Abstract
A modified spectrophotometric method based on the selective diazotization-coupling reaction has been developed capable of detecting 1ppm nitrite in dry milk products. Nitrate can be determined by the same reaction following quantitative reduction to nitrite with a cadmium column. Zinc hydroxide satisfactorily precipitated the milk fat and protein. Nitrate and nitrite levels have been determined in nonfat dry milk samples prepared on a single pilot plant dryer designed for either indirect (steam) heating or direct (gas) firing with natural gas. Slight increases in nitrate content attributable to gas firing were detected, whereas increases in nitrite were nil. A survey of 30 dry milk samples from 13 commercial plants revealed that products produced by direct-firing contained 1 to 3ppm more nitrate-nitrogen than those produced by indirect heating designs.
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