Behaviour of a protein isolate from rapeseed (Brassica napus) and its main protein components - globulin and albumin - at air/solution and solid interfaces, and in emulsions

The behaviour of a rapeseed protein isolate (RI) and its main protein components - globulin (RG) and albumin (RA) - in adsorbed and spread monolayers, as well as in emulsions was investigated. Tensiometry, film-pressure area and Langmuir-Blodgett-techniques, and emulsion parameters were used to characterise the behaviour of the rapeseed proteins at various interfaces. The adsorption isotherms for albumin showed a plateau value for the surface pressure (Pi(e)) of 11.6 mN/m at the low critical association concentration (CAC) of 5.6x10(-8) g/ml. Both values were found to be distinctly higher for the globulin and the protein isolate. The isotherms of a mixture of RG and RA, which corresponds to the composition of RI, seems to be a superimposition of the isotherms of RA and RG. Contact angle measurements showed that all samples used were able to form LB-layers and to make hydrophilic glass surfaces more hydrophobic and vice versa. The changes in contact angle were more pronounced on hydrophobic glass surfaces. Monolayer and emulsion characteristics are dominated by the interfacial properties of albumin. The maximum film pressure reached by globulin was only about 8 mN/m. The globulin also possesses the lowest emulsifying activity. From the mean molecular area calculated for spread globulin, it is concluded that the globulin maintains its globular conformation at surfaces, which explains the low surface activity. Albumin and the protein isolate were highly surface active in monolayers and emulsion formation. The slightly different interfacial behaviour of the protein isolate compared with the corresponding mixture is probably due to additional effects of non-protein components and a partially denatured state of the protein.     

The rheology of lupin seed (Lupinus albus ssp. graecus) protein isolate films at the corn oil–water interface

Lupin seed protein isolates adsorbed at the corn oil–water interface formed, after long ageing times, interfacial films with viscoelastic properties. The viscoelastic parameters of the films, derived by analysis of creep compliance–time curves, were markedly influenced by the aqueous phase protein concentrations, pH, ageing time and isolate preparation methods. Instantaneous elastic modulus, E₀(s), showed maxima at a certain concentration which probably corresponded to monolayer saturation coverage and at pH 5.5, i.e. near to its isoelectric point, where the protein molecules are in a more compact form than at other pH values. The full fat lupin seed protein fractions gave the highest viscoelasticity values under all conditions and this in turn have an effect on the corresponding emulsion/foam stability.     

Foaming and Structural Studies on the Acidic Subunit of Amaranth 11S Globulin Modified with Antihypertensive Peptides as a Function of pH and Ionic Strength

Some studies aimed at revealing the relationship between protein structure and their functional properties. However, the majority of these reports have been carried out using protein isolates. There are limited reports on the possible relationship between the functional properties and the structure of a purified protein. In this work the amaranth 11S globulin acidic subunit (AAC) and five mutations of the same protein that were modified in their variable regions with antihypertensive peptides (VYVYVYVY and RIPP), were analyzed at two ionic strength (2.9 and 17.6 g/L NaCl) and pH (3.0–7.0). Results revealed better solubility for the proteins mutated at the terminal ends (AACM.1 and AACM.4) and lower solubility for the protein inserted with RIPP peptide. Spectroscopy studies revealed an increase of β-sheet structure at high salt concentration for all proteins. It was also observed that salt concentration acted as a modulator, which allowed a better foam features for all modified proteins limiting movement of side chains and reducing red-shifted displacement of λmax. All proteins showed foam capacity ranging from 76 to 93% although foam stability was twofold better for modified proteins than for AAC at high salt concentration. This study allowed better understanding about the structural changes that influence the foaming properties of engineered proteins.     

Comparisons of the foaming and interfacial properties of whey protein isolate and egg white proteins

