water High Internal Phase Emulsions with Improved Physicochemical Stability and Their Application in Mayonnaise

Egg-free mayonnaise is receiving greater attention due to its potential health benefits. This study used whey protein isolate (WPI) as an emulsifier to develop high internal phase emulsions (HIPEs) based on beeswax (BW) oleogels through a simple one-step method. The effects of WPI, NaCl and sucrose on the physicochemical properties of HIPEs were investigated. A novel simulated mayonnaise was then prepared and characterized. Microstructural observation revealed that WPI enveloped oil droplets at the interface, forming a typical O/W emulsion. Increase in WPI content led to significantly enhanced stability of HIPEs, and HIPEs with 5% WPI had the smallest particle size (11.9 ± 0.18 μm). With the increase in NaCl concentration, particle size was increased and ζ-potential was decreased. Higher sucrose content led to reduced particle size and ζ-potential, and slightly improved stability. Rheological tests indicated solid-like properties and shear-thinning behaviors in all HIPEs. The addition of WPI and sucrose improved the structures and viscosity of HIPEs. Simulated mayonnaises (WE-0.3%, WE-1% and YE) were then prepared based on the above HIPEs. Compared to commercial mayonnaises, the mayonnaises based on HIPEs exhibited higher viscoelastic modulus and similar tribological characteristics, indicating the potential application feasibility of oleogel-based HIPEs in mayonnaise. These findings provided insights into the development of novel and healthier mayonnaise alternatives.

Recent trends in design of healthier fat replacers: Type, replacement mechanism, sensory evaluation method and consumer acceptance

In recent years, with the increasing awareness of consumers about the relationship between excessive fat intake and chronic diseases, such as obesity, heart disease, diabetes, etc., the demand for low-fat foods has increased year by year. However, a simple reduction of fat content in food will cause changes in physical and chemical properties, physiological properties, and sensory properties of food. Therefore, developing high-quality fat replacers to replace natural fats has become an emerging trend, and it is still a technical challenge to completely simulate the special function of natural fat in low-fat foods. This review aims to provide an overview of development trends of fat replacers, and the different types of fat replacers, the potential fat replacement mechanisms, sensory evaluation methods, and their consumer acceptance are discussed and compared, which may provide a theoretical guidance to produce fat replacers and develop more healthy low-fat products favored by consumers.

Interfacial crystallized oleogel emulsion with improved freeze-thaw stability and tribological properties: Influence of cooling rate

In this study, the influence of cooling rate on the freeze-thaw stability, rheological and tribological properties of interfacial crystalized oleogel emulsion was investigated. Results showed that slower cooling rate could promote formation of larger crystals and stronger network in oleogels. Additionally, oleogel emulsions showed higher freeze-thaw stability than those stabilized solely by emulsifiers. The slower cooling rate resulted in larger crystals adsorbed at the droplet surface. This led to greater steric hindrance that prevented the migration of oil droplets with higher resistance to disruption by ice crystals. The rheological and tribological measurements suggested that with appropriate amount of crystals, the tribological properties were better maintained for emulsions prepared at slow cooling rate after freeze-thaw treatment. This strategy greatly enriched oleogel emulsion formulations and provided important clues for potential applications in food products involved with freeze-thaw treatment.

Understanding mechanisms behind the oily mouthcoating perception of pure vegetable oils using tribology

Tribology is the science of measuring friction between surfaces. While it has been widely used to investigate texture sensations of food applications, it is seldom applied in pure edible oil systems. In this research, we measured friction, viscosity, and solid fat content (SFC) of nine vegetable oils at 30 and 60°C. Polarized static microscopy was used to assess crystal formation between 60 and 30°C. Descriptive sensory analysis and quantification of oral oil coatings were performed on the oils at 60°C. Expressing the friction factor of oil over the Hersey number (calculated using high sheer-viscosity values) showed no differences in friction between 30 and 60°C, except for shea stearin. Static microscopy revealed crystallization occurred at 30°C for shea stearin, whereas no or few crystals were present for other oils. At 30°C, friction at 1 × 10-2 m/s showed an inverse correlation with SFC (R = -0.95) and with high shear rate viscosity (R = -0.84), as well as an inverse correlation (R = -0.73) with "oily mouthcoating" perception. These results suggest that friction could be a predictor of fat-related perceptions of simple oil systems. Additionally, we hypothesize that the presence of crystals in oils could lower friction via a ball-bearing lubrication mechanism.

