Microbial exopolysaccharides have found a wide range of applications in the food, pharmaceutical as well as other industries due to their unique structure plus physical properties. A number of of these applications include their use as emulsifiers, stabilizers, binders, gelling agents, coagulants, lubricants, film formers, thickening plus suspending agents. These biopolymers are rapidly emerging as industrially significant, moreover are gradually becoming economically competitive by means of natural gums produced as of marine algae as well as other plants. Microbial polysaccharides are water-soluble polymers plus might be ionic or non-ionic. The repeating units of these exopolysaccharides are regular, branched or un-branched, moreover are connected by glycoside linkages. A number of microbial polysaccharides are commercially accepted, while others are at various stages of growth. Currently a small number of biopolymers are produced commercially on a large scale. Among the biopolymers which are either currently commercial products or which have been the subject of extensive studies are xanthan as of Xanthomonas campestris, gellan in addition to a range of structurally related polysaccharides as of the strain of
Sphingomonas paucimobilis, bacterial alginates secreted by Pseudomonas sp., Azotobacter vinelandii as well as Azotobacter chrococcum. (Adams, 2004)
Gel definition:
Gellan gum is high molecular mass polysaccharide gum produced by a pure culture fermentation of carbohydrates by Pseudomonas elodea, purified by recovery by means of isopropyl alcohol, dried, plus milled. The high molecular mass polysaccharide is principally composed of tetra cyclic repeating unit of one rhamnose, one glucuronic acid, and two glucose units and is substituted by means of acyl group as the O-glycosidically-linked esters. The glucuronic acid is converted to potassium, sodium, calcium as well as magnesium salt. It usually contains small amount of nitrogen-containing compounds resulting as of fermentation procedures (Adams, 2004).
Gellan gum structure in addition to properties:
Gellan gum is a high molecular weight polysaccharide (i.e., complex sugar) gum produced as a fermentation product by a pure culture of the microbe Sphingomonas elodea1. The production organism is an aerobic, well characterized, non-pathogenic, gram-negative bacterium (JECFA, 1990). The general chemical structure of gellan gum is presented in Figure 1. Its structure consists of four linked monosaccharide (i.e., simple sugars), including one molecule of rhamnose (a sugar found in various plants), one molecule of glucuronic acid (an oxidize glucose molecule), moreover two molecules of glucose (a component of sucrose, which is common sugar). The exact molecular formula of gellan gum might vary slightly (e.g., depending on the degree to which the glucuronic acid is neutralized by means of various salts. (Adams, 2004)
There are three basic forms of gellan gum products, which are distinguished by their polysaccharide content, the percent substitution of o-acetyl functional groups, plus/or the protein content (including nucleic residues and other organic nitrogen sources) (Liu, 2006)
Properties of the Substance:
Gellan gum is a water soluble, off-white powder. It has a molecular weight greater than 70,000 Daltons by means of 95 percent above 500,000 Daltons. It forms gels when positively charged ions (i.e., cations) are added.
Thus, the thickness as well as texture of gellan gum in various products can be controlled by manipulating the addition of potassium, magnesium, calcium, and/or sodium salts. In the same way, its melting temperature can be modified to either be below or above 100° C. (Crocker, 1996)
Specific Uses of the Substance:
Gellan gum is a food additive that acts as a thickening or gelling agent, and can produce gel textures in food products ranging as of hard plus brittle to fluid. Types of products that typically contain gellan gum include: bakery fillings, confections, dairy products, dessert gels, frostings, icings in addition to glazes, jams as well as jellies, low-fat spreads, microwavable foods, puddings, sauces, structured foods, and toppings. (Ketz, 1988)
According to the petitioner's Internet site2, gellan gum in addition can be used in lotions moreover creams, make-up, face masks and packs, hair care products, toothpaste, plus air freshener gels. Gellan gum in addition might be used in canned cat in addition to dog food.