Whipped foams (10%, w/v protein, pH 7.0) were prepared from commercially available samples of whey protein isolate (WPI) and egg white protein (EWP), and subsequently compared based on yield stress (τ₀), overrun and drainage stability. Adsorption rates and interfacial rheological measurements at a model air/water interface were quantified via pendant drop tensiometry to better understand foaming differences among the ingredients. The highest τ₀ and resistance to drainage were observed for standard EWP, followed by EWP with added 0.1% (w/w) sodium lauryl sulfate, and then WPI. Addition of 25% (w/w) sucrose increased τ₀ and drainage resistance of the EWP-based ingredients, whereas it decreased τ₀ of WPI foams and minimally affected their drainage rates. These differing sugar effects were reflected in the interfacial rheological measurements, as sucrose addition increased the dilatational elasticity for both EWP-based ingredients, while decreasing this parameter for WPI. Previously observed relationships between τ₀ and interfacial rheology did not hold across the protein types; however, these measurements did effectively differentiate foaming behaviors within EWP-based ingredients and within WPI. Interfacial data was also collected for purified β-lactoglobulin (β-lg) and ovalbumin, the primary proteins of WPI and EWP, respectively. The addition of 25% (w/w) sucrose increased the dilatational elasticity for adsorbed layers of β-lg, while minimally affecting the interfacial rheology of adsorbed ovalbumin, in contrast to the response of WPI and EWP ingredients. These experiments underscore the importance of utilizing the same materials for interfacial measurements as used for foaming experiments, if one is to properly infer interfacial information/mechanisms and relate this information to bulk foaming measurements. The effects of protein concentration and measurement time on interfacial rheology were also considered as they relate to bulk foam properties. This data should be of practical assistance to those designing aerated food products, as it has not been previously reported that sucrose addition improves the foaming characteristics of EWP-based ingredients while negatively affecting the foaming behavior of WPI, as these types of protein isolates are common to the food industry.     

Deactivation efficiency of stabilized bactericidal emulsions

Biocide emulsions stabilized with various stabilizing agents were prepared and characterized, and their efficiency in bacteria deactivation was evaluated. A number of stabilizing agents were tested for their stabilizing effect on emulsions of thiocyanomethylthiobenzothiazole (TCMTB) biocide. Two agents, the most successful in stabilizing the biocide, were chosen for further studies: high molecular weight polyethyleneimine (PEI) and an amphiphilic block copolymer of poly(caprolactone)-b-poly(acrylic acid) (PCL(33)-b-PAA(33)). The emulsion droplet sizes varied between 325 and 500 nm. Deactivation of bacteria was studied by exposing E. coli ATCC 11229 bacteria dispersions to emulsions stabilized by positively charged PEI or negatively charged PCL-b-PAA micelles and by measuring their absorbance; E. coli do not grow with time in the presence of biocide emulsions. PEI molecules alone act as biocide and deactivate the bacteria. PCL-b-PAA micelles as stabilizing agent do not affect the growth of the E. coli ; bacteria are deactivated by TCMTB released from the emulsion droplets. The kinetics of emulsion dissolution studies revealed for both stabilizing agents a decrease in droplet size with time while the emulsions were subjected to dialysis. The biocide was released from the emulsions within ～250 min; the droplet shells consist mostly of PEI or PCL-b-PAA insoluble complexes with the biocide, which do not dissolve during dialysis. SEM images confirm the presence of residual crumbled shells with holes after 24 h of dialysis.     

酸碱-氧化还原双重刺激响应型表面活性剂的合成与性能

以11-氨基十一酸为原料制备了酸碱-氧化还原双重刺激响应型表面活性剂中间体11-叔胺十一烷基羰基二茂铁(C_(11)-N-Fe);采用~1H NMR和MS等手段对产物进行了结构表征;并通过透光率、循环伏安法和紫外光谱分析等研究了其酸/碱和氧化/还原开关响应性能.研究发现,C_(11)-N-Fe的盐酸盐在水溶液中进行自组装时,可制备具有酸碱-氧化还原双重刺激响应性的泡沫,且采用2种刺激方式的消泡均可在2 min之内完成;将C_(11)-N-Fe的盐酸盐作为乳化剂用于乳化正癸烷/水体系,可以制得颗粒均匀稳定的乳状液,同时可以通过酸碱-氧化还原双重刺激可逆调控乳液的稳定与破乳.     

新型孪尾Gemini两性离子表面活性剂应用性能

分别采用改进的Ross-Miles法及分水时间法,对3种新型孪尾Gemini两性离子表面活性剂(C8C8L3Sz、C8C8L4Sz和C10C8L3Sz)的泡沫性能及乳化性能进行了研究,并考察了表面活性剂浓度、分子结构和温度等对其的影响。 结果表明,该系列表面活性剂具有较好的泡沫性能,且随其浓度的增加,泡沫最大高度和半衰期均存在一个稳定值,疏水链越长,其起泡性能越差,泡沫稳定性越好;温度升高,起泡性能变好,泡沫稳定性变差;当表面活性剂浓度一定时,体系中加入低浓度的短链醇及无机盐均能提高泡沫的稳定性;C8C8L3Sz、C8C8L4Sz和C10C8L3Sz作乳化剂的最适宜的用量分别为6×10-4、6×10-4和4×10-4 mol/L,疏水基越长,乳化性能越好,而连接基对其影响较小;温度升高,乳化性能变差;当油相烷烃碳数相同时,环烷烃要比直连烷烃更易达到最佳乳化效果,但二者的乳状液稳定时间相当;对于油相烷烃碳数不同时,烷烃的碳链越长,乳状液的稳定性越差,乳化效果越不好。     