Incorporation of curcumin-loaded solid lipid nanoparticles into yogurt: Tribo-rheological properties and dynamic in vitro digestion

The incorporation of nanostructures loaded with bioactive compounds into food matrices is a promising approach to develop new functional foods with improved nutritional, health profiles and good sensorial properties. The rheological and tribological properties of yogurt enriched with curcumin-loaded solid lipid nanoparticles (SLN) were evaluated. Also, the TCA solubility index, the bioaccessibility of curcumin and cell viability were assessed after dynamic in vitro digestion. The presence of SLN in yogurt did not affect its rheological properties; however, SLN addition increased the lubrication capability of yogurt. After in vitro digestion, yogurt with added SLN (yogurt_SLN) presented a lower TCA solubility index (22 %) than the plain yogurt (39 %). The bioaccessibility and stability of curcumin were statistically similar for yogurt_SLN (30 % and 42 %, respectively) and SLN alone (20 % and 39 %, respectively). Regarding cell viability results, the intestinal digesta filtrates of both controls (i.e., SLN alone and plain yogurt) did not affect significantly the cell viability, while the yogurt_SLN presented a possible cytotoxic effect at the concentrations tested. In general, the incorporation of SLN into yogurt seemed to promote the mouthfeel of the yogurt and did not adversely affect the bioaccessibility of curcumin. However, the interaction of SLN and yogurt matrix seemed to have a cytotoxic effect after in vitro digestion, which should be further investigated. Despite that, SLN has a high potential to be used as nanostructure in a functional food as a strategy to increase the bioactive compounds' bioaccessibility.

Perspectives on the yogurt rheology

The oral processing of yogurt is a dynamic process involving a series of deformation processes. Rheological knowledge is essential to understand the structure and flow properties of yogurt in the mouth and to explore its relationship with sensory perception. Yogurt is rheologically characterized as a non-Newtonian viscoelastic material. The rheological properties of yogurt are affected by many factors, from production to consumption. Therefore, rheological measurements are widely used to predict and control the final quality and structure of yogurts. Recent studies focus on the elucidation of the effects of cultures and processes used in production, as well as the design of different formulations to improve the rheological properties of yogurts. Moreover, the science of tribology, which dominates the surface properties of interacting substances in relative motion to evaluate the structural sensation in the later stages of eating in addition to the rheological properties that give the feeling of structure in the early stages of eating, has also become the focus of recent studies. For a detailed comprehension of the rheological properties of yogurt, this review deals with the factors affecting the rheology of yogurt, analytical methods used to determine rheological properties, microstructural and rheological characterization of yogurt, and tribological evaluations.

The role of membrane components on the oleosome lubrication properties

HYPOTHESIS

Oleosomes are natural oil droplets with a unique phospholipid/protein membrane, abundant in plant seeds, from which they can be extracted and used in emulsion-based materials, such as foods, cosmetics and pharmaceutics. The lubrication properties of such materials are essential, on one hand, due to the importance of the in-mouth creaminess for the consumed products or the importance of spreading the topical creams. Therefore, here, we will evaluate the lubrication properties of oleosomes, and how these properties are affected by the components at the oleosome membrane.

