Influence of Interfacial Composition on Droplets Flocculation of Oil-in- Water Emulsions Stabilized By Garden Cress Seed Gum 1-Arezoo Fazeli 2- Masoud Najaf Najafi Young Researchers Club Institute of Scientific Quchan Branch, Islamic Azad University Quchan, Applied Higher-Education Jihad-e-Agriculture Iran Mashad, Iran [email protected] [email protected] 3- Ali Mohamadi Sani 4-Arash Koocheki Department of Food Science and Technology Department of Food Science and Technology Quchan Branch, Islamic Azad University Ferdowsi University of Mashhad Quchan, Iran Mashhad, Iran [email protected] [email protected] Abstract—Both keeping emulsion droplets away from I. INTRODUCTION instability and using natural components are important factors in making colloidal systems. Directly interaction between oil and water is not Garden cress seed gum as a novel natural thermodynamically favorable because of hydrocolloid source used in 0, 0.5 and 1% hydrophobic effects [1]. So we need a third party concentrations to determine the gum efficiency on which may have surface activity or electrical droplets interface and its ability to avoid flocculation. charge. Surface active molecules have both For this purpose surface and interfacial tensions, hydrophilic and lipophilic regions distributed along creaming index and microscopic images studied. their backbones. In emulsion science an interface is 0 Hydrocolloid solutions kept for 24 h at 4 C to attain a narrow region that separates the two phases maximum hydration. Surface and interfacial tensions commonly oil and water [2]. Bulk physicochemical measured at 250C after reaching to their equilibrium time. Storage time considered to be 28 days for all properties of emulsions, such as their ease of treatments. The result showed surface and interfacial formation, stability and texture are governed by the tensions parameters decreased by increasing gum nature of the interface and therefore it is important concentration. Surface tension was least for 1% to understand its composition [3]. Flocculation concentration but it was not much less than 0.5% occurs when droplets smash to each other but, they level. In the control sample (without gum), emulsions keep their initial membrane. The magnitude of droplets flocculated immediately and consequently flocculation depends on colloidal interaction which phase separation occurred at the first day. At the relative to thickness and electrical charge of 0.5% concentration hydrocolloids associated at the interfacial layer in turn [1,4]. interface and made a stable emulsion. Partial flocculation happened at this level but no In recent years many studies done on plant gravitational separation observed. Emulsions made seeds to find a good source of hydrocolloids being by 1% gum concentration were completely stable able to substitute instead of synthetic ones. during storage. At this level, the interface was Lepidium perfoliatum [5,6], mesquite [7], tamarind saturated of hydrocolloids and the extra amount [8], Jatropha curcas [9], okra [10], fenugreek stayed at media. Non-adsorbed hydrocolloids [11,12] are some examples. Although these increased solution viscosity and also produced polysaccharide are able to form stable emulsions repulsion forces with adsorbed ones. It assumes that but, there is still some debate about the molecular Garden cress seed gum can prevent origin of their surface activity. dropletaggregation by thickening effect and electrostatic repulsion rather than interfacial Garden cress seeds are bitter and find activities. applications in a wide range of biological functions and diseases such as leprosy, skin diseases and as a Keywords-interfacial properties; garden cress; diuretic [13,14]. The seeds contain a large amount emulsion stability; surface activity; flocculation of mucilaginous substances and a gum of high molecular weight has been identified [15,16]. The tests were carried out in triplicate at ambient macromolecular component of the gum has a temperature. molecular weight of 540 kDa, and is nearly as rigid as xanthan with regard to chain conformation [17]. C. Microscopic Observation Also, it was measured that the gum powder To find out the main mechanism which is contains 77 % carbohydrate, 2.45 % protein and responsible for droplets instability we conducted 1.85 % fat [15]. microscopic observation. Every emulsion diluted There is no published information about how with 1 g/L SDS and stirred to reach desired Garden cress seed gum can affect the interface concentrations (1:1000 SDS). Afterwards, a small composition, flocculation amount and in drop of these mixtures were placed onto glass consequence the emulsions long term stability slides covered with slips and observed by optical against gravitational separation. This