Enhanced Foam Stability Research Articles

Whipped oil stabilised by surfactant crystals.

We describe a protocol for preparing very stable air-in-oil foams starting with a one-phase oil solution of a fatty acid (myristic acid) in high oleic sunflower oil at high temperature. Upon cooling below the solubility limit, a two-phase mixture consisting of fatty acid crystals (length around 50 μm) dispersed in an oil solution at its solubility is formed which, after whipping, coat air bubbles in the foam. Foams which do not drain, coalesce or coarsen may be produced either by increasing the fatty acid concentration at fixed temperature or aerating the mixtures at different temperatures at constant concentration. We prove that molecular fatty acid is not surface-active as no foam is possible in the one-phase region. Once the two-phase region is reached, fatty acid crystals are shown to be surface-active enabling foam formation, and excess crystals serve to gel the continuous oil phase enhancing foam stability. A combination of rheology, X-ray diffraction and pulsed nuclear magnetic resonance is used to characterise the crystals and oil gels formed before aeration. The crystal-stabilised foams are temperature-sensitive, being rendered completely unstable on heating around the melting temperature of the crystals. The findings are extended to a range of vegetable oil foams stabilised by a combination of adsorbed crystals and gelling of the oil phase, which destabilise at different temperatures depending on the composition and type of fatty acid chains in the triglyceride molecules.

Effect of Xanthan Gum on the Performance of Aqueous Film-Forming Foam

Solution properties of aqueous film-forming foam (AFFF) formulations containing different xanthan gum contents were investigated first by varying the mass fraction of xanthan gum in the range of 0.1–0.5%. Foam properties and fire-extinguishing performance of the AFFF formulations were then evaluated. Results indicated that xanthan gum content slightly affected surface tension of foam solutions. However, xanthan gum significantly affected viscosity of AFFF concentrates. Foaming of the AFFF formulations was hardly affected by xanthan gum, but foam stability of the compounds was obviously enhanced with the addition of xanthan gum. Optimal xanthan gum content was determined as 0.3%, which resulted in the shortest 90% control time and fire extinguishment time. Burnback time of foams increased with the addition of xanthan gum because of the enhanced foam stability.

Foams stabilized by tricationic amphiphilic surfactants

Abstract The unique surface properties of amphiphilic molecules have made them widely used in applications where foaming, emulsifying or coating processes are needed. Novel surfactant architectures with multi-cephalic and multi-tailed molecules have reportedly enhanced their anti-bacterial activity in connection with tail length and the nature of the head group, but their ability to produce and stabilize foam is mostly unknown. Here we report on experiments with tris-cationic, triple-headed, double- and single-tailed amphiphiles and their foamability and foam stability with respect to head group, tail number and tail length. The amphiphiles are composed of an aromatic mesitylene core and three benzylic ammonium bromide groups, with alkyl chains attached to one or two of the head groups. Whereas shorter (14 carbons in length) double-tailed molecules are found to produce very stable foams, foams made with single tail molecules of the same length show poor foamability and stability, and foams with longer (16 carbons in length) double-tail molecules do not foam with the methods used. By contrast, the structure of the non-tail-bearing head group (trimethylammonium vs. pyridinium) has no impact on foamability. Furthermore, observations of the coarsening rate at nearly constant liquid content indicate that the enhanced foam stability is a result of lower gas permeability through the surfactant monolayer. Finally, the critical aggregation concentration (CAC) of the surfactants demonstrates to be a good predictor of foamability and foam stability for these small molecule surfactants. These results inform how surfactant architecture can be tailored to produce stable foams.

Interfacial and foaming characterisation of mixed protein-starch particle systems for food-foam applications

This work presents mixed protein-starch systems as effective foaming agents and stabilisers. The starch size and hydrophobicity play a dominant role in determining the levels of synergy observed. Egg White Protein (EWP) and Pea Protein Isolate (PPI) were selected at two concentrations (0.5, 1 wt. %) along with three starch species of concentrations between 0.5, 1, 3 & 5wt. %. Two commercial OSA-modified starches are compared to a native granule and its heat-treated counter part. The system's effectiveness to incorporate air (overrun) as well as its capacity to hold structure (half life) is evaluated. starch's physical properties (contact angle and size) and their effect on the nature of the Air/Water (A/W) interface (interfacial dilatation rheology, surface tension) are also explored. The effect of protein species as well as starch size and hydrophobicity on foam stability is determined and discussed. The study demonstrates that addition of OSA modified starch (0–5wt%) to (EWP) foams can enhance foam stability by up to 1200% without compromising the foaming capacity, mainly due to a hypothesised exclusion volume effect. Where as the larger heat-treated starch granule is found to increase stability of wet foams by 800%, through a combination of mechanisms.

