Content uploaded by Saphwan Al-Assaf
Author content
All content in this area was uploaded by Saphwan Al-Assaf on Aug 30, 2015
Content may be subject to copyright.
A preview of the PDF is not available
Hydrocolloids: Structure-Function Relationships
Abstract and Figures
The factors influencing the functionality of acacia gum and other hydrocolloids of interest to the food industry, are studied. Hydrocolloids are made up of monosaccharides glycosidically linked, through water elimination, to produce mixtures of similar but not identical molecules of differing molecular dimensions, with the distribution often dependent on the source, method of extraction and subsequently processing conditions. Acacia gum is the exudate from the Acacia tree, which is one of the most ubiquitous genera in the plant kingdom. Recent EC legislation has approved gum arabic as an ingredient which can be labeled as a food dietary fibre. Gum arabic's role as an emulsifier is achieved as a consequence of its ampliphilic character due to the presence of protein and polysaccharide moieties. Pectin is widely used in the food industry as an emulsifier, stabilizer and a gelling agent. Hyaluronan is an example of animal source and is type AB polymer. This hydrocolloid traditionally has been used in a wide variety of areas such as biomedical and bioengineering applications.
Figures - uploaded by Saphwan Al-Assaf
Author content
All figure content in this area was uploaded by Saphwan Al-Assaf
Content may be subject to copyright.
... To function as an emulsifier, the hydrophobic protein and hydrophilic carbohydrate parts are required to adsorb oil droplets to the surface and to block protrusion into the solution, respectively [13]. The carbohydrate component is believed to provide a strong steric barrier against flocculation and coalescence [1,14]. Several physical and chemical approaches have been applied to improve the emulsion properties of gum Arabic [15][16][17][18][19][20]; however, only one enzymatic approach, which improved the oil-in-water emulsifying function of the gum via treatment with β-galactosidase, has been reported [21]. ...
A plant glycosyltransferase was utilized to modify the properties of gum arabic as an oil-in-water emulsifier. We previously reported that recombinant beta-glucuronosyltransferase (AtGlcAT14A) from Arabidopsis thaliana produced in Pichia pastoris possesses glucuronosyltransferase activity to transfer glucuronic acid (GlcA) from UDP-GlcA to beta-1,3-galactan main chain and beta-1,6-galactan side chains of type II arabinogalactan. In this paper, we report that AtGlcAT14A can also transfer GlcA from UDP-GlcA to gum arabic at the optimal pH value of 5 in the absence of dicationic ion. In the modified gum Arabic, GlcA was primarily incorporated into the beta-1,6-galactans. The oil-in-water emulsions created by the modified gum arabic were smaller, less flocculated and threefold more stable than that produced by the unmodified gum arabic. It is conceivable that the additional GlcA on the surface of gum arabic prevents flocculation by increasing surface electrostatic repulsion, which leads to more stable oil-in-water emulsions. Our study implicates the structure-function relationship and provides a potential method for the enzyme-based manipulation of gum arabic.
... Gum arabic is a mixture of heterogeneous substances, of which AGP is essential for its function as an emulsifier by having both hydrophobic protein and hydrophilic carbohydrate portions that interact with oil droplets and aqueous solutions, respectively [23]. The carbohydrate portions of gum arabic are believed to provide a strong steric barrier against the flocculation and coalescence of oil-in-water emulsions [24,25]. ...
Arabinogalactan proteins (AGPs) are abundant extracellular proteoglycans that are found in most plant species and involved in many cellular processes, such as cell proliferation and survival, pattern formation, and growth, and in plant microbe interaction. AGPs are synthesized by posttranslational O-glycosylation of proteins and attached glycan part often constitutes greater than 90% of the molecule. Subtle altered glycan structures during development have been considered to function as developmental markers on the cell surface, but little is known concerning the molecular mechanisms. My group has been working on glycosylation enzymes (glycosyltransferases) of AGPs to investigate glycan function of the molecule. This review summarizes the recent findings from my group as for AtGalT31A, AtGlcAT14A-C, and AtGalT29A of Arabidopsis thaliana with a specific focus on the (i) biochemical enzyme activities; (ii) subcellular compartments targeted by the glycosyltransferases; and (iii) protein-protein interactions. I also discuss application aspect of glycosyltransferase in improving AGP-based product used in industry, for example, gum arabic.
