The emulsifying and foaming properties of Amuniacum gum (Dorema ammoniacum) in comparison with gum Arabic

Abstract In this study, the emulsifying and foaming properties of a novel exudate gum from Dorema ammoniacum (AMG) were assessed in comparison with the well‐known gum Arabic from Acacia tree (GAC). The sunflower oil‐based emulsion (10% v/v) containing various concentrations (5%–15% w/v) of AMG and GAC was prepared. At all concentrations, AMG showed higher surface and interface activity than GAC. Increasing in AMG and GAC concentrations caused to increase and decrease in Z average, respectively. Overall, the GAC‐stabilized emulsion showed lower Z average and PDI value than the AMG‐stabilized emulsion during storage time. The sample containing AMG showed higher emulsion capacity and lower emulsion stability in comparison with the one containing GAC at all concentrations. The storage stability decreased and increased with increasing in AMG and GAC concentrations, respectively. After two‐week storage, the emulsions containing 10 and 15% AMG showed higher phase separation than those containing GAC; however, this was opposite about sample containing 5% AMG. At thermal, centrifuge, and freezing conditions, the emulsion containing 5% AMG indicated significantly higher stability than GAC samples; however, at higher concentration, opposite effect could be observed. The foaming capacity of the samples containing AMG increased from 81% to 93% by increasing gum concentration from 5% to 15%. The solutions containing AMG showed higher foam capacity than control samples (without gum) and those containing GAC at all concentrations. Increasing in AMG and GAC concentrations slightly improved foam stability, and the highest value (92%) belonged to 15% AMG solution.

are related to their water holding capacity and their ability in the improvement of rheological properties. Oil-in-water emulsions are widely used in food, cosmetic, and pharmaceutical formulations. They are thermodynamically unstable systems, because the contact between oil and water molecules is energetically unfavorable. Several types of instability such as creaming, Ostwald ripening, flocculation, and coalescence of the oil droplets can lead to phase separation in emulsion (Sun, Zhou, Sun, & Zhao, 2013). In the formulation of kinetically stable emulsion systems, two types of ingredient are usually used: emulsifying agents and stabilizers.
Emulsifiers are surface active compounds that decrease surface tension and prevent droplet flocculation by adsorption on droplet surfaces. Stabilizers are hydrophilic biopolymers (proteins and polysaccharides), and they have ability of rheological modifications and induce long-term emulsion stability.
Hydrocolloids can increase viscosity of continuous phase in colloidal solutions (sol, emulsions, and foams) that results in retarding the movement of particle, droplets, and bubbles, which in turn leads to enhancing of stability. On the other hand, a few of them act as surface active compounds and are used as emulsifying and foaming agents (Dickinson, 2009). Surface activity of polysaccharides normally depends to the presence of two types of chemical agents in their structure: (a) hydrophobic components such as methyl or acetyl groups attached to the hydrophilic polysaccharide backbone (in hydrophobically modified starch/cellulose, tragacanth, and pectin) and (b) existence of small fractions of proteins linked covalently or physically to the polysaccharide (gum Arabic, some type of pectin, etc.) (Dickinson, 2009). Gum exudates such as gum Arabic (GA), tragacanth, karaya, and Ghatti are amongst the oldest natural gums and have been used for thousands of years in the food and pharmaceutical products (Verbeken, Dierckx, & Dewettinck, 2003). Gum Arabic is the most convenient hydrocolloid, which is used as an emulsifier in emulsions, and it is commonly used at high levels (up to 20% of the total emulsion) in emulsions containing small quantities of oil (Nissim Garti & Leser, 2001). In practice, high gum/oil ratio (~1:1) is required to produce fine stable emulsion droplets (D4, 3 ≪ 1 µm), so it is expensive to be used (Dickinson, 2009). Emanuel et al. (2016) reported that exudate gum from Prosopis alba is able to stabilize emulsions better than GA based on its lower droplet size distributions, higher z-potential, higher interfacial film elasticity, and lower values of the polydispersity and creaming indexes during storage. The study of Razavi, Cui, and Ding (2016) examined the surface activity of Balangu Shirazi and claimed that the surface tension of water at concentrations lower than 0.75% was reduced. In a recent study, Dabestani and Yeganehzad (2018) used a combination of Persian gum as an exudate gum with xanthan gum to have improving the foaming properties of the liquid egg white prior to pasteurization. The authors inferred that both hydrocolloids showed positive effects on foam stability; nevertheless, their negative effect on overrun and foam density was undeniable. Romdhane et al. (2017) studied the emulsifying and foaming properties of polysaccharide extracted from watermelon rinds (WMRP). Results showed that WMRP foam capacity and emulsifying property increased in a dose-dependent manner at a concentration range of 1%-4% and 2%-4%, respectively. Amuniacum gum is obtained from Dorema ammoniacum D. Don (Umbelliferae) exudate and also is locally known as Kandal, Vasha, and Koma-kandal in Persia. This gum exists in yellow colors and is consumed traditionally for the treatment of some diseases such as anthelmintic, gastrointestinal disorders, antispasmodic, and expectorant (Amin, 2005). There has been no report about the structurefunction relationship of this natural hydrocolloid. Therefore, the objective of current research study was evaluation of emulsifying and foaming properties of Amuniacum gum in comparison with gum Arabic.