Gellan Gum Properties:
Gellan Gum is the white powder devoid of special flavour and odour as well as can disintegrate devoid of melting in 150℃. Gellan gum can be dissolved in the cold water, the conditions for the formation of gelling are:
Need to heat up first
The existence of a certain amount of cations. In this way, the gellan gum solution can form gel after It is cooled down. The gel strength, gel forming temperature and the melting temperature is bound up by means of the concentration and category of the cations. (Liu, 2006)
Characteristic plus Efficacy of Gellan Gum:
Characteristic
Efficacy
Form high qualified gel under low concentration of 0.05~0.25%
Gellan gum is an efficient gelling agent
High stability at high temperature moreover low pH value
Heating as well as sterilization has little effect on gel strength, acid gel has comparatively long shelf life
Gel formed by Na+ in addition to K+ can renew after heating, while gel formed by Mg2+ and Ca2+ can not
Can produce reversible as well as irreversible gel
Retains excellent flavour releasing ability
Improve product quality
Can be used together by means of other gums like starch, mixture of xanthan gum/locust bean gum
Structure of gums formed by gellan gum can be transformed as of brittle to elastic(Liu, 2006)
Gellan gum gel formation (gelation):
Gel Formation:
The preparation of alginate beads containing an assortment of substances can be achieved through various means. These approaches cover large bead preparation, micro bead preparation, matrix block preparation, plus in situ gelling systems. In general, alginate beads are formed when a solution of sodium alginate in addition to the desired substance is extruded as droplets into a divalent solution to encourage cross-linking of the polymers. Such cross-linking solutions might include
cations such as Ca2+, Sr2+, or Ba2+, while monovalent cations and Mg2+ do not induce gelation, as well as Ba2+ and Sr2+ ions produce very strong alginate gels. (Liu, 2006)
Numerous other cations including Pb2+, Cu2+, Cd2+, Co2+, Ni2+, Zn2+, plus Mn2+ will induce gelation, however due to their toxicity they are rarely used. In the gelation process, the polymer chains are cross-linked by the exchange of sodium ions as of gluronic acids by means of divalent cations, forming what is referred to as the "egg-box" as represented in Figure 3. (Liu, 2006)
In the case of Ca2+ ions, the cation binds to the a-L-gluronic acid residues forming dimerizing junctions by means of other chains, producing soluble gallous networks (Rees and Welsh, 1997). Unfortunately, in biological systems the Ca 2+ ion is lost to phosphate, resulting in the breaking of all preformed cross-links. However, this problem might be avoided through the modification of alginate by means of long alkyl chains, as the hydrophobic interactions of the divalent cation are not required to form the gallous networks, as the hydrophobic interactions in the alkyl chains are sufficient to bond the polymer. Moreover, this interaction is strengthened by salt concentrations, in addition to the greater the salt concentration, the greater the stability of the modified alginate networks. (Liu, 2006)
Texture definition:
The repeating unit of the polymer is a tetrasacharide which consists of two residues of D-glucose as well as one of each residue of L-rhamnose moreover D-glucuronic acid. The tetrasacharide repeat has the subsequent structure:
[D-Glc(β1→4)D-GlcA(β1→4)D-Glc(β1→4)L-Rha(α1→3)]n. As it is evident as of the formula the tetrasacharide units are linked by means of each other using an (α1→3) glycoside bond.
Mechanical properties definition such as hardness, work, strain, stress, brittleness, cohesiveness, deformability, springiness... which are related to texture:
Combinations of further than one hydrocolloid are widely used in foods. In fact, use of blends rather than a single hydrocolloid might be considered standard practice. Non-gelling hydrocolloids are normally used together to obtain optimal theology. In a number of cases, xanthan gum guar gum being a good instance, the combination is used to obtain a synergistic augment in viscosity. The changes in viscosity that result form blending non-gelling hydrocolloids can be predicted using the so-called log-mean blending law. Viscosity values that differ form those predicted indicate synergistic (greater than expected) or anti-synergistic behaviour. (Liu, 2006)
Combinations of gelling plus non-gelling hydrocolloids or two or further gelling hydrocolloids are much further complex, in addition to various possible network structures have been proposed. Since not a great deal is known regarding mixed polysaccharide gelling systems, the concept of synergism applied to these systems is generally in appropriate. Despite this lack of fundamental knowledge, mixed polysaccharide gels are well established commercially. Combinations of k-carrgeenan or agar as well as locust-bean gum are perhaps the best instances. The inclusion of locust-bean gum provides textural modification and allows reduction of the total polymer concentration required for gel formation. Use of the gelling system xanthan gum locust-bean gum to modify the textures of gels such as those form agar and carrageenan has in addition been suggested. (Liu, 2006)
