Investigating the effect of surfactants on lipase interfacial behaviour in the presence of bile salts

It is known that non-ionic surfactants and phospholipids provide large protection in emulsions against lipase-induced destabilization as compared to proteins, even in the presence of bile salts. In relation to this, the aim of this study is to probe the ability of two surfactants of industrial interest, poloxamer Pluronic F68 (non-ionic) and Epikuron 145V (phospholipid), to modify the adsorption of lipases at an oil–water interface under the physiological conditions existing in the duodenum. We have designed an experimental procedure by means of a pendant drop film balance equipped with a subphase exchange technique, which allows sequential adsorption of the compounds. This allows the investigation of the interfacial behaviour of lipase in the presence and absence of surfactant. According to this experimental approach, the lipase is added directly into the subphase only after the surfactant has been adsorbed onto the oil–water interface. We have used interfacial dilatational and shear rheology techniques to characterise the interfacial layers. The results suggest that Pluronic F68 reduces the interfacial activity of lipase more efficiently than Epikuron 145V. Furthermore, it seems that Pluronic F68 affects the accessibility of the lipase to the oil–water interface, even in the presence of the bile salts. These results may have applications in the development of novel strategies to rationally control lipid digestion in the diet.     

Stability of emulsions for parenteral feeding: Preparation and characterization of o/w nanoemulsions with natural oils and Pluronic f68 as surfactant

For hydrophobic bioactive compounds, poor water solubility is a major limiting factor for their use in different applications in the field of food industry or pharmacy. For this reason they are administrated as emulsions, in which the substance is dissolved in an organic compound, which is dispersed in an aqueous phase as droplets stabilized by a surfactant. It has been demonstrated that the colloidal stability of the nanoemulsion formulations can be precisely controlled by the chemical structure of the interface. In this paper, a promising delivery system has been studied. As surfactant, we have used the amphiphilic uncharged tri-block copolymer Pluronic F68, and natural oils from soybean, sesame and olive as the organic phase. The nanoemulsions were prepared by ultrasonication, and their stability at different synthesis conditions such as ultrasound power and surfactant concentration has been studied by monitoring backscattering using a Turbiscan. The more stable emulsions have been characterized by DLS, and their droplet size was below 500 nm, which has resulted very appropriate for parenteral administration. A destabilization of the system always takes place above certain surfactant concentration. This phenomenon was described as a depletion–flocculation effect caused by non-adsorbed micelles. This destabilization was modelled by adding to the DLVO interaction energy a contribution addressing the force between two spherical particles in the presence of non-adsorbing spherical macromolecules.     

The effect of surfactant type on the rheology of ovalbumin layers at the air/water and oil/water interfaces

The aim of this work is to investigate the simultaneous adsorption of a globular protein, ovalbumin, and two different types of food emulsifiers, non-ionic Tween 60 and anionic Admul DATEM, at the air–water and sunflower oil–water interfaces. A commercial non-purified oil was used, aiming at investigating the behaviour of interfaces close to real systems. A pendant drop tensiometer was used to carry out transient interfacial tension measurements and small amplitude oscillations. A constant protein concentration (0.1 g/l) and different emulsifier/protein ratios (ranging between 0 and 0.6) were used during the tests.     

Structure and stability of heat-treated concentrated dairy-protein-stabilised oil-in-water emulsions: A stability map characterisation approach

Emulsion instabilities such as depletion flocculation, coalescence, aggregation and heat-induced protein aggregation may be detrimental to the production of sterilised food emulsions. The type and the amount of protein present in the continuous phase and at the oil–water interface are crucial in the design of emulsions with appropriate stability. In this study, four oil-in-water model emulsion systems (pH 6.8–7.0) were formulated, characterised and categorised according to the potential interactions between protein-coated or surfactant-coated emulsion droplets and non-adsorbed proteins present in the continuous phase. The heat stability, the creaming behaviour and the flow behaviour of the model emulsions were influenced by both the emulsifier type and the type of protein in the continuous phase. The results suggest that this stability map approach of predicting droplet–droplet, droplet–protein and protein–protein interactions will be useful for the future design of heat-stable emulsion-based beverages with good creaming stability at high protein concentrations.     

