The role of rheological behaviour in flavour perception in model oil/water emulsions

Decreasing the fat content of a food produces changes in a range of physical, chemical and sensory properties that are important in flavour perception. The aim of this paper was to study the role of rheological behaviour in flavour perception in model oil/water emulsions, using a series of samples with different hydroxypropyl methyl cellulose (HPMC) and oil content. The composition of the emulsions was adjusted to deliver iso-release aroma in vivo and to produce samples with the same viscosity in-mouth (measured as the Kokini oral shear stress). The results showed that there was no significant difference in perceived thickness between the three samples providing further evidence that the Kokini oral sheer stress is well correlated with in-mouth thickness. However, there was a significant difference in perceived volatile fruity flavour and sweetness. Samples containing the highest oil content were perceived as significantly less fruity and sweet despite having the same volatile release and in-mouth thickness.     

Partial coalescence as a tool to control sensory perception of emulsions

This study evaluates the role of partial coalescence of whey protein-stabilized emulsions on sensory perception. The selection of fats was restricted to vegetable fats that are essentially melted at oral temperatures. The sensitivity to partial coalescence was controlled by a variation in the fat melting curve and by addition of unsaturated monoglyceride. Most fat-related sensory attributes appear to be well-correlated to an increase in viscosity and coalescence in the mouth due to partial coalescence. Moreover, it was found that in-mouth aeration induces extra coalescence, which increases the perception of fat-related sensory attributes significantly.     

Flavor release and sensory characteristics of o/w emulsions. Influence of composition, microstructure and rheological behavior

Influence of fat content and thickener type on rheology, structure, stability, in-vivo aroma release and sensory perception was studied in lemon flavored o/w model emulsions. Six formulations were prepared by varying the oil content (5 and 30% w/w) and the matrix composition (carboxymethyl cellulose, modified starch and no thickener). The effect of the interaction between fat content and matrix type was significant on most of the flow and viscoelastic parameters but not on flow index or loss modulus values. There were differences in the creaming index due to oil content and thickener type. Higher emulsion stability was obtained with the starch-based emulsions. Fat content affected the delivery to the nasal cavity of the most lipophilic compound (linalool) but did not affect the delivery of the least lipophilic (cis-3-hexen-1-ol) while both thickeners influenced the cumulative area under the aroma release profiles from nose breath analyses. Differences in perceived flavor and texture attributes were affected for both fat content and matrix type, which could be explained by instrumental data in most cases.     

花生油高频剪切黏度超声检测

为对多次高温加热食用油品质进行评价,以反复煎炸花生油为研究对象,基于超声水平剪切波(SH波)在固体/黏弹性液体界面的复反射系数与液体黏弹性模量、黏度系数等关系模型,以固体/空气界面为参考,采用固/气、固/液界面回波对比方法,测量了不同劣化状态花生油在室温时的剪切黏度,并与流变仪测试结果进行比较。结果表明,超声SH波与流变仪均很好地反映了样品黏度随加热次数的变化关系。研究证明超声方法在线评价油品劣化状态具有可行性。     

The formation of oil droplets in a pectin solution and the viscosity of the oil-in-pectin solution emulsion

Oil droplets were produced in a pectin solution by microchannel emulsification and by conventional homogenization, and the rheological properties of the oil-in-pectin solution emulsion were investigated. The effect of the pectin concentration on the emulsification ability was studied using a dead-end-type microchannel plate. A monodisperse emulsion was produced when the pectin concentration was 1 wt% or lower. When the pectin concentration was 2 wt%, a polydisperse emulsion was produced due to the increase in the viscosity of the continuous phase (the pectin solution). Oil-in-pectin solution emulsions were also continuously produced using a crossflow-type microchannel plate. The viscosity of the emulsion increased as the volume fraction of oil increased. The relationship between the volume fraction of oil and the viscosity was well explained by a simple equation, which describes the viscosity of emulsions.     

Perception of creaminess in foods

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.     

