INFLUENCE OF GEL NETWORKS IN CONTROLLING CONSISTENCY OF O/W EMULSIONS STABILISED BY MIXED EMULSIFIERS

A coherent explanation is presented of the mechanisms by which mixed emulsifiers of the surfactant/fatty alcohol type both stabilise and control the consistencies of oil-in-water emulsions. Original and published data are used to develop a theory in which the semisolid and other flow properties of emulsions are related to the nature, strength and extent of viscoelastic networks present in the continuous phases. These networks form from the interaction of surfactant solution with fatty alcohol and have similar properties to ternary system gels formed when the mixed emulsifiers disperse in water, in the absence of an oil. The theory is discussed with particular reference to liquid paraffin-in-water emulsions prepared with the surfactants anionic sodium dodecyl sulphate, cationic alkyltrimethylammonium bromides or non-ionic cetomacrogol and fatty alcohols cetyl and stearyl and their mixtures, especially cetostearyl. It may be used also to explain the properties of emulsions prepared with a variety of oils, surfactants and amphiphiles. The effects of variation in storage time, surfactant type (ionic or non-ionic), temperature, mixed emulsifier concentration, and alcohol and surfactant chain lengths on the rheological and microscopical properties of ternary systems and emulsions support this theory. The importance of small strain experiments (creep and oscillatory) in providing a true measure of consistency is emphasized. Continuous shear experiments, although theoretically less satisfactory, provide useful additional information when correlated with the small strain data.     

Rheological characterization of experimental dairy creams formulated with locust bean gum (LBG) and λ-carrageenan combinations

The influence of the locust bean gum (LBG)–λ-carrageenan stabilizer combination on the rheology of dairy creams was analyzed. A central composite factorial design was used to choose the LBG–λ-carrageenan ratio, the weight fraction of each gum ranging from 0 to 0.1 g per 100 g cream. Cross’ rheological model was closely fitted to describe the flow curves of the samples and Cross parameters were correlated with gum concentrations. The rheological behaviour of model aqueous gum solutions, with the same pH, ionic strength, and competitive solute concentration as the cream serum, was also examined to analyze gum interactions. Strong interaction of λ-carrageenan with cream components, probably with caseins, may be anticipated based on a great increase in viscosity. The functional role of LBG seems to be associated with an increase in the emulsion shear stability.     

Physical and Oxidative Stabilities of O/W Emulsions Formed with Rice Dreg Protein Hydrolysate: Effect of Xanthan Gum Rheology

The shortening of shelf-life of food emulsions is frequently due to poor creaming and lipid oxidation stability. The lipid oxidation of O/W emulsions can be inhibited by rice dreg protein hydrolysate (RDPH); however, emulsions were stabilized by Tween-20. Polysaccharides can control the rheology and network structure of the aqueous continuous phase by increasing viscosity and yield stress, hence retarding phase separation and gravity-induced creaming, especially for xanthan gum. The objective of this research was to evaluate whether emulsions formed with 2 wt% RDPH and stabilized by xanthan gum (0–0.5 wt%) could produce 20 % (v/v) soybean oil-in-water emulsions that had good physical and oxidative stability. The degree of flocculation of droplets as a function of xanthan gum concentration was assessed by the microstructure, rheology, and the creaming index of emulsions. Addition of xanthan gum prior to homogenization had no significant effect on the mean droplet diameter in all emulsions studied. Increase in xanthan gum concentration led to the increase in creaming stability of emulsions, due to an increase in viscosity of the continuous phase and/or the formation of a droplet network with a yield stress, as well as the enhanced steric and electrostatic repulsion between the droplets. Lipid oxidation of the emulsions was significantly inhibited at xanthan gum concentrations of 0.12 wt% or above with RDPH, which could due to the fact that xanthan gum increases the viscosity of the aqueous phase and hindered the diffusion of oxidants to the oil droplet surface area, synergistic effect between RDPH and xanthan gum to suppress oil peroxidation, and metal ion chelation capability of xanthan gum. Thus, stable protein hydrolyzates-type emulsions could be obtained with increasing concentration of xanthan gum.     