Optimization of dry heat treatment of egg white in relation to foam and interfacial properties

The properties of foams processed with reconstituted egg white were investigated as a function of the denaturation undergone by the proteins during the pasteurization stage in dry state. Various time-temperature tables were applied on the original egg white powder, ranging from 1 to 7 days, and from 60 to 80 °C. Differential Scanning Calorimetry was used to determine the denaturation degree of each EWP induced by the dry heat treatment. The rheological properties of the interface, using the drop tensiometer method, were shown to be significantly affected by the denaturation and to be a relevant parameter for foamability, stability and foam texture. The bulk properties of the foams were interrelated with interfacial properties by using principal component analysis (PCA) and cluster analysis (HCA). The resulting classification of the heat treatments reveals that mild treatment offers a good compromise between the heating cost and the functional properties of the foams.     

Effects of ultra-high pressure homogenization on the properties and structure of interfacial protein layer in whey protein-stabilized emulsion

The effect of high pressure homogenization on the properties of whey protein adsorbed on emulsion interface was determined by competitive adsorption with Tween 20, Fourier transform infrared (FT-IR) spectroscopy, and RP-HPLC. The amount of whey proteins desorbed by Tween 20 increased at higher pressure. The results of FT-IR spectroscopy showed that higher homogenization pressures led to decrease of α-helix and increase of β-sheet indicating the formation of fewer interactions with the lipid phase and more interaction between adsorbed whey proteins, respectively. In RP-HPLC profile, the retention time of whey protein desorbed from high pressured emulsion was shorter than that from low-pressured emulsion. From these results, we have shown that higher pressures cause the formation of a more compact interfacial protein layer. Finally, “high pressure” emulsions are more stable than “low-pressure” ones, because of the protein layer formed by protein-protein interactions as well as the decrease of droplet size.     

Crosslinking of interfacial layers in multilayered oil-in-water emulsions using laccase: Characterization and pH-stability

The enzymatic crosslinking of polymer layers adsorbed at the interface of oil-in-water emulsions was investigated. A sequential two step process, based on the electrostatic deposition of pectin onto a fish gelatin interfacial membrane was used to prepare emulsions containing oil droplets stabilized by fish gelatin-beet pectin membranes (citrate buffer, 10 mM, pH 3.5). First, a fine dispersed primary emulsion (5% soybean oil (w/v), 1% (w/w) gelatin solution) (citrate buffer, 10 mM, pH 3.5) was produced using a high pressure homogenizer. Second, a series of secondary emulsions were formed by diluting the primary emulsion into pectin solutions (0 - 0.4% (w/w)) to coat the droplets. Oil droplets of stable emulsions with different oil droplet concentrations (0.1%, 0.5%, 1.0% (w/v)) were subjected to enzymatic crosslinking. Laccase was added to the fish gelatin-beet pectin emulsions and emulsions were incubated for 15 min at room temperature. The pH- and storage stability of primary, secondary and secondary, laccase-treated emulsions was determined. Results indicated that crosslinking occurred exclusively in the layers and not between droplets, since no aggregates were formed. Droplet size increased from 350 to 400 nm regardless of oil droplet concentrations within a matter of minutes after addition of laccase suggesting formation of covalent bonds between pectin adsorbed at interfaces and pectin in the aqueous phase in the vicinity of droplets. During storage, size of enzymatically treated emulsions decreased, which was found to be due to enzymatic hydrolysis. Results suggest that biopolymer-crosslinking enzymes could be used to enhance stability of multilayered emulsions.     

