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This is a review of mucus, and its principal component, mucins, in oral processing; it examines oral processing from the viewpoint of mucins being integral functional constituents of the food after the latter's insertion into the mouth. Under this light, mucins are treated as an omni‐present functional ingredient. The chemical physics of the bolus formation is examined, focused on the role of mucins in the process. The colloidal and rheological aspects of hydrocolloids–mucin systems are subsequently examined, highlighting the role of the oral glycoproteins in complex food models and complex foods. Following the physicochemical and mechanical description of the topic, mucus is examined as a determinant of a food's sensory attributes. Its role in oral sensations such as astringency is reviewed, with a special focus on phenol–mucin interactions. The effect of mucus on the perception of saltiness is then reviewed, and the ensuing strategies for structurally‐based reduction of salt are considered. The review critically discusses the challenges and opportunities that emerge from the above, highlighting the role of mucins and their effect on food function. [ABSTRACT FROM AUTHOR]

Breakage of food influences eating experience and sensory perception. The aims of the study were to identify an appropriate breakage index and to develop an in vitro method for predicting the ease of oral breakage of nuts. Kernels of five types of nuts were fragmented in vitro using a texture analyzer and 12 subjects therefore performed molar bites. In addition, peanuts were differently roasted (over 0, 15, 25, and 35 min) to vary texture within the same nut type. Projected particle areas were determined using imaging. Two Breakage Indices were compared (1) BI‐I, the difference, after and before fragmentation, in square root values of ratios between total projected area and volume [Agrawal et al., 1997, Archives of Oral Biology, 42(1), 1–9], and (2) BI‐II, the ratio of the total projected area after and before fragmentation. BI‐II gives a stronger linear regression than BI‐I between in vivo and in vitro index values for different types of nuts; Pearson's r = 0.834 versus 0.499 (12 subjects with all data pooled). Using BI‐II, a subject's regression result in fragmentation tests with differently roasted peanuts was as strong as when testing different nut types: Pearson's r = 0.984 versus 0.964. Since the range of the in vitro BI‐II values was 5.5 times smaller in the peanut tests, the finding of a similarly strong regression indicates a high sensitivity of BI‐II to detect differences in food texture. BI‐II is useful for food industry to determine how easily solid foods break down and thereby compare the potential of flavor release between foods during chewing. [ABSTRACT FROM AUTHOR]

Food texture is a collective term for all texture‐related features of a food product. A comprehensive description of food texture is therefore practically challenging due to too many parameters that are associated simultaneously with the food. Using every day, non‐technical (layman's) language, we attempt in this work to rationalize the different dimensions that contribute to the texture of foods, and we explain the rheological reasons behind the concept. For solid foods, three dimensions are identified being the "hard–soft," "strong–weak," and "brittle–plastic." For liquid foods, three further dimensions are suggested, being "elastic–viscous," "thick–thin," and "shear thinning–shear thickening." As these dimensions are bipolar, for foods where any of the dimensions are not relevant, we conceive that dimension takes on a zero value, aligning at the center of the scale. [ABSTRACT FROM AUTHOR]

Eating capability (EC) is a term used to represent individual's ability in food consumption. Consumers with weakened capabilities of eating and drinking may suffer various difficulties during food oral processing. Sometimes specific environmental conditions may also create difficulties of food consumption. Eating difficulty may lead to aspiration, coughing, choking and other health risks. Therefore, foods specially designed according to consumer's EC are required imperatively in order to ensure safe eating. It is now generally accepted that proper evaluation of EC is very meaningful not only in helping dietary selection to special consumers, but also in guiding food industry in texture design of special food. Unfortunately, no appropriate method and/or technique is currently available for such purpose and texture grading of special food becomes groundless. Therefore, this review aimed to provide new directions and new thinking to the food industry in designing foods for special consumers, by summarizing various health risks of eating and drinking. A concept of 'Eating Safety' was specifically proposed. Furthermore, it was hoped that the review would give useful guidelines to the food industry in establishing texture standard and designing texture of special food. [ABSTRACT FROM AUTHOR]

