Retention of propanal in protein-stabilised tuna oil-in-water emulsions

Propanal concentrations in the static headspace (HS) above water, aqueous protein solutions and freshly made tuna oil-in-water emulsions spiked with propanal (an indicator of omega-3 fatty acid oxidation) were compared. In the presence of proteins, HS propanal concentration was reduced and its decrease above aqueous hydrolysed whey protein isolate (HWPI) solutions was significantly greater than that above whey protein isolate (WPI) solutions. Similar trends were found for emulsions stabilised by HWPI and WPI. The results suggested that there was stronger binding of propanal to HWPI compared to WPI. Emulsification decreased the HS propanal concentration even further for both the WPI and HWPI matrices, but its effect was less in comparison to the protein type. Phosphate buffer decreased the HS propanal concentration, but this effect was minor. The difference in the release of propanal from protein stabilised tuna oil-in-water emulsions was interpreted in terms of the chemical interaction between propanal and protein.     

Caffeine metabolism rate influences coffee perception,preferences and intake

Several factors – genetic, demographic and environmental – contribute to individual differences in sensitivity to the pharmacological effects of caffeine. Caffeine metabolism influences coffee consumption, but its effect on bitterness perception in, and preference for, coffee is unknown.This study explores the possible relationship between caffeine metabolism rate and coffee preferences and consumption habits. In addition, the extent to which caffeine metabolism interacted with variations in bitterness perception was investigated. Caffeine metabolism rate was assayed by competitive immuno-enzymatic assay in one-hundred thirty-five coffee consumers who provided saliva samples after 12 h caffeine abstinence and at 30 and 90 min after ingestion of caffeine (100 mg). A caffeine metabolism index (CmI) was computed as the ratio between the amount of residual caffeine in saliva 60 min after the adsorption peak and the amount of caffeine at the adsorption peak corrected with the baseline. Ninety-one subjects were selected to investigate the relationships between inter-individual variation in caffeine metabolism, bitterness perception and coffee preference. Subjects rated liking for, and sourness, bitterness and astringency of, six unsweetened and freely sweetened coffee samples varying in roasting degree, caffeine content and bitterness. They also rated the bitterness of six caffeine and six quinine (equi-intense) solutions. Finally, subjects choose coffee to drink on the basis of a label (strong vs balanced flavor) both after caffeine abstinence and after no restrictions on caffeine intake. The CmI was strongly associated with the frequency of daily coffee consumption. Subjects with lower CmI gave higher bitterness ratings than other subjects for both coffee and caffeine solutions, but not for quinine solutions. They also added more sugar to the coffee samples. Following caffeine abstinence, all subjects chose the “strong flavor” coffee, while without caffeine restrictions, subjects with lower CmI preferentially tended to choose the “balanced flavor” coffee. These results provide the first link between caffeine metabolism and bitterness perception, and to the use of sugar to modify coffee bitterness.     

Bitterness and Astringency of Sinapine and Its Components

Sinapine, choline chloride, and sinapic acid were evaluated for bitterness and astringency, at suprathreshold concentrations in water, by a trained sensory panel using magnitude estimation. Power functions (S = kCⁿ) were established for the bitterness of each of the three chemicals and the reference caffeine; none of the exponents for bitterness was significantly different from caffeine (n = 0.98) suggesting that, for any of these taste precursors, a doubling of concentration would double the bitterness perceived. Equimolar solutions of caffeine and sinapine were considered similar in intensity and significantly more bitter than choline chloride; sinapic acid was intermediate in bitterness. The sum of the bitterness values calculated from the power functions for choline chloride and sinapic acid accounted for approximately 80% of the bitterness of sinapine, at equimolar concentrations. Fifty to 94% of the bitterness perceived from tasting water slurries of rapeseed flour and protein concentrate was explained by the bitterness expected from their content of sinapine and free choline. Reliable power functions could not be established for the astringency of sinapine, choline chloride, and sinapic acid at the concentrations used. However, a clear psychophysical function was established for the astringency of the reference alum.     

Influence of NaCl and CaCl2 on Cold-Set Gelation of Heat-denatured Whey Protein

Heat‐denatured whey‐protein isolate (HD‐WPI) solutions were prepared by heating a 10 wt% WPI solution (pH 7) to 80 °C for 10 min and then cooling it back to 30 °C. Cold‐set gelation was initiated by adding either NaCl (0 to 400 mM) or CaCl₂ (0 to 15 mM). Both salts increased the turbidity and rigidity of the HD‐WPI solutions. Gelation rate and final gel strength increased with salt concentration and were greater for CaCl₂ than NaCl at the same concentration because the former is more effective at screening electrostatic interactions and can form salt bridges.     

