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Hydrocolloids As Food Emulsifiers and Stabilizers

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Hydrocolloids As Food Emulsifiers and Stabilizers Food Structure Volume 12 Number 4 Article 3 1993 Hydrocolloids as Food Emulsifiers and Stabilizers Nissim Garti Dov Reichman Follow this and additional works at: https://digitalcommons.usu.edu/foodmicrostructure Part of the Food Science Commons Recommended Citation Garti, Nissim and Reichman, Dov (1993) "Hydrocolloids as Food Emulsifiers and Stabilizers," Food Structure: Vol. 12 : No. 4 , Article 3. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol12/iss4/3 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Food Structure by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. Food Structure, Vol. 12, 1993 (Pages 411-426) 1046-705X/93$5.00+ .00 Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA HYDROCOLWIDS AS FOOD EMULSIFIERS AND STABILIZERS Nissim Garti and Dov Reichman Casali Institute of Applied Chemistry, School of Applied Science and Technology The Hebrew University of Jerusalem, Jerusalem, Israel 91904 Abstract Introduction Hydrocolloids are water-soluble biopolymers con­ Water soluble high molecular weight polysaccha­ sisting of high molecular weight polysaccharides known rides have been known for generations as food stabi­ as viscosity builders, gelification agents and stabilizers lizers; the main application being modification of the of food systems. rheological properties of aqueous systems, viscosity Several hydrocolloids such as gum arabic (acacia), builders, gelification agents and stabilizers (Whistler, tragacanth, xanthan and certain modified gums have 1973; Glicksman, 1969; BeMiller, 1988; Dickinson, been mentioned as food additives having special func­ 1988). tions such as: "retardation of precipitation of dispersed The primary beneficial effect was related to the abil­ solid particles and coalescence of oil droplets". The role ity of the hydrocolloid to interact with water and change of these gums as emulsifiers remained somewhat ob­ its rheological properties. However, the functionality of scure. The present review is an attempt to bring the rel­ certain hydrocolloids was correlated also to phenomena evant studies together and to throw some light on the such as: "retardation of precipitation of dispersed solid functionalities of the gums as surface active agents and particles", "decreased creaming rates of oil droplets and food emulsifiers. In addition, some recent results foams", "prevention of aggregation of dispersed parti­ obtained in our laboratory are discussed. cles", "prevention of syneresis of gelled systems contain­ Gum arabic is compared to colloidal microcrystal ­ ing oils", and "retardation of coalescence of oil droplets" line-cellulose (M CC) and galactomannans (recent results) (Dickinson, 1988). Those functionalities are difficult to in view of their abihty to reduce surface tensions, inter­ explain in terms of viscosity and water-gum interactions. facial tensions and to stabilize oil in water emulsions via Adsorption onto, or interaction with the oil phase had to the 'steric' and 'mechanical' stabilization mechani sms. be considered in oil-in-water emulsions. Adsorption of It is demonstrated that while gum arabic adsorbs solid particles had to be adapted for solid dispersions of strongly and effectively onto the oil droplets via its solid particles in aqueous systems (fadros and Vincent, proteinaceous moieties, guar gum and locust bean gum 1983). (LBG) adsorb weakly and for the most part only Most of the water soluble polysaccharides are "precipitate" on the oil surface, and form birefringent known to be high molecular weight polymers with a lim­ layers of the polymer oriented with its hydrophobic ited number of repeating monomers composing the poly­ mannose backbone facing the oil. The stabilization with mer, low hydrophobicity and limited flexibility (derived MCC is claimed to be achieved via adsorption of solid from the rotational restrictions of the functional groups), particles on the oil droplets (mechanical stabilization). and interfacial density packing limitations. This is con­ trary to proteins that are composed of both hydrophilic Key Words: Hydrocolloids, food emulsifiers, food sta­ and hydrophobic moieties, which display a high degree bilizers, food emulsions, gums, galactomannans, gum of flexibility and hydrophobicity (Figure I; Yalpani, arabic. 1988). It is therefore believed that gums will adsorb (onto solid or liquid surfaces) very slowly, weakly and with very limited surface load if at all (Stainsby, 1988). Nevertheless, certain polysaccharides, i.e., gum Paper received June 22, 1993 arabic (Banerji, 1952; Silber and Mizrahi, 1975), Manuscript received November 26, 1993 xanthan (Prud'homme and Long, 1983), and tragacanth Direct inquiries to N. Garti (Dea and Madden, 1986; Bergenstabl et al., 1986; Telephone number: 972 2 633779 Yokoyama er al., 1988) have been noted to display spe­ FAX number: 972 2 520262 cific surface activities and stabilize dispersed particles of oil droplets in aqueous systems. 