Effect of preservatives on milk solids in cow and buffalo milk

Abstract

Pooled milk samples were collected from cow and buffaloes maintained at the University Livestock Farm at weekly intervals. Three chemical preservatives viz., formalin (0.4 per cent), potassium dichromate (0.4 per cent) and bronopol (0.1 per cent) were studied for their efficiency of preservation. Calculated levels of preservatives were added and the samples were stored at room temperature in dark place. Major milk constituents like fat, total solids and solids not fat were estimated in control and preserved samples. Physical properties of milk such as pH, titratable acidity, clot on boiling test, lactometer reading as well as efficiency of preservation were studied in control and preserved milk samples .. Milk samples treated with formalin could be stored up to 90 days without any spoilage changes. A cream plug formed after 24 hours of storage and a white sedimentation at the bottom appeared after one month of storage. Potassium dichromate treated samples could be stored for 30 days. There after the samples curdled and became green in colour towards the end of the storage period.

11 Bronopol preserved cow and buffalo milk samples could be stored for 24 and 16 days respectively and samples became mild pink in colour as the storage period advanced. There was a significant increase in titratable acidity in cow and buffalo milk samples preserved with all the three chemical preservatives. The increase in acidity was steady and progressive in formalin and bronopol preserved samples. But an abrupt increase in acidity was noticed in potassium dichromate preserved samples immediately after the addition of preservative and there after a successive decrease was noticed. The pH values showed a significant decline during storage in preserved milk samples. Decline in pH was abrupt in potassium dichromate treated samples whereas it was gradual in samples treated with the other two preservatives. Formalin heated milk samples remained COB negative throughout the storage period of 90 days, whereas potassium dichromate and bronopol treated samples became COB positive after 15 and eight days of storage respectively. No significant variation was noticed in fat percentage of preserved milk samples estimated by Gerber method. But a slight decrease in fat per cent was observed in formalin and

III potassium dichromate treated samples. The concentration of Sulphuric acid used was increased to 94 per cent for estimating fat percentage in formalin preserved milk samples. Formalin preserved samples showed inconsistent changes in fat percentage estimated by Milko- Tester. So this method cannot be recommended for formalin preserved milk samples. Bronopol treated milk samples showed lesser variation in milk fat percentage estimated by Milko-Tester when compared to potassium dichromate and formalin. There was a non-significant increase in total solids and solids not fat content in potassium dichromate preserved samples. Potassium dichromate preserved samples showed significant increase in lactometer reading, where as formalin and bronopol treated samples did not show any significant changes in lactometer reading. Formalin appears to be ideal for the existing standard methods of estimating milk solids. With the popularization of instrumental methods for fast and accurate analysis of milk constituents, formalin will not be suitable as a milk sample preservative in future. Further, formalin and potassium dichromate have deleterious effects on human health and environment. Even though bronopol is little expensive, it is best suited for instrumental analysis of milk constituents and safe for handlers. So, bronopol is recommended as a preservative for the near future.