Lubricating properties of human whole saliva as affected by β-lactoglobulin

The effect of β-lactoglobulin (β-LG) at pH 3.5 and 7.0 on lubricating property of saliva as related to astringency perception was investigated using tribology. Saliva was adsorbed onto surfaces of a rotating poly dimethylsiloxane (PDMS) ball and disc to form a film under conditions that mimic the rubbing contacts in the oral cavity (Bongaerts, Rossetti, & Stokes, 2007) and the lubricity of saliva films upon exposure to astringent compounds was measured. While addition of non-astringent β-LG at pH 7.0 slowly increased friction of saliva film between tribopair surfaces, β-LG at pH 3.5 rapidly increased the friction coefficients of saliva, similar to other astringent compounds (epigallocatechin gallate and alum). This supports the hypothesis that astringency of β-LG arises from the loss of lubrication of saliva which is in agreement with the well-accepted astringency model of polyphenols. Increasing β-LG concentration at pH 3.5 (0.5–10% w/w) caused a rapid increase in friction coefficient; however, at the highest protein concentration, the friction coefficient, although higher than observed for water, was below the values observed for the lower protein concentrations. This suggests that static tribology testing is different from the dynamic in-mouth system such that a simple relationship between friction and sensory astringency cannot be found for all conditions.     

Adapting tribology for use in sensory studies on hard food: The case of texture perception in apples

Application of tribology in food systems has primarily focused on liquids and semi-solids. The present study examined texture perception in a solid food, using apples as the proof-of-concept. The study aimed to assess a) the ability of tribological measurements to predict a multicomponent sensory property (mealiness) in hard food, and b) the impact of two common motion patterns (rotational and linear reciprocating) on tribological measurements and mathematical correlations with sensory texture of a hard food. The textures of ten apple varieties were evaluated by a trained sensory panel while friction and wear behavior were measured instrumentally. Spearman correlations indicated that texture attributes (crisp, juicy, mealy, and rate of melt) significantly correlated with total penetration depth (p < 0.05) and with friction coefficients during the transient (non-equilibrium) phase (p < 0.05), but not with friction coefficients from the steady-state phase in both rotational and linear tribology (p > 0.05). This was an important finding as the steady-state phase is predominantly used in food tribology research, yet our findings showed poor correlations with steady-state data, while showing strong correlations with sensory perception in the transient phase. The strong mathematical correlations found in the transient phase suggest that test conditions that provoke a dynamic friction response from the sample may more closely resemble the conditions under which humans perceive friction during oral processing.     

口腔软摩擦理论与测量技术及其在食品感官感知研究中的应用

食品口腔加工是一个复杂的动态过程，包括食物持续破碎、食团尺寸减小、唾液分泌和食团形成等一系列过程。它既是食品的口腔物理处理过程，又是食品的感官感知过程。在此过程中，食品颗粒之间以及食品颗粒与口腔表面之间普遍存在着相对移动。因此，如何准确描述与该过程控制相关的物理原理，已超出了传统的流变学范畴，而且许多感官特性（如光滑感、脂肪感、油腻感、后余味等）亦不可用简单的流变学测量来表征。近年来兴起的口腔软摩擦研究被认为是研究食品口腔加工与口腔感官的可行技术手段。本文阐述了摩擦学基本原理和口腔软摩擦的基本知识，主要包括口腔软摩擦的生物学基础和测量方法，同时介绍了软摩擦技术在食品研发与感官品质评定中应用的最新进展。     

新定纤感知器纤度感知理论模型的建立

针对在定纤感知器感知机制方面的学术争论问题,借用摩擦学理论,对感知器运动各个过程的摩擦性质进行定性归类。依据摩擦学对固体摩擦、边界摩擦、流体摩擦的定义,从建立的丝条与感知器接触的宏观模型、微观模型等方面进行分析,指出原有定纤感知理论模型存在的不足。利用摩擦学的简单黏着理论,重新建立丝条与感知器玻璃片接触的摩擦力公式。公式显示在正常感知情况下同时存在固体摩擦、边界摩擦、流体摩擦3种摩擦,当纤度直径小于感知器垫片厚度时,与原有定纤感知理论模型一致,认为新理论更适用于目前所用全部类型的自动缫丝机的管理。     

In vitro oral simulation based on soft contact: The importance of viscoelastic response of the upper jaw substitutes

Real oral processing is the squeezing and shearing between two soft surfaces. The importance of soft palate surface cannot be ignored while focusing on tongue substitutes. Thus the effects of viscoelasticity, roughness of upper jaw substitutes, and fluid rheological properties on lubrication properties were explored by in vitro oral tribology experiments. Different palate substitutes significantly changed the friction curves of pure water, milk, and yogurt. The boundary friction coefficients of pure water and milk are higher under softer or smooth palate substitutes due to stronger viscoelastic responses of friction pairs. Their boundary friction coefficients are lowest at rigid upper jaw substitutes owing to smaller contact angles and deformation. However, the boundary friction coefficient of yogurt is lower owing to its high viscosity, low loss factor, and large particle size under soft friction pairs. In addition, it is highest at rigid palate friction pair because a smaller contact area reduces the entrainment of yogurt, resulting in poor lubricating performance.     

