Functionality of emulsifiers in sponge cake production

The effects of emulsifiers (glyceryl monostearate and polyglycerol ester) and air inclusion on the structure of sponge batters were studied. Batter samples, immediately after mixing in a continuous mixer, were imaged for bubbles using an optical microscope and a CCD video camera. The bulk rheology of the batters was also determined to characterise their physical properties. The aqueous phases of the batters were separated by centrifugation and their surface tension was measured. The crumb structure of the finished sponge cakes was studied using a commercial texture analyser. The results showed that addition of an emulsifier helped in binding water and decreased the fluidity of the batter as well as the tension of the air/aqueous phase interface. Increasing the concentration of the emulsifier affected the distribution and size of the air bubbles trapped in the batter during mixing as well as the texture and volume of the baked sponge. Copyright © 2003 Society of Chemical Industry     

Characterization of bread dough: Rheological properties and microstructure

The change in rheological and microstructural properties of wheat flour dough as a function of water and yeast content, and with addition of hydrocolloids is described. The rheological properties vary with the size of the bubbles and measurements were made on controlled shear/stress rheometer. Confocal laser scanning microscope (CLSM), accompanied with image analysis technique, was used to obtain microstructure of the dough. It was found that with an increase in water content the moduli values decreased and the mean bubble diameter increased. As concentration of yeast increased, the bubbles became smaller and the moduli values increased. Addition of hydrocolloids like sodium alginate and xanthan gum led to increased moduli values and generally caused the bubbles in the dough to shift towards narrower distributions. An inverse relation between bubble size and storage modulus is found.     

Selective solubilization of polycyclic aromatic hydrocarbons from multicomponent nonaqueous-phase liquids into nonionic surfactant micelles

This research investigates the equilibrium solubilization behavior of naphthalene and phenanthrene from multicomponent nonaqueous-phase liquids (NAPLs) by five different polyoxyethylene nonionic surfactants. The overall goal of the study was to achieve an improved understanding of surfactant-aided dissolution of polycyclic aromatic hydrocarbons (PAHs) from multicomponent NAPLs in the context of surfactant-enhanced remediation of contaminated sites. The extent of solubilization of the PAHs in the surfactant micelles increased linearly with the PAH mole fraction in the NAPL. The solubilization extent and micelle-water equilibrium partition coefficient of the PAHs increased with the size of the polar shell region of the micelles rather than the size of the hydrophobic core of the micelle. The presence of both PAHs in the shell region of the micelles was confirmed by 1H NMR analysis. This is an important observation because it is commonly assumed that in multi-solute systems the solutes with relatively greater hydrophobicity are solubilized only in the micellar core. A comparison of the 1H NMR spectra of pure surfactant solutions and solutions contacted with various NAPLs demonstrated that the distribution of PAHs between the shell and the core changed with the concentration of PAHs in the micelles and in the NAPL. Competitive solubilization of the PAHs was observed when both PAHs were present in the NAPL. For example, in surfactant solutions of Brij 35 and Tween 80, the solubilization of phenanthrene was decreased in the presence of naphthalene as compared to systems that contained phenanthrene as the only solute. In contrast, with micellar solutions of Tergitol NP-10 and Triton X-100, phenanthrene solubilization was enhanced in the presence of naphthalene. The activity coefficients of the PAHs in the micellar phase were generally found to increase with PAH concentrations in the micelle.     