| Materials
The AMG exudates were purchased from local herbal shops, Tabriz, Iran. For the comparison studies, commercial acacia gum (GAC) (generally referred as gum Arabic from Acacia tree) was purchased from Sigma-Aldrich, USA (GA:G9752). Sunflower oil was purchased from local shop, Tabriz, Iran. Other reagents were provided by industrial manufacturers in analytical grades.

| Extraction and purification of the AMG
Extraction and purification of the AMG was carried out based on a protocol by Saeidy et al. (2019) with modifications. Yellowish crude mucilage was milled to powder using blender. Extraction was carried out as dispersed mucilage in preheated distilled water with a water:mucilage ratio of 10:1 at a constant temperature of 50°C for 2 hr under mechanical stirring (200 rpm). The gum solution was stored overnight at 4°C for full hydration. Solution was centrifuged at 3,000 g for 30 min at 20°C, and then, the supernatant was collected, filtered (cloth filters), and precipitated using three volumes of 95% ethanol (w/v). Precipitation with ethanol removed lipophilic substances, pigments, and low molecular weight (LMW) proteins (Anvari et al., 2016). The sediment was collected, dried at room temperature, dissolved with 10 volumes of water (w/v), mixed with acetone for depigmentation, and precipitated with three volumes of ethanol (w/v) to increase its purity. The precipitate was collected as described previously and then was grounded and screened using mesh-18 sieve. This was packed and stored at a cool dry condition.

| Preparation of AMG and GAC solutions
In brief, AMG and GAC emulsions were prepared one day before emulsification by dissolving 5, 10, and 15% w/v of the gums in 60°C distilled water with a constant stirring for at least 12 hr using magnetic stirrer. Stock emulsions were stored at 4°C for at least 18 hr for complete hydration.

| Preparation of the emulsions
Oil-in-water emulsions were prepared by adding 10% v/v drop-wise of sunflower oil into the aqueous phase while stirring at 447.2 for 5 min using high-speed stirrer (Fater, Iran). The emulsion was prepared by homogenization at 4472g for 6 min at alternate cycles of homogenization (1 min) and rest (2 min). The whole process was carried out using ice bath to minimize possible lipid oxidations. Then, 0.02% v/v of sodium azide was added to the samples as antimicrobial agent. Each sample emulsion was prepared at five various concentrations for surface and interfacial tension measurements.
Concentrations included 15.00, 10.00, 5.00, 1.50, 1.00, and 0.5% w/v for AMG and GAC emulsions. Emulsions were prepared by dissolving samples in distilled water at 70°C for 12 hr with constant stirring followed by cooling at room temperature with stirring for 2 hr before the measurements.

| Surface and interfacial tensions
Surface tension of the air-water interfaces was assessed based on a method described by Izydorczyk, Biliaderis, and Bushuk (1991). Forces on the ring were measured as it moved upward from an airgum dispersion surface. Equal volumes of the emulsions (50 ml) were transferred into 100-ml glass beakers. Changes in the surface tension were recorded every 10 min at 22.0°C ± 0.5 for 2 hr. Values of the surface tension included the average of 12 measurements from 10 to 120 min. Sunflower oil was used for interfacial tension assessments. The oil was added to a constant volume of the aqueous gum emulsion and set for 3 min. The force needed to pull the Wilhelmy plate from one phase to another one was equal to interfacial tension. All assessments were carried out at 25°C.