Enhanced foam stability by adding comb polymer gel for in-depth profile control in high temperature reservoirs

Abstract A long-term stability of gel enhanced foam as an in-depth profile control agent in high temperature reservoirs was successfully prepared by adding comb polymer gel. The increased viscosity of gel brings a negative effect on surface tension which reduces the gel enhanced foam volume. In turn, the increased viscosity could enhance the thickness and strength of foam film which increases foam stability and plugging capacity in porous media. The morphology results show that the gel enhanced foam has a thicker bubble film which enhances its foam stability. The effect of injection mode, gas–liquid ratio, gas injection velocity and formation permeability on the plugging capacity was investigated by single sand-pack experiments. When the gas–liquid ratio and gas injection velocity were respectively set at 1:1 and 0.5 ml/min, co-injection of gel enhanced foaming solution and gas could obtain a better plugging capacity in high permeability sand-packs. Parallel sand-pack experiments show that the profile improvement capacity of high formation permeability ratio is much better than that of low formation permeability ratio. The visual simulation experiment was also conducted to illustrate the flowing behavior of gel enhanced foam. By Jiamin effect or Jamin superimposed effect, directly plugging and bridging in the large pore space, the gel enhanced foam can effectively reduce the permeability of porous media in high permeability zones and divert fluid into low permeability zones, thus increases the swept volume. The treatment has been successfully used in Henan oilfield of China which provides a reference to water production control in other similar high temperature oilfields.

Three-phase-foams for foam concrete application

Minerally bound foams are used throughout in the building industry for their combination of load bearing capacity and thermal insulation. Nowadays this can be achieved by lightweight concretes, especially with aerated and foam concretes. Blocks made of aerated concrete as well as prefabricated components are well-known. Typically the mechanical properties are enhanced by autoclaved treatment and thus result in high energy consumption. Also, the production of aerated concretes is factory based due to stationary autoclaves and the components are limited in their dimensions. Another category of mineral foams are foam concretes. They are produced by mixing a mortar and aqueous tensides or protein foam. The problem in production is to get a controlled and homogeneous air entry and thin, high strength borders surrounding the air pores. The latter has to be achieved on the basis of a dense packing of the materials within the borders. On a laboratory scale, significantly enhanced foam stability could be achieved and the most stable samples showed no destabilizing effects. The improved handling, workability and reproducibility of the modified foam are also leading to an increased reproducibility of the foam concrete quality. The study of the influence of three-phase-foams on microstructure, phase development and mechanical properties of lightweight concrete will be shown and explained.

Effects of environmental factors on functional properties of Chinese chestnut (Castanea mollissima) protein isolates

Chestnut is a nutritious food source. The effects of physical force on the functional properties of chestnut protein isolates were investigated. Maximum protein solubility, emulsion activity, emulsion stability, and foam capacity, as well as minimum protein solubility, emulsion activity, and foam capacity were observed at pH 12 and 4, respectively. The highest foam stability rate was observed at pH 4, particularly after 60 min. At the same ionic strength, the protein in NaCl showed better solubility than CaCl2. The presence of Ca2+ significantly enhanced the foam capacity and stability of chestnut protein, and the maximum foam capacity was 77.3 % at 0.8 mol/L ionic strength of Ca2+. Sugar could enhance foam stability but inhibit foam capacity, and appropriate concentrations (0.05–0.1 mol/L) increased emulsion activity and stability. The chestnut protein isolates had good emulsification and foam properties, and can be used as additives in food products requiring specific functional properties.

