The role of friction in perceived oral texture

Instrumentally measured in vitro friction in semi-solid foods was related to oral texture sensations. Increased fat content resulted in lower sensations of roughness, higher sensations of creaminess, and lower friction, suggesting that lubrication is the mechanism by which fat affects oral texture in low fat foods. Starch breakdown by salivary amylase in low fat foods resulted in reduced friction, possibly through the release of fat from the starch food matrix, and the migration of fat to the surface of the bolus where it becomes available for lubrication. No evidence was found that salivary mucins or salivary viscosity play a role in lubrication. Astringent sensations may be related to reduced lubrication and increased friction caused by particles, either resulting from precipitation of salivary protein rich proteins or from flocculation of dead cells.     

Impact of Fat Replacers on the Rheological,Tribological, and Aroma Release Properties of Reduced-Fat Model Emulsion Systems and Processed Cheese

Due to the increasing prevalence of overweight and obesity and their associated health problems, the demand for low-calorie and low-fat foods is growing worldwide, especially in the fast food and convenience sectors. However, fat- or calorie-reduced products are often accompanied by sensory deficiencies. Although fat reduction in foods has been addressed in literature, an ideal fat replacer has not been identified due to the variety of fats, their multifarious functions in foods, and the wide range of food products. The aim of this work was to investigate the influence of selected fat replacers on the properties of reduced-fat model emulsion systems and processed cheese. The use of dietary fibers as fat replacers was of particular interest due to their intrinsic health benefits. In addition, both new and established methods of measurement of sensory attributes were applied and compared to determine correlations of findings between different methods of measurement. Chapter 1 addresses the influence of fat replacers on attributes such as energy density, flowability, and firmness in a real food product, processed cheese. To this end, microparticulated whey protein (MWP), which has been widely used as a fat replacer, and three dietary fibers (corn dextrin (CD), inulin, and polydextrose), were used in reduced-fat processed cheese slices. A reduction in energy density of about 30 to 40% was achieved using a fat replacer compared to standard commercial full-fat processed cheese. Higher CD and inulin concentrations reduced the flowability of the cheese slices upon heating, but only had a minor impact on the firmness of the unheated cheese. The addition of MWP resulted in firmer cheese slices with higher flowability compared to the other fat replacers. However, changes in the MWP concentration had little effect on either property. The results demonstrated that different fat replacers with varying concentrations need to be applied to achieve desired attributes for specific conditions of use, e.g., unheated cheese in sandwiches or heated cheese in cheeseburgers. To evaluate newly developed reduced-fat foods, the impact of fat replacers on sensory properties and aroma release also needs to be investigated, which is addressed in chapters 2 to 4. Due to the complex composition of cheese, systematic investigation of the mode of action of fat replacers is difficult. Therefore, emulsion-based model foods were used to eliminate interfering factors and natural variations of ingredients. The second study (chapter 2) focused on developing and validating appropriate methods to investigate the effects of fat, fat reduction and the use of fat replacers on emulsion systems. Tribology, a comparatively new method in food research, was used to instrumentally analyze selected aspects of food mouthfeel. Reduced-fat salad mayonnaises were prepared as separate samples containing different CD concentrations, and characterized using textural, rheological and tribological analyses together with measures of spreadability and human-sensory analysis. The results showed a very high correlation between tribological measurements and the sensory evaluation of the attribute stickiness. In addition, it was shown that some correlations between instrumental and sensory data were best described by a non-linear correlation (Stevens’ power law), such as the relationship between Texture Analyzer measurements and sensory sensations of firmness. Furthermore, the Kokini oral shear stress correlated very well with the sensory attribute creaminess. Hence, the instrumental analytical methods used showed the potential to predict elements of the sensory analysis and reduce the overall analytical effort. While aroma release plays a key role in consumer acceptance, the influence of fat replacers on this attribute has rarely been studied. The third study (chapter 3) therefore investigated not only techno-functional properties but also the release of typical cheese aromas using a liquid emulsion as a model food. While both MWP and CD exhibited a retarding effect on the release of lipophilic aroma compounds, MWP also reduced the release of hydrophilic aroma compounds. It was also shown that aroma release is not only influenced by a change in viscosity, but also by interactions between aroma compounds and fat replacers. In this context, CD exhibited a similar ability to interact with aroma compounds as fat, which is desirable for the development of low-fat foods. In the final study (chapter 4), the findings and methods developed in chapters 1-3 of this work, supplemented with additional methods, were used to investigate the effect of fat reduction and CD concentration on a model processed cheese spread (PCS). By replacing 50% of fat completely with CD, the fat content of the PCS could be reduced without causing any significant changes in properties compared to the full-fat version, e.g. in firmness, flowability upon heating and aroma release. CD was determined to be a promising fat replacer, mimicking important properties of fat. Additional correlations, such as those between the parameters of Winter's critical gel theory (gel strength and interaction factor) and spreadability and lubrication properties were identified and can help to further reduce the analytical effort. In conclusion, CD has been confirmed as a promising fat replacer in both liquid and semi-solid food emulsion products. Furthermore, this work contributes to closing the research gap in the instrumental measurement of sensory attributes by outlining correlations, for example, between tribological methods and mouthfeel sensations. Thus, the evaluation tools of this work can help to assess the potential applications of new fat replacers without extensive application and sensory testing which significantly shortens the development time for food manufacturers. In addition, the results contribute to a better understanding of the interactions between fat, fat replacers and aroma compounds in food matrices. This facilitates the systematic development of reduced-fat processed cheese and other dairy- and emulsion-based products which meet consumer preferences and accelerate the trend towards healthy eating.     