Thickened fluids are commonly used in the medical management of individuals who suffer from swallowing difficulty (known as dysphagia). International Dysphagia Diet Standardization Initiative (IDDSI) developed a standardized terminology and description for texture‐modified foods and thickened fluids to allow dysphagia patients to receive the correct consistency of food/drink. Syringe flow test and fork drip test are suggested by IDDSI to identify the drink category (IDDSI Levels 1–4). These practical methods are widely welcomed by carers and patients because of their simplicity. However, these methods are not most feasible for industrial applications, where objective measurements are required for industry for the purpose of quality control of such products. Therefore, our aim in this work was to develop quantitative and objective measurements that best describe IDDSI level category for use as an objective framework. Two measuring techniques, syringe flow test and fork drip test, recommended by IDDSI were evaluated in two different sets of experiment. Participants were recruited to categorize fluid samples of known texture parameters using syringe flow test and fork drip test techniques. The apparent stress measured from Ball‐Back Extrusion (BBE) technique for each of the fluid category (IDDSI Levels 1–4) was calculated. Bands of apparent stress for each of the fluid category were developed from two measuring techniques, syringe flow test and fork drip test. An inconsistency was observed between these two measuring techniques for IDDSI Level 3 fluid due to different dominating factors in the two tests. However, we proposed to combine the results from the two experiments to develop a quantitative range for each IDDSI Level as objective complements to the IDDSI Framework. Thickened fluid manufacturers are encouraged to follow the proposed guidelines presented once they are clinically validated and use them fine‐tune their products, thus enhancing the safety of individuals with dysphagia. [ABSTRACT FROM AUTHOR]

Texture‐modified foods and thickened fluids play a major role in clinical treatment for individuals who suffer from swallowing difficulties (known as dysphagia). International Dysphagia Diet Standardization Initiative (IDDSI) developed a standardized terminology and description for texture‐modified foods and thickened fluids to allow dysphagia patients to receive the correct consistency of food/drink. While the IDDSI framework provides a consistent texture description (Levels 0–7) and is widely accepted as an international standard, testing and assessment of IDDSI texture level are qualitative in nature and subjective in manner. These methods were proposed primarily for use by frontline carers, but are not most ideal for industrial purposes of quality control of such products. Therefore, the main aim of this work was to develop a quantitative instrumental method that best describes IDDSI levels as an objective framework. A set of test samples, including commercially available instant mashed potato, baby rice cereal, and cooked potato cubes of varying texture, were prepared. Two IDDSI measuring techniques, fork pressure test and spoon tilt test, were used to evaluate texture grades of these samples. Puncture and compression tests based on texture analyzer were used to assess cohesiveness, adhesiveness, firmness, and hardness for each food category (Levels 4–7). Thresholds of cohesiveness and adhesiveness, as well as bands of acceptable firmness and hardness for each food category were clearly identified and are proposed as objective complements to the IDDSI framework. [ABSTRACT FROM AUTHOR]

Rheological approach has been widely applied to investigate the flow behavior of fluid food for the understanding as well as prediction of oral textural sensation of such products. However, since oral textural sensation is highly dynamic and influenced by multiple contributing factors (i.e. oral temperature, oral processing time, saliva mixing, and varied shear rate), conventional rheological measurements can hardly be precise in predicting oral textural sensation and mouthfeel. Here, we propose a very different rheology approach, which synchronizes four major dimensions/variables in one set of rheological measurements: the oral residence time, the bolus temperature, the saliva ratio, and the oral shear rate. Results indicated that the multiple dimensional rheology approach improved the predictive accuracy of the in-mouth thickness of low-temperature yogurt and provided a new measure for quantifying the mouth-melting of yogurt. It appeared that apparent viscosity at a temperature of 13 °C, a saliva ratio of 20 %, and a shear rate of 1 s−1 gave the most reliable prediction of the in-mouth thickness of yogurt. This novel approach provides a much-improved accuracy of texture prediction which requires a minimal number of rheology tests. We believe that, even though this experimental approach was initially designed for low-temperature yogurt drinks, it is also applicable to the texture and mouthfeel prediction of many other food products. [Display omitted] • A novel rheological approach synchronizes oral residence time, bolus temperature, saliva ratio, and oral shear rate in a single measurement. • Multiple dimensional rheology approach provides faster and more accurate rheological predictions for oral texture perception. • Measurements taken at approximately 40 % of oral processing time are optimal for predicting perceived thickness. • A faster change in apparent viscosity corresponds to a stronger sensory mouth-melting in yogurts. • Temperature of 13 °C, saliva ratio of 20 %, and shear rate of 1 s−1 appear to be the best combination for predicting texture sensation. [ABSTRACT FROM AUTHOR]

