detection of margarine in butter

milk fat is frequently adulterated to meet the demand which exceeds the supply and to increase profit margins. samples of butter adulterated with different levels (5, 10 and 15% w/w) of margarine were prepared and analysed using different methods including refractive index, iodine, reichert-meissl and polenske values. gc and hplc were utilized to determine fatty acid and tocol profiles of samples, respectively. results showed that margarine addition up to the level of 15%, had a significant (p<0.05) effect on refractive index, reichert-meissl, polenske values and increased unsaturated fatty acids; oleic, linoleic acids while decreased saturated fatty acids; myristic, palmitic and stearic acids. the addition of margarine to the butter in the ratios of 5% and 10% significantly (p<0.05) increased c18:2/c18:0 ratio up to 1.5 and 2 times, respectively, while decreased c14:0/c18:2 ratios nearly to half. tocopherol content in genuine butter was 28.89±2.8 mg/kg. in addition to observing β+γ-tocopherol and β+γ-tocotrienol in the presence of 15% margarine in butter, quantity of these tocols, α-tocopherol and total tocols increased significantly (p<0.05) that allowed the detection of as low as 5% levels of margarin in butter.