Infrared spectroscopy of the skin: influencing the stratum corneum with cosmetic products

The stratum corneum is the outermost layer of the skin and, as such, represents the decisive barrier between the body and the environment. The combination of horny cells and lamellar lipid layers prevents water loss from the body and protects it against penetration by exogenous substances. For selective investigation of the thin outermost stratum corneum layer ATR-FTIR (attenuated total reflection Fourier transform infrared) spectroscopy has proved itself in practice. It provides information about the sebum content, type of fatty substances, water content and degree of order of the lamellar lipid film in the stratum corneum. Different types of skin (dry, normal and greasy) differ mainly in their sebum content but also in the composition of their fats and the degree of order of their lipids. A comparison with model lipid mixtures shows that the stratum corneum lipids are mainly present in a fixed gel form under physiological conditions. In cleansing processes a large part of the sebum is removed from the skin. The skin reacts to the defatting process by the rapid secretion of sebum. After cleansing with a mild face cleansing emulsion the re-achievement of the same fat status takes longer than with a surfactant shower gel. Skin creams cause alterations to the skin moisture and in the degree of order of the stratum corneum lipids. A lamellar cream with a structure similar to that of the stratum corneum lipids increases the degree of order of the alkyl chains of the skin lipid film (biomimetic principle), whereas a conventional w/o cream reduces this degree of order. Skin moisture increases after the use of the creams.     

Cryo-gelation of galactomannans in ice cream model systems

Locust bean gum (LBG) and guar gum (GG) are two galactomannan stabilizers that help maintain smooth textures in ice cream by slowing down ice crystal growth during constant and fluctuating temperatures. LBG and GG were dissolved in sucrose solutions without or with milk solids-not-fat (MSNF), fat, and/or emulsifier. Solutions were temperature cycled at subzero temperatures and measured after each cycle with a controlled stress rheometer to obtain yield stress and frequency sweep data. LBG solutions developed weak gel structures with temperature cycling, especially in the presence of MSNF, but GG solutions did not. Fat droplets interfered with the formation of LBG weak gel networks while emulsifiers did not change the rheological properties of emulsions. The ability of a polysaccharide to cryo-gel with temperature cycling and protein/stabilizer incompatibility leading to phase separation both helped create elastic structures. More realistic ice cream model emulsions containing fat showed different rheological responses, emphasizing caution in comparing model systems to real systems.     

Acidified sodium caseinate emulsion foams containing liquid fat: A comparison with whipped cream

Aeration properties of acidified casein-stabilized emulsions containing liquid oil droplets have been compared to the whipping of dairy cream. The foam systems were characterized in terms of overrun, microstructure, drainage stability, and rheology. With acidification using glucono-δ-lactone, the casein-stabilized emulsions could be aerated to give foams of far higher overrun (>600%) than whipped cream (∼120%). The development of foam volume, stability and rheology in the aerated casein-stabilized emulsion systems was found to be strongly dependent on the pH and the concentration of added calcium ions. Whereas whipped cream is stabilized by partially coalesced fat globules, the casein emulsion foams are stabilized by aggregation (gelation) of the protein coat surrounding the oil droplets. Casein emulsion foams formed at low pH were found to be more stable than whipped cream, whilst those formed at high pH were predominantly liquid-like and unstable. Instability arose in the acidified casein emulsion foams mainly through gel syneresis. We conclude that there are substantial textural differences between whipped cream and acidified casein emulsion foams, especially in terms of the small-deformation rheology and the extent of the linear viscoelastic regime.     

