RAPID DETERMINATION OF TOTAL NITROGEN IN SOY SAUCE BY KJELDAHL METHOD WITH MICRO-WAVE HEATED SAMPLE DIGESTION

Digestion of soy sauce sample by heating with microwave was studied and used in combination with the Kjeldahl method for determination of total nitrogen.It was found that the sample was digested completely in 20 min by micro-wave heating.Precision test was made on 3 samples of different brands,values of RSD′s calculated from the results of 7 determinations for each sample were found less than 2%.To 100 mL of different soy sauce samples,portions of 0.50 g of nitrogen added as (NH4)2SO4 were added for test of recovery,results obtained were in the range of 96%-103%.In the analysis of 7 samples of soy sauce of different brands for their total nitrogen contents by both the method presented in this paper and the method given in GB/T 18186-2000,the results obtained were in consistency with each other,and no significant difference was found by the result of t-test.