Lower Foam Stability Research Articles

Foaming and surface rheological behaviors of gliadin particles: Effect of solvent and concentration of gliadin stock solution

The anti-solvent method was a green and facile approach to prepare water-insoluble proteins-based colloidal particles. The structure and functional properties of the resulting particles strongly depend on the preparation parameters of the anti-solvent process. Herein, two main parameters, solvent and concentration of protein stock solution, were chosen to investigate their effects on the structural, foaming, and surface rheological properties of gliadin particles. When the solvent was 70% ethanol solution (v/v), gliadin particles exhibited a uniform spherical structure. They could fast adsorb to the air/water interface and form a viscoelastic surface layer to prevent foam drainage, coalescence, and disproportionation, thus leading to impressive foamability (~250%) and high foam stability (~60 h) even the concentration of particles was very low (1.5 mg/mL). Besides, when the solvent was acetic acid, gliadin particles possessed spherical and wire-like hybrid structures. They had slower adsorption rate and weaker interaction at the interface when compared to the ethanol-based particles, resulting in poorer foam capacity and lower foam stability. The particles prepared by different solvents had evidently different nonlinear surface rheological responses. Besides, the concentration of gliadin stock solutions did not affect the foaming and surface behaviors of particles. The particle shape played a crucial role in affecting the foaming properties and surface behaviors of gliadin particles. Results imply that 70% ethanol aqueous solution is a good solvent for gliadin, which can endow strong foaming and surface rheological behaviors to gliadin particles.

Physicochemical properties, protein digestibility and thermal stability of processed African mesquite bean (Prosopis africana) flours and protein isolates

The physicochemical, in vitro protein digestibility and thermal properties of dehulled (DPAF) and dehulled–defatted (DDPAF) African mesquite bean (Prosopis africana) flours and protein isolates produced by micellization and isoelectric precipitation were evaluated. Isoelectric precipitation method gave higher yield of protein isolate (30.46%) with higher protein content (81.34%) compared to the micellization which yielded 7.95% and 72.04%, respectively. Significant (p < 0.05) differences occurred among the total colour difference (23.63–53.12), whiteness (40.17–67.78), yellowness (36.81–49.26), browning (− 123.22 to 471.59) and flour colour (26.63–55.04) indexes and functional properties except dispersibility of the samples, indicating the effects of defatting and protein extraction methods. Micellized protein isolate recorded the highest oil (322%), water (300%) absorption and emulsion (64.67%) capacities, while the isoelectric precipitated protein had the highest protein solubility (81.75%). The protein isolates exhibited lower foam stability than the flours with micellized protein being the least. Thermal properties of the flours and protein isolates also varied with defatting and extraction methods. The dehulled P. africana flour and isoelectric precipitated protein showed single endothermic peaks with higher thermal stability compared to the dehulled–defatted flour and micellized protein which had two endothermic peaks. Flours and protein isolates showed in vitro protein digestibility between 76.44 and 80.00%, with micellized protein exhibiting the highest digestibility. Knowledge of the physicochemical properties of P. africana seed products would enhance their utilization in various food formulations, thereby contributing to food security in Africa.

Influence of energy density and viscosity on foam stability – A study with pea protein (Pisum Sativum L.)

A high foam stability (FS) is important for manufacturers and is mainly achieved through high protein concentrations. Consequently, the increase of FS at lower protein concentrations is desirable from an economic point of view, especially for proteins that show a lower foamability and FS, such as pea protein isolate (PPI). The hypothesis of this study was that if the viscosity of a PPI dispersion is adjusted to a higher protein concentration (i.e. 5 wt% PPI adjusted to the viscosity of 7.5 wt% PPI), a similar FS can be obtained, while reducing the needed protein concentration. Therefore, the influence of energy density (Evol) and viscosity on FS was examined. For this, foams were prepared (Evol = 3.6 × 108 J m−3 to 14.4 × 108 J m−3) with PPI (c = 5, 7.5, 10 wt%), as well as with mixtures of PPI and non-surface-active maltodextrin (MD) to modulate the viscosity of the continuous phase. Overall, it was shown that MD was able to considerably improve FS of PPI. Mixtures of PPI and MD with the same viscosity as the pure PPI dispersions exhibited a similar FS. For example, the addition of MD to 5 wt% PPI for adjustment of the viscosity to that of the pure 7.5 wt% PPI facilitated a FS of 1664 s ± 2 s compared to 1354 s ± 122 s. Generally, the addition of MD led to a higher viscosity of the continuous phase and an increase in protein surface load, which both attributed positively to FS.