The effect of modifying the distribution of sucralose and quinine on bitterness suppression in model gels

This study investigated the effect of simultaneously manipulating the spatial distribution of a sweet masking agent and bitter tastant within gelatine–agar gels on bitterness suppression, using sucralose and quinine. Sixty subjects participated in a series of paired comparison tests comparing different gel designs containing both sucralose and quinine, against a homogeneous control gel of identical overall sucralose (0.3 mM) and quinine content (0.3 mM). Twenty subjects also determined the bitterness reduction achieved in the homogeneous control gel by the addition of 0.3 mM sucralose to 0.3 mM quinine. Separating quinine and sucralose into different portions of the gel had no influence on bitterness suppression. Inhomogeneously distributing the quinine and sucralose into the same parts of the gel reduced the effectiveness of bitterness suppression. Inhomogeneously distributing the sucralose, while maintaining a homogeneous distribution of quinine, had no influence on bitterness suppression. Although an inhomogeneous distribution of sucralose increased sweetness perception and the addition of sucralose (0.3 mM) was found to substantially reduce bitterness in the homogeneous control, bitterness suppression was not enhanced when distributing the masking agent (sucralose) inhomogeneously.     

EGCG与乳清蛋白相互作用的光谱分析

探究表没食子儿茶素没食子酸酯(epigallocatechin gallate,EGCG)与乳清分离蛋白(whey protein isolate,WPI)间的相互作用。测定不同pH值与不同离子浓度条件下WPI的紫外吸收光谱、导数光谱和荧光光谱,利用SternVolmer方程判断荧光猝灭机制,采用位点结合模型公式计算结合常数和结合位点数。结果表明,紫外吸收光谱和导数光谱结果显示EGCG改变了WPI中酪氨酸和色氨酸残基所处的微环境,使WPI的分子构象发生了变化。荧光光谱结果显示EGCG可以有规律地猝灭WPI的内源荧光,猝灭机理为静态猝灭,EGCG与WPI结合常数在pH 2.0~9.0范围内随pH的增大先减小后增大,在离子浓度0.10 mol/L^0.20 mol/L范围内随离子浓度的增大而增大,结合位点数约为1。EGCG与WPI间存在静电相互作用。     

Personality traits and bitterness perception influence the liking and intake of pale ale style beers

Bitterness is classically considered undesirable in foods and beverages. Yet, widespread commercial success of beers (like Bitters in the UK or IPAs in the US) indicate bitterness is desirable for some consumers. Here, we tested whether personality traits influence beer liking and intake. Under laboratory conditions, beer consumers (n = 109) rated liking and intensity of 2 pale ales and a lager, and intensity of two bitter solutions (quinine, Tetralone®). Participants also completed intake and personality questionnaires (Sensation Seeking, Sensitivity to Punishment and Reward, and Food Involvement). A liking ratio for each beer was calculated from each participant’s liking for that specific beer and their total liking for all beers. Participants were classified as weekly, monthly, or yearly pale ale consumers using intake data. Using intensity ratings, personality measures, and other parameters, hierarchical linear regression was used to predict liking ratios, and logistic regression was used to predict beer intake frequency. A significant interaction between Sensation Seeking and quinine bitterness (p = 0.03) was found for the liking ratio of a pale ale. The interaction revealed liking of the pale ale increased with Sensation Seeking but only if quinine bitterness was also high. Intake models showed increased odds of frequent pale ale intake with greater quinine bitterness and lower liking for lager beer. These data suggest liking and intake of pale ales is positively related to Sensation Seeking and bitter taste perception. Contrary to findings in other bitter foods and beverages, the high bitterness found in pale ales may be desirable for some consumers.     

