Screening procedure for evaluating heat load in commercial milks

Abstract

The evaluation of heat damages in commercial milk samples has been studied by an ana lytical procedure which uses two different and complementary methods. The first is the rapid total sul- phydryl (SH) group measurement which evaluates whey protein denaturation. The second involves the measurement of absorbance at 340 nm (A340) of milks modified with the Clarifying Reagent', At .this wavelength sorne coloured compounds resulting from the non-enzymic browning still absorb. There is a satisfying correlation between A340 and lactulose content (r =0.98) measured in commercial milk samples by using capillary electrophoresis or high performance liquid chromatography (HPLC). Our analytical procedure using SH and A340 measurements has been applied to 130 raw and commercial milk samples. Analysis by Student's r-test shows that the values of the two parameters obtained for raw and heat-treated milk samples were significantly different (P < 0.01). This study demonstrates that this simple protocol makes possible rapid evaluation of heat damages in commercial milk sam- pies as il could be done with official but more sophisticated methods. © Inra/Elsevier, Paris. heat damage / commercial milk / sulphydryl group / absorbance A340 / transparent-modified miIk / analytical procedure