The effect of both gelling and non-gelling hydrocolloids on the texture of low-acyl gellan gum gels has been extensively studied. Commonly used thickeners such as guar gum, locust-bean gum, xanthan gum, carboxy-methylcellulose plus tamarind gum, when added to gellan gum in progressively augmenting amounts while maintaining a constant total gum concentration, cause a progressive reduction in hardness as well as modulus. Brittleness remains essentially constant, by means of an accompanying slight augment in elasticity. These effects are shown for low-acyl gellan gum/xanthan gum combinations in figure below. For the key textural parameters, hardness, modulus moreover brittleness, modulus in addition to brittleness, these thickeners function essentially as inert diluents and the texture of the resulting blends is similar to the texture of low-acyl gellan gum alone at a concentration equivalent to that in the blend. It is common practice to include thickeners in gelled systems to reduce syneresis, improve freeze thaw stability and, in a number of cases, eliminate unfavourable interactions flanked by ingredients. Thus, a number of products formulated by means of gellan gum in addition require the presence of thickener. The textural similarity flanked by gels form low-acyl gellan gum, k-carrageenan plus agar has already been mentioned. Blends of low-acyl gellan gum as well as agar (0.50% and 0.25% total gum concentration) provide gels in 4mM Ca2+ that show a decrease in hardness and modulus as the blend becomes richer in the agar gum component, the decrease being further pronounced at the higher gum concentration. Brittleness in addition to elasticity values remain virtually constant around 34% moreover 14%, respectively. Similar blends of k-carrgeenan as well as low-acyl gellan gum in 0.16mM K+ show a rapid drop in hardness(4.5 to 2) in going form 0.5% low-acyl gellan gum, k-carrageenan plus then rises to around 4 for carrageenan alone at 0.5%. Modulus falls sharply form 4.6 in going form 0.5% low-acyl gellan gum alone to the 80:20 blend and remains flanked by 1.5 and 2 thereafter. At 0.25% total gum concentration the same trends are apparent however less pronounced. As in the case of the low-acyl / agar blends, the low-acyl / carrgeenan blends have a fairly constant brittleness and elasticity irrespective of blend composition. The values for these latter textural parameters are almost identical to those for the low-acyl / agar blends. These data indicate that the characteristic brittle texture of low-acyl gellan gum gels cannot be substantially changed by progressive substitution by means of other brittle gelling agents. (Liu, 2006)
This is not the case when low-acyl gellan gum is used in combination by means of the xanthan gum / locust-bean gum gelling system. As can be seen in Figure below the xanthan gum gels become less brittle as the blend becomes richer in xanthan/locust-bean gum; Figure below indicates the other textural changes that take place. Hardness as well as modulus are abridged, while elasticity is augmented. Similar textural changes are induced when locust-bean gum is replaced by other hydrocolloids, such as Cassia gum and konjak mannan , both of which are capable of interacting by means of xanthan gum to form gels by means of texture similar to those obtained form xanthan gum plus locust-bean gum gels in addition to native or high-acyl gellan gum is evident by comparing Figs18 and 19 . Consequently, it si perhaps not surprising, as indicated in Fig.19, that blends of high- and low-acyl gellan gum provide textural variations similar to those obtained by blending different ratios of low-acyl gellan gum as well as xanthan gum / locust-bean gum. For labelling purposes, achievement of textural modification by blending gellan gum alone would clearly be referred. Figure below demonstrates the rang of different textures that can be obtained simply by using different proportions of the high-acyl form. (Mason, 2000)
If starch is excluded, gelatine is the most widely used gelling agent. In contrast to the strong, brittle, non-elastic gels produced by low-acyl gellan gum, gelatine gels have a low modulus or perceived firmness moreover gelatine offer another avenue to textural diversity. For instance, addition of progressively augmenting amounts of 250 Bloom type a gelatine to 0.25% low- acyl gellan gum, a typical in-use concentration, causes a gradual augment in hardness, modulus plus elasticity and a gradual reduction in brittleness. Conversely, addition of low levels of low-acyl gellan gum, up to 0.05%, to replace up to around 1% gelatine in a 5% gelatine gel has no marked influence on the characteristic gelatine texture. It is conceivable, however, that the melting / setting temperatures of the gelatine might be advantageously augmented by inclusion of low levels of the higher melting in addition to setting low-acyl gellan gum. Low-acyl gellan gum / gelatine combinations might in addition help prevent toughening of gelatine gels upon refrigerated storage, allow low-grade gelatins to be upgraded in quality or permit lower gum concentrations to be used in certain applications. A recent patent describes combinations of gelatine and different forms of deacylated gellan gum. In the context of gelatine, the excellent flavour release form low-acyl gellan gum gels is worthy of mention. This flavour release is a consequence of gellan gum's ability to structure water in the gelled state at very low use levels rather than the gels having the 'melt in the mouth' characteristics associated by means of gelatine. (Miyazaki, 2006)