蜜蜡中气泡特征与品质的关系

蜜蜡是半透明-不透明的琥珀,其不透光性是由内部大量的微小气泡对入射光产生的反射和散射作用造成的。通过扫描电子显微镜观察和测量了蜜蜡样品中气泡的大小、分布、单位面积内的数量及面积,得到以下结论:(1)蜜蜡中的气泡与其自身携带的挥发成分有关,气泡呈浑圆状,较均匀分布在琥珀片层状结构中,气泡直径范围大致为100nm~15μm,每平方毫米(mm~2)上气泡数量通常为几百至几千个,而白蜜中可达数百万个;(2)蜜蜡中气泡密集程度与不透明度呈正相关关系,单位面积内气泡所占面积越大,蜜蜡越不透明;(3)蜜蜡质地的细腻程度与气泡大小呈反相关关系,气泡的直径越小,蜜蜡的质地越细腻。本研究对建立蜜蜡质地的定量评价体系有重要参考价值。     

Comparison of the rheology of bubbly liquids prepared by whisking air into a viscous liquid (honey) and a shear-thinning liquid (guar gum solutions)

Many bubbly liquids found in food applications feature non-Newtonian liquid phases whereas most investigations of bubbly liquid rheology have employed Newtonian liquids as the continuous phase. The influence of the nature of the continuous phase on bubbly liquid rheology was investigated using bubbly liquids prepared in the same planetary mixer using a viscous liquid, honey (almost constant shear viscosity with a small elastic contribution) and a shear-thinning liquid (1 wt% aqueous solution of guar gum). The viscosity of the honey was similar to the low-shear-rate limit viscosity of the guar gum solution. Although similar bubble volume fractions (up to 25%) were entrained in each liquid under identical mixing conditions, the bubble diameters in the shear-thinning liquid were about two to three times larger than those in the honey. Introduction of a surfactant into the shear-thinning liquid increased the volume fraction of bubbles to approx. 40% and further increased the size of the bubbles. The presence of the bubbles in the honey caused it to become shear-thinning, to exhibit noticeable elastic effects and exert significant normal stress differences. The honey-based bubbly liquids exhibited many of the features in the simulations of Loewenberg and Hinch (1996) and fitted the model of Llewellin et al. (2002) well. In the guar gum solution, these characteristics, already present, were accentuated strongly by the presence of the bubbles. Subjecting both types of bubbly liquids to high shear rates caused the volume fraction of bubbles to decrease and made the bubbly liquids less shear-thinning. Noticeable thixotropy was observed. Shear-thinning, associated with bubble deformation, was observed at lower values of the relative shear stress in the shear-thinning liquid.     

Stabilization of air bubbles in oil by surfactant crystals: A route to produce air-in-oil foams and air-in-oil-in-water emulsions

The incorporation of air in vegetable oils is highly sought after as it allows reducing the total fat content, while providing a light and pleasant texture. To meet consumers' requirements, nonaqueous foams must remain kinetically stable for several months and must withstand large deformations and flows. In this paper, we describe the fabrication of air-in-oil foams of outstanding stability, both at rest and under flow, based on the use of crystallizable surfactants (mixture of mono- and diglycerides). The air volume fraction is close to 55%, irrespective of the surfactant concentration. The air bubbles are protected against coalescence and Ostwald ripening by a dense layer of crystals. Moreover, the firmness of the surfactant crystal network formed in the oil bulk is large enough to hinder buoyancy driven phenomena. Finally, we demonstrate that the oil foams can be dispersed in an aqueous phase containing hydrocolloids to form a novel type of material: air-in-oil-in-water (A/O/W) emulsions.     

The microstructure of foamed maltodextrin/sodium caseinate powders: a comparative study by microscopy and physical techniques

Microscopy followed by image analysis is combined with physical characterisation techniques in order to obtain information about the structure of solid foams consisting of maltodextrin DE12 and sodium caseinate (10–30% w/w) processed under varying foaming conditions. Thin sections of solid foam were analysed by microscopy and image analysis for closed porosity, bubble size distribution and bubble connectivity. The bubble size distribution in the range up to about 25 μm was found to be largely independent of the degree of foaming. The total porosity of the solid foams, as determined by image analysis, was in very good agreement with the results from helium pycnometry and a direct relationship between the porosity and surface area as measured by BET nitrogen adsorption is obtained. Mercury intrusion porosimetry was found to be of limited use for the analysis of the open pore structure because of the fragility of the powders and the overlap in size between bubbles and interstitial spaces between the powder particles.     