EXPERIMENT

Oleosomes were extracted, and their oral lubricating properties were evaluated using tribology. To understand the influence of the oil droplet membrane composition, reconstituted oleosomes were also studied, with membranes that differed in protein/lecithin ratio. Additionally, whey protein- and lecithin-stabilised emulsions were used as reference samples. Confocal laser scattering microscopy was used to study the samples visually before and after tribological analysis.

FINDINGS

Oleosomes followed a ball-bearing mechanism, which was probably related to their high physical stability due to the presence of membrane proteins. When the membrane protein concentration at the surface was reduced, the droplet stability weakened, leading to plating-out lubrication. Following our results, we elucidated the oleosome lubrication mechanism and showed their possible control by changing the membrane composition.

Effect of soy peptides with different hydrolysis degrees on the rheological, tribological, and textural properties of soy protein isolate gels

This study was performed to examine the effect of two soy peptides addition with hydrolysis degrees of 90% and 30% (hydrolysis degree (DH)90, DH30) at various concentrations (1-10 mg/mL) on soy protein isolate (SPI) gel behavior and pure SPI gel was set as control. SPI gels with adding peptides were prepared, and their rheological, textural, and tribological properties, as well as water-holding capacity, zeta potential, and particle size, were determined. During the rheological measurement, adding peptides reduced storage modulus (G') compared to the control, with larger particles formed. However, peptide addition could significantly reduce gelation time, showing a more significant effect with DH30. The gels' firmness, adhesiveness, and water-holding capacity decreased as peptide concentration increased. Syneresis was observed in gels with peptides, whereas the control sample showed no syneresis. Based on the rheological results, the shear stress in the control sample was higher than in the gels containing peptides indicating more resistance to shear. The gels with DH30 showed greater G' and G″ than DH90 at all studied concentrations. Nevertheless, there was an improvement in the lubrication behavior of SPI gels with peptide addition. DH30 showed a relatively more significant friction reduction than DH90, indicating their slightly better lubrication properties.

Correlating instrumental measurements and sensory perceptions of foods with different textural properties for people with impaired oral and swallowing capabilities - A review

The rising global life expectancy has underlined the necessity of designing novel and tasty food products, suitable for seniors and people with impaired oral and swallowing functions. For developing these products, texture should be optimised from rheological, colloidal, tribological, and masticatory points of view. The current review provides an overview of different studies based on shear rheological, tribological, and in vitro mastication properties of model or real food systems intended for the elderly and/or people with swallowing dysfunctions, with special emphasis on the relation between the instrumental measurements and sensory perceptions of foods. Several works demonstrated that instrumental data from shear rheological and tribological tests complement the sensory evaluations of foods, providing useful information when designing food commodities for specific populations. Conversely, only few works correlated the instrumental data obtained from artificial mouths and/or simulated masticators with the sensory attributes generated by trained assessors. Broaden knowledge of these topics will help in formulating and adapting foods with enhanced functionalities for people with impaired oral and swallowing capabilities. Shear rheology, soft oral tribology, and simulated mastication tests are crucial in designing safe- and easy-swallowing food products.

Exploring the textural dynamics of dairy and plant-based yoghurts: A comprehensive study

The mouthfeel and texture of dairy and non-dairy yoghurts play a critical role in food acceptance and liking. The present study aimed to understand the oral perception of commercially available dairy and non-dairy yoghurts. Four dairy and four non-dairy yoghurts with different levels of protein and fat were analyzed to understand the impact of particle size, textural properties and frictional coefficient on the dynamic sensory mouthfeel characteristics measured by the temporal dominance of sensations (TDS) method. Differences in friction coefficients of dairy and non-dairy yoghurts were observed. The friction factor was lower for high-fat dairy yoghurts than for non-dairy yoghurts. The particle size d₉₀ in yoghurts was positively related to graininess perception (r=0.81) and negatively associated with mouthfeel liking (r=-0.87) and overall liking (r=-0.80). For the TDS results, "creaminess" and "thickness" were significantly dominant for dairy yoghurts, while "melty" and "easy to dissolve" were dominant attributes for non-dairy yoghurts. Creaminess perception improves the mouthfeel liking (r=0.72) and overall liking (r=0.59) of yoghurts and is the driver of liking. The findings of this study help understand the intrinsic mouthfeel properties of commercial dairy and non-dairy yoghurts, which will provide valuable insight to product developers during the new product formulation.