... Commercially available mechanical powder of A. Senegal gum was supplied by Sudanese Gum Arabic Company. The physicochemical properties of supplied A. Senegal gum are given inTable 2.Rabah et al., [3] ) Tanzania (Mhinzi and Mrosso, [4]) Kenya (Lelon et al., [5] ) Ethiopia (Yebeyena, et al., [6] ) [7] ) Demineralized water is prepared at Chemical Engineering Laboratory by double distillation. The viscosity was measured using DV III Ultra Rheometer with an accuracy of ±1.0 % of range and repeatability of ±0.2%. ...
The objective of this study is to provide rheological data of Acacia senegal (A. senegal) gum of Kordofan origin. The density of A. senegal gum at room temperature is found to be higher than that of water only at higher concentration (>5 g/L). The density is aslo found to be strong function of temperature. At medium temperature >45 °C becomes lower than that of water even at low concentration (<2.5 g/L). The viscosity is found to be shear rate independent indicating Newtonian behavior. At low concentration A. senegal gum viscosity varies linearly with concentration and at high concentration (>10 g/L) varies exponentially. The study also provides review information on physicochemical and mineralogical characteristics as well as the structure of A. senegal gum.
This chapter describes the use of hydrocolloids and gum as encapsulating agents. It introduces the traditionally used materials, primarily gum Arabic and sodium alginate, detailing their origins, structures, and functionality as an encapsulating agent. The chapter outlines some of the most common applications for hydrocolloids and gums as encapsulating agents: antioxidants, flavors, and microorganisms, as well as some emerging applications such as lipids and enzymes. This section includes specific case studies related to the use of gum Arabic as a wall material for both spray-dried flavors and medium-chain triglyceride oils.
The aim of this study was to replace gelatin and albumin with three levels of xanthan gum and guar gum (1, 1.5 and 2%) and three levels of chubak extract (0.2, 0.4 and 0.6%) in marshmallow and evaluate physicochemical and organoleptic properties of new formulations. The results of physicochemical experiments showed that in all samples containing 0.6% of Chubak extract, density and overrun significantly decreased and increased, respectively. The moisture content and water activity in samples containing different levels of gum and chubak extract significantly increased in comparison to control (P
Exudate gums play an important role in day-today life applications from food to non-food applications. Due to advancements in technology and interest has been devoted to modifying the natural structure, developing a new product, or enhancement of existing properties to achieve desired end quality. It also improves the eating quality, increases the shelf life of food commodities besides its functional, pharmacological, nutraceutical properties. Gums are cheap, non-toxic, easily biodegradable, and abundant availability quenches the thrust among the scientist. However, animal and microbial gum are also served better food application but in some instances are least accepted by the consumer. Plant gum being polysaccharides and hydrocolloids, offers numerous commercial applications in cosmetics, pharmaceuticals, and non-food. This review summarizes recent food applications and their importance in the food system of major exudates.
Emulsifiers are generally relatively small molecules, whereas stabilizers and thickeners are typically biopolymers such as hydrocolloids and proteins. Emulsifiers are therefore used within food systems to decrease the surface tension of dispersions, emulsions, foams and suspensions, where stabilization of the two phase products is required. In practical terms, interfaces are formed simply by mixing oil and water, but this simple bipartite co-existence is insufficient to form the basis of stable emulsions. The hydophilic-lipophilic balance (HLB), value is assigned based on the chemical structure of the emulsifier, that is, an emulsifier with a high HLB has a high ratio of hydrophilic groups compared to lipophilic groups, and vice versa. Emulsifiers are recognised ingredients which impart function to foods and, as such, their use is regulated by most governments.
Objective: This study focused on evaluating the physicochemical and tablet formulation properties of shea tree (Vitellaria paradoxa) gum, using
paracetamol as a model drug.
