Section 7
Chapter 6,358

Routine testing of farm tank milk with the milko scan 203 3. comparative evaluation of polarimetry high performance liquid chromatography enzymatic assay and reductometry for the determination of lactose calibration for ir analysis of lactose calculation of total solids from ir measurements

Koops, J.; Olieman, C.

Netherlands Milk and Dairy Journal 39(2): 89-106


ISSN/ISBN: 0028-209X
Accession: 006357869

The results of the determination of lactose in milk by polarimetry (POL), high-performance liquid chromatography (HPLC), enzymatic assay (ENZ) and reductometry (RED) were compared. A few crucial details of POL, i.e., the value for the specific rotation of anhydrous lactose .**GRAPHIC**. and the volume of the precipitated mass of fat and protein were re-evaluated. The HPLC-technique was improved, introducing raffinose as an internal standard and applying a highly sensitive [refraction index] RI-detection system. POL, HPLC and RED analyses were performed at the Institute, ENZ was carried out in collaborative tests by 6 laboratories. The average difference between the values for HPLC and ENZ was 0.01% lactose, suggesting that both methods, which are based on entirely different principles, are accurate. POL indicated a slightly higher level (0.02-0.03%) and the RED values were, on average, 0.17% too high. The merits of POL, HPLC and ENZ are fully discussed, also in view of the calibration of IR instruments by lactose. The value of the constant factor in the calculation of the total solids of milk from IR measurements of fat, protein and lactose is discussed.

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