Milk analysis water content

One of the first attempts to use a biological RM was for the analysis of the fat content of milk. This was carried out in London in the late i88o s by a number of analytical chemists who were trying to identify adulterated milk. At that time milk was sold impackaged and at least 20 % of the miUc sold in London was adulterated by dilution with water. This work appears to be the first empirical round-robin approach for characterization of a RM. 

The same derivatization was applied to the HPLC determination of STR and DHS in milk. The comparison of HPLC and ELISA methods was also performed for DIHS. After removal of fat by extracting a milk sample with oxalic acid and centrifuging, proteins were precipitated with TCA. The supernatant was treated by SPE on a Cl8 column. The cartridge was washed with water, and the analytes were eluted with ion-pair in MeCN. The eluate was reconcentrated by evaporating and dissolving in water. Postcolumn reaction took place at 65°C. Recoveries were dependent on the concentration level and the batch of SPE columns used, and independent of the fat content and homogenization. The sample cleanup was not sufficient for the analysis of cheese. The DIHS concentrations of incurred samples determined by ELISA were higher than those obtained by the LC method (107). 

Fatty acids (in milk fat) to a total of up to 10 mg were treated with 250 1 of di-n-butyl carbonate and 0.5 ml of 0.2 M sodium butoxide. The tube was capped and the mixture was heated for 2 minutes on a steam bath. The contents of the tube were transferred to a Babcock milk fat test bottle and rinsed in with 0.5 ml of water, 0.5 ml of acetone and a further 0.5 ml of water. Saturated NaCl (10 ml) was added and the volume was adjusted to the mark with water. The layers were separated by centrifugation and the upper layer was taken directly for analysis by gas chromatography [142]. 

Milk fats provide a unique challenge with their high content of short-chain FAs (C4 to CIO) that show a lower than expected flame ionization detector (FID) response in GC. Therefore, the short-chain FAMEs require appropriate correction factors (64-67). In addition, the short-chain FAME are water soluble and can be easily removed by using an aqueous wash. Isopropyl and butyl esters have been used for the analysis of short-chain FA to eliminate the use of correction factors (24,25,64—71), but this requires merging the results of the butyl (or isopropyl) esters with FAMEs (24,25,69,70). In addition to the differences in the FID response of short-chain FAME, attention should also be focused at optimizing the accuracy and reliability of the hydrogen flame in the FID (72). 

Mambrini et al. used NMR as a tool for quantitative analysis in the process of biodiesel formation. They identified longitudinal relaxation as an important factor and reported measurements of Ti. Moller et studied motion of water molecules in skim milk powder solutions at varying pH and dry matter content, using T2 measurements for O and H. 

One example of the use of the spin echo technique is to measure moisture and oil content simultaneously in many agriculture and food products such as oilseeds, nuts, chocolate, milk powder, cheese, cookies, and sausages. The total oil and moisture analysis using TD-NMR for seeds and seed residues have become international standard methods (ISO CD 10565 and ISO CD 10632). In seeds, oil and water molecules all have hydrogen and they all contribute to NMR signals. In dried seeds, the water molecules are bound, and the mobility of the water molecules is much more restricted than that of oil molecules, which remain free in the seeds. Therefore, the water in the... 

Here we have applied PTR-MS to the nosespace analysis of a series of 12 liquid samples. These included one water sample and three milk samples with different fat content (0.033%, 2.7%, and 3.8% fat), containing five aroma compounds at three different concentrations. The nosespace from all samples was analyzed by five different panelists (two women and three men) in five repetitions. After a short discussion of recent technical developments of our nosespace setup, the discussion focuses on the inter-and the intrapersonal variability of the nosespace intensity for five-compounds— -damascenone, hexanal, ethylbutyrate, benzaldehyde, and 2,3-butanedione. Further interpretation of the results is found in Ref. 7. 

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