Influence of diesel engine combustion parameters on primary soot particle diameter

Effects of engine operating parameters and fuel composition on both primary soot particle diameter and particle number size distribution in the exhaust of a direct-injected heavy-duty diesel engine were studied in detail. An electrostatic sampler was developed to deposit particles directly on transmission electron microscopy (TEM) grids. Using TEM, the projected area equivalent diameter of primary soot particles was determined. A scanning mobility particle sizer (SMPS) was used for the measurement of the particle number size distribution. Variations in the main engine operating parameters (fuel injection system, air management, and fuel properties) were made to investigate soot formation and oxidation processes. Primary soot particle diameters determined by TEM measurements ranged from 17.5 to 32.5 nm for the diesel fuel and from 24.1 to 27.2 nm for the water-diesel emulsion fuel depending on the engine settings. For constant fuel energy flow rate, the primary particle size from the water-diesel emulsion fuel was slightly larger than that from the diesel fuel. A reduction in primary soot particle diameter was registered when increasing the fuel injection pressure (IP) or advancing the start of injection (SOI). Larger primary soot particle diameters were measured while the engine was operating with exhaust gas recirculation (EGR). Heat release rate analysis of the combustion process revealed that the primary soot particle diameter decreased when the maximum flame temperature increased for the diesel fuel.     

The stability and physical properties of egg white and whey protein foams explained based on microstructure and interfacial properties

The goal of this investigation was to determine if physical models, based on micro-scale (bubbles) and nano-scale (interface) properties, can be used to explain the macroscopic foaming properties of egg white protein (EWP) and whey protein isolate (WPI). Foam properties were altered by adding different amounts of sucrose (4.27–63.6 g/100 mL) and microstructures were observed using confocal laser scanning microscopy and bubbles were quantitatively measured using image analysis. Addition of sucrose decreased the initial bubble size, corresponding to higher foam stability and lower air phase fraction. EWP foams were composed of smaller bubbles and lower air phase fractions than WPI foams. Increased sucrose concentration caused a decreased liquid drainage rate due to a higher continuous phase viscosity and smaller bubble sizes. WPI foams had faster rates for liquid drainage and bubble coarsening than EWP foams. The differences were attributed to faster bubble disproportionation in WPI foams, caused by lower interfacial elasticity and lower liquid phase fractions. The experimentally fitted parameters for foam yield stress did not follow universal trends and were protein type dependent. EWP foams had higher yield stress than WPI foams due to smaller bubble sizes and higher interfacial elasticity. The yield stress of WPI foams increased slightly with addition of sucrose and cannot be accounted for based solely on model parameters. It appears that changes in stability of EWP and WPI foams can be explained based on physical models while unaccounted for protein-specific effects remain regarding foam yield stress.     

Structure–fracture relationships in gas-filled gelatin gels

Food aeration has become one of the fastest growing unit operations practiced in the food industry. Dispersed air (or other gases) provides an additional phase within the gel that may accommodate new textural and functional demands. This paper addresses the relationships between structural characteristics and fracture properties of gas-filled gelatin gels (GGG), and compare these properties with those of control gelatin gels (CGG). Three gases were used in the fabrication of GGG: air, nitrogen and helium. Experimental methods to determine density, gas hold-up, bubble sizes and bubble size distributions as well as fracture properties of GGG are presented. Increasing protein concentration produced higher density, lower gas hold-up and decreased polydispersity of bubbles due to its effect on increased solution viscosity. Type of gas affected density and gas hold-up due to the different diffusivities of gases and structures (bubble size, size distribution and number of bubbles per area) formed in GGG. Fracture values increased for both GGG and CGG with increasing protein concentration for the three gases used. GGG were weaker and less ductile than CGG, the decrease in stress and strain at fracture being between 70 and 80%, and 40 and 65%, respectively. A power law relationship (σ_f = 2.73 × 10⁻¹²ρ_G^4.76) was found between the fracture stress and gel density for the three gases studied. This study shows that the presence of bubbles in gel-based food products results in unique textural properties conferred by the additional gaseous phase.     

