Smoothness as a tactile percept: Correlating ‘oral’ tribology with sensory measurements

Effect of in vitro food oral coating and lubricity on satiety: a randomized controlled trial using milk protein beverages

We investigated the effects of complex textural attributes of food i.e. lubricity and oral coating, on appetite ratings, food intake, salivary and gut peptides for the first time. Milk protein-rich beverages (whey and casein) were instrumentally analyzed (tribology, viscosity and adsorption, latter representing oral coating) using in vitro measurements. Then these protein beverage preloads differing in their coating properties (low coating, medium coating and high coating) were assessed in two cross-over satiety trials (Study 1, n=37; Study 2, n=15; Total n= 52). Fullness ratings increased in the high coating beverage condition (p<0.05) only after 20 min with limited effects on other time points, suggesting a sporadic effect of oral coating on appetite ratings (n=37). There was a correlation between concentration of protein in saliva and appetite ratings; the higher the concentration of protein in saliva the lower the desire to eat (r = - 0.963; p <0.05) and prospective food consumption ratings (r =- 0.980; p <0.05). Human saliva was more lubricating after ingesting preload with high coating properties, thus explaining the results on appetite ratings. There was no effect of oral coating on energy intake and gut peptides (n=15), suggesting that complex textural attributes having influence on oral processing might not have any effect on the later parts of the satiety cascade. Oral coating/ lubricity appears to have a subtle and sporadic effect on appetite suppression, which needs further investigation with changing macronutrients/energy load and degree of coating/ lubricity.

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.

Oral tribology of dairy protein-rich emulsions and emulsion-filled gels affected by colloidal processing and composition

Designing nutritious food for the elderly population often requires significant quantities of leucine-rich whey proteins to combat malnutrition, yet high-protein formulations can cause mouth dryness and increased oral friction. This study investigated how various colloidal processing methods and compositions impact the in vitro oral tribological properties of protein-rich emulsions and emulsion-filled gels. Oil-in-water emulsions with oil fractions from 1 wt% to 20 wt% were prepared, alongside emulsion-filled gels containing whey protein isolate (WPI), hydrolysed whey protein (HWP), or a blend of both (10 wt% protein content). Two processing approaches were employed: creating emulsions with an initial 10 w% protein content (M1) and initially forming emulsions with 0.1 wt% protein content, then enriching to a final 10 wt% concentration (M2). The hypothesis was that formulations with HWP or method 2 (M2) would offer lubrication benefits by inducing droplet coalescence, aiding in the formation of a lubricating boundary tribofilm. Surprisingly, the tribological behavior of high-protein emulsions showed minimal dependence on oil droplet volume fraction. However, both HWP-based emulsions and those processed with M2 for WPI exhibited significant friction reduction, which may be attributed to the presence of coalesced oil droplets, supporting our hypothesis. Substituting 50 wt% of WPI with HWP in emulsion-filled gel boli resulted in very low friction coefficients in the boundary lubrication regime, suggesting oil droplet release from the gel matrix. These findings provide insights into designing high-protein foods with improved mouthfeel for the elderly population, necessitating further validation through sensory studies.

Perspective on oral processing of plant-based beverages

Around the world, the market for plant-derived beverages is one of the fastest-expanding segments in the functional and specialty beverage areas of newer food product development. Consumers are increasingly likely to choose alternatives to bovine beverages due to factors including lactose intolerance, hypercholesterolemia prevalence, allergies to bovine beverages, and preference for vegan diets that contain functionally active ingredients with health-promoting characteristics. Due to health, ecological, and ethical concerns, many customers are interested in reducing their usage of animal products like bovine milk. A variety of plant-based beverage substitutes are being created by the food sector as a result. To create viable alternatives, it is first necessary to provide an overview of the chemical composition, structure, features, and nutritional attributes of ordinary bovine milk. Sensory acceptability in the case of substitutes for beverages made from legumes is a significant barrier to their widespread acceptance, and thus saliva acts as a sophisticated fluid that serves a variety of purposes in the cavity of the mouth. Designing and producing next-generation plant-based beverages that mimic the physicochemical and functional qualities of conventional bovine-based beverages is gaining popularity, and many of these products can be thought of as colloidal materials that contain the particles or polymers that give them their unique qualities NG-PB foods can have a wide range of rheological qualities, such as fluids with low viscosity (such as plant-based beverages), high-viscosity liquids (like creams), soft liquids (like yogurt), as well as hard solids (such as some cheeses).