The effects of the combined use of stabilizers containing locust bean gum and of the storage time on Kahramanmaraş-type ice creams

This study was aimed primarily at determining the suitability of locust bean gum and various stabilizers in the production of Kahramanmaraş-type ice creams, the physical, chemical and sensory properties of the ice creams produced, and the stabilizer combination that could produce the best quality ice cream. With a total amount of stabilizer of 1.0%, ice creams of four different combinations containing locust bean gum, carboxymethyl cellulose, guar gum and sodium alginate were produced and their properties during a 6-month storage period compared with the control sample produced using only salep extract ( Orchis orchida ).
  The ice cream produced using only the salep extract had significantly higher ( P  < 0.05) levels of titratable acidity, lower pH and viscosity values, and were harder and less resistant to melting compared to those produced with the stabilizer combinations. The stabilizer mixtures containing locust bean gum yielded better results than those with the salep extract. An analysis of the effect of storage time on the properties of the ice creams indicated that, of the physical properties examined, only the decrease in the penetrometer values was significant ( P  < 0.05). Apart from the difference observed in the third month during the storage of the ice creams produced with the salep extract, the differences during the storage time were not found to be significant ( P  > 0.05).     

The effect of rheological properties of experimental moisturizing creams/lotions on their efficacy and perceptual attributes

Although anecdotal evidence suggests that the rheology of creams and lotions might affect their moisturizing efficacy and perceptual qualities, to date no systematic investigation of these effects has been carried out. We prepared 12 prototype moisturizing creams that had identical overall formulae but differed in as far as they contained three different polymers (Carbopol 981, Carbopol 5984 and Permulen TR.-2) each at four concentration levels. Using these creams, we carried out two series of experiments. In the first series, we applied pre-determined quantities of creams to defined areas of skin on the forearms of eight panelists and then measured the subsequent changes in Transepidermal Water Loss (TEWL) and Skin Capacitance (SC) values as a function of time. In the second series, the panelists were asked to spread and rub over their entire two hands as much of the creams as they deemed necessary for achieving satisfactory perceived moisturization. In this latter series, we also weighed the amounts of cream used and measured the TEWL and SC values at several skin sites as a function of time subsequent to the cream application. The panelists also scored 14 skin attributes for each of the 12 creams used. The same procedures were also carried out with a commercial skin moisturizing cream (Keri(R)) that was used as a control. In separate laboratory experiments, the rheological properties (i.e. the elastic and viscous moduli) of the various creams at a number of frequencies were measured. The analysis of the experimental results suggested that the overall rheology of creams had little direct effect on both, the moisturizing efficacy and the perceived perceptual attributes. Neither did the overall viscoelasticity or the esthetic attributes of the preparations seem to affect the amounts of creams/lotions that the panelists judged to be necessary for achieving satisfactory perceived hand moisturization. Although all preparations contained the same occlusive material (oil) at identical concentration, nevertheless some of the preparations appeared to show different efficacies depending on the nature and the levels of the polymeric ingredient present.     

The Effects of Fat Structures and Ice Cream Mix Viscosity on Physical and Sensory Properties of Ice Cream

The purpose of this work was to investigate iciness perception and other sensory textural attributes of ice cream due to ice and fat structures and mix viscosity. Two studies were carried out varying processing conditions and mix formulation. In the 1st study, ice creams were collected at ?3, ?5, and ?7.5 °C draw temperatures. These ice creams contained 0%, 0.1%, or 0.2% emulsifier, an 80:20 blend of mono‐ and diglycerides: polysorbate 80. In the 2nd study, ice creams were collected at ?3 °C draw temperature and contained 0%, 0.2%, or 0.4% stabilizer, a blend of guar gum, locust bean gum, and carrageenan. Multiple linear regressions were used to determine relationships between ice crystal size, destabilized fat, and sensory iciness. In the ice and fat structure study, an inverse correlation was found between fat destabilization and sensory iciness. Ice creams with no difference in ice crystal size were perceived to be less icy with increasing amounts of destabilized fat. Destabilized fat correlated inversely with drip‐through rate and sensory greasiness. In the ice cream mix viscosity study, an inverse correlation was found between mix viscosity and sensory iciness. Ice creams with no difference in ice crystal size were perceived to be less icy when formulated with higher mix viscosity. A positive correlation was found between mix viscosity and sensory greasiness. These results indicate that fat structures and mix viscosity have significant effects on ice cream microstructure and sensory texture including the reduction of iciness perception.     

