Biomedical subjects

D A Biggs

Publications and source records attributed to D A Biggs.

4 recordsLinked to original sources

PubMed1979

Infrared estimation of fat, protein, and lactose in milk: evaluation of multispec instrument.

Thirty-eight milks (including homogenized and unhomogenized herd milks, individual cow milks, and packaged milks) were pre-analyzed by accepted standard methods and then analyzed in duplicate with a Multispec instrument on 2 different days. For the combined data, mean differences between duplicates were 0.01% or less within days and 0.025% or less between days. Standard deviations of difference between duplicates were 0.02% or less. Overall mean differences between Multispec and standard results were 0.02% or less with standard deviations of difference of 0.041%, but means for protein in packaged milks were 0.038% lower and means for lactose in individual cow milks were 0.04% higher than standards. Standard deviations of difference for fat were lower (0.016%) than average for packaged milks and higher (0.06%) than average for individual cow milks. Differences between Multispec results for homogenized and unhomogenized samples of the same herd milks were small, averaging 0.013% for fat, 0.005% for protein, and 0.011% for lactose. Regression equations for the combined data gave standard errors of estimate of about the same magnitude as the standard deviations of difference. Single calibrations would give good estimates for all of the types of milk analyzed, but for best accuracy the instrument should be calibrated with the type of milk to be analyzed.

Animals↗

PubMed1979

Performance specifications for infrared milk analysis.

Maximum limits of 0.02% are recommended for precision of IR analysis for fat, protein, and lactose, and 0.04% for total solids. Recommended maximum systematic errors are 0.06% for fat, protein, and lactose, and 0.12% for total solids, when instrument results are compared with results of specified AOAC methods. Recommended maximum mean differences between instrument and standard results are based on 95% confidence limits for the mean of 8 samples; precision and systematic errors are calculated as the standard deviation of difference between duplicates for 8 samples, and systematic errors are calculated as the standard deviation of difference between instrument and reference results for 8 samples. Automated sections for milk of Official Methods of Analysis were rewritten to eliminate references to individual instruments, to eliminate possible differences between calibration procedures for different instruments, and to stress important instrument operational characteristics which can have significant effects on instrument performance.

Animals↗

PubMed1978

Instrumental infrared estimation of fat, protein, and lactose in milk: collaborative study.

Thirty-six milks pre-analyzed by accepted standard methods were analyzed with Milko-scan instruments at 6 laboratories. Using pairs comparisons as described by Youden, precision errors for fat were about 0.033% for the first and 0.022% for the second of duplicate tests, indicating a carry-over effect for the first tests. Precision errors for protein were about 0.021% for both tests. Systematic errors for fat were about 0.17% with calibrations based on reference analyses at each laboratory but were reduced to about 0.044% with calibrations by reference analyses from one laboratory. With homogenized milks, systematic errors for fat increased to about 0.07% and were larger at high fat levels. This effect could be minimized by changing the wavelength of maximum transmission for the fat filter. Systematic errors of about 0.067% for protein were reduced to about 0.03% with calibrations based on common reference analyses. Satisfactory calibrations for lactose were obtained with the 2 Milko-scan 203 models with standard errors of estimate of 0.034 and 0.033%. Results for homogenized and unhomogenized milk were different for most instruments, indicating the need to calibrate for them separately.

Animals↗

PubMedDate not supplied

Alternative methods for infrared analysis of fat in milk: interlaboratory study.

A study in 3 laboratories has demonstrated that accuracy of infrared analysis of fat in milk can be improved relative to results by AOAC method 16.083-16.092 by measuring IR absorption by CH2 and CH3 groups in fat molecules instead of or in addition to measuring absorption by carbonyl groups. Theoretical implications for alternative choices of measurements for fat analysis are discussed, and data are presented to indicate the agreement between theory and practice. Mathematical formulas developed from the Beer-Lambert law are presented to describe mechanisms for dual wavelength, double beam, and single beam optical arrangements. A mathematical description of circuitry for these arrangements is included. Methods for multiple linear regression estimates of calibration parameters are discussed. Comparison data indicate optimum situations regarding frequency of calibration and random selection of calibration samples. With optimum control of calibration parameters, mean bias for randomly chosen check samples was reduced to less than 0.01%. Standard deviation of difference for fat estimates was reduced to range from 0.026 to 0.034%. Quality control procedures and calibration techniques for individual instruments are described. The use of the Fat B filter and a combination of the Fat A and Fat B filters has been adopted official first action as a revision in method 16.083-16.092.

Animals↗