Accuracy and Repeatability of Milk Total Solids Analysis by Microwave Moisture Oven

Abstract

A microwave moisture tester (CEM AVC80) was evaluated as an alternative to the official AOAC (Association of Official Analytical Chemists) oven drying method for calibration of the solids-non-fat function of Multispec infra-red (IR) milk analyzers. Reference samples used to calibrate the IR instruments were analyzed by both AOAC and CEM procedures during a period from October to December, 1987. Chemical solids-non-fat (SNF) values were determined as AOAC or CEM total solids less Mojonnier fat. SNF values based on each drying method were independently used to calibrate the SNF function of the IR instruments and compared using mean difference values (estimates less chemical values). Residual plots showed uniform distribution of residuals with respect to SNF levels indicating that the calibration models fit both CEM and AOAC data equally well. The CEM produced mean total solids values 0.09% higher than AOAC values. Two separate repeatability trials showed that a 1988 model of the CEM AVC-80 was more repeatable than the 1987 model (standard deviation of duplicate differences was 0.020 versus 0.029) but both were less repeatable that the AOAC method (standard deviation of differences was 0.011).