Contribution to the understanding of consumers’ creaminess concept: A sensory and a verbal approach

Creaminess is an integrated term, which is reported to depend on textural properties, fattiness, flavour and pleasantness of food products. We aimed to determine whether consumers weight these attributes similarly or not when assessing creamy products. To determine this, sensory properties of 12 dairy products were characterized by a trained panel. Then, new consumers rated the creaminess and their liking for these products, and wrote down their own definition of creaminess. A cluster analysis done on the consumers’ creaminess scores revealed three clusters, which were characterized through correlation with trained panel data, liking data and definition data. For all clusters, consumers used words related to texture and pleasantness when defining creaminess. Nevertheless, from verbal and sensory data, product properties underlying creaminess construct vary among clusters. While a first cluster put emphasis on texture, a second one put emphasis on fattiness and natural flavour, and a last put emphasis on sweetness.     

MECHANISMS UNDERLYING THE ROLE OF FRICTION IN ORAL TEXTURE

The role of friction in food texture sensations are reviewed with the focus on results from our own laboratory, concentrating on texture sensations that are affected by the lubricative properties (e.g., roughness and creaminess), by the viscosity (e.g., melting and thickness) and by the used thickeners (e.g., airiness and heterogeneity). A food's lubricative properties are affected by its fat content, fat droplet size, particle size and shape and thickener. Foods with lower fat contents, larger fat droplets, larger particles and specific thickeners exhibited higher friction while their creaminess and fattiness sensations, associated with good lubrication, are reduced. Roughness and dryness sensations, associated with poor lubrication, are increased. Taste and flavor compounds also affected these texture sensations, albeit via a different mechanism. Specific compounds can affect the lubricative properties of saliva resulting in friction‐related sensations, such as astringency. Astringent compounds interact with proline‐rich proteins in saliva, causing precipitation that may be sensed as discrete particles and/or increased roughness. Alternatively, the compounds may precipitate dead cells and other debris present in saliva. Astringent compounds may also directly affect the surface properties of the oral mucosa.     

Perception of melting and flavor release of ice cream containing different types and contents of fat

Temporal effects of dairy and vegetable fats (0 to 18%) on perception of strawberry flavor release and melting of ice cream were studied using the time intensity sensory method. Also, aroma and flavor attributes of the ice cream samples were evaluated. Only slight effects of fat on the rate of flavor release and flavor intensity were perceived. A slightly faster flavor release from the vegetable fat compared with dairy fat was noticed. Polydextrose and maltodextrin as bodying agents in the fat-free ice cream significantly increased flavor release and melting rate of the ice cream. Increasing fat content slightly retarded melting of ice cream in the mouth. No significant effect of the fat quality on perceived melting was noticed. Significant differences in aroma and flavor attributes of the fat-free and other samples were perceived. Intensity and sharpness of the strawberry aroma and flavor were greater in fat-free samples and they were perceived as nontypical. Fattiness and creaminess were highly correlated. Maltodextrin and polydextrose increased perceived fattiness and creaminess of fat-free ice cream.     