Raw as well as modified starches are often used to impart a characteristic heavy-bodied consistency and, in a number of cases, a gel-like structure to foods. Cold-water-dispersible instant starches are available however several starches require cooking to cause gelatinization plus generate the desired functional properties. The molecular changes that occur when starch is cooked and cooled are still poorly understood. However, it is generally accepted that a cooked starch paste consists of swollen intact moreover ruptured granules inside a continuous aqueous phase containing the solubilized amylase in addition to amylopectin, the two component polysaccharides of starch. When starch is used, additional hydrocolloids are often required to modify texture, reduce syneresis as well as improve freeze thaw stability. Although possible mechanisms for the interaction flanked by these hydrocolloids and starch have been suggested, current understanding is again poor. Consequently, starch hydrocolloid combinations are usually selected on an empirical basis. A standard indicator of performance of a starch system is the viscosity changes that occur during heating plus cooling as measured on an amylograph. Amylograph data on the influence of low-acyl gellan gum on the modified starch, Col-Flo67 (National Starch as well as Chemical Corp.), are shown in Fig, 21. The gellan gum produces a further rapid augment in initial build-up of viscosity. Viscosity subsequently remains fairly constant on further cooking moreover then rises less rapidly than the viscosity of the Col-Flo 67 alone upon cooling. These limited results are difficult to interpret on a fundamental basis however suggest that starch gellan gum combinations are worthy of further detailed study. In practical terms, it has already been shown that in certain pudding and pie fillings the levels of modified starch can be abridged by a half by inclusion of around 0.1% Kelcogel gellan gum. In these products, the structure imparted by the gellan gum results in a fifmer shorter texture; (Miyazaki, 2006)
The compatibility of polysaccharides by means of proteins depends on a number of factors such as relative concentrations, pH, ionic strength, temperature time in addition to, in case of foods, the nature of the other ingredients present. As of a compatibility standpoint, model studies are thus of limited value plus, as for starches, incompatibility problems that occur in products are most quickly solved by empiricism. Our experience by means of the interactions flanked by gellan gum kk as well as proteins has in addition been similar. Limited model studies indicated that while low-acyl gellan gum was compatible at neutral pH by means of milk proteins, soy, egg albumen, whey and sodium caseinate precipitation by means of all of these proteins occurred around pH 4. In contrast, it has been shown possible to produce a number of direct acidified and cultured dairy products using low-acyl gellan gum in combination by means of protective colloids such as guar gum moreover carboxymethylcellulose. Low-acyl gellan gum in addition shows good compatibility by means of proteins in non-acidified mile systems. The need to study protein / polysaccharide interactions under specific in-use conditions is emphasized by the fact that. Although low-acyl gellan gum and gelatine combinations are potentially useful as already discussed, precipitation can occur under certain conditions. The observation that sodium caseinate plus soy protein can prevent gelation of low-acyl gellan gum devoid of causing precipitation in addition requires further investigation to define further fully the conditions under which this occurs. (Miyazaki, 2006)
Effect of salt on gellan gum texture
Native gellan gum on heating as well as cooling in the presence of cations forms cohesive, elastic gels similar to those obtained by heating in addition to cooling mixtures of xanthan gum and locust-bean gum. Since this texture dose not appeal to most consumers, native gellan gum alone is not expected to see widespread utility as a gelling agent. However, when dispersed in cold water, it provides extremely high viscosities. A possible limitation to its use as a thickener is high sensitivity to salt. This effect is shown in Fig.3, which compares the viscosities of 0.3% solutions of xanthan gum and native gellan gum at different concentrations of salt. The viscosities recorded are K values derived as of the 'power-law' equation, η=Kγ n-1, and are approximations of the viscosities at one reciprocal second. The well-known stability of xanthan gum viscosity to changes in salt concentration is apparent. In contrast, the viscosity of the native gellan gum displays a strong dependence on salt concentration. The native gellan gum solutions are highly thixotropic plus the apparent high viscosities appear to be the result of the formation of a gel-like network. Similar thixotropic behaviour is observed when low concentrations of xanthan gum /locust-bean gum are dispersed in cold water. (Chandrasekaran, 1995)
