Guar Gum is a gum obtained from the ground endosperms of Cyamopsis tetragonolobus (Linné) Taub. (Fam. Leguminosae). It consists chiefly of a high molecular weight hydrocolloidal polysaccharide, composed of galactan and mannan units combined through glycosidic linkages, which may be described chemically as a galactomannan.
Sample: 2 g
Analysis: Place the Sample in a 400-mL beaker, and moisten it with 4 mL of isopropyl alcohol. Add 200 mL of cold water with vigorous stirring, and continue stirring until the Sample is completely and uniformly dispersed.
Acceptance criteria: An opalescent, viscous solution results.
Analysis: Transfer 100 mL of the solution prepared in Identification test A to a 400-mL beaker, heat in a boiling water bath for about 10 min, and cool.
Acceptance criteria: No appreciable increase in viscosity is produced. (Distinction from locust bean gum: see Reagents, Indicators, and SolutionsReagents).
• Content of Galactomannans
Analysis: Subtract from 100.0 the total percentages from the tests for Articles of Botanical Origin, Total Ash; Acid-Insoluble Matter; Protein; and Loss on Drying.
Acceptance criteria: NLT 66.0%
• Arsenic, Method II 211: NMT 3 ppm
• Lead 251
Analysis: Prepare a Test Preparation as directed in the chapter, and use 10 mL of Diluted Standard Lead Solution (10 µg of Pb) for the test.
Acceptance criteria: NMT 10 ppm
• Heavy Metals, Method II 231: NMT 20 ppm
• Articles of Botanical Origin, Total Ash 561: NMT 1.5%
• Acid-Insoluble Matter
Sample: 1.5 g
Analysis: Transfer the Sample to a 250-mL beaker containing 150 mL of water and 1.5 mL of sulfuric acid. Cover the beaker with a watch glass, and heat the mixture on a steam bath for 6 h, rubbing down the wall of the beaker frequently with a rubber-tipped stirring rod, and replacing any water lost by evaporation. At the end of the 6-h heating period, add 500 mg of a suitable filter aid, and pass through a suitable tared, ashless filter. Wash the residue several times with hot water, dry the filter and its contents at 105 for 3 h, cool in a desiccator, and weigh. Determine the amount of acid-insoluble matter by subtracting the weight of the filter aid from that of the residue.
Acceptance criteria: NMT 7.0%
Sample: 1.0 g
Analysis: Transfer the Sample to a 500-mL Kjeldahl flask, and proceed as directed in Nitrogen Determination 461, Method I. Determine the percentage of nitrogen. Calculate the amount of protein by multiplying the percentage of nitrogen by 6.25.
Acceptance criteria: NMT 10.0%
Analysis: To a solution (1 in 10) of Guar Gum add a few drops of iodine TS.
Acceptance criteria: No blue color is produced.
• Loss on Drying 731: Dry a sample at 105 for 5 h: it loses NMT 15.0% of its weight.
• Packaging and Storage: Preserve in well-closed containers.