Stabilization of olive oil – lemon juice emulsion with polysaccharides

An olive oil – lemon juice Greek salad dressing was developed employing xanthan gum as stabilizer and gum arabic or propylene glycol alginate as emulsifier in various combinations. In general, samples containing xanthan gum arabic were more stable against oil droplet coalescence and less stable against creaming. The use of propylene glycol alginate in the place of gum arabic, on the other hand, resulted in emulsions of higher creaming stability. Application of steady shear rheology and determination of rheological parameter values from the shearing stress-rate of shear curves, indicated that the rheological properties of the dressings were decreased with storage. Dressing texture assessment preference tests indicated that potential consumers of the product may opt for a medium viscosity product and this has to be taken into consideration when designing polysaccharide – stabilized dressings exhibiting a decrease in their textural characteristics with storage time.     

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.     

添加茶油胶对植物油基酸奶品质特性的影响

以脱脂牛乳和茶油为主要原料,经发酵工艺制成茶油基酸奶。以全乳脂酸奶和脱脂酸奶为对照,研究酸奶的理化、质构、流变性及感官品质等特性并进行相关性分析。结果表明,添加茶油胶能明显改善酸奶的凝乳品质。当茶油胶添加量为3.4%时,酸奶的酸度最高（104 °T）,其硬度、黏稠度、表观黏度等指标均优于对照样品;其感官评分最高（93.99分）,表明其良好的品质和感官接受度,以茶油为原料开发植物油基酸奶具有可行性。     

UTILIZATION OF INVERSE WATER-IN-OIL EMULSIONS AS FAT REPLACERS IN FRANKFURTER MODEL SAUSAGES: INFLUENCE OF FAT EMULSION CONTENT ON THE ORGANOLEPTIC AND MECHANICAL PROPERTIES

The effect of fat content on the oral perception and the mechanical properties of frankfurter-type sausages was studied by means of absolute and hedonic organoleptic and mechanical tests. Panelists were able to discriminate changes of 5–10% in fat content. A correlation between fat content and organoleptic attributes was found, supporting a perception that the full-fat product is the de facto preferable product, to whose attributes others must conform.
Substituting fat with water-in-fat globules was found to imitate a full-fat sausage adequately in mechanical tests; however, organoleptic tests assessed the true fat content of the sausages. The tests indicate that it might be the absolute amount of fat, not the surface area of fat-covered globules, that correlates to the perception of fattiness. The above should be attributed to the lubrication and flocculation–coalescence of fat droplets with saliva in the mouth.

PRACTICAL APPLICATIONS

The substitution of fat globules by inverse water-in-fat globules in sausages was found to imitate a full-fat sausage adequately in mechanical tests; however, sensory tests confidently assessed the exact, true fat content of the sausages. This observation points out some limitations concerning the use of inverse emulsions as fat substitutes in relevant products.
Correlations between sensory attributes and fat level in sausages could imply that specific norms relating to fat level exist in the consumers, to which low-fat products may have to conform to.
The testers were able to attribute different scores, thus, discriminate sausages different at times by just 5–10% fat content. This could be of importance in the development of new low-fat sausage products.     

Enhancing expected food intake behaviour,hedonics and sensory characteristics of oil-in-water emulsion systems through microstructural properties,oil droplet size and flavour

Food reformulation, either to reduce nutrient content or to enhance satiety, can negatively impact upon sensory characteristics and hedonic appeal, whilst altering satiety expectations. Within numerous food systems, perception of certain sensory attributes, known as satiety-relevant sensory cues, have been shown to play a role in food intake behaviour. Emulsions are a common food structure; their very nature encourages reformulation through structural design approaches. Manipulation of emulsion design has been shown to change perceptions of certain sensory attributes and hedonic appeal, but the role of emulsions in food intake behaviour is less clear. With previous research yet to identify emulsion designs which promote attributes that act as satiety-relevant sensory cues within emulsion based foods, this paper investigates the effect of oil droplet size (d_4,3: 0.2–50 μm) and flavour type (Vanilla, Cream and No flavour) on sensory perception, hedonics and expected food intake behaviour. By identifying these attributes, this approach will allow the use of emulsion design approaches to promote the sensory characteristics that act as satiety-relevant sensory cues and/or are related to hedonic appeal. Male participants (n = 24) assessed the emulsions. Oil droplet size resulted in significant differences (P < 0.05) in ratings of Vanilla and Cream flavour intensity, Thickness, Smoothness, Creamy Mouthfeel, Creaminess, Liking, Expected Filling and Expected Hunger in 1 h’s time. Flavour type resulted in significant differences (P < 0.05) in ratings of Vanilla and Cream flavour intensity, Sweetness and Liking. The most substantial finding was that by decreasing oil droplet size, Creaminess perception significantly increased. This significantly increases hedonic appeal, in addition to increasing ratings of Expected Filling and decreased Expected Hunger in 1 h’s time, independently of energy content. If this finding is related to actual eating behaviour, a key target attribute will have been identified which can be manipulated through an emulsions droplet size, allowing the design of hedonically appropriate satiating foods.     