| Droplet size, polydispersity index, and zetapotential
Droplet size distribution of the emulsions was studied at 25°C using dynamic light scattering instrument (Zetasizer Nano-ZS90, Malvern Instruments), immediately after preparation and subsequently at 25°C on days 3, 7, 14, and 30. The studies were carried out after appropriate dilutions of the emulsion samples using Milli-Q ultrapure water to avoid multiple scattering effects (Gu, Decker, & McClements, 2007). The Z-average diameter of the emulsion droplets, z-potential, and polydispersity index (PdI) were automatically calculated by the instrument as mean of ten reading values per sample. Refractive index values used for dispersed and continuous phases included 1.52 and 1.33, respectively.

| Optical microscopy
Microstructure of the emulsions was visualized using optical microscope (Leica Microsystems) equipped with a camera. Emulsions were gently agitated in glass test tubes before analysis to ensure their homogeneity and then were diluted using sodium dodecyl sulfate (1:40). A droplet of emulsion was transferred onto a microscope slide, covered by a cover-slip, and studied using digital USB camera linked to a light microscope. Images were recorded at 100× objective magnifications.

Emulsifying capacity
Fresh emulsions were centrifuged at 135.278g for 10 min. The emulsifying capacity (EC) was calculated based on the following formula by Jindal, Kumar, Rana, and Tiwary (2013a): where f ev was the final emulsion volume and I t was the total volume.

Stability during storage
A 10-ml freshly prepared emulsion was transferred into a test tube, and the tube was capped and stored at 25°C. Stability of the emulsion was monitored immediately after the preparation and subsequently on days 3, 7, 14, and 30 of storage. During storage, samples were separated to opaque cream layers at top and transparent serum layers at bottom. Then, initial height (H i ) and final height (H f ) of the emulsions were measured. Stability was expressed as the ratio of height of the final emulsion to initial height of the emulsion in tubes (Koocheki, Kadkhodaee, Mortazavi, Shahidi, & Taherian, 2009;Nikiforidis & Kiosseoglou, 2007).

Centrifuge stability measurement
Centrifugation method was used for ES by centrifugation 10 ml of emulsions at 1369g for 15 min. The ES was calculated as follows: where f ev was the final emulsion volume and I ev was the initial emulsion volume (Sciarini, Maldonado, Ribotta, Perez, & Leon, 2009).

Thermal stability
Emulsions were heated at 80°C for 30 min using water bath and then centrifuged at 3,500 rpm for 10 min. The ES was calculated as follows: where f ev was the final emulsion volume and I ev was the initial emulsion volume (Bi, Yang, Fang, Nishinari, & Phillips, 2017).

Freeze-thaw treatment
Effects of Freeze-thaw cycles on emulsions were assessed using a method previously described by Gu et al. (2007). Emulsion samples (10 ml) were incubated at −20°C for 22 hr. Then, samples were incubated at 40°C for 2 hr. This Freeze-thaw cycle was repeated tree times with creaming stability comparisons between the emulsion samples.

| Foam characterization
The AMG and GAC dispersions were prepared at 5%, 10%, and 15% w/v concentrations and stored at 4°C overnight. After complete gum hydration, 1% of ovalbumin (Applichem) was added to the samples and agitated vigorously for 4 min. Immediately after agitation, foam was gently transferred to a measuring cylinder (100 ml) and weighed.
The drained liquid was measured after 30 min. Foam, stability, and density values were calculated using the following equations: where i fv was the initial foam volume and t sv was the total suspension volume; where f fv was the foam volume after 30 min and i fv was the initial foam volume; and where m 100f was weight of 100 ml of foam (g) and V 100f was volume of 100 ml of foam (ml). All samples were prepared four times

| Statistical analysis
Data statistical analysis was carried out using ANOVA method.
Furthermore, Duncan's post hoc comparison was used with a significance level of p < .05. Data were analyzed using SPSS Software v.17.0 (SPSS Inc.). Charts were drawn using Origin 2018 Software (Origin Lab).