EFFECTS OF IONIC STRENGTH ON THE FOAMING PROPERTIES OF WHEY PROTEIN ISOLATE AND EGG WHITE IN THE PRESENCE OF POLYSACCHARIDES

ABSTRACT The effect of ionic strength on the foaming properties of whey protein isolate (WPI) and egg white (EW) proteins was investigated in protein–polysaccharide mixtures in the presence of NaCl and pectin/guar gum. Foaming properties were assessed based on the total foam volume produced and foam stability as the time required for the collapse of the foam to half of its initial foam volume. The foam volume and stability of WPI significantly (P < 0.05) increased when NaCl concentration rose from 0 to 0.05 M, and decreased with further increase with and without polysaccharides. Initial increase in salt concentration up to 0.03 M improved both foam volume and stability of EW solutions with and without polysaccharides. Further increase in salt concentration progressively reduced the foaming properties of EW. Foam volume of both WPI and EW decreased with the addition of polysaccharides. However, the addition of polysaccharide had a significant effect (P < 0.05) on foam stability. PRACTICAL APPLICATIONS Food dispersions often take the form of emulsions and foams. Whey protein isolate (WPI) and egg white (EW) proteins are extensively utilized foaming agents in the food industry. Stability is an important property of food dispersions, since consumer perception of quality is influenced by appearance and would be controlled by the addition of polysaccharides. Real food systems very often contain a mixture of proteins and other ingredients such as sugars, salt, etc. The addition of such molecules may affect the functionality of proteins, which may result in gain or loss of handling properties. However, there has been limited reported work on the effect of ionic strength on the foaming properties of WPI and EW in the presence of polysaccharides. To overcome this inadequacy, in this study, the effect of ionic strength on the foaming properties of proteins in the presence of an ionic and a neutral polysaccharide was investigated. Results showed that the addition of salt up to a certain level enhanced foam stability, both in the absence and presence of polysaccharides, while further increase in salt concentration decreased stability. Therefore, the ionic strength or salt concentration in food foam would be determined carefully to have good stability during storage.

Importance of Tetrahydroiso -acids to the Microbiological Stability of Beer

While beer provides a very stable microbiological environment, a few niche microorganisms are capable of growth in malt, wort, and beer. The production of off-flavors and development of turbidity in the packaged product are due to the growth and metabolic activity of wild yeast, certain lactic acid bacteria (LAB) and anaerobic Gram-negative bacteria. Beer also contains bitter hop compounds, which are toxic to Gram-positive and Gram-negative bacteria, and contribute to preventing the spoilage of this beverage. In the boiling process, the hop alpha-acids (humulones) are isomerized into iso alpha-acids. These products are responsible for the bitter taste of beer, but they also play an essential role in enhancing foam stability. Antibacterial activity of iso alpha-acids and their hydrogenated derivates (rhoiso alpha-acids and tetrahydroiso alpha-acids) in MRS broth and beer have been evaluated against different LAB (Lactobacillus and Pediococcus) for the determination of their beer-stabilizing capabilities. Besides this, we have determined the minimum inhibitory concentration and the bacteriostatic effect of each compound against Pediococcus. We found that tetrahydroiso alpha-acids (added directly to beer during production processes) are the compounds that present the greatest antibacterial activity against the main agents implicated in beer spoilage.

Defect and microstructural evolution during drying of soapnut-based alumina foams

The present study demonstrates the use of soapnut, a naturally occurring surfactant for producing alumina ceramic foams. A range of slurry compositions with soapnut amounts ranging from 2 to 20 wt% in water, alumina loading of 35–55 vol% were studied. Though all slurry compositions foamed when subjected to mechanical agitation the formation of green ceramic foams free of macroscopic defects was found to be strongly dependent on conditions during drying of foamed slurries. Addition of guar gum to the slurries was shown to enhance foam stability and thus produce defect-free foams from compositions that otherwise either collapsed or resulted in other macroscopic defects during drying. Drying conditions also had a strong effect on microstructural parameters such as cell size and cell connectivity. Soapnut-based foams appear to have a greater connectivity between cells than foams produced by other comparable processes.