A Potentially Ecosustainable Hazelnut/Carob-Based Spread

Commercial cocoa and hazelnut-based sweet spreads typically present a poor nutribiochemical level due to their ingredients and recipes, while nowadays, there is the need of developing sustainable food products addressing both an improved nutritional and environmental profile. The aim of this work was then to develop an innovative hazelnut/carob-based spread with potential high sustainability and nutritional profile, including the exploitation of grape-processing residues (grape skin flour and grapeseed oil) and carob pulp as cocoa surrogate. Rheological (rotational/oscillatory), oxidative, and thermal features of the spread were assessed and compared with two commercial nut-cocoa-based products. Tribology was used to mimic and evaluate the spreads' behavior during oral consumption, and sensory profile (by quantitative descriptive analysis) was also assessed. All products exhibited a pseudoplastic behavior, with the elastic component prevailing over the viscous one. The innovative product showed the highest lubricity from both rheological and sensory analysis, thus well correlating to the obtained lowest viscosity and friction factor trends. Grapeseed oil provided a better nutritional profile, but the largest amount of unsaturated fatty acids promoted oxidation, despite the higher total phenolic content and antioxidant capacity coming from the use of carob and grape skin powders. The sensory perception investigation revealed a characteristic mouthfeel/flavor for the new spread identified having a more fluid consistency and a bitter/sour taste, together with a greater stickiness and a poorer smoothness due to a higher fiber content and solid fat absence.

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.

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.

Role of polysaccharide structure in the rheological, physical and sensory properties of low-fat ice cream

Polysaccharides can be used as fat replacers in ice cream, as they contribute to an increase of viscosity. However, no research has clarified the exact role of viscosity from that of the structure of the polysaccharides on the properties of ice cream. In this study, the effect of polysaccharide structure on different properties of low-fat ice cream was investigated. The polysaccharides taken into consideration varied from flexible (locust bean gum and guar gum) to rigid (xanthan gum and iota carrageenan). Relationships between rheological properties of ice cream mixes and microstructural characteristics and sensory perception of the final ice cream were established. To separate the effect of the polysaccharide structure from that of viscosity, two series of ice cream were prepared: one in which the mix viscosity of the various samples was similar (approximately 68.3 mPa· s), and one in which the serum phase viscosity was similar (approximately 15563 mPa· s). Flexible polysaccharides showed a lower degree of shear-thinning and a more liquid-like viscoelastic behavior compared with rigid polysaccharides. In addition, flexible polysaccharides led to higher overrun (47-58%) than other samples (approximately 30%), which resulted in lower hardness of the ice cream (<3.2 MPa). Rigid polysaccharides caused gelation of the serum phase, which made the ice cream more difficult to scoop. Based on the results of the sensory evaluation, flexible polysaccharides could provide higher softness and creaminess-related properties, while rigid polysaccharides resulted in higher coldness and grittiness. Therefore, polysaccharides with a flexible structure are a better choice for improving the textural and sensory properties of low-fat ice cream.

Rheology and tribology of chitosan/Acacia gum complex coacervates

Acacia gum (Gum Arabic; GA) and chitosan (CTS) form complex coacervates in acidic environments, providing a polymer-rich aqueous material with interesting bio-lubricant properties. We investigate the interplay of the tribology and rheology of these coacervates, demonstrating that they dramatically reduce the friction coefficient between lubricated soft model surfaces as compared to solutions of the individual polymers. We characterize the phase separation behavior using microscopy, electrophoretic mobility and thermogravimetric analysis. The macroscopic rheological behaviour is predominantly viscous and ranges from weakly to strongly shear thinning: viscosity levels and strength of shear thinning increase with decreasing ionic strength, but no apparent yield stress or predominant elasticity were observed even in the absence of salt. Conversely, friction coefficients measured between soft and rough surfaces increase with a rise in ionic strength and can be scaled onto a Stribeck-type master curve across varying ionic strength and pH in the mixed and hydrodynamic lubrication regimes.