Serum separation in molten ice creams produced by low temperature extrusion processes

The microstructure and kinetics of serum separation due to creaming of air bubbles in molten ice creams produced using the novel twin and single screw low temperature extrusion processes are investigated. The measured fat globule size distributions are bimodal for both ice creams. However, the concentration of primary fat globules is much larger for the twin screw extruded ice cream than that obtained using single screw. The latter contained higher concentration of fat aggregates. A broader bubble size distribution involving larger bubbles is observed for the single screw extruded ice cream compared with that for twin screw process. The initial rate of serum separation in molten twin screw extruded ice cream. This is because the former ice cream contained smaller bubbles and the serum separated from it is more viscous due to the presence of more small fat globules. The initial rate of serum separation in molten twin screw extruded ice cream is less than half of that for the single screw extruded ice cream.     

Influence of pH on surface properties of aqueous egg albumen solutions in relation to foaming behaviour

The surface properties of aqueous egg albumen protein solutions (0.1 g litre⁻¹) were studied at pH values of 4.8, 7.0, 9.2 and 10.7 and related to foaming behaviour such as bubble size distribution, overrun and drainage. By measurements far from equilibrium of dynamic steady state surface dilation using the overflowing cylinder technique, egg albumen showed ability to slow down surface expansion and to lower the dynamic surface tension. The pH‐effect was small, but at pH 4.8 the film length, at which a motionless surface was created, was longer than at higher pH indicating a somewhat more rigid surface at low pH. Near equilibrium sinusoidal surface area deformation resulted in relatively high moduli of egg albumen, with a significant effect of pH. The surface modulus E showed at pH 4.8 an increase in the course of time, but at higher pH it was constant. Large deformation of egg albumen surface was not destructive, and for all pH values the surface behaved viscoelastic, with highest loss modulus E″ and tan θ values at pH 4.8. Surface deformation frequency sweeps revealed the relaxation processes to be relatively slow at pH 4.8 and faster at pH 7.0–10.7. Foamability measured as overrun of foam as a result of shaking and stirring was highest at pH 4.8 and lowest at pH 10.7. Foam stability against drainage was best at pH 7.0 after 30 min, but at a long‐term scale foam at pH 4.8 was most resistant to drainage. Foam samples were subjected to microscopy and image analysis. The smallest bubbles were found at pH 4.8 (mean diameter 142 µm) and the largest at pH 7.0 (mean diameter 328 µm). In conclusion, the foaming behaviour of an aqueous egg albumen solution at pH 4.8 can be related to dynamic surface properties as follows: the more rigid behaviour of the surface at this pH favours a small bubble size and slow drainage of liquid from the foam. The high overrun at this pH can be explained by a lower dynamic surface tension, but also here film stability during foam making can be promoted by a more rigid liquid surface. © 1999 Society of Chemical Industry     

Identifying industrial food foam structures by 2D surface image analysis and pattern recognition

Bubbles are fundamental structural elements in several food products modulating density, rheology, texture, appearance and mouthfeel. Foams and aerated structures are characterized by their gas content, stability, bubble size and distribution. However, these measures alone cannot fully describe the complexity of bubble-containing structures. We have used three image analysis methods (Euler characteristic, Minkowski fractal and image texture) to characterize foam structure, and canonical and Bayesian discriminant analysis to identify/classify different foam architectures. This work describes results of this methodology on liquid foams stabilized by proteins at varying concentration and pH levels. Results indicated that groups of three structural parameters (among the 57 calculated) could successfully identify foam structures with different characteristics but unfortunately no single set of features could be used ubiquitously. Additional foam structure information as determined in this work can help to better understand these systems and the impact of bubbles on the physical properties of aerated foods.     

