Effects of Preservatives on Raw Milk Components Analyzed by Infrared Spectrophotometry

Abstract

The effects of preservatives on milk component analysis using infrared spectrophotometric method were investigated. Raw milk samples from sixty farms were collected. Thirty ml from each milk sample was kept in plastic vial containing either 0.02 % bronopol, 0.40 % potassium dichromate or sodium azide tablet (0.03 %) as preservatives. All milk sub-samples were stored under refrigeration at  4^oC then analyzed for milk components at 0, 7, 14, 21 and 28 days of storage. Control samples (without preservative) were analyzed only at 0 day. The means of milk fat, protein, lactose and total solids for the non-preserved milk at 0 day storage were 4.10, 3.00, 4.84 and 12.65 %, respectively. Analysis result of milk components among the control, milk preserved with bronopol and milk preserved with potassium dichromate showed no statistical different at 0 day storage. At this storage day, however, raw milk with sodium azide had lower (P<0.01) fat, protein and total solids. Prolonged storage of milk preserved with the three chemicals over 7 days illustrated a potential decline in most components analyzed. Changing pattern of the analysis results of milk preserved with the three respective chemicals at 28 days when compared with those of 0 day storage were -5.39, -4.79 and -8.36 % for fat, -0.30, -1.17 and +0.13 % for protein, -1.22, -0.91 and -0.91 % for lactose, and -2.45, -2.29 and -3.11 % for total solids. It is concluded that bronopol, potassium dichromate and sodium azide are effective preservatives for raw milk component analysis by infrared spectrophotometry. However, commercial sodium azide in the tablet form contains sodium salt, which can depress milk component analysis result. In addition, preserved raw milk samples should be kept under refrigeration at 4^oC and analyzed within 7 days.