Textural properties of a food not only influence consumers' sensory preference of the product but also more importantly influence the strategy of food oral manipulation. Availability of reliable instrumental techniques has always been sought by food industry for proper assessment of food texture both in lab and online quality control. In this work a set of ball back extrusion (BBE) geometries with various ball/cup diameters (38/40, 35/40, 31.5/40, 24.5/28, all in mm) have been assessed as a fixture of a standard texture analyzer for flowability and consistency test of fluid foods. The feasibility of the new design has been tested against plate back extrusion (PBE), a current standard, for a set of fluid food materials (3 near Newtonians and 2 non‐Newtonians). Pressing force and apparent maximum stress were used to quantify the flowability of fluid materials. It was observed that both techniques were able to reflect the rheological nature of the samples and were able to distinguish flowability for both Newtonian and Non‐Newtonian fluids. However, the new design shows advantages against the plate back extrusion with much improved stability. Results show that BBE could replace the conventional plate‐back extrusion to evaluate the flow properties of fluid foods in an industrial environment. The geometries of 35/40 or 24.5/28 ball/cup diameters (aspect ratio 0.875) were shown to give most satisfactory performance. The device is specifically suitable for texture classification of fluid foods for dysphagia management. [ABSTRACT FROM AUTHOR]

Thickened fluids and texture‐modified foods are commonly used in the medical management of individuals who suffer from swallowing difficulty (known as dysphagia). However, how to reliably assess texture properties of such food systems is still a big challenge both to industry and to academic researchers. This article aims to identify key physical parameters that are important for objective assessment of such properties by reviewing the significance of rheological or textural properties of thickened fluids and texture‐modified foods for swallowing. Literature reviews have identified that dominating textural properties in relation to swallowing could be very different for thickened fluids and for texture‐modified foods. Important parameters of thickened fluids are generally related with the flow of the bolus in the pharyngeal stage, while important parameters of texture‐modified foods are generally related with the bolus preparation in the oral stage as well as the bolus flow in the pharyngeal stage. This review helps to identify key textural parameters of thickened fluids and texture‐modified foods in relation to eating and swallowing and to develop objective measuring techniques for quality control of thickened fluids and texture‐modified foods for dysphagia management. [ABSTRACT FROM AUTHOR]

Food texture and mouthfeel play a crucial role in product and consumer acceptability. Creaminess, enjoyed by consumers, is a complex, multimodal sensory perception involving olfactory, gustatory and tactile cues. Oral viscosity and lubrication are the key underlying physical properties that define the mechanism of creaminess perception. Thickness, smoothness, mouth‐coating, and dairy flavor can together play roles in the sensation of creaminess. The aim of this review is to present an understanding of the term" creaminess" along with different modalities involved in its perception, and to explore the oral physiological parameters and key physical properties that may be involved in the different oral modalities. An analysis of the previously examined links between food structure and composition and oral physiological parameters is presented. The review also presents a brief summary of previous models describing contributions of taste, aroma, and textural sensations. It emphasizes on the role of oral processing in testing proposed models with experimental evidence supporting those models and the future trends to enhance creaminess. [ABSTRACT FROM AUTHOR]