Influence of emulsion composition on lubrication capacity and texture perception

The role of fat content and type of surfactant for oral friction processes and texture perception of oil-in-water emulsions was assessed. Emulsions at 22% and 33% fat content containing either sodium caseinate or a sucrose ester as emulsifier were compared with viscosity-adapted aqueous solutions of dextran using both sensory evaluation and friction coefficient measurements on a tongue-palate contact model. The impact of saliva on the emulsion droplet size distribution was studied using tribology, differential interference contrast microscopy and light diffraction measurements. Emulsions at 33% and the corresponding iso-viscous aqueous solutions were discriminated in the sensory experiment whereas emulsions at 22% were not. Friction was significantly different for emulsions at 33% and the corresponding iso-viscous aqueous solutions. The difference was not significant for emulsions with 22% fat level when compared with the iso-viscous aqueous solutions. Saliva significantly decreased the friction coefficient of emulsions depending on the surfactant and amount of fat used.     

Tribology and its growing use toward the study of food oral processing and sensory perception

Here we provide a comprehensive review of the knowledge base of soft tribology, the study of friction, lubrication, and wear on deformable surfaces, with consideration for its application toward oral tribology and food lubrication. Studies on “soft-tribology” have emerged to provide knowledge and tools to predict oral behavior and assess the performance of foods and beverages. We have shown that there is a comprehensive set of fundamental literature, mainly based on soft contacts in the Mini-traction machine with rolling ball on disk configuration, which provides a baseline for interpreting tribological data from complex food systems. Tribology-sensory relationships do currently exist. However, they are restricted to the specific formulations and tribological configuration utilized, and cannot usually be applied more broadly. With a careful and rigorous formulation/experimental design, we envisage tribological tools to provide insights into the sensory perception of foods in combination with other in vitro technique such as rheology, particle sizing or characterization of surface interactions. This can only occur with the use of well characterized tribopairs and equipment; a careful characterization of simpler model foods before considering complex food products; the incorporation of saliva in tribological studies; the removal of confounding factors from the sensory study and a global approach that considers all regimes of lubrication.     

New insight in characterization of red wine astringency using soft tribology method

The variation of friction coefficient (μ) of model wine and model saliva mixtures with entrainment speed (V_R) on simulated oral surfaces was evaluated by oral tribology. Combined with techniques of dynamic light scattering (DLS), atomic force microscopy (AFM), rheometer, and quartz crystal microbalance with dissipation monitoring (QCM-D), the correlation between characteristics of the model wine and model saliva mixtures (particle size and morphology, suspension viscosity, adsorption film thickness, and viscoelasticity) and the oral lubrication loss was established. The results showed that the higher the concentration of tannin in the model wine, the larger the size of the complexes with the model saliva, and the higher the thickness, viscoelasticity, and roughness of the adsorption film formed, which resulted in the increase of friction coefficient in the boundary lubrication regime. Different from previous results, it is found that the maximum value of the friction coefficient (μ_max) in the boundary regime has the best positive correlation with the astringency perception intensity of the model wine accordingly.     

Reducing the deposition of fat and protein covered particles with low energy surfaces

Deposition behavior of spray dried full cream milk, skim milk and whey particles were observed in a pilot scale dryer. Particle surface dominated with fats exhibit gradual decrease in deposition fluxes when transition from the initial adhesion to the subsequent cohesion mechanism. Whey protein, however, displayed significant differences in the adhesion and cohesion fluxes. Reduction of particle deposition on low energy chamber wall surface is more significant for the hydrophobic whey particles. Further analysis shows that the reduction in droplet–wall contact energy is larger for the more hydrophobic droplet, delineating weaker adhesion interaction. The results suggest that the hydrophobicity of the depositing particles in an important consideration when using lower chamber wall with lower surface energy. This is in addition to the effect of particle rigidity and deposition strength as reported previously.     

