Validity of Gerber butyrometric method compared with Röse Gottlieb method for milk fat determination

Abstract

A validity methodology of the Gerber method through a comparison study to the Rose Gottlieb reference method is presented.
The analysis of Gerber (G) and Röse Gottlieb (RG), in a total of 100 raw milk samples, with a range of 1.80 and 5.50% (m/m) of fat, were carried out according to oificial FIL-IDF 152 A: 1997 and FIL-IDF ID: 1996 rules respectively. The regression equation found (RG = 0.9998 G + 0.0278) presented a gradient not significantly different to 1.000 (0.9846 < b < 1.0149) and an intercept not significantly differing from 0 (-0.0274 < a < 0.0830). The residual standard deviation was Sy,x = 0.0853 and the accuracy of the method was therefore + 0.17g/100 g (+ 1.987 Sy,x) at present conditions. Gerber method exactuess, expressed as repeatability, presented a repeatability standard deviation of Sr= 0.0308 and a repeatability of r = 0.087 g/100 g, according to FIL-IDF 128: 1985; thus allowing to estimate both the method reproducibility (R = 2 r) and confídence Ínterval, including the mean precisión and accuracy (random error and systematic error). On the other hand, the analysis of media values indicated the acceptance of the nule hypotesis, t_0.05 = -0.1645 (P = 0.86) and a correlation coefficient of r = 0.9972.
It is concluded that Gerber Method for milk, carried out according to FIL-IDF 152A: 1997 rule, with a milk volume of 10.77 ml presented acceptable validity parameters, in lineal, precision and accuracy terms.