Impact of ethanol on the air-water interfacial properties of enzymatically hydrolyzed wheat gluten

Studying the air-water (A-W) interfacial characteristics of enzymatically hydrolyzed wheat gluten proteins contributes to understanding their potential as alternatives to animal proteins as foaming agents in food products. In this paper, the impact of the presence of ethanol on the A-W interfacial behavior of gluten hydrolysates (GHs) was studied. Regardless of protein concentration, foaming capacity (FC), i.e. the initial amount of foam formed after a standardized whipping procedure, of four structurally different GHs was higher in a solution containing ethanol than in water. However, the rates of diffusion to and adsorption at the A-W interface of the GH constituents was lower in the presence of ethanol than in water. This suggests that the affinity of the GHs for the interface was lower when ethanol was present, which may be due to ethanol-induced conformation changes in the GH constituents or to some kind of competitive effect due to the surface activity of ethanol. It is hypothesized that the latter effect also contributes to the elevated FC values in the presence of ethanol. The strength of adsorbed GH films was generally lower in a in the presence of ethanol than in water. This was in line with the overall lower foam stability, which is the amount of foam remaining after one hour, of GH solutions containing ethanol compared to that in water. Thus, it is important to take the impact of other food constituents into account when evaluating the potential of plant protein hydrolysates as foaming agents in food systems.

Obtaining and purification of a highly soluble hydrolyzed rice endosperm protein

Abstract Rice endosperm proteins are quite insoluble and have low commercial value mainly due to their poor functional properties. In this study the influence of enzymatic hydrolysis and tangential flow ultrafiltration were evaluated in obtaining a hydrolyzed rice endosperm protein of high solubility and reduced sodium content. Initially, enzymatic hydrolysis kinetics was evaluated to select the enzyme/substrate ratio and hydrolysis time appropriate to the process. The rice endosperm proteins were extracted by the alkaline method and hydrolyzed with Alcalase® until reaching degree of hydrolysis of 9.40% when 40% of the protein became solubilized. The molar masses of the soluble peptides were evaluated via LC-MS QTOF MS/MS. The hydrolyzed soluble fraction was recovered by centrifugation, pre-treated by microfiltration and then concentrated by tangential flow ultrafiltration using a 1 kDa membrane. The sample was subjected to two diafiltrations with reduced solvent volume, after it was dried and analyzed with respect to their protein, mineral, sodium and potassium contents, solubility and foaming properties. The hydrolyzed protein showed 71.28% of protein; ultrafiltration removed 70% of the total mineral content. Even so, the sample still showed 1.97% of sodium, demonstrating the need to carry out more diafiltrations. The hydrolysate has solubility higher than 88.5% in the pH 3 to 7, reaching 99.8% at pH 6. The sample had high foaming capacity, but low foam stability. Thus, enzymatic hydrolysis associated with ultrafiltration can be a suitable alternative for obtaining a soluble fraction with low sodium content, improving the quality of rice endosperm protein.

