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 sulphydryl (SH) group measurement which evaluates whey protein denaturation. The second involves the measurement of absorbance at 340 nm (A 340 ) 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 A 340 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 A 340 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 sampies as il could be done with official but more sophisticated methods. © Inra/Elsevier, Paris.heat damage / commercial milk / sulphydryl group / absorbance A 340 / transparent-modified miIk / analytical procedure Résumé -Protocole rapide d'évaluation des traitements thermiques dans les laits de consommation. L'évaluation des dénaturations induites par les traitements thermiques appliqués au lait a été étudiée à l'aide d'un protocole utilisant deux méthodes rapides, différentes mais complémentaires. La première évalue la dénaturation des protéines Iactosériques en mesurant les groupements sulfhydryles totaux. La seconde consiste à mesurer l'absorbance à 340 nm (A 340 ) des laits rendus transparents par l'ajout du réactif de transparisation. A 340 est due aux composés issus des réactions de

Improvement of the ammonia measurement using a clarifying reagent and application to evaluate heat damage in commercial milk samples

“…It correlates ammonia with other measured parameters such as absorbance at 340 nm of the transparent-modified milk samples (A 340 ) or lactulose, these two being well correlated (Guingamp, Humbert, Midon, Nicolas, & Linden, 1999).…”

Capillary electrophoresis in food authenticity

“…It has been proposed as an analytical index to distinguish UHT (Ultra High Temperature Treated) from sterilized milk. The content of lactulose in milk was successfully determined by CE and compared with HPLC [63]. HMF as another heat-load marker of milk was determined by MEKC (phosphate buffer with SDS, pH 7.5) and good agreement with HPLC results was found [64].…”

The Clarifying Reagent, or how to make the analysis of milk and dairy products easier

“…Chemical determinations NH 2 groups Humbert et al 1990 Milk and cheese SH groups Guingamp et al 1993 Raw and heated milks Coloured compounds (A 340 ) Guingamp et al 1999 Raw and heated milks Ammonia, urea Guingamp et al 1994 Milk and whey Linden et al 1987 Milk analysis with the Clarifying Reagent …”

“…The Clarifying Reagent was used to quantify SH groups (Guingamp et al 1993) and to measure absorbance at 340 nm (A 340 ; Choukri et al 1991 ;Guingamp et al 1995) which reflects the presence of coloured compounds derived from the Maillard reactions. Levels in SH and A 340 values allow discrimination between raw, pasteurised, UHT-treated and sterilised milks and then to classify heated milk samples (Guingamp et al 1999). …”