Influence of sodium dodecyl sulfate on the physicochemical properties of whey protein-stabilized emulsions

The influence of sodium dodecyl sulfate (SDS) on the flocculation of droplets in 20 wt.% soybean oil-in-water emulsions stabilized by whey protein isolate (WPI) was investigated by light scattering, rheology and creaming measurements. The SDS concentrations used were low enough to prevent depletion flocculation by surfactant micelles and extensive protein displacement. In the absence of SDS, emulsions were prone to droplet flocculation near the isoelectric point of the proteins (4<pH<6), but were stable at a higher and lower pH. Flocculation led to an increase in emulsion viscosity, pronounced shear thinning behavior and accelerated creaming. When the surfactant-to-protein molar ratio was increased from 0 to 10, the emulsion instability range shifted to lower pH values due to binding of the negatively charged SDS molecules to the droplets. Our results indicate that the physicochemical properties of protein-stabilized emulsions can be modified by utilizing surfactant–protein interactions.     

卵磷脂类液晶乳液的性能

以卵磷脂为主乳化剂制备了一款液晶乳液。 该乳液在皮肤上具有良好的稳定性能,在皮肤表层停留6 h仍能保持完整的液晶结构,克服了一般液晶乳液中液晶织构无法在皮肤上长时间停留的问题。 液晶结构在皮肤温度范围内具有较高的稳定性,可为液晶乳液其他性能的发挥提供条件。 基于此,我们采用体外称重法研究了液晶乳液的锁水性,发现液晶乳液锁水性能明显优于传统乳液,实验7 h后仍能保持原有水分总质量的50%;体外透析实验证实,液晶乳液表现出显著的缓释性能且能释放完全,7 h后目标分子(水杨酸钠)释放率可达96%;耐温性能研究表明,液晶乳液耐高温性能及低温冻融性能优良,且温度对乳液中层状液晶的影响是可恢复的;采用离心法、高低温循环和高低温长时间(3个月)放置的方法探究了乳液储运稳定性,结果表明,液晶乳液产品储运稳定性极佳,便于实际的应用和储运。 该研究不仅可为开发多效的高端化妆品提供必要信息和参考数据,而且有望拓展卵磷脂类液晶乳化剂体系的应用范畴。     

DSC studies on protein isolate of guava seeds <Emphasis Type="Italic">Psidium guajava</Emphasis>

Glutelin, the major protein fraction from guava seed, was obtained by fractioning as described by Osborne. The total proteins were extracted and the isolates obtained by isoelectric precipitation presented similar DSC curves, concordant with the results obtained by gel filtration chromatography and electrophoresis in polyacrylamide gel (PAGE-SDS). However, the DSC curves showed a higher enthalpy with regard to the denaturing protein isolate (PI) extracted at pH 10.0 when compared to a PI at pH 11.5. Such results are in accordance with those obtained for PI extracted at pH 10.0 using chromatography, this one being present in the form of molecular aggregates of greater molecular mass. The glutelin fraction, however, did not present a denaturation peak in the DSC curve, showing that the process for obtaining the same significantly altered its conformation.     

Complexation of bovine serum albumin and sugar beet pectin: Stabilising oil-in-water emulsions

In a previous study (Langmuir 28 (2012) 10164-10176.), we investigated the complexation of bovine serum albumin (BSA) with sugar beet pectin (SBP). A pH-composition phase diagram was established and structural transitions in relation to the phase diagram during complexation were identified. The present study examines the implications of these interactions on the emulsifying performance of BSA/SBP mixtures. Middle-chain triglycerides (MCTs) in water emulsions were prepared using conditions corresponding to different regions of the phase diagram. At high pHs and in the stable region of mixed individual soluble polymers where complexation is absent, there is no improved emulsifying performance, compared with the individual protein and polysaccharide. For these mixtures, the emulsion characteristics are controlled by the major component in the solutions, as determined by the competitive adsorption of the two components at the oil-water interface. At low pHs and low BSA/SBP ratios, and so mainly within the stable region of intramolecular soluble complexes, BSA/SBP mixtures greatly improve the stability of emulsions. Here, stabilisation is controlled by the cooperative adsorption of the two components at the oil-water interface. Through electrostatic complexation BSA promotes the adsorption of SBP on to interfaces to form a thick steric layer around emulsion droplets and thus providing better stability. At low pHs and high BSA/SBP ratios, that is, mainly within the unstable region of intermolecular insoluble complexes, emulsions prepared are extremely unstable due to bridging flocculation between emulsion droplets.     