The Effects of Okara Ratio and Particle Size on the Physical Properties and Consumer Acceptance of Tofu

Okara, the solid byproduct of soymilk production, poses a sustainability concern, despite being rich in fiber and other healthful compounds. In this study, the physical properties of tofu made from soymilk fortified with differing levels of okara-either whole or fine (<180 µm)-and made with the traditional coagulant nigari were examined. The yield increased linearly with the okara concentration with values of 18.2-29.5% compared to 14.5% for the control. The initial moisture in the fortified samples was higher than the control (79.69-82.78% versus 76.78%), and both the expressible moisture and total moisture after compression were also greater in the fortified samples. With a few exceptions, the texture parameters did not differ between samples. Dynamic rheology showed that all samples had G' > G″. The storage moduli increased at different rates during each gelling step, with G' before and after gelling increasing with the fortification level, and was greater for the samples with fine particles than with whole particles. Consumer sensory panels using the hedonic scale showed traditional tofu had a slightly higher acceptability, but the panelists indicated they would be more willing to purchase okara-fortified tofu because of the health and sustainability benefits it might have. Thus, tofu could be produced with added okara with predictable but not profound changes in its physical properties.

Texture analysis – a versatile tool for pharmaceutical evaluation of solid oral dosage forms

In the past few decades, texture analysis (TA) has gained importance as a valuable method for the characterization of solid oral dosage forms. As a result, an increasing number of scientific publications describe the textural methods that evaluate the extremely diverse category of solid pharmaceutical products. Within the current work, the use of texture analysis in the characterization of solid oral dosage forms is summarised with a focus on the evaluation of intermediate and finished oral pharmaceutical products. Several texture methods are reviewed regarding the applications in mechanical characterization, and mucoadhesion testing, but also in estimating the disintegration time and in vivo specific features of oral dosage forms. As there are no pharmacopoeial standards for pharmaceutical products tested through texture analysis, and there are important differences between reported results due to different experimental conditions, the choice of testing protocol and parameters is challenging. Thereby, this work aims to guide the research scientists and quality assurance professionals involved in different stages of drug development into the selection of optimal texture methodologies depending on the product characteristics and quality control needs.

A review of recent advances and applications of machine learning in tribology

In tribology, a considerable number of computational and experimental approaches to understand the interfacial characteristics of material surfaces in motion and tribological behaviors of materials have been considered to date. Despite being useful in providing important insights on the tribological properties of a system, at different length scales, a vast amount of data generated from these state-of-the-art techniques remains underutilized due to lack of analysis methods or limitations of existing analysis techniques. In principle, this data can be used to address intractable tribological problems including structure-property relationships in tribological systems and efficient lubricant design in a cost and time effective manner with the aid of machine learning. Specifically, data-driven machine learning methods have shown potential in unraveling complicated processes through the development of structure-property/functionality relationships based on the collected data. For example, neural networks are incredibly effective in modeling non-linear correlations and identifying primary hidden patterns associated with these phenomena. Here we present several exemplary studies that have demonstrated the proficiency of machine learning in understanding these critical factors. A successful implementation of neural networks, supervised, and stochastic learning approaches in identifying structure-property relationships have shed light on how machine learning may be used in certain tribological applications. Moreover, ranging from the design of lubricants, composites, and experimental processes to studying fretting wear and frictional mechanism, machine learning has been embraced either independently or integrated with optimization algorithms by scientists to study tribology. Accordingly, this review aims at providing a perspective on the recent advances in the applications of machine learning in tribology. The review on referenced simulation approaches and subsequent applications of machine learning in experimental and computational tribology shall motivate researchers to introduce the revolutionary approach of machine learning in efficiently studying tribology.