| Chemical composition
The protein and carbohydrate contents of gums directly affect their emulsifying properties. The chemical composition of AMG and GAC powders used in this study is shown in

| Surface and interface activity
Results of surface tension assessments of the AMG and GAC solutions are shown in Figure 1a. Surface tensions of both polysaccharide solutions were concentration-dependent, and it decreased with increasing of polysaccharide concentration. A sharp decrease was seen in both solutions from 0.5% to 5%, which shifted to a plateau when the concentration was greater than 5%. The surface tension decreased from 72.5 mNm −1 to 52 and 57 mNm −1 by AMG and GAC at 15% concentration, respectively.
Timilsena, Adhikari, Kasapis, and Adhikari (2016) suggested that at higher concentrations, surface active biopolymers have lower freedoms to move due to steric phenomenon and they migrate with difficulty to air-water surfaces. Upon increasing quantities of the hydrocolloids, diffusional transport to the air-water surface decreases due to the chain overlap or molecular flocking, which results less decrease in surface tension per unit of the gum concentration. At all concentrations, AMG showed higher surface activity than GAC, and as a result, lower surface tension could be observed which it could be attributed to lower molecular weight of AMC than GAC or having higher hydrophobic groups such as methyl on its backbone (Dickinson, 2003). Koocheki, Taherian, and Bostan (2013) and Najitabasi, Mohammad, and Razavi (2016) indicated that tendency to adsorb at air-water surface increased with decreasing of molecular weight of polysaccharides. Molecular weight has direct influence on viscosity. At the same concentration (5%), the viscosity of the emulsions was 0.1 and 0.3 Pa.s for AMG and GAC samples at a shear rate of 10 s −1 . Garti, Slavin, and Aserin (1999) (Huang, Kakuda, & Cui, 2001), which were lower than that at 0.5% AMG solution (63.5 mN/m). The 1.5% yellow mustard mucilage and pectin solution decreased surface tensions to 47 and 55 mN/m, respectively, which were lower than that in 1% AMG solution (60.2 mN/m) (Wu, Eskin, Cui, & Pokharel, 2015).
Results of interfacial tension measurements in the sunflowerwater emulsion containing AMG and GAC are presented in Figure 1b.
Interfacial activity of both gums was similar to behaviors observed for the surface tension. The oil-water interfacial tension decreased from 27 to 8.6 and 12.4 mN/m in the presence of 15% AMG and GAC, respectively. GAC was interfacially less active than AMG.
Polysaccharides are mostly hydrophilic polymers, which do not expect to exhibit significant surface activities (Dickinson, Murray, Stainsby, & Anderson, 1988). However, some polysaccharides can slowly migrate to air-water or oil-water interfaces and exhibit surface and interface activities (Garti et al., 1999). The surface activity of gum Arabic is related to its proteinaceous moieties (Chanamai & McClements, 2001). Osano, Hosseini-Parvar, Matia-Merino, and Golding (2014) demonstrated that decreasing of proteins levels in basil seed gum significantly decreased its surface active properties.
The ability of gums in decreasing of surface and interfacial tension affects droplet size and emulsion stability; however, it is not only effective factor on these properties, and other factors such as effect of hydrocolloid on rigidity of surface layer, amount of depletion force, and viscosity are also important.

| Droplet size distribution and polydispersity index (PDI)
Emulsions with lower droplet sizes show higher stability because creaming rate is proportional to the square of the droplet diameter, and hence, a decrease in droplet size decreases the rate of gravitational separation (Golkar et al., 2018). Figures 2 and 3  Garcia-Rojas (2018) reported that the average particle size distribution increased with increasing pectin or xanthan gum concentration.
Bimodal distribution was observed in the AMG stabilized emulsions immediately after preparation and on day 30 at 5% and 15% AMG concentrations, respectively ( Figure 2). This behavior was observed for the GAC stabilized emulsions immediately after preparation and on day 14, at 5% and 10% GAC (Figure 3). Similarly, bimodal distribution was observed by Huang et al. (2001) for the emulsion containing xanthan and by Osano et al.(2014) (Vicente et al., 2018). The Z-average of the emulsions stabilized with β-lactoglobulin-acacia seyal gum conjugates decreased from 10 to 6.7 µm with increasing incubation time (Bi et al., 2017).
The surface load (Γ s ) is a further reliable mean of estimating the minimum emulsifier quantity necessary to cover all droplets (Mcclements, 2007): where C s is the concentration of emulsifier in the emulsion (kg/ m 3 ), Γ is the surface load of the emulsifier at saturation (kg/m 2 ), φ is the dispersed phase volume fraction, and d 3,2 is the mean vol-