Linking oral processing behavior to bolus properties and dynamic sensory perception of processed cheeses with bell pepper pieces

The addition of food particles to food matrices is a convenient approach that allows to steer oral behavior, sensory perception and satiation. The aim of this study was to determine the influence of physical-chemical properties of heterogenous foods on oral processing behavior, bolus properties and dynamic sensory perception. Bell pepper gel pieces varying in fracture stress and concentration were added to processed cream cheese matrices differing in texture. Addition of bell pepper gel pieces to processed cheeses increased consumption time, decreased eating rate and led to harder and less adhesive bolus with more saliva incorporated. Addition of bell pepper gel pieces to processed cheeses decreased dominance rate and duration of creaminess, smoothness, melting and dairy flavor and increased graininess and bell pepper flavor. Increasing fracture stress of bell pepper gel pieces from 100 to 300 kPa resulted in longer consumption time and lower eating rate. For hard/non-adhesive processed cheese matrices increasing gel pieces fracture stress lead to a boli with larger particles and more saliva. These changes were accompanied by decreased dominance perception of creaminess and bell pepper flavor and increased dominance of graininess. Increasing the concentration of bell pepper gel pieces from 15 to 30% did not affect oral behavior but led to the formation of harder and less adhesive bolus with larger particles and less saliva that were perceived with reduced dominance of creaminess, meltiness and dairy flavor while dominance of graininess and bell pepper flavor increased. Changing the texture of the cheese matrix from soft/adhesive to hard/non-adhesive decreased consumption time, increased eating rate, did not influence bolus properties and decreased dominance rate of creaminess, smoothness and melting sensations. Number of chews and total consumption time were positively correlated with saliva content of the bolus, number of bolus particles, bolus hardness, dominance of firmness, chewiness and graininess. We conclude that the modification of physical-chemical properties of processed cheeses and embedded bell pepper gel pieces can be a strategy to steer oral behavior and bolus properties which consequently determine dynamic sensory perception.     

Effect of emulsifier type on sensory properties of oil-in-water emulsions

This work investigates the fundamental properties of emulsifiers that may contribute to the fat-associated sensory attributes of emulsions. Model oil-in-water emulsions were prepared with 0, 12, 24, 36 and 48% oil and emulsified with seven different emulsifiers; two proteins; sodium caseinate and whey protein, and five different sucrose esters. Emulsions were rated for perceived ‘fat content’, ‘creaminess’ and ‘thickness’ on nine-point category scales. Instrumental measurements of particle size, viscosity, thin film drainage, surface dilational modulus and interfacial tension were made. The sensory results indicate significant main and interactive effects of fat level and emulsifier type. At higher fat levels, emulsions prepared with sodium caseinate and whey protein emulsifiers had higher viscosities and higher sensory scores than those prepared with the sucrose esters. Results indicate that emulsifier type has a significant effect on the sensory properties of oil-in-water emulsions, and relationships between instrumental and sensory measures suggest that this may be due to the interfacial properties of emulsifiers at the oil–water interface. © 1998 SCI.     

Effects of CD36 Genotype on Oral Perception of Oleic Acid Supplemented Safflower Oil Emulsions in Two Ethnic Groups: A Preliminary Study