Lubrication behavior of ex-vivo salivary pellicle influenced by tannins, gallic acid and mannoproteins

The objective of this study was to investigate the influence of tannins and gallic acid on the salivary lubrication behavior. Furthermore, the effects of pH and mannoproteins in combination with gallic acid on the lubrication of saliva were studied. The addition of gallic acid and tannins were found to increase friction caused by the removal of the saliva film. Tannins resulted in higher friction compared to gallic acid. Lowering pH increased friction of gallic acid mixtures with saliva, due to stronger interactions between gallic acid and saliva. The increased friction caused by gallic acid was inhibited by the addition of mannoproteins due to the hydrogen bond interactions between gallic acid and mannoproteins, thereby decreasing the complex formation between gallic acid and salivary proteins. A correlation of 0.96 was found between the hydrodynamic diameter of the aggregate and the delta friction suggesting that the formation of aggregates determined the lubrication behavior.

Stability, Structure, Rheological Properties, and Tribology of Flaxseed Gum Filled with Rice Bran Oil Bodies

In this study, rice bran oil bodies (RBOBs) were filled with varying concentrations of flaxseed gum (FG) to construct an RBOB-FG emulsion-filled gel system. The particle size distribution, zeta potential, physical stability, and microstructure were measured and observed. The molecular interaction of RBOBs and FG was studied by Fourier transform infrared spectroscopy (FTIR). In addition, the rheological and the tribology properties of the RBOB-FG emulsion-filled gels were evaluated. We found that the dispersibility and stability of the RBOB droplets was improved by FG hydrogel, and the electrostatic repulsion of the system was enhanced. FTIR analysis indicated that the hydrogen bonds and intermolecular forces were the major driving forces in the formation of RBOB-FG emulsion-filled gel. An emulsion-filled gel-like structure was formed, which further improved the rheological properties, with increased firmness, storage modulus values, and viscoelasticity, forming thermally stable networks. In the tribological test, with increased FG concentration, the friction coefficient (μ) decreased. The elasticity of RBOB-FG emulsion-filled gels and the ball-bearing effect led to a minimum boundary friction coefficient (μ). These results might contribute to the development of oil-body-based functional ingredients for applications in plant-based foods as fat replacements and delivery systems.

Rheology and Tribology of Ethylcellulose-Based Oleogels and W/O Emulsions as Fat Substitutes: Role of Glycerol Monostearate

Rheological and tribological properties of oleogels and water-in-oil (W/O) emulsions are important for application in fat substitutes. This study investigated the roles of glycerol monostearate (GMS) in tailoring the structural, rheological and tribological properties of ethylcellulose (EC)-based oleogels and W/O emulsions as potential fat substitutes. The addition of GMS contributed to more round and compact oil pores in oleogel networks. The oleogel with 5% GMS had higher crystallinity, leading to solid state (lower tanδ value), mechanical reversibility (higher thixotropic recovery), but a brittle (lower critical strain) structure in the samples. GMS gave the oleogels and emulsions higher oil binding capacity, storage modulus and yield stress. Under oral processing conditions, GMS addition contributed to higher textural attributes and viscosity. Friction coefficients in mixed and boundary regions of oleogels and emulsions were reduced with the increase in GMS content from 0~2%, but increased with 5% GMS. Rheological and tribological properties of lard, mayonnaise and cream cheese can be mimicked by EC oleogels with 5% GMS, or emulsions with 2% GMS and 2-5% GMS, respectively. The study showed the potentials of oleogel and W/O emulsions in designing low-fat products by tuning the structures for healthier and better sensory attributes.

