§ 172.695 Xanthan gum.
The food additive xanthan gum may be safely used in food in accordance with the following prescribed conditions:
（a） The additive is a polysaccharide gum derived from Xanthomonas campestris by a pure-culture fermentation process and purified by recovery with isopropyl alcohol. It contains D-glucose, D-mannose, and D-glucuronic acid as the dominant hexose units and is manufactured as the sodium, potassium, or calcium salt.
（b） The strain of Xanthomonas campestris is nonpathogenic and nontoxic in man or other animals.
（c） The additive is produced by a process that renders it free of viable cells of Xanthomonas campestris.
（d） The additive meets the following specifications:
（1） Residual isopropyl alcohol not to exceed 750 parts per million.
（2） An aqueous solution containing 1 percent of the additive and 1 percent of potassium chloride stirred for 2 hours has a minimum viscosity of 600 centipoises at 75 °F, as determined by Brookfield Viscometer, Model LVF （or equivalent）, using a No. 3 spindle at 60 r.p.m., and the ratio of viscosities at 75 °F and 150 °F is in the range of 1.02 to 1.45.
（3） Positive for xanthan gum when subjected to the following procedure:
Locust Bean Gum Gel Test
Blend on a weighing paper or in a weighing pan 1.0 gram of powdered locust bean gum with 1.0 gram of the powdered polysaccharide to be tested. Add the blend slowly （approximately1/2minute） at the point of maximum agitation to a stirred solution of 200 milliliters of distilled water previously heated to 80 °C in a 400-milliliter beaker. Continue mechanical stirring until the mixture is in solution, but stir for a minimum time of 30 minutes. Do not allow the water temperature to drop below 60 °C.
Set the beaker and its contents aside to cool in the absence of agitation. Allow a minimum time of 2 hours for cooling. Examine the cooled beaker contents for a firm rubbery gel formation after the temperature drops below 40 °C.
In the event that a gel is obtained, make up a 1 percent solution of the polysaccharide to be tested in 200 milliliters of distilled water previously heated to 80 °C （omit the locust bean gum）. Allow the solution to cool without agitation as before. Formation of a gel on cooling indicates that the sample is a gelling polysaccharide and not xanthan gum.
Record the sample as “positive” for xanthan gum if a firm, rubbery gel forms in the presence of locust bean gum but not in its absence. Record the sample as “negative” for xanthan gum if no gel forms or if a soft or brittle gel forms both with locust bean gum and in a 1 percent solution of the sample （containing no locust bean gum）.
（4） Positive for xanthan gum when subjected to the following procedure:
Pyruvic Acid Test
Pipet 10 milliliters of an 0.6 percent solution of the polysaccharide in distilled water （60 milligrams of water-soluble gum） into a 50-milliliter flask equipped with a standard taper glass joint. Pipet in 20 milliliters of 1 N hydrochloric acid. Weigh the flask. Reflux the mixture for 3 hours. Take precautions to avoid loss of vapor during the refluxing. Cool the solution to room temperature. Add distilled water to make up any weight loss from the flask contents.
Pipet 1 milliliter of a 2,4-dinitrophenylhydrazine reagent （0.5 percent in 2 N hydrochloric acid） into a 30-milliliter separatory funnel followed by a 2-milliliter aliquot （4 milligrams of water-soluble gum） of the polysaccharide hydrolyzate. Mix and allow the reaction mixture to stand at room temperature for 5 minutes. Extract the mixture with 5 milliliters of ethyl acetate. Discard the aqueous layer.
Extract the hydrazone from the ethyl acetate with three 5 milliliter portions of 10 percent sodium carbonate solution. Dilute the combined sodium carbonate extracts to 100 milliliters with additional 10 percent sodium carbonate in a 10-milliliter volumetric flask. Measure the optical density of the sodium carbonate solution at 375 millimicrons.
Compare the results with a curve of the optical density versus concentration of an authentic sample of pyruvic acid that has been run through the procedure starting with the preparation of the hydrazone.
Record the percent by weight of pyruvic acid in the test polysaccharide. Note “positive” for xanthan gum if the sample contains more than 1.5 percent of pyruvic acid and “negative” for xanthan gum if the sample contains less than 1.5 percent of pyruvic acid by weight.
（e） The additive is used or intended for use in accordance with good manufacturing practice as a stabilizer, emulsifier, thickener, suspending agent, bodying agent, or foam enhancer in foods for which standards of identity established under section 401 of the Act do not preclude such use.
（f） To assure safe use of the additive:
（1） The label of its container shall bear, in addition to other information required by the Act, the name of the additive and the designation “food grade”。
（2） The label or labeling of the food additive container shall bear adequate directions for use.
更多关于美国 FDA 已批准的直接用于人类食品的添加剂种类法规，请点击美国FDA 21 CFR 第172部分已批准的直接用于人类食品的添加剂种类汇总