Methods: Crude shea gum was purified and the physicochemical properties, namely: Moisture content, insoluble matter, solubility, swelling capacity,
viscosity, hydration capacity, flow properties, and metallic ion content evaluated. The binding properties of shea gum (5-20% w/v) were investigated,
using acacia gum as a standard binder. The physical properties, in vitro dissolution and dissolution efficiency (DE) of the tablets, were determined.
The dissolution data were statistically evaluated using the T-test and the similarity factor (f2).
Results: The physicochemical properties of the gum evaluated were found to be satisfactory and within official specifications. Atomic absorption
spectrophotometric analysis of the gums showed that the crude gum had higher metallic ion content than the purified gum. The gum purification
process caused a substantial reduction (17-74%) in the mineral ion content of shea gum. Granules prepared with shea gum exhibited good flow
properties evidenced by their optimal Hausner ratio, angle of repose and Carr’s index values. The granule flow properties, as well as the physical
properties of shea gum tablets, were similar to that prepared with acacia gum. The DE of both shea gum and acacia gum tablets decreased with
increase in binder concentration. Comparative studies on the tablets using DE, T-test and similarity factor (f2), showed that the binding effect of shea
gum was comparable to that of acacia gum (p>0.05; f2 ≥50) at the same concentration.
Conclusion: Shea tree gum has potential as a binder in pharmaceutical tablet formulations.
Keywords: Vitellaria paradoxa, Viscosity, Wet granulation, Tablet binder, Dissolution efficiency, Similarity factor
The tendency of polysaccharides to associate in aqueous solution has long been recognised. Molecular associations can profoundly
affect their performance in a given application due to its influence on the molecular weight, shape and size. This will ultimately
determine how the molecules will interact with each other, with other molecules and with water. There are several factors,
such as hydrogen bonding, hydrophobic association, ion mediated association, electrostatic interaction, concentration dependence
and the presence of proteinaceous components, which affect this behaviour. Our objective is to highlight the role of the proteinaceous
component, present in acacia gum, to promote associations when the gum is subjected to various processing treatments such
as maturation, spray drying and irradiation. The results demonstrate the ability of the proteinaceous component to promote
hydrophobic associations which influence the size and proportion of the arabinogalactan high molecular weight component (AGP).
Heat treatment in solid state (maturation) increases the hydrophobic character of the gum and hence its emulsification performance.
Spray drying also involves aggregation through hydrophobic association but changes the surface properties of peptide moieties
to become more hydrophilic compared to the association promoted by the maturation treatment in the solid state. Irradiation
induced cross-linking, in the presence of unsaturated gas, was used to introduce C–C bonds into the carbohydrate moiety and
thus confirms the hydrophobic association prompted by the heat used in the maturation and spray drying. This association can
be reversed by treatments, such as filtration or high pressure homogenisation. The results reported here reconcile the contradiction
about structure of gum arabic proposed by the wattle-blossom and twisted hairy rope models and shows that the AGP fraction
is basically an aggregated fraction made up of AG units stabilized by low molecular weight highly proteinaceous components.
Gum from Acacia senegal has been fractionated using hydrophobic affinity chromatography. Characterization, including identification of sugars and determination of protein and amino acid contents, has been undertaken for each fraction together with measurements of molecular mass and molecular mass distribution using laser light scattering and gel permeation chromatography. The results have indicated that the gum consists of three distinct components. Fraction 1. which represents 88.4% of the total, is an arabinogalactan with molecular mass 2.79 x 10(5) and is deficient in protein. Fraction 2, which represents 10.4% of the total. is an arabinogalactan-protein complex with a molecular mass of 1.45 x 10(6), containing similar to 50% of the total protein. It is envisaged that on average each molecule of fraction 2 consists of five carbohydrate blocks of molecular mass similar to 2.8 x 10(5) covalently linked through a chain of amino acid residues. Fraction 3 represents only 1.24% of the total gum but contains similar to 25% of the total protein and has been shown to consist of one or more glyeoproteins. Whereas the proteinaceous components of fractions 1 and 2 contain predominantly hydroxyproline and serine. this is not the case for fraction 3.