Progress in the Application of Food-Grade Emulsions

The detailed investigation of food-grade emulsions, which possess considerable structural and functional advantages, remains ongoing to enhance our understanding of these dispersion systems and to expand their application scope. This work reviews the applications of food-grade emulsions on the dispersed phase, interface structure, and macroscopic scales; further, it discusses the corresponding factors of influence, the selection and design of food dispersion systems, and the expansion of their application scope. Specifically, applications on the dispersed-phase scale mainly include delivery by soft matter carriers and auxiliary extraction/separation, while applications on the scale of the interface structure involve biphasic systems for enzymatic catalysis and systems that can influence substance digestion/absorption, washing, and disinfection. Future research on these scales should therefore focus on surface-active substances, real interface structure compositions, and the design of interface layers with antioxidant properties. By contrast, applications on the macroscopic scale mainly include the design of soft materials for structured food, in addition to various material applications and other emerging uses. In this case, future research should focus on the interactions between emulsion systems and food ingredients, the effects of food process engineering, safety, nutrition, and metabolism. Considering the ongoing research in this field, we believe that this review will be useful for researchers aiming to explore the applications of food-grade 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.

Physicochemical properties and microstructural behaviors of rice starch/soy proteins mixtures at different proportions

Rice starch (RS) and soy protein (SP) were mixed at various ratios and the physicochemical, rheological and tribological properties of the resulted pastes were analyzed. Microscopy and spectral techniques were applied to follow the structural changes during cooling and heating processes. Higher proportion of SP resulted in lower swelling power. According to DSC and RVA results, SP inhibited the gelatinization of starch, leading to higher pasting temperature; the peak, trough, final viscosities, set back and enthalpy changes were decreased with increasing SP concentration. All the samples presented a shear thinning behavior and the mixtures with soy proteins showed lower viscosity, yield stress and consistency coefficient than pure starch paste. The creep-recovery test showed that the addition of soy proteins resulted in more liquid-like mixtures, causing weakening of instantaneous elastic recovery. The combination of rice starch and soy proteins increased the friction, compared with their individual components, except RS/SP 9/1 at sliding speed >20 mm/s. According to the microstructure and spectra analysis, the soy protein adhered on the surface of starch granules, which might have hindered the leaching of amylopectin; and the association between starch and soy proteins mainly occurred when the starch granules were gelatinized, which could be reinforced during starch retrogradation.

Regulation Effects of Beeswax in the Intermediate Oil Phase on the Stability, Oral Sensation and Flavor Release Properties of Pickering Double Emulsions

Double emulsions (W/O/W) with compartmentalized structures have attracted a lot of research interests due to their diverse applications in the food industry. Herein, oil phase of double emulsions was gelled with beeswax (BW), and the effects of BW mass ratios (0-8.0%) on the stability, oral sensation, and flavor release profile of the emulsions were investigated. Rheological tests revealed that the mechanical properties of double emulsions were dependent on the mass ratio of BW. With the increase in BW content, double emulsions showed a higher resistance against deformation, and lower friction coefficient with a smoother mouthfeel. Turbiscan analysis showed that the addition of BW improved the stability of double emulsions during a 14 days' storage, under freeze-thawed, and osmotic pressure conditions, but it did not improve the heating stability of double emulsions. The addition of BW contributed to lower air-emulsion partition coefficients of flavor (2,3-diacetyl) compared to those without the addition of BW at 20 °C and 37 °C, respectively. Furthermore, the addition of BW and its mass ratio significantly altered the flavor release behavior during the open-bottle storage of double emulsions. The response value of 0% BW dropped sharply on the first day of opening storage, showing a burst release behavior. While a slow and sustained release behavior was observed in double emulsions with 8.0% BW. In conclusion, gelation of the intermediate oil phase of double emulsions significantly enhanced the stability of double emulsions with tunable oral sensation and flavor release by varying the mass ratio of beeswax.

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.

Current Perspectives on Food Oral Processing

Food oral processing (FOP) is a fast-emerging research area in the food science discipline. Since its first introduction about a decade ago, a large amount of literature has been published in this area, forming new frontiers and leading to new research opportunities. This review aims to summarize FOP research progress from current perspectives. Food texture, food flavor (aroma and taste), bolus swallowing, and eating behavior are covered in this review. The discussion of each topic is organized into three parts: a short background introduction, reflections on current research findings and achievements, and future directions and implications on food design. Physical, physiological, and psychological principles are the main concerns of discussion for each topic. The last part of the review shares views on the research challenges and outlooks of future FOP research. It is hoped that the review not only helps readers comprehend what has been achieved in the past decade but also, more importantly, identify where the knowledge gaps are and in which direction the FOP research will go.