Effect of processing conditions and composition on sodium caseinate emulsions stability

Many food products such as ice cream, yoghurt, and mayonnaise are some examples of emulsion-based food. The physicochemical properties of emulsions play an important role in food systems as they directly contribute to texture, sensory and nutritional properties of food. One of the main properties is stability which refers to the ability of an emulsion to resist physical changes over time. The aim of the present work was to analyze the effect of processing conditions and composition on sodium caseinate (NaCas) emulsions stability. The main destabilization mechanisms were identified and quantified. The relationship between them and the factors that influence them were also investigated. Emulsions stabilized with NaCas were prepared using an ultrasound liquid processor or a high pressure homogenizer. Stability of emulsions was followed by a Turbiscan (TMA 2000) which allows the optical characterization of any type of dispersion. The physical evolution of this process is followed without disturbing the original system and with good accuracy and reproducibility. To further describe systems, droplet size distribution was analyzed with light scattering equipment. The main mechanism of destabilization in a given formulation depended on different factors such as NaCas concentration, droplet size or processing conditions. The rate of destabilization was markedly lower with addition of sugar or a hydrocolloid to the aqueous phase. Xanthan (XG) and locust bean (LBG) gums produced an increase in viscosity of the continuous phase and structural changes in emulsions such as gelation. Sugars interacted with the protein decreasing particle size and increasing emulsion stability. The stability of caseinate emulsions was strongly affected not only by the oil-to-protein ratio but also by processing conditions and composition of aqueous phase. The structure of the protein and the interactions protein–sugar or the presence of a hydrocolloid played a key role in creaming and flocculation processes of these emulsions.     

Relevance of the air–water interfacial and foaming properties of (modified) wheat proteins for food systems

A shift from animal protein- to plant protein-based foods is crucial in transitioning toward a more sustainable global food system. Among food products typically stabilized by animal proteins, food foams represent a major category. Wheat proteins are ubiquitous and structurally diverse, which offers opportunities for exploiting them for food foam and air–water interface stabilization. Notably, they are often classified into those that are soluble in aqueous systems (albumins and globulins) and those that are not (gliadins and glutenins). However, gliadins are at least to an extent water extractable and thus surface active. We here provide a comprehensive overview of studies investigating the air–water interfacial and foaming properties of the different wheat protein fractions. Characteristics in model systems are related to the functional role that wheat proteins play in gas cell stabilization in existing wheat-based foods (bread dough, cake batter, and beer foam). Still, to further extend the applicability of wheat proteins, and particularly the poorly soluble glutenins, to other food foams, their modification is required. Different physical, (bio)chemical, and other modification strategies that have been utilized to alter the solubility and therefore the air–water interfacial and foaming properties of the gluten protein fraction are critically reviewed. Such approaches may open up new opportunities for the application of (modified) gluten proteins in other food products, such as plant-based meringues, whippable drinks, or ice cream. In each section, important knowledge gaps are highlighted and perspectives for research efforts that could lead to the rational design of wheat protein systems with enhanced functionality and overall an increased applicability in food industry are proposed.     

A facile approach for controlled synthesis of hydrophilic starch‐based nanoparticles from native sago starch

A facile approach for the preparation of hydrophilic starch‐based spherical nanoparticles from native sago (Metroxylon sagu) starch using the drop‐wise solvent exchange method was reported. Starch‐maleate monoester (SM) was initially synthesized from native sago starch and maleic anhydride in an aqueous medium, and SM nanoparticles was subsequently precipitated in absolute ethanol under controlled conditions. The present study was focused mainly on modulating of the solvent and non‐solvent systems to prepare SM nanoparticles of different morphologies. The pH of the solvent system and the nature of surfactants being added into the solvent system could influence the morphology of regenerated SM nanoparticles. SM nanoparticles of discrete and spherical shape were regenerated from a basic SM sample solution, or an acidic sample solution in the presence of an appropriate surfactant. SM nanoparticles with mean diameter of about 250 nm was obtained by precipitation in absolute ethanol in the presence of Brij 35 as the surfactant.     

