The Clarifying Reagent, or how to make the analysis of milk and dairy products easier
Difficulties with the analysis of opaque milk and dairy products can be resolved by rendering the sample transparent. This allows direct photometric measurements of the reaction mixtures, and all sample pre-treatment steps become unnecessary. For this, several reagents have been reported in literature. Among them, the ‘Clarifying Reagent’ is mainly described here: its composition is given because it is now released from patenting restrictions. Its main property is a low absorbance between 340 and 800 nm. So it can be used in many chemical and enzymatic colorimetric measurements for estimating the quality of milk and dairy products.
Interrelationships between the content of oxidative markers, antioxidative status, and somatic cell count in cow’s milk
Bovine mastitis is a major disease affecting dairy cattle worldwide. The milk collected from cows with different type of inflammation, including mastitis, is characterized by an increased number of somatic cells (SCC), especially polymorphonuclear cells (PMN). It was proved that the antibacterial activity of PMN generates reactive oxygen species and nitric oxide-derived metabolites. The accumulation of the reactive species correlating with a decrease in the antioxidant activity specific for milk can lead to oxidative and nitrosative stress. The aim of this study was to evaluate the antioxidant/oxidant status in normal cow’s milk and in subclinical mastitis milk using three parameters: total antioxidant status (TAS); levels of malondialdehyde (MDA) – a degradation product of lipid peroxidation; and levels of proteins oxidation expressed as carbonylated proteins analyzed in the reaction with dinitrophenilhydrazine (DNPH). Subclinical mastitis was diagnosed using an electrical conductivity method and by determining the number of SCC in milk. Comparative analysis of TAS in normal and mastitis milk revealed extremely significant differences (P = 0.0005), the average of this parameter was lower for mastitis milk samples. The results describing the antioxidant status were correlated with those on lipid and protein oxidative degradation. The average level of MDA in mastitis milk was higher compared with normal milk, the mean difference was 40.69 nmol/ml. A similar variation was observed for DNPH, the mean difference was 191.24 μmol/ml. The levels of SCC, MDA, and DNPH were significantly higher in subclinical mastitis milk compared to milk from healthy cows due to the occurrence of oxidative stress state in subclinically inflamed mammary gland.
The free and masked sulphydryl groups of heated milk and milk powder and a new method for their determination
Summary A new method is described for the determination of the free and masked sulphydryl (-SH) groups in heated milk and milk products. The procedure is based on the use of the specific -SH reagent p-chloromercuribenzoate, and utilizes another specific -SH reagent, 5,5' -dithiobis(2-nitrobenzoate), as an indicator producing yellow colours which are matched with the aid of standard glasses in the Lovibond Comparator. The method was applied to heated skim-milks and a series of commercially prepared milk powders. Measurements were made in particular of the -SH content of UHT-treated milk. The changes in the -SH content of such milks on storage were studied; these changes could not be explained by a reversal of the denaturation of the whey proteins, although evidence was obtained that small amounts of heatdenatured whey protein can revert to the native state.