Foam properties of algae soluble protein isolate: Effect of pH and ionic strength

In this study the foam properties of algae soluble protein isolate (ASPI), a mixture of mainly proteins and polysaccharides, were investigated as function of isolate concentration (0.1–1.0 mg/mL) and pH (3.0–7.0) at 10 mM and 200 mM NaCl. In addition, adsorption kinetics and dilatational elasticity at the air–water interface were studied. Whey protein isolate (WPI) and egg white albumin (EWA) were used as reference proteins. The consistent dilatational behaviour of ASPI at all pH values and ionic strengths tested indicated a similar interfacial composition at all these conditions. Adsorption kinetics, in contrast, were influenced by varying environmental conditions. At increased ionic strength and close to the theoretical isoelectric point calculated based purely on the amino acid composition of ASPI (pH 7) adsorption increased. Since similar adsorption behaviour was also observed for WPI and EWA, the interfacial properties of ASPI are most likely dominated by its protein fraction. This is further confirmed by the fact that ζ-potential measurements suggested an overall isoelectric point of ASPI below pH 3, while adsorption kinetics varied between pH 5 and pH 7 (the theoretical protein-based isoelectric point of ASPI). The overall foam stability of ASPI stabilized foams was superior to those of WPI and EWA in the pH range 5–7. In conclusion, the molecular and interfacial properties of ASPI, a mixture of proteins and polysaccharides, seem to favour the production of very stable foams in this pH range by the selective adsorption of its protein fraction to the air–water interface.     

Rheological characterization of dispersions and emulsions used in the preparation of microcapsules obtained by interfacial polymerization containing <Emphasis Type="Italic">Lactobacillus</Emphasis> sp.

The main objectives of this work were the rheological characterization of dispersions and emulsions used in the microcapsules preparation and the microcapsules obtain from gum arabic (A), gellan gum (G) and mesquite seed gum (M) to keep lactic bacteria (Lactobacillus sp.) viable using the interfacial polymerization technique (IP). Dispersions of A, G and M were prepared to obtain microcapsules, as well as binary mixtures of gum arabic and gellan gum (AG), gum arabic and mesquite seed gum (AM) and gellan gum and mesquite seed gum (GM); these dispersions exhibited a shear thinning non-Newtonian behavior. The emulsions were prepared using sunflower oil as the oily phase in a 1:1, 1:3 and 1:5 ratio with the disperse phase; the oily phase was added with Span 85 (surfactant) at 1, 2 and 3% concentrations; the emulsions A (1:5 and 3% Span 85) and GM (1:5 and 2% Span 85) showed higher viscosity and stability. Microcapsules were obtained using 0.05 mol L⁻¹ glutaraldehyde (crosslinking agent) with a reaction time of 3 min. The mean diameter of the microcapsules obtained was 30.17, 16.86 and 10.34 μm according to the AG, AM and GM mixtures, respectively. In the AG and AM dispersions, the microcapsules diameters became larger as the viscosity increased. The microorganism microencapsulates using gum arabic, gellan gum, and mesquite seed gum, was possible. The highest viability (46.7%) of Lactobacillus sp. was obtained with the GM mixture.     

Composition of interfacial layers in complex food emulsions before and after aeration: effect of egg to milk protein ratio

Whipped emulsions were prepared at pilot scale from fresh milk, whole egg, and other ingredients, for example, sugars and stabilizers (starch, polysaccharides). Egg content was varied: 4 recipes were studied differing in their egg to milk protein ratio (0, 0.25, 0.38, and 0.68). Protein and fat contents were kept constant by adjusting the recipes with skim-milk powder and fresh cream. Emulsions were prepared by high-pressure homogenization and whipped on a pilot plant. Particle-size distribution determined by laser-light scattering showed an extensive aggregation of fat globules in both mix and whipped emulsions, regardless of recipe. Amount of protein adsorbed at the oil-water interface and protein composition of adsorbed layer were determined after isolation of fat globules. Protein load is strongly increased by the presence of egg in formula. Values obtained for the whipped emulsions were dramatically lower than those obtained for the mix by a factor of 2 to 3. Sodium dodecyl sulfate-PAGE indicated a preferential adsorption of egg proteins over milk proteins at the oil-water interface, regardless of recipe. This phenomenon was more marked in aerated than in unaerated emulsions, showing evidence for desorption of some milk proteins during whipping. Egg proteins stabilize mainly the fat globule surface and ensure emulsion stability before whipping. Air bubble size distribution in whipped emulsions was measured after 15 d storage. When the egg to milk protein ratio is decreased to 0.25, large air cells appear in whipped emulsions during storage, indicating mousse destabilization. The present work allows linking the protein composition of adsorbed layers at the fat globule surface to mousse formula and mousse stability.     