The effect of inhomogeneous quinine and hydrocolloid distributions on the bitterness of model gels

This study investigated the effect of inhomogeneous distributions of quinine on bitterness intensity of gelatine–agar composite gels. It also investigated the effect of inhomogeneous distributions of the gel’s hydrocolloid constituents (the gelatine and agar) on the bitterness intensity of the quinine. Fifty-two screened subjects participated in four paired comparison tests comparing inhomogeneous designs of quinine (with a homogeneous hydrocolloid distribution) and inhomogeneous designs of the hydrocolloids (with a homogeneous quinine distribution), against a homogeneous control of identical overall quinine and hydrocolloid composition. Using the same gel designs, a mastication trial was undertaken where ten subjects were asked to chew each gel system until the point of swallowing, and eleven subjects participated in a time-intensity trial where bitterness intensity was monitored during mastication and after expectoration. Paired comparison tests showed that the inhomogeneous distribution of quinine increased bitterness intensity, while inhomogeneous distributions of the hydrocolloids did not. Mastication was not influenced by changes in the distribution of quinine or the hydrocolloids. Time intensity curves showed the gels having an inhomogeneous distribution of quinine had greater bitterness intensity throughout mastication, however no differences in bitterness intensity were observed between any gel designs in the latter stages of aftertaste measurements. Time intensity curves also showed a slight delay in time to maximum bitterness intensity for the gels with inhomogeneous distributions of hydrocolloids. Results suggest a homogeneous distribution of bitter compounds is the most suitable structure for minimising bitterness perception.     

Modification of the bitterness of caffeine

Caffeine is the worlds most consumed psychoactive chemical and as such is a valuable commodity to the food and beverage industry. Caffeine also activates the bitter taste system causing a potential problem for manufacturers wanting to develop products containing caffeine. In the present study both oral peripheral and central cognitive strategies were used in an attempt to suppress the bitterness of caffeine. Subjects (n = 33) assessed the influence of sodium gluconate (100 mM), zinc lactate (5 mM), sucrose (125 mM and 250 mM), milk (0%, 2% and 4% milk fat), and aromas (coffee, chocolate, mocha) on the bitterness of caffeine (1.5, 3 and 4.5 mM). The oral peripheral strategies proved most effective at suppressing the bitterness of caffeine: zinc lactate (−71%, p < 0.05), non-fat milk (−49%, p < 0.05), and sodium gluconate (−31%). Central cognitive strategies were partially effective: 250 mM sucrose (−47%, p < 0.05) and mocha aroma (−10%) decreased bitterness, while chocolate (+32%) and coffee (+17%) aromas increased perceived bitterness. Overall, zinc lactate was the most effective bitterness inhibitor, however the utility of zinc in foods is negated by its ability to inhibit sweetness.     

Controlling denaturation and aggregation of whey proteins during thermal processing by modifying temperature and calcium concentration

Whey protein isolate solutions (8.00 g protein/100 g; pH 6.8) were treated for 2 min at 72, 85 or 85 °C with 2.2 mM added calcium Ca to produce four whey protein systems: unheated control (WPI‐UH), heated at 72 °C (WPI‐H72), heated at 85 °C (WPI‐H85) or heated at 85 °C with added Ca (WPI‐H85Ca). Total levels of whey protein denaturation increased with increasing temperature, while the extent of aggregation increased with the addition of Ca, contributing to differences in viscosity. Significant changes in Ca ion concentration, turbidity and colour on heating of WPI‐H85Ca, compared to WPI‐UH, demonstrated the role of Ca in whey protein aggregation.     

Characterisation of binding of iron to sodium caseinate and whey protein isolate

The fortification of dairy products with iron is an important approach to delivering iron in required quantities to the consumer. The binding of iron (ferrous sulfate) to two commercial milk protein products, sodium caseinate and whey protein isolate (WPI), dissolved in 50 mM HEPES buffer, was examined as a function of pH and iron concentration. Sodium caseinate had more sites (n = 14) than WPI (n = 8) for binding iron, and the affinity of caseinate to bind iron was also higher than that of WPI. These differences were attributed to the presence of clusters of phosphoserine residues in casein molecules, which are known to bind divalent cations strongly. The amount of iron bound to sodium caseinate was found to be independent of pH in the range 5.5–7.0, whereas acidification (pH range 7.0–3.0) caused a marked decrease in the amount of iron bound to WPI.     