Boosting the stability of protein emulsions by the synergistic use of proteins and clays

The preparation and the properties of high-pressure emulsions based on five different proteins are reported. As proteins, we used the well-studied bovine serum albumin (BSA), a biotechnical produced hydrophobin called H Star Protein B? (HPB), a protein isolate from soybeans, a wheat protein isolate (Plantasol W), and a commercially available yeast extract. All emulsions were characterized by visual appearance, light microscopy, conductivity, and rheological measurements. Beside the emulsion based on soy protein isolate, all other samples showed phase separation under the used conditions (0.5 wt.% protein; 50 wt.% oil). Plantasol W and yeast extract formed the most unstable emulsions showing typical instability processes like coalescence. Gel-like properties have been observed for emulsions based on BSA, soy protein isolate, and HPB. The same proteins were also used to stabilize emulsions after their adsorption on clay particles. Interestingly, all emulsions had gel-like properties with a yield stress value and were stable to the used conditions. It is concluded that the gel character results from the stickiness of the protein covered oil droplets and is independent from the used protein type. The proteins which are adsorbed on the oil droplets can still interact and bind to proteins on other oil droplets.     

Foaming properties of potato proteins recovered by complexation with carboxymethylcellulose

A protein isolate, with a 74.4% (w/w) protein content, was recovered from a simulated potato processing plant waste effluent by complexation with carboxymethylcellulose. The protein solubility of the isolate was satisfactory, it decreased in the presence of NaCl, but was not markedly affected by heat treatment. The isolate exhibited remarkable foaming and foam stabilizing properties, compared with lyophilized egg white, which are attributed to the very high surface activity of the potato protein molecules, which following adsorption at a/w interfaces, result in a much higher surface pressure development compared with egg albumen. A significant part of the foaming ability and the high surface activity of the isolate should be connected with the presence in the isolate of a small fraction of proteins with a relatively low molecular weight. The sulfhydryl groups of these proteins, following adsorption at the a/w interface, during the process of foam formation and denaturation are oxidized leading to the possible formation of intermolecular disulfide linkages.     

Development of non-denaturing off-gel isoelectric focusing for the separation of uranium–protein complexes in fish

An off-gel non-denaturing isoelectric focusing (IEF) method was developed to separate uranium–biomolecule complexes from biological samples as a first step in a multidimensional metalloproteomic approach. Analysis of a synthetic uranium–bovine serum albumin complex demonstrated the focusing ability of the liquid-phase IEF method and the preservation of most of the uranium–protein interactions. The developed method was applied to gill cytosol prepared from zebrafish (Danio rerio) exposed to depleted uranium. The results were compared in terms of resolution, recovery, and protein identities with those obtained by in-gel IEF using an immobilized pH gradient gel strip.     

FOAMING PROPERTIES OF SURFACTANT-OIL-VATER SYSTEMS IN THE NEIGHBOURHOOD OF OPTIMUM FORMULATION

The foaming properties of. surfactant-oil-water systems are found to be closely related to the phase behavior at equilibrium. In Winsor I systems both the surfactant-oil-water emulsion and its aqueous phase produce stable foams. The foaminess and the foam stability follow the same pattern of variation than the emulsion stability. In Winsor III (three phase microemulsion-oil-water) and Winsor II systems no foam can be formed. The changes are the same no matter the formulation variable used to scan the physico-chemical formulation or the method used to measure the foam stability.     

Hematite nanoparticle monolayers on mica preparation by controlled self-assembly

In this research, a simple, green and effective strategy was developed to produce long-term stable oil in water emulsion from soy protein and soy polysaccharide. Soy protein and soy polysaccharide formed dispersible complexes at pH around 3.25 aqueous solution through electrostatic and hydrophobic interactions. A high pressure homogenization produced the protein/polysaccharide complex emulsion having a droplet size about 250 nm. A heat treatment of the emulsion resulted in the protein denaturation, forming irreversible oil-water interfacial films composed of soy protein/soy polysaccharide complexes. The droplets of the emulsion were characterized by dynamic light scattering, ζ-potential, transmission electron microscopy, polysaccharide digestion via pectinase, and confocal laser scanning microscopy observation via dual fluorescence probes. As a result of the polysaccharide being fixed on the droplet surface, the emulsions exhibited long-term stability in the media containing pH values of 2-8 and 0.2 mol/L NaCl. The stable soy protein/soy polysaccharide complex emulsion is a suitable food-grade delivery system in which lipophilic bioactive compounds can be encapsulated.     