Oral lubrication has attracted a growing research interest in recent years because of its importance in influencing food texture and mouth-feel sensation. A number of tribometers have been developed for oral tribology studies, but all are designed for in vitro applications only. In this work, a new experimental set up has been established for in situ oral lubrication measurements; and further to determine oral lubrication as influenced by food consumption in relation to texture and mouth-feel. The design was based on a mechanical coupling between a texture analyzer and an intra-oral pressure sensor, and on a simultaneous digitizing of signals from both devices. Feasibility and reliability of the set up was firstly tested using hard–hard frosted glass surfaces with varying sliding speeds and two different normal forces; then using pig's tongue – polydimethylsiloxane soft surfaces with artificial saliva and food samples varying fat content at different sliding speeds. Consistent friction coefficients were observed in hard-hard surface lubrication tests and fat content-dependent friction coefficients were seen in soft surface lubrication tests. After these, in situ friction coefficients were measured in 10 healthy subjects, both under unstimulated oral conditions and after consumption of fluid foods. It was found that friction coefficient measured with no food consumption (unstimulated) was correlated to the salivary viscosity as well as salivary flow rate. The oral friction coefficient showed a strong correlation with the sensory intensity perception of astringency and slipperiness. Results from this work demonstrate that this simple experimental set up is feasible and reliable. Our work provides a new experimental technique for oral lubrication studies in relation to the controlling mechanisms of oral sensation of food texture and mouth-feel. Image 102191 • An in situ tribometer is designed and developed using a texture analyzer and Iowa Oral Performance Instrument (IOPI) with simple fittings. •Its feasibility and reliability was successfully tested using hard–hard contact and pig's tongue–PDMS soft contact tribological experiments. •10 volunteers' oral lubrication measured was correlated with oral physiological properties, salivarycompositions and sensory evaluations. [ABSTRACT FROM AUTHOR]

An editorial is presented that talks about the research on food texture. Topics discussed food texture research has established as an influential multiple disciplinary subject of food science, dealing with the complicated sciences; mentions the challenges faced by food industry and consumers related to food texture; and along with information on the contributors who work in food texture research.

'Oral' tribology has become a new paradigm in food texture studies to understand complex texture attributes, such as creaminess, oiliness, and astringency, which could not be successfully characterized by traditional texture analysis nor by rheology. Stick-slip effects resulting from intermittent sliding motion during kinetic friction of oral mucosa could constitute an additional determining factor of sensory perception where traditional friction coefficient values and their Stribeck regimes fail in predicting different lubricant (food bolus and saliva) behaviors. It was hypothesized that the observed jagged behavior of most sliding force curves are due to stick-slip effects and depend on test velocity, normal load, surface roughness as well as lubricant type. Therefore, different measurement set-ups were investigated: sliding velocities from 0.01 to 40 mm/s, loads of 0.5 and 2.5 N as well as a smooth and a textured silicone contact surface. Moreover, dry contact measurements were compared to model food systems, such as water, oil, and oil-in-water emulsions. Spectral analysis permitted to extract the distribution of stick-slip magnitudes for specific wave numbers, characterizing the occurrence of jagged force peaks per unit sliding distance, similar to frequencies per unit time. The spectral features were affected by all the above mentioned tested factors. Stick-slip created vibration frequencies in the range of those detected by oral mechanoreceptors (0.3-400 Hz). The study thus provides a new insight into the use of tribology in food psychophysics. Practical applications Dynamic spectral analysis has been applied for the first time to the force-displacement curves in 'oral' tribology. Analyzing the stick-slip phenomenon in the dynamic friction provides new information that is generally overlooked or confused with machine noise and which may help to understand friction-related sensory attributes. This approach allows us to differentiate samples that have similar friction coefficient, but are perceived differently in the mouth. The next step of our research will be to combine spectral attributes, such as the magnitudes of specific wave number bands and possibly their evolution during sliding, together with friction coefficient and viscosity values of foods with sensory results. The highest potential lies in predicting smoothness in opposition to roughness of a surface, such as a rough tongue when eating astringent or dry foods, or of particles when eating grainy foods. The effects of food ingredients at the nano to macroscales can then be used to optimize a specific lubrication behavior. [ABSTRACT FROM AUTHOR]