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.

Role of Flaxseed Gum and Whey Protein Microparticles in Formulating Low-Fat Model Mayonnaises

Flaxseed gum (FG) and whey protein microparticles (WPMs) were used to substitute fats in model mayonnaises. WPMs were prepared by grinding the heat-set whey protein gel containing 10 mM CaCl₂ into small particles (10–20 µm). Then, 3 × 4 low-fat model mayonnaises were prepared by varying FG (0.3, 0.6, 0.9 wt%) and WPM (0, 8, 16, 24 wt%) concentrations. The effect of the addition of FG and WPMs on rheology, instrumental texture and sensory texture and their correlations were investigated. The results showed that all samples exhibited shear thinning behavior and ‘weak gel’ properties. Although both FG and WPMs enhanced rheological (e.g., viscosity and storage modulus) and textural properties (e.g., hardness, consistency, adhesiveness, cohesiveness) and kinetic stability, this enhancement was dominated by FG. FG and WPMs affected bulk properties through different mechanisms, (i.e., active filler and entangled polysaccharide networks). Panellists evaluated sensory texture in three stages: extra-oral, intra-oral and after-feel. Likewise, FG dominated sensory texture of model mayonnaises. With increasing FG concentration, sensory scores for creaminess and mouth-coating increased, whereas those of firmness, fluidity and spreadability decreased. Creaminess had a linear negative correlation with firmness, fluidity and spreadability (R² > 0.985), while it had a linear positive correlation with mouth-coating (R² > 0.97). A linear positive correlation (R² > 0.975) was established between creaminess and viscosity at different shear rates/instrumental texture parameters. This study highlights the synergistic role of FG and WPMs in developing low-fat mayonnaises.

Correlation between Instrumental and Sensory Properties of Texture Modified Carrot Puree

This study was undertaken to determine the correlation between instrumental and sensory evaluation on texture modified carrot puree. Texture modified foods (TMF) are prescribed to dysphagia individuals to aid in the oral manipulation and facilitate swallowing of food. There is a lack of correlation between instrumental measurements and sensory attributes on TMF. Understanding this correlation will aid in the formulation of safe foods with desired sensory properties for dysphagia patients. Instrumental measurements of carrot purees were performed by back extrusion method using a texture analyser and the attributes obtained were firmness, consistency, cohesiveness and adhesiveness. Quantitative Descriptive Analysis (QDA) with eight trained panellists was employed to characterize the texture of the carrot puree based on seven sensory attributes: Firmness, viscous, adhesive (mouth), smoothness, adhesive (throat), rate of breakdown, difficulty to swallow. Five thickeners, namely gellan gum, xanthan gum, Suberakaze, UNI-PURE® Dys-sperse instant thickener, ULTRA-SPERSE® M Starch were evaluated against carrot puree without any thickener as control. The correlation results obtained from texture analysis and sensory evaluation were statistically significant (p < 0.05). The firmness attributes from instrumental and sensory results were positively correlated. The consistency parameter was positively correlated to sensory attribute viscous and negatively correlated to smoothness. The sensory attribute rate of breakdown was negatively correlated to instrumental parameter of cohesiveness. Lastly, instrumental adhesiveness was positively correlated to sensory attributes adhesive to mouth and throat, and difficulty to swallow. The correlation results showed a well-designed instrumental technique can be used to understand the impact of thickeners on TMF for dysphagia subjects. This article is protected by copyright. All rights reserved.

