A Spectrophotometric Method for the Detection of Cheese Whey in Milk

Abstract

A spectrophotometric method for the detection of cheese whey in milk is described. The method is based on the colour reaction of sialic acid bound to the glycomacropeptide (GMP) - a marker peptide of cheese whey. In this method, GMP present in adulterated milk is first selectively precipitated by employing double precipitation method, wherein, trichloroacetic acid (TCA) concentration in milk is first raised to 8% to precipitate all the major proteins from milk followed by raising the TCA concentration to 14% to precipitate out GMP. The sialic acid in washed GMP precipitates was reacted with acidic ninhydrin reagent which gave yellowish- brown colour (maxima 470 nm), the intensity of which increases with the increase in the level of cheese whey in milk. The reagent blank as well as control milk sample (unadulterated milk) also gave faint yellow colour with OD values of 0.004±0.002 and 0.032±0.01, respectively. The method can detect presence of 10% cheese whey in milk where OD value increased to 0.1±0.01. The method was validated in milk samples added with different levels of cheese whey.