The effect of the type and the concentration of the lipophilic surfactant on the stability and release kinetics of the W/O/W multiple emulsions

Stable multiple emulsions that contain different lipophilic surfactants in the internal aqueous phase have been formulated. The multiple systems were assessed by evaluating several parameters such as macroscopic aspect, droplet size, percent release and accelerated stability under centrifugation or elevated temperature. The effect of polymeric and monomeric surfactants on the release mechanism and stability was examined. An excess of monomeric surfactant in the oil phase enhances the release rate and decreases stability. The release rate can be decreased by an increase of the lipophilic surfactant concentration. It appears that the more the oil globule swells, the less hydrosoluble drug is released. As a result a high swelling capacity is associated with better stability.     

The broader usage of sugars and fillers in milk chocolate made possible by the new EC cocoa directive

The European Community directive 2000/36/EC now allows the addition of any sugar to chocolate and also adding up to 40% (w/w) of any foodstuff. Milk chocolates with lactose‐replacing sucrose and also with added fillers were tested for physical and sensory properties. Helianthus tuberosus flour, pea and oat fibres made the taste of the chocolate unacceptable. The addition of cellulose and wheat fibre at low dosages resulted in tolerable flavour; however, fat absorption of fibres caused worse flow properties and toughness made particle sizes to increase. Sugar beet fibres introduced bitter and cereal notes. The three products mentioned above would be useable only after modifications to the upstream process. Lupin gave a higher yield value because of its lecithin content but otherwise showed positive impact and could be used to supplement milk ingredients after adjustments to the recipe. As inulin improved the flow and sensory characteristics, it could be recommended both for its physical and nutritional properties. Lactose was not detectable up to 20%, but had some negative effects at higher levels in a low‐fat formulation and could require refining modifications. Further development seems worthwhile.     

Studying the effects of adsorption,recoalescence and fragmentation in a high pressure homogenizer using a dynamic simulation model

The emulsification in a high pressure homogenizer was studied using a dynamic simulation model based on the population balance equation. The model includes fragmentation, recoalescence and adsorption of macromolecular emulsifier and uses a simple flow model in order to link the hydrodynamics in the homogenizer to the three physical processes mentioned above.     

Extreme pH treatments enhance the structure-reinforcement role of soy protein isolate and its emulsions in pork myofibrillar protein gels in the presence of microbial transglutaminase

Alkali (pH₁₂) and acid (pH_1.5) pH-treated soy protein isolates (SPI) were incorporated (0.25–0.75% protein) into sols of myofibrillar protein (MP, 3%, in 0.6 M NaCl at pH 6.25) with or without 0.1% microbial transglutaminase (TG) to investigate the potential as meat processing ingredients. Static and dynamic rheological measurements showed significant enhancements of MP gelling ability by the inclusion of pH_1.5-treated as well as preheated SPI (90 °C, 3 min). A 7-h incubation with TG accentuated the gel-strengthening effect by these SPI samples. The B subunit in 11S of SPI was the main component manifesting structure reinforcement in the mixed gels. The MP gelling properties were also greatly improved (P < 0.05) by the addition of 10% canola oil emulsions stabilized by pH-treated SPI. The principal force in the MP gels incorporated with pH-treated SPI was hydrophobic patches; in the presence of TG, cross-linking of previously dissociated A and B subunits of 11S was also intimately involved.     

Combining quality and antioxidant attributes in the strawberry: The role of genotype