A Method for the Tribological Assessment of Oral Pharmaceutical Liquids

OBEJECTIVE Patient acceptance of pediatric formations is critical to compliance and consequently therapeutic outcomes; thus, having an in vitro method to evaluate sensory perception of pharmaceutical products would be beneficial. The objective of this research is to develop a sensitive and reproducible tribological method to characterize pharmaceutical suspensions at low force and sliding speeds.METHODS The discriminating potential of the method was examined using tribology profiles (coefficient of friction (COF) vs sliding speed) for commercially available products and products made for this study with widely varying sweetness, thickness and grittiness; these formulations were used to judge the sensitivity of the method. Samples were measured using 3M Transpore™ surgical tape to simulate the tongue surface, steel half ring geometry, constant gap setting, target axial force of 2 N in a 600 second exponential ramp for rotation speed.RESULTS The COF ranged from 0.1 to 0.6. For the speeds studied, the high viscosity commercial suspension Ibuprofen Drops and Acetaminophen suspension show a classic Stribeck Curve with an increasing COF at the higher rotation speeds, which indicates these formulations entered the hydrodynamic lubrication phase, while the lower viscosity suspensions only reached the mixed lubrication phase.CONCLUSIONS The contribution of particles seems to affect the COF in a dynamic pattern compared to products that are categorized as either low gritty or high viscosity. These results are important as they provide a potentially rapidly in vitro method for screening pediatric medications and help to identify the factors that affect the palatability of pediatric formulations.

Oil Bodies Cream from Olive Paste: Extraction of a Functional Ingredient for Developing a Stable Food Emulsion

Oil bodies (OBs) dispersed in an aqueous medium form a natural emulsion with high physical and microbiological stability. This work was focused on the development of a new protocol for extracting OBs from olive paste, through the extraction of an olive oil body cream (OOBC) with a yield of about 43% (wt/wt) in approximately 2 h. The proximate analysis revealed the presence of moisture, lipids and proteins as well as the contents of polyphenols and flavonoids, and the antioxidant powers were determined. The rheological and tribological performances of the OOBC were evaluated. Moreover, we measured a size distribution in the range of 0.7–1.7 m, by using a standard optical microscope. The results have demonstrated clearly that the OOBC extracted from the olive paste can be used as a functional and vegan ingredient in food emulsions.

Soft Tribology and Its Relationship With the Sensory Perception in Dairy Products: A Review

Nowadays, dairy products, especially fermented products such as yogurt, fromage frais, sour cream and custard, are among the most studied foods through tribological analysis due to their semi-solid appearance and close relationship with attributes like smoothness, creaminess and astringency. In tribology, dairy products are used to provide information about the friction coefficient (CoF) generated between tongue, palate, and teeth through the construction of a Stribeck curve. This provides important information about the relationship between friction, food composition, and sensory attributes and can be influenced by many factors, such as the type of surface, tribometer, and whether saliva interaction is contemplated. This work will review the most recent and relevant information on tribological studies, challenges, opportunity areas, saliva interactions with dairy proteins, and their relation to dairy product sensory.

Modernising Orodispersible Film Characterisation to Improve Palatability and Acceptability Using a Toolbox of Techniques

Orodispersible films (ODFs) have been widely used in paediatric, geriatric and dysphagic patients due to ease of administration and precise and flexible dose adjustments. ODF fabrication has seen significant advancements with the move towards more technologically advanced production methods. The acceptability of ODFs is dependent upon film composition and process of formation, which affects disintegration, taste, texture and mouthfeel. There is currently a lack of testing to accurately assess ODFs for these important acceptability sensory perceptions. This study produced four ODFs formed of polyvinyl alcohol and sodium carboxymethylcellulose using 3D printing. These were assessed using three in vitro methods: Petri dish and oral cavity model (OCM) methods for disintegration and bio-tribology for disintegration and oral perception. Increasing polymer molecular weight (MW) exponentially increased disintegration time in the Petri dish and OCM methods. Higher MW films adhered to the OCM upper palate. Bio-tribology analysis showed that films of higher MW disintegrated quickest and had lower coefficient of friction, perhaps demonstrating good oral perception but also stickiness, with higher viscosity. These techniques, part of a toolbox, may enable formulators to design, test and reformulate ODFs that both disintegrate rapidly and may be better perceived when consumed, improving overall treatment acceptability.