| The zeta-potential
The z-potential values of the emulsions immediately after preparation are reported in Table 3. Results showed similar behaviors for AMG-and GAC-stabilized emulsions in terms of variations in zpotential as a function of concentration which varied from −17.2 to −11.1 and −19 to −18.3 mV, respectively. However, the absolute z-potential of GAC emulsions was significantly higher than that of AMG emulsions, which could be consider as a factor contributing to stability of the GAC emulsions. In the present study, negative surface charge of the emulsion droplets decreased with increased gum concentration. Similar results were reported by Emanuel et al. (2016), who indicated that increased concentration of exudate gum Acacia from 2% to 5% decreased negative surface charge of the emulsion droplets (−41.20 to −36.10 mV for 2%-5% w/v Acacia-stabilized emulsions). A possible explanation for this drop in z-potential might be that by the addition of AMG and GAC surface pressure has caused denser packing of chains extending from the droplet surface thereby resulting in a less negative charge (Chivero, Gohtani, Yoshii, & Nakamura, 2015). Higher flocculation phenomena have been reported in emulsions prepared with acidic polysaccharides with low z-potentials (z-potential < |−30| mV) (Guo et al., 2014). In this study, z-potentials of all emulsions were lower than |−30| mV, indicating low role of electrostatic repulsion in stability of these emulsion systems. Wu, Eskin, and Cui (2015) showed that when z-potential is small, the interfacial activity and emulsifier concentration for full surface coverage are important.  Table 2). The emulsion containing 5% AMG was relatively stable; however, at 10% and 15% AMG concentrations, extensive flocculation has been occurred during three days storage, which could be attributed to depletion flocculation mechanism.

| Emulsion capacity and stability
Comparisons between the emulsion capacities of the formulations containing AMG and GAC are shown in Table 4  reported for corn fiber gum, in which visible creaming was observed at high polysaccharide levels (Bai et al., 2017). However, opposite behavior has been observed in some other hydrocolloids AMG gum has very low molecular weight (35 KDa) and cannot greatly increase viscosity in continues phase and so depletion flocculation mechanism can predominate on stabilizing mechanism at 10% and 15% concentration. Figure 6 shows appearance of the emulsions stabilized by different concentrations of AMG and GAC stored at room temperature (25°C). In the emulsions containing 5% AMG, phase separation occurred after 14 days of storage; however, this time was three days for those containing 10% and 15% of AMG. In all days of storage, the emulsions containing 15% AMG were significantly more stable than those containing 10% AMG (p ˂ .05). At higher hydrocolloid concentrations, creaming is retarded due to the high viscosity and forming of gel network in continues phase of emulsion (Dickinson, 2009;Li, Sun, & Yang, 2012). Similar behavior in emulsion containing xanthan gum has been previously reported by Vicente et al. (2018). Creaming occurred on 3th day in the emulsions containing 10 and 15% AMG; however, it occurred on 7th day in those containing 10 and 15% of GAC.
In 14th, the emulsions containing 10% and 15% AMG showed higher phase separation than those containing GAC; however, this was opposite about sample containing 5% AMG. This can be attributed to higher molecular weight or presence of higher protein moiety in GAC in comparison with AMG. The effect of polysaccharides on emulsion stability depends on two important parameters: (a) their ability in modification of continues phase rheology (b) and their ability in adsorbing to interface and covering of droplets. The viscosity of continues phase plays an important role in stability of colloidal systems such as foams and emulsions, and hydrocolloids can increase viscosity and forming gel network, which in turn lead to slowing down of droplets movement and decreasing of water drainage during droplet collision (Dickinson, 2009;Martinez, Baeza, Millan, & Pilosof, 2005;Ruiz-Henestrosa, Martinez, Sánchez, Patino, & Pilosof, 2014 (Qian, Cui, Wang, Wang, & Zhou, 2011). GAC has higher molecular weight than AMG; hence, it would have more effect on viscosity. On the other hand, it can cover droplet surface due to higher protein moiety content, which in turn prevent better from re-coalescence (Brummer, Cui, & Wang, 2003;Dickinson, 2003). Figure 7 shows stability of the emulsions at different concentrations of AMG and GAC against thermal, centrifuge, and freezing conditions. At these three conditions, the emulsion containing 5% AMG indicated significantly higher stability than those containing 10% and 15% AMG. On the other hand, this 5% AMGstabilized emulsion was more stable in freeze-thaw stability test than thermal and centrifugal experiments. However, the 10% and 15% AMG emulsion samples showed higher centrifugal stability. Heating, centrifuge, and freezing-thawing process can increase frequency of collision and destroy protective films around the droplets, which in turn lead to flocculation and coalescence (Sathivel, Huang, & Prinyawiwatkul, 2008). No significant differences were seen for heat and freeze-thaw stabilities in 10% and 15% AMG emulsions (p ˃ .05). At these three tests, the emulsions containing 5% AMG showed higher stability than those containing GAC; however, at higher concentration, opposite effect could be observed. The GAC-stabilized samples had good stability at all concentrations and showed the highest stability against centrifugal condition. This shows 5% GAC was not sufficient for coverage of droplet surface or effectively increasing of viscosity. In fact, thermal, centrifugation, and freeze-thaw assays showed that AMG-stabilized emulsions at 5% concentration had acceptable higher stabilities compared to the GAC-stabilized emulsions.

