[Code of Federal Regulations]
[Title 21, Volume 3]
[Revised as of January 1, 2007]
From the U.S. Government Printing Office via GPO Access
[CITE: 21CFR173.20]
[Page 122]
TITLE 21--FOOD AND DRUGS
CHAPTER I--FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN
SERVICES (CONTINUED)
PART 173 SECONDARY DIRECT FOOD ADDITIVES PERMITTED IN FOOD FOR HUMAN
Subpart A Polymer Substances and Polymer Adjuvants for Food Treatment
Sec. 173.20 Ion-exchange membranes.
Ion-exchange membranes may be safely used in the processing of food
under the following prescribed conditions:
(a) The ion-exchange membrane is prepared by subjecting a
polyethylene base conforming to Sec. 177.1520 of this chapter to
polymerization with styrene until the polystyrene phase of the base is
not less than 16 percent nor more than 30 percent by weight. The base is
then modified by reaction with chloromethyl methyl ether, and by
subsequent amination with tri methyl amine, di methyl amine, di ethyl
ene triamine, or di methyl ethanol amine.
(b) The ion-exchange membrane is manufactured so as to comply with
the following extraction limitations when subjected to the described
procedure: Separate square-foot samples of membrane weighing
approximately 14 grams each are cut into small pieces and refluxed for 4
hours in 150 cubic centimeters of the following solvents: Distilled
water, 5 percent acetic acid, and 50 percent alcohol. Extraction from
each sample will not exceed 0.4 percent by weight of sample.
(c) The ion-exchange membrane will be used in the production of
grapefruit juice to adjust the ratio of citric acid to total solids of
the grapefruit juice produced.
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