Future foods: Alternative proteins, food architecture, sustainable packaging, and precision nutrition

There are numerous challenges facing the modern food and agriculture industry that urgently need to be addressed, including feeding a growing global population, mitigating and adapting to climate change, decreasing pollution, waste, and biodiversity loss, and ensuring that people remain healthy. At the same time, foods should be safe, affordable, convenient, and delicious. The latest developments in science and technology are being deployed to address these issues. Some of the most important elements within this modern food design approach are encapsulated by the MATCHING model: Meat-reduced; Automation; Technology-driven; Consumer-centric; Healthy; Intelligent; Novel; and Globalization. In this review article, we focus on four key aspects that will be important for the creation of a new generation of healthier and more sustainable foods: emerging raw materials; structural design principles for creating innovative products; developments in eco-friendly packaging; and precision nutrition and customized production of foods. We also highlight some of the most important new developments in science and technology that are being used to create future foods, including food architecture, synthetic biology, nanoscience, and sensory perception.Supplemental data for this article is available online at https://doi.org/10.1080/10408398.2022.2033683.

In situ oral lubrication and smoothness sensory perception influenced by tongue surface roughness

BACKGROUND

The human tongue is important in the oral processing of food and in sensory perception. Tongue topography could influence delicate differences in sensory perception. It is hypothesized that tongue surface roughness could alter oral lubrication status and affect perception of smoothness. Fifteen participants with varying levels of tongue surface roughness were recruited and tested. Participants' in situ oral lubrication status without and after consumption of fluid food (milk with varying fat content and maltodextrin solutions with different shear viscosities) was measured. Participants' smoothness sensory scores were also recorded.

RESULTS

The in situ friction coefficient (0.299-1.505) was significantly positively correlated with tongue-surface roughness (54.6-140.0 μm) in all types of test fluid samples across participants. Oral lubrication was significantly decreased when participants consumed the test fluid samples compared with no liquid food consumption, for all test fluid sample types (P < 0.05). No significant differences in in situ friction coefficient were found after participants consumed different test fluid samples, and this was mainly attributed to the limited quantities of fluid residuals in the oral cavity after expectoration. Participants whose tongue surface roughness differed did not exhibit significant differences in smoothness perception with different test fluid samples.

CONCLUSION

Tongue surface roughness has a strong impact on in situ oral lubrication, and fluid food intake reduces in situ oral lubrication significantly. Saliva film and tongue surface roughness might play greater roles in oral lubrication and smoothness sensory perception if fluid is expectorated after consumption. The association between oral physiology and texture perception still needs further elucidation. © 2021 Society of Chemical Industry.

Roles of viscosity, applied load and surface wettability on the lubrication behaviour of model liquid/semi-solid foods: Measurements with a bespoke tribo-cell fixture and rotational rheometer

Thin film sliding and friction phenomena of food bolus confined between tongue-palate surfaces during oral processing can be explored using tribological measurements. However, these measurements are still limited within the food industry due to the requirement of expensive commercial instruments which are not commonly used in the food industry. This work has designed and manufactured a modular "tribological cell" (tribo-cell) that can simulate lubricated soft-hard contact interfaces and can be mounted on a rotational rheometer to perform tribological measurements. The tribo-cell was validated by performing tribological measurements using a range of corn syrup solutions as model liquid foods. It was shown that the Stribeck curve describing the change in friction behaviour with entrainment speed or with the product of entrainment speed and liquid viscosity could be obtained. Since tribology deals with surface property, the cell was then used in the further studies to demonstrate the effects of applied normal load and surface wetting on the tribological response of lubricated hard-soft contact of the designed fixture. These parameters were shown to have a marked influence on in the boundary and mixed-lubrication regimes. The designed tribo-cell was also used to illustrate the impact of fat content on the lubrication properties of commercial liquid and semi-solid foods with different fat contents, thus, pointing out to the importance of tribology as a vital tool for product formulation designs in food and beverage industry.