Foam fractionation as a tool to study the air-water interface structure-function relationship of wheat gluten hydrolysates

Enzymatic hydrolysis of wheat gluten protein improves its solubility and produces hydrolysates with foaming properties which may find applications in food products. First, we here investigated whether foam-liquid fractionation can concentrate wheat gluten peptides with foaming properties. Foam and liquid fractions had high and very low foam stability (FS), respectively. In addition, foam fractions were able to decrease surface tension more pronouncedly than un-fractionated samples and liquid fractions, suggesting they are able to arrange themselves more efficiently at an interface. As a second objective, foam fractionation served as a tool to study the structural properties of the peptides, causing these differences in air-water interfacial behavior. Zeta potential and surface hydrophobicity measurements did not fully explain these differences but suggested that hydrophobic interactions at the air-water interface are more important than electrostatic interactions. RP-HPLC showed a large overlap between foam and liquid fractions. However, a small fraction of very hydrophobic peptides with relatively high average molecular mass was clearly enriched in the foam fraction. These peptides were also more concentrated in un-fractionated DH 2 hydrolysates, which had high FS, than in DH 6 hydrolysates, which had low FS. These peptides most likely play a key role in stabilizing the air-water interface.

The Potential Use of Fermented Chickpea and Faba Bean Flour as Food Ingredients

Apart from being a rich and inexpensive protein source, legumes provide essential vitamins, minerals and dietary fibre. Considering the nutritional benefits, legumes flour can potentially be incorporated in the development of new products. The aim of this study was to investigate whether fermentation affects the protein content, in vitro protein digestibility, trypsin inhibitor activity and the functionality of proteins in faba bean, desi and kabuli chickpea. Australian grown chickpea and faba bean were selected and initially soaked, de-hulled, dried and milled into flour. This was fermented with lyophilised yoghurt cultures in a 30 °C orbital shaker for 16 h. While protein contents in fermented desi and kabuli flour were lower than their raw counterparts (p > 0.05), it was significantly higher in fermented faba bean. A significant increase (9.5%) in in vitro protein digestibility was found in fermented desi. Trypsin inhibitor activity in fermented desi, kabuli and faba bean reduced by 2.7, 1.1 and 4.7%, respectively (p > 0.05). Overall, the in vitro protein digestibility in flour samples increased, while simultaneously reducing the trypsin inhibitor activity. The water absorption capacity of the fermented kabuli flour significantly increased by 11.3%. All fermented flour samples had significantly higher oil absorption capacity than their corresponding raw flour that was likely due to increased insoluble hydrophobic protein. Although, the foaming capacity in all fermented flour samples was significantly lower than their respective raw samples, only fermented desi and faba bean flour showed lower foaming stability (p > 0.05). The present study suggests that fermented legume flour could fulfill the demand for innovative products of higher nutritional value.

Enzymatic treatment of soy protein isolates: effects on the potential allergenicity, technofunctionality, and sensory properties.

Soybean allergy is of great concern and continues to challenge both consumer and food industry. The present study investigates the enzyme-assisted reduction in major soybean allergens in soy protein isolate using different food-grade proteases, while maintaining or improving the sensory attributes and technofunctional properties. SDS-PAGE analyses showed that hydrolysis with Alcalase, Pepsin, and Papain was most effective in the degradation of the major soybean allergens with proteolytic activities of 100%, 100%, and 95.9%, respectively. In the course of hydrolysis, the degree of hydrolysis increased, and Alcalase showed the highest degree of hydrolysis (13%) among the proteases tested. DSC analysis confirmed the degradation of major soybean allergens. The sensory experiments conducted by a panel of 10 panelists considered the overall improved sensory properties as well as the bitterness of the individual hydrolysates. In particular, Flavourzyme and Papain were attractive due to a less pronounced bitter taste and improved sensory profile (smell, taste, mouthfeeling). Technofunctional properties showed a good solubility at pH 7.0 and 4.0, emulsifying capacity up to 760mLg(-1) (Flavourzyme) as well as improved oil-binding capacities, while the water-binding properties were generally decreased. Increased foaming activity for all proteases up to 3582% (Pepsin) was observed, whereas lower foaming stability and density were found. The hydrolysates could potentially be used as hypoallergenic ingredients in a variety of food products due to their improved technofunctional properties and a pleasant taste.

