An Overview on Applications of Guar Gum in Food systems to Modify Structural Properties

Polysaccharides define as complex polymers composed of units interlinked with glycosidic bonds originated naturally. Polysaccharides are categorizing in several groups and among them, Gums are those with critical roles in food systems. Guar Gum is imparting softness, emulsification, stabilizing via its addition to formulas. This Gum is a fast soluble in cold water and can be active in a wide range of pH. The aim of this overview is giving an initial concept about guar gum and then convey to an introduction of its applications in food industries.


INTRODUCTION
Guar Gum or guaran is extracting from endosperm of Cyamopsis tetragonolobus (figure 1) and C. psoraloides [1]. Guar plant belongs to family Fabaceae or Leguminaceae. Common name, is guar, from "sankrist word" "go" or "gav". Guar bean contains a large endosperm rich in galactomannan, a gel forming agent in water. As depicting in figure 1 Guar gum is composed of chain (1→4)-linked β-D mannopyranosyl units substituted at O-6 by single-unit side-chains of α-D-galactopyranose (figure 3) [2]. The germ and hull of the guar seeds are called Guar meal, which is rich in protein. Figure 2 depicts different part of Guar seed.

Fig-2: Schematic of different parts of Guar seed
There are some parameters effects on characteristics of Guar gum such as particle size, temperature [4].

RESULTS AND DISCUSSIONS
Increase the molecular weight and concertation increases the non-Newtonian behavior of guar solutions [5,6]. It is native in India, Pakistan, united states and some parts of Sudan are the originality of Guar plant.
Guar is a plant exudate and can participate in viscosity and gelling process characteristics. A distinctive properties of polysaccharides in performance of natural systems are their hydrogen bonding potentials which makes them appropriate in useful services.
Dietary polysaccharides refer to a group with inert structure, mainly non soluble, by which some rheological and sensory characteristic of a food system modifies. Remained polysaccharides can drive compactness thickening quality etc. First time, guar found as source of gum in 1945 and started to become a global prominence crop [7].
Mostly the application of guar gum can summarize as below; 1. Drying and preserving of pod for future [8,9]. 2. With respect to be a high protein source, it uses as Mammals' feeding [10].
Rheological properties of Guar gum could be arising from random coil polymers of this gum in solutions [12,13]. Gum behaves thixotropic and immediately forms a high viscous solution in cold water [14].
In addition, stability of guar gum in acidic condition is reasonable the lowest possible pH found to be stable is 2 at 25°C [9]. Indeed, guar gum is a kind with a wide range of food applications such as ice cream, meat and dairy products. Some roles of Guar which has found suitable in food systems are reduction of chewiness, prevention of ice growth, enhancing organoleptic and sensory properties [10]. High viscosity makes guar suitable in case of bakery products in which moisture retention influenced by while in frozen foods it prevents synersis [15] Ice cream, a food product with superiority of being normal healthy, easy digestibility and a good source of Vits [16] indicates a pseudo plastic behavior. [17].
Certainly, guar gum plays in improving of ice cream in both consistency and viscosity. It also aids the stabilization while changing in flavor [18,19]. In cold water, guar gum swells and its technical degree depends on the rate of thickening and final viscosity. Guar gum is commonly considerable as a locust bean gum replacer. The main difference arises from their interaction to viscosity; Guar dissolves in cold water, whereas locust bean gum needs cooking for reaching to Max of viscosity [7].
Overall, guar gum gives a time, concentration and temperature dependent viscosity. up to a 0.5% concertation of guar gum we can see a linear Newtonian like behavior while in more concentrations pseudo plastic flow gives a concept of molecular interactions [20,21].
The amount of 0.1-1.15% of Guar gum to finished cake creates better icing and frosting along with more moisture retention during shelf life. Guar gum causes that bakery products have a more integrate structure as well as yields to an easy slicing texture with no crumbling. Salad dressing also can be formulated by addition of guar gum owing to its high binding capacity. Guar gum also can prevent migration of food constituents mainly fat, controlling of WHC [7].
Guar can increase the viscosity of the aquatic phases followed by reduction in separation rate of W/O phases [22]. Since beverage is processing under cold conditions therefore solubility of guar in cold water is a point which along with resistance at low pH conditions consider a precedence. In order of beverage a 0.1-0.15% of weight can be sued [7]. Table 1 has summarized recent studies on the guar applications in food industries. CONCLUSION Based on the current overview, it can be said that guar gum considers as a source of human nutrition. This hydrocolloid is one of the practical gums in food industries and systems which has been used historically as food, additive. It is also a supplement additive to enhance the quality of food materials. The following study is still needed to discover the novelty of this gum for various sections.