Understanding relations between rheology, tribology, and sensory perception of modified texture foods

The aim of this work was to examine relations between instrumental and sensory parameters in a texture modified food matrix, with and without saliva. Nine pureed carrot samples (eight thickened and a control) were developed with starch (0.4 and 0.8% wt/wt), xanthan (0.2 and 0.4% wt/wt) or starch-xanthan blends that met International Dysphagia Diet Standardisation Initiative (IDDSI) Level 4 guidelines using fork and spoon tests. Rheological and tribological tests were conducted on the food and simulated bolus prepared by adding fresh stimulated saliva to the food (1:5, saliva:food) to mimic oral processing. Perceived sensory properties were identified using a temporal dominance of sensations (TDS) test (n = 16) where panelists were given a list of nine attributes. The area under the curve was extracted from TDS curves for each attribute/sample and this was correlated with rheological (viscosity at 10 s^-1 , G', G″, and tan δ at 1 Hz) and tribological (friction coefficient in three regimes) data. The viscosity of the control sample decreased after adding hydrocolloids (except Starch_0.8%) and with saliva incorporation. G' and G″ either increased or were similar for xanthan and blends and decreased for starch-thickened samples. Hydrocolloid addition increased friction for all samples and was higher with saliva addition. Sensory results showed that samples with starch were perceived as thick and grainy while xanthan was perceived as smooth and slippery. A greater number of sensory attributes correlated with viscoelastic parameters compared to friction coefficients. Correlations were highest with the saliva added samples, further highlighting the importance of including saliva during instrumental testing.

Rheological and tribological characterization of different commercial hazelnut and cocoa-based spreads

Five commercial hazelnut/cocoa spreads with different compositions were tested by rheology/tribology. The impact of each formulation on the structural/lubricant performances was investigated. Rotational/oscillatory rheology was chosen to assess material behavior during flow. Viscosity variation as a function of temperature and chamber geometry was evaluated. Oscillatory mode tests were carried out to obtain information on product viscoelasticity. Tribological analysis was performed at different temperatures aiming at simulating the chewing/swallowing process. All samples were categorized as pseudo-plastic and viscoelastic materials, with the elastic component prevailing over the viscous one. Major differences were detected in terms of consistency index, depending on the total lipid content. Temperature increase enhanced spread fluidity with a decreasing viscosity according to the Arrhenius model (R² > 0.942) and greater values of activation energy reflecting higher sensitivity to microstructural changes. An inverse relationship between Casson viscosity η c and sugar/fat ratio highlighted additional correlations between structural parameters and spread formulation. Tribological measurements at 25°C highlighted that, at the initial eating stage, the friction factor (0.112 - 0.262 at sliding velocity of 8∙10^-6 m/s) was strongly affected by either the amounts of solid fat or hazelnut percentage. Tribological data corroborated the theory for which tribology and rheology cover different domains. This article is protected by copyright. All rights reserved.

Lubrication and Sensory Properties of Emulsion Systems and Effects of Droplet Size Distribution

The functional and sensory properties of food emulsion are thought to be complicated and influenced by many factors, such as the emulsifier, oil/fat mass fraction, and size of oil/fat droplets. In addition, the perceived texture of food emulsion during oral processing is mainly dominated by its rheological and tribological responses. This study investigated the effect of droplet size distribution as well as the content of oil droplets on the lubrication and sensory properties of o/w emulsion systems. Friction curves for reconstituted milk samples (composition: skimmed milk and milk cream) and Casein sodium salt (hereinafter referred to as CSS) stabilized model emulsions (olive oil as oil phase) were obtained using a soft texture analyzer tribometer with a three ball-on-disc setup combined with a soft surfaces (PDMS) tribology system. Sensory discrimination was conducted by 22 participants using an intensity scoring method. Stribeck curve analyses showed that, for reconstituted milk samples with similar rheological properties, increasing the volume fraction of oil/fat droplets in the size range of 1-10 µm will significantly enhance lubrication, while for CSS-stabilized emulsions, the size effect of oil/fat droplets reduced to around 1 µm. Surprisingly, once the size of oil/fat droplets of both systems reached nano size (d₉₀ = 0.3 µm), increasing the oil/fat content gave no further enhancement, and the friction coefficient showed no significant difference (p > 0.05). Results from sensory analysis show that consumers are capable of discriminating emulsions, which vary in oil/fat droplet size and in oil/fat content (p < 0.01). However, it appeared that the discrimination capability of the panelist was significantly reduced for emulsions containing nano-sized droplets.