Previous studies demonstrate humans can detect fatty acids via specialized sensors on the tongue, such as the CD36 receptor. Genetic variation at the common single nucleotide polymorphism rs1761667 of CD36 has been shown to differentially impact the perception of fatty acids, but comparative data among different ethnic groups are lacking. In a small cohort of Caucasian and East Asian young adults, we investigated if: (1) participants could detect oleic acid (C18:1) added to safflower oil emulsions at a constant ratio of 3% (w/v); (2) supplementation of oleic acid to safflower oil emulsions enhanced perception of fattiness and creaminess; and (3) variation at rs1761667 influenced oleic acid detection and fat taste perception. In a 3‐alternate forced choice test, 62% of participants detected 2.9 ± 0.7 mM oleic acid (or 0.08% w/v) in a 2.8% safflower oil emulsion. Supplementation of oleic acid did not enhance fattiness and creaminess perception for the cohort as a whole, though East Asians carrying the GG genotype perceived more overall fattiness and creaminess than their AA genotype counterparts (P < 0.001). No differences were observed for the Caucasians. These preliminary findings indicate that free oleic acid can be detected in an oil‐in‐water emulsion at concentrations found in commercial oils, but it does not increase fattiness or creaminess perception. Additionally, variation at rs1761667 may have ethnic‐specific effects on fat taste perception.     

Flavor Manipulation Can Enhance the Impression of Fat in Some Foods

The objective of this study was to investigate the effects of fat and flavor (aroma) on the sensory impression of fat. One hundred and six naive subjects rated 4 food systems varying in fat and flavor content (prepared according to a factorial design) for fattiness first without and then with nose clips, and for liking. On average, subjects gave higher fatty scores to the high fat samples. There was a significant effect of flavor concentration on the fattiness ratings without the nose clips; however the effect was product specific. The nose clips significantly reduced the fattiness ratings for all products (p < 0.001), indicating that the flavor components of fat‐based foods can influence fat perception.     

Persistence of oral coatings of CMC and starch-based custard desserts

Food coatings that remain after swallowing starch-based or CMC-based custard desserts were investigated for 19 subjects. Foods were orally processed for 5 s using a pre-defined protocol, after which the food was swallowed. The remaining food coating was assessed sensorially as well as instrumentally using turbidity of rinse water. The instrumental and sensory results indicated a gradual decline of food coatings over intervals up to 180–270 s. Decline rates of coatings of individual subjects related significantly to their decline rates in perceived fattiness.     

不同结晶态脂肪比例对乳液奶油感感知的影响

通过调配无水乳脂肪的脂肪酸组成，构建含不同结晶态比例的乳脂肪模型和与牛奶脂肪含量和粒径匹配的乳液体系，进而模拟口腔加工，测定含不同结晶态脂肪比例乳液的口腔聚合性和摩擦学特性，并评价其奶油感。成功构建了含不同结晶态比例（10%～85%）的乳脂肪模型（F10～F85），所构建乳液（E10～E85）中脂肪球平均粒径为4 μm，在模拟口腔加工后，乳液粒径显著增大，其中E40样品增大程度最大。随着结晶态脂肪比例的增加，乳液口腔摩擦系数（μ20）先减小后增加，其中E40样品μ20最小，为（0.04±0.01）。描述性感官评价结果显示，随着结晶态脂肪比例的增加，乳液样品的整体奶油感先增大后减小，其中E40样品得分最高，为8.06±0.73。主成分分析结果显示，乳液的口腔光滑感和糊口感与整体奶油感相关性最强，其中E40样品与整体奶油感相关性最强。暂时性感官支配评价结果显示，口腔加工中后期，乳液在口腔感知中最显著的优势感官属性为口腔光滑感和糊口感，其中E40样品的口腔光滑感和糊口感优势率最高。本研究明确了结晶态脂肪比例对乳液奶油感感知的影响，为开发低脂但具备全脂口感的乳制品提供理论依据。     

Relating Creamy Perception of Whey Protein Enriched Yogurt Systems to Instrumental Data by Means of Multivariate Data Analysis

Yogurts differing in fat content, protein content, and casein to whey protein ratio were produced, and structurally as well as sensorially examined. The objective of the current research was to evaluate the predictive value of rheological and particle size measurements concerning sensory appearance and texture attributes in 13 differently composed stirred yogurt systems, with a focus on graininess, viscosity, and creaminess. Structural and sensory analyses showed large differences in texture properties between the tested yogurt systems. Both data sets were correlated by means of multivariate statistical methods. Sensory graininess was highly correlated with particle size‐related parameters, sensory viscosity was highly correlated with destructive rheological parameters, and creamy perception was highly correlated with particle size‐related parameters and destructive rheological parameters but was not as well described by any oscillatory parameter. Best predictive ability (r² > 0.89) was found for creaminess combining particle size related‐ and destructive rheological parameters tested within this study. Practical Application : Knowing the instrumental parameters describing sensory textural attributes provides important information for having a better understanding of the underlying processes during consumer's perception. Knowledge about the sensory behavior of a product and its oral processing imparts an opportunity to fasten the product development process. By means of yogurt systems instrumental parameters derived from particle size analysis and rheological measurements were correlated with sensory attributes in order to determine the main factors leading to the mouthfeel sensations grainy, viscous, and creamy of semisolid milk products.     