411 N. Garti and D. Reichman HYDROCOLLOID • s '- a HrfffH .;- 0 ~H,OH--0~ - - 0 H 0 OH ~ 1J1 , G(d I /kT PEPTIDE Ill Figure 1. Comparison of polysaccharide and peptide chain conformation. Chain conformations are deter­ mined by tbe dihedral angle Y, and ¢ between adjacent peptides and sugar rings, or planar peptide groups. - s Broken lines indicate "virtual bonds" representing individual residues (Yalpani, 1988). Figure 2. Interaction free energy G(d), in units of kT, Dickinson and Stainsby (1988) distinguish between as a function of surface-to-surface separation d for pairs emulsifiers and stabilizers in food systems and stress the of polymer-coated particles: (I) thin polymer layer; (II) difference between the two using an interesting defini­ thick polymer layer (good solvent); and (III) thick poly­ tion: "An emulsifier is a single chemical or mixture of mer layer (poor solvent); ---- shows Van der Waals components having the capacity for promoting emulsion interaction (Dickinson, 1988). formation and short term stabilization by interfacial ac­ tion. A stabilizer is a single chemical component o r b mixture of components which can offer long tenn stabili­ ty on an emulsion, possibly by a mechanism involving adsorption but not necessarily so." This definition will '_{L~ ·~~;;;;; be referred to as a guideline for determining efficacy of , ) ;;; )))J)j)J))}) ;;;;;;; ;; ;;;;;;; an emulsifier or stabilizer later in this paper. In considering stability witb respect to coalescence d and flocculation, it is important to distinguish between adsorbing polymers and non-adsorbing polymers . Covering particle surfaces with a thick protective layer of adsorbing polymer inhibits coalescence. The coated particles strongly repel one another at close range through a combination of polymeric elastic and osmotic effects, and at this point, tbe colloid is said to be - d - sterically stabilized. This type of stabilization is most effectively achieved using copolymers having a combina­ tion of anchoring groups and dangling chains. The an­ choring groups should have a strong affinity for tbe sur­ face and a low affinity for the continuous phase, and the opposite is true for tbe dangling chains. In addition, tbere should be enough adsorbing copolymer to cover tbe particle surface quite completely, and tbe layer thick­ Figure 3. Sketches of interfacial configurations of ness should be sufficient for two particles to be prevent­ chains witb adsorbing ( • l and non-adsorbing (0) ed from approaching a pair separation of which tbe in­ groups: (a, top left) copolymer; (b, top right) homo­ terparticle (Van der Waals) attraction is of an apprecia­ polymer; (c, bottom left) bridging; (d, bottom right) ble magnitude in relation to tbe thermal energy, kT. A depletion (Dickinson, 1988). 412 Hydrocolloids as Food Emulsifiers and Stabilizers high molecul ar mass favors thick film formation and ,---- - - ------- thus good steric stabilization (Figure 2). A homopoly­ mer composed of many identical ad sorbing segments is not a good steric stabilizer, since it produces too thin a layer, leading to free energy interaction with an attrac­ tive minimum, whose depth may be several kT (Figure 3). Where surface coverage is incomplete, a single polymer chain may become attached to more than one particle, as illustrated in Figure 3. Such bridging fl oc­ culation is most likely when the polymer concentration is approximately half of that required for saturation 0 coverage (Dickinson, 1988). As a result, it seems clear that proteins known to 24------.-----.------.------1 have significant hydrophobicity and flexibility, can readi­ 0 10 15 20 ly adsorb onto particles or oil droplets, and therefore, Gum arabic concentration (% w/w) will be considered as emul sifiers with short term stabili­ ty action on dispersed particles (termed "steric stabili­ Figure 4. The average droplet diameter of emulsions zation mechanism" by Dickinson and Stainsby, 1988). (20% w/w orange oil) as a function of gum arabic con­ Hydrocolloids, on the other hand, will be considered as centration. Measurements were performed on diluted stabilizers with limited adsorption ability and long term dispersions (1/1000) with distilled water using a ZM stability (termed "depletion stabilization mechanism" by model Coulter counter equipped with a 50 I'm orifice Dickinson and Stainsby, 1988). electrode. Recent studies have concentrated on the role of gum arabic as an emulsifier,
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