9种谷物均一熟化后物性的变化

为使9种谷物在混合煮制时达到均一熟化,本实验通过感官评价确定各谷物最佳破碎粒径范围,同时对破碎与未破碎谷物在煮制过程中的感官、质构以及摩擦学特性的变化进行比较分析。结果表明,当黑米、燕麦、粘白高粱、大麦、小麦颗粒的破碎粒径范围在1.6~2.0、1.6~2.0、1.6~2.0、2.5~3.5、2.0~2.5 mm,荞麦、小米、大米和圆糯米未破碎时,9种谷物可在25~35 min内达到均一熟化。经破碎处理后,谷物在煮制过程中的硬度先急剧降低,再缓慢降低,最后保持平稳,粘度无显著变化,弹性减小,咀嚼性显著降低(p<0.05)。另外,均一熟化后谷物摩擦系数的大小与感官评价中剌嗓子的轻重程度呈正相关,破碎处理能有效降低谷物的摩擦系数。综上所述,破碎处理可缩短煮制时间,改善熟化谷物的品质,降低摩擦系数。     

Understanding of the influence of composition,structure and texture on salty perception in model dairy products

The aim of this study was to better understand salt release and perception in model dairy products, having different composition, structure and/or texture. Sensory and instrumental methods were used to quantify and relate texture to salt mobility and perception. A high dry matter content (protein and fat jamming) and a gel structure with a protein network formation induced a decrease of diffusion coefficient of salt in matrices. Moreover, salty perception was higher for non-renneted products than for gelled ones. For gels, saltiness was enhanced in fat products. These results were discussed in regards with textural and physico-chemical food properties: the structural parameter tan δ was the most correlated with salty perception highlighting the impact of product structure on saltiness. Results also demonstrated that physiology and complex events (mastication, dilution and mixing with saliva, dynamic of bolus formation) occurring during food consumption must be considered to go further in understanding.     

增稠剂对酸奶质地的影响研究

对酸奶的硬度、黏度、凝聚性、保水性进行测定，研究了不同增稠剂对酸奶质地和感官特性的影响。结果表明。果胶、明胶、耐酸CMC、海藻酸钠分别提高了酸奶的黏度，而槐豆胶、瓜尔豆胶、魔芋胶则相反；只有果胶和明胶提高了酸奶的保水力；果胶、明胶时酸奶质地的影响随着浓度的增加而增加。统计结果表明，当增稠剂添加量为0．1％时，不同增稠剂对酸奶的质地存在显著影响；同时．增稠荆浓度对酸奶质地的影响也显著。     

Texture as a reflection of microstructure

The perception of texture has been correlated to the microstructure of particulate whey protein gels. A full, two-level, factorial experimental design was used in which the processing conditions, pH, heating rate and addition of salt were used as design factors. The texture of the gels was analysed by a sensory panel, and the microstructure was analysed by light and electron microscopy. The microstructure was quantified by using different types of image analysis.

In this study of particulate whey protein gels, the test principles of analysing texture were divided into two groups: destructive tests and non-destructive tests. The microstructural parameters can also be divided into two groups: overall network dimensions (pore size and particle size) and strand characteristics. The texture as measured with destructive methods was sensitive to overall network dimensions, whereas texture as measured with non-destructive methods was sensitive to the strand characteristics of particulate protein gels.     

EFFECT OF FRICTION ON THE PERFORMANCE OF TEXTURE TEST CELLS*

The relationship was measured between the normal contact force and the force required to overcome friction between food samples and a surface simulating a typical texture test cell. Peas produced frictional behavior that combined the characteristics of dry friction and fluid flow. Friction coefficients for selected foods ranged from 0.04 to 0.52. Friction force was linearly related to the normal contact force and non-linearly to the area of contact between the sample and the surface, and the speed of the sample relative to the surface. This verifies the fact that, with empirical texture test devices, these test variables must be held constant. The estimated friction forces represented a significant amount of the total force required to operate a wire extrusion cell and a back extrusion cell. It was concluded that standardization of the test cell would be easier to achieve if the contact area between the sample and the cell surfaces was minimized and if low friction materials were used to construct the cells.     