Stability of whipped dairy creams containing locust bean gum/λ-carrageenan mixtures during freezing–thawing processes

The role of locust bean gum (LBG)-λ-carrageenan mixtures on the stability of whipped dairy creams in freezing-thawing processes was analysed as a function of the gum concentration (between 0 and 0.1% w/w). DSC analysis of ice crystallisation in the cream aqueous phase was carried out in order to know the influence of the hydrocolloid ratio on freezable water content. From this analysis, a potential cryostabiliser effect of whey proteins could be deduced since they provoked an increase in the T_m′ value. Changes in overrun, viscoelastic behaviour (creep compliance parameters) and stiffness (extrusion test) due to freezing–thawing and frozen storage (1 month at −18 °C) of the whipped cream were analysed in samples. Freezing provoked collapse of the foam structure, but samples containing λ-carrageenan at concentration greater than 0.085% showed a well preserved firmness, as deduced from the small changes observed in their viscoelastic parameters. The λ-carrageenan cryoprotection mechanism is not based on the freezable water content reduction since this value was similar for all gum mixtures.     

Influence of xanthan gum on the formation and stability of sodium caseinate oil-in-water emulsions

Studies have been made of the changes in droplet sizes, surface coverage and creaming stability of emulsions formed with 30% (w/w) soya oil, and aqueous solution containing 1 or 3% (w/w) sodium caseinate and varying concentrations of xanthan gum. Addition of xanthan prior to homogenization had no significant effect on average emulsion droplet size and surface protein concentration in all emulsions studied. However, addition of low levels of xanthan (≤0.2 wt%) caused flocculation of droplets that resulted in a large decrease in creaming stability and visual phase separation. At higher xanthan concentrations, the creaming stability improved, apparently due to the formation of network of flocculated droplets. It was found that emulsions formed with 3% sodium caseinate in the absence of xanthan showed extensive flocculation that resulted in very low creaming stability. The presence of xanthan in these emulsions increased the creaming stability, although the emulsion droplets were still flocculated. It appears that creaming stability of emulsions made with mixtures of sodium caseinate and xanthan was more closely related to the structure and rheology of the emulsion itself rather than to the rheology of the aqueous phase.     

Effect of Sweeteners and Stabilizers on selected Sensory Attributes and Shelf Life of Ice Cream

Guar and locust bean gums were combined with sucrose, 36 DE corn syrup and/or 42 high fructose corn syrup (HFCS) in a minimum fat (10%) ice cream formulation. A total of 27 combinations were evaluated for sweetness, iciness, chewiness and vanilla intensity. Replacing 50% of the sucrose with 42 HFCS did not significantly affect sweetness or vanilla intensity. Chewiness was enhanced when high corn syrup levels were combined with a high guar to locust bean gum ratio. Storage study data showed that ice creams containing high levels of HFCS became objectionably icy earlier than ice creams containing low levels or no HFCS. With a high guar to locust bean gum ratio ice creams became both detectably and objectionably icy sooner than if a low ratio of these gums was used.     