Oxidative stability of olive oil–lemon juice salad dressings stabilized with polysaccharides

Lipid oxidation is a major cause of quality deterioration in food emulsions. Polysaccharides used to improve emulsion stability and texture may also affect lipid oxidation. In the present study, the oxidative stability of olive oil–lemon juice salad dressings, stabilized with gum arabic or propylene glycol alginate in admixture with xanthan, was investigated. Oil-in-water emulsions (50:50, v/v) were prepared with lemon juice and extra virgin olive oil and then homogenized at various homogenization rates to form different particle sizes. Keepability was followed by storing at room temperature for 6–8 months and measuring the formation of primary and secondary oxidation products. The shelf life was compared to that of the bulk olive oil. It was shown that the polysaccharides had the ability to inhibit lipid oxidation, probably due to their amphiphilic character (gum arabic and propylene glycol alginate) as well as their ability to induce viscosity increase. Olive oil–lemon juice emulsions were also assessed for consumer acceptance. The panellists were asked to smell the samples and rate them according to rancidity using a four-point (1 = no perception, 4 = extreme) intensity scale. The results were in accordance to those of chemical analysis. Lipid oxidation was not affected by the oil droplet size, as demonstrated by peroxide value measurements and sensory evaluation.     

Tuna oil and Mentha piperita oil emulsions and microcapsules stabilised by whey protein isolate and inulin: characterisation and stability

Whey protein isolate (WPI) and its polysaccharide complexes have been widely used to prepare oil‐in‐water emulsions. The aim of this study was to evaluate the emulsions and spray‐dried microcapsules containing tuna oil and/or mint oil and stabilised by combination of WPI with inulin in terms of physicochemical characteristics and storage stability. Stable emulsions were formed before drying. Tuna oil + Mentha piperita oil emulsions had smaller viscosity, surface tension and size than did tuna oil emulsions. Surface morphology showed that spray‐dried microcapsules were spheres but had many dents and apparent shrinkage. During storage, tuna oil and tuna oil + M. piperita oil microcapsules became larger. In the blend oil microcapsules, menthone was reduced to form menthol, loss of DHA and EPA was slightly less, the degree of oxidation characterised using peroxide value and headspace propanal was less but basically greater than half of that of WTI microcapsules.     

Impact of effervescent atomization on oil drop size distribution of atomized oil-in-water emulsions

In this work the application of effervescent atomization to spray drying of food liquids like emulsions is explored. Therefore the influence of the atomization process on the breakup of oil drops inside the emulsion is investigated. It is expected that the oil drop size distribution of the emulsion is influenced by the stress inside the nozzle orifice and the following atomization. According to Grace the viscosity ratio between disperse and continuous phase is a crucial factor for drop breakup. A model oil-in-water emulsion was used. The viscosity of the continuous phase was adjusted by adding maltodextrin or gelatinized corn starch thus varying the viscosity ratio in the range between 15 and 0.1. The dry matter content and corresponding viscosity show only low influence on the spray drop size distribution. However, the atomized emulsions contain mostly smaller oil drops compared to the original emulsions. The influence of the atomization on the oil drop size distribution decrease with decreasing viscosity ratios. An influence of increasing stress due to increased atomization gas mass flow is present but less significant. The viscosity ratio thus allows controlling the influence of the atomization on the oil drop size distribution in the spray. The invariance of the spray drop size distribution on minor changes in fluid properties like viscosity is a favorable characteristic in food processing where such changes are common.     