A Combination of Freeze Drying and Microwave Vacuum Drying of Duck Egg White Protein Powders

High energy consumption during freeze drying (FD) is a major concern that limits its application on common food product manufacturing. In this research, fresh duck egg white protein (FDEWP) powder and desalted duck egg white protein (DDEWP) powder were obtained by a combined two-stage tandem drying technologies (FD and microwave–vacuum drying [MVD]) in order to reduce energy consumption while maintaining good product quality. The results showed that the drying time for the FDEWP and DDEWP powders was significantly decreased by FD + MVD compared to those obtained by the FD-only process. The FDEWP powders dried by FD + MVD had a better color (higher L* and lower b*), lower apparent density, and lower foaming stability but higher emulsifying index than those dried by FD only. The DDEWP powder dried by FD + MVD had a product quality similar to that of FDEWP powder, suggesting that the DDEWP powder could be widely used as a food ingredient.

Effects of additives on the foaming properties of Aculyn 22 and Aculyn 33 polymeric solutions

Foam stability and foam drainage of aqueous solutions of Aculyn™ 22 and Aculyn™ 33 polymers are considered. Measurements of both bulk and surface rheology of A22 and A33 solutions in the presence of sodium chloride and iso-propanol are performed for the polymer concentrations 1–1.5%. Properties of mixtures of these polymers are investigated. Addition of iso-propanol does not change bulk properties of the A33 solutions but decreases their surface viscoelasticity. Addition of iso-propanol decreases bulk viscosity as well as the bulk and surface viscoelastic moduli of the A22 solutions and moves the region of pronouncing shear thinning behaviour to the smaller shear rates. The last effect depends on the salt concentration. Solutions of both polymers form foams, which are stable during several hours. Characteristic time of foam drainage increases with the polymer concentration and decreases with the salt concentration and iso-propanol content. The decrease in the surface viscoelastic modulus results in faster foam coarsening and lower foam stability.

Effect of Xanthan and Arabic Gums on Foaming Properties of Pumpkin (Cucurbita pepo) Seed Protein Isolate

&lt;p&gt;Understanding how foaming properties of proteins are affected by factors such as pH, salt concentration and temperature is essential in predicting their performance and utilisation. In this study, the effects of pH and salt concentration were studied on the foaming properties of pumpkin seed protein isolate (PSPI) and PSPI- xanthan (XG)/Arabic (GA) gum blends. The foaming properties of the PSPI-GA/XG blends were also compared with egg white. Foam stability (FS) was significantly affected by pH with PSPI: GA (25:4) and PSPI: XG (25:1) having a significantly higher stability at pH 2 with the lowest foam stability at pH 4. Sodium chloride (0.2-1.0 M) did not significantly affect foaming properties although PSPI: GA (25:4) had the highest FC (89.33 ± 3.24%) and FS (76.83 ± 1.53 min) at 0.2 M sodium chloride concentration. The foaming capacity (FC) of PSPI: GA (25:4) blend (128.00 ± 0.91%) was significantly higher (&lt;em&gt;p &lt;/em&gt;&lt;em&gt;&amp;lt; &lt;/em&gt;0&lt;em&gt;.&lt;/em&gt;05) than that of egg white (74.00 ± 1.33%) but its FS was significantly lower. It was further revealed that the FC of egg white (74.00 ± 1.33%) was comparable to the PSPI:XG (25:1) blend (74.00 ± 1.46%) but the FS for egg white (480.00 ± 2.67 min) was significantly higher (&lt;em&gt;p &lt;/em&gt;&lt;em&gt;&amp;lt; &lt;/em&gt;0&lt;em&gt;.&lt;/em&gt;05) than the FS (116.21 ± 0.86 min) of PSPI:XG (25:1). The foaming properties of PSPI and PSPI-xanthan (XG)/Arabic (GA) blends were significantly affected by pH. Optimum foaming properties, PSPI:XG (25:1) and PSPI:GA (25:4) were observed at pH 2 and heat treatment temperature of 80 ºC.&lt;/p&gt;

Effect of Variations in the Fatty Acid Chain of Oligofructose Fatty Acid Esters on Their Foaming Functionality