The effect of concentration, ageing and enzyme degradation on the interfacial rheology at the liquid/air (L/A) and liquid/liquid (L/L) interface of aqueous solutions of the gum exudates from Acacia senegal and Acacia seyal have been studied. Both gums had film forming capabilities which increased as a function of time and concentration. The interfacial elasticity of the A. senegal gum samples was greater than that of the A. seyal gums and increased with increasing arabinogalactan protein (AGP) content of the A. senegal gums and their overall protein content. When the AGP was degraded by proteolytic enzyme the interfacial viscoelasticity was lost for both A. senegal and A. seyal gums. The different interfacial elasticity and viscosity of these two gums at the oil–water interface may reflect their well known differing abilities to maintain long term emulsion stability.
There have been substantial developments recently concerning the regulatory aspects of gum arable and the elucidation of its structure and functional characteristics. The aim of this paper is to present the position with regard to its current legal definition, to summarize what is now known about the structure of this complex polysaccharide and to illustrate how the structural features relate to its functional properties, notably its ability to stabilize oil-in-water emulsions and to form concentrated solutions of low viscosity.
The Acacia gum (Acacia senegal var. senegal), which is a food additive approved by Codex Alimentarius, is defined within the Acacia subgenus (family Leguminosae). The structural characteristics associated with a “poor” and “good” emulsifying A. senegal var. senegal exudate gum are identified and it is shown that it is possible to maturate the “poor” emulsifier in a process comparable to that which occurs to the exudate gum as the age of the tree increases from 1 to 15 years and when the gum is stored naturally after collection. Thus, the molecular parameters of the “good” gum can be matched, and the emulsification effectiveness can attain the level of the “good” emulsifier.The process can be further continued to produce a series of gums of precisely structured molecular dimensions with improved properties and if the maturation is continued can yield a hydrogel form of Acacia. The new forms of A. senegal which are described here, and which have not previously been available are designated Acacia (sen) SUPER GUM™ which are constant in properties and with precisely structured molecular dimensions, unlike the naturally occurring gum. The viscosity can be increased up to 20 times compared to the starting material. The controlling factor is the agglomeration of the proteinaceous components within the molecularly disperse system that is A. senegal gum to increase the amount of arabinogalactan protein (AGP) emulsifying component up to more than double the amount present originally. This results in a dramatic increase in the interfacial surface properties and coverage of the oil droplet in oil in water emulsion. No other chemical change is initiated by the maturation process.
A process is described which enables the molecular structure of a wide range of food hydrocolloids to be modified in a controlled manner. It involves treating the hydrocolloid in the solid state with ionising radiation in the presence of a mediating gas. The molecular weight can be increased to the point where it ceases to be completely water soluble, and thereafter, with further dose increases, a hydrogel state results. The paper describes the changes which have been introduced into globular structures such as arabinogalactan proteins, branched chain polysaccharides such as pullulan and dextran, chemically modified structures such as carboxymethyl cellulose and gelling plysaccharides such as xanthan, pectin and carrageenan. Proteins can also be similarly modified and gelatin is used as an example. The change in physical properties and functionality, reflect the molecular changes, particularly emulsification, water binding, viscosity and viscoelasticity. Interactive blends can be produced when solid state mixtures of these materials are co-processed.
Gum arabic has been separated into five molecular mass fractions using gel permeation chromatography. Each fraction was shown to be present in varying proportions. A high proportion of the proteinaceous material (60%) is associated with one high molecular mass component, which constitutes <10% of the total gum. This fraction can be degraded enzymically to give products with similar molecular masses to the other fractions. Although gum arabic solutions of >12% (w/w) were required to give stable 20% (w/w) orange oil emulsions of small droplet size, it was demonstrated that only 1–2% of the gum actually adsorbed at the oil-water interface. Further investigation revealed that it was the high molecular mass, protein-rich fraction which predominantly adsorbed and hence is responsible for the gum's emulsifying ability. Stable emulsions could not be produced using enzyme-degraded gum arabic.
Gum Technology in the Food Industry
- M Clicksman
Clicksman, M. (1969). Gum
Technology in the Food Industry,
Academic Press, Inc.