On the Effect of Tastant Excluded Fillers on Sweetness and Saltiness of a Model Food

ABSTRACT: In this study, the effect on taste due to the addition of air bubbles to a water-based gel was investigated. The gel phase contained either sucrose to give a sweet taste or sodium chloride to give a salty taste. For the sweet gels, taste intensities were evaluated for samples with different volume fractions of the air bubbles (up to 40%, v/v) and different concentrations of the sucrose. For the salty gels, samples were evaluated at 40% volume fraction of air bubbles. It was found that a reduction of the sodium chloride or sucrose by the same weight percentage as the volume fraction of the air bubbles in the samples gave equal taste perception as the nontastant-reduced samples. Moreover, saltiness and sweetness perception were clearly enhanced at 40% volume fractions of air bubbles if the sodium chloride or sucrose was not reduced. Thus, the overall tastes of the samples appeared to depend mainly on the concentration levels of the salt or the sucrose in the aqueous phase irrespective of the volume fraction of the air bubbles. However, the air bubbles were found to change the texture and appearance of the samples. It has been demonstrated that the inclusion of air bubbles offers scope for the reduction of sodium chloride or sucrose in food products.     

Effect of surfactants and dispersed components on the activity and reactivity of sorbic acid

In common with many other carboxylic acids, sorbic acid shows significant solubility in aqueous and non-aqueous solvents. The presence of a non-aqueous phase (e.g. fat) can markedly affect the concentration of the preservative in the aqueous phase. Solute distribution between the two phases is pH- and concentration-dependent. The presence of dissolved surfactants in the aqueous phase will also affect the activity of sorbic acid. This effect is due to the partitioning of the solute into surfactant micelles. The presence of dispersed components and surfactant micelles also has a marked effect on the reactivity of sorbic acid. Whereas thiols react slowly with sorbic acid, the rate of reaction is increased many-fold by the addition of low molecular weight surfactants. The mechanism of this catalysis will be explained. It has been suggested that sorbic acid inhibits enzymes by reacting with sulphydryl groups of the proteins. Kinetic data from model system studies suggest that the sorbic acid-thiol reaction may be too slow for it to be an obvious means of enzyme inhibition. However, this does not take account of possible catalysis of the reaction in the microenvironment of the protein, perhaps in a manner similar to that identified with low molecular weight surfactants.     

奇亚籽皮多糖对冰淇淋乳化稳定性及品质的影响

考察不同质量浓度（0.5、1.0、1.5、2.0 mg/mL）的奇亚籽皮多糖作为乳化稳定剂在冰淇淋产品中的应用,通过对冰淇淋浆料稳定性和冰淇淋膨胀率、融化率、质构、气泡分布及结构特性等指标的测定,考察不同质量浓度奇亚籽皮多糖对冰淇淋品质的影响规律。结果表明：随着奇亚籽皮多糖质量浓度的增加,冰淇淋浆料的稳定性及冰淇淋的膨胀率、质构特性（弹性、黏附性、咀嚼性）提高,融化率和硬度降低,冰淇淋中气泡分布更加均匀,气泡直径均一,数量增多。添加奇亚籽皮多糖可提高冰淇淋浆料的表观黏度,冰淇淋浆料均表现出假塑性非牛顿流体。与空白冰淇淋样品对比,添加0.5 mg/mL质量浓度的奇亚籽皮多糖冰淇淋,其各性质测定结果略有改善,但质量浓度大于1.5 mg/mL时,可显著提高冰淇淋抗融性及稳定性,降低其硬度,改善其微观结构,气泡分布更均匀,使冰淇淋组织更加光滑。相较于空白冰淇淋样品,奇亚籽皮多糖的添加对冰淇淋的品质特性、结构特性及稳定性方面均有显著改善作用,为奇亚籽皮多糖应用于冰淇淋食品生产提供一定科学依据。