Evaluation of Thermal Processing of Commercially Available Milk Brands in Lahore A

Abstract

Raw milk and commercially available milk samples were tested for the alkaline phosphatase activity to evaluate the efficacy of the pasteurization of milk. A colorimetric assay used for the kinetic determination of serum alkaline phosphatase was employed to detect ALP in the targeted samples. The colorimetric assay uses p-nitrophenyl phosphate as the reaction substrate. When ALP acts upon this substrate, it breaks down into a phosphate group and p-nitrophenol which produces the characteristic yellow color in the solution. The increase in absorbance of the solution measured at 405 nm is directly related to the ALP activity in the respective sample. Sample solution and reagents were mixed well and then subjected to spectrophotometric readings using 405 nm. Three raw milk samples were tested firstly as a whole and then after fat removal through centrifugation at 4000 rpm for 30 min. Seven UHT and three naturally pasteurized commercial milk samples available in the local market were used for the ALP detection in this study. Significant values for ALP activity in raw milk samples were observed whereas, for all the pasteurized samples, the test was observed to be negative. This negative result for the pasteurized samples indicated that effective pasteurization was carried out before the milk was packed to be sold in the market. Casein is the major protein found in milk in the concentration of 35g/L. It exists in the form of a heterogeneous mixture of phosphorous-containing proteins. It is a slow-digesting dairy protein that reduces muscle breakdown and improves recovery and muscle growth. In addition to the ALP activity determination, casein isolation and measurement were also carried out in 1 raw milk sample and all the 10 pasteurized samples. The obtained mean value of casein was 3.43g per 100 ml of milk sample, whereas the values for standard deviation and relative standard deviation were 0.08 and 2.54 respectively. Based on the negative results for ALP and actual yield of casein found to be closer to the theoretical yield for all the samples it can be suggested that all of the targeted milk brands were safe to be consumed