study aimed microscope (Lx-400 Labomed, USA) equipped to determine the properties of interface composition with 9 mp (TSTD Tucsen, China) digital camera at and its effects on droplets flocculation by using × 10 magnifications. All samples were observed Garden cress seed gum as a surface active immediately after preparation and 28 days after polysaccharide. being kept at 4 0C. One droplet of the 0.5 % emulsion monitor for 3 hours to understand the II. MATERIAL AND METHOD phenomena involved on droplets instability. Images Analytical grade chemicals were provided by took every hour with different magnifications. Merck (Germany). Garden cress seed gum was extracted based on the method presented by Karazhiyan et al. [18]. Commercial corn oil D. Creaming Measurement purchased from local markets in Mashad. Fifteen ml of each fresh emulsion was transferred into test tubes, tightly covered to A. Emulsion Preparation prevent air penetration, and then stored at 4 0C for The dispersions were prepared by dissolving 0, 28 days. Creaming index was measured every 0.5 and 1 g of gum powder into 80 g distilled water seven days by the method presented by Sciarini while stirring with IKA-RCT basic (Germany) [20]. The measurement was performed in triplicate magnetic stirrer for 30 min. Sodium azide in 0.01 samples. The extent of creaming was determined as % proportion added to all dispersions to avoid a creaming index: bacterial growth. Afterward, the solutions kept at 4 0 HS C overnight to attain complete hydration. The final CI(%) = × 100 pH of all dispersion adjusted to be neutral by using HE 1 molar hydrochloric acid and sodium hydroxide. Corn oil in water emulsions were prepared by The height of the serum layer (HS), the total height adding 20 ml corn oil into dispersions while stirring of the emulsion (HE) by a magnetic stirrer for 10 min. Homogenization III. RESULT AND DISCUSSION done with a laboratory rotor stator homogenizer A. Surface and Interfacial tensions (Ultra Turrax T-25, IKA Instruments, Germany) at 20000 rpm for 5 min at room temperature. Surface and interfacial tensions give useful information about emulsifying properties of a B. Surface and Interfacial Tensions Measurement component and stability of droplets against aggregation and Ostwald ripening [19]. The surface Wilhelmy plate and Du Nouy ring method of and interfacial tension activities of Garden cress Kruss K100 tensiometer (Germany) used to seed gum solutions presented in Fig. 1. According measure surface and interfacial tensions to this Figure, adding gum decreased surface and respectively. The equilibrium time for interfacial tensions significantly. Although there measurements obtained to be 30 min. To minimize were more hydrocolloids available at the 1 % level the movement and to maximize the steady but the 0.5 % concentration was more effective in condition the sample holder fixed at the hairbreadth reducing both surface and interfacial tension. At the to sensitive force measuring device. The force 1 % level, gum concentration was more than the exerted on the plate when goes upward shows interface requirement while at 0.5 % it has been surface tension while the force acting on the ring enough to cover newly formed oil droplets. Spatial when the vessel holding is lowered indicates oil- prevention at higher concentration hampered gum interface [19]. The ring caught at the air–water hydrocolloid to cover oil droplets, so additional interface was progressively and carefully covered hydrocolloid molecules in the media led to gelation with oil, and the interfacial tension was and viscosity enhancement and we could not continuously recorded. The reported surface measure logical interface value. Huang et al. (2001) tension and interfacial tension numeral are mean compared physical properties of 14 kinds of gums values of 15 and 3 measurements respectively. All with 0.5 % concentration in 40 % canola oil-in- water emulsions [21]. They found that all the gums flocculation [19]. In higher level (1%) due to reduced surface and interfacial tensions except viscosity effect and repulsion interaction of high carrageenan and xanthan because of the mentioned charge biopolymers, droplets moved slower and reason. Bouyer et al. (2011) investigations on therefore they clashed too tardy. interfacial properties of gum arabic indicated this According to Fig. 4, at the first two hours the gum needed time to diffuse towards the interface, droplets arrangement changed from open to adsorption, and rearrange itself [22]. Unlike to this compact and they started to share their membranes. research, no change was observed for Garden seed Flocculation occurred because the interfacial layer during the measuring time. was not hydrocolloid rich, so there were not It deduced that