Deformation and fracture of emulsion-filled gels: Effect of gelling agent concentration and oil droplet size

The effect of the ratio between the modulus of the oil droplets and that of the gel matrix (varied by changing gelling agent concentration and oil droplet size) on the large deformation properties of gelatine, κ-carrageenan and whey protein isolate (WPI) gels was studied at different compression speeds. The effect of gelling agent concentration and oil droplet size on strain-dependency of modulus and viscoelastic properties was also studied. An increase in the concentration of gelling agent resulted in denser gels with more bonds between structural elements. This induced an increase of both Young's modulus and fracture stress for all gels. With increasing gelling agent concentration, polymer gels (gelatine and κ-carrageenan) became less strain-hardening, and the particle gels (WPI) even became strain-softening. The effect of a decrease in the oil droplet size on the Young's modulus was generally according to the Van der Poel theory, unless when the oil droplets were aggregated. Moreover, a decrease in oil droplet size induced a decrease of the fracture strain in gels with non-aggregated bound droplets. The extent of these changes was shown to depend on the gelling agent concentration. The effect of a decrease of the oil droplet size on other fracture parameters and in other gel systems was minor. With decreasing oil droplet size gelatine gels with unbound droplets and WPI gels became more viscous and less elastic.     

Pilot-scale formation of whey protein aggregates determine the stability of heat-treated whey protein solutions—Effect of pH and protein concentration

Denaturation and consequent aggregation in whey protein solutions is critical to product functionality during processing. Solutions of whey protein isolate (WPI) prepared at 1, 4, 8, and 12% (wt/wt) and pH 6.2, 6.7, or 7.2 were subjected to heat treatment (85°C × 30 s) using a pilot-scale heat exchanger. The effects of heat treatment on whey protein denaturation and aggregation were determined by chromatography, particle size, turbidity, and rheological analyses. The influence of pH and WPI concentration during heat treatment on the thermal stability of the resulting dispersions was also investigated. Whey protein isolate solutions heated at pH 6.2 were more extensively denatured, had a greater proportion of insoluble aggregates, higher particle size and turbidity, and were significantly less heat-stable than equivalent samples prepared at pH 6.7 and 7.2. The effects of WPI concentration on denaturation/aggregation behavior were more apparent at higher pH where the stabilizing effects of charge repulsion became increasingly influential. Solutions containing 12% (wt/wt) WPI had significantly higher apparent viscosities, at each pH, compared with lower protein concentrations, with solutions prepared at pH 6.2 forming a gel. Smaller average particle size and a higher proportion of soluble aggregates in WPI solutions, pre-heated at pH 6.7 and 7.2, resulted in improved thermal stability on subsequent heating. Higher pH during secondary heating also increased thermal stability. This study offers insight into the interactive effects of pH and whey protein concentration during pilot-scale processing and demonstrates how protein functionality can be controlled through manipulation of these factors.     

Sequential preheating and transglutaminase pretreatments improve stability of whey protein isolate at pH 7.0 during thermal sterilization

Whey protein isolate (WPI) is a potential ingredient to manufacture shelf-stable transparent beverages if proteins are heat stable, i.e., without causing turbidity, precipitation and gelation after the required thermal processing to obtain commercial sterility (138 °C for 8 s or longer). However, information is lacking about stability of WPI during heating at 138 °C. Furthermore, novel technology and mechanistic understanding on how to produce clear products after heating systems with >5% WPI, particularly with salt, is needed. In this work, 5% w/v WPI was pretreated by microbial transglutaminase (mTGase) at three levels for 1–15 h at 50 °C, with and without prior preheating at 80 °C for 15 min. Heat stability of the pretreated samples at pH 7.0 and 0, 50, and 100 mM NaCl was evaluated at 138 °C. Samples pretreated by mTGase for a greater extent demonstrated improved heat stability. Samples subjected to sequential preheating and mTGase pretreatments produced clear dispersions even after heating at 138 °C for 30 min in the presence of 0 and 50 mM NaCl at pH 7. All pretreatments increased the magnitude of zeta-potential and resistance against thermal denaturation. The sequentially-pretreated WPI was the most heat-resistant, having decreased hydrodynamic diameter (<36 nm) during extended heating at 138 °C and 50 mM NaCl. The present study demonstrates the feasibility of using sequential preheating and mTGase pretreatments to develop sterilized beverage products with a high content (5% w/v) of whey protein and yet of transparent appearance at ambient temperatures.     

Heat Stability of Oil-in-Water Emulsions Containing Milk Proteins: Effect of Ionic Strength and pH

Emulsions (20 wt% soybean oil; 2 wt% protein) made with caseinate at pH 7 and with whey protein isolate (WPI) at pH 7 and 3 were stable to heating at 90 and 121°C. WPI emulsions destabilized at pH values between 3.5 and 4.0. In the presence of KCI (12.5–200 mM), large particles were formed in WPI emulsions at pH 3 and the emulsions were viscous. At pH 7, moderate concentrations of KCI decreased the heat stability and gels were formed. KCI had less effect on WPI emulsions made at pH 3. Combining the emulsions with caseinate allowed some control of the heat-induced gelation.     

