From: Common milk adulteration and their detection techniques
Adulterant | Procedure | Observation | Limit of detection (v/v) (Sharma et al. 2012) | References |
---|---|---|---|---|
Hydrogen peroxide | A. Add to 5Â mL of suspected milk sample in attest tube, an equal volume of raw milk and 5 drops of 2% solution of paraphenylenediamine. | Appearance of blue color indicates the presence of hydrogen peroxide as adulterant. | 0.025% | (Arvind Singh et al. 2012); (Kamthania et al. 2014); (Sharma et al. 2012) |
B. Take 1Â mL milk sample in a test tube and add 1Â mL of potassium iodide-starch reagent solution and mix well. | Appearance of blue color indicates the presence of hydrogen peroxide as adulterant. | 0.004% | (Sharma et al. 2012) | |
Formalin | A. Take 10Â mL milk sample in attest tube. Add 5Â mL conc. sulfuric acid with a little amount of ferric chloride without shaking. | Appearance of violet or blue color at the junction of two liquid layers indicates the presence of formalin. | Â | |
B. Take about 5Â ml of milk in a test tube. Take 1Â ml of 10% ferric chloride solution in a 500Â ml volumetric flask and make up the volume using concentrated hydrochloric acid. Add 5Â mL from this solution to the sample in test tube. Keep the tube in boiling water bath for about 3-4Â min. | Appearance of brownish pink color indicates the presence of formalin. | 0.1% | (Sharma et al. 2012) | |
C. Take 1Â mL of sample milk in a test tube. Take saturated solution of 1, 8- dihydroxynaphthalene-3, 6- disulphonic acid in about 72% sulfuric acid to make chromotropic acid solution. Add 1Â mL of chromotropic acid solution to the sample in test tube. | Appearance of brownish pink color indicates the presence of formalin. | 0.05% | (Sharma et al. 2012) | |
Ammonium sulfate | A. Take 2Â ml. milk in a test tube and add 0.5Â ml NaOH (2%) 0.5Â ml sodium hypochlorite (2%) and 0.5Â ml phenol (5%) Heat in boiling water bath for 20Â sec | A bluish colour forms immediately, which turns deep blue afterward. Pure milk shows salmon pink colour which gradually changes to bluish after 2Â hours. | Â | (Kumar et al. 2002) |
B. Take 10Â ml of milk in a 50Â ml stoppered test tube. Add 10Â ml of TCA solution. Filter the coagulated milk through Whatman filter paper Grade 42. Take 5Â ml of clear filtrate. Add few drops of barium chloride solution. | Formation of milky-white precipitates indicates the presence of added sulfates like ammonium sulfate, sodium sulfate, zinc sulfate and magnesium sulfate etc. to milk | 0.05% (w/v) | (Sharma et al. 2012) | |
Urea | A. Take 5Â mL milk sample in a test tube. Add equal volume of 24% TCA to precipitate fat and proteins of milk. Take 1Â mL filtrate and add 0.5Â mL 2% sodium hypochlorite, 0.5Â mL 2% sodium hydroxide and add 0.5Â mL 5% phenol solution, then mix. | A characteristic blue or bluish green colour develops in presence of added urea whereas pure milk remains colourless. | Â | (Meisel 1995) |
B. Take 5Â ml milk in a test tube, add 0.2Â ml urease (20Â mg/ml) Shake well at room temperature and then add 0.1Â ml Bromothymol Blue (BTB) solution (0.5%) | Appearance of blue colour after 10-15Â min. indicates the presence of urea in milk. Normal milk shows faint blue colour due to natural urea present in milk. | Â | ||
C. Take 5Â mL milk sample in a test tube. Add 5Â mL p-Dimethyl Amino Benzaldehyde reagent. | Appearance of distinct yellow color indicates presence of added urea whereas formation of slight yellow color indicates natural urea in milk. | 0.2% (w/v) | (Sharma et al. 1993); (Arvind Singh et al. 2012); (Bector et al. 1998); (Kavita, 2000) | |
Nitrate | Take 10Â ml sample milk in a beaker. Add 10Â ml mercuric chloride solution to it. After mixing, filter through what man No 42 filter paper. Take 1Â ml filtrate in a test tube and add 4Â ml of diphenyl amine sulphate or diphenylbenzidine reagent. | Appearance of blue colour indicates the presence of nitrates. Pure milk sample will not develop any color. | 0.2% | (Sharma et al. 2011) |
Benzoic and salicylic acid | Take 5Â mL milk sample in a test tube. Upon acidification with sulfuric acid, 0.5% ferric chloride solution is added to it drop by drop. Mix it. Five ml of milk is taken in a test tube and acidified with concentrated sulphuric acid. 0.5% ferric chloride solution is added drop by drop and mixed well. Development of buff colour indicates presence of benzoic acid and violet colour indicates salicylic acid. | Appearance of buff color indicates the presence of benzoic acid whereas that of violet color indicates salicylic acid. | Â | (Arvind Singh et al. 2012) |
Borax and boric acid | Take 5 mL milk sample in a test tube. Add 1 mL conc. HCl to it. A turmeric paper is dipped and it is dried in a watch glass at 100 °C. | If the turmeric paper turns red, it indicates the presence of borax or boric acid. |  | (Arvind Singh et al. 2012) |