Chromatographic studies of mitomycin C degradation in albumin microspheres

Serum albumins and polylactic acid (PLA) have been used as bioerodable polymers in the preparation of drug-containing microspheres for parenteral drug delivery. The albumin microsphere may be prepared via either chemical cross-linking or heat denaturation of the protein. Heat-denatured albumin microspheres containing mitomycin C (MMC) have been used in pre-clinical and clinical investigations. Due to the high reactivity of MMC as a bifunctional alkylating agent, a study on the stability of MMC in the albumin and PLA microspheres has been carried out using a high-performance liquid chromatographic (HPLC) method. Human serum albumin (HSA) microspheres were prepared using an emulsion method via either heat denaturation at 120 or 170 degrees C or the use of 0.5 M biacetyl as a cross-linking agent. The PLA microspheres were prepared by an emulsion method at 55 degrees C. HPLC analysis of the HSA microspheres showed that about 37% of MMC was converted to 2,7-diaminomitosene derivatives in microspheres prepared by heat denaturation at 120 degrees C. The degradation increased to 82% when the microspheres were prepared with a denaturation temperature of 170 degrees C. The use of biacetyl as a cross-linking agent in the preparation of HSA microspheres resulted in a complete degradation of the incorporated MMC. Biacetyl was found to interact with MMC leading to the formation of 7-aminomitosene derivatives. In contrast to the albumin system, MMC may be incorporated into PLA microspheres without degradation.     

Effect of Three Defatting Solvents on the Techno-Functional Properties of an Edible Insect (Gryllus bimaculatus) Protein Concentrate

Edible insects have received global attention as an alternative protein-rich food. However, their structural characteristics make them difficult to digest. To overcome this obstacle, we assessed the techno-functional properties of three protein concentrates from the cricket Gryllus bimaculatus. Freeze-dried G. bimaculatus powder was defatted using ethanol, hexene, or acetone as solvents, and the techno-functional properties (protein solubility, water and oil holding capacity, foaming properties, emulsion capacity, and gel formation) of the protein concentrates were determined. Freeze-dried G. bimaculatus powder comprised approximately 17.3% crude fat and 51.3% crude protein based on dry weight. Ethanol was the most effective solvent for reducing the fat content (from 17.30% to 0.73%) and increasing the protein content (from 51.3% to 62.5%) of the concentrate. Techno-functionality properties drastically differed according to the defatting solvent used and foaming properties were most affected. Thus, the techno-functional and whole properties must be considered for proper application of edible insects to achieve global food sustainability.     

Studies on metal — protein interactions: Inter-comparison among various approaches

Binding ability of mercury, thallium, lead and bismuth with Erythrina variegata seed protein have been investigated using tracer packet technique. Due to the lack of standard methods, inter-comparisons have been made among three different approaches, like trichloroacetic acid (TCA) precipitation, isoelectric precipitation and dialysis of protein after incubation with the metals. Good agreement was observed for all the cases except that of lead.     

Protein adsorption at the electrified air-water interface: implications on foam stability

The surface chemistry of ions, water molecules, and proteins as well as their ability to form stable networks in foams can influence and control macroscopic properties such as taste and texture of dairy products considerably. Despite the significant relevance of protein adsorption at liquid interfaces, a molecular level understanding on the arrangement of proteins at interfaces and their interactions has been elusive. Therefore, we have addressed the adsorption of the model protein bovine serum albumin (BSA) at the air-water interface with vibrational sum-frequency generation (SFG) and ellipsometry. SFG provides specific information on the composition and average orientation of molecules at interfaces, while complementary information on the thickness of the adsorbed layer can be obtained with ellipsometry. Adsorption of charged BSA proteins at the water surface leads to an electrified interface, pH dependent charging, and electric field-induced polar ordering of interfacial H(2)O and BSA. Varying the bulk pH of protein solutions changes the intensities of the protein related vibrational bands substantially, while dramatic changes in vibrational bands of interfacial H(2)O are simultaneously observed. These observations have allowed us to determine the isoelectric point of BSA directly at the electrolyte-air interface for the first time. BSA covered air-water interfaces with a pH near the isoelectric point form an amorphous network of possibly agglomerated BSA proteins. Finally, we provide a direct correlation of the molecular structure of BSA interfaces with foam stability and new information on the link between microscopic properties of BSA at water surfaces and macroscopic properties such as the stability of protein foams.