Hydrocolloids from coffee: physicochemical and functional properties of an arabinogalactan–protein fraction from green beans

The arabinogalactan–protein (AGP) fraction of green coffee beans accounts for 15% of the dry bean. A procedure was developed to solubilise most of the AGP content of the beans so that its properties as a hydrocolloid could be investigated. An AGP fraction was partially purified from green arabica coffee beans, its rheological properties characterised and compared to those of some commercially important hydrocolloids, particularly acacia gum. The coffee AGP fraction dissolved readily in water to give colourless clear solutions. The polymer was a polyelectrolyte with a high molecular weight (M_w 3.78×10⁶), characterised by a narrow polydispersity index (M_w/M_n 1.3). The intrinsic viscosity was close to that of acacia gum ([η]=0.23 dL g⁻¹), but a 1 wt% solution of coffee AGP was three times more viscous than acacia gum at the same concentration. Coffee AGP showed Newtonian flow for concentrations below 6 wt%, but above this concentration the flow behaviour entered a shear-thinning regime. The coffee AGP fraction possessed interesting foaming properties providing that the biopolymer concentration was high enough to initially stabilize the interface that is created. The high molecular weight of coffee AGP combined with its globular structure conferred upon it a high ability to retain water within a foam thin film. However, the structure of the interfacial film was less effective than that of acacia gum to entrap efficiently the gas into the foam. In summary, coffee AGP shows some interesting rheological features which suggest that coffee beans could be used as an alternative source of the class of surface-active polymers which find many commercial applications.     

A novel water-repellent o/w emulsion using a new water-soluble amphiphilic polymer

A novel O/W (oil-in-water) emulsion cosmetic that has strong water repellency and a >>water-splash feel« was prepared using the amphiphilic polymer hydrophilic-hydrophobic modified polysaccharide (INCI/Sodium Stearoxy PG-Hydroxyethylcellulose Sulfonate). This emulsion is composed of a hydrophobic–hydrophilic modified polysaccharide/water/oil system with a small amount of lipophilic non-ionic surfactant (hydrophilic–lipophilic balance<5) added to obtain finely emulsified oil particles. Hydrophilic–hydrophobic modified polysaccharide was used as a thickener and polymer surfactant, and it produced a stable O/W emulsion without the addition of a hydrophilic surfactant. Several types of oil droplets decrease in size upon addition of various kinds of lipophilic surfactant due to the lowering of tension at the water/oil interface. Rheological measurements revealed that the strong network structure of hydrophilic–hydrophobic modified polysaccharide retained oil droplets without occurrence of phase inversion. Such an emulsion is very different from those made using conventional hydrophilic surfactants, and it is water repellent. This system was characterized by the presence of hydrophilic–hydrophobic modified polysaccharide, and the state of the emulsion could be controlled by the ratio of hydrophobic/hydrophilic moieties introduced into the polysaccharide.     

Lipoprotein creams: utilization of multifunctional ingredients for the preparation of cosmetic emulsions with excellent skin compatibility

Lipoproteins are plant-derived surface-active biopolymers, which act as emulsifying as well as viscosity-enhancing agents in oil-in-water emulsions. Depending on the degree of hydrolization, lipoproteins are dispersible or even soluble in water. In the presence of low to medium polar oils, lipoproteins are adsorbed and align at the oil-water interface, whereas in mixtures with high polar oils the lipoproteins are repelled from the oil-water interface. The water-dispersible lipoproteins show higher interfacial activity than the hydrolysates. Lipoproteins bear a negative electric charge in aqueous dispersions at pH 6.5, which is probably the reason for the stabilization of oil droplets against coalescence. Lipoprotein creams were characterized in terms of particle size, rheology, and emulsion stability against sedimentation, which was evaluated by a near-infrared sedimentometer. After topical application, emulsion stability breaks down and an emulsion film is formed on the skin surface. Lipoprotein creams cause a distinct increase in skin pliability and skin moisture and show excellent skin compatibility. In a home use test the panelists appreciated the cosmetic and caring properties of the lipoprotein cream.     