In this article the effect of variations in the fatty acid chain of oligofructose fatty acid esters (OFAE) on foamability and foam stability is described. First, oligofructose (OF) mono-esters containing saturated fatty acid chains ranging between C4 and C18 were studied. Additionally, a mono-ester containing a C16 mono-unsaturated fatty acid chain and a C12 di-ester were studied. Finally, to investigate the influence of the size of the hydrophilic group, commercially available sucrose esters were studied. The surface tension and surface rheological properties of air/water interfaces stabilized by the esters were determined, as well as the foaming properties of the esters, at a bulk concentration of 0.2 % (w/v). OF mono-esters with intermediate fatty acid chain lengths (C10-C16) were able to migrate quickly to the interface producing foams with small bubbles (0.4 mm), a relatively narrow bubble size distribution, and a high stability. For oligofructose mono-esters containing fatty acids C4 and C8, the bulk concentration of 0.2 % (w/v) was below the CMC, resulting in insufficient surface coverage, and low foamability and foam stability. The OF C18 mono-ester and the OF C12 di-ester were slow to migrate to the interface resulting in low foamability. Despite similar surface tension values, the foam half-life time of OFAE was higher than of the corresponding sucrose esters. OFAE gave higher surface dilatational moduli compared to sucrose esters. Based on the frequency dependence of the modulus and analysis of Lissajous plots, we propose that OFAE may be forming a soft glass at the interface.

Chemical composition and some functional properties of soluble fibro-protein extracts from Tunisian date palm seeds

This study is a contribution to give value addition to date palm seeds by extracting an enriched fibroprotein fraction (DSFPE) and to examine the effect of pH on some of its functional properties. For this purpose, DSFPE was prepared from water soluble extracts of defatted Deglet Nour and Allig seeds and obtained by precipitation at pH 4.5. Then, DSFPE was examined for their proximate chemical composition. Significant differences were observed between Deglet Nour and Allig DSFPE: Carbohydrate was 64 against 58%, protein was 33 against 38%, and ash was 2 against 3%, respectively. Glutamic acid presented the largest amount, varying from 17.14% for Deglet-Nour DSFPE to 14.71% for the Allig DSFPE. The essential amino acids (lysine, leucine, threonine, methionine, valine, isoleucine and phenylalanine) were present in the DSFPE of the two studied varieties. Effect of pH on colour and some functional properties were analysed. Colour profiles of Deglet Nour and Allig water soluble extracts were affected by pH (2 to 10). Minimum protein solubility was obtained at pH 3.5 to 4.5 and the maximum at pH 10. Water holding capacity (WHC) and oil holding capacity (OHC) of Deglet Nour and Allig DSFPE were 3.50 to 4.50 g H2O g -1 of DSFPE and 5.50 to 6.10 g oil g -1 DSFPE respectively. Emulsion and foam proprieties were analysed at pH 7 and 10. DSFPE presented a slightly higher foam capacity (11 to 14 cm) and lower foam stability at pH 7 or 10. Emulsion capacity of DSFPE was significantly higher at pH 10 (2800 to 3000 ml oil g -1 of protein) than those at pH 7 (2000 to 2400 ml of oil g -1 of protein). Emulsion stability was improved with increase in pH from 7 to 10. These results suggested that the DSFPE have a good potential in food industry and can be used to improve the techno-functional quality for neutral and alkaline food applications with a high commercial value.

Application Property and Structural Characteristics of Bark Lignosulfonate Superplasticiser

The application property and structural characteristics of bark lignosulfonate (LS) was studied. Results showed that bark LS had perfect application property in concrete. The fluidity of cement paste was 214mm, which was 87.0% of commercial superplasticiser of naphthalene sulfonate; the loss on fluidity of cement paste of bark LS was very small, which was much better than that of naphthalene sulfonate. The loss on fluidity of cement paste of bark LS after 60 min was only 5.6%, but that of naphthalene sulfonate was 30.6%. Bark LS had low foaming capacity and high foam stability. Surface tension of 1% bark LS solution was 48.1 mN/m. Structural characteristics of bark LS was also studied. It showed that the reason that bark LS had good application property was that it had high content of hydrophilic sulfonic group, carboxyl group and phenolic hydroxyl group, and uniform molecular weight distribution.