The sensation and perception of food texture is regulated by tactile-dominated mechanisms and therefore, it is believed that one's capability in discriminating food textural properties could be related to one's tactile sensitivity. However, evidence to support this hypothesis is currently not available. This work aims to test this hypothesis by examining tactile sensitivity of individuals' (touch detection threshold and two-point discrimination threshold) and texture discrimination capability. A range of soft-solid food samples with controlled firmness and elastic moduli were designed for textural discrimination tests. A total of 32 healthy subjects threshold of touch detection was found to be 0.028 g for the fingertip and 0.013 g for the tongue. Similarly, the mean threshold of two-point discrimination was 1.42 mm and 0.62 mm for the fingertip and tongue, respectively. Threshold for firmness discrimination (compressing until yielding) of the gel samples was 13.3% for the fingertip and 11.1% for the tongue. However, the elasticity discrimination threshold (by gentle pressing) of the population was found to be much smaller at 2.3% and 1.2% for the fingertip and the tongue respectively. Results show that tongue is slightly more sensitive than the fingertip in discriminating food texture (P < 0.05). An expected correlation between individual's capability of texture discrimination and their tactile sensitivity was not observed. [ABSTRACT FROM AUTHOR]

The capacity to discriminate the viscous nature of food materials is critically important in the sensory evaluation and subsequent perception of food texture and acceptability. It is generally assumed that this capability is closely linked to individual's tactile sensitivity, which in itself is a function of the individual's specific capabilities due to experience, age, lifestyle and health status for example. However, no experimental evidence is yet available to validate or disprove this assumption. By comparing the touch sensitivity and the capability of viscosity discrimination among individuals (using finger and tongue sensory perception), this work aims to establish if a correlation exists. Semmes-Weinstein monofilaments were used for touch sensitivity tests of the index fingers and tongue surfaces. A series of syrup solutions were prepared to give a wide range of viscosities with a viscosity scale factor of 1.2 ± 0.009. A total of 30 healthy subjects (16 female and 14 male; mean age 29.9 ± 9 years; mean body mass index 22.5 ± 2.9 kg/m2) participated in this study. A similar touch sensitivity threshold, 0.023 and 0.021 g, was observed for the index fingertip and for the tongue, respectively. However, the tongue appears to be more sensitive to touch than the fingertips when the force range they cover was compared. The viscosity discrimination threshold was found to be approximately 53% for the index fingertip and around 47% for the tongue. By comparing individual capabilities of viscosity discrimination against touch sensitivity, no significant correlation was observed between the two factors. The results from this work suggest that the capability to discriminate viscosity differences is more likely attributed to experience and is little influenced by one's physiological capability of tactile sensation, e.g., the touch sensitivity. Practical Applications The capability to discriminate differences in viscosity and the subsequent perception is an important factor for food texture appreciation. Establishment of the underlying factors that characterize the variation in the ability for such discrimination across individuals is not only critically important for our fundamental understanding of the viscosity perception but is also hugely important for the food industry in development of new food products, and in particular for specific food design for individuals with special needs, e.g., elderly, dysphagia patients, etc. Differential threshold for certain tastes and aroma compounds has been investigated. However, little has been reported in the literature about the tactile interpretation of viscosity sensation and perception. Findings from this work could provide new insight for researchers in the food industry and in food development by giving them flexibility to redesign their ingredients especially the one that has thickening effect on the product viscosity. Methodologies used in this experiment could also be applied for general food sensory studies in establishing relationships between sensory psychology and sensory physiology and especially the threshold studies with a similar approach of finding just noticeable difference values of any stimuli. The method could also be applicable to sensory capability studies of some particular groups such as elderly people to assess how weakened physiology affects their sensory capability. [ABSTRACT FROM AUTHOR]