TA B L E 4 Emulsion capacity of AMG and GAC
According to interfacial activity data, AMG gum shows higher surface activity than GAC, which could be lead to higher emulsion stability due to better droplet coverage. Furthermore, the ability of hydrocolloids in increasing of viscosity had not great role in emulsion stability (Golkar et al., 2018). These results are similar to results by Golkar et al. (2018)  Foam stability usually refers to ability of foams to sustain foam volumes and/or bubble sizes in a certain time period (Naji, Razavi, & Karazhiyan, 2012). Foam stability of the control albumin solutions was 66% and was improved by both AMG and GAC at all concentrations. Increasing in AMG concentrations slightly improved foam stability and the highest value (92%) belonged to 15% AMG solution.
Various instabilities can be occurred in foam systems including gravitational separation, drainage, air-bubble coalescence, mechanical disruption, and Ostwald ripening. Foam systems are subjected to phase separation due to density differences between the gas bubbles and continues phase (Jahanbin, Moini, Reza, Emam-djomeh, & Masi, 2012). Air bubbles in foam systems have a tendency to approach and join together (coalescence). The result will be larger bubbles that are thermodynamically unstable and cause the foam system to collapse. Hydrocolloids prevent from these instabilities by modifying viscosity of aqueous phases, forming biopolymer gel networks, and forming viscoelastic layer on the bubble surface. The higher foaming stability in the AMG can be related to the presence of high content of hydrophobic groups, low MW, and flexible structure. Also, AMG and GAC showed surface activities that potentially could affect properties of the gas-liquid surface, including rigidity and permeability of the surface layer (Makri & Doxastakis, 2007).
The foams produced from pure albumin solutions showed low density (ρ = 0.07 g/m 3 ) (Figure 8c). Addition of 5% AMG increased density of foam nearly twofold (ρ = 0.12 g/m 3 ). Previous studies have demonstrated increase in foam density with adding hydrocolloids such as carrageenan and xanthan (Dabestani & Yeganehzad, 2018;Ptaszek et al., 2014). Hydrocolloids are thickener agents and create heavier foams than the foams produced from pure albumin (Ptaszek et al., 2014). In the present study, a significant increase was observed in density of foams containing GAC (ρ = 0.27 G m −3 for 15% GAC system). Binding of a large volume of water induces positive and negative effects on foaming properties; foam easily undergoes pumping and is resistant to destruction; however, if these products are dried, the high water content in their structures can be unfavorable (Ptaszek et al., 2014).

| CON CLUS ION
In this study, the emulsifying and foaming properties of ammoniacum gum were investigated in comparison with Arabic gum. AMG showed higher surface and interface activities also emulsifying capacity than Arabic one that could be attributed to low molecular weight and or having hydrophobic group in AMG backbone. However, generally the emulsion containing Arabic gum had lower particle size and higher stability during different conditions, which could be related to its higher protein content or higher molecular weight. The emulsion containing AMG gum showed smaller mean particle size and higher stability at the lowest used concentration (5% w/w). The AMG and GAC increased and decreased foaming capacity of albumin solution; however, both increased foam stability at all concentrations. As a result, it appears the AMG can be used as good foaming agent; however, it is not suitable by alone for long-term stability of emulsions despite of its good emulsifying capacity.

ACK N OWLED G M ENTS
We appreciate for financial support of this work by Tabriz University of Medical Sciences, Tabriz, Iran (No. IR.TBZMED.VCR. REC.1397.438) and Food Biophysics laboratory of Tabriz University.

CO N FLI C T O F I NTE R E S T
The authors declare that they do not have any conflict of interest.

E TH I C A L A PPROVA L
Ethical Review: This study does not involve any human or animal testing.

I N FO R M E D CO N S E NT
Written informed consent was obtained from all study participants.