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Microdetermination of Keltrol (Xanthan Gum)

Departmet of Chemistry, University of Puerto Rico, Mayaguez 00708

ABSTRACT

Keltrol added to milk, ice cream, chocolate milk and other products was determined colorimetrically in the presence of carboxymethylcellulose. Alginate and pectic acid were removed by precipitation as the insoluble calcium salts, while sulfated polysaccharides were removed by precipitation with cetylpyridinium chloride in 0.5 m NaCl. Without locust bean gum, filtration was over Reeve angel 202 paper. Without locust bean gum in the mixture, filtration was over a column of acid-washed silica (sand) instead of over filter paper. Finally, Keltrol and CMC were coprecipitated by cetylpyridinium chloride in 0.2 m NaCl. The mixed precipitate was trapped on a Hyflo Super Cel column, washed with 0.2 m Na₂SO₄ and then with hot (80 C or higher) 30% (v/v) H₂SO₄ to disperse the gum complexes and elute the Keltrol and CMC. Carboxymethylcellulose in the eluate was determined by the chromotropic acid method (Keltrol does not react). Carboxymethylcellulose + Keltrol was determined by the phenol-H₂SO₄ and the anthrone methods. The amount of Keltrol present was determined by difference, using standard curves for the hydrocolloids when reacted with the aforementioned reagents. Recoveries of 90 to 96% were achieved from milk, chocolate milk, and salad dressing. The method determined Keltrol in milk and other food products at 0.05% (w/w) or lower.