Some previous studies have revealed a great variation of tongue muscle strength among healthy individuals. However, the implication of different tongue muscle strengths to individuals' oral capability of food handling is yet to be determined. In this work, vege-gels (with a resilient consistency of jelly) and pastry food (mashed potato) were used to investigate tongue-only oral breaking (smashing) of these foods by individuals who have different tongue muscle strengths. The aim of the work is to determine whether a correlation exists between the tongue muscle strength and its capability of food breaking. A series of vege-gels and mashed potato samples ranging from soft to hard were constituted with increasing consistency. Mechanical/textural properties of test food samples were characterised by a texture analyser. Three experimental tasks were designed: characterisation of individual's tongue muscle strength by measuring the maximum isometric tongue pressure (MITP) (Task 1); assessment of individual's capability of tongue-only food breaking (Task 2); and measurement of tongue–palate pressure generation for food oral breaking (Task 3). Our results confirm the great variability of tongue muscle strength among healthy individuals, with the highest MITP reaching 75 kPa and the lowest at only 17 kPa. The correlation study of tongue strength and the threshold gel/mashed potato strength for tongue-only oral breaking reveals a positive relationship between the two factors, which suggests that strong tongue muscle strength is always advantageous for oral handling (break/smashing) of viscoelastic and pastry foods. Conclusions obtained from this work can be a useful guidance to food design for elderly consumption. [ABSTRACT FROM AUTHOR]

Studies of “oral” tribology and “oral” lubrication have attracted growing interests among food researchers because of their important roles in oral textural sensation. However, to access a feasible technique for such studies is still a challenge to many food researchers due to the high cost of a commercial tribometer. In this work, a simple experimental set up has been constructed and tested for its feasibility and reliability for lubrication studies. The ultimate aim is to develop a reliable and low-cost technique for food lubrication studies and oral texture sensation studies. The design is based on a standard texture analyser manufactured by Stable Microsystems, with few additional simple fittings and attachments. This design is capable of conducting friction/lubrication measurements over a wide range of sliding speed (0.01–40 mm/s) and at any chosen surface load. The set up is convenient to operate and easy to set controlled experimental conditions (e.g. sliding speed, surface load, temperature, etc). Syrup solutions and evaporated milk were used as examples of near-Newtonian and non-Newtonian fluids for feasibility tests and results were reliably reproducible. Friction coefficients obtained for syrup solutions were comparable to those reported in literature. Stribeck curves covering the boundary regime, mixed regime, and hydrodynamic regime can also be constructed. Our results demonstrate that this design provides a low-cost alternative for food lubrication studies. Details of experimental set up, its advantages and limitations were discussed in this paper. [ABSTRACT FROM AUTHOR]

Oral processing of food is a dynamic process involving a range of deformation processes. The mechanical properties and the rheology of food have been widely used to understand and predict in mouth flow properties and to discover relationships with sensory perception. However, only limited success has been realised using such approaches to characterise and to interpret food texture. Tribology is emerging as a contributing discipline for understanding oral processing of food as well as texture and mouthfeel, since it encompasses both the fluid’s (lubricant’s) rheological properties as well as the surface properties of the interacting substrates in relative motion. [Copyright &y& Elsevier]

Abstract: Food oral processing is an essential procedure not only for the consumption and digestion of foods but also for the appreciation and pleasure of food texture and food flavour. The consumption of a food inside mouth involves various oral operations, including first bite, chewing and mastication, transportation, bolus formation, swallowing, etc. Exact mechanisms and governing principles of these oral operations are still not fully understood, despite of continuous efforts made by scientists from food, psychology, physiology, dental and clinical studies, and other disciplines. This article reviews recent progresses and literature findings about food processing and transformation in mouth, with particular attention on the physiology and rheology aspects of oral operations. The physiological behaviour of human''s oral device is discussed in terms of biting capability, tongue movement, saliva production and incorporation, and swallowing. The complexity of oral processing is analysed in relation to the rheology and mechanical properties of foods. The swallowing and oral clearing process is also examined for its criteria, triggering mechanism, bolus deformation, and the rheology of swallowing. [Copyright &y& Elsevier]