TEXTURE OF SEMI-SOLIDS: SENSORY FLAVOR-TEXTURE INTERACTIONS FOR CUSTARD DESSERTS

Possible interactions between flavor and oral texture sensations were investigated for four flavorants, diacetyl, benzaldehyde, vanillin, and caffeine, added in two concentrations to model vanilla custard desserts. The flavorants affected viscosities and resulted in corresponding changes in perceived thickness and melting sensations. In addition, flavorants affected prickling sensations, probably via activation of the trigeminal nerve system, and sensations of roughness, astringency, and dryness/mealiness. Finally, the effects of flavorants on these individual texture attributes also resulted in flavorant effects on creaminess and fattiness, sensations based on combinations of the above attributes.     

Temperature of served water can modulate sensory perception and acceptance of food

Cross-cultural differences exist in the typical temperature of water served with meals. North American people typically drink iced water/beverages while eating, whereas European or Asian people show a preference for room temperature water or hot water/tea, respectively. It has been reported that food perception and acceptance are influenced by oral temperature, as well as by serving temperature of food. Based on the fact that the iced or hot water served with meals can alter the oral temperature, the present study aimed to determine whether the temperature of served water can affect the sensory perception and acceptance of food subsequently consumed. Following a mouth rinse with water served at 4, 20, and 50 °C for 5 s, two different types of food, dark chocolate and cheddar cheese, were evaluated in terms of sensory intensity and overall liking. For the dark chocolate, the intensity ratings for sweetness, chocolate flavor, and creaminess were significantly lower when following water at 4 °C than when following water at either 20 or 50 °C. However, the modulatory effect of water temperature on sensory perception was not obtained with cheddar cheese. In addition, the temperature of served water altered the acceptance for the foods subsequently presented. Specifically, the overall liking for the dark chocolate was significantly lower when following water at 4 °C than when following water at either 20 or 50 °C. In conclusion, the present study demonstrates new empirical evidence that the consumption of iced water can decrease perceived intensities of sweetness, chocolate flavor, and creaminess for subsequently consumed chocolate. Our findings may provide one of plausible answers to the question of why North American people, who are more used to drinking iced water, show a strong preference for more highly sweetened foods.     

Texture changes in bolus to the “point of swallow” - fracture toughness and back extrusion to test start and end points

The change in texture of a food bolus during chewing, from first bite to swallow, is dramatic for solid foods and a variety of analytical techniques are required to quantify the texture at any given point in the chewing cycle. The objective of the work presented in this paper is to develop mechanical and rheological tests relevant to a model food, allowing the texture of the bolus to be quantified at first bite, and when masticated to the point of swallowing. This paper presents one aspect of the “Food Structure Platform” programme, a multi-disciplinary New Zealand programme investigating the influence of structure on the textural attributes of solid foods. The programme team is developing model foods and novel techniques to test their mechanical and rheological properties.The first model food developed by the Food Structure Platform is a biscuit with a well defined range of hardness within one basic recipe. This was tested in 3-point bending to determine fracture stress and relate that to texture perceived on first bite. The biscuit samples were also masticated to the point immediately prior to where the subject would have normally swallowed then expectorated for rheological testing. Modified TPA and back extrusion, based on a cup and piston test piece, were used to test the rheological properties of the bolus from each of the biscuit models. Good correlations were found with fracture stress of the biscuit and sensory hardness for first bite. At the point of swallow the bolus had a consistent cohesiveness and saliva content irrespective of starting texture, whilst the hardness and adhesiveness was affected by starting texture/recipe.