Correlating wine astringency with physical measures - Current knowledge and future directions

Oral tribology receives growing attention in the field of food sciences as it offers great opportunities to establish correlations between physical parameters, such as the coefficient of friction, and sensory effects when interacting with components of the human mouth. One important aspect covers the astringency produced by wine, which can be described as the sensation of dryness and puckering in the mouth, specifically occurring between the tongue and the palate after swallowing. Therefore, this article aims at shedding some light on recent trends to correlate physical measures, such as the coefficient of friction derived by oral tribology, with prevailing theories on underlying physiological causes for sensory perception of wines. Some successful cases reported the potential of correlating wine astringency perception with the coefficient of friction in tribological experiments. Our critical assessment demonstrates that the findings are still contradictory, which urgently asks for more systematic studies. Therefore, we summarize the current challenges and hypothesize on future research directions with a particular emphasis on the comparability, reproducibility and transferability of studies using different experimental test-rigs and procedures.

Impact of Processing Conditions on Rheology, Tribology and Wet Lubrication Performance of a Novel Amino Lipid Hair Conditioner

The objective of this work was to carry out a comprehensive evaluation of the performance of a novel cationic amino lipid surfactant, Brassicyl Valinate Esylate (BVE), in contrast to conventional alkyl quaternary ammonium surfactants (quats), through a study of the effects of process mixing speed on its overall rheological, tribological and wet lubrication performance in comparison to BTAC and CTAC, two cationic surfactants widely used in cosmetics. The major cosmetic application of cationic surfactants is in the preparation of hair conditioners. Hence, this analysis was done firstly by conducting tensile combing tests to evaluate reduction in wet lubrication which translates to conditioning performance. The combing results serve as a testing metric that adequately corresponds to consumer perception of conditioned hair. To correlate this technically, yield stress measurements were conducted to establish rheologic profiles of the conditioner formulations, and in vitro tribological testing of the emulsion systems between two steel surfaces were done to technically simulate the spreading and rubbing of conditioner on the hair. The effect of processing conditions on the formulations was then evaluated. BVE was found to be an effective conditioning surfactant suitable as an eco-friendly replacement for BTAC and CTAC in hair conditioner formulations. The results showed that higher shear mixing rates during formulation lead to poorer performance effects evident through decreased yield stress values, lower percentage reduction in combing force and a higher coefficient of friction.

Stabilization of directly acidified protein drinks by single and mixed hydrocolloids-combining particle size, rheology, tribology, and sensory data

BACKGROUND

High methoxyl pectin and carboxymethylcellulose (CMC) can be used as a stabilizer for directly acidified protein drinks (DAPDs). Use of pectin or CMC together with other polysaccharides and their impacts on product's rheological properties and tribological behavior are still largely unknown. This project investigated the impact of pectin and CMC, alone or in combination with guar gum, locust bean gum (LBG), and gellan gum when preparing DAPDs. The particle size distributions, rheological properties, tribological properties, and sensory properties were determined.

RESULTS

Pectin and CMC were dominating in the mixed system with other stabilizers. Increasing the concentration of hydrocolloids resulted in higher viscosity and better lubrication (lower friction coefficient). The sensory viscosity, smoothness, coating, and stickiness intensified as the concentration of hydrocolloids increased. The type and amount of hydrocolloids had a strong effect on the sensorial texture perception, but the flavor perception was only slightly affected.

CONCLUSION

Use of combined stabilizers may contribute to providing an effective viscosity enhancement without affecting the flavor in acidified milk beverages.

Measurement of molten chocolate friction under simulated tongue-palate kinematics: Effect of cocoa solids content and aeration

The perception of some food attributes is related to mechanical stimulation and friction experienced in the tongue-palate contact during mastication. This paper reports a new bench test to measure friction in the simulated tongue-palate contact. The test consists of a flat PDMS disk, representing the tongue loaded and reciprocating against a stationary lower glass surface representing the palate. The test was applied to molten chocolate samples with and without artificial saliva. Friction was measured over the first few rubbing cycles, simulating mechanical degradation of chocolate in the tongue-palate region. The effects of chocolate composition (cocoa solids content ranging between 28 ​wt% and 85 ​wt%) and structure (micro-aeration/non-aeration 0–15 ​vol%) were studied. The bench test clearly differentiates between the various chocolate samples. The coefficient of friction increases with cocoa solids percentage and decreases with increasing micro-aeration level. The presence of artificial saliva in the contact reduced the friction for all chocolate samples, however the relative ranking remained the same.