Influence of oat gum, guar gum and carboxymethyl cellulose on the perception of sweetness and flavour

The influence of three pseudoplastic hydrocolloids, oat gum, guar gum and carboxymethyl cellulose (CMC) on sensory perception of sweetness and flavour was studied in model systems at two viscosity levels. The sweeteners studied were sucrose, fructose and aspartame, the flavour substances ethyl caproate, a-pinene and cinnamic acid. Sweetness was best perceived from oat gum solutions and most weakly from guar gum solutions. The effect of the composition of the thickener on the perception of sweetness was greater than that of viscosity. Reduction of sweetness by hydrocolloids was weaker for aspartame than for fructose or sucrose. In the perception of flavours, both the total length of perception and the time-intensity pattern were more dependent on the model aroma substance than on the thickener. Possible explanations for the differences are discussed.     

Effect of ethylcellulose on the structure and stability of non-aqueous oil based propylene glycol emulsions

The hydrophobic polymer ethylcellulose (EC) has been used to structure vegetable oils and as a stabilizer of oil/water (o/w) emulsions, among other non food uses. In this work we show that EC dissolved in medium chain triglycerides (MCT) or soybean oil (SO) is able to stabilize non-aqueous emulsions of propylene glycol (PG) as a dispersed phase. Cream-like emulsions can be obtained at both low and high homogenization speeds which show a very good stability for at least one month without the requirement of co-surfactants. PG-in-oil emulsions at concentrations of EC below 5% (w/w) display pseudoplastic behavior and greater viscosity than the respective solutions of the polymer in MCT or SO. However, at concentrations of EC above 5% (w/w) firm gels are formed in MCT or SO and after the addition of PG, the emulsions formed have lower viscosity than the original solutions of the polymer in MCT or SO. Such effects were independent of the mean molecular weight (MMW) of the EC at high shear stress and inversely proportional at low shear stress. These results indicate that the stabilizing effect of EC in PG-in-oil emulsions might not be caused mainly by an increase in the viscosity of the continuous phase. Comparing all the results obtained, we can infer that EC, despite being insoluble in PG, is promoting interactions which are responsible for the observed effects.These PG-in-oil emulsions have interesting structural and flow properties which make them attractive to be used in food formulations, either as emulsions themselves or as potential vehicles for active ingredients.     

Effect of potato deep-fat frying conditions on temperature dependence of olive oil and palm oil viscosity

This work investigates how the temperature dependence of oil viscosity varies with the type of frying oil, initial oil temperature, frying load and number of frying repetitions, during potato deep fat frying. Viscosity is measured in small temperature increments over a broad temperature range. A non-linear model is proposed which gives more statistically significant results than other known models in describing the temperature dependence of viscosity. Multiple quasi-linear regression analysis is applied to derive an expression that predicts oil viscosity from important frying conditions such as oil type, frying load, average oil temperature and frying time. For applications where only the initial oil temperature is known, a correlation is proposed for the prediction of the average oil temperature from the initial oil temperature and other frying conditions. The overall accuracy of the model in predicting the temperature dependence of viscosity on the examined frying conditions is better than 95.0%.     

Soya bean oil/soya protein isolate and carrageenan emulsions as fat replacer in fat‐reduced Oaxaca‐type cheese

Milk fat was replaced in Oaxaca‐type cheese with soya bean oil emulsions stabilised with soya protein isolate and different carrageenans (kappa, iota and lambda). Inclusion of soya bean oil emulsion increased yield, moisture and protein content and reduced fat content. Fat reduction and moisture incorporation provoked a tougher but less ductile texture. Specific interaction of carrageenans with milk proteins resulted in larger spreading area when melted and a softer and more adhesive texture, particularly in samples containing lambda‐carrageenan. These results are useful to improve the nutritional composition of Oaxaca‐type cheese, allowing the control of textural properties during cheese melting.