Effect of carbohydrates on the emulsifying, foaming and freezing properties of whey protein suspensions

The aim of this study was to examine interactions between whey proteins (whey protein isolate (WPI), whey protein concentrate (WPC) and β-lactoglobulin) and carbohydrates (glucose, sucrose, starch and inulin) on some physical and functional properties of whey proteins and carbohydrates suspensions (10% dry matter (w/v)). Model systems were therefore investigated related to their foam expansion and foam stability. Carbohydrate addition in model suspensions of whey proteins resulted in significantly ( P < 0.05) enhanced foam stability of protein suspensions (FSI; MFS). Model systems were also analyzed for emulsion activity index (EAI) and emulsion stability index (ESI) by the turbidometric technique. EAI and ESI values increased significantly ( P < 0.05) in model suspensions prepared with WPI and β-lactoglobulin in combination with mono and disaccharides, while significant decrease ( P < 0.05) were remarked in model suspensions prepared with inulin and starch addition. The phase-transition temperatures of investigated model systems were determined using differential thermal analysis with continuous scanning. In all model suspensions, significant lowering ( P < 0.05) of initial freezing temperature has occurred.

Effect of thermal treatment on interfacial properties of β-lactoglobulin

The changes in the secondary conformation and surface hydrophobicity of β-lactoglobulin subjected to different thermal treatments were characterized at pH values of 7, 5.5 and 4 using circular dichroism (CD) and hydrophobic dye binding. Heating resulted in a decrease in α-helix content with a corresponding increase in random coil at all pH values, this change being more pronounced for small heating times. Heating also resulted in an increase in surface hydrophobicity as a result of partial denaturation, this increase being more pronounced at pH 4. Thermal treatment resulted in a shift of the spread monolayer isotherm at air–water interface to smaller area per molecule due to increased flexibility and more loop formation. Thermal treatment led to an increase in interfacial shear elasticity and viscosity of adsorbed β-lactoglobulin layer at pH 5.5 and 7. Interfacial shear elasticity, shear viscosity, stability of β-lactoglobulin stabilized emulsion and average coalescence time of a single droplet at a planar oil–water interface with adsorbed protein layer exhibited a maximum for protein subjected to 15 min heat treatment at pH 7. At pH 5.5, the interfacial shear rheological properties and average single drop coalescence time were maximum for 15 min heat treatment whereas emulsion stability was maximum for 5 min heat treatment. At pH 7, thermal treatment was found to enhance foam stability. Analysis of thin film drainage indicated that interfacial shear rheological properties do not influence thin film drainage.

Beer Polypeptides and Silica Gel Part I. Polypeptides Involved in Haze Formation

Beer contains approximately 500 mg/L protein depending on the brewing procedures employed. This protein is in the form of polypeptides, the majority of which lie within the 10–40 kD size range. Some of these polypeptides are responsible for causing colloidal haze, others enhance foam stability and the remainder appear to have no function in beer except to contribute to mouth-feel. The polypeptides responsible for haze formation are those that can combine with polyphenols to produce a visible cloudy haze. This is undesirable as it can have a negative effect on the beer's shelf life. One way to reduce this effect is to remove these polypeptides using silica gels. It is important that this removal is selective, and the desirable foam enhancing polypeptides are not removed. Data will be presented to show that beer polypeptides are glycosylated and that silica preferentially adsorbs glycoproteins, particularly those with protein components rich in the amino acid proline. The molecular size and composition of glycoproteins recovered from untreated beer, cooked adjunct, silica exposed to beer and beer aged for one year are presented. Glycoproteins involved in foam, and the apparently functionless polypeptides, will be discussed in a subsequent paper.