The nutritional value of fruit has been widely studied and is demanded by consumers, especially for protection against cardiovascular disorder, cancer and other diseases, as well as for general health benefits. These benefits can also be ascribed to the total antioxidant capacity (TAC) of fruit.Fruit nutritional quality can be described by a standard quality parameter and the analyses of nutritional parameters, such as antioxidant capacity (and specific related compounds). In this study, firmness, colour, soluble solids content and titratable acidity were considered as quality parameters and TAC and total phenolic content as nutritional parameters. All these attributes were screened in 20 strawberry genotypes (cultivars and selections) for the selection of new improved genetic material (offspring) originating from different cross combinations, including an F1 Fragaria virginiana spp. glauca among parents.Results indicate that the effect of the genotype on strawberry nutritional quality is stronger than that of the cultivation conditions. However, commercial cultivation did not show a high range of variation of fruit nutritional quality, particularly for the nutritional parameters.The study of offspring originating from different cross combinations showed that fruit nutritional quality can be considered an inheritable trait and that the variability of fruit nutritional quality among commercial cultivars can be improved by breeding.Finally, results demonstrate the role of F. virginiana spp. glauca as an important genetic source of the fruit nutritional quality.     

The possibility of using fluid whey in comminuted meat products: capacity and viscosity of the model emulsions prepared using whey and muscle proteins

The emulsion capacity (EC) of whey and sarcoplasmic proteins were low when they were used alone, but the EC and viscosity (EV) of total meat proteins (TMP) were higher than those values of other proteins investigated, including a combination of whey plus TMP. However, the solubility of the TMP proteins was lower than that of the other proteins investigated, probably due to the differences in the physico-chemical properties of whey and muscle proteins and the buffer used. In general, EC of whey proteins showed a significant alteration when used in combination with muscle proteins, while its solubility was not changed. The present results suggest that it is possible to use fluid whey in emulsion-type meat products and these studies should continue using actual meat emulsion systems.     

诱导Fuzzy拓扑空间中闭包与内部的分解定理

利用Ｆｕｚｚｙ集的分解定理出给了诱导Ｆｕｚｚｙ拓扑空间中闭包与内部分解定理的另一种形式,还证明了Ｌ－Ｆｕｚｚｙ拓扑空间中的正则性与正规性是Ｌ－好的推广。     

A combined approach in characterization of an effective w/o hand cream: the influence of emollient on textural, sensorial and in vivo skin performance

To formulate a consumer-acceptable cosmetic product, numerous demands have to be fulfilled, and as the most important, efficacy (both real and perceived), adequate aesthetic (visual perception) and all sensorial characteristics have to be achieved. In this study, four model water-in-oil creams intended for hand care, varying in one emollient component, were submitted to rheological, sensory and textural characterization, and their efficacy was evaluated in in vivo study on human volunteers. Our results indicate that certain alteration restricted to the oil phase induced a change in all investigated characteristics, showing that each instrumental measurement can be used as a sensitive tool in the characterization of cream samples. Regarding the correlation between physical measurements and certain sensory attributes, it is possible to formulate a product with specific sensory characteristics by using pre-defined rheological or textural parameters. To obtain a complete sensory profile of a cosmetic product, a detailed sensory evaluation should be carried out according to the existing standard practices, which are both time- and money-consuming. However, a modified sensory study could be useful for fast in-line screening along with instrumental characterization of a novel cosmetic emulsion product and could be particularly helpful in the process of distinguishing a single formulation from several differing in one component.     

表面活性剂脱氧胆酸钠在单增李斯特菌死活细胞EMA-PCR鉴别中的应用

通过脱氧胆酸钠(sodium deoxycholate,SD)结合染料叠氮溴乙锭(ethidium bromide monoazide,EMA)与PCR反应体系相结合,建立纯培养条件下区分单增李斯特菌死活细胞的方法,即SD-EMA-PCR鉴别单增李斯特菌死活细胞检测法。结果表明:向浓度为2.0×108CFU/mL的单增李斯特死菌悬液中加入终浓度为1.5 mg/mL的表面活性剂脱氧胆酸钠后,EMA激活光解最佳曝光时间为25 min。SD-EMA-PCR检测体系中,对死菌细胞DNA的PCR扩增抑制的EMA最小浓度为1.6μg/mL;而对活菌细胞DNA的PCR扩增不抑制的EMA最大浓度为9μg/mL,活菌细胞的最低检出限为20 CFU/mL。SD-EMA-PCR检测法能够减小EMA-PCR漏检死菌细胞给检测结果带来假阳性的可能,降低了检测的成本,为单增李斯特菌的快速检测提供了一种新的有效途径。