Effect of salt on gellan gum gelation:
Effects of the substitution by potassium chloride (KCl) as well as calcium chloride (CaCl2) by means of sodium chloride (NaCl) on mechanical properties in addition to salt intensities of 0.8%, 1.2% agar gels moreover 1.2%, 1.6% gellan gum gels containing 1.0% sodium chloride were examined using physical measuring apparatus and a sensory evaluation. In case of the same agar concentration and the same kind of salt, there were no dependences of salt concentrations in rupture stress, rupture strain as well as rupture energy. Rupture stress of 1.2% plus 1.6% gellan gum gels containing 0.5% NaCl and 0.5% CaCl2 was significantly small as compared by means of that of gellan gum gel containing 1.0% NaCl (p<0.001), in addition to rupture stress of 1.2% and 1.6% gellan gum gels containing 0.8% NaCl moreover 0.2% CaCl2 was larger than that containing 1.0% NaCl (p<0.001). Syneresis of gellan gum gel by means of NaCl as well as CaCl2 augmented by means of augmenting the substitution ratio of CaCl2 by means of NaCl (p<0.001). In the same polysaccharide concentration and the same kind of salt, there were no significant differences in syneresis of the other gels (p>0.05). Salt intensity of agar gels or gellan gum gels by means of 0.5% NaCl plus 0.5% CaCl2 was evaluated to be smaller than that of gels by means of 1.0% NaCl (p<0.001). In gellan gum gels by means of CaCl2, the salt intensity was correlated by means of the syneresis ratio (p<0.01), however the salt intensity of agar gels did not recognized the correlations by means of rupture properties and syneresis (p>0.05).
Effects of the substitution by KCl in addition to CaCl2 by means of NaCl on salt intensities were assumed to be stronger by flavor of KCl as well as CaCl2 than by the chemical and physical restraint of ions.
Effect of sugar on gellan gum texture:
Studies of gellan gum reported the effects of cations, sugars and pH on the physicochemical properties of gellan dispersions as well as the mechanisms of interactions of gellan gum by means of other gelling agents. However, most of these studies focused on LA gellan, while few studies were reported on the basic properties of HA gellan. Investigations on the properties of
HA gellan are necessary to promote utilization of this bacterial polysaccharide in food plus pharmaceutical industry. (Chilvers, 1987)
Gellan random coils form double helices and subsequently aggregate to form three dimensional networks in an appropriate aqueous environment. Both monovalent as well as divalent cations stabilize the networks through cross-linking gellan double helices via carboxylate groups of gellan molecules. However, monovalent moreover divalent cations follow different mechanisms on gellan gelation.
Divalent cations (Mþþ) cross-link double helices directly (double helix-Mþþ-double helix), while monovalent cations (Mþ) cross-link double helices indirectly. As a result of different gelation mechanisms, divalent cations are further effective on gel formation than monovalent cations.
The objectives of the study were to investigate the effects of Naþ, Kþ, Caþþ in addition to Mgþþ cations on the sol-gel transitions of HA gellan dispersals, as well as to decide the gelling temperatures of HA gellan dispersions containing selected cations.
Effect of sugar on gellan gum gelation:
Sugars are commonly used in food gels to provide desired functional properties. For instance, high concentration of sugars was used to form high methoxyl pectin gels (Lopes da Silva & Goncalves, 1994; Ptitchkina, Danilova, Doxastakis, Kasapis & Morris, 1994; Rao & Cooley, 1993; Rao, Van Buren & Cooley, 1993). Addition of sugars augmented the dynamic Young's modulus and the melting point of k-carrageenan gels. Sucrose abridged the strength of k-carrageenan/ locust bean gum mixed gels, however augmented the strength of alginate gels. Sucrose augmented the water holding ability however abridged the strength of whey protein gels. Watase, Nishinari, Williams plus Phillips (1990) observed that the dynamic elastic modulus of agarose gels augmented by means of augmenting concentration of sugars up to a certain amount, however decreased by means of excessive addition of sugars. The glass transition and rheological properties of gellan gels by means of sugars were reported by several researchers. Papageorgiou et al. (1994) observed that augmenting the concentration of sucrose to 50% gradually augmented the gelling temperatures of gellan gels. Sworn and Kasapis (1998b) studied the effects of monomeric as well as dimeric sugars, and starch hydrolysates on the modulus moreover the yield stress in addition to strain of gellan gels.