Factors Contributing to Petroleum Foaming. 2. Synthetic Crude Oil Systems

The influence of petroleum asphaltenes and resins on stabilizing model oil foams comprised of light mineral oil mixed with toluene (minerol) was investigated. Two factors contribute significantly to foam volume and stability: bulk viscosity and asphaltene state of aggregation. An increase in bulk viscosity was found to increase foam stability as gauged by the total time required for a foam to collapse. Asphaltene aggregation is governed primarily by the solvent aromaticity and resin/asphaltene (R/A) ratio. There is a threshold size in the state of asphaltene aggregation above which the ability of these aggregates to stabilize foams is markedly reduced. This appears to be closely related to asphaltene flocculation and precipitation at compositions beyond the solubility limit of the asphaltenes. Solvent systems generating the highest foam volume were found to reduce the air-oil surface tension to the greatest extent. Addition of an asphaltene dispersant increased the foamability of asphaltenes in minerol and seems to indicate that asphaltenes enhance foam stability when they are well dispersed or dissolved and in solvent mixtures in which they are highly surface active. By analogy to the role of asphaltenes in stabilizing emulsions, the highest foam stability was observed for asphaltenes near their solubility limit, the thermodynamic state at which asphaltenic aggregates are most surface-active. Addition of resins, similar to addition of dispersants, increased foam stability, presumably by decreasing the size of asphaltene aggregates.

Foam Boosting by Amphiphilic Molecules in the Presence of Silicone Oil

The effect of several surface active additives (called for brevity “foam boosters”) on the foaming properties of solutions of the anionic surfactant sodium dodecyl polyoxyethylene-3 sulfate (SDP3S) is studied in the presence of silicone oil. As foam boosters we study lauryl amide propyl betaine (LAPB), lauryl acid diethanol amide (LADA), lauryl alcohol (LA), and a nonionic surfactant, which is a glycerin derivative (denoted as Booster A). All these substances are used or have a potential to be used as commercial foam boosters in different formulations. The silicone oil is predispersed in the foaming solution in the form of micrometersized droplets, which act as foam breaking entities (antifoams). A set of several experimental methods is employed to clarify the main characteristics that are affected by the boosters. Foam tests show that LADA and Booster A enhance mainly the foaminess of the solutions and that LA improves mainly the foam stability, whereas the LAPB increases both. The enhanced foam stability in the presence of LAPB and LA correlates well with the higher barriers to oil drop entry, measured by the film trapping technique (FTT). No correlation of the film stability with the so-called entry, E, spreading, S, and bridging, B, coefficients of the silicone oil is observed. Optical observations of foam films show that the boosting effect cannot be explained by a reduced rate of the foam film thinning. Only the addition of LA leads to deceleration of the final stage of the film thinning process. The obtained results demonstrate that the various boosters affect different characteristics of the foaming solution, and which of the additives is appropriate for a particular application depends strongly on the time-scale of interest.

Stabilization of emulsions and foams using barley β-glucan

Barley β-glucan (BBG) is receiving increasing attention as a food hydrocolloid. Stability of foams and emulsions was assessed using whey protein concentrate (WPC) as an emulsifier and foaming agent, and BBG gum extracted at pilot plant or laboratory scale as a stabilizer. WPC had a significant lowering effect ( P⩽0.05) on surface tension of water and water–oil interfacial tension, while the effect of β-glucan was time dependent. Differential scanning calorimetry (DSC) showed that BBG formed a gelled network, responsible for stabilizing, that melts at 58–62°C. Reversible gels of BBG melt around 63°C. Emulsion (50% o/w) droplet size decreased several fold when prepared with BBG gum and phase separation was substantially decreased. Foam volume and 50% drainage were significantly ( P⩽0.05) improved upon addition of β-glucan. Sugar significantly enhanced foam stability only when used together with β-glucan. BBG shows potential as a stabilizer in foam- and emulsion-type food products.

Modified Soy Proteins with Improved Foaming and Water Hydration Properties

ABSTRACTSoy proteins were modified by alkali treatment at pH 10.0, followed by papain hydrolysis. Solubility, water hydration capacity (WHC), surface hydrophobicity, foaming and emulsifying properties of unmodified, alkali‐treated, and papain‐modified soy protein (PMSP) were compared. PMSP exhibited higher solubility (100% at pH &gt; 7.0), WHC (3.13) and hydrophobicity (40.8) than unmodified soy protein which had solubility 68.5%, WHC 0.21, and hydrophobicity 8.1. The PMSP had foaming capacity (22.0 mL) similar to egg white (21.2 mL) at pH 7.0; and enhanced foam stability (36.4) compared to the unmodified control (32.9). In general, alkali‐treated soy had lower functional properties. Emulsifying properties of PMSP and alkali treated soy were unchanged by the modification. PMSP could be used as an egg white substitute in foaming applications at neutral pH.