Abstract: This work applied a probe tensile separation method for quantitative characterisation of the stickiness of fluid foods and investigated its correlation to consumers’ sensory perception. Altogether 12 commercial fluid food products were tested. The maximum tensile force (F m) and the work till the maximum force (W m) were found to be useful parameters for stickiness prediction. Both of the parameters showed positive correlations with the results from sensory perception tests. It was found that, for some fluids, the total work done over the whole tensile separation (W) showed great discrepancy with the sensory perception, due to the existence of long force tail. The separation tests were performed over a wide range of probe speed (from 0.1mm/s to 40mm/s), but the inertial effect was found to be negligible. It was also demonstrated that, although the absolute value of force and work were highly dependent on the separation speed, the relative stickiness of foods was not affected as far as the tests were conducted under the same experimental setup. Possible mechanisms governing food stickiness were discussed. It was believed that pressure drop and cavitation of a suddenly stretched fluid could be critical in influencing consumers’ sensual perception of food stickiness. [Copyright &y& Elsevier]

From tastes good to mouth-feels good: A remark for the 50 years success of the Journal of Texture Studies From food material only to "food + saliva" or food-saliva interactions (Boehm, [2]; Lillford, [13]; Mosca, Feron, & Chen, [15]); Food texture research is now in a very different era, when consumers have very different attitude towards food and the quality of food. A review on the rheological properties of food emulsions deals with the fundamental causes of food texture (Zhu, Gao, Liu, Zou, & McClements, [14]). [Extracted from the article]

The article present the list of top 50 most influential article published in the journal in past 50 years as in 2019 including "The Perception of Food Texture - The Philosophy of the Breakdown Path," "The Chemistry of Texture in Fruits and Vegetables," and "Rheology of Liquid Foods - A Review."

Extensional and shear viscosities were studied for mixtures comprising artificial saliva and okra mucilage, the latter acting as a model thick-liquid food. These experiments aimed to obtain information on the flow-behavior information of the systems, underpinning the texture sensation of foods as perceived by dysphagic and xerostomic populations. Mixing okra mucilage with artificial saliva dramatically increases the shear viscosity of artificial saliva throughout the studied ranges of concentrations and deformation rates. Particle tracking does not suggest direct interactions between the components of artificial saliva and of okra mucilage. The rheology of the okra polymer (OP)–artificial saliva (AS) mixture is dominated by its extensional viscosity: Trouton ratios are in the order of tens to hundreds, while they decrease with increasing okra-mucilage concentration; this highlighs the dominance of the extensional rheology and the increasing importance of the shear mechanics with increasing okra content. The relaxation times and extensional moduli are also reported for the systems under study. Extensional and shear flows are of equal importance concerning the elastic behavior. Texture sensation: rheological data guide artificial saliva formulation Artificial saliva is usually formulated to help people with dysphagia or xerostomia. Their mouth feels of food textures are largely dependent on the flow behaviors of the food–artificial saliva mixtures. Christos Ritzoulis and coworkers from Zhejiang Gongshang University now studied the rheological and structural properties of artificial saliva when mixed with okra mucilage. They found the shear viscosity and storage modulus of the artificial saliva were much higher in the presence of okra polysaccharide, suggesting the formation of a macromolecular-interacting network. Moreover, it was found the overall rheological behaviors of the mixtures were always dominated by the extensional viscosity, though the shear behavior became more and more obvious with the increasing amount of okra polymer. Together with the data obtained with real saliva, these on artificial saliva could guide the future formulation of artificial saliva. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue about the works of food scientist Alina Surmacka Szczesniak and Prof. Malcolm Cornelius Bourne in the field of food texture.