Interaction of Whey Proteins with Phenolic Derivatives Under Neutral and Acidic pH Conditions

Integration of gallic acid (GA) and its derivative epigallocatechin gallate (EGCG; 20, 120, and 240 μmol/g, protein basis) into whey protein isolate (WPI) at room temperature and pH 3.0 and pH 7.0 was investigated. At pH 7.0, both phenolics caused significant structural changes and EGCG induced greater digestibility of WPI. Total sulfhydryl in WPI decreased from 28.6 to 7.6 μmol/g and surface hydrophobicity declined by nearly 50% with 240 μmol/g EGCG at pH 7.0. Similar but less appreciable changes were produced by GA and at pH 3.0. Isothermal titration and fluorescence quenching tests showed moderately weak binding of WPI with GA but strong binding with EGCG at pH 7.0. Both phenolics at high concentrations lowered the thermal transition temperature of β‐lactoglobulin by 0.5 °C to 1.4 °C and promoted its digestion. The phenolics also displayed a remarkable synergism with peptides in the WPI digest exerting radical scavenging activity.     

Partition and stability of resveratrol in whey protein isolate oil-in-water emulsion: Impact of protein and calcium concentrations

Whey protein isolate (WPI) is often used in food emulsions and can also interact with resveratrol, a natural amphiphilic polyphenol, this interaction being improved by heat-denaturation. In this study, oil-in-water emulsions stabilised by heat-denatured WPI in the absence and presence of CaCl₂ were characterised in terms of size, ζ-potential and protein partition. Partition and stability of resveratrol were also studied as a function of WPI and calcium concentrations. Size of WPI emulsions was dependent on the protein content at the oil–water interface. Partition of resveratrol and WPI was positively proportional at the oil–water interface and in the continuous phase. The stability of resveratrol increased as the concentration of WPI increased, but decreased when the concentration of calcium exceeded 0.20 mm. These data should be useful for simultaneous encapsulation of hydrophobic and amphiphilic bioactive components in a single emulsion and the protection of the inner oil by combination of antioxidant addition.     

Anchored ratio scale values in the assessment of perceived sweetness,bitterness and chocolate flavour intensity in chocolate confetti and flakes

The sensory profile of a particular food product depends on the context of sensations of the products with which that particular product is compared. This implies that the profile obtained is only valid for the period of time during which the physicochemical composition of each of the investigated products remains constant. This disadvantage can be overcome by assessing the perceived intensities of the products within the context of clearly defined physicochemical stimuli which are known to elicit a constant sensory impression over a long period of time. In the present study the perceived sweetness of 16 brands of chocolate confetti and flakes was anchored and assessed within the context of different sucrose solutions by 31 subjects. The bitterness and chocolate flavour intensities were anchored and assessed within the contexts elicited by different solutions of a mixture of quinine sulphate and caffeine, and cocoa powder/sucrose solutions, respectively. The subjective intensities were assessed on a validated ratio scale by making use of a functional measurement approach. Any changes in the sweetness, bitterness or chocolate flavour intensities of these products are now detectable over a long period of time.     

Antioxidant properties of caseins and whey proteins in model oil-in-water emulsions

The oxidative stabilities of both wheyproteinisolate (WPI)- and sodiumcaseinate-stabilized linoleic acid emulsions with different droplet sizes, protein concentrations and protein concentrations in the continuous phase were examined by determining lipid hydroperoxide and hexanal in the headspace. Emulsions with small droplet size had greater oxidative stability than emulsions with large droplet size in both WPI and sodiumcaseinate-stabilized emulsions. Lipid oxidation was in general lowered by an increase in the protein concentration. At high protein concentrations, the antioxidative effect of the protein in the emulsions appeared to offset the effects of emulsion droplet size and protein type. Replacing the unadsorbed protein in the continuous phase with water markedly decreased the oxidative stability of the emulsions. In contrast, the oxidative stability of the emulsions increased with increasing protein concentration in the continuous phase. This suggests that the antioxidative mechanism of protein in the interfacial region, such as binding trace metal ions from the lipid phase and free-radical-scavenging activity, may involve a dynamic exchange process with protein molecules from the continuous phase.