There are many methods of test for detection of skim milk powder in whole milk which have depended on changes brought about by heat treatment and drying of milk powder in the molecular structure of milk constituted. Some of these methods include:

- the determination of ultra violet and visible spectra (700 to 240 nm) (The determination of milk powder added to whole milk. Madkour MA, Moussa BM Nahrung. 1989; 33(1):77-82.);

- the detection of furosine as an indicator of presence of reconstituted milk powder in raw and in pasteurized milk by HPLC (Resmini P, Pellegrino L, Masotti F, Tirelli A, Prati F. Detection of reconstituted milk powder in raw and in pasteurized milk by HPLC of furosine. Scienzae Tecnica Lattiero Casearia. 1992;43(3):169–186);

- the detection of hydroxymethylfurfural as an indicator of dried powder in liquid milk (Rehman et al., 2000).

- measurements of δD and 18O stable isotope ratios have been used to distinguish reconstituted milk (Lin GP, Rau YH, Chen YF, Chou CC, Fu WG. Measurements of δD and 18O stable isotope ratios in milk. J Food Sci. 2003;68(7):2192–2195);

- The simple and rapid test for detection of skim milk powder in whole milk is based on the fact that the coagulum obtained from reconstituted skim milk powder by addition of acetic acid, gives intense blue colour on boiling with Phosphomolybdic acid due to certain reducing groups present in the proteins of milk powder which are able to cause reduction of molybdenum blue resulting in formation of blue colour.

(G.K.Murthy,.L.Kaylor. U.S. Detection of Nonfat Dried Milk in Whole Milk. Journal of Dairy Science. Volume 54, Issue 6, June 1971, Pages 826-829. Department of Health, Education, and Welfare, Food and Drug Administration, Cincinnati, Ohio 45226. https://doi.org/10.3168/jds.S0022-0302(71)85926-X).

- And some articles from IJLTEMAS (www.ijltemas.in/DigitalLibrary/Vol.5Issue5/78-81.pdf):

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Detection of Skimmed Milk Powder in Milk:

Principle: The reducing groups present in the proteins of milk

powder reduce molybdenum resulting in formation of blue

colour.

Reagents:

• Diluted acetic acid: 4% (v/v).

• Phosphomolybdic acid solution: 1% (w/v) solution in

distilled water.

Procedure:

• Take 50 ml of milk in a 60 ml centrifuge tube.

• Place the tube in the centrifuge and balance it properly.

Centrifuge at 3000 rpm for 15 minutes.

• Decant the supernatant creamy layer carefully.

• Add 0.5 ml of diluted acetic acid for coagulation and

then add 2 ml of phosphomolybdic acid solution. Mix

the contents thoroughly.

• Heat in a water bath at boiling temperature for 15

minutes and then cool.

• Observe the colour of the curd obtained.

Interpretation: The curd obtained from pure milk shall be

greenish in colour whereas the curd of sample containing

skimmed milk powder shall be bluish in colour. The intensity

of bluish colour depends on the amount of the skim milk

powder present in the sample.

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I hope this helps.

Regards,

Du

https://www.ijltemas.in/DigitalLibrary/Vol.5Issue5/78-81.pdf

Dear Apirom

I don't know spectrophotometric method for this but it is possible by measuring the density and the total soluble substances content of milk as standardized values exist for normal fresh milk. But I am concerned: why should somebody add milk powder to fresh milk?

Regards!

NOBOSSE.

I agree with Pierre. Milk solids (proteins and triglycerides)  would be increased in case of mixing.

Regards,

Alfredo.

Because the price of fresh or raw  cow milk is higher than milk powder , then somebody added milk powder to increase milk solid and get more money form milk collecting center. It's not fair for milk collecting center.

I agree with pierre, aside from comparing it with standardized value of  normal fresh/raw milk, you can also try conducting physico-chemical analysis of your suspected adulterated milk and compare it with fresh/raw milk from the same source/farm for further confirmation. You can use Ekomilk analyzer if available. I hope this helps.

Regards,

Kevin

Thank you for your comments and suggestions.

This process is difficult

I think HPLC is the method appropriate method

There is an AOAC spectrophotometric analytical procedure that can be used indirectly to detect milk powder added to raw milk ou the mixture of reconstituted milk to fresh milk. This is the evaluation of the protein reducing substances (PRS) in milk, based on the reducing power of milk, which increases with heat processing of milk and is higher in milk powder than in fresh milk. It works well if we have the possibility to evaluated the PRS in both fresh milk and milk powder used in the preparation of the mixtures. However the results must be carefully analyzed as the reducing power of milk can vary greatly with the milk composition (protein content) and with the heat treatment (mainly whey protein denaturation), and this means difficulties in absolute conclusions.