Malnutrition in older adults is partly attributable to decreasing muscle strength leading to inadequate intakes. It is therefore important to investigate ways of identifying eating capability both through objective measures of strength and subjective measures of perceived difficulty and liking. In addition, food texture design might affect the oral processing and the difficulty perceived. Therefore the present study sets out to examine the relationship between various quantitative measures of eating capability (EC) and perceived difficulty of processing foods and gels varying in hardness in older adults. Tests were conducted on 30 participants (mean age 79 ± 9.4 years) using non-invasive techniques (hand gripping force, tongue pressure, biting force, and hand dexterity) in conjunction with frame-by-frame video recording analysis of chewing and swallowing of food stimuli and ratings of eating difficulty. The EC scores were computed to grade the population into three different groups. Stimuli were classified into two categories: food products and flavourless hydrocolloid gels with different inhomogeneity (textures). The EC parameters did not correspond to oral residence time, or the difficulty perceived. Bite force differed by EC group, and was significantly different by dental status [ F (3,4.26) = 3.842, p = 0.022], and influenced both liking and number of chews. The food hardness (r = 0.915, p = 0.01) was significantly correlated with the number of chews. Gel heterogeneity influenced food oral processing behaviour. Oral residence time was significantly correlated with number of chews, liking and difficulty perceived. In summary, dental status and bite force of older adults are determining EC parameters to design optimized food-texture. [ABSTRACT FROM AUTHOR]

Abstract: Oral texture is one of the most important quality attributes that contribute to consumers’ acceptance and preference of a food product. Oral processing of food is intricate and involves a series of processes—ingestion, mastication and finally swallowing. The mechanical and rheological properties have been widely applied to understand and describe in-mouth flow properties of a food and associated sensory perception. However, as the oral processing continues and food particle size reduces, rheology alone is no longer effective in explaining the textural and mouthfeel properties of food, but the lubrication behaviour between oral surfaces becomes a dominating mechanism in relation to food texture and mouthfeel. For this reason, tribology is emerging as a new discipline for food texture studies, where lubricating properties of food are measured by using an equipment that operates on the same principle used in mechanical engineering for determining the frictional properties of lubricants. While there are many instruments and equipments available for engineering lubrication studies, choice is limited for food applications. This article will review various tribological systems currently utilised for various food systems, whether commercially purchased, custom-made, or by use of attachment tools for rheometers. The operation principles, advantages and disadvantages of these devices are discussed. Examples of food application are also given in each case, where measured frictional properties are used to interpret sensory mouthfeel properties. [Copyright &y& Elsevier]

This paper presents a comprehensive design approach for an electro-mechanical system for food oral processing research. The bespoke design and prototype of the proposed device is a standalone and compact table top model and can be operated using a customized software interface. The design considered a bi-directional chewing motion to enable nearly similar mandible movement pattern as in human. Food texture profile can be estimated using a load cell with capacity up to 300 N. This design included a section of real shaped teeth assembly consisting of three teeth; and a controlled supply line for multi-point saliva injections. The device is fitted with easily replaceable sensors for in situ measurements of conductivity, pH, and temperature. Operating volume of the device can be kept in equivalence with the volume of human oral and nasal space. The device chamber can be hermetically sealed and temperature controlled. A duct system is fitted to connect the device with external analytical systems, such as electronic nose, for measuring gaseous substance release during experimentation. The system also enables easy retrieval of the processed sample so as to use the masticated samples and processed saliva for subsequent analysis by analytical instruments, such as electronic tongue, to identify released soluble compounds and taste profiles. Moreover, the design emphasized on easy cleaning and maintainability. Based on the proposed design, two working prototypes are developed. It is envisaged that the device will be a novel contribution to the progress in the field of food science, new product development, training to future professionals, and strengthening industry-academic collaborations in foreseeable future. • Detailed engineering and design features for a novel electro-mechanical chewing system. • Experimental validation of the prototypes. • Review on the potential of the novel system in food oral processing research and food product assessment. [ABSTRACT FROM AUTHOR]