A SURVEY OF NITRATE CONTENTS IN INDONESIAN MILK BY ENZYMATIC ANALYSIS

In this paper, a rapid and simple enzymic method is described for the determination of nitrate in 32 fresh and five dry Indonesian milk samp les, deproteinized by Carrez reagents. Interference from albumin, case in, lactose and chloride ions was controlled. The calibration graph wa s linear over the range 1-12.5 mu g/ml NO3- r = 0.9998. The Limits of detection and quantification were found to be 0.45 mu g/ml NO3- and mu g/ml NO3- respectively. Standard nitrate solutions (10 mu g/ml NO3-) were used to evaluate the precision. The results showed an average of 10.1 mu g/ml, a standard deviation of 0.3 and a relative standard devi ation of 3.4%. Adequate agreement was found between results obtained b y the enzymic method and those of the French official reduction/photom etric reference method (AFNor). Good recoveries (100% +/- 5%) were fou nd for nitrate added to milk. The nitrate levels were in the range 1-2 .6 mg/kg NO3- for fresh milk and 1.1-18 mg/kg NO3- for dry milk. All t he results are in good agreement with those previously published for U K and American milk.