Effect of cooking vessel composition on fluoride.

Abstract

Cooked foods that are prepared in water containing fluoride are a source of dietary fluoride (OSIS ET AL, J Dent Res 52 (Special Issue): Abstract No. 239, 1973) . The evaporation that occurs with boiling is a potential source of more concentrated fluoride solutions. The material that the cooking vessel is made from also may have an effect on the fluoride content of water used in food preparation. Several metals form insoluble compounds with fluoride. Pyrex glass may absorb fluoride on its surface. Newer coatings applied to ease cleansing such as Teflon are chemically less reactive and could alter the effect of the structural material. To evaluate the effect of container composition on the fluoride available for incorporation into cooked foods, water was boiled in typical cooking vessels and the changes in fluoride concentration were measured. Tap water in a community whose water supply had been studied previously for fluoride content (FULI and PARKINS, J Dent Res 51: 666, 1972) was used. One-quart sauce pans that had received moderate prior use were selected. Four vessels of different composition (aluminum, stainless steel, Pyrex, and Teflon) were heated on a heavy duty hot plate. A quantity of one pint of tap water was analyzed for fluoride and placed in each vessel. The highest temperature setting on the hot plate control was used to bring the water to a vigorous boil. The heat then was reduced to maintain a moderate degree of boiling for 15 minutes. A sample portion was transferred to a clean polyethylene bottle for storage. The fluoride concentration in the samples was determined with a fluoride ion specific electrodea and a sleeve junction calomel reference electrode connected to a digital electrometer.b The buffer suggested by McCann (Arch Oral Biol 13: 475577, 1968) for pH and ionic strength adjustments were used in a 1:1 dilution of all samples (Applications Bulletin No. 5, Orion Research Inc., Cambridge, Mass, 1967). All measurements were made at room temperature by recording the stabilized potential. The standards were dilutions of a standard fluoride solutionc in deionized water. The fluoride concentrations observed before and after boiling for each container and the change in fluoride concentrations are shown in the illustration. A pronounced increase was seen with the Teflon-coated vessel. The boiled water from the aluminum vessel showed notable decrease. Little change was noted in the fluoride