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Development of a reciprocating sliding friction test to mimic tongue-palate motion.

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Variations in friction coefficient depending on chocolate composition and structure.

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Higher cocoa content samples had higher friction coefficient.

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Friction coefficient decreased with aeration (0–15% vol).

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The presence of an artificial saliva film reduced chocolate friction.

Drinking tastes of Chinese rice wine under different heating temperatures analyzed by gas chromatography-mass spectrometry and tribology tests

Drinking tastes and lubrication properties of Chinese rice wine (CRW) under different heating temperatures were studied by tribology tests, gas chromatography-mass spectrometry (GC-MS) and sensory evaluations. CRW's drinking tastes were evaluated by taste panelists. Flavor compounds were detected by GC-MS. Lubrication properties of CRW were measured by tribometer. Drinking tastes changed under different heating temperatures and were the best at 60°C assessed by panelists. Four key compounds, furfural, benzaldehyde, butanedioic acid diethyl ester, and phenylethyl alcohol, were determined by GC-MS affecting drinking tastes of CRW. Their variation trends were consistent with the changes of CRW's tastes. The variation of CRW's lubrication properties had a positive correlation with that of CRW's taste, especially astringency. The lowest friction coefficient implied the best lubrication performance and taste at 60°C. Therefore, it was possible to rapidly evaluate drinking tastes of CRW using tribology technology based on the results. Reasons for temperatures influencing CRW's lubrication properties and drinking tastes were also analyzed in this study.

Characteristics of fish gelatin-anionic polysaccharide complexes and their applications in yoghurt: Rheology and tribology

In this study, the rheological and tribological properties of complex solutions comprising of fish gelatin (FG)-Arabic gum (AG), FG-xanthan gum (XG), and FG-κ-carrageenan (κC), respectively, were measured, as well as the effects of the complex on the physical properties of yoghurt. Results showed that with increased XG and κC concentrations, the viscosity of FG-XG and FG-κC complex solutions both increased. It was also found that the lubrication properties of FG-anionic polysaccharide (AP) solutions decreased with the increased AP contents. The applications of FG-AP complexes (FG:AP = 9:1) improved firmness, water holding capacity and viscosity of yoghurt by the formation of large aggregates, but gels were easily destroyed at high frequency. Moreover, compared with gelatin, FG-AP complexes made yoghurt better lubrication properties during low and medium sliding speed, especially for FG-XG complexes. Thus, FG-AP complexes have the potential to be applied in producing yoghurt with good quality.

Contributions of viscosity and friction properties to oral and haptic texture perception of iced coffees

Creaminess is affected by bulk properties (i.e. viscosity) and surfaces properties (i.e. friction). This study aimed (i) to assess contributions of viscosity and friction properties to creaminess, thickness and slipperiness perception; and (ii) to compare oral and haptic thickness and slipperiness perception of iced coffees. Three iced coffees differing in viscosity and friction properties were prepared: low viscosity - high friction (LV-HF); low viscosity - low friction (LV-LF) and high viscosity - low friction (HV-LF) iced coffee. Viscosity of iced coffees was adjusted by addition of maltodextrin, and viscosity of HV-LF was 2.5 times higher than that of LV-HF and LV-LF (10 vs. 4 mPa s at 100 s-1). Friction coefficients of LV-LF were reduced by addition of polyethylene glycol (PEG, Mw 6000), and were up to 25% lower than those of LV-HF. Forty-seven untrained panellists (18-27 years) performed two-alternative forced choice (2-AFC) and rank-rating tests to compare creaminess by oral assessment, and thickness and slipperiness by oral and haptic assessment. Results from 2-AFC and rank-rating congruently showed that HV-LF was creamier, thicker and more slippery than LV-HF and LV-LF, both orally and haptically. LV-LF was orally perceived as less creamy and less thick, but haptically as more slippery than LV-HF. Creaminess was more strongly correlated to thickness than to slipperiness. Oral and haptic evaluation of thickness was congruent, whereas differences between oral and haptic slipperiness evaluation were product-dependent. We conclude that increasing viscosity enhances creaminess, whereas increasing lubrication is not necessarily sufficient to increase creaminess in iced coffees.