Screening procedure for evaluating heat load in commercial milks

The evaluation of heat damages in commercial milk samples has been studied by an analytical procedure which uses two different and complementary metho ds. The first is the rapid total sulphydryl (SH) group measurement which ev aluates whey protein denaturation. The second involves the measurement of a bsorbance at 340 nm (A(340)) of milks modified with the Clarifying Reagent( R). At this wavelength some coloured compounds resulting from the non-enzym ic browning still absorb. There is a satisfying correlation between A(340) and lactulose content (r = 0.98) measured in commercial milk samples by usi ng capillary electrophoresis or high performance liquid chromatography (HPL C). Our analytical procedure using SH and A(340) measurements has been appl ied to 130 raw and commercial milk samples. Analysis by Student's t-test sh ows that the values of the two parameters obtained for raw and heat-treated milk samples were significantly different (P < 0.01). This study demonstra tes that this simple protocol makes possible rapid evaluation of heat damag es in commercial milk samples as it could be done with official but more so phisticated methods. (C) Inra/Elsevier, Paris.