The sol±gel transition plus rheological properties of gellan gels devoid of sugars have been extensively investigated. Further investigation on the effect of sugars on gellan gels will provide useful information to the food trade. Large bend collapse properties of gellan gels as concerned by the addition of fructose or sucrose;
The objectives were to study the gelling temperatures of gellan explanations, the clarity as well as The effects of cooling techniques on selected gel properties were in addition investigated.
Materials and techniques:
Gelling temperature:
Deacylated gellan gum powder (KELCOGEL F) was provided by Kelco Biopolymers (San Diego, CA). Gellan powder at 0.6 and 1%w/v concentrations in final solutions was dispersed in distilled and deionised water in a 400 ml beaker by means of a magnetic stirrer. The mixtures were heated to the boiling point and the temperature was maintained for 30 s to fully hydrate the polymers. Fructose (ACS reagent) or sucrose (ACS reagent) was added to the hot solutions to prepare sugar concentrations of 15, 25 as well as 35%w/v in solutions, plus the solutions were stirred for 30 s. Calcium chloride (`Baker Analyzed' reagent) or sodium chloride (`Baker Analyzed' reagent) was added to arrange solutions containing eight selected calcium absorptions (2±40 mM), or seven sodium concentrations (20±450 mM). The gelling temperatures were determined by dynamic rheological tests on a Bohlin Rheometer (Model VOR, Bohlin Rheology system C24.4HS. The dynamic testing was conducted at a incidence of 1 Hz in addition to 0.5% strain amplitude in sinusoidal oscillation mode. During testing, the temperature of the solution was abridged as of 808C to 208C at a constant rate of 0.68C/min. The dynamic shear storage modulus (G0) at each temperature (T) was recorded by a computer. The gelling temperature (Tgel) was determined by extrapolating a tangent line as of the steepest slope for the portion of the G0 ±T to intersect the abscissa moreover was averaged as of two duplicate tests. Details of testing technique have been demonstrated previously.
Gel clarity:
Gellan solutions were prepared as described in the previous section. After adding calcium chloride or sodium chloride, each solution was continuously stirred for 2 to 3 min as well as poured into six 4.5 ml 1 £ 1 cm2 square shape polystyrene cuvettes; three cuvettes were cooled in still air to room temperature (228C), as well as other three cuvettes were cooled by placing them in cold running water (158C).
All cuvettes containing the gels were stored at room temperature for 24 h. Light absorbance of the gellan gels was calculated at l. 490 nm by means of spectrophotometer using water as the reference. Initial scanning of gellan solutions and gels as of UV-visible light region (190± 800 nm) indicated an absorption peak at 290±296 nm in the UV region. Even though the maximum absorbance peak might be appropriate for other quantitative analysis, such as the determination of gellan concentration or other constituents, the absorbance peak at 290±296 nm might not be associated to the visible clearness of the gels. In the visible region (400±800 nm), the absorbance was highest at the lower end (400nm).
Thus 490 nm was selected as a reasonable cooperation flanked by having enough absorbance plus avoiding the interference as of UV region. The mean absorbance at 490 nm of gels cooled in air or in water was resolved as of three replicates. (Johnston, 1990)
Gelling temperatures of 1.0% gellan solutions containing sodium as well as sugar
Small absorbance represents little turbidity and fine clarity of the gels.