Oil-in-water emulsions stabilized by sodium caseinate: Influence of pH,high-pressure homogenization and locust bean gum addition

The effect of pH, addition of a thickening agent (locust bean gum) or high-pressure homogenization on the stability of oil-in-water emulsions added by sodium caseinate (Na-CN) was evaluated. For this purpose, emulsions were characterized by visual analysis, microstructure and rheological measurements. Most of the systems were not stable, showing phase separation a few minutes after emulsion preparation. However, creaming behavior was largely affected by the pH, homogenization pressure or locust bean gum (LBG) concentration. The most stable systems were obtained for emulsions homogenized at high pressure, containing an increased amount of LBG or with pH values close to the isoelectric point (pI) of sodium caseinate, which was attributed to the size reduction of the droplets, the higher viscosity of continuous phase and the emulsion gelation (elastic network formation), respectively. All the studied mechanisms were efficient to decrease the molecular mobility, which slowed down the phase separation of the emulsions. In addition, the use of sodium caseinate was also essential to stabilize the emulsions, since it promoted the electrostatic repulsive interactions between droplets.     

Physicochemical interactions in processing

The manufacturing of toiletries is a complex procedure and many process routes are possible for a given formulation. In the past, considerable attention has been given to the design of manufacturing equipment but there has been relatively little appreciation of the influence of physicochemical interactions during processing. These interactions are likely to be particularly important during the manufacture of dispersions such as emulsions and pastes where phase and interfacial behaviour or particle interactions can be affected by the introduction of electrolytes or surface active species. For emulsions consisting of cetyl trimethyl ammonium chloride/long chain alcohol/water, the final rheological behaviour is governed by the formation of a 'frozen' lamellar structure in the continuous phase. The phase changes occurring during processing can significantly affect the degree of structure obtained. With powder dispersions, the rheology is affected by the introduction of surface active species due to deflocculation of the particles. Even in complex product systems such as toothpastes, these changes due to powder/detergent interactions are still apparent.
Les interactions physico-chimiques dans les processus de fabrication     

Modifications in stability and structure of whey protein-coated o/w emulsions by interacting chitosan and gum arabic mixed dispersions

The influence of chitosan and gum arabic mixtures on the behaviour of o/w emulsions has been investigated at pH = 3.0. The emulsion behaviour, properties and microstructure were found to be greatly dependent on the precise gum arabic to chitosan ratio. Mixing of gum arabic with chitosan leads to the formation of coacervates of a size dependent on their ratio. Incorporation of low gum arabic to chitosan weight ratios into whey protein-coated emulsions causes depletion flocculation and gravity-induced phase separation. Increasing the polysaccharide weight ratio further, a droplet network with a rather high viscosity (at low shear stress) is generated, which prevents or even inhibits phase separation. At even higher gum arabic to chitosan ratios, the emulsion droplets were immobilised into clusters of an insoluble ternary matrix. Although the emulsion droplet charge had the same sign as that of the coacervates, clusters of oil droplets in a ternary matrix were generated. A mechanism to explain the behaviour of the whey protein-stabilised o/w emulsions is described on the basis of confocal and phase contrast microscopic observations, rheological data, zeta potential measurements, particle size analysis and visual assessment of the macroscopic phase separation events.     

Ice cream structural elements that affect melting rate and hardness

Statistical models were developed to reveal which structural elements of ice cream affect melting rate and hardness. Ice creams were frozen in a batch freezer with three types of sweetener, three levels of the emulsifier polysorbate 80, and two different draw temperatures to produce ice creams with a range of microstructures. Ice cream mixes were analyzed for viscosity, and finished ice creams were analyzed for air cell and ice crystal size, overrun, and fat destabilization. The ice phase volume of each ice cream were calculated based on the freezing point of the mix. Melting rate and hardness of each hardened ice cream was measured and correlated with the structural attributes by using analysis of variance and multiple linear regression. Fat destabilization, ice crystal size, and the consistency coefficient of the mix were found to affect the melting rate of ice cream, whereas hardness was influenced by ice phase volume, ice crystal size, overrun, fat destabilization, and the rheological properties of the mix.