Food for the elderly based on sensory perception: A review

Background

The impairments of physiological functions caused by aging are common problems in the elderly, especially the impairments of sensory perception. Besides, close relationship between food sensory perception and nutritional status also suggests the importance of dietary management for the elderly population. The foods taking sensory perception into account are urgently needed by the elderly.

Scope and approach

This review analyzed sensory perception changes and their effects on food behaviors and nutritional status. Besides, sensory properties essential for aged-foods and acquisition methods, as well as current status of such foods were summarized.

Key findings and conclusions

Soft, smooth and moisty foods were more suitable for the elderly with chewing and swallowing dysfunction, which can be prepared by gelation, enzyme treatment, blade tenderization and other non-thermal technologies. Flavor enhancement/enrichment, irritant addition and packet sauces were recommended to compensate the impairment of chemical sensory. Molds, piping bag and 3D printing were suggested for refining appearance of pureed foods, and improving appetite of the elderly.

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Sensory perception changes of the elderly affect food behaviors and health.

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Soft, smooth, and moisty foods are more suitable for the elderly.

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Gelation and enzyme treatment are applied to modify the texture of aged food.

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Packet sauces may meet the heterogenetic flavor requirements of the elderly.

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Visually attractive food made by 3D printing can increase the appetite of elderly.

Tailoring structure and properties of long-lived emulsion foams stabilized by a natural saponin glycyrrhizic acid: Role of oil phase

Novel supramolecular nanofibrils assembled from food-grade saponin glycyrrhizic acid (GA) are effective building blocks to make complex multiphase systems, e.g., emulsion foams. In this work, the effects of different oil phases (castor oil, sunflower oil, dodecane, and limonene) on the formation, stability and structural properties of long-lived emulsion foams prepared by GA nanofibrils (GNs) were investigated. The obtained results showed that soft-solid emulsion foams (4 wt% GNs) can be fabricated, independently of oil phase, and their structural properties, viscoelasticity, and tribological properties can be well tuned by oil phase polarity. Compared to the GNs aqueous foams, the presence of jammed emulsion droplets in the liquid channels and at the surfaces of bubbles can provide a higher bubble stability for emulsion foams. For more polar oil phase (castor oil), GNs showed a higher affinity to the oil-water interface with a lower interfacial tension, thus forming smaller oil droplets and bubbles, which leads to the higher mechanical strength, denser network microstructures, and lower friction coefficients of emulsion foams. However, the limonene foam exhibited weak storage stability and rheological properties, as well as the relatively low lubrication, which may be related to the formation of oil droplet aggregates and clusters induced by the volatility of limonene. GN-based emulsion foams are thermoresponsive, independently of oils, and the temperature-switchable process for the destabilization and regeneration of foams can be controlled and repeated. These emulsion foams based on natural saponin nanofibrils with tunable properties have potential sustainable applications in foods, pharmaceuticals, and personal care products.

Lubrication study of representative fluid foods between mimicked oral surfaces

The lubricities of glycerol solutions with different viscosities were investigated at various frictional pairs, speeds, and loads to explore the lubrication regulations of diverse foods in mouths of different people. The friction pairs were characterized in terms of mechanical properties, surface morphology, and hydrophobicity. The results showed that the partial or complete Stribeck curves occurred with different speeds and viscosities. Various friction pairs had great influences on the boundary lubrication zone, but little influences on the elastohydrodynamic lubrication (EHL) zone. Increasing loads caused the friction coefficient decreasing in boundary lubrication zone; however, the friction coefficient changed a little in the mixed lubrication and EHL zones.