Gel preparation (1.5 and 1% low acyl gellan gum by means of 1% NaCl):
A yielding capsule application, where gelation is at present worn, is one of the areas of interest for LA gellan gum/xyloglucan mixed systems. In this kind of application, large modulus values at low temperatures as well as a low melting temperature are required as final capsule products are scaled by melting the periphery of two parts of a capsule by means of heat. Weighed amounts of gums were dispersed into an aqueous solution of 15% glycerol at room temperature in addition to heated for 15 min in boiling water. The hot solution was loaded into a cone as well as plate test fixture of a stress-controlled Bohlin rheometer preset over 80.degree. C. and immediately covered by means of silicone oil to prevent water loss. The sample was cooled to 10.degree. C. at a rate of 4.degree C/min. equilibrated at 10.degree. C. for 120 s, plus then heated >90.degree. C. at a rate of 4degree C/min; during the thermal treatments, the storage moreover loss modulus values were determined by applying a strain of 0.1. A mixture of 1% LA gellan gum and 1.5% xyloglucan forms a fairly strong gel by means of a storage modulus (G') value around 2,500 Pa at 10.degree. C. Furthermore, the melting temperature, defined as the temperature where the value of the loss modulus (G') becomes greater than the value of storage modulus, remains low at 40.degree. C. This melting temperature corresponds to thermal hysteresis of less than 10.degree. C also at the same time falls inside a range where typical gelatin gels used for soft capsule application melt; Stronger gels are obtainable at higher gum levels, while the melt temperature in addition augments, presumably due to a proportional augment in the levels of counterions as well as other ions contained as impurities in the gums. FIG. 5b shows that a gel comprising 1.2% LA gellan gum in addition to 1.8% xyloglucan gives a very large storage modulus value around 4,200 Pa at 10.degree. C. However, the melting temperature and thermal hysteresis become regarding 48.degree. C plus 15degree C, respectively Figure below shows that a gel comprising 1.5% LA gellan gum and 2.25% xyloglucan has a very large storage modulus value around 8,500 Pa at 10.degree. C. however the melting temperature as well as thermal hysteresis turns out to be regarding 67.degree. C. moreover over 30.degree C, respectively; (Clark, 1987)
2) Texture analysis:
The gels were separated as of the glass tubes, cut into cylinders of 20 mm length and 30 mm diameter and then subjected to an active texture profile analysis (TPA) similar to that described by Bourne (1982). The gel specimens were placed flanked by parallel at plate fixtures fitted to a TA.XT2 Texture Analyzer (Stable Micro Systems, Surrey, UK) interfaced by means of a micro-computer. The examples were lubricated by means of mineral oil on both ends prior to measurement, plus all measurements were made on gels equilibrated to ambient temperature. The gels were squashed twice at 0.5 mm/s to 30% of their original height. The outcomes are reported as the means of replacement tests. Textural strictures such as rigidity, fragility, cohesiveness as well as springiness can be attained as of the TPA curve as shown in figure below. The textural parameters measured in the present learning were defined as: (Fernandes, 1994)
Hardness Ð the peak force during the first compression cycle.
Brittleness Ð the first significant break during the first compression cycle divided by the original sample height, reported as a percentage. Note that a little brittleness value designates a further brittle gel.
Cohesiveness Ð the ratio of the area beneath the first in addition to second compression (A2/A1).
Springiness Ð the detachment the example was compressed during the second compression to the peak force, divided by the initial sample height, reported as a percentage.
Conclusion:
Adding fructose up to 35%w/v to 0.6 and 1.0% gellan solutions exhibited little effect on the gelling temperatures. The addition of 10% increment of sucrose augmented the gelling temperatures by 1.5±38C. However when both cation moreover sucrose concentrations were high, the gelling temperatures of gellan solutions were decreased by the addition of sucrose. The different effects of sucrose plus fructose on the gelling temperatures of gellan solutions can be attributed to the different ability of these two sugars to stabilize orderly packing of gellan double helices in water solutions. Adding sucrose or fructose augmented gellan gel clarity by reducing the differences in refractive index flanked by gellan polymer as well as the medium, i.e. by reducing the optical contrast flanked by gellan and the surrounding environment. The higher viscosity of sugar solutions might in addition contribute to gel clarity because viscose media hindered the growth of the junction zones. Sucrose exhibited similar effect as cations to stabilize the orderly packing structure of gellan. However like cations, excessive sucrose in addition hindered the formation and growth of junction zones. Thus at low cation concentrations, sucrose strengthened gellan gels; however at high cation concentrations, sucrose weakened the gels. Gellan gels formed by slow cooling in air were further turbid in addition to stronger than the gels formed by rapid cooling in water due to the prolonged gelation time that augmented the dimension of junction zones. (Kasapis, 1993)