间歇式定纤感知器接触模型分析与研究

通过分析不同粗细丝条在感知器中的运动状态，利用摩擦学润滑状态的定义，阐明润滑膜厚度是衡量摩擦性质的关键，并通过感知器间隙与丝条直径的计算，建立了间歇式感知器的纤度感知理论模型，指出间歇式感知器主要属于混合摩擦而不是液体摩擦。     

To see is to hold: Using food surface textures to communicate product healthiness

In this paper, we test whether the evaluation of food healthiness is affected by tactile surface qualities that are seen but not touched. Furthermore, we explored if visually based tactile surface cues influence perception more or less depending on whether they are explicitly or implicitly presented. Participants were shown 3 implicitly and 3 explicitly textured biscuits that were identical apart from the surface texture. The surfaces were either smooth, medium or rough and were rated on perceived healthiness. Additionally, the biscuits were rated on tastiness, likelihood of purchase, crunchiness and chewiness, aspects that can affect consumer choice outcomes. A pattern emerged whereby implicit surface textures affected perception more than explicit textured surfaces. Specifically, perceived product healthiness was greater for medium textured implicit surfaces. Thus, it seems that food healthiness is influenced by cross-sensory cues. Implicitly rough textures were found to be perceived as crunchier. Determining food properties usually relies on exposing receptors within the mouth to the components of ingested food. However, we demonstrate here that properties such as crunchiness also can be dependent on surface texture. The findings can be used to encourage consumers to purchase healthier food products.     

Influence of texture on the temporal perception of sweetness of gelled systems

The aim of this work was to study how the texture of two hydrocolloid gelled systems with different mechanical properties – κ-carrageenan and gellan gum – sweetened with two sweeteners with different sweetening power – sucrose and aspartame – influence the temporal perception of sweetness using a time–intensity test. The results show that the different aspects of temporal perception of sweetness of hydrocolloid gels were related to their mechanical properties in different ways. Maximum sweetness intensity was closely related to the amount of deformation required to break the network and with its resistance to deformation. Meanwhile resistance to rupture was also an important factor influencing the variation in the rate of intensity decrease. The time needed to reach maximum sweetness intensity was only dependent on sweetener concentration.     

Hydrophobic properties of textile materials: robustness of hydrophobicity

Extremely hydrophobic surfaces have been receiving considerable interest, such as in the contexts of self-cleaning glass or clothes, antifouling paintings, and the reduction of friction drag. A large variety of treatments permits the obtainment of (super)hydrophobic textile surfaces. The point here is to investigate the role of different geometrical textile parameters on the hydrophobicity, and more particularly, on the robustness of this property. The influences of solid surface roughness on the wetting behavior are commonly studied for model solid textures while textile roughness is largely deformable. A laboratory test method is suggested to evaluate this robustness. Some hydrophobic fibrous structures were prepared (using classical woven fabrics and pile fabrics) to investigate the influence of textile structures on their static and forced wetting properties. Static contact angles, contact angle hysteresis, and the contact angle after compression were measured. The meso- and micro-structures appeared to influence either the static wetting or the robustness of the hydrophobicity after compression.     

不同淀粉对饼干口感润滑质地的影响

为了掌握淀粉对饼干口感润滑质地的影响规律,本研究采用质构仪、流变仪、模拟口腔摩擦、及感官差异检验等手段,通过添加六种淀粉考察其对饼干质地、口腔润滑及感官属性的影响。结果显示,添加淀粉后,不同淀粉饼干的明度(L^*),黄蓝色(b*),硬度、酥脆性、弹性、咀嚼性和回复性,均存在显著性差异(P＜0.05)。动态流变学结果显示绿豆、小麦、玉米淀粉的添加可以一定程度上增强了面团中淀粉分子之间发生交联,形成稳定的凝胶网络结构。口腔摩擦学结果显示,添加淀粉可以改善饼干的润滑特性,绿豆、红薯、豌豆、马铃薯淀粉对饼干润滑度的提升具有显著性(P＜0.05)。不同淀粉饼干的润滑性结果为：马铃薯淀粉饼干＞豌豆淀粉、红薯淀粉饼干＞绿豆淀粉饼干,其结果与感官差异分析结果一致。淀粉作为润滑质地调节剂,可以提高饼干产品口腔润滑性能,同时该研究也为口腔摩擦学用于主观感官分析的提供参考。     

Structural parameters that determine the rheological properties of apple puree

The objective of this work is to better understand how the structural parameters (particle content, particle size and serum viscosity) influence the rheological properties of apple purees. An apple puree (called “native”) was ground to obtain dispersions with three different particle size distributions. This mechanical treatment induced the separation of parenchyma irregular cell clusters into regular single cells, modifying both the morphology and the particle size distribution of purees. A separation–reconstitution step made it possible to obtain samples with a wide range of insoluble solids (8–24 g/kg). Pectin was added to some of the samples in order to increase the viscosity of the continuous phase. The rheological behaviour and structural properties of the modified apple purees were investigated using flow and oscillatory rheological measurements, particle size measurements and confocal laser scanning microscopy. Rheological properties such as apparent viscosity, yield stress and elastic modulus decreased as particle size decreased and they increased as insoluble solids content increased. Modelling of rheological properties with master curves made it possible to take into account the apparent relative volume occupied by the particles of different sizes.