Synergistic Effect of High and Low Molecular Weight Molecules in the Foamability and Foam Stability of Sparkling Wines

The foam of sparkling wines is a key parameter of their quality. However, the compounds that are directly involved in foam formation and stabilization are not yet completely established. In this work, seven sparkling wines were produced in Bairrada appellation (Portugal) under different conditions and their foaming properties evaluated using a Mosalux-based device. Fractionation of the sparkling wines into four independent fractions, (1) high molecular weight material, with molecular weight higher than 12 kDa (HMW), (2) hydrophilic material with molecular weigh between 1 and 12 kDa (AqIMW), (3) hydrophobic material with molecular weigh between 1 and 12 kDa (MeIMW), and (4) hydrophobic material with a molecular weight lower than 1 kDa (MeLMW), allowed the observation that the wines presenting the lower foam stability were those that presented lower amounts of the MeLMW fraction. The fraction that presented the best foam stability was HMW. When HMW is combined with MeLMW fraction, the foam stability largely increased. This increase was even larger, approaching the foam stability of the sparkling wine, when HMW was combined with the less hydrophobic subfraction of MeLMW (fraction 3). Electrospray tandem mass spectrometry (ESI-MS/MS) of fraction 3 allowed the assignment of polyethylene glycol oligomers (n = 5-11) and diethylene glycol 8-hydroxytridecanoate glyceryl acetate. To observe if these molecules occur in sparkling wine foam, the MeLMW was recovered directly from the sparkling wine foam and was also analyzed by ESI-MS/MS. The presence of monoacylglycerols of palmitic and stearic acids, as well as four glycerylethylene glycol fatty acid derivatives, was observed. These surface active compounds are preferentially partitioned by the sparkling wine foam rather than the liquid phase, allowing the inference of their role as key components in the promotion and stabilization of sparkling wine foam.

Profile and functional properties of seed proteins from six pea (Pisum sativum) genotypes.

Extractability, extractable protein compositions, technological-functional properties of pea (Pisum sativum) proteins from six genotypes grown in Serbia were investigated. Also, the relationship between these characteristics was presented. Investigated genotypes showed significant differences in storage protein content, composition and extractability. The ratio of vicilin:legumin concentrations, as well as the ratio of vicilin + convicilin: Legumin concentrations were positively correlated with extractability. Our data suggest that the higher level of vicilin and/or a lower level of legumin have a positive influence on protein extractability. The emulsion activity index (EAI) was strongly and positively correlated with the solubility, while no significant correlation was found between emulsion stability (ESI) and solubility, nor between foaming properties and solubility. No association was evident between ESI and EAI. A moderate positive correlation between emulsion stability and foam capacity was observed. Proteins from the investigated genotypes expressed significantly different emulsifying properties and foam capacity at different pH values, whereas low foam stability was detected. It appears that genotype has considerable influence on content, composition and technological-functional properties of pea bean proteins. This fact can be very useful for food scientists in efforts to improve the quality of peas and pea protein products.

Effect of Extraction Temperature on Functional Properties and Antioxidative Activities of Gelatin from Shark Skin

Physico-chemical properties, functional properties, and antioxidative acitivities of gelatin from the skins of brownbanded bamboo shark (BBS; Chiloscyllium punctatum) and blacktip shark (BTS; Carcharhinus limbatus), as affected by extraction temperature, were investigated. α-Amino acid group content and surface hydrophobicity of both gelatins from both species increased as the extraction temperature increased (P < 0.05). Both gelatins had a high solubility (more than 80%) in a wide pH range (1–10). Both gelatins extracted at 60 °C exhibited the highest emulsion activity index (EAI), emulsion stability index (ESI) and foam expansion (FE). The lowest foam stability (FS) was obtained when gelatin was extracted at 75 °C (P < 0.05). The BBS gelatin had lower EAI, ESI, and FE than did BTS gelatin. Nevertheless, a higher FS was found in the former (P < 0.05). Antioxidative activities of both gelatins increased with coincidental increase in α-amino group content as the extraction temperature increased (P < 0.05). The BTS gelatin generally exhibited the higher antioxidative activities, compared with the BBS gelatin (P < 0.05). Gelatin extracted at 60 °C showed the highest interfacial properties, while those extracted at higher temperature (75 °C) had enhanced antioxidative activities. Extraction temperature may therefore be regulated to maximize applications.

Foaming and Emulsifying Properties of Porcine Red Cell Protein Concentrate

This work focuses on studying the effects of pH (7.0 and 4.5) and protein concentration on the foaming and emulsifying properties of fresh (F) and spray-dried (SD) porcine red cell protein (RCP) concentrates in order to evaluate the proper use of this blood protein as a functional food ingredient. Also, protein solubility is measured through the pH range from 3.0 to 8.0. In each case, all concentrates show a high solubility, although this is significantly affected by pH. Spray drying slightly reduces the solubility at mild acid and neutral conditions. The foaming capacity is found to be dependent on pH as well as on the drying treatment. SD-RCP concentrates show better foaming capacity than F-RCP. The minimum protein concentration required to attain the highest foaming capacity is found under acid pH for the spray-dried concentrates. Although F-RCP shows low foam stability at acid and neutral pH, spray drying and protein content enhance the stability of foams. Emulsifying properties show dependence on pH as well as on protein content. Furthermore, spray drying affects the emulsifying properties but in different ways, depending on pH and protein concentration.

Aqueous foam stabilized by hydrophobically modified silica particles and liquid paraffin droplets

The foamability and foam stability of hydrophilic silica particles (A200) and cationic surfactant cetyltrimethylammonium bromide (CTAB) dispersion in the presence and absence of liquid paraffin were evaluated by interface tension, zeta potential and dilatational rheology. At low surfactant concentration, both the foamability and foam stability of A200/CTAB dispersion in the presence of liquid paraffin are decreased, due to the low coverage degree of silica particles on the air/water interface of the foam films. At the intermediate surfactant concentration, in the absence of liquid paraffin, the foam stability is enhanced by the adsorption of silica particles on the air/water interface. In the presence of liquid paraffin, there is a synergistic stabilization by the adsorption of hydrophobically modified silica particles and oil droplets on the air/water monolayer of foam film. At the same surfactant concentration range, the foamability increases until a plateau value is reached. At high surfactant concentration, the surface of silica particles is hydrophilic and so the silica particles become to disperse in the aqueous phase again. In this case, both the air/water and oil/water interfaces are mainly covered by CTAB molecules, resulting in a slight decrease of foam stability.

Foam-Stabilizing Effects and Cling Formation Patterns of Iso-α-acids and Reduced Iso-α-acids in Lager Beer

Foam-stabilizing properties and cling formation patterns of iso-alpha-acids and reduced iso-alpha-acids were investigated using an unhopped lager beer. Unhopped beer was dosed with iso-alpha-acid (Iso), rho-iso-alpha-acid (Rho), tetrahydro-iso-alpha-acid (Tetra), and hexahydro-iso-alpha-acid (Hexa), separately, over a range of concentrations from 2 to 10 ppm. A uniform foam was created by Inpack 2000 Flasher Head and was measured by a NIBEM Foam Stability Tester (NIBEM-TPH) followed by a NIBEM Cling Meter (NIBEM-CLM) to determine the relationship between the concentration and NIBEM-30 and the cling formation ability of each compound. The foam-stabilizing power was determined to be Tetra, Hexa, Iso, and Rho from the strongest to weakest. Linear regression models were created using the NIBEM-TPH data set, and on the basis of 95% confidence intervals, the foam stability of Tetra or Hexa became significantly larger than that of Iso when 2.4 or 4.2 ppm of Tetra or Hexa was used as a replacement for Iso, respectively. Cling formation patterns could be categorized into three groups: "ring", "mesh", and "powdery". The control beer had the lowest foam stability and did not yield any foam cling.