Sensor System for Online Detection of Somatic Cells in Bovine Milk

Abstract

The objectives of this study were to develop an assay to quantify somatic cells in raw milk using fluorescent double-stranded DNA (dsDNA) markers and to develop a sensor implementing the detection chemistry. Three methods were used to extract DNA from somatic cells in milk. Method one involved a fat removal step via centrifugation and a commercial kit to extract DNA. Method two involved a fat removal step via centrifugation and cell lysis via mechanical shearing. Protease was added to eliminate enzymes that denature DNA and to degrade milk proteins that contribute to sample opacity. Syringe filters were used to clarify the solution even further. Method three involved a detergent and mechanical shearing for cell lysis and a high pH to deactivate enzymes and reduce casein micelle size; no mechanical measures were taken to reduce turbidity in the final solution. For all three methods, 13 µL of fluorescent dsDNA markers were added to the final DNA solution and buffer was used to bring the final volume to one mL in a cuvette. The markers were given one minute to bind to dsDNA before a voltage output was read from the sensor, which was designed to hold the cuvette and light detection equipment. The sensor was calibrated using calf-thymus DNA in buffer and raw milk of known somatic cells counts with assays using methods one, two, and three. Preliminary